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Front Cover: The 1913 facade of the Natural History Museum of Los Angeles County.
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NOV 23 2016
J-/BRAR1&S
Contributions
in Science
Volume 520 2012
CONTENTS
A Key to Neotropical Region Frog-Egg-Feeding Species of Megaselia
(Diptera: Phoridae), with a New Species from Panama 1
Brian V. Brown and Robert V Horan III
Additions to Late Cretaceous Shallow-Marine Limopsid Bivalves and
Neogastropods from California 5
Richard L. Squires
Polyplacophora (Mollusca) from the San Diego Formation: A Remarkable
Assemblage of Fossil Chitons from the Pliocene of Southern California .... 15
Michael J. Vendrasco, Douglas J. Eernisse, Charles L. Powell II, and
Christine Z. Fernandez
Late Pliocene Megafossils of the Pico Formation, Newhall Area,
Los Angeles County, Southern California 73
Richard L. Squires
Published by Natural History Museum of Los Angeles County
i
Scientific Publications Committee
Luis M. Chiappe, Acting Vice President for Research and Collections
John M. Harris, Committee Chairman
Joel W. Martin
Xiaoming Wang
Karen V. Brown, Managing Editor
ISSN 0459-8113 (Print); 2165-1868 (Online)
NATURAL
HISTORY
MUSEUM
LOS ANGELES COUNTY
Natural History Museum of Los Angeles County
900 Exposition Boulevard
Los Angeles, California 90007
Printed at Allen Press, Inc., Lawrence, Kansas
Contributions in Science, 520:1-4
16 May 2012
A Key to Neotropical Region Frog-Egg-Feeding Species oe
Megaselia (Diptera: Phoridae), with a New Species
from Panama1
Brian V. Brown2 and Robert V. Horan IIP
ABSTRACT. A new species of phorid fly, Megaselia randi sp. nov., is described from Panama. Adults of both sexes were reared from eggs
of the frog Agalycbnis spurrelli Boulenger. A key to the three species of phorid flies so far reared from neotropical frog eggs is given.
INTRODUCTION
The genus Megaselia Rondani is one of the largest genera in the
Diptera, and perhaps one of the largest genera of living organisms
(Bickel, 2009). The 1,500 species currently described in this
genus are a small fraction of the true diversity, which may be ten
times larger than this number. Single sites can have tremendous
species richness, with the current record going to a site in Sweden
where 330 species were identified (Bonet, 2006). No estimates
are available for tropical sites, for which diversity is presumably
much higher (as it is for many phorid genera).
Species of Megaselia have a wide variety of lifestyles (Disney,
1994), but are commonly thought of as generalized scavengers,
probably because of the ubiquitous, polyphagous, often synan-
thropic species Megaselia scalaris (Loew) (Disney, 2008). It is
difficult to imagine 300 or more species of generalized scavengers
sharing the same lifestyle at one site, however, and as expected,
research is continually uncovering examples of extremely special-
ized larval feeding in this genus (Ceryngier et al., 2006; Disney and
Weinmann, 1998; Disney et al., 2001; Gonzalez et al., 2002).
In addition to opportunistic depredation by M. scalaris (Villa
and Townsend, 1983), larvae of at least one other Megaselia
species are known to attack frog eggs in the New World tropics
(Downie et a!., 1995; Neckel-Oliveira and Wachlevski, 2004).
Herein we describe another species of Megaselia with this
lifestyle.
METHODS AND MATERIALS
The study site, Barro Colorado Island (BCI), Panama, is a 1,500-ha island
located in the center of the Panama Canal. The vegetation is characterized
as a tropical moist forest with a canopy height of 35-40 m. Average
rainfall is 2,600 mm a year, with a distinct dry season from December to
April (Leigh, 1999). Kingfisher Pond, the breeding location of the frog
Agalycbnis spurrelli Boulenger (Hylidae), is located on the northwestern
section of BCI and is a seasonally filled pond approximately 175 square
meters in size. The pond typically fills during the early rainy season, in
July, and dries by February.
Larvae were collected directly from infested frog eggs, and adults
reared within test tubes under ambient outdoor conditions.
1 URL: www.nhm.org/scholarlypublications
Entomology Section, Natural History Museum of Los Angeles
County, 900 Exposition Boulevard, Los Angeles, California 90007
USA. E-mail: bbrown@nhm.org
' Warnell School of Forestry and Natural Resources, University of
Georgia, Athens, Georgia 30602, USA. E-mail: rvhoran@uga.edu
Specimens are deposited in the Natural History Museum of Los
Angeles, CA, USA (LACM), Museo de Invertebrados Graham B.
Fairchild, Universidad de Panama, Estafeta Universitaria, Panama
(MIUP), and the Smithsonian Institution, Washington, DC, USA
(USNM).
Megaselia randi new species
(Figs. 1-6)
DESCRIPTION. Body length 1.5-1. 7 mm. Frons brown,
matte, frontal setae long (Fig. 1). Ventral interfrontal setae
displaced laterally to eye margin. Ventral supra-antennal setae
about one-half length and thickness of dorsal supra-antennal
setae. Flagellomere 1 round, brown. Palpus yellow, with well-
developed setae. Scutum and scutellum brown; anterior scutellar
setae small, similar in size to scutal setulae. Pleuron brown,
except venter of anepisternum, all of katepisternum and meron
yellow. Anepisternum without setae. Legs yellowish, except
anterior face of hind femur light yellowish-brown with brown
spot apically. Hind femur with long ventral setae on basal one-
half. Hind tibia with differentiated row of posterodorsal setae
only. Mean wing length 1.54 mm, range 1.43-1.78 mm (Fig. 2);
mean costal length 0.57 wing length, range 0.56-0.58. Mean
costal sector ratio 3.15:2.91:1, range 2.67-4.00: 2.44-3.50:1.
Wing vein R1+3 present. Halter brown.
Male abdomen. Tergites brown. Ventral membrane gray, with
scattered setae. Epandrium brown, hypoproct and cercus
yellowish brown. Left lobe of hypandrium with long, truncate
process (Fig. 3).
Female abdomen. Dufour’s mechanism broadly rounded, large
(Fig. 4). All tergites present and well developed (Fig. 5), brown in
color. Ventral membrane gray, with scattered setae. Tergite 7
quadrate, sternite 7 triangular (Fig. 6). Tergite and sternite 8
both pair of separate sclerites.
HOLOTYPE. S , PANAMA: Barro Colorado Island, Kingfisher
Pond, 2.X.2009, R. Horan, reared from Agalycbnis spurrelli eggs
[LACM ENT 237515] (LACM).
PARATYPES. 5 <?, 11?, same data as holotype (LACM,
MIUP, USNM).
RECOGNITION. This species keys easily to the genus
Megaselia in the latest key to world phorid genera (Disney,
1994). In traditional classifications of this genus, M. randi would
be placed in subgenus Megaselia, because of the lack of setae on
the anepisternum, and in “group VII” because of its relatively
long costa and short anterior scutellar setae. Such groups have
recently been abandoned, however, with the realization that they
are not monophyletic assemblages.
© Natural History Museum of Los Angeles County, 2012
ISSN 0459-8113 (Print); 2165-1868 (Online)
2 ■ Contributions in Science, Number 520
Brown and Horan III: Frog-Egg-Feeding Species of Megaselia
Figures 1-6 1. head; 2. wing; 3. Dufour’s mechanism; 4. male abdomen: lateral; 5-6. female abdomen: 5, dorsal; 6, ventral apex.
Contributions in Science, Number 520
Brown and Horan III: Frog-Egg-Feeding Species of Megasclia ■ 3
Figures 7-10 7. adult female Agalycbnis spurrelli-, 8. phorid larvae on frog eggs; 9. healthy egg mass; 10. infected egg mass.
One of the difficulties presented by this genus is the scattered
nature of its associated literature. In the latest keys to
neotropical Megaselia (Borgmeier, 1962, 1969, 1971), M.
randi does not key to any known species. In Borgmeier (1962),
it keys to couplet 45 of the Group VII key on page 309, but
does not fit either option. The first lead in couplet 45 is
(translated from German) “ventral interfrontal setae almost
immediately under ventral fronto-orbital setae; costa 0.47 wing
4 ■ Contributions in Science, Number 520
Brown and Horan III: Frog-Egg-Feeding Species of Megaselia
length ... M. zeno n. sp. ” and fits M. randi in the first character,
hut not in the second (the costal length is much longer in M. randi).
Furthermore, the halter is yellow in M. zeno , but brown in M.
randi, and M. zeno is found in southern Brazil. Keying is similarly
unsuccessful in Borgmeier’s other papers (1969, 1971). All of the
22 species described since Borgmeier’s last work (Boesi et al. 2006;
Disney, 1982, 1989, 1995; Disney and Berghoff, 2007; Disney and
Rettenmeyer, 2007; Disney and Sakai, 2001; Disney and Sinclair,
2008; Disney and Weinmann, 1998; Downie et al., 1995;
Gonzalez et al., 2002; Kung and Brown, 2004; Weinmann and
Disney, 1997) also differ from ours.
The adults of the three known phorid flies reared from eggs of
neotropical frogs can be identified using the following key:
1 Halter knob yellow; all abdominal tergites dark brown with
yellow markings; male with extremely robust, feathered (with
small microtrichia) seta at tip of proctiger clearly longer and
thicker than setae on cercus; female with tergite 6 short,
extremely broad, extending laterally on segment
Megaselia scalaris (Loew)
- Halter knob brown; at least some tergites wholly brown; seta
at tip of male proctiger subequal in size to those on cercus and
not feathered; female with tergite 6 of normal size, smaller
and narrower than tergite 5 2
2 Anepisternum bare; anterior scutellar setae much smaller
than posterior pair; all female tergites large, only gradually
reduced in size posteriorly; tergite 4 larger than tergite 5
Megaselia randi sp. nov.
- Anepisternum with small setae; anterior scutellar setae
subequal to posterior pair; female tergite 4 greatly re-
duced, rounded, about one-half size of tergite 5 or less
Megaselia nidanurae Disney
NATURAL HISTORY OBSERVATIONS. First observations
of egg clutches of Agalychnis spurrelli, the gliding leaf frog (Fig. 7),
were made on August 11, 2009. Frogs sporadically laid clutches
with no sign of fly infestation (Fig. 9) until mid-September, when
maggot-infested clutches were observed (Figs. 8, 10). By October 2,
2009, the majority of clutches appeared to be infested with maggots.
Larvae were collected on this date and reared in moist-cotton-filled
test tubes capped with aluminum foil and held at ambient
temperature in an outdoor field lab. Maggots appeared to become
dormant soon after being placed within the tubes. Adult flies
emerged on October 18, when most were discovered already dead in
the tubes and preserved in ethanol immediately. All clutches infested
with larvae were considered completely failed. It is not known
whether the eggs were infertile, damaged by another organism and
scavenged by the flies, or directly preyed upon by the flies.
DERIVATION OF SPECIFIC EPITHET. We name this species
in honor of herpetologist Stan Rand, who was a key influence on
R.V.H.’s work.
ACKNOWLEDGMENTS
Figures 1-6 were skillfully produced by Brian Koehler. Figures 7-10 were
photographed by Robert Horan. David Donoso provided critical
assistance in rearing larvae and other early stages of this discovery. Brian
Brown was supported by National Science Foundation grant DEB-
1025922 to Brian Brown and Paul Smith. Robert Horan was partially
supported by the Latin American and Caribbean Studies Institute of the
University of Georgia and the Smithsonian Tropical Research Institute
during the field portion of this research, as well as by the LInited States
Department of Energy Contract DE-FC-09-96SR18546 with The
University of Georgia Research Foundation.
LITERATURE CITED
Bickel, D. 2009. Why Hilaria is not amusing: The problem of open-ended
taxa and the limits of taxonomic knowledge. In Diptera diversity:
Status, challenges, and tools, ed. T. Pape, D. Bickel, and R. Meyer,
279-301. Leiden and Boston: E. J. Brill.
Boesi, R., C. Polidori, and R.H.L. Disney. 2006. Two new species of scuttle
fly (Diptera: Phoridae) associated with cellophane bees (Hymenop-
tera: Colletidae) in Chile. Pan-Pacific Entomologist 82:341-345.
Bonet, J. 2006. Diversity of two nordic scuttle fly faunas (Diptera:
Phoridae). PhD thesis. Stockholm: Zoologiska Institutionen.
Borgmeier, T. 1962. Versuch einer Uebersicht ueber die neotropischen
Megaselia- Arten, sowie neue oder wenig bekannte Phoriden verschie-
dener Gattungen (Diptera, Phoridae). Studia Entomologica 5:289—488.
. 1969. New or little-known phorid flies, mainly of the neotropical
region. Studia Entomologica 12:33-132.
. 1971. Further studies on phorid flies, mainly of the neotropical
region (Diptera, Phoridae). Studia Entomologica 14:1-172.
Ceryngier, P., E. Durska, and R.H.L. Disney. 2006. The surprising larval
habits of Megaselia minor (Zetterstedt, 1848) (Diptera: Phoridae).
Studia Dipterologica 12:357-361.
Disney, R.H.L. 1982. A curious new species of Megaselia from Brazil (Diptera:
Phoridae). Zeitschrift fiir Angewandte Zoologie 68(1981 ):4 15 — 418.
. 1989. Two new species of Megaselia (Dipt., Phoridae) from the
Falkland Islands (Malvinas), and a replacement name in the genus.
Entomologist’s Monthly Magazine 125:183-186.
. 1994. Scuttle flies: The Phordiae. London: Chapman and Hall,
480 pp.
. 1995. Cave Phoridae (Diptera) of Trinidad. Giornale itahano di
Entomologia 6( 1993):41 7 — 436.
. 2008. Natural history of the scuttle fly, Megaselia scalaris.
Annual Review of Entomology 53:39-60.
Disney, R.H.L., and S.M. Berghoff. 2007. New species and records of
scuttle flies (Diptera: Phoridae) associated with army ants (Hyme-
noptera: Formicidae) in Panama. Sociobiology 49:59-92.
Disney, R.H.L., and C.W. Rettenmeyer. 2007. New species and revisionary
notes on scuttle flies (Diptera: Phoridae) associated with neotropical
army ants (Hymenoptera: Formicidae). Sociobiology 49:1-58.
Disney, R.H.L., and S. Sakai. 2001. Scuttle flies (Diptera: Phoridae)
whose larvae develop in flowers of Aristolochia (Aristolochiaceae) in
Panama. European journal of Entomology 98:367-373.
Disney, R.H.L., and B.J. Sinclair. 2008. Some scuttle flies (Diptera:
Phoridae) of the Galapagos Islands. Tijdschrift voor Entomologie
151:115-132.
Disney, R.H.L., and D. Weinmann. 1998. A further new species of
Phoridae (Diptera) whose larvae associate with large spiders
(Araneae: Theraphosidae). Entomologica Scandinavica 29:19-23.
Disney, R.H.L., E.L. Zvereva, and M.B. Mostovski. 2001. A scuttle fly
(Diptera: Phoridae) parasitizing a beetle (Coleoptera: Chrysome-
lidae) in Russia. Entomologica Pennica 12:59-63.
Downie, J.R., R.H.L. Disney, L. Collins, and E.G. Hancock. 1995. A new
species of Megaselia (Diptera, Phoridae) whose larvae prey upon the
eggs of Leptodactylus fuscus (Anura, Leptodactylidae). Journal of
Natural History 29:993-1003.
Gonzalez, V.H., B.V. Brown, and M. Ospina. 2002. A new species of
Megaselia (Diptera: Phoridae) associated with brood provisions of
nests of Neocorynura (Hymenoptera: Halictidae). Journal of the
Kansas Entomological Society 75:73-79.
Kung, G., and B.V. Brown. 2004. Two new species of Megaselia Rondani
(Diptera: Phoridae) from Costa Rica. Proceedings of the Entomo-
logical Society of Washingtott 106:751-756.
Leigh, E.G.J. 1999. Tropical forest ecology: A view from Barro Colorado
Island. New York and Oxford: Oxford University Press, 264 pp.
Neckel-Oliveira, S., and M. Wachlevski. 2004. Predation on the arboreal
eggs of three species of Phyllomedusa in central Amazonia. Journal
of Herpetology 38:224-248.
Villa, J., and D.S. Townsend. 1983. Viable frog eggs eaten by phorid fly
larvae. Journal of Herpetology 17:278-281.
Weinmann, D., and R.H.L. Disney. 1997. Two new species of Phoridae
(Diptera) whose larvae associate with large spiders (Araneae:
Theraphosidae). Journal of Zoology, London 243:319-328.
Received 31 May 2011; accepted 3 August 2011.
Contributions in Science, 520:5-14
23 May 2012
Additions to Late Cretaceous Shallow-Marine Limopsid Bivalves
and Neogastropods from California1
Richard L. Squires2
ABSTRACT. A search of collections at four museums in California revealed new mollusks that improve the poorly known geologic record
of limopsid bivalves and neogastropods from shallow-marine Upper Cretaceous strata in California. A single specimen of the bivalve
Limopsis sp. (Cenomanian undifferentiated) from central California is significant because it is the earliest record of this genus from the
northeast Pacific and the only known Cenomanian record. The morphology and distribution of Limopsis silveradoensis Packard, 1 922,
which was previously the only known Cretaceous Limopsis in the study area, are better established because newly detected specimens have
much better preservation than previously known ones. The geologic range of this species is extended downward from late Turanian to
include the early Turonian, and its geographic distribution is extended northward from Southern California to northern California. It is the
only known Turonian record of this genus. Locally abundant specimens of Limopsis demerei new species (late Campanian to possibly early
Maastrichtian) from Southern California represent the first post-Turonian Limopsis recognized from the northeast Pacific.
Two single specimens of large-sized neogastropods of latest Campanian to possibly early Maastrichtian age are reported from San Diego,
in Southern California. Their familial and generic identifications are tentative because the specimens are not well preserved; nevertheless,
the specimens are significant because the Late Cretaceous record of neogastropods is meager. One specimen is possibly the volutid
Misricymbiolat sp., which is otherwise only known from similar age strata in Egypt and Tunisia. The San Diego specimen is 15.6 cm in
height (incomplete) and is the largest known gastropod from Upper Cretaceous strata of the northeast Pacific. The other specimen is
possibly the turbinellid Turbinella ? sp.
INTRODUCTION
This study concerns the description and geologic implications of some
shallow-marine bivalves and gastropods whose geologic records in
the northeast Pacific region are poorly known. The geologic record of
the limopsid bivalve Limopsis Sassi, 1 827, in this area was heretofore
known from only a single species, the Turonian Limopsis silver-
adoensis Packard, 1922. The Cenomanian Limopsis sp. and the latest
Campanian to possibly early Maastrichtian Limopsis demerei new
species are now added to this record. Two single specimens of
neogastropods of latest Campanian to possibly early Maastrichtian
age are described from Southern California. Although incompletely
preserved, each represents an important addition to the scarce record
of Cretaceous neogastropods. One specimen is possibly the volutid
gastropod Misricymbiola ? sp., and the other specimen is possibly the
turbinellid gastropod Turbinella ? sp.
The areas where the species were collected are shown on
Figure 1, and their designations are used throughout the paper
(e.g., Area 2). Locality details are in the Localities section. The
localities west of the San Andreas Fault have been tectonically
transported from a more southerly region (see Saul and Squires,
2008). Temporal ranges of the studied species are plotted on
Figure 2. Their combined Cretaceous range in the study area spans
the Cenomanian to possibly early Maastrichtian, an interval of
approximately 30 million years. The paleoclimate that existed
during this interval in the study area was generally warm
temperate (Saul and Squires, 2008; Squires and Saul, 2009).
MATERIALS AND METHODS
This study is based on 232 specimens found in Cretaceous holdings of
four major museums in California. Preservation is generally good. The
1 URL: www.nhm.org/scholarlypublications
Department of Geological Sciences, California State University,
18111 Nordhoff Street, Northridge, California, 91330-8266, USA;
Research Associate, Invertebrate Paleontology, Natural History Museum
of Los Angeles County, 900 Exposition Boulevard, Los Angeles,
California, 90007, USA. E-mail: richard.squires@csun.edu
fragile bivalve specimens were cleaned by use of very sharp needles. The
gastropod specimens were cleaned by means of a high-speed drill and
diamond-coated drilling wheels. Morphologic terms for the bivalves are
from Newell (1969), and those for the gastropods are from Cox (1969).
The studied specimens identified as “sp.” probably represent new
species, but they are not named here because they are based on single
specimens that represent either a juvenile or an incomplete adult.
Current summaries of the geological details of the formations and
members containing the studied specimens can be found in the following
papers (listed in ascending chronostratigraphic order): Panoche Forma-
tion, Big Tar Canyon area, Reef Ridge (Squires and Saul, 2004); Budden
Canyon Formation, lower Gas Point Member (Squires and Saul, 2004);
Ladd Formation, upper Baker Canyon Member (Squires and Saul, 2001)
and lower Holz Shale Member (Saul, 1982); Point Loma Formation
(Loch, 1989; Coombs and Demere, 1996; Squires and Saul, 2001); and
Cabrillo Formation (Squires and Saul, 2009).
ABBREVIATIONS: Abbreviations used for locality and/or catalog and
numbers are CASG (California Academy of Sciences, Geology Section,
San Francisco), LACM1P (Natural History Museum of Los Angeles
County, Invertebrate Paleontology Section), SDSNH (San Diego Society
of Natural History), and UCMP (University of California Museum of
Paleontology, Berkeley, California).
LOCALITIES
LACMIP: 4898. 117°23'W, 33°08'26"N. Dark gray mudstone in
east-facing roadcut on El Camino Real; opposite and south of
drive to Madonna Hill Guest Home (5392 El Camino Real);
outside of the Carlsbad city limits (in June, 1973). Locality is
1.4 km (0.85 mi.) north of the intersection of Palomar Airport
Road and El Camino Real. San Luis Rey Quadrangle (7.5-
minute, 1968), northern San Diego County, Southern California.
Point Loma Formation. Age: Late Campanian to possibly early
Maastrichtian. Collector: G.L. Kennedy, June 10, 1973. 7792.
117°20'W, 33°08'N. Temporary cut bank (now covered) in
mudstone near some “claypits” south of Letterbox Canyon, at
the Carlsbad Research Center on north side of Faraday Avenue,
east of the intersection with Rutherford Road, approximately
1088 m (3570 ft.) north, 2966 m (9730 ft.) west of southeast
corner of San Luis Rey Quadrangle (7.5-minute, 1968), northern
San Diego County, Southern California. Locality is approximately
© Natural History Museum of Los Angeles County, 2012
ISSN 0459-8113 (Print); 2165-1868 (Online)
6 ■ Contributions in Science, Number 520
Squires: California Cretaceous Mollusks
Figure 1 Localities map and latitudinal distribution of the studied species.
1.6 km (1 mi.) east of the city limits of Carlsbad. Point Loma
Formation. Age: Late Campanian to possibly early Maas-
trichtian. Collector: J. D. Loch, 1984. 8198. 117°37'25"W,
33°44'15"N. Very fine-grained sandstone, NW 1/4 of SW 1/4 of
section 16, T 5 S, R 7 W, Santiago Peak Quadrangle (7.5-minute,
1954), Santa Ana Mountains, Orange County, Southern Cali-
fornia. Ladd Formation, upper Baker Canyon Member. Age:
Late Turonian. Collector: W.P. Popenoe, March 14, 1934.
[= California Institute of Technology loc. 1069], 23817.
122 '32'45"W, 40 24'45"N. Graywacke in mudstone section, third
major west-heading tributary of the North Fork of Cottonwood
Creek south of the mouth of Fluling Creek, 762 m (2500 ft.) east
and 549 m (1800 ft.) south of the SE corner of section 29, T 30 N,
R 6 W, Ono Quadrangle (15-minute, 1952), Shasta County,
northern California. Budden Canyon Formation, Gas Point
Member. Age: Early Turonian. Collector: P.U. Rodda, August
1956. [= CASG loc. 70509], 23930. 122:33'25"W, 40°25'30"N.
Red-brown limestone nodule in gray mudstone in low east bank of
canyon, 213 m (700 ft.) west and 747 m (2450 ft.) south of NE
corner of section 29, T 30 N, R 6 W, Ono Quadrangle (15-minute,
1952), Bald Hills, Shasta County, northern California. Budden
Canyon Formation, Gas Point Member. Age: Early Turonian.
Collector: P. Rodda, August 1956. [= CASG^loc. 70508], 25526.
120 09'10"W, 35 54'45"N. On ridge with conglomerate beds
west of Roof Spring and just east of the Big Tar Canyon Road,
887 m (2910 ft.) north and 518 m (1700 ft.) west of SE corner of
section 20, T 23 S, R 17 E, Reef Ridge area, Garza Peak
Quadrangle (7.5-minute, 1953), Kings County, central California.
Panoche Formation. Age: Cenomanian (undifferentiated) clasts in
a Campanian conglomerate. Collector: E.V. Tamesis, early 1960s.
SDSNH: Both listed below are in mudstone exposed during
grading but now covered by development at Carlsbad Research
Center, in vicinity of Letterbox Canyon, Carlsbad area, San Luis
Rey Quadrangle (7.5-minute, 1968), northern San Diego County,
Southern California. Point Loma Formation. Age: Late Campa-
nian or possible early Maastrichtian. 3456. 117 25'45"W,
33 08'30"N. Near north end of College Boulevard. Collector:
Museum Field Party, 1987. 3458. 117°26'50"W, 33°08'08"N.
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Limopsis Misricymbiola? Turbinella ?
demerei sp. sp.
Limopsis
silverodoensis
Limopsis
sp.
Figure 2 Geologic ranges of the studied species. Ages of stage bound-
aries are from Gradstein et al. (2004).
Elevation 69 m (225 ft.), cut into and below a large abandoned
clay pit shown on old topographic maps, is slightly east of
intersection of Faraday Avenue with College Boulevard. Collec-
ter: B.O. Riney, February 4, 1987.
UCMP: 2143. 117°38'30"W, 33°44'38"N. Black mudstone
from elevation 366 m (1200 ft.) on east side of Silverado Canyon,
below the narrows 228 m (750 ft.) north on section line between
sections 7 and 8, T 5 S, R 7 W, El Toro Quadrangle (7.5-minute,
1949), Santa Ana Mountains, Orange County, Southern California.
Ladd Formation, Holz Shale Member. Age: Late Turonian.
Collector: E.L. Packard, late 1910s.
SYSTEMATICS
Class Bivalvia Linnaeus, 1758
Order Arcida Gray, 1854
Superfamily Limopsoidea Dali, 1895
REMARKS. Oliver and Holmes (2006) reported that limposids
and philobryids alone make up the Limoposoidea.
Family Limopsidae Dali, 1895
REMARKS. Malchus and Waren (2005) reported that
Limopsidae evolved from parallelodontids and that limopsids
gave rise to philobryids, but not to glycymeridids.
Contributions in Science, Number 520
Squires: California Cretaceous Mollusks ■ 7
2 mm
Figures 3-13 Limopsis silver adoensis Packard, 1922. 3-4. Holotype UCMP 12324, UCMP loc. 2143, left valve: 3. exterior, 4. dorsal view; 5. paratype
UCMP 12323, UCMP loc. 2143, mostly an internal mold of left valve; 6-7. hypotype LACMIP 13712, LACMIP loc. 8198, left valve: 6. exterior, 7.
dorsal view; 8. hypotype LACMIP 13713, LACMIP loc. 8198, right valve; 9-10. hypotype CASG 70937, LACMIP loc. 23930, right valve: 9. exterior,
10. interior; 11-12. hypotype CASG 70936, LACMIP loc. 23817, right valve: 11. exterior, 12. dorsal view; 13. hypotype CASG 70938, LACMIP loc.
23930, left valve.
Genus Limopsis Sassi, 1827
TYPE SPECIES. Area aurita Brocchi, 1814, by original
designation, Recent, Mediterranean Sea.
REMARKS. The genus name is derived from the Latin Lima, a
file, and the Greek, opsis, aspect; the gender is feminine (Coan
et ah, 2000). Tevesz (1977) reported about 17 available generic
or sugbeneric names for Limopsis, based on species that resemble
Limopsis aurita (Brocchi). He reported, furthermore, that this
proliferation of names stemmed from a lack of information about
the range of morphologic variation in Limopsis and from
workers not bothering to compare their prospective genus with
L. aurita. Limopsis has been split into several groups on the basis
of sculpture, especially whether the ventral margin is crenulate or
not, but, according to Coan et al. (2000), these characters are
mutable and numerous intergrades occur.
Limopsis silveradoensis Packard, 1922
(Figs. 3-13)
Limopsis silveradoensis Packard, 1922:419, pi. 27, figs. 2, 4.
SUPPLEMENTAL DESCRIPTION. Shell size medium small
(up to height 20.1 mm and length 17.5 mm, same specimen). Shell
ovate, forwardly oblique, anterior-dorsal margin commonly
concave. Equilateral. Valves moderately convex. Shell smooth
but juveniles can have weak, flat commarginal ribs; adults can
have commarginal undulations, especially on medial part of disk.
Umbones prominent and dorsally projecting, slightly anterior of
center to centrally located. Ligament alivincular, short, located in
central triangular resilifer. Dorsal margin of valves long and
straight or short and sloped. Hinge plate arched, especially on
adults. Taxodont dentition in two unequal curving series, with
posterior series longest and extending more ventrally with growth.
Approximately five teeth in anterior series and six to seven teeth in
posterior series. Pallial line entire. Inner margin of valves smooth.
DIMENSIONS. Table 1.
HOLOTYPE. UCMP 12324 (left valve).
TYPE LOCALITY. UCMP loc. 2143.
PARATYPE. UCMP 12323, UCMP loc. 2143.
GEOLOGIC AGE. Turonian.
STRATIGRAPHIC DISTRIBUTION. Lower Turonian. Bud-
den Canyon Formation, lower Gas Point Member, Tehama
County, Bald Hills, northern Ono area, northern California (new
stratigraphic occurrence) (Area 1). Upper Turonian. Ladd
Formation, upper Baker Canyon and lower Holz members, Santa
Ana Mountains, Orange County, Southern California (Area 3).
REMARKS. The examined material consisted of 33 specimens:
26 from the Gas Point Member, and seven from the Baker
Canyon and Holz Shale members. The specimens of L.
silveradoensis in the Gas Point Member are from the member’s
lower part and represent juveniles. The Gas Point Member
juvenile specimen (height 4.3 mm) illustrated in Figure 10 is
the first to show the actual teeth of L. silveradoensis and the
first to show the right-valve dentition. The paratype (Fig. 5),
8 ■ Contributions in Science, Number 520
Squires: California Cretaceous Mollusks
Table 1 Measurements (mm) of specimens figured herein.
Taxa
Height
Length or
diameter*
Convexity
(single valve)
Bivalves
Limopsis silveradoensis
UCMP holotype 12324
17.2
14.7
4.9
UCMP paratype 12323
20.0
17.0
3.5
LACMIP hypotype 13712
7.1
6.3
1.4
LACMIP hypotype 13713
8.9
7.3
1.1
GASG hypotype 70937
4.3
4.7
1.5
CASG hypotype 70936
7.2
6.2
2.5
CASG hypotype 7093
5.2
4.2
1.8
Limopsis demeri
LACMIP holotype 13714
7.9
8.0
1.8
LACMIP paratype 13715
6.2
6.9
1.3
LACMIP paratype 13716
7.8
8.0
1.7
LACMIP paratype 13717
7.0
6.9
1.5
LACMIP paratype 13718
6.1
6.3
1.3
Limopsis sp.
LACMIP hypotype 13719
4.5
4.6
1.6
Gastropods
Misricymbiola ? sp.
SDSNH hypotype 32678
156.0
133.0
Turbinella ? sp
SDSNH hypotype 86561
72.4
(incomplete)
89.8
* Length refers to bivalves; diameter refers to gastropods.
which is from the Ladd Formation, is the largest known specimen
(height 20.1 mm). It is mostly an internal mold, including its
hinge.
The valves of L. silveradoensis exhibit morphologic variability.
Juveniles (less than height 9 mm) have a longer and straighter
dorsal-shell margin than do the adults, which have noticeably
shorter and sloped dorsal-shell margins. This variability might be
a function of paleoecology, given that Limopsis is an endobyssate
bivalve (Tevesz, 1977:4). The juveniles might have needed a
straighter dorsal margin for shell stability in the substrate than
did the adults. The location of the umbones is variable but is not
a function of growth stage. For example, a juvenile (Fig. 9) has a
central umbo, as does an adult (Fig. 3). Other specimens, juvenile
and adult, have an anteriorwardly located umbo (e.g., Figs. 6, 8,
and II). All the examined specimens show valve obliqueness,
except for the paratype (Fig. 3). The specimen shown in
Figure 13 has an incomplete posterior ventral area, thus its
obliqueness cannot be adequately discerned.
Limopsis silveradoensis is commonly found associated with
Glycymerita pacifica (Anderson, 1902). Sundberg (1980) reported
that L. silveradoensis was a shallow-infaunal, nonsiphonate
suspension feeder in the shallow-marine “Parallelodon-
Eriphyla-Limopsis Association” within the Holz Shale Member,
Orange County, Southern California.
Limopsis demerei new species
(Figs. 14-23)
Limopsis n. sp. Sundberg, 1979:table 2; Sundberg and Riney,
1984:table 1.
DIAGNOSIS. Shell size small, subquadrate, lowly convex,
numerous and closely spaced commarginal ribs, hinge teeth in
two nearly equal series with maximum of 15 anterior and 16
posterior teeth, central interior of valves with radial striae.
DESCRIPTION. Shell size small (up to height 7.9 mm, diameter
8.1 mm, same specimen). Shell subquadrate, slightly forward oblique.
Equivalved and equilateral. Valves lowly convex. Shell with numerous
and closely spaced commarginal ribs. Umbones commonly low,
central or slightly anterior of center. Ligament alivincular, short,
located in central triangular resilifer. Cardinal area long, smooth.
Hinge plate arched. Taxodont dentition in two, nearly equal-length
curving series. Number of hinge teeth increases with growth stage;
maximum of 15 teeth in anterior series and 16 teeth in posterior series.
Heteromyarian, with anterior adductor scar approximately one-half
size of posterior adductor scar. Pallial line entire. Central interior area
of valves with radial striae. Inner margin of valves smooth.
COMPARISON. The new species has the same subquadrate
shape as Limopsis maggae Heinberg (1979:105-106, fig. 1) from
Maastrichtian chalk beds in Denmark, but the new species has
sculpture, whereas L. maggae is smooth. The new species can
have the same ornament as Limopsis ravni Heinberg (1976:64-
66, figs. 11-12) from Maastrichtian chalk beds in Denmark, but
the new species has less prominent and much less projected
beaks, a much less inflated umbonal region, a much longer dorsal
anterior margin, and approximately twice as many teeth in both
the anterior and posterior series.
The new species also has the same subquadrate shape as
Limopsis kogata (Ichikawa and Maeda, 1958:90, pi. 5, figs. 4-7,
10) from Campanian to Maastrichtian beds in southern Japan,
but the new species has more, narrower, and more closely spaced
commarginal ribs.
The new species differs from L. silveradoensis by having smaller
maximum size, subquadrate shape, less-oblique and much less-
inflated valves, sculpture of prominent commarginal ribs (unless
abraded, e.g.. Fig. 20), dorsal-shell margin not short, muscle scars
prominent, central valve-interior striae prominent, and many more
hinge teeth. In addition, the new species differs by having umbones
that are smaller, much less inflated (almost flat on some specimens),
commonly much less projecting, and commonly central. If located
anteriorward, the umbones are less so than those found on L.
silveradoensis. A specimen of L. demerei (Fig. 18) approximately
the same size as L. silveradoensis (Fig. 6, interior filled with matrix)
also shows the exterior differences listed above.
DIMENSIONS. Table 1.
HOLOTYPE. LACMIP 13714 (right valve).
TYPE LOCALITY. LACMIP loc. 4898.
PARATYPES. LACMIP 13715 to 13718, all from LACMIP
loc. 4898.
GEOLOGIC AGE. Late Campanian to possibly early Maas-
trichtian.
STRATIGRAPHIC DISTRIBUTION. Point Loma Formation,
southeast of Carlsbad, northern San Diego County, Southern
California (Area 4); reworked Point Loma Formation fossils in
Cabrillo Formation, Bird Rock, south of La Jolla, San Diego
County, Southern California (Area 5).
REMARKS. The new species is based on 195 specimens: 182
from mudstone at LACMIP loc. 4898 (Madonna Hill Guest
Home) and 13 from mudstone at LACMIP loc. 7792 (Carlsbad
Research Center). Locality 7792 is approximately 1 km southeast
of locality 4898. Nearly all the specimens show excellent
preservation. Of the 195 specimens, eight are closed-valved and
four show gastropod boreholes. On some specimens (e.g.,
Figs. 14, 20), the sculpture is abraded, thereby producing a
smooth appearance.
The geology at LACMIP loc. 7792 (Carlsbad Research Center)
was discussed by Loch and Bottjer (1986), who also recognized an
aporrhaid -Limopsis paleocommunity there. This paleocommu-
nity, later named the Teneposita-Limopsis paleocommunity by
Loch ( 1989), does not represent a diminutive fauna, in spite of the
Contributions in Science, Number 520
Squires: California Cretaceous Mollusks ■ 9
mm
Figures 14-23 Limopsis demerei n. sp., LACMIP loc. 4898. 14-15. Paratype LACM1P 13715, left valve: 14. exterior, 15. interior; 16, 17, 22. paratype
LACMIP 13716, right valve: 16. exterior, 17. interior, 22. dorsal view; 18-19. paratype LACMIP 13717, right valve: 18. exterior, 19. interior; 20-21.
holotype LACMIP 13714, right valve: 20. exterior, 21. interior; 23. paratype LACMIP 13718, closed-valved, dorsal view (dorsal valve on top).
2 mm
2 mm
assertions by Loch and Bottjer (1986) and Loch (1989). The
species are actually of normal size in comparison to their size
elsewhere.
ETYMOLOGY. Named for Thomas Demere, in recognition of his
many contributions to the study of fossils found in the San Diego area.
Limopsis sp.
(Figs. 24-26)
REMARKS. The new species is based on a well-preserved,
single left valve (hypotype LACMIP 13719) of a presumed
juvenile collected from reworked clasts of Cenomanian age from
LACMIP loc. 25526 in central California (Area 2). The valve is
small (height 4.5 mm; Table 1) and differs from a same-sized
specimen (Fig. 9) of Limopsis silveradoensis by having an
orbicular rather than an oblique shape, no apparent obliqueness,
commarginal undulations, nine (rather than five) anterior teeth,
and nine (rather than six) posterior teeth. Although L. sp. has a
shape similar to L. demerei , the former differs by having more
rounded ends of the dorsal-shell margin, commarginal undula-
tions rather than prominent and closely spaced commarginal ribs,
and a more inflated umbo.
Class Gastropoda Cuvier, 1797
Clade Neogastropoda Wenz, 1938
PFamily Volutidae Rafinesque, 1815
PSubfamily Caricellinae Dali, 1907
REMARKS. Although workers (e.g., Wenz, 1943) tradition-
ally relegated Caricellinae to the volutid subfamily Scaphellinae
Gray, 1857, Bandel (2003) reinstituted Caricellinae as a
separate taxon based on newly found and well-preserved fossil
material. There is no consensus as to which genera should be
included in this subfamily. In this present paper, genera that
comprise it are Cariceila Conrad, 1835, and Misricymbiola
Bandel, 2003.
10 ■ Contributions in Science, Number 520
Squires: California Cretaceous Mollusks
Figures 24-26 Limopsis sp., hypotype LACMIP 13719, LACMIP loc.
25526, left valve. 24. exterior, 25. interior, 26. dorsal view.
PGenus Misricymbiola Bandel, 2003
TYPE SPECIES. Caricella ckalmasi Quaas, 1902, by original
designation; Late Cretaceous (Maastrichtian), Egypt.
REMARKS. Misricymbiola is characterized by a pear-shaped
shell with a constricted base, large rounded protoconch, low
conical spire, angular periphery, flattened sides of whorls with or
without with short axial ribs, three oblique columellar whorls on
early whorls, single columellar swelling on last whorl, and a long
siphonal canal (Bandel, 2003).
Misricymbiola differs from Caricella by having a larger size,
subquadrate shell (rather than fusiform), possible presence of
strong nodes on shoulder, wider aperture, one less columellar
fold on its early whorls, and a single columellar swelling on last
whorl. The protoconch of Misricymbiola differs from that of
Caricella by having no spiral cords or fine axial ribs that together
form a cancellate pattern where the protoconch ends and the
teleoconch begins. Also the protoconch of Miscymbiola has no
tendency to have a pointed apex.
Misricymbiola ? sp.
(Figs. 27-31)
REMARKS. This species is based on a single, very large
incomplete specimen (height 156 mm; Table 1); despite missing its
spire and probably some of its anterior canal, the specimen is the
largest known gastropod from Upper Cretaceous strata of the
northeast Pacific. The apparent absence of ornament on the shell
might be the result of poor preservation. The abapertural exterior
surface is riddled with boreholes, most likely made by the boring
sponge Cliona. This specimen cannot be unequivocally assigned to
Misricymbiola because it is missing its protoconch, and because it
cannot be determined if the specimen has three columellar folds on
its early whorls. On the mature last whorl, it has one fold on its
columella, and the fold is moderately strong and located deep
inside on the middle part of the columella (Fig. 28). The specimen
is pseudo-umbilicate (chink) and has a raised columellar shield.
The posterior canal region near outer lip has a large subsutural
welt that causes the growth line to arch backward over the welt.
Elsewhere, its growth line is nearly orthocline.
Misricymbiola ? sp. resembles specimens of Misricymbiola
chalmasi (Quaas, 1902) illustrated by Bandel (2003, figs. 15-
19, 21-24, 31-36) from Maastrichtian beds in the Western
Desert of Egypt, but the California species differs by having
a subsutural welt near the outer lip, shorter siphonal canal,
and an absence of the following: a raised columellar shield, a
pseudo-umbilicus, and nodes on the shoulder of the last whorl.
Misricymbiola ? sp. also resembles Misricymbiola conocoi Bandel
(2003, p. 88-89, figs. 20, 25-28, 37, 38) from Maastrichtian
beds in the Western Desert in Egypt, but the California species
differs by having a subsutural welt near the outer lip, and an
absence of the following: distinct carina along the shoulder of the
last whorl, parietal callus, spiral keel near base of last whorl,
raised columellar shield, and pseudo-umbilicus.
Misricymbiola ? sp. is very similar to a specimen identified as
Aitlica stromboides (Munier-Chalmas, 1881) by Collignon
(1971:157-158, pi. C, fig. 3), who reported it from Tunisia
and near the Campanian-Maastrichtian boundary in age. His
specimen is not an Aulica Gray, 1847 and is quite unlike Aulica
stromboides (Munier-Chalmas, 1881:80-81, pi. 5, figs. 10-11).
The columellar area of Collignon's specimen is not exposed and
needs cleaning. It is very likely a Misricymbiola and has the
overall shape, pseudo-umbilicus, and raised columellar shield just
like the new species. The California specimen differs by having a
larger size and a tabulate ramp.
PFamily Turbinellidae Swainson, 1835
[= Vasidae H. Adams and A. Adams, 1853 = Xancidae Pilsbry,
1921]
REMARKS. Although the classification of this family has
undergone revision in recent years, according to Harasewych
(2011), it currently comprises three subfamilies: Turbinellinae
Swainson, 1835; Vasinae H. Adams and A. Adams, 1853; and
Columbariinae Tomlin, 1928. Vasines and turbinellines are
shallow-marine dwellers, whereas the columbariines are bathyal
to abyssal (Harasewych, 2011).
PSubfamily Turbinellinae Swainson, 1835
REMARKS. There is no consensus as to which genera should
be included in this subfamily. In this present paper, genera that it
comprises are Turbinella Lamarck, 1799, and Syrinx Roding,
1798. Harasewych and Petit (1989) placed Syrinx , which they
reported as being the known largest-shelled gastropod (nearly 1 m
in height), in Turbinellinae because the radula of Syrinx auranus
(Linnaeus, 1758) is nearly identical to that of Turbinella pyrum.
PGenus Turbinella Lamarck, 1799
TYPE SPECIES. Voluta pyrum Linnaeus, 1767, by original
designation; Recent, southern India region.
REMARKS. According to Bandel (1975), Turbinella has a
multi-whorled, high protoconch whose first whorls are usually
destroyed and whose end is demarcated by a septum, and this
protoconch distinguishes this genus from similar-looking gastro-
pods (e.g., the volutid Misricymbiola ). Other distinguishing
characteristics of Turbinella are a possible pyriform shell,
ornament of spiral ribs and weak nodes becoming obsolete on
the last whorl, low siphonal fasciole adjacent to a narrow
umbilical slit, aperture oval, outer lip internally smooth, three to
five columellar folds, and a long siphonal canal long that has an
anterior notch (Davies, 1935).
Turbinella differs from Syrinx by having a smaller size, possible
pyriform shell, and several columellar folds (i.e., none on Syrinx).
Turbinella ? sp.
(Figs. 32-34)
REMARKS. This species is based on a single moderately
large specimen (height 72.4 mm [incomplete]; Table 1) that is
Contributions in Science, Number 520
Squires: California Cretaceous Mollusks ■ 1 I
Figures 27-31 Misricymbiola ? sp., hypotype SDSNH 32678, SDSNH loc. 3458. 27. apertural view; 28. oblique apertural view showing deep inside
columellar lip; 29. right-lateral view; 30. abapertural view; 31. dorsal view.
somewhat crushed and is missing the early half of its spire
and its siphonal canal. Crushing probably accounts for the
ramp being more steeply sloping and the shoulder being more
angular on the abapertural side of the specimen versus the
apertural side. The crushing also apparently created a wide
depression on the ramp near the outer lip. The shell is pseudo-
umbilicate and the columella bears at least two strong folds,
with the posterior one stronger. The anterior end of the
columella is missing, thus it cannot be determined if the
specimen had additional folds. The growth line is preserved
only on the ramp of the last quarter-turn of the last whorl, near
the outer lip. In the medial part of that area, the growth line is
arched adaperturally, but near the suture, the growth line is
bent in the opposite direction.
The rapidly descending last whorl of Turbinella ? sp. is like that
of the extant Turbinella angulata (Lightfoot, 1786). Turbinella ?
sp. cannot be unequivocally assigned to Turbinella because the
specimen is incomplete, especially in regard to its missing
protoconch.
Turbinella ? sp. differs from the Point Loma Formation
Misricymbiola ? sp. by having a much smaller size, at least two
columellar folds, no subsutural welt, a growth line on the ramp
that bends in the opposite direction, and a narrow, triangular
aperture. In addition, the last whorl of T.? sp. rapidly descends.
AGE AND BIOGEOGRAPHIC IMPLICATIONS OF THE
NEW MATERIAL
The earliest Limopsis was reported as Middle Jurassic (Bath-
onian) in age by Newell (1969) and Hallam (1977), but they did
not cite which species this age is based on. Tevesz (1977:39)
reported that the earliest Limopsis is the Middle Jurassic
(Bathonian) Limopsis minimus (Sowerby, 1824:114, pi. 472,
fig. 5) of England and southern Europe, but Oliver (1981:71)
12 ■ Contributions in Science, Number 520
Squires: California Cretaceous Mollusks
Figures 32-34 Turbinella ? sp., hypotype SDSNH 86561, SDSNH loc. 3456. 32. apertural view; 33. abapertural view; 34. dorsal view.
disputed this claim and asserted that the first truly recognizable
Limopsis is the Early Cretaceous (Albian) Limopsis albiensis
(Woods, 1899:71-72, pi. 15, figs, la-d, 2-4) from England.
Marliere (1939) put L. albiensis in synonymy with Limopsis
coemansi Briart and Cornet, 1868 from upper Albian strata of
France. Casey (1961) refined the lower limit of the geologic range
of L. albiensis to be latest Aptian. He reported Limopsis
dolomitica Casey (1961:576, pi. 79, fig. 4) of middle late Aptian
age from England but, unfortunately, the rare specimens do not
show the hinge.
Oliver (1981) reported that the entire Cretaceous fossil record
of Limopsis is scant. Based on an inspection of the literature,
the present author found the same results. Limopsis sp. from
northern California is apparently the only known Cenomanian
record of this genus. Limopsis silver adoensis, which is apparently
the only Turanian record of this genus, was the most widespread
Cretaceous Limopsis in the northeast Pacific. The author found
no Coniacian or Santonian reports of Limopsis anywhere. Gabb
(1864) reported a so-called Limopsis transversa Gabb (1864:200,
pi. 26, fig. 186) from Texas Flat, Placer County, northern
California. Squires and Saul (2009) reported that this locality is
the same as the “Granite Bay” or “Rock Corral” locality and that
the strata there are early Campanian in age. This “Granite Bay”
species, however, is not a Limopsis because its shape is
rectangular and its resilifer is not centrally located.
Oliver (1981:71) reported that Limopsis underwent a radiation
during the Maastrichtian, when species became more quadrate
than earlier ones. Limopsis demerei shows this change in shape. It
also is less oblique than earlier species, has a straighter dorsal
margin, less projecting beak, more hinge teeth, and has
commarginal ribbing. Limopsis demerei shows that this “Maas-
trichtian” radiation began as early as late Campanian.
Volutidae ranges from Cenomanian to Recent, with the earliest
member being Carota Stephenson, 1952 from Texas (Stephenson,
1952; Taylor et ah, 1980). Although the earliest record of
caricellines is very poorly known, a tentative geologic range of
this group is Maastrichtian (Bandel, 2003) to Eocene (Palmer and
Brann, 1966). If future collecting does establish that the latest
Campanian to possibly early Maastrichtian Misricymbiolai sp.
from Southern California does belong to this genus, then it would
be the earliest known caricelline and the first record of this genus
outside of the tropical western Tethys Sea region in western
Egypt (Bandel, 2003) and possibly Tunisia (Collignon, 1971).
The record of Misricymbiolal in Southern California is slightly
earlier than the Egyptian occurrence and approximately the same
age as the presumed Tunisian occurrence of this genus. Known
species of Misricymbiola , however, have large protoconchs that
indicate direct development (Bandel, 2003), and this type of
larval stage (i.e., no planktonic stage) would have made it
difficult for genus to achieve widespread distribution during only
the latest Campanian to possibly early Maastrichtian. Future
collecting might show that it was present earlier elsewhere.
Taylor et al. (1980:text, fig. 7) reported that Turbinellidae [ =
Vasidae] originated during the middle Albian but did not provide
any documentable evidence. The earliest known Turbinellidae is
the vasine Fimbrivasum robustum Squires and Saul, 2001 of
latest Santonian age from Vancouver Island, British Columbia,
Canada. The earliest known columbariine is Columbarium
heberti (Briart and Cornet, 1880) of Maastrichtian age from
the Netherlands (Darragh, 1969:64). Prior to the detection of
Turbinella ? sp., the geologic record of turbinelline genera was
reported to be Oligocene to Recent for Turbinella (Cossmann,
1901; Davies, 1935) and Pliocene to Recent for Syrinx (see Wenz,
1943). The latest Campanian to possibly earliest Maastrichtian
Turbinella ? sp. potentially represents the earliest known turbinel-
line. Weller (1907) and Richards and Ramsdell (1962) reported a
few species of so-called Turbinella mainly from Maastrichtian
and, to a lesser degree, from Campanian rocks in New Jersey, but
these species are based on internal molds that are also mostly very
incomplete. Much better specimens are needed to establish the
presence of turbinellids in Cretaceous beds of New Jersey.
Turbinella ? sp. potentially helps establish that turbinellines, like
vasines and columbariines, evolved during the Late Cretaceous.
Taylor et al. (1980) and Sohl (1987) hypothesized that the
Neogastropoda originated in temperate seas. At least for
Turbinellidae, the northeast Pacific record supports their
hypothesis. Using the approximate latitudinal limits depicted
for the northeast Pacific during the Late Cretaceous (Saul and
Contributions in Science, Number 520
Squires: California Cretaceous Mollusks ■ 13
Squires, 2008 : fig. 3), Fimbrivasum robustum, the earliest known
vasine would have lived in somewhat northerly warm-temperate
waters. Turbinella ? sp., as well as Misricymbiola ? sp., would
have lived in more southerly waters nearer the boundary of
warm-temperate and tropical waters. The molluscan species
found at the type localities of both new species lived elsewhere
on the northeast Pacific in warm-temperate environments.
Additional evidence for warm-temperate seas is the presence of
rudist bivalves found elsewhere in intertidal sandstones of the
Point Loma Formation in the Carlsbad area. Although the
rudists and the studied neogastropods did not inhabit a common
ecotope, the rudists are indicators of at least marginal tropicality
because of their wider reported low-latitude occurrence (e.g.,
Sohl, 1987).
ACKNOWLEDGMENTS
Jean DeMouthe (CASG), Harry Filkorn, Mark Goodwin (UCMP), and
Thomas A. Demere (SDSNH) allowed access to the collections. LouElla
R. Saul (LACMIP) helped in finding some of the Limopsis specimens in
the CASG collection, and she and Edward Petuch (Florida Atlantic
University, Boca Raton, Florida) shared their considerable knowledge
about neogastropod genera. Scott Rugh provided locality information
about both Point Loma Formation specimens. |im Haggart (Geological
Survey of Canada, Vancouver, British Columbia) and Steffen Kiel
(University of Gottingen, Germany) critically reviewed the manuscript
and gave insightful comments and constructive suggestions.
LITERATURE CITED
Anderson, F.M. 1902. Cretaceous deposits of the Pacific coast.
Proceedings of the California Academy of Sciences, Series 3,
Geology 2:1-54.
Bandel, K. 1975. Entwicklung der Schale im Lebenslauf zweier
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Received 5 July 2011; accepted 13 October 2011.
Contributions in Science, 520:15-72
16 October 2012
POLYPLACOPHORA (MOLLUSCA) FROM THE SAN DlEGO FORMATION:
A Remarkable Assemblage of Fossil Chitons
FROM THE Pi jocene of Southern California1
Michael J. Vendrasco,2 Douglas j. Eernisse,3 Charles L. Powell II,4 5
and Christine Z. Fernandez"
ABSTRACT. A rich chiton assemblage consisting of more than 15,000 valves (shell plates) was collected by George P. Kanakoff (1897-
1973) from Pliocene exposures of the San Diego Formation just north of the U.S./Mexican border. The assemblage includes 16 extant
species, three extinct species ( Callistocbiton sphaerae n. sp., Lepidozona kanakoffi n. sp., and Amicula solivaga n. sp. ), and three
indeterminate species. The collection is dominated by the genus Callistocbiton and also includes the genera Leptocbiton , Oldroydia ,
Lepidozona , Stenoplax, Amicula , Mopalia, Placipborella , Tonicella , Dendrocbiton, and Nuttallimi.
This assemblage expands the known stratigraphic and paleogeographic ranges of many chiton genera and species and provides
information about an apparent late Cenozoic diversification of chitons along the Pacific Coast of North America. Chitons appear to have
diversified in the northeastern Pacific from the middle Miocene to Pleistocene, driven in part by regional increases in productivity and
environmental heterogeneity during that time.
The chitons are interpreted to have been deposited at inner-neritic depths (~25 m) in the mouth of a bay or in a continental shelf
environment, and the annual temperature range and seasonality are inferred to have been similar to those that occur off the nearby San
Diego coast today. However, the fossil assemblages also include a mixture of taxa that today range only to the north or to the south.
The large sample sizes of chiton valves allow rigorous analysis of the ratio of valve types, revealing a divergence from the expected
pattern. This divergence is even greater on average than what occurs in assemblages of chiton valves in Holocene sediments, revealing that
taphonomic factors bias valve ratios long after valves are disarticulated.
New foraminiferan and molluscan data indicate a middle or late Pliocene age of deposition for these beds, between 3.3 to 2.5 million
years ago (Ma), and possibly about 3.0 Ma.
INTRODUCTION
George P. Kanakoff and assistants in the 1950s and 1960s
collected more than 15,000 chiton valves from outcrops of the
San Diego Formation near the international border between
California and Mexico (Figure 1, Appendix 1). At the time,
Kanakoff was the curator of invertebrate paleontology at the
Natural History Museum of Los Angeles County Invertebrate
Paleontology Department (LACMIP), a position he held from
1948 to 1966 (Marincovich, 1974). Kanakoff led groups of
volunteers, many of whom were high school students, to collect
and subsequently sort vast amounts of fossil material from the
Border localities (E.C. Wilson and P.I. LaFollette, personal
communication to M.J.V., 2006). Kanakoff instructed his
students to “save everything” during field and laboratory work
(Marincovich, 1974:64), and so these collections probably
provide an accurate representation of the fossil assemblages at
the localities collected and are not as highly skewed towards well-
preserved or complete valves as is normal for chiton fossil
collections. As a result of his thorough methodology and because
1 URL: www.nhm.org/scholarlypublications
“ Department of Biological Science, California State University, Full-
erton, California 92834-6850, USA; Invertebrate Paleontology, Natural
History Museum of Los Angeles County, 900 Exposition Boulevard, Los
Angeles, California 90007, USA. E-mail: mvendrasco@fullerton.edu
' Department of Biological Science, California State University, Full-
erton, California 92834-6850, USA; Malacology, Natural History
Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles,
California 90007, USA. E-mail: deernisse@fullerton.edu
4 U.S. Geological Survey, Menlo Park, California 94025, USA. E-mail:
cpowell@usgs.gov
5 14601 Madris Ave., Norwalk, California 90650, USA. E-mail:
cfernandez@bren.ucsb.edu
of the incredible richness of this fauna, Kanakoff and colleagues
managed to recover the largest and most diverse assemblage of
fossil chitons known in the world.
Most of the fossil chitons from LACMIP historic locality 305
were originally examined by Spencer R. Thorpe, Jr., then at the
California Academy of Sciences (E.C. Wilson, personal commu-
nication to M.J.V., 2006). Thorpe provided some identifications
and advised Leo G. Hertlein on geographic ranges of modern
chitons for the summary of the chiton fauna that was to appear in
their intended paper on the gastropods and chitons of the San
Diego Formation, although the description of the chiton fauna in
their draft is only two pages long.
Few chitons have been described, or even listed, from fossil
localities in California, and most of these are from Pleistocene
deposits. Chitons have been described from Cenozoic sedimen-
tary rocks in California by Pilsbry (1892), Chace (1916a, b),
Chace and Chace (1919), Berry (1922, 1926), Kennedy (1978),
Roth (1979), Squires and Goedert (1995), and Dell’Angelo et al.
(2011). Chitons, as minor faunal elements, have also been
mentioned by Orcutt (1889), Ashley (1895), Oldroyd (1914),
Moody (1916), Clark (1918), Valentine (1961), Valentine and
Meade (1961), Chace (1966), Marincovich (1976), Kennedy
et al. (1981, 1992 [1993]), Davis (1998), Powell (1998), and
Powell et al. (2002). Perhaps as testament to their typical rarity in
California fossil assemblages, chitons were entirely omitted from
the Check list of California Tertiary Marine Mollusca (Keen and
Bentson, 1944), as well as from compilations by Grant and Gale
(1931) and Weaver (1942 [1943]). The collection described
herein therefore provides significant additional information on
the diversification of late Cenozoic chitons along the Pacific
Coast of North America. The rich San Diego Formation chiton
fauna from the Pliocene stands in striking cotrast to the paucity
of reported chitons from the older and warmer Miocene deposits
© Natural History Museum of Los Angeles County, 2012
ISSN 0459-8113 (Print); 2165-1868 (Online)
16 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Fine-grained sandstone,
high diversity of fossils
Fine-grained sandstone,
many concretions,
high diversity of fossils
1 0.5 m
Medium-grained sandstone,
packed with urchin spines
Figure 1 Locality and stratigraphy. 1, map showing location of the three main historic localities described here; 2, stratigraphy of the exposed portion
of the San Diego Formation at the Border locality near or at LACMIP locality 305 (A=SDNHM locality 6241; B=SDNHM locality 6242; C=SDNHM
locality 6243).
along the Pacific Coast of North America, even though the latter
have extensive molluscan fossils and these are generally well
studied. Dell’Angelo et al. (2011) have recently described multiple
new chiton species, represented by 140 total valves, from even
older Paleogene deposits from Washington State. These appear to
have little in common with the Pliocene fauna described here,
instead having affinities to more southern or Old World chiton
faunas, but their discovery could indicate that Miocene chitons
will eventually be found if they are searched for specifically.
Herein we describe the chiton fauna from the San Diego
Formation and discuss the following: (1) how this assemblage
provides evidence for a major, recent chiton diversification event
on the Pacific Coast; (2) migration of chitons during the
Cenozoic; (3) new evidence on the age of the localities of the
San Diego Formation from which these fossils were collected; (4)
aspects of the paleoenvironment of these fossils; and (5) the
taphonomy of chiton valves. These analyses were based primarily
on fossil specimens from LACMIP as well as modern specimens
from the Natural History Museum of Los Angeles County,
Malacology Department (LACM).
STRATIGRAPHY OF THE SAN DIEGO FORMATION
The San Diego Formation consists of up to 84 m of terrestrial and
continental-shelf marine sediments exposed over a nearly 60-km-
long arc extending from Pacific Beach, San Diego, to northern
Baja California (Rowland, 1972; Demere, 1982, 1983). The
informal lower member is characterized by up to 75 m of
massive, fine-grained, friable, marine sandstone with occasional
thin conglomerate layers, and the informal upper member
consists of up to 9 m of nonmarine, massive, fine-grained, friable
sandstone with occasional thin conglomerate layers (Demere,
1983). In addition, Wagner et al. (2001) described the presence of
nonmarine beds below the lower member described by Demere
( 1983) exposed in the eastern part of the San Diego depositional
basin.
The fossils of the San Diego Formation were first listed by Dali
(1874, 1898), who assigned the name “San Diego beds” to
fossiliterous rocks extracted in the process of digging a well in
Cabrillo Canyon near San Diego, California (now Balboa Park).
Arnold (1903) later referred to the sediments as the “San Diego
Formation” and described the fauna from a different stratigraph-
ic section at Pacific Beach, San Diego. Hertlein and Grant (1944)
argued that the old San Diego well in Balboa Park should be
considered the type locality. However, the well has since been
filled and the Pacific Beach section is the best remaining exposure
of the San Diego Formation. Arnold (1903:57-58) recognized
two biostratigraphic divisions of the San Diego Formation at the
Pacific Beach section; a “lower horizon” characterized by the
bivalves Flabellipecten stearnsii (Dali, 1874) f = Euvola stearnsii ]
and Patinopecten healeyi (Arnold, 1906), and the gastropod
Opalia anomala Stearns, 1875 and its synonym Opalia varicos-
tata Stearns, 1875; and an “upper horizon” characterized by the
bivalve Pecten bellus (Conrad, 1856b) replacing E. stearnsii , rare
Patinopecten healeyi , the gastropod Crepidula princeps Conrad,
1855, and the echinoid Dendraster asbleyi (Arnold in Arnold and
Anderson, 1907). Demere (1982) followed Arnold’s (1903) lead
in recognizing a lower biostratigraphic unit at Pacific Beach
characterized by Euvola (as Flabellipecten) stearnsii , Patinopec-
ten healeyi , and O. varicostata, and an upper unit with Pecten
bellus, D. asbleyi, and the gastropod Nucella lamellosa (Gmelin,
1791).
The specimens described here are from localities of the San
Diego Formation near the international border between the
United States and Mexico. The following discussions of
stratigraphic correlation, age, taphonomy, and paleoenvironment
focus specifically on three primary localities from which Kanak-
off collected chitons, LACMIP localities 305, 16817 (ex 305A),
and 16862 (ex 305C) (“Border beds” or “Border localities”
herein).
CORRELATION OF THE BORDER BEDS OF THE SAN
DIEGO FORMATION
The LACMIP Border locality collections reveal abundant
specimens of Opalia varicostata, Euvola stearnsii, and Patino-
pecten healeyi, characteristic of the lower unit of the San Diego
Formation at the Pacific Beach section sensu Demere (1982), but
also abundant Pecten bellus, characteristic of Demere’s upper
unit. Paleoenvironmental data also provide equivocal evidence
for correlation. Ingle (1967, 1980) observed foraminifers from
Pacific Beach and inferred a warm-water, outer-shelf assemblage
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 17
Figure 2 Fossils of biostratigraphic and paleoenvironmental significance from LACMI1’ locality 305. 1, Patinopecten bealeyi (Arnold, 1906) (scale
bar=l cm); 2, Lucinoma annulatum (Reeve, 1850) (scale bar=l cm); 3, Strictispira ( Crassispira ) zizypbits (Berry, 1940) (scale bar=0.5 cm); 4, Eiwola
stearnsii (Dali, 1874) (scale bar=l cm); 5, Opalia varicostata Stearns, 1875 (scale bar=0.5 cm); 6-7, Arcbitectonica nobilis Roding, 1798 (scale
bar=l cm); 8, Neogloboquadrina asanoi (Maiya, Saito, and Sato, 1976) (scale bar=250 pm); 9, Globigerinoides ruber (d’Orbigny, 1839) (scale
bar=250 pm); 10, Globorotalia tumida (Brady, 1877) (scale bar=100 pm); 11, Globigerina bulloides (d’Orbigny, 1826) (scale bar=250 pm); 12,
Hanzawaia nitidula (Bandy, 1953) (scale bar=250 pm); 13, Quinqueloculina lamarckiana d’Orbigny, 1839 (scale bar=250 pm).
in the lower part of the section and a cool-water, shallower
assemblage in the upper part of his section. Wicander (1970)
examined planktonic Foraminifera from Pacific Beach and other
localities of the San Diego Formation, and inferred cooler water
throughout the formation. Later, Mandel (1973) examined
planktonic foraminifers from exposures near the border (includ-
ing localities he listed as LACMIP 305A and C) and recognized a
decidedly warm-water, outer-shelf assemblage. Demere (1982)
regarded Mandel’s (1973) warm-water fauna to be correlative
with the warm-water facies of the lower unit at Pacific Beach.
Most of the fossils from the Border localities occur off of San
Diego today, with a few extralimital southern and northern
species (species whose ranges are entirely south or north of the
fossil locality). Nearly all of the species in these assemblages
today occur in the Californian biogeographic province (also
“warm-temperate” sensu Valentine, 1966, or “San Diegan”
sensu Briggs, 1974). The Border localities show a mixture of
warm and cold, moderately deep-water fauna (see “Discussion”),
which matches neither the warm, shallow-water characteristic of
the lower part of the section at Pacific Beach, nor the cooler,
deep-water characteristic of the upper part in the same section
(Demere, 1982, 1983). However, the fauna from the Border
localities is overall more similar to that in the lower part of the
Pacific Beach section, and so we conclude that the Border beds
probably correlate with the lower part or with a hypothetical
transitional zone between the lower and upper parts.
A detailed record of the stratigraphy of the fossiliferous section
from which Kanakoff collected is unknown. Kanakoff listed the
height (in feet) above the dirt road at each of his fossil localities
(Appendix 1), which indicates each sample was collected from
within a narrow stratigraphic range. LACMIP localities 305,
16862 (305A), and 16817 (305C) occur within 1 km of each
other and all contain very similar faunas, indicating they came
from the same, or closely spaced, stratigraphic horizons.
Most of the chitons studied are from LACMIP localities 305
and 16817 (305C). With assistance from Scott Rugh (San Diego
Natural History Museum |SDNHM|), we (C.Z.F. and M.J.V.)
were able to locate exposures near or at Kanakoff’s original
collecting localities. The locality we discovered near LACMIP
locality 305 had the most easily accessible fossiliferous expo-
sures, with three shell beds within a 2-m section (Figure 1,
SDNHM localities 6241-6243) exposed along a road-cut. The
18 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Figure 3 Known stratigraphic ranges of chitons on the Pacific Coast of
North America. Gray bars show previously reported range; black bars
show range extension based on specimens described herein. The first
appearance datum of Eocene/Oligocene for Lepidozona is based on one
valve, and that for Stenoplax is based on just a few valves (Dell’Angelo et
al., 2011); otherwise the San Diego Formation assemblage provides the
oldest records of these genera on the Pacific Coast of North America.
shell beds were separated by units of structureless fine-grained
sand that lacked obvious fossils. The lowest fossil bed averaged
about 5 cm in thickness and consisted of shell hash dominated by
sea urchin spines in a medium-grained sand matrix. The middle
bed averaged about 20 cm in thickness and contained a more
diverse fossil assemblage dominated by mollusks. This shell bed
had a matrix of fine-grained sand but with common massive
concretions that in places encompassed the entire fossil bed. The
uppermost shell bed averaged about 20 cm in thickness and
contained abundant fossils dominated by mollusks in a fine-
grained sand matrix. The upper two shell beds contain abundant
fossils in diverse orientations, a good incidence of complete
shells, and many examples of articulated bivalves.
AGE OF THE BORDER BEDS
The precise age range of the San Diego Formation at the Border
localities remains unclear. Estimates of the age of the San Diego
Formation have ranged, in general, between early Pliocene and
earliest Pleistocene. Whereas some have considered it exclusively
Pliocene (Hertlein and Grant, 1944, 1972; Corey, 1954; Milow
and Ennis, 1961; Oakeshott, 1964; Ingle, 1967; Rowland, 1969;
Wicander, 1970), others have argued that it extends into the
earliest Pleistocene (Arnold, 1903; Allison, 1964; Demere, 1983;
Wagner et al., 2001). Demere (1982, 1983) tentatively suggested
that known planktonic foraminiferans from the formation
indicated an age range from no older than from 3.0 million
years ago (Ma) to at least as young as 1.5 Ma, although he did
not state which species allowed such inferences. Barnes
(1976:332-334) assigned fossil vertebrates, mainly marine
mammals, from the formation to the Blancan North American
Land Mammal Age (4. 8-1. 8 Ma). Recently, combined land
mammal biostratigraphic and magnetostratigraphic dating has
been applied to nonmarine facies within the lower part of the San
Diego Formation in Chula Vista where an age of 3.6 to 3.5 Ma
was assigned (Wagner et ah, 2001). Planktonic foraminifera and
calcareous nannoplankton from the San Diego Formation on the
south side of Mount Soledad (LACMIP locality 17228) indicate a
probable early Pliocene age of between 3.8 and 4.2 Ma
(Boettcher, 2001; Kling, 2001) and correlated with Calcareous
Nannoplankton Zone CNllb. The combined data currently
available thus indicate an age range from as old as 4.2 Ma to
possibly as young as 1.5 Ma for the San Diego Formation.
Schatzinger (1972) concluded that beds at localities he
considered LACMIP 305 and 16862 (305A) were deposited
during the Pliocene, citing the occurrence of many fossils inferred
to have gone extinct during that epoch. Mandel (1973) used
ranges of foraminifers to conclude that the sediments at what he
considered to be LACMIP 16862 (305A) and 16817 (305C) were
deposited during the latest Pliocene, but possibly ranging into the
earliest Pleistocene. Extinct mollusks from the Border localities
include the bivalves Anadara trilineata (Conrad, 1856b), Area
sisquocensis Reinhart, 1937, Barbatia illota (Sowerby, 1833),
Basterotia bertleini Durham, 1950, Chlamys hastata ellsi
Hertlein and Grant, 1972, C. jordani (Arnold, 1903), Euvola
stearnsii, Limaria orcutti (Hertlein and Grant, 1972), Lyropecten
cerrosensis (Gabb, 1866), Myrakeena veatebii (Gabb, 1866),
Patinopecten healeyi, Pecten bellus, Protothaca tenerrima alta
(Waterfall, 1929), Rhamphidonta frankiana (Hertlein and Grant,
1972), Securella kanakoffi (Hertlein and Grant, 1972), Swifto-
pecten parmeleei (Dali, 1898), Thracia trapezoides Conrad,
1 849, and the gastropods Calliostoma coalingense catoteron
Woodring and Bramlette, 1950, Calyptraea filosa Gabb, 1866, C.
inornata (Gabb, 1866), Cancellaria fergusoni Carson, 1926,
Crepidula princeps , Nassarius sp. cf. N. grammatus (Dali, 1917),
Opalia varicostata, and Tegula hemphilli Oldroyd, 1921.
Rhamphidonta frankiana and Limaria orcutti are restricted to
the San Diego Formation and so are of little use in refining the
age of this part of the San Diego Formation. In addition, detailed
stratigraphic ranges of most mollusks are poorly known in
California because of the lack of appropriate dating techniques
and thus have not been correlated with a numerical time scale.
Nevertheless, the molluscan assemblage indicates a middle to late
Pliocene, and not Pleistocene, age for the Border localities.
Observations in support of this claim include the occurrence in
the Border beds of the following: (1) common Patinopecten
healeyi and Opalia varicostata (Figures 2.1, 2.5), two index
fossils for the Pliocene (Shinier and Shrock, 1944; Groves and
Squires, 1988; Groves, 1991); (2) Turcica brevis Stewart in
Woodring, Stewart, and Richards 1940 [1941], a fossil restricted
to the Pliocene (Powell et al., 2004); (3) Pecten bellus and
Crassispira zizyphus , which may indicate middle/late Pliocene to
early Pleistocene age (Powell and Stevens, 2000); and (4) the
terminal Pliocene fossils Lyropecten cerrosensis and Terebra
martini English, 1914 (Groves, 1991). More recently, Powell
Contributions in Science, Number 520
Vendrasco et a!.: Chitons of the San Diego Formation ■ 19
Table 1 Summary of taxonomy of chitons from the San Diego
Formation.
Class Polyplacophora Gray, 1821
Order Lepidopleurida Thiele, 1910
Suborder Lepidopleurina Thiele, 1910
Family Leptochitonidae Dali, 1889
Leptochiton Gray, 1847b
Leptochiton rugatus (Pilsbry, 1892)
Leptochiton nexus Carpenter, 1864
Oldroydia Dali, 1894a
Oldroydia percrassa (Dali, 1894a)
Order Chitonida Thiele, 1910
Suborder Chitonina Thiele, 1910
Family Ischnochitonidae Dali, 1889
Callistochiton Dali, 1879
Callistochiton palmulatus Dali, 1879
Callistochiton spbaerae n. sp.
Lepidozona Pilsbry, 1892
Lepidozona mertensii (von Middendorff, 1847)
Lepidozona pectinulata (Carpenter in Pilsbry, 1893)
Lepidozona sp. cf. L. rothi Ferreira, 1983
Lepidozona sp. cf. L. radians (Carpenter in Pilsbry, 1892)
Lepidozona kanakoffi n. sp.
Stenoplax Dali, 1879
Stenoplax circumsenta Berry, 1956
Stenoplax fallax (Carpenter in Pilsbry, 1892)
Stenoplax sp. cf. S. heathiana Berry, 1946
Suborder Acanthochitonina Bergenhayn, 1930
Family Mopaliidae Dali, 1889
Amicula Gray, 1847a
Amicula solivaga n. sp.
Dendrochiton Berry, 1911
Dendrochiton sp. indeterminate
Mopalia Gray, 1847a
Mopalia sinuata Carpenter, 1864
Mopalia sp. cf. M. swanii Carpenter, 1 864
Mopalia sp. indeterminate
Placiphorella Dali, 1879
Placiphorella velata Dali, 1 879
Placiphorella sp. cf. P. mirabilis Clark, 1 994
Tonicella Carpenter, 1873
Tonicella sp. cf. T. venusta Clark, 1999
Family Lepidochitonidae Iredale, 1914
Nuttallina Dali, 1871
Nuttallina sp. indeterminate
et al. (2008a, b, 2009) used the presence of the extralimital
southern gastropod Architectonica (Figures 2. 6-2. 7) and other
warm-water mollusks to correlate several sites in Southern
California, including the Border localities, with the mid-Pliocene
warm event that occurred between about 3.3 and 3.0 Ma
(Dowsett and Robinson, 2009). If Architectonica is a valid
indicator of this warm event (but see “Discussion”), it would
indicate a possible age of 3.3 to 3.0 Ma for these deposits.
The collections from LACMIP locality 16817 (305C) contain
the planktonic foraminifer Neogloboquadrina asanoi (Maiya,
Saito, and Sato, 1976; Figure 2.8), identified by J.P. Kennett
(personal communication to M.J.V., 2007), and lack any
foraminifers exclusively younger than middle Pliocene, indicating
deposition during the California margin planktonic foraminiferal
zone 6 of Kennett et al. (2000) and a likely age between 3.25 and
2.5 Ma (see fig. 2 in Kucera and Kennett, 2000). Kennett’s age
determination matches up well with that estimated by Powell
et al. (2008a, b, 2009) for the San Diego Formation Border
localities; the overlap of the two age ranges is 3.25 to 3.0 Ma.
SYSTEMATICS
This massive chiton assemblage consisting of more than 15,000
valves from about 22 species, including three new species, is the
largest and most diverse fossil chiton assemblage known. The
chitons comprise three suborders, four families, and 1 1 genera.
The assemblage extends the known fossil record for nine chiton
genera along the Pacific Coast (Figure 3). A summary of the
taxonomy of these chitons is provided in Table I.
The taxonomy of chitons in the temperate northeastern Pacific
is far from settled, and key distinguishing characters among
similar chiton species are often not preserved in fossils. For
example, species of Mopalia are often characterized by the nature
of girdle setae (Eernisse et al., 2007). This makes taxonomic
assignments of fossil chiton valves difficult, and in some cases
here we favor an open nomenclature, including indications of
uncertainty such as “cf.” or “indeterminate.” Many valve
fragments in this assemblage could not be reliably assigned to
genus, and we have left them unnamed. Nevertheless, the
exquisite preservation of the tegmental sculpture in thousands
of valves and the abundance of each type of valve (head,
intermediate, tail) in many species has allowed detailed taxo-
nomic analyses in those cases. Measurements here were made on
digital photographs using ImageJ software (Rasband 1997-
2009). Chiton shell terminology is depicted in Figure 4; readers
are referred to Schwabe (2010) for a more detailed description of
chiton terminology.
Unfigured specimens of the three new species from their type
localities should be considered to be paratypes. By necessity here
instead we refer to them as part of “unfigured topotype lots.”
However, these specimens did inform us in our descriptions of
the new species and we have no reason to doubt their
classification as such.
Hertlein and Grant’s original unpublished manuscript con-
tained a list of 15 chiton species from LACMIP locality 305 that
were identified by Spencer Thorpe. This list differs from ours in a
number of ways, but the overall classification is similar. We could
find no indication of which sets of specimens at LACMIP were
examined and/or identified by either Thorpe or Hertlein, and so
we have reidentified all of the specimens ourselves.
Institutional abbreviations used herein include the following:
ANSP, Academy of Natural Sciences of Philadelphia; LACM,
Natural History Museum of Los Angeles County, Malacology
Department; LACMIP, Natural History Museum of Los Angeles
County, Invertebrate Paleontology Department; PRM, Peter
Redpath Museum, McGill University, Montreal, Canada;
SBMNH, Santa Barbara Museum of Natural History, and
USNM, United States National Museum of Natural History.
Class Polyplacophora Gray, 1821
Order Lepidopleurida Thiele, 1910
Genus Leptochiton Gray, 1847b
DISTRIBUTION. This genus occurs worldwide (see Kaas and
Van Belle, 1985a). Five described species of Leptochiton are
known from the eastern Pacific (Ferreira, 1979a), although this is
likely an underestimate. For example, specimens collected from
greater than 15-m depth in Southern California previously
identified as the wide-ranging Leptochiton rugatus (Pilsbry,
1892) belong to a second, undescribed deeper-water species,
based primarily on DNA evidence (D.J. Eernisse and R. Kelly,
unpublished data; see also Stebbins and Eernisse, 2009).
Fossils classified as Leptochiton have been found worldwide,
and may date back to the Mesozoic (Van Belle, 1981). However,
Sirenko (2006) recorded a range of only Eocene to Recent for
Leptochiton , and according to his list the Eocene occurrence is
20 B Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Dorsal View
Anterior
Ventral View
Anterior View, Intermediate Valves
width ^
Dorsal View, Intermediate Valves
height
Carinated
Rounded
tegmentum
(reduced)
Figure 4 Terminology for chiton valves. Note there is some overlap and gradation in tegmental sculpture terminology. For example, “lattice” by
definition contains “longitudinal ridges.” Also, the small, closely spaced bumps labeled “granules” grade into the larger, more widely spaced bumps
labeled “tubercles.” See Schwabe (2010) for more details on chiton terminology.
the oldest record of an extant chiton species. Sigwart et al. (2007)
subsequently described Leptochiton faksensis from the Paleocene
of Denmark. In any case, there is a sparse fossil record of this
genus in the temperate eastern Pacific, although the modern
species Leptochiton alveolus (Loven, 1846) is reported from the
latest Eocene and earliest Oligocene of Washington (Squires
and Goedert, 1995), one valve assigned to Leptochiton sp. was
described from the latest Eocene or earliest Oligocene of
Washington (Dell’Angelo et al., 2011), and one valve of
Leptochiton nexus Carpenter, 1864, was reported from a
Pleistocene marine terrace at Upper Newport Bay, California
(Kanakoff and Emerson, 1959).
Leptochiton rugatus (Pilsbry, 1892) species complex
Figure 5 (1-17)
Leptochiton internexus rugatus: Dali, 1879:319 ( nomen nudum).
Lepidopleurus rugatus Pilsbry, 1892:11, pi. 3, figs. 67-70.
Leptochiton rugatus Thiele, 1909:12-13, pi. 1, figs. 41-50;
Ferreira 1979a: 146, figs. 1-2, 7, 33-34 (contains more
complete synonymies).
Lepidopleurus internexus Dali, 1879:319 ( nomen nudum).
Leptochiton internexus: Smith 1947a:4; 1947b: 17.
Leptochiton cancellatus: Dali, 1879:315 (not Chiton cancellatus
Sowerby, 1839).
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 21
? Lepidopleurus alascensis Thiele, 1909:11, pi. 1, figs. 51-60;
Taki and Taki, 1929:162.
? Leptochiton alascensis : Smith, 1947a:3.
Not Lepidopleurus assimilis Thiele, 1909: Kaas and Van Belle,
1994:15, 17 (contra synonymy by Ferreira 1979a).
DISTRIBUTION. LACMIP locality 305 (3 head valves, LACMIP
13730-13732, 3 intermediate valves, LACMIP 13733-13734,
13736, and 2 tail valves, LACMIP 13737-13738).
TYPE SPECIMENS. Three syntypes (ANSP 35586); two
complete specimens and one with disarticulated valves (Ferreira,
1979a).
TYPE LOCALITY. Designated as Monterey, California, to
Bahia Todos Santos, Baja California, Mexico, but label on
syntypes indicates these specimens were collected near San
Tomas River, Baja California (Ferreira, 1979a).
REMARKS. These fossil valves share with modern represen-
tatives of Leptochiton rugatus the same small size, low
!ength:width ratio, rounded anterior profile (argued by Ferreira
[1979a: 147] to be “a constant diagnostic feature” of this species),
tegmental sculpture of faint longitudinal rows of granules on
head/tail valves and lateral areas of intermediate valves, and
rounded lateral margins on intermediate valves. They also show
slightly raised lateral areas and occasional “coarse concentric
wrinkles” (Pilsbry, 1892:11) that characterize this species.
Some head and tail valves here assigned to this species are
larger than what has been reported for this species by Ferreira
(1979a), who stated the largest specimen he observed was
15.8 mm in length excluding girdle. For example, one head valve
(Figures 5. 5-5. 6) is 2.5 mm long, corresponding to an animal
that would have been about 20 mm in length. However, the
similar tegmental sculpture of irregular “wrinkles” overlying
faint longitudinal ridges and similar overall shape (including
rounded anterior profile in all valves and shape of sutural
laminae in the tail valve) indicates that these specimens are best
classified in this species.
These recovered tail valves are more elongate and have more
prominent rugae than in the similar Leptochiton nexus. One tail
valve (Figures 5.16-5.17) has only faint rugae, and is slightly
wider than those of most modern L. rugatus specimens, but it is
within the typical size range for this species. The valve is similar
enough to the figured tail valve in the original description
(Pilsbry, 1892:pl. 3, fig. 70) that we identify it as this species. The
specimens differ from L. nexus in having a more rounded
anterior profile of intermediate valves (Figure 5.10). These fossils
differ from L. alveolus (Loven, 1846) in having a lower aspect
ratio (greater width) of intermediate valves and in lacking the
prominent granules of L. alveolus-, they differ from L. albemar-
lensis Smith and Ferreira, 1977, in lacking the prominent
quincunx arrangement of tegmental granules; and from L.
incongruous (Dali, 1908) in lacking its prominent longitudinal
ridges on the valve surface.
Leptochiton rugatus has been considered by some to be
widespread throughout the North Pacific (Ferreira, 1979a; Kaas
and Van Belle, 1985a), whereas others have considered the
northwestern Pacific specimens to belong to L. assimilis (Saito,
1994, 2000; Sirenko and Agapova, 1997). Specimens from the
Aleutians are considered distinct from either L. rugatus or L.
assimilis (R.N. Clark, personal communication to D.J.E., 2009).
Both mitochondrial and nuclear DNA sequences (D.J. Eernisse
and R. Kelly, unpublished data) have indicated all of these are
distinct species and have revealed several more undescribed
species. One of these is so far only known from greater depths
than L. rugatus in Southern California. Although Ferreira
(1979a) reports L. rugatus to occur at depths ranging from the
intertidal zone to 458 m, this might correspond to a summary for
the entire species complex. In central California, most individuals
of L. rugatus occur most commonly at about 8-to-12-m depths,
but can also be found in the intertidal zone, and some occur
within kelp holdfasts (Eernisse et al., 2007). Because the syntypes
(ANS 35586) of L. rugatus were collected from the intertidal
zone of northern Baja California, it is likely that the specimens
often found in the intertidal zone between Baja California and
central California are also L. rugatus, whereas the putative
deeper-water species must be a different species.
This is the first fossil report of L. rugatus or a member of the
L. “ rugatus ” species complex. If evidence indicates that the
members of this species complex lack diagnostic valve differenc-
es, then it might never be possible to distinguish between such
apparently cryptic species.
Leptochiton nexus Carpenter, 1864
Figure 5 (18-34)
Leptochiton nexus Carpenter, 1864:612, 650; Ferreira, 1979a: 149,
figs. 3-6, 8, 35-36 (contains more complete synonymies).
Lepidopleurus nexus-. Pilsbry, 1892:11.
Chiton ( Leptochiton ) nexus : Dali in Orcutt, 1885:544.
Lepidopleurus ( Xiphiozona ) heathi Berry, 1919a:5.
Lepidopleurus heathi : Dali, 1921:187.
Leptochiton (Xiphiozona) heathi : Berry, 1 9 1 9b:6— 8, pi. 1, figs 1-
2, pi. 2.
Leptochiton heathi: Smith, 1947a:4.
Lepidopleurus ambustus Berry, 1907:47 ( nomen nudum).
Lepidopleurus (Leptochiton) ambustus: Dali, 1919:499.
Lepidopleurus ambustus: Dali, 1921: 187.
Lepidopleurus (Pilsbryella) ambustus: Leloup, 1940:4, figs. 1-7.
Lepidopleurus (Leptochiton) lycurgus Dali, 1919:500.
Lepidopleurus lycurgus: Dali, 1921:187.
Leptochiton lycurgus: Smith, 1947a:4.
DISTRIBUTION. LACMIP localities 305 (3 head, 29 inter-
mediate, and 64 tail valves; 4 figured intermediate valves,
LACMIP 13739-13742, and 4 figured tail valves, LACMIP
13743-13746; all remaining valves in unfigured lot LACMIP
14294), 16817 (305C; 1 tail valve, LACMIP 14295) and 16862
(305A; 1 tail valve, LACMIP 14296).
TYPE SPECIMEN. Holotype, USNM 16270.
TYPE LOCALITY. Santa Catalina Island, California.
REMARKS. The specimens from the San Diego Formation are
very similar to modern representatives of Leptochiton nexus in
terms of valve sculpture and shape in anterior profile. In
particular, the valves are characterized by a uniform ornamen-
tation of fine granules, with poorly defined lateral areas, and with
a gothic arch in anterior view (Pilsbry, 1892) compared with a
rounded arch in the similar L. rugatus. Some modern specimens
assigned to this species and some fossils in this sample have faint
rugae in the lateral areas that are reminiscent of those on L.
rugatus, but the sculpture on the latter is much more prominent.
These specimens differ from Leptochiton asellus (Gmelin,
1791) in having less distinct granules on the tegmental surface
and in being much smaller (maximum length 18 mm; Kaas and
Van Belle, 1985a). These fossils differ from L. rugatus in having
a subcarinated anterior profile of intermediate valves (Fig-
ure 5.20). They also differ from L. alveolus (Loven, 1846) and
L. albemarlensis Smith and Ferreira, 1977 in lacking the
prominent granules of these species; and from L. incongruous
(Dali, 1908) in lacking its prominent longitudinal ridges on the
valve surface.
Some valves in the fossil sample are from individuals much
larger than modern specimens of L. nexus. These valves are
22 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Figure 5 Leptochiton spp. 1-34, from LACM1P locality 305. 1-17, Leptochiton rugatus Pilsbry, 1892: head (1-7), intermediate (8-13), and tail (14-
17) valves. 1-3, LACMIP 13730; 4, 7, LACMIP 13731; 5-6, LACMIP 13732; 8-10, LACMIP 13733; 11-12, LACMIP 13734; 13, LACMIP 13736; 14-
15, LACMIP 13737; 16-17, LACMIP 13738; 18-34, Leptochiton nexus Carpenter, 1864: intermediate (18-26) and tail (27-34) valves. 18-20, LACMIP
Contributions in Science, Number 520
Vendrasco ct al.: Chitons of the San Diego Formation ■ 23
~5 mm long, indicating an animal length of ~45 mm long (based
on measurements of modern specimens); in comparison, Ferreira
(1979a) claimed L. nexus usually ranges up to 20 mm in length,
with one specimen he observed to be 25 mm in length. However,
there is not a good reason to exclude the smaller valves in the
fossil sample from L. nexus , and the larger valves may indicate
variation in that population unknown in modern populations.
Modern members of L. nexus range from the intertidal zone to
139-141-m depths, with a median depth of 50 m (Ferreira,
1979a). They typically live on the sides and tops of rocks well
covered or surrounded by sand (Eernisse et al., 2007). Seven
specimens were reported from six stations at depths of 1 8 to 82 m
sampled as part of local benthic monitoring programs off of Palos
Verdes, Santa Monica Bay, and the northern Channel Islands
(Stebbins and Eernisse, 2009). These fossils extend the range of
this species to the Pliocene.
Genus Oldroydia Dali, 1894a
REMARKS. Oldroydia is a monotypic genus with a distinct
valve morphology. However, its single species Oldroydia
percrassa (Dali, 1894a) is closely aligned with members of the
genus Deshayesiella Dali, 1879, including the recently revived
Deshayesiella spicata (Berry, 1919b), which was argued by
Sirenko and Clark (2008) to differ mainly in having a less distinct
jugal area and longer pleural areas than O. percrassa. The San
Diego Formation fossil valves differ from those of other
lepidopleurids in having the Oldroydia characteristics of a thick
tegmentum, prominent jugal ridge that extends anterior to the
other regions of tegmentum, coarse tegmental sculpture, and
subtriangular sutural laminae.
Oldroydia percrassa (Dali, 1894a)
Figure 6
Lepidopleurus percrassus : Dali, 1894a:90 (original description).
Lepidopleurus (Oldroydia) percrassus: Berry, 1907:47.
Oldroydia percrassa: Thiele, 1910: 71, 105, pi. 7, figs. 1-8; Ferreira,
1979a: 160, fig. 20 (contains more complete synonymies).
Not Deshayesiella spicata (Berry, 1919b): Sirenko and Clark,
2008:2 (contra synonymy by Ferreira 1979a).
DISTRIBUTION. LACMIP localities 305 (26 head, 132
intermediate, and 52 tail valves; 3 figured head valves, LACMIP
13747-13749, 2 figured intermediate valves, LACMIP 13750-
13751, 2 figured tail valves, 13735, 13755; all remaining valves
in unfigured lot LACMIP 14297), 16817 (305C; 2 head, 9
intermediate, and 5 tail valves; 2 figured intermediate valves,
LACMIP 13752-13753, and 1 figured tail valve, LACMIP
13754; all other valves in unfigured lot LACMIP 14298), and
16868 (305A; 1 head and 1 tail valve, in unfigured lot LACMIP
14299).
TYPE SPECIMENS. Holotype and two paratypes (USNM
107274).
TYPE LOCALITY. 137-m depth, near Catalina Island,
California (33°45'N, 118°11'W).
REMARKS. Valves of O. percrassa are thick and with
prominent callus underneath (Dali, 1894a); intermediate and tail
valves with a raised, relatively smooth jugal area that extends
farther anteriorly than the rest of the tegmentum; latero-pleural
areas coarsely sculptured with rows of irregular granules that are
often merged into wavy ridges; and prominent sutural laminae.
The Border locality fossils show all these features and otherwise
do not differ from valves of modern representatives of this
species.
Oldroydia percrassa ranges from Monterey Bay, California, to
the Sea of Cortez, Mexico, and is found at depths from the
intertidal zone to 730 m, with a median depth of 40 m (Ferreira,
1979a). This species typically occurs under rocks (Eernisse et al.,
2007). This species is one of the more common chiton species
recovered from rock dredges off San Pedro, California (D.J.E.,
personal observation), but it was not found in any of the benthic
(>30-m water depth) samples from the Southern California Bight
surveys (Stebbins and Eernisse, 2009) or in benthic (50-250 m)
samples from the Santa Maria Basin and western Santa Barbara
Channel (Eernisse, 1998).
This is the first published record of an O. percrassa fossil,
although Itoigawa et al. (1976) reported “ Oldroydia ? sp.” from
the Pleistocene of Japan. Subsequently, Sirenko and Clark (2008)
demonstrated that Deshayesiella currently occurs in place of the
similar form Oldroydia in the northwestern Pacific, and thus the
specimen Itoigawa et al. (1976) noted may belong to Deshaye-
siella instead.
Order Chitonida Thiele, 1910
Suborder Chitonina Thiele, 1910
Family Ischnochitonidae Dali, 1889
Genus Callistochiton Dali, 1879
DISTRIBUTION. This genus Is widespread, occurring in cool
to warm waters worldwide (Kaas and Van Belle, 1994).
Several specimens, primarily of Callistochiton palmulatus Dali,
1 879, and to a lesser extent C. decoratus Pilsbry, 1 893, C.
crassicostatus Pilsbry, 1893, and others, are known from
Pleistocene marine terrace deposits on the Southern California
coast (e.g., Chace, 1916a, 1966; Chace and Chace, 1919; Berry,
1926; Kanakoff and Emerson, 1959; Valentine, 1961; Valentine
and Meade, 1961; Marincovich, 1976). Davis (1998) reported it
as rare (<10 specimens) in the Upper Pliocene Pico Formation of
downtown Los Angeles, California. Globally, Callistochiton has
been reported from as early as the Miocene in Japan (Itoigawa
et al., 1981) and Tanzania, East Africa (Davis, 1954).
REMARKS. Coan (1985; followed by Turgeon et al., 1998)
suggested recognition of Josiah Keep’s (1887) little-known
descriptions of several Callistochiton species that occur in
California. Keep based his descriptions on the unpublished
manuscript by P. Carpenter that was also used extensively by W.
Dali, H. Pilsbry, and other contemporary conchologists after
Carpenter’s untimely death. Stebbins and Eernisse (2009)
clarified that following Coan’s suggestion would both affect the
authority for C. decoratus, potentially giving priority to Keep
(1887) instead of Pilsbry, 1893 (from Carpenter manuscript), and
could potentially make C. crassicostatus Pilsbry, 1893 a junior
synonym of C. fimbriatus Keep, 1887. A third Carpenter
manuscript name had already been validated earlier, as Calli-
stochiton palmulatus Dali, 1879 (from Carpenter manuscript), so
Keep’s 1887 description of it would not have priority. Despite the
possible priority that Keep’s descriptions of C. decoratus and C.
fimbriatus might have over the more commonly recognized
13739. 21; LACMIP 13740; 22, 26, LACMIP 13741; 23-25, LACMIP 13742; 27-29, LACMIP 13743; 30, LACMIP 13744; 31-32, LACMIP 13745;
33-34, LACMIP 13746. Scale bars=l mm.
24 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Figure 6 Oldroydia percrassa (Dali, 1894a): head (1-6), intermediate (7-13), and tail (14-17) valves. 1-9, 16-17, from LACMIP locality 305; 10-15,
from LACMIP locality 16817 (305C). 1-2, LACMIP 13747; 3M, LACMIP 13748; 5-6, LACMIP 13749; 7, LACMIP 13750; 8-9, LACMIP 13751; 10,
13, LACMIP 13752; 11-12, LACMIP 13753; 14-15, LACMIP 13754; 16, LACMIP 13755; 17, LACMIP 13735. Scale bars=l mm.
names or authorities, Stebbins and Eernisse (2009) concluded
that Keep’s 1887 names remain nomina dubia because the
corresponding type material for these two species could not be
located and because Keep’s descriptions, by themselves, are
entirely inadequate to distinguish any of the three co-occurring
species. It is still possible that someone could select neotypes for
Keep’s C. decoratus and C. fimbriatus but, until then, we agree
with Stebbins and Eernisse (2009) that the conventional names
and authorities are best used.
Callistocbiton palmulatus Dali, 1879
Figure 7
Callistocbiton palmulatus Dali, 1879:297, pi. 2, fig. 20; Ferreira,
1979b:445, fig. 1 (contains more complete synonymies); Kaas
and Van Belle, 1994:168 (contains more complete synony-
mies).
Callistocbiton palmulatus mirabilis Pilsbry, 1893:263, pi. 58,
figs. 7-11.
Callistocbiton acinatus Dali, 1919:510.
Callistocbiton celetus Dali, 1919:510.
Callistocbiton connellyi Willett, 1937:25, pi. 2, fig. 13.
DISTRIBUTION. LACMIP localities 305 (about 2,500 head
valves, 196 intermediate valves, and about 6,100 tail valves; 1
figured head valve, LACMIP 13757 and 3 figured tail valves,
13764-13766; all other specimens in unfigured lot LACMIP
14300), 16817 (305C; 125 head, 15 intermediate, and 449 tail
valves; 3 figured head valves, LACMIP 13756, 13758-13759, 3
figured intermediate valves, 13760-13762, and 1 figured tail
valve, 13763; all other specimens in unfigured lot LACMIP
14301), and 305A (23 head, 31 intermediate, and 65 tail valves,
all in unfigured lot LACMIP 14302).
TYPE SPECIMENS. The holotype is apparently lost, and the
original description covers only the radula (Ferreira, 1979b).
Ferreira (1979b) designated a neotype, PRM 48. Syntypes of the
subspecies Callistocbiton palmulatus mirabilis Pilsbry, 1893
(ANSP 118682) are from San Diego, California.
TYPE LOCALITY. Santa Barbara, California.
MATERIAL EXAMINED. Topotypes of Callistocbiton pal-
mulatus from modern collections at the SBMNH.
REMARKS. The San Diego Formation fossils share with
modern representatives of this species strong sculpture of the
following: prominent rows of large granules in the head valve,
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 25
Figure 7 Callistochiton palmulatus Dali, 1879: head (1-8), intermediate (9-17), and tail (18-25) valves. 3—4, 20-25, from LACM1P locality 305; 1-2,
5-19, from LACMIP locality 16817 (305C). 1-2, LACMIP 13756; 3-4, LACMIP 13757; 5-6, LACMIP 13758; 7-8, LACM1P 13759; 9-11, LACMIP
13760; 12-14, LACMIP 13761; 15-17, LACMIP 13762; 18-19, LACMIP 13763; 20-21, LACMIP 13764; 22-23, LACMIP 13765; 24-25, LACMIP
13766. Scale bars=l mm.
26 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Contributions in Science, Number 520
Vendrasco et at.: Chitons of the San Diego Formation ■ 27
lateral areas of intermediate valves, and postmucronal area of tail
valves; and longitudinal ridges with weak cross-hatching in the
central area of intermediate valves and premucronal area of tail
valves. Moreover, the lateral areas of intermediate valves and
postmucronal area of the tail valve are significantly raised (this is
one of the main diagnostic characters of the San Diego subspecies
C. palmulatus mirabilis Pilsbry, 1893). However, Leloup (1953)
and Ferreira (1979b) pointed out the morphological and
ecological gradation between C. p. mirabilis and C. palmulatus
sensu stricto, so we refrain from using the subspecific name
mirabilis. An extensive study of the allometry of this species (D. J.
Eernisse and A. Draeger, unpublished) supports this taxonomic
opinion.
The raised, heavily sculptured lateral areas of these fossil
intermediate valves are seen in both Callistochiton palmulatus
and C. crassicostatus. However, the San Diego Formation fossils
differ from C. crassicostatus in having more longitudinal riblets
in the central area of intermediate valves ( — 15 vs. 12) and more
ribs on tail valves, and a tail valve with a much shorter
premucronal area. Although there appears to be much variation
in valve morphology in C. decoratus , these fossils differ from C.
decoratus in having lateral areas raised higher and more
prominent longitudinal ridges (vs. more of a lattice in C.
decoratus) and more distinctly by a much taller, more spherical
tail valve. These fossils differ from C. astbenes (Berry, 1919b) in
having more distinct, less smooth tegmental sculpture, and by
having a taller, subspherical tail valve; they differ from C. leei
Ferreira, 1979b, in having much more arched valves; from C.
colimensis (Smith, 1961) in having more arching of valves,
especially the tail valve; and from C. elenensis (Sowerby, 1832) in
having more highly arched, thicker valves, and in lacking a jugal
articulamentum plate.
Callistochiton palmulatus is continuously distributed between
Mendocino County, California, and Punta San Pablo (27°12'N),
Baja California, Mexico, and ranges from the intertidal zone to
73-82 m (Ferreira, 1979b). This species is particularly common
in the shallow subtidal zone under rocks or in mussel borings in
rocks on a sandy or silty substrate (Eernisse et ah, 2007). It is also
the most common chiton collected from rock dredges off San
Pedro at depths up to 85 m, and it is often found inside empty
mudstone burrows vacated by boring bivalves (Stebbins and
Eernisse, 2009).
Callistochiton sphaerae n. sp.
Figure 8
DISTRIBUTION. LACMIP localities 305 (35 head, 92
intermediate, and 86 tail valves; 2 figured head valves, LACMIP
13767-13768, 5 figured intermediate valves, LACMIP 13769-
13773, and 3 figured tail valves, LACMIP 13774-13776; all
other specimens in the topotype lot, LACMIP 14303), 16817
(305C; 3 head, 9 intermediate and 1 1 tail valves; 1 figured tail
valve, LACMIP 13854; all other specimens in unfigured lot,
LACMIP 14304), and 16862 (305A; 2 head and 6 tail valves, all
in unfigured lot, LACMIP 14305).
TYPE SPECIMENS. Holotype (LACMIP 13769; Figures 8.5-
8.7) and 8 figured paratypes (LACMIP 13767-13768, and
13770-13776; Figures 8. 1-8.4, 8.8-8.27); 33 head, 87 interme-
diate, and 83 tail valves in topotype lot, LACMIP 14303.
TYPE LOCALITY. LACMIP locality 305.
DIAGNOSIS. Valves of moderate size, between 0.5 and 1 cm
in width; tegmental sculpture a lattice dominated by longitudinal
ridges in central area of intermediate valves, and branching rows
of large, distinct granules in the somewhat raised lateral areas.
DESCRIPTION. Head valves half-moon— shaped in dorsal
profile; 12 slits; about 22 branching rows of large, distinct
granules; apical area prominent; slit rays distinct; anterior profile
rounded (not carinate). Intermediate valves with relatively low
aspect ratio; lateral areas with branching rows of distinct
granules; central areas with lattice dominated by longitudinal
ridges; about 30-35 longitudinal ridges in one intermediate valve;
sutural laminae long and broad, but with a distinct jugal sinus;
apical area prominent; pores in jugal sinus distinct; muscle scars
tend to be prominent; anterior region of ventral surface of
intermediate valves thin; valve rounded in anterior profile. Tail
valves low; 13-14 slits; mucro near midpoint but slightly closer
to anterior margin; sutural laminae rounded and broad, but with
distinct jugal sinus; ventral surface shows thickening at the
posterior margin, thin anterior to that; muscle scars tend to be
prominent; anterior view broadly rounded.
ETYMOLOGY. From Latin sphaerae meaning spheres or
balls, so named because this species differs from California
species of Callistochiton in having rows of more distinct, less
merged, subspherical granules on the lateral areas of the valves.
REMARKS. This species is known from more than 130
specimens, but it is not as common as C. palmulatus , which is
known from thousands of specimens in this assemblage. Callis-
tochiton sphaerae n. sp. is distinct from all other California
species of Callistochiton in having much more distinct granules in
the rows of the lateral areas. Moreover, it differs from most
eastern Pacific forms in having low elevation of the tail valve
even when large. Callistochiton sphaerae n. sp. differs from C.
crassicostatus and C. palmulatus in having much less raised
lateral areas. Although C. decoratus and C. elenensis , species
otherwise similar to C. sphaerae, can have a similar low eleva-
tion of the tail valve at small sizes, C. sphaerae differs from
those species in having more isolated and smaller granules and
a significantly shorter premucronal area in the tail valve.
Callistochiton sphaerae n. sp. also differs from C. elenensis in
lacking a distinct jugal plate, and in having more distinct
granules. Callistochiton expressus and C. gabbi are considered
junior synonyms of C. elenensis. Callistochiton sphaerae differs
from C. asthenes in being much larger and having stronger
tegmental sculpture; from C. leei Ferreira, 1979b, in having a
more strongly sculptured tegmental surface; from C. colimensis
in having more distinct granules that are somewhat less raised,
and in having a relatively longer premucronal area on tail valves;
and from the more southern species C. pulchellus (Gray, 1828),
which ranges from Ecuador to Patagonia, and C. periconis Dali,
1 908, a species from the Panamic biogeographic province, in
Figure 8 Callistochiton sphaerae n. sp.: head (1-4), intermediate (5-18), and tail (19-27) valves. 1-18, 20-27, from LACMIP locality 305; 19, from
LACMIP locality 16817 (305C). 1-2, LACMIP 13767, paratype; 3M, LACMIP 13768, paratype; 5-7, LACMIP 13769, holotype; 8-10, LACMIP
13770, paratype; 11-13, LACMIP 13771, paratype; 14-16, LACMIP 13772, paratype; 17-18, LACMIP 13773, paratype; 19, LACMIP 13854; 20-22,
LACMIP 13774, paratype; 23, 24-26, LACMIP 13776, paratype, 27, LACMIP 13775, paratype. Scale bars= 1 mm.
28 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Figure 9 Lepidozona mertensii (von Middendorff, 1847): intermediate (1-9) and tail (10-15) valves. 1-6, 10-13, from LACMIP locality 16817
(305C); 7-9, 14-15, from LACMIP locality 305. 1-4, LACMIP 13777; 5, LACMIP 13778; 6, LACMIP 13779; 7-8, LACMIP 13780; 9, LACMIP 13781;
10-11, LACMIP 13782; 12, LACMIP 13783; 13, LACMIP 13784; 14, LACMIP 13785; 15, LACMIP 13786. Scale bars=l mm.
having much more distinct longitudinal ridges in central areas of
the valves.
Genus Lepidozona Pilsbry, 1892
DISTRIBUTION. This genus is best known from the
northeastern and northwestern Pacific Ocean, although a few
species have been described from the central Indo-Pacific region,
one is known from New Zealand, and one deepwater member is
thought to range as far south as Chile. One species of Lepidozona
reported from South Africa (Ferreira, 1974; Strack, 1996) was
shown to have been incorrectly assigned to this genus (Schwabe,
2006). The genus is particularly well represented in the
northeastern Pacific, with at least 23 species described from
temperate and tropical waters, and multiple new species awaiting
description (Eernisse et ah, 2007; Stebbins and Eernisse, 2009;
D. J. Eernisse and A. Draeger, unpublished observations). In fact,
this is the most species-rich genus in western North America. One
problem for the identification of fossils is that features of the
girdle scales are sometimes more diagnostic than valve distinc-
tions, and such girdle elements are generally not available in
fossils.
Fossils of Lepidozona have been described from numerous
Pleistocene marine terrace deposits in Southern California (e.g.,
Chace and Chace, 1919; Berry, 1926; Flertlein and Grant, 1944;
Kanakoff and Emerson, 1959; Valentine, 1961; and Valentine
and Meade, 1961), but they have not been reported from older
deposits in California. A few specimens assigned to Lepidozona
have been described from the Pliocene (Oinomikado, 1938) and
Miocene of Japan (Itoigawa et ah, 1981). One intermediate valve
from the latest Eocene or earliest Oligocene of Washington was
assigned to this genus (Dell’Angelo et ah, 2011).
REMARKS. The sculpture of the valve tegmentum of this
genus bears strong similarities to that of Callistocbiton and
Iscbnocbiton, and in fact some more weakly sculptured species of
Lepidozona were previously included in Iscbnocbiton. Lepidozona
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 29
can be separated from Callistochiton based mainly on features of
the articulamentum (e.g., in Callistochiton but not Lepidozona the
slits in the head valve generally correspond in number and position
to the radial ribs of the tegmentum), and Lepidozona can be
separated from Ischnochiton based mainly on weaker tegmental
sculpture (Ferreira, 1974, 1978, 1985). Van Belle (1983) and Kaas
and Van Belle (1987) emphasize as a diagnostic character of
Lepidozona the presence in intermediate valves of a delicately
denticulate jugal plate (or lamina) across the sinus, separated from
the sutural laminae (or apophyses) on each side by small notch. A
molecular analysis (D.J. Eernisse, unpublished) supports the recent
reassignments of northeastern Pacific species once considered as
Ischnochiton to Lepidozona , and these are closely aligned with
Tripoplax Berry, 1919b (sensu Clark, 2008). Lepidozona sinu-
dentata (Pilsbry, 1892) has recently been shown to be a junior
synonym of L. scrohiculata (von Middendorff, 1847) (Clark,
2004).
Numerous valves in the Kanakoff collection belong to
Lepidozona, characterized by lateral valve areas of radial ribs
that are often composed of granules or larger, more-isolated
tubercles; central areas with longitudinal, often cross-hatched,
riblets; and head and tail valves with about 10-12 slits (Ferreira,
1974, 1978). However, the distinctions between species of
Lepidozona are often quite subtle, and many modern specimens
share a mixture of characters used to characterize different
species. In addition, for many species of Lepidozona from the
temperate eastern Pacific, Ferreira (1978) separated them from
other species from the region but did not directly compare them
to the Panamic and Gulf of California species that occur farther
south (Ferreira, 1974, 1985), many of which he remarked were
very similar to the temperate species. We have tried to be
conservative in assigning specimens to specific species of
Lepidozona and have set aside a number of specimens at
LACMIP as indeterminate Lepidozona.
Lepidozona mertensii (von Middendorff, 1847)
Figure 9
Chiton mertensii von Middendorff, 1847:118.
Lepidopleurus mertensii : Cooper, 1867:22.
Ischnochiton mertensii : Pilsbry, 1892:125, pi. 26, figs. 20-26.
Ischnochiton (Lepidozona) mertensii : Berry, 1917:26.
Lepidozona mertensii: Is. Taki, 1938:390, pi. 14, fig. 6, pi. 29,
figs. 1-6, pi. 30, figs 6-9, pi. 31, figs 9-10; Ferreira 1978:20,
figs. 1-2, 20-21, 34 (contains more complete synonymies);
Kaas and Van Belle, 1987:188 (contains more complete
synonymies).
DISTRIBUTION. LACMIP localities 305 (200 head, 180
intermediate, and 335 tail valves; 2 figured intermediate valves,
LACMIP 13780-13781, and 2 figured tail valves, 13785-13786;
all other specimens in unfigured lot, LACMIP 14306), 16817
(305C; 9 head, 51 intermediate, and 14 tail valves; 3 figured
intermediate valves, LACMIP 13777-13779, and 3 figured tail
valves, 13782-13784; all other specimens in unfigured lot,
LACMIP 14307), and 16862 (3Q5A; 2 head, 19 intermediate,
and 8 tail valves, all in unfigured lot, LACMIP 14308).
TYPE SPECIMENS. Type specimens were not mentioned and
no specimen was illustrated in the original description by von
Middendorff (1847). Lerreira (1978) reported that the original
type specimens were likely lost, and thus he designated a neotype,
LACM 1855, from the original type locality, Fort Ross, Sonoma
County, California. Other specimens from the neotype lot (e.g.,
LACM 1856) are in various institutions worldwide (see Ferreira,
1978).
TYPE LOCALITY. I .ocality listed in original description as
“California” (von Middendorff, 1847). Neotype from intertidal
zone, about 1 km south of Lort Ross, Sonoma County, California
(Ferreira, 1978).
MATERIAL EXAMINED. Neotype (LACM 1855) and
neotype lot (LACM 1856; 10 specimens) of Lepidozona (as
Chiton ) mertensii.
REMARKS. Ferreira (1978) differentiated Lepidozona mer-
tensii from the similar L. cooperi (Dali, 1879) based mostly on
coloration (reddish in the former; grayish, brownish, or otherwise
“dingy” in the latter) and shape of tubercles (rounded in the
former, elongated in the latter). The shape of the tubercles in
fossils from the Border localities indicates they should be assigned
to L. mertensii, as the tubercles appear more rounded than
elongate and are widely spaced and sporadically occurring, all
characters consistent with L. mertensii and inconsistent with L.
cooperi. Ferreira (1978) argued that L. guadalupensis Ferreira,
1978, is a southern sibling species to L. mertensii, but the largest
specimen of the latter species known at the time of its description
was 31.0 mm long, including girdle. Intermediate valves here
assigned to L. mertensii are up to 5 mm long at the midline,
corresponding to a chiton about 37.5 mm in length, indicating
an animal larger than L. guadalupensis. These valves can be
differentiated from those of most other species of Lepidozona by
the presence of tall, isolated tubercles. The tubercles in L.
pectinulata (Carpenter in Pilsbry, 1893) are more densely
arranged than the tubercles in these specimens. These specimens
differ from valves of L. willetti (Berry, 1917) in having larger
tubercles and more prominent and widely spaced longitudinal
riblets, although these species can be difficult to separate
without careful comparison of girdle scales. The specimens
differ from L. golischi (Berry, 1919a) in having more closely
spaced tubercles and in being much larger; from L. scabricostata
(Carpenter, 1864) in having much more distinct tubercles in
lateral areas; from L. retiporosa (Carpenter, 1864) in having
distinct longitudinal ridges in central areas (instead of a
reticulate pattern) and more closely spaced tubercles in lateral
areas; and from L. scrohiculata (von Middendorff, 1847) in
having more rounded tubercles in lateral areas. These fossils
differ from L. interstincta (Gould, 1852) and L. radians
(Carpenter in Pilsbry, 1892) in having more distinct tegmental
sculpture, especially in the central areas of intermediate valves;
they differ from L. clathrata (Reeve, 1847) in having fewer
longitudinal ridges in central areas and more distinct tubercles in
lateral areas. They differ from L. subtilis Berry, 1956 in having
greater prominence of, and more spacing between, tubercles in
lateral area and ridges in central area of intermediate valves.
Stebbins and Eernisse (2009) described but did not name three
species of Lepidozona from 30+ m depth off of San Diego. The
fossils here differ slightly from their Lepidozona sp. A in having
relatively larger tubercles; from their Lepidozona sp. B in having
more distinct sculpture overall, in particular more protruding
longitudinal ridges and tubercles; and from their Lepidozona sp.
C in having larger tubercles.
Lepidozona mertensii occurs from Alaska to northwestern Baja
California, and from the intertidal zone to around 100 m
(Ferreira, 1978), but is most common to about 8 m in depth on
the bottoms and sides of rocks (Eernisse et al., 2007). Stebbins
and Eernisse (2009) reported three specimens of L. mertensii
from the Southern California Bight benthic monitoring programs,
from depths between 56 and 85 m. It commonly co-occurs
with Hanleyella oldroydi (Dali, 1919), Lepidozona retiporosa,
and Callistochiton palmulatus. However, L. mertensii is gener-
ally rare south of Point Conception, Santa Barbara County,
California.
30 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Lepidozona pectinulata (Carpenter in Pilsbry, 1893)
Figure 10
Iscbnocbiton (Lepidoplewus) pectinatus Carpenter, 1864:612
{nomen nudum).
Isclmoplax pectinatus: Keep, 1887:112.
Ishcnochiton pectinulatus: Berry, 1922:412, 414, 421, table 1
(fossil).
Iscbnocbiton clatbratus : Pilsbry, 1892:128.
Lepidozona pectinulata: Ferreira, 1974:165; Ferreira, 1978:25,
figs. 5-6, 28 (contains more complete synonymies); Kaas and
Van Belle, 1987:203 (contains more complete synonymies).
Iscbnocbiton bryanti Dali, 1919:503.
Iscbnocbiton bntnneus Dali, 1919:504.
Iscbnocbiton ( Lepidozona ) californiensis Berry, 1931:255, pi. 29,
figs. 1-2.
Lepidozona californiensis: Smith, 1960:56, fig. 38.8 (from
Pleistocene).
DISTRIBUTION. LACMIP localities 305 (133 head, 502
intermediate, and 298 tail valves; 2 figured head valves, LACMIP
13787-13788, 4 figured intermediate valves, 13789-13792, and
5 figured tail valves, 13794-13798; all other specimens in
unfigured lot, LACMIP 14309) and 305C (1 head, 10 interme-
diate, and 2 tail valves; 1 figured intermediate valve, LACMIP
13793, and 2 figured tail valves, 13799-13800; all other
specimens in unfigured lot, LACMIP 14310).
TYPE SPECIMENS. Ferriera (1978) designated a lectotype and
two specimens as paralectotypes (PRM 70) based on inferences
from the description in Palmer (1958).
TYPE LOCALITY. Ferreira (1978) inferred that the locality
attributed to the syntypes (“La Paz”) is inaccurate, and he chose
to restrict the type locality to Santa Catalina Island, California.
REMARKS. The complicated history of the name Lepidozona
pectinulata and its taxonomic authority is described in detail by
Ferreira (1978).
Valves of Lepidozona pectinulata from the San Diego
Formation differ from those of L. mertensii, L. cooperi, L.
willetti, L. scabricostata, L. retiporosa, L. scrobiculata, and L.
goliscbi in having more closely spaced tubercles. In addition, the
fossils differ from L. mertensii and L. cooperi in lacking the slight
divergence of longitudinal ridges near the midline of intermediate
valves except valve 2, and from L. retiporosa in having distinct
longitudinal ridges in the central area of intermediate valves. In
addition, one of the fossil tail valves (Figure 10.18) has 15 or
more slits, consistent with L. pectinulata (range 10-17) and
inconsistent with the other temperate eastern Pacific species of
Lepidozona , whose tail valves have up to 14 slits (Ferreira,
1978). Some Panamic species of Lepidozona have a similar
number of slits, but the San Diego Formation valves differ from
those of L. clatbrata in lacking pronounced ridges in the lateral
areas, and from L. subtilis in having distinct pustules. These
fossils differ from L. guadalupensis (endemic to Isla Guadalupe)
in having more closely spaced tubercles. These fossils differ from
L. interstincta and L. radians in having more distinct tegmental
sculpture, especially in the central area of intermediate valves;
they differ from L. clatbrata in having more distinct tubercles in
lateral areas. They differ from L. subtilis in having more
prominent tubercles in lateral areas and more widely spaced
ridges in central area of intermediate valves. The fossils here
differ from Lepidozona spp. A and C of Stebbins and Eernisse
(2009) in having more closely spaced tubercles and longitudinal
ridges; and from Lepidozona sp. B (Stebbins and Eernisse, 2009)
in having more distinct sculpture overall, in particular more
protruding longitudinal ridges and tubercles.
In some specimens the longitudinal riblets seem to be more
pronounced relative to the cross-hatching compared to most
specimens assigned to L. pectinulata. However, there is variation
in modern specimens of the latter species and specimens of L.
pectinulata at the SBMNH and LACM from near the type
locality share more pronounced longitudinal riblets.
Lepidozona pectinulata occurs from 35°N to 24°N along the
coast of California and Baja California, and from the intertidal
zone to about 20-m depth (Ferreira, 1978), but most commonly
under rocks in the low intertidal and shallow subtidal zones
(Eernisse et al., 2007).
Lepidozona sp. cf. L. rotbi Ferreira, 1983
Figure 11 (1-5)
[Lepidozona rotbi Ferreira, 1983:316, figs. 19-22.
Lepidozona macleaniana Ferreira, 1985:425, figs. 6-10. (syn. by
Kaas and Van Belle, 1987)]
DISTRIBUTION. LACMIP locality 305 (3 intermediate
valves; LACMIP 13801-13803).
TYPE LOCALITY. Off of Bahia Sulphur, Isla Clarion, Islas
Revillagigedo, Mexico, 82-91 m (Ferreira, 1983).
MATERIAL EXAMINED. Holotype of L. rotbi (LACM
1818).
REMARKS. The fossil valves share with Lepidozona rotbi a
similar tegmental sculpture of longitudinal riblets with cross-
hatching in the central area and rows of merged tubercles in the
lateral areas. The lateral areas are highly raised in both as well,
and valve 2 has a prominent wedge in the longitudinal riblets in
the central area near the midline (see discussion of this character
in Ferreira, 1978). These fossils are larger than expected based on
the original description of the species (“up to 1.5 cm long”;
Ferreira, 1983:316), but Kaas and Van Belle (1987) expanded the
description , suggesting that the species ranges up to 2.0 cm in
length. The fossil specimens fall within the latter size range.
The fossils differ from L. clatbrata , L. cooperi , L. goliscbi, L.
guadalupensis, L. mertensii, L. pectinulata, L. retiporosa, L.
scabricostata, L. scrobiculata, L. willetti, and Lepidozona spp.
A-C (Stebbins and Eernisse, 2009) in lacking distinct tubercles on
lateral areas of intermediate valves. The San Diego Formation
fossils also differ from L. retiporosa in having distinct longitu-
dinal ridges in the central area of intermediate valves, and from
L. interstincta and L. radians in having a greater elevation of
ridges on the tegmentum, especially in the central area of inter-
mediate valves.
Lepidozona rotbi is known only from Isla Clarion, Islas
Revillaggedo, Mexico, and Isla del Coco, eastern Pacific, from
55-110 m. It is unknown from the fossil record, and this report is
tentative.
Lepidozona sp. cf. L. radians (Carpenter in Pilsbry, 1892)
Figure 11 (6-10)
[Iscbnocbiton radians Carpenter in Pilsbry, 1892:121; Carpenter
in Pilsbry, 1893:75, pi. 16, figs. 48-49; Thiele, 1909:80; Berry,
1917:231, 235; Dali, 1921:191; Oldroyd, 1927:275.
Lepidozona radians: Eernisse et ah, 2007:710; Stebbins and
Eernisse, 2009:68, pi. 3, fig. 9).]
DISTRIBUTION. LACMIP localities 305 (1 head, 25 inter-
mediate, and 10 tail valves; 2 figured intermediate valves,
LACMIP 13804-13805, and 1 figured tail valve, LACMIP
13806; all other specimens in unfigured lot, LACMIP 14311)
and 16817 (305C; 5 intermediate valves, all in unfigured lot
LACMIP 14312).
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 31
Figure 10 Lepidozona pectinulata (Carpenter in Pilsbry, 1893): head (1-4, 7), intermediate (5-6, 8-15), and tail (16-28) valves. 1-12, 14-24, from
LACMIP locality 305; 13, 25-28 from LACMIP locality 16817 (305C). 1-3, LACMIP 13787; 4, 7, LACMIP 13788; 5-6, LACMIP 13789; 8-10,
LACMIP 13790; 11, LACMIP 13791; 12, LACMIP 13792.;13, LACMIP 13793; 14-15, LACMIP 13794; 16, 20, LACMIP 13795; 17-19, LACMIP
13796; 21-22, LACMIP 13797; 23-24, LACMIP 13798; 25-26, LACMIP 13799; 27-28, LACMIP 13800. Scale bars=l mm.
32 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Figure 1 1 Lepidozona spp. 1-20, 23-28, from LACMIP locality 305; 21-22, from LACMIP locality 16817 (305C). 1-5, Lepidozona sp. cf. L. rothi Ferreira,
1983: intermediate valves. 1-2, LACMIP 13801; 3, LACMIP 13802; 4-5, LACMIP 13803; 6-10, Lepidozona sp. cf. L. radians: intermediate (6-8) and tail (9-10)
valves. 6, LACMIP 13804; 7-8, LACMIP 13805; 9-10, LACMIP 13806; 1 1-28, Lepidozona kanakoffi n. sp.: intermediate (1 1-20) and tail (21-28) valves. 11,
LACMIP 13807, paratype, L. kanakoffi-, 12, LACMIP 13808, paratype; 13-14, LACMIP 13809, paratype; 15-16, LACMIP 13810, holotype, L. kanakoffi-, 17,
LACMIP 13811, paratype, L. kanakoffi ; 18-20, LACMIP 13812, paratype; 21-22, LACMIP 13813; 23-24, LACMIP 13814, paratype; 25-26, LACMIP 13815,
paratype; 27-28, LACMIP 13816, paratype. Scale bars=l mm.
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 33
TYPE SPECIMENS. The only figured specimen associated
with the original description (Carpenter in Pilsbry, 1892, pi. 16,
figs. 48-49) was a secondary, non-type specimen (USNM 19471;
Palmer, 1958). Palmer (1958) found what she believed were
Carpenter’s original specimens, on which the description was
based, and chose one of these as a lectotype and three other
valves as paratypes (all PRM 25).
TYPE EOCALITY. Monterey, California (based on label
associated with Carpenter’s specimens, PRM 25, as reported by
Palmer, 1958).
REMARKS. The valves described here share with those of
Lepidozona radians faint radiating ridges in the central areas;
periodic growth increments; wide tail valve with anterior mucro;
slightly raised lateral areas with merged granules; and central
areas of faint lineations of pores.
Smith (1977) synonymized Ischnochiton radians Carpenter
in Pilsbry, 1892, with Ischnochiton interstinctus (Gould, 1846),
and Kaas and Van Belle (1990) reassigned it to Lepidozona
interstincta (Gould, 1846). Eernisse et al. (2007; see also Kelly
and Eernisse, 2007; Stebbins and Eernisse, 2009) revised
Lepidozona radians as distinct from the more northern L.
interstincta , and emphasized that L. radians was much more
colorful and variable in its color than the mostly tan to orange L.
interstincta. Lacking color features and because of the general
lack of sculpturing in both species, the isolated valves of the San
Diego Formation cannot be separated from either of these
species. Thus we have used open nomenclature and choose the
species that occurs in California.
These fossils differ from L. clathrata, L. cooperi , L. golischi, L.
guadalupensis, L. mertensii, L. pectinulata, L. retiporosa, L.
scabricostata, L. scrobiculata, L. willetti , and Lepidozona spp.
A-C (Stebbins and Eernisse, 2009) in lacking distinct tubercles in
lateral areas of intermediate valves.
Lepidozona radians ranges from northern Baja California,
Mexico, north to at least Port Hardy, British Columbia, Canada
(D.J.E., unpublished observations). It normally occurs in the
intertidal to shallow subtidal zones, most commonly from 5-to-
13-m depth under rocks or on rocky surfaces buried in sand
(Eernisse et al., 2007), although it has been found in depths up to
150 m (Stebbins and Eernisse, 2009). To our knowledge neither
L. radians nor L. interstincta has yet been reported as a fossil.
Lepidozona kanakoffi n. sp.
Figure 11 (11-28)
DISTRIBUTION. LACMIP localities 305 (31 intermediate
and 25 tail valves; 6 figured intermediate valves, LACMIP
13807-13812, and 3 figured tail valves, 13814-13816; all other
specimens in unfigured topotype lot, LACMIP 14313) and 16817
(305 C; 1 intermediate and 2 tail valves; 1 figured tail valve,
LACMIP 13813; all other specimens in unfigured lot, LACMIP
14314).
TYPE SPECIMENS. Holotype (Figures 1 1 .15-1 1. 1 6; LAC-
MIP 13810) and eight figured paratypes (Figures 11.11-11.14,
11.17-11.20, 11.23-11.28, LACMIP 13807-13809, 13811-
13812, 13814-13816); 25 intermediate valves and 22 tail valves
in topotype lot, LACMIP 14313.
TYPE LOCALITY. LACMIP locality 305.
ETYMOLOGY. Named for the late George P. Kanakoff,
whose collecting efforts produced the massive chiton assemblage
described herein.
DIAGNOSIS. Intermediate valves with a relatively low aspect
ratio; distinct longitudinal ridges in central area of intermediate
valves and premucronal area of tail valves; many closely spaced
rows of distinct but closely spaced granules in lateral areas of
intermediate valves and postmucronal area of tail valves.
Typically about 10 rows of granules in lateral areas of
intermediate valves and about 30 rows in postmucronal area of
tail valves.
DESCRIPTION. Intermediate valves relatively wide; central
areas with prominent, somewhat curving longitudinal ridges,
about 50 to 60 in one intermediate valve; cross-hatching more or
less noticeable in central areas; lateral areas raised somewhat and
with about 10 rows of closely spaced but distinct, rounded
granules; sutural laminae short and broad, but with distinct jugal
sinus, and without a sign of a jugal plate; distinctly carinate in
anterior profile, with straight sides; jugal angle about 122 to
127°; 1 slit per side; apical area distinct and broad but short.
Tail valves with mucro at midline (Fig. 15.25) or more
commonly just in front of it (Figures 11.21, 11.23, 11.27);
premucronal areas with about 30 distinct longitudinal ridges but
with cross-hatching also apparent; postmucronal area with about
30 rows of distinct, rounded granules, closely spaced; sutural
laminae broad, more or less rounded, with distinct jugal sinus
and no sign of an extended jugal plate; about 9 to 11 slits; slit
rays distinct; ventral surface of valve shows much sculpturing,
including from possible muscle scars.
REMARKS. These valves share a resemblance to other
Lepidozona species in tegmental sculpture and shape of the
projections of the articulamentum. However, they differ from all
known members of Lepidozona in having a large number of
granule rows in the lateral areas (this species has 10 or more,
compared to a maximum of eight in all other eastern Pacific
species; Ferreira, 1978, 1983, 1985). The fossils also differ from
most other members of Lepidozona in having a large jugal angle
and more prominent longitudinal ridges. In addition, this species
is larger than most species of Lepidozona and is perhaps most
similar to L. formosa Ferreira, 1978, but differs from that species
in having more rows of granules in the lateral areas and more
prominent longitudinal ridges in the central areas. The fossils also
differ from L. retiporosa in having distinct longitudinal ridges in
the central area of intermediate valves, and from L. interstincta
and L. radians in having more distinct tegmentum sculpture. The
fossils share with L. scabricostata numerous granule rows in the
tail valves and lateral areas of intermediate valves, and
pronounced longitudinal ridges. However, the granules in the
rows and ridges are much more distinct and closely spaced than
in L. scabricostata.
Genus Stenoplax Dali, 1879
DISTRIBUTION. About half of the approximately 22
worldwide living species of Stenoplax occur in the temperate or
tropical eastern Pacific, but a few New World species occur
exclusively in the Caribbean, and one species, Stenoplax boogii
(Haddon, 1886), is reported in both regions (Kaas and Van Belle,
1987). Stenoplax typically inhabits the low intertidal or shallow
subtidal zones, typically found under rocks, at least during
daylight hours.
A few valves from the Oligocene of Italy were assigned to this
genus (Dell’Angelo and Palazzi, 1992) and additional species are
known from the Eocene of Europe (Wrigley, 1943; Van Belle,
1981; Bielokrys, 1999). A few valves from the latest Eocene or
earliest Oligocene of Washington were assigned to this genus
(Dell’Angelo et al., 2011). Stenoplax conspicua Pilsbry, 1892, S.
fallax (Carpenter in Pilsbry, 1892), S. heathiana Berry, 1946, and
S. magdalenensis (Hinds, 1845) can be relatively common in
Pleistocene marine terrace deposits in California (e.g., Chace,
1916a, 1916b, 1966; Chace and Chace, 1919; Hertlein and
Grant, 1944; Kanakoff and Emerson, 1959; Valentine and
34 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Figure 12 Stenoplax spp. 1-4, 8-14, 17-21, from LACMIP locality 305; 5-7, 15-16, from LACMIP locality 16817 (305C). 1-7, Stenoplax
circumsenta Berry, 1956: head (1-4) and tail (5-7) valves. 1-2, LACMIP 13817; 3-4, LACMIP 13818; 5-6, LACMIP 13819; 7, LACMIP 13820; 8-21,
Stenoplax fallax (Carpenter in Pilsbry, 1892): head (8-11), intermediate (12-18), and tail (19-21) valves. 8, LACMIP 13821; 9, LACMIP 13822; 10-11,
LACMIP 13823; 12, LACMIP 13824; 13, LACMIP 13825; 14, LACMIP 13826; 15-16, LACMIP 13827; 17-18, LACMIP 13828; 19, LACMIP 13829;
20, LACMIP 13830; 21, LACMIP 13831. Scale bars=l mm.
Meade, 1961; Marincovich, 1976; Kennedy, 1978; Valentine,
1980).
REMARKS. The most familiar species of Stenoplax (e.g., S.
conspicua, S. magdalanensis, and S. heathiana), as well as smaller
and less well known species, can each have distinctive girdle
elements, coloration, or latitudinal distribution, and DNA
sequence comparisons are generally effective for distinguishing
species (Kelly and Eernisse, 2007; D.J. Eernisse, unpublished
data). However, several pairs or complexes of species in this
genus overlap substantially in valve morphology. This adds
uncertainty to taxonomic hypotheses based on fossil valve
material only, but here we point out specific sources of ambiguity
in each case.
Stenoplax is a distinct taxon whose members are highly
elongate, and whose intermediate valves have prominent sutural
laminae and generally raised lateral areas. The much more
elongated (relative to other valves) tail valve with prominent
diagonal line is diagnostic for this genus.
Stenoplax circumsenta Berry, 1956
Figure 12 (1-7)
Stenoplax circumsenta Berry, 1956:72; Kaas and Van Belle,
1987:151 (contains more complete synonymies).
DISTRIBUTION. LACMIP localities 305 (3 head, 1 interme-
diate, and 5 tail valves; 2 figured head valves, LACMIP 1381 7—
13818; all other specimens in unfigured lot, LACMIP 14315) and
16817 (305C; 1 head, 1 intermediate, and 3 tail valves; 2 figured
tail valves, LACMIP 13819-13820; all other specimens in
unfigured lot, LACMIP 14316).
TYPE SPECIMEN. Holotype (SBMNH 34425).
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Vendrasco et al.: Chitons of the San Diego Formation ■ 15
TYPE LOCALITY. Sand flats, Isla Concha, Laguna Ojo de
Liebre (Scammon’s Lagoon), Baja California Sur, Mexico.
MATERIAL EXAMINED. Holotype (SBMNH 34425) of
Stenoplax circumsenta.
DESCRIPTION. The fossil tail valves are about 3.7 mm long,
4.8 mm wide, with a 2-mm-long premucronal region and 1.5-
mm-long postmucronal area. The sutural laminae are small and
widely spaced (0.15 mm long, each about 0.80 mm wide).
REMARKS. The fossil tail valves have an unusual shape in the
prominent premucronal area, distinct and somewhat jagged
growth lines, prominent change in slope at diagonal line, subdued
premucronal sculpture that consists of rows of small pores, and
small size, all of which match Stenoplax circumsenta. Although S.
circumsenta was previously synonimized with S. corrugata
(Pilsbry, 1892) by Ferreira (1983) based on a number of
arguments, each of these arguments was refuted by Kaas and
Van Belle (1987). In his original description of S. circumsenta ,
Berry (1956:72) noted the similarity between these two species,
but stated the difference based on the presence of “curious” acute
spines in the girdle of S. circumsenta. We maintain the separation
of S. circumsenta and S. corrugata based on a number of
characters, including those of tegmental sculpture (Kaas and Van
Belle, 1987). In particular, the valves of S. circumsenta as well as
the tail valves from the San Diego Formation differ from those of
S. corrugata in having finer, more-jagged growth lines in the
postmucronal area. The fossil tail valves differ from those of S.
purpurascens (Adams, 1845) sensu Bullock (1985) in having
shorter sutural laminae, a more rounded anterior margin, and a
relatively smooth premucronal area (instead of the prominent
longitudinal ridges in S. purpurascens). These fossils differ from
the larger species of Stenoplax, S. fallax , S. conspicua , S.
heathiana , S. limaciformis (Sowerby, 1832), and S. magdalenen-
sis in having wavy ridges in the head valve and postmucronal area
of the tail valve. These fossils differ from the much smaller S.
mariposa (Dali, 1919) in having much finer valve sculpture, and
from the otherwise similar (and more southern) S. rugulata
(Sowerby, 1832) in lacking the longitudinal ridges in the
premucronal area of the tail valve.
The tail valve length is typically 3.5-4 mm, which is similar to
the tail valve length of the holotype of S. circumsenta (3.85 mm).
The length:width ratio in the tail valve is about 0.7 (ratio in
holotype is 0.62); placement of mucro is about 0.5 the valve
length (value in holotype is 0.53). Based on their close similarity
in form, we cannot see any good reason to exclude these valves
from S. circumsenta.
Kaas and Van Belle (1987:294, map 48) show an occurrence of
S. circumsenta off the coast of Los Angeles, California, and the
type locality is farther south on the Pacific Coast, but it is possible
that the reports farther north should have been for the poorly
known S. corrugata instead. Stenoplax circumsenta is primarily
known from Baja California and the Sea of Cortez (Berry, 1956;
Ferreira, 1972; Hanselman, 1973; Kaas and Van Belle, 1987; D.J.
Eernisse, unpublished observations). The depth range for this
species is 0 to 72 m (Kaas and Van Belle, 1987). This is the first
known occurrence of this species in the fossil record.
Stenoplax fallax (Carpenter in Pilsbry, 1892)
Figure 12 (8-21)
Iscbnochiton (Stenoplax) fallax Carpenter in Pilsbry, 1892:59, pi.
16, figs. 17-18.
Stenoplax fallax : Palmer, 1945:101; Kaas and Van Belle,
1987:146 (contains more complete synonymies).
DISTRIBUTION. LACMIP localities 305 (8 head, 13 inter-
mediate, and 13 tail valves; 3 figured head valves, LACMIP
13821-13823, 4 figured intermediate valves, LACMIP 1 3824—
13826, 13827, and 3 figured tail valves, LACMIP 13829-13831;
all other specimens in unfigured lot, LACMIP 14317), 16817
(305C; 1 intermediate and I tail valve; I figured intermediate
valve, LACMIP 13827; other specimen 14318), and 16862
(305A; 1 head and 3 intermediate valves, all specimens in
unfigured lot, LACMIP 14319).
TYPE SPECIMEN. Holotype (PRM 64), as reported by Palmer
(1958).
TYPE LOCALITY. Bodega Bay, Sonoma County, California.
MATERIAL EXAMINED. Numerous topotypes of Stenoplax
fallax at LACM and SBMNH.
REMARKS. The fossil intermediate valves have a fine, pitted
sculpture in the central area, radiating riblets in the lateral areas,
and a narrow and elongate valve shape, all characters consistent
with Stenoplax fallax and inconsistent with the most similar forms
S. magdalenensis and S. conspicua (see Pilsbry, 1892 and Berry,
1922). The fossils differ from S. heathiana, S. limaciformis, S.
hoogii, S. purpurascens, and S. rugulata in having distinct pitted
sculpture in the central area of intermediate valves. Moreover, the
large size also differentiates these fossils from S. limaciformis,
S. circumsenta, S. rugulata, and S. mariposa (Dali, 1919).
These fossils are very similar to valves of a specimen of the rare
species S. corrugata at the SBMNH (currently unnumbered) collected
by George Hanselman. Although Kaas and Van Belle (1987)
mentioned that the holotype of S. corrugata is small (13.7 mm long)
and claim the species ranges only to 22 mm in length, Hanselman’s
specimen is 42 mm long. Hanselman’s specimen bears the character-
istic color markings of S. corrugata, different from that in S. fallax, so it
is likely a member of the former species, as indicated on the specimen
label. However, most specimens of S. corrugata are much smaller. In
his original description of S. fallax, Pilsbry (1892) lists a length of
27.5 mm for this species. Kaas and Van Belle (1987), however, refer to
S. fallax as a large species, ranging up to 75 mm in length. The fossil
valves are all more than 5 mm long (in some cases closer to 10 mm),
corresponding to a chiton of estimated total length 48 to 76 mm. The
specimens here are much larger than what Pilsbry (1892) suggested for
S. fallax but are within the range suggested by Kaas and Van Belle
(1987), and are similar in size to the topotype material (e.g., SBMNH
1002440) of S. fallax. The fossils thus have a size range that better
matches that of modern S. fallax than S. corrugata.
Berry (1922) mentions terracing from pronounced growth lines
in the lateral areas, and this can be seen in some Border locality
specimens (Figures 12.13, 12.16), but not on others. Terracing is
likewise present in some extant specimens (e.g., LACM 60-24),
but not others assigned to this species from Southern California.
The radiating riblets in the head valves, lateral areas of
intermediate valves, and postmucronal area of tail valves are
more distinct and less wavy than in most modern specimens of S.
fallax, although there appears to be a high degree of intraspecific
variability in this character.
Stenoplax fallax is primarily a subtidal species; adults occur
along the sides of rocks buried in sand (Eernisse et al., 2007). This
species occurs from Vancouver Island, Canada, to Bahia Todos
Santos, Baja California, Mexico (Kaas and Van Belle, 1987).
Stenoplax sp. cf. S. heathiana Berry, 1946
Figure 13
[Stenoplax (Stenoradsia) heathiana Berry, 1946:161, figs. 1-6, pi.
4, figs. 7-9; Kaas and Van Belle, 1987:128 (contains more
complete synonymies).
Stenoplax heathiana: Smith, 1963:148.]
DISTRIBUTION. LACMIP locality 305 (2 head valves,
LACMIP 13832-13833, 5 intermediate valves, LACMIP
36 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Figure 13 Stenoplax sp. cf. S. heathiana Berry, 1946: head (1-4), intermediate (5-13), and tail (14-19) valves. 1-13, 16-19, from LACMIP locality
305; 14-15 from LACMIP locality 16817 (305C). 1-2, LACMIP 13832; 3-4, LACMIP 13833; 5, LACMIP 13834; 6-8, LACMIP 13835; 9, 12-13,
LACMIP 13836; 10, LACMIP 13837; 11, LACMIP 13838; 14-15, LACMIP 13839; 16, LACMIP 13840; 17-19, LACMIP 13841. Scale bars=l mm.
13834-13838, and 2 tail valves, LACMIP 13840-13841) and
16817 (305C; 1 tail valve, LACMIP 13839).
MATERIAL EXAMINED. Paratypes of Stenoplax heathiana
Berry, 1946 (SBMNH 34415-34417).
REMARKS. The fossil intermediate valves are large, with a
tegmentum sculpture in the central area of faint growth lines, similar to
that of most specimens of S. heathiana , but different from that of the
similar S. conspicua and S. magdalenensis , which tend to have more
prominent, coarser radiating ridges (but see below), and S. fallax and S.
corrugata, which have a pitted texture. The large size of the fossils
differentiates them from S. limaciformis , S. boogii, S. circumsenta, S.
corrugata , S. rugulata, and S. mariposa. The lack of somewhat wavy,
equally spaced ridges over the entire tegmental surface differentiates
these fossils from the Caribbean species S. purpurascens.
However, species of Stenoplax vary with respect to their
tegmentum sculpture (Kaas and Van Belle, 1987; MJV, personal
observation) and many species of Stenoplax can have 10 slits in
the tail valve, as observed in the fossil tail valve, so we only
provisionally assign these valves to S. heathiana. Some of the
fossils may belong to S. conspicua, S. magdalenensis, or 5.
sonorana, but from abraded and in some cases fragmented valves
alone it is difficult to distinguish these species.
Stenoplax heathiana is known from the intertidal to shallow
subtidal zones (to 7 m) under rocks buried in sand (Eernisse et al.,
2007). It ranges from Fort Bragg, Mendocino County (in
northern California), to where it is fairly common in central
California. Like several other mostly more northern species, it is
absent or rare in the relatively warm Southern California Bight
but is found at cooler upwelling-affected localities farther south:
it is specifically reported from Punta Santo Tomas, Baja
California, Mexico (Kaas and Van Belle, 1987).
Suborder Acanthochitonina Bergenhayn, 1930
Family Mopaliidae Dali, 1889
Genus Amicula Gray, 1847a
DISTRIBUTION. Members of this genus are typically found
at moderate subtidal depths of about 20 to 100 m, and are
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 37
Figure 14 Amicula solivaga n. sp.: head (1-7), intermediate (8-13), and tail (14-17) valves. 1-10, 13-17, from LACMIP locality 305; 1 1-12, from
LACMIP locality 16817 (305C). In dorsal views (all except 7, 12), anterior is toward the top of the page. 1, LACMIP 13842, paratype; 2, LACMIP
13843, paratype; 3, LACMIP 13844, paratype; 4, LACMIP 13845, paratype; 5, LACMIP 13846, holotype; 6-7, LACMIP 13847, paratype; 8, LACMIP
13848, paratype; 9, LACMIP 13849, paratype; 10, LACMIP 13850, paratype; 11-12, LACMIP 13851; 13, LACMIP 13852, paratype; 14-15, LACMIP
13853, paratype; 16, LACMIP 13855, paratype; 17, LACMIP 13856, paratype. Scale bars=l mm.
particularly common in the North Pacific and Arctic but extend
also to the cool temperate northwestern Pacific, the Aleutian
Islands, and even a few localities in the northwestern Atlantic as
far south as Cape Cod, Massachusetts (Jakovleva, 1952; Okutani
and Saito, 1987; Kaas and Van Belle, 1994). Besides the
occurrence described here, Amicula vestita (Broderip and
Sowerby, 1829) from the Pleistocene of “Lower Canada”
(Pilsbry, 1893:45) is the only member of this genus known with
a fossil record.
REMARKS. Amicula is characterized by a significant reduc-
tion of the tegmentum, medium to large body size, and slit
formula 6-8/l/sinus+2 (Kaas and Van Belle, 1994). The sinus in
the tail valve is also seen in other mopaliid genera. The taxonomy
of Amicula is unsettled. Jakovleva (1952) recognized four species:
A. vestita (including the junior synonym Amicula amiculata
Pilsbry, 1892), Amicula pallasii (von Middendorff, 1847),
Amicula gurjanovae Jakovleva, 1952, and A. rosea Jakovleva,
1952. Okutani and Saito (1987) and Saito (1994) maintained this
taxonomy, but Kaas and Van Belle (1994) recognized only two
species: A. amiculata (with junior synonym A. gurjanovae) and
A. vestita, with junior synomyms A. rosea and A. pallasii.
Amicula solivaga n. sp.
Figure 14
DISTRIBUTION. Restricted to the San Diego Formation
exposures near the U.S. -Mexico border, at LACMIP localities
305 (9 head, 29 intermediate, and 7 tail valves; 6 figured head
valves, LACMIP 13842-13847, 4 figured intermediate valves,
LACMIP 13848-13850, 13852, and 2 figured tail valves,
LACMIP 13853, 13855; all other specimens in unfigured
topotype lot, LACMIP 14320), 16817 (305C; 2 intermediate
valves; 1 figured, LACMIP 13851 and I unfigured, LACMIP
14321), and 16862 (305A; 1 head, 1 intermediate, and 1 tail
valve, all in unfigured lot, LACMIP 14322).
TYPE SPECIMENS. Holotype (LACMIP 13846; Figure 14.5;
head valve) and 11 figured paratypes (5 head, 4 intermediate, and
2 tail valves; LACMIP 13842-13845, 13847-13850, 13852-
13853, 13855); 3 head, 25 intermediate, and 5 tail valves in the
topotype lot, LACMIP 14320; all from LACMIP locality 305.
TYPE LOCALITY. LACMIP locality 305.
DIAGNOSIS. Valves of relatively large size, between 0.5 and
1 cm in width; length:width ratio of intermediate valves ~0.36;
38 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
tegmentum covers about 1/4 of dorsal surface of valves, suboval,
with faint ornamentation of growth lines; posterior margin of
valves straight or bent only slightly posteriorly; tail valve with
three slits and with only a tiny sinus in the region of the middle
slit.
DESCRIPTION. Head valves with shallow posterior sinus; 8-9
slits (n = 2); insertion slits deep; tegmentum covers about 1/4 of
dorsal surface.
Intermediate valves about 3.5-4 times wider than long;
shallow anterior sinus; rounded edges of valves; 1 slit, groove
from slit extends far towards apex; prominent slit rays on ventral
surface of valve; pronounced v-shaped ridge on undersurface of
valve, extending from the midpoint of the lateral margins of the
valves to the apex.
Tail valves subhexagonal in outline; 3 slits, middle slit
occurring in a shallow sinus; slight raised triangular area from
mucro to anterior margin.
ETYMOLOGY. From solits, Latin for “alone,” and vagus ,
Latin for “wandering,” so named because this species of Amicula
lived far from modern representatives of the genus.
REMARKS. The reduced tegmentum, presence of two slits
total (one on each side) in each intermediate valve, and overall
shape indicate this is a species of Amicula. However, some
prominent characters are unique to this species, in particular the
presence of eight or nine slits in head valves, as opposed to six to
eight that were previously reported for the genus (Jakovleva,
1952). Also, the tegmentum, although reduced, is proportionally
larger than that in other species of Amicula. In addition, the lack
of an anterior embayment in the tail valve of this species
differentiates it from others in the genus.
This species is distinct from A. vestita (Broderip and Sowerby,
1829) and A. amiculata (Pallas, 1787), and all of their putative
synonyms, in having a much greater valve surface coverage by
tegmentum; a typically suboval, less heart-shaped tegmentum;
relatively straight posterior margins; three slits in the tail valve;
and a much shallower anterior sinus in the tail valve.
Amicula is today found in the cold, boreal regions, mostly from
the North Pacific and Artie (Jakovleva, 1952; Okutani and Saito,
1987), but it also ranges as far south as Hokkaido, Japan, in the
northwestern Pacific (Saito, 1994). The complete absence of the
genus from western North America, and the warmer-water
affinities of some of the other chitons reported here, make its
discovery in the San Diego Formation of Southern California a
surprise.
Genus Mopalia Gray, 1847a
DISTRIBUTION. This genus occurs in the temperate eastern
and western Pacific but is particularly common in the temperate
northeastern Pacific, with a remarkable diversity of species there
(Kelly and Eernisse, 2008). Mopalia tends to occur in intertidal to
shallow subtidal environments.
This genus has been reported from Miocene rocks in Japan
(Itoigawa et al., 1981, 1982). Those fossils consist of only four
intermediate valve fragments so their identification as Mopalia is
problematic. However, a Miocene occurrence is consistent with
molecular dating of a Miocene divergence between northwestern
and northeastern Pacific species, and it is inconsistent with a Late
Pliocene origin of the genus (Kelly and Eernisse, 2008). Fossils in
the San Diego Formation therefore represent among the oldest
northeastern Pacific records of Mopalia , but the genus is expected
to have been in the northeastern Pacific since the Miocene.
Mopalia has previously been reported from a few specimens from
the Pliocene by Davis (1998:21), who listed the rare (<10
specimens) occurrence of “? Mopalia ciliata ” from the Pico
Formation in downtown Los Angeles, and Berry (1922:452),
who listed one intermediate valve of “ Mopalia , sp. indet.” from
the “Santa Barbara” Formation in Santa Monica, and suggested
that its age is Pliocene. The latter locality is likely the same (same
general area) as what Hoots (1931) referred to as the “San
Diego” Formation, which appears to be Pliocene based on the
occurrence of the bivalve Patinopecten healeyi. Fossils of
Mopalia also have been reported from the Pleistocene of the
eastern Pacific (e.g., Arnold, 1903; Chace and Chace, 1919;
Kennedy, 1978; Roth, 1979; and Valentine, 1980) and western
Pacific (Itoigawa et al., 1978).
REMARKS. Mopalia species are often differentiated by
aspects of girdle setae. Although they typically have the same
slit pattern of 8/l/sinus+2 (Kaas and Van Belle, 1994), most
species have a somewhat unique tegmental sculpture. However,
the range of tegmental sculpture does overlap in some species,
and this, plus the small sample size for each species of Mopalia
here, prompted us to choose an open nomenclature for most of
the species.
Mopalia sinuata Carpenter, 1864
Figure 15 (1-3)
Mopalia sinuata Carpenter, 1864:603, 648; Palmer, 1958:282,
pi. 33, figs. 6-13 (contains more complete synonymies); Kaas
and Van Belle, 1994:240 (contains more complete synony-
mies).
Placipborella (Osteochiton) sinuata : Dali, 1879:303, 306.
Osteochiton sinuata : Dali, 1886:211.
Mopalia goniura Dali, 1919:513.
DISTRIBUTION. LACMIP localities 305 (13 head, 42
intermediate, and 4 tail valves; 1 figured head valve, LACMIP
13894, and 1 figured intermediate valve, LACMIP 13895; all
other specimens in unfigured lot, LACMIP 14323) and 16862
(305A; 2 head and 1 intermediate valve, all in unfigured lot,
LACMIP 14324).
TYPE SPECIMENS. Syntypes, USNM 4473 and PRM 58
(Palmer, 1958).
TYPE LOCALITY. Puget Sound, Washington.
MATERIAL EXAMINED. Numerous specimens from at or
near the type locality at SBMNH and LACM.
REMARKS. Characteristics of M. sinuata seen in the fossils
include pores arranged in slightly curving rows, a single, pro-
minent ridge separating central from lateral areas of the
intermediate valves, and intermediate valves with a straight
posterior margin that is angled backwards from the apex.
The fossils share with Mopalia imporcata Carpenter, 1864, the
same size and length:width ratio, and the same tegmentum
sculpture in the lateral area consisting of two prominent rows of
granules and central area sculpture of gently curving longitudinal
ridges overlying a less prominent cross-pattern. However, the
granules in the major valve-delineating ridges are much more
distinct and the longitudinal ridges in the central areas much
more prominent in modern specimens of M. imporcata than in
these fossils. These fossils share with M. sinuata a similar, unique
shape of the intermediate valve with straight posterior margins
that trend posteriorly, a tegmental sculpture of cross-hatching,
and a prominent, straight ridge that separates the lateral from
central areas.
These fossils differ from M. middendorffii (von Schrenck,
1861) in being narrower, having a slightly more prominent ridge
delineating valve areas, and having narrower lateral areas; from
M. retifera Thiele, 1909, M. schrencki Thiele, 1909, and M. seta
Jakovleva, 1952, in having much finer sculpture; from M. ciliata
(Sowerby, 1840) in lacking longitudinal ridges in the central
areas; from M. lignosa (Gould, 1846) in lacking distinct granules
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 39
Figure 15 Mopalia spp. 1-3, 5-6, 8-27, from LACM1P locality 305; 4, 7, from LACMIP locality 16817 (305C). 1-3, Mopalia sinuata Carpenter,
1864: head (1) and intermediate (2-3) valves. 1, LACMIP 13894; 2-3, LACMIP 13895; 4-26, Mopalia sp. cf. M. swanii Carpenter, 1864: head (4-10),
intermediate (11-19), and tail (20-26) valves. 4, 7, LACMIP 13857; 5-6, LACMIP 13858; 8-9, LACMIP 13859; 10, LACMIP 13860; 1 1-12, LACMIP
13861; 13, LACMIP 13862; 14, LACMIP 13863; 15, LACMIP 13864; 16, LACMIP 13865; 17, LACMIP 13866; 18, LACMIP 13867; 19, LACMIP
13868; 20-21, LACMIP 13869; 22-23, LACMIP 13870; 24, LACMIP 13871; 25-26, LACMIP 13872; 27, Mopalia sp. indeterminate: 27, intermediate
valve. LACMIP 13873. Scale bars=l mm.
40 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
in lateral areas and in being less wide; from M. muscosa (Gould,
1846) in lacking prominent rows of granules in the central area;
from M. hindsii (Reeve, 1847) in having pores instead of merged
granule rows in the central area; from M. vespertina (Gould,
1852) in having more prominent tegmental sculpturing; from M.
acuta (Carpenter, 1855), M. plumosa Carpenter in Pilsbry, 1893,
and M. swanii Carpenter, 1864, in being wider and with more
prominent ridges separating central area from lateral areas; from
AL lowei Pilsbry, 1918, in having finer pores and less of a beak to
intermediate valves; from M. lionata Pilsbry, 1918, and AL
cirrata Berry, 1919a, in having much finer sculpture; from M.
egretta Berry, 1919a, in having finer sculpture, narrower lateral
areas, and in being less wide; from M. phorminx Berry, 1919a, in
lacking prominent ridges in central area; from AL spectabilis
Cowan and Cowan, 1977, in lacking granules in central area but
having distinct pores instead; and differ slightly from AL ferreirai
Clark, 1991, in lacking a prominent beak on intermediate valves
and with less prominent longitudinal ridges in central areas of
intermediate valves and less curving posterior margin of
intermediate valves.
Mopalia sinuata ranges from Cook Inlet, Alaska, to Avila
Beach, San Luis Obispo County, California, and occurs from the
intertidal zone to 200-m depth (Kaas and Van Belle, 1994), but is
subtidal (8 m or deeper) in central California (Eernisse et al,
2007). Mopalia sinuata has been described from the fossil record
previously only by Berry (1922) who noted the occurrence of
Mopalia sp. cf. AL sinuata from the Pleistocene of Deadman
Island, San Pedro, California.
Mopalia sp. cf. AL swanii Carpenter, 1864
Figure 15 (4-26)
[Mopalia kennerleyi swanii Carpenter, 1864:648.
Mopalia muscosa swanii: Dali, 1921:195.
Mopalia swanii: Berry, 1951:214, pi. 26, fig. 15; Palmer,
1958:283; Kaas and Van Belle, 1994:238 (contains more
complete synonymies).]
DISTRIBUTION. LACMIP localities 305 (142 head, 212
intermediate, and 46 tail valves; 3 figured head valves, LACMIP
13858-13860, 8 figured intermediate valves, 13861-13868, and
4 figured tail valves, 13869-13872; all other specimens in
unfigured lot, LACMIP 14325), 16817 (305C; 5 head and 4
intermediate valves; 1 figured head valve, LACMIP 13857; all
other specimens in unfigured lot, LACMIP 14326), and 16862
(305A; 1 head, 4 intermediate, and 1 tail valve, all in unfigured
lot, LACMIP 14327).
MATERIAL EXAMINED. Numerous topotypes of Mopalia
swanii at SBMNH and LACM; type locality for M. swanii is
Tatoosh Island, Washington.
REMARKS. The fossils have the same reticulate pattern in the
central areas and isotropic granulose pattern in the lateral areas
as seen in specimens of Mopalia swanii. The fossil valves fall
easily within the size range for this species (listed as “up to 5 cm”;
Clark, 1991:309).
The following members of the species-rich genus Mopalia have
much coarser valve sculpturing than the San Diego Formation
fossils and are not further compared here: M. cirrata, M. egretta,
M. lionata, M. lowei, M. phorminx, M. porifera, M. retifera, M.
schrencki, and M. seta. These fossils differ front valves of M.
middendorffii in having wider valves with smaller pores; from M.
ciliata in lacking longitudinal ridges in the central area and
having pores instead; from M. lignosa in lacking distinct granules
in lateral areas of intermediate valves, and in having more
prominent pattern of pores in central area; from M. muscosa in
lacking prominent rows of granules in central area; from M.
hindsii in having pores instead of merged granule rows in the
central area; from M. vespertina in having more prominent
tegmental sculpture; from M. sinuata in being wider and with a
much less prominent ridge separating valve areas; from M.
imporcata in being wider and with less prominent ridges dividing
valve areas; from M. spectabilis in lacking granules in central
area but having distinct pores instead; and from M. ferreirai
in lacking prominent longitudinal ridges in central area or so
prominent major ridges dividing valve areas.
The fossil head valve has a tegmental sculpture dominated by a
reticulate pattern of pores throughout the central areas of
intermediate valves, and such sculpturing is typical for modern
specimens of M. swanii. However, such reticulate pores can also
be found to varying degrees in certain congeners, including M.
ciliata, M. kennerleyi, M. ferreirai, and M. spectabilis (all closely
related to M. swanii based on molecular results of Kelly and
Eernisse, 2008), and occasional specimens of M. egretta and M.
muscosa. However, the fossil intermediate valves also appear
similar to those of modern M. acuta and the closely related M.
plumosa (Eernisse et al., 2007; Kelly and Eernisse, 2008),
although the tail valves have more prominent ridges than is
typical for M. acuta or M. plumosa. However, because of the
overlaps in valve form among species of Mopalia, and because
extant M. swanii are uncommon south of Oregon, our
identification remains tentative.
Mopalia swanii occurs in the intertidal zone from Alaska to
Los Angeles, California (Kaas and Van Belle, 1994), but is
uncommon south of Oregon (Eernisse et al., 2007). Mopalia
swanii has not been previously recorded as a fossil.
Mopalia sp. indeterminate
Figure 15 (27)
DISTRIBUTION. LACMIP locality 305 (1 well-preserved
intermediate valve embedded in matrix; LACMIP 13873).
REMARKS. This valve has a uniform, lattice-like sculpture in
the central area. The lateral areas also have a lattice sculpture,
although with a greater development of granules in between the
spaces of the lattice. The two areas are separated by a row of larger
granules. This sculpture is similar to that of a number of Mopalia
species, including M. ferreirai, M. spectabilis, and M. swanii. The
sutural laminae extend nearly to the valve midline, and the valve is
large, both consistent with assignment to this genus.
Genus Placiphorella Dali, 1879
DISTRIBUTION. This genus occurs primarily in the north-
eastern to northwestern Pacific (Clark, 1994).
A single isolated intermediate valve of Placiphorella from the
Miocene of Japan was illustrated by Itoigawa et al. (1981). It is
also known from the Pleistocene of Japan (Itoigawa et al., 1978).
In North America, the oldest previous record of Placiphorella is
from the Pleistocene (e.g., Chace and Chace, 1919; Valentine and
Meade, 1961; Marincovich, 1976; Kennedy, 1978).
REMARKS. Placiphorella is characterized by a prominent
anterior extension of the girdle with scaled bristles, and short and
wide valves embedded in a circular or oval body (Clark, 1994).
Placiphorella velata Dali, 1879
Figure 16 (1-8)
Placiphorella velata Dali, 1879:298, pi. 2, fig. 36; Clark,
1994:291, figs. 1—3, 26, 27 (contains more complete synon-
ymies).
Placiphorella stimpsoni Dali, 1921:197.
Placiphorella sp.: Kohl, 1974:214.
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 41
DISTRIBUTION. LACMIP localities 305 (1 figured tail valve,
LACMIP 13878, and 1 unfigured intermediate valve, LACMIP
14328), 16817 (305C; 1 head, 4 intermediate, and 1 tail valve; 1
figured head valve, LACMIP 13874, 2 figured intermediate
valves, LACMIP 13875-13876, and 1 figured tail valve,
LACMIP 13877; other specimens in unfigured lot, LACMIP
14329), and 16862 (305A; 1 head and 1 tail valve, in unfigured
lot, LACMIP 14330).
TYPE SPECIMENS. Lectotype and two paralectotypes (col-
lection numbered ANSP 35756) designated by Clark (1994).
TYPE LOCALITY. Bahia Todos Santos, Baja California,
Mexico.
MATERIAL EXAMINED. Numerous specimens from at or
near the type locality, at SBMNH and LACM.
REMARKS. Placiphorella velata is similar to both P. hansel-
mani Clark, 1994, and P. mirabilis Clark, 1994. The characters
that Clark (1994) used to separate these species do not include
tegmental sculpture, and in fact many Placiphorella species have a
tegmental sculpture similar to these fossils. However, the large size
of the fossil valves (many greater than 5 mm in length at the
midline) is consistent only with P. velata. Placiphorella velata has
a combined tegmental length up to 6 cm whereas the other
Placiphorella species have a maximum size of 5 cm, and all species
of the genus have a girdle that extends anteriorly (Clark, 1994).
The distinct growth lines and slightly raised lateral areas are also
consistent with P. velata. Otherwise these fossils are similar also to
P. rufa Berry, 1917, although the holotype of P. rufa has two
ridges in the lateral areas of intermediate valves, separated by a
shallow sulcus, whereas the Pliocene fossils and P. velata have one
sharp change in slope in the lateral areas.
These fossils also differ from P. borealis Pilsbry, 1893, in
lacking the prominent ridges at the posterior margin of the
valves; from P. blainvillii (Broderip, 1832) in being less wide;
from P. mirabilis in having more prominent growth lines and
major ridges delineating valve areas and in having relatively
longer intermediate valves; and from P. hanselmani in having
more delicate and distinct valve sculpture.
Placiphorella velata occurs from Alaska to central Baja
California in depths from 0 to 20 m (Clark, 1994), but it is
more commonly found from 5-to-10-m depths on sides and
bottoms of rocks (Eernisse et al., 2007). This species has not been
previously recorded from rocks older than the Pleistocene.
Placiphorella sp. cf. P. mirabilis Clark, 1994
Figure 16 (9-15)
[ Placiphorella mirabilis Clark, 1994:303, figs. 20-22, 34, 35
(contains more complete synonymy).]
DISTRIBUTION. LACMIP locality 305 (3 head, 14 interme-
diate, and 5 tail valves; 4 figured intermediate valves, LACMIP
13879-13882, and 1 figured tail valve, LACMIP 13883; all other
specimens in unfigured lot, LACMIP 14331).
MATERIAL EXAMINED. Holotype of Placiphorella mirabilis
(LACM 2703) and paratypes of P. mirabilis (LACM 2704-
2706).
REMARKS. These fossil valves are much smaller than those
identified as P. velata (see above), and these valves share with P.
mirabilis Clark, 1994 intermediate valves with a sharp beak,
lateral margins that curve gently anteriorly, and a faint diagonal
rib. Open nomenclature is used here, however, because the valves
of P. mirabilis are similar to those of both P. rufa and P.
hanselmani. The characters that Clark (1994) used to separate P.
mirabilis from all other species are all nonvalve features.
The fossils differ from P. borealis in lacking the prominent
ridges at the posterior margin of the valves and from P. blainvillii
in being less wide. These fossils are difficult to separate absolutely
from P. hanselmani , but the overall shape of valves, in particular
the tail valve, and fine tegmental sculpture of the fossils are more
similar to those of P. mirabilis. The fossils are also similar to P.
rufa, although they have less raised lateral areas than is typical
for the latter species.
Placiphorella mirabilis occurs between Gaviota, Santa Barbara
County, California, and Isla Asuncion, Baja California Sur,
Mexico, at depths from 28 to 155 m on rocks (Clark, 1994).
Placiphorella mirabilis has not been previously reported in the
paleontological literature.
Genus Tonicella Carpenter, 1873
DISTRIBUTION. This genus occurs in the North Pacific,
Arctic, and North Atlantic oceans (Kaas and Van Belle, 1985b).
In North America it occurs from Arctic Alaska to Baja California,
Mexico (Clark, 1999).
The fossil record of Tonicella extends back to the Eocene in
Europe (Bielokrys, 1999), the Miocene in Japan (Itoigawa et al.
1981), and the Pleistocene of North America (e.g., Chace and
Chace, 1919; Zullo, 1969; Kennedy, 1978; Roth, 1979).
REMARKS. The valves in this genus are characterized by a
smooth tegmental surface that is ornamented at most by tiny
granules, and with weakly defined lateral areas (Ferreira, 1982).
Tonicella sp. cf. T. venusta Clark, 1999
Figure 16 (16-30)
[Tonicella venusta Clark, 1999:41, figs. 25-32, 34 (contains
more complete synonymies).]
DISTRIBUTION. LACMIP locality 305 (2 head, 55 interme-
diate, and 3 tail valves; 6 figured intermediate valves, LACMIP
13884-13889, and 2 figured tail valves, 13890-13891; al! other
specimens in unfigured lot, LACMIP 14332).
REMARKS. Although lacking color, the fossil specimens
appear to show some remnant patterns that are indicative of
Tonicella (Figure 20.20), in particular the Tonicella lineata
species complex (sensu Clark, 1999). The sharp beak, posteriorly
curved lateral margins, indistinct tegmental sculpture of faint
growth lines, broad W-shaped posterior margin of valves,
rounded sutural laminae with broad jugal sinus, anterior mucro
and concave postmucronal area of tail valve, and presence of one
insertion tooth on each side of the intermediate valve are all
consistent with the range in modern Tonicella venusta.
Without the color patterns and details of the girdle, it is
difficult to classify these fossils with certainty. However, some
species can be excluded. For example, the fossils differ from T.
undocaerulea Sirenko, 1973, and T. lineata (Wood, 1815) in
having a concave, not straight, postmucronal area of tail valve.
The fossils differ from T. lokii Clark, 1999, in having more
rounded sutural laminae on intermediate valves, and from T.
insignis (Reeve, 1847) in having a dark band along jugum flanked
by pale strips, compared with a lateral wavy pattern in that
region of the T. insignis intermediate valves. The remnant color
pattern (Figure 20.20), although faint, shows a dark triangle at
the jugum with apex at valve apex, adjacent white bands, and an
apparent splotchy pattern elsewhere. The splotchy pattern is
consistent with T. venusta and also with the Arctic/circumboreal
T. submarmorea (von Middendorff, 1847) and T. marmorea
(Fabricius, 1780), which have been considered to be species
complexes by some (e.g., Clark, 1999). The splotchy pattern is
inconsistent with the other species of Tonicella. It is more difficult
to differentiate these fossil intermediate valves from those of T.
marmorea and T. submarmorea. However, the mucro very near
42 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 43
Figure 17 Dendrochiton sp. indeterminate (Berry, 1911) and Nuttallina sp. indeterminate. 1-15, 19, from LACMIP locality 305; 16-18 from
LACMIP locality 16882 (305A); 20-22 from LACMIP locality 16817 (305C). 1-19, Dendrochiton sp.: 1-19, intermediate valves. 1-3, LACMIP 14285;
4, LACMIP 14288; 5-7, LACMIP 14286; 8, LACMIP 14289; 9-11, LACMIP 14287; 12, LACMIP 14290; 13-15, LACMIP 14292; 16-18, LACMIP
14293; 19, LACMIP 14291. 20-22, Nuttallina sp.: 20-22, intermediate valves. LACMIP 13892. Scale bars=l mm.
the anterior margin of the tail valve is not seen in T. submarmorea.
Some modern T. marmorea individuals have an anterior mucro,
but it is not usually as close to the anterior margin as in these
fossils. Of the two well-preserved tail valves in this assemblage,
one has nine slits and the other 10, close to, but not the same as in
modern T. vemista with 1 1 slits. Tonicella marmorea has five to 1 1
slits (Kaas and Van Belle, 1985b), consistent with our fossils.
Boreochiton Sars, 1878 bears similarities with Tonicella, and
in fact has been synonymized with the latter by Ferreira (1982)
and Kaas and Van Belle (1985b). Sirenko (2000), in contrast,
demonstrated that Boreochiton is distinct from Tonicella. These
fossils differ from the three species of Boreochiton, Boreochiton
ruber (Linnaeus, 1767), B. beringensis (Jakovleva, 1952), and B.
granulata (Jakovleva, 1952), in that the tail valve has a shorter
premucronal area and the sutural laminae are more rounded and
less subquadrate.
Because of the mixture of characters and because some of the
distinguishing characters between species of Tonicella are missing
Figure 16 Placiphorella spp. and Tonicella cf. vemista Clark, 1999. 1-6 from LACMIP locality 16817 (305C); 7-30, from LACMIP locality 305. 1-8,
Placiphorella velata Dali, 1879: head (1-2), intermediate (3-4), and tail (5-8) valves. 1-2, LACMIP 13874; 3, LACMIP 13875; 4, LACMIP 13876; 5-6,
LACMIP 13877; 7-8, LACMIP 13878; 9-15, Placiphorella sp. cf. P. mirabilis Clark, 1994: intermediate (9-14) and tail (15) valves. 9-10, LACMIP
13879; 11-12; LACMIP 13880; 13, LACMIP 13881; 14, LACMIP 13882; 15, LACMIP 13883; 16-30, Tonicella cf. vemista : intermediate (16-26) and
tail (27-30) valves. 16, LACMIP 13884; 17-18, LACMIP 13885; 19, LACMIP 13886; 20-22, LACMIP 13887; 23, LACMIP 13888; 24-26, LACMIP
13889; 27-28, LACMIP 13890; 29-30, LACMIP 13891. Scale bars= 1 mm.
44 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
in the fossils, we identify them with some uncertainty as
Tonicella sp. cf. T. venusta. These fossils are also very similar
to the Arctic/circumboreal T. marmorea, but that species does
not occur in the eastern Pacific south of the Aleutian Islands,
Alaska (Kaas and Van Belle, 1985b). Tonicella marmorea is
sometimes recognized as a separate species, T. snbmarmorea (von
Middendorff, 1847), in the North Pacific. Tonicella venusta,
however, ranges as far south as Baja California.
Tonicella venusta occurs from south-central Alaska to Isla
Cedros, Baja California, Mexico, in depths from the intertidal
zone to 140 m (Clark, 1999). It is more common off of central
California and farther north, and only four of the 137 reported
specimens were collected from Baja California (Clark, 1999).
Stebbins and Eernisse (2009) recorded one specimen from 15-m
depth off of San Miguel Island (Channel Islands), California,
which has a cool-water fauna more typical of central rather than
Southern California. Tonicella marmorea, the other species that
these fossils might represent, is most common in the Arctic and
circumboreal regions where it ranges from 0-to-230-m depths
(Kaas and Van Belle, 1985b). Tonicella venusta was previously
unknown from the fossil record.
Genus Dendrochiton Berry, 1911
DISTRIBUTION. This genus of small, brightly colored chitons
is restricted to the northeastern Pacific, occurring between the
latitudes 49°N and 26°N (Ferreira, 1982). The only previously
published reference to a fossil representative of this genus is from
Vedder and Norris (1963), who listed Dendrochiton cf. D.
thamnoporus from a Pleistocene terrace on San Nicholas Island,
California.
REMARKS. Berry (1911) initially proposed this name as a
subgenus of Mopalia, but later he (Berry, 1917) considered it a
full genus. Based on the presence of girdle bristles and eight slits
in the head valve, Dendrochiton was first considered to be a
member of the Mopaliidae (Berry, 1911, 1917; Smith, 1960;
Thorpe in Keen, 1971). Ferreira (1982) later transferred the
genus to the Lepidochitonidae, noting that the radula, tegmen-
tum sculpture, and lack of a sinus in the tail valve of
Dendrochiton were all more similar to lepidochitonids than to
mopaliids. The outline of the intermediate valves of Dendrochi-
ton is likewise very similar to that of lepidochitonids such as
Cyanoplax and Lepidochitona. Kaas and Van Belle (1985)
seconded the classification of this genus in the Lepidochitonidae,
proposing Dendrochiton as a subgenus of Lepidochitona. More
recently, however, Kelly and Eernisse (2008) proposed returning
Dendrochiton to the Mopaliidae based primarily on high genetic
similarity between Mopalia and Dendrochiton.
Dendrochiton sp. indeterminate
Figure 17 (1-19)
DISTRIBUTION. LACMIP localities 305 (11 intermediate
valves; 8 figured intermediate valves, LACMIP 14285-14292;
other valves in unfigured lot, LACMIP 14333) and 16862 (305A;
1 intermediate valve; LACMIP 14293).
REMARKS. The fossil intermediate valves are small, relatively
short, have posterio-lateral edges curved back, and a central area
tegmental sculpture of thick but flat faintly curving longitudinal
ridges. All of these characters are consistent with Dendrochiton.
The central area tegmental sculpture is the diagnostic character
allowing assignment of these valves to Dendrochiton, consisting
of more or less broad, flat-topped, somewhat sinuous ridges
separated laterally from each other by deep grooves. This
tegmental sculpture indicates that these valves are not from
Dendrochiton flectens, which has smooth sculpture, but the
characters preserved in these fossils do not allow distinguishing
between the other species of Dendrochiton. Dendrochiton
thamnoporus (Berry, 1911), D. lirulatus Berry, 1963, D.
semilirulatus Berry, 1927, and D. gothicus (Carpenter, 1864)
all are small and have longitudinal ridges in the central area of
intermediate valves (see Ferreira, 1982). Similarly, the distin-
guishing characters between D. thamnoporus and D. semiliratus
listed by Stebbins and Eernisse (2009) in their identification key
all relate to girdle ornament and tail valve shape, features that do
not occur in these fossils.
Family Lepidochitonidae Iredale, 1914
Genus Nuttallina Dali, 1871
DISTRIBUTION. This genus occurs only in western North
America, mostly restricted to the region from central California
south to the Gulf of California. Ferreira (1982) recognized only
two of the nominal species in this genus: Nuttallina californica
(Reeve, 1847) and N. crossota (Berry, 1956). Eernisse et al.
(2007) and others have continued to recognize the more southern
N. fluxa (Reeve, 1847), which has broader valves, is genetically
distinct (Kelly and Eernisse, 2007), and is by far the most
common chiton species in Southern California. Eernisse et al.
(2007) also recognized a fourth distinct species first documented
in a Ph.D. dissertation but not yet formally described, referred to
as “ Nuttallina sp. of Piper, 1984.” The valves of the latter are
very similar to N. californica, but this species is generally more
southern in its distribution, although all three species are known
from Southern California and northern Baja California.
This genus is widely known from Pleistocene marine terrace
deposits of Southern California (e.g., Berry, 1922; Chace, 1966;
Marincovich, 1976; Valentine, 1980), but this is the first Pliocene
record of Nuttallina.
REMARKS. Valves of Nuttallina are distinct and characterized
by a granulose tegmentum (when not eroded), well-developed
sutural laminae, spongy eaves, and elongate form with insertion
teeth directed anteriorly especially in the tail valve, (Ferreira,
1982). In addition, Nuttallina valves have a relatively extensive
apical area on the ventral surface.
Nuttallina sp. indeterminate
Figure 17 (20-22)
DISTRIBUTION. LACMIP locality 16817 (305C; one well-
preserved intermediate valve; LACMIP 13892).
DESCRIPTION. Intermediate valve triangular in overall
shape, with prominent rounded sutural laminae and an extensive
jugal sinus. Valve areas difficult to discern, but do not appear to
be well delineated. Anterio-lateral regions of valve rounded.
Broad emargination in anterior margin. Apical area relatively
large, 1 slit per side, jugal area about 90°.
REMARKS. This valve has all the trademark features of
Nuttallina, but with only one shell plate known it is difficult to
identify the species. Nuttallina occurs exclusively in the intertidal
or shallowest subtidal zone (Eernisse et al., 2007), whereas the
fossil beds appear to have formed in deeper water (—25 m),
perhaps explaining the paucity of Nuttallina therein.
DISCUSSION
DIVERSIFICATION OF CHITONS ON THE PACIFIC COAST
OF NORTH AMERICA
Chitons are abundant and diverse on the Pacific Coast of North
America, a pattern that Jakovleva (1952) noted for the
Oregonian Province and one that prompted E.M. Chace (1940)
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 45
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46 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
to call the Pacific Coast of North America “the metropolis of
chitons” with more than 150 of the world’s ~950 known species
occurring there. Thorpe (1962) estimated that chiton diversity
along the California coast is second only to that of southern
Australia. However, the early to middle Cenozoic history of
Pacific Coast Polyplacophora is largely unknown. In part the
poor fossil record of chitons may be due to the low preservation
potential of chiton valves (Puchalski and Johnson, 2009) and
because chiton fossils are often fragmentary and rare in
sedimentary deposits and so are often overlooked by collectors
and researchers (Puchalski et ah, 2008). Even chitons in calm-
water aquaria rapidly disarticulate after death, and sometimes
their valves break just before then (M.J.V., personal observation).
But oddly, known chiton diversity was far greater in the
Paleozoic than in the Mesozoic (Smith, 1973) or earliest
Cenozoic (Puchalski et ah, 2008). Perhaps this is because chitons
suffered major mass extinctions at the Permo-Triassic and
Cretaceous-Tertiary boundaries. Nevertheless, our knowledge
of global chiton diversity is greatest for the late Cenozoic
(Vendrasco, 1999), based mostly on the Holocene and Pleisto-
cene records. A great proportion of this modern chiton diversity
is on the Pacific Coast of North America.
The collective fauna described here reveals that chitons were
relatively diverse on the Pacific Coast by the Pliocene. This
diversity is in stark contrast to that of the Miocene of western
North America, which has so far yielded very few chitons. Only a
few chitons are known from the Eocene of Southern California,
but as yet these remain unidentified (G. Kennedy, personal
communication, 2010). A possible explanation for the apparent
increase in chiton diversity there is that chitons diversified as food
for them increased. Beginning in the middle Miocene, seawater
temperatures in the eastern Pacific began to drop. This trend was
interrupted by a Pliocene warm period from about 4.6 to 3 Ma,
and then the cool temperatures returned (Lyle et ah, 2008). The
cool middle Miocene has been inferred as the time when fleshy
algae like kelp first became abundant along the coast of western
North America (Estes and Steinberg, 1988, 1989), increasing the
primary productivity of the region and providing more food for
grazing mollusks (Estes et ah, 2005). In addition, upwelling is
thought to have begun along midlatitude west coasts during the
late middle Miocene (15 to 12 million years ago), perhaps due to
increased polar cold deep-water production at that time, which
strengthened shore-parallel winds at midlatitudes that produced
the upwelling (Jacobs et ah, 2004). Increased upwelling is
correlated with higher primary productivity and a more diverse
rocky shore invertebrate fauna due to more food for filter feeders
and organic matter for detritivores (Jacobs et ah, 2004). Grazers
such as chitons would also benefit from the increased organic
matter and primary producers on the rocks. Overall, higher
productivity can correlate with more diverse marine ecosystems
(Vermeij, 1989; Leigh and Vermeij, 2002), although this is not
always the case (e.g., coral reefs in the tropics that have high
diversity in a low productivity zone, and the Arctic Ocean, which
has high productivity but apparently low diversity). This increase
in productivity was followed by the development of a heteroge-
neous coastline (late Miocene) with abundant rocky shores
(Pliocene to Pleistocene) (Jacobs et ah, 2004), all factors that
should have increased the diversification rate of chitons and other
organisms in the rocky intertidal zone. Along a similar line of
reasoning, Tsuchi (2002) documented an increase in the rate of
evolution of mollusks on both sides of the Pacific that correlated
with a stepwise cooling that began in the middle Pliocene. So
perhaps the pattern inferred from the chiton fossil record is in
large part real — the spread of upwelling and fleshy algae along
the Pacific Coast beginning in the late Miocene combined with
the increased heterogeneity of the coastline from tectonic activity
in the Pliocene and Pleistocene (Jacobs et al., 2004) may have
promoted increases in chiton abundance and diversity through-
out the region during the Neogene.
The San Diego Formation provides the earliest known detailed
view of the “modern” chiton fauna in the temperate eastern
Pacific Ocean. This assemblage records the first appearance of
many genera and species that are now common along the Pacific
Coast of North America (Figure 3; Table 2). One common
Pacific Coast chiton genus is Mopalia, and current information
indicates it diversified in the North Pacific relatively recently.
Kelly and Eernisse (2008) used molecular data to infer a middle
Miocene ( — 16 Ma) spread across the North Pacific for Mopalia ,
and noted many other rocky-shore taxa in the Pacific probably
spread across the North Pacific at the same time. They inferred
that Mopalia experienced a major diversification in the north-
eastern Pacific beginning about 5 Ma (Kelly and Eernisse, 2008).
This contrasts with the known range of Mopalia from the fossil
record (back to —3.2 Ma; Figure 3).
Another genus that likely diversified relatively recently in the
North Pacific is Lepidozona, which is mostly restricted to that
region. The greatest diversity of Lepidozona is in the north-
eastern Pacific (Stebbins and Eernisse, 2009), with the oldest
fossils apparently being from the Miocene of Japan (Itoigawa and
Nishimoto, 1975) and one valve from the latest Eocene or earliest
Oligocene of Washington (Dell’Angelo et ah, 2011). Lepidozona
is abundant and relatively diverse in the San Diego Formation,
providing evidence that the genus also diversified in the North
Pacific since the Miocene.
The fact that early to middle Cenozoic chitons are largely
missing from the fossil record of western North America is
surprising given the abundance of marine nearshore sedimentary
rocks in the region from that time. One possible explanation for
this pattern is that the rocky intertidal environments, where
chitons are abundant, are erosional environments that have been
less likely to be preserved (Johnson, 2006). In fact, the excellent
fossil record of the rocky shore on the Pacific Coast over the past
million years or so is mainly due to tectonic uplift and emergence
of marine terraces (Jacobs et al., 2004). However, chiton valves
are common in bioclastic subtidal sediment today (cf. LACM
collections), and the combined evidence indicates that the San
Diego Formation sediments were deposited in a moderately deep
subtidal environment. The San Diego Formation collections show
that a diverse assemblage and abundance of chitons can be
preserved seaward from rocky shore environments, in predom-
inantly depositional rather than erosional situations, further
highlighting the discrepancy between the lack of early-mid-
Cenozoic chitons and their striking abundance in the Border beds
of the San Diego Formation.
CHITON MIGRATION
The chiton fauna front the San Diego Formation extends the
stratigraphic range of many chiton species along the Pacific Coast
into the middle Pliocene (Figure 3). The data can be used to help
assess hypotheses about the origin and timing of migration of
some chiton species. Some of the eastern Pacific chiton genera
have a slightly older fossil record in the western Pacific (e.g., to
the Miocene for Mopalia and Placiphorella). The northeastern
Asian (e.g., Hokkaido, Japan) and western North American
chiton faunas share some genera in common (Jakovleva, 1952),
including Mopalia , Lepidozona , Tonicella , Placiphorella , Ami-
cula , Schizoplax, Cryptochiton , Leptochiton, Tripoplax , and
Boreochiton. This similarity reflects the overall pattern for
mollusks on both sides of the northern Pacific (Keen, 1941).
Contributions in Science, Number 520
Figure 18 Modern geographic ranges of chitons from the Border
localities— LACMIP localities 305, 16862 (305A), and 16817 (305C)— of
the San Diego Formation. Dashed line shows current latitude of the San
Diego Formation Border beds. Key: 1, Callistochiton palmulatus; 2,
Leptocbiton nexus ; 3, L. rugatus; 4, Placiphorella velata; 5, P.mirabilis
(San Diego Formation representative: Placiphorella sp. cf. P. mirabilis ); 6,
Oldroydia percrassa; 7, Lepidozona rotbi (as Lepidozona sp. cf. L. rothi);
8, L. pectinulata; 9, L. mertensii ; 10, L. radians (as Lepidozona sp. cf. L.
radians); 11, Stenoplax heathiana (as Stenoplax sp. cf. S. heathiana ); 12,
S. fallax; 13, S. circumsenta; 14, Mopalia sinuata; 15, M. swanii (as
Mopalia sp. cf. M. swanii); 16, Tonicella venusta (as Tonicella sp. cf. T.
venusta); 17, Amicula (as Amicula solivaga n. sp.).
Amano (2005) compiled evidence from the fossil record for
Cenozoic molluscan migrations through or to the cool North
Pacific, documenting apparent cases of migration westward
( Penitella , Platyodon , Panomya, Littorina, Liracassis , Nucella ,
Ceratostoma , Macoma, Kaneharaia, and Lirabuccinum ), east-
ward ( Mya , Neptunea , Mizubopecten , Turritelloidea, and
Buccinoidea), and from the Arctic to the North Pacific (e.g.,
Cyrtodaria). Vermeij (2001) previously suggested that many of
these eastward or westward migrating mollusks originated during
the late Eocene to early Oligocene cooling, and Squires (2003)
documented an influx of cool-water taxa along the coast of
Washington to California during this time period. Amano (2005)
classified North Pacific mollusks into subgroups and inferred that
(1) most of the taxa that appear to have originated in the
northwestern Pacific migrated eastward (21 of 25 genera or
subgenera), and of the migrating taxa, eight genera first appear in
the fossil record during the late Eocene in Asia and most migrated
during the Oligocene or Miocene and (2) most of the taxa
thought to have originated in the northeastern Pacific migrated
westward (22 of 26 genera or subgenera), mostly originating
during the late Eocene or early Oligocene and a vast majority
migrating during the early or early middle Miocene.
Among chitons that exclusively or predominantly occur in the
North Pacific, some genera only have a fossil record in the
northeastern Pacific: Amicula (from Pliocene — -this paper; mod-
ern distribution trans-Pacific); Cryptochiton (from Pliocene —
Vendrasco et ah: Chitons of the San Diego Formation ■ 47
Arnold, 1903; Berry, 1922; modern distribution trans-Pacific);
Nuttallina (from Pliocene — this paper; modern distribution
northeastern Pacific only); Cyanoplax (from Pleistocene — Berry,
1922; modern distribution northeastern Pacific only); Katbarina
(from Pliocene — Berry, 1922; modern distribution northeastern
Pacific only); Dendrochiton (from Pliocene — this paper; modern
distribution northeastern Pacific only); and Oldroydia (from
Pliocene — this paper; modern distribution northeastearn Pacific
only). Other North Pacific chitons have a trans-Pacific fossil
record and modern distribution, but with earlier records in the
western Pacific: Mopalia (from Miocene — Itiogawa and Nishi-
moto, 1975); and Placiphorella (from Miocene — Itiogawa and
Nishimoto, 1975).
The very high diversity of chitons endemic to the North Pacific
indicates diversification in the region. A large proportion of
species of many chiton genera occur in the northeastern Pacific
and some chiton genera have a slightly earlier fossil record in the
western Pacific than in the eastern Pacific. If the fossil record is
taken at face value, these observations indicate an eastward or
southeastward migration for genera such as Mopalia and
Placiphorella prior to their apparent diversification along the
Pacific Coast of North America. Sirenko and Clark (2008)
inferred a similar migration pattern for Deshayesiella.
A marine connection has existed between the Arctic and Pacific
basins at different times since the late Miocene (Marincovich and
Gladenkov, 1999), and hence it is possible that some eastern
Pacific chiton genera originated in the Arctic and spread to the
eastern and western Pacific. However, this migration path could
not have been common, as many Pacific chiton genera are known
from the earlier Miocene of Japan before the Arctic opened to the
Pacific. As another alternative, chitons may have migrated
northward along the Pacific Coast of North America from
tropical regions during these time intervals, but migrations of
mollusks northward during this time appear to have been much
less common than southward migrations (Roy et ah, 1995).
Nevertheless, some chiton genera that occur off the San Diego
coast today, such as Stenoplax, Callistochiton, Acanthochitona,
and Chaetopleura, do not occur north of California and appear
to have greater affinities with the warm-tropical Panamic rather
than the cool-temperate Oregonian chiton faunas.
Patchy local upwelling localities extend to across the equator
along the eastern Pacific margin, allowing for a potential
interchange of temperate faunas on either side of the equator
(Lindberg, 1991). This potential, however, does not seem to have
impacted chiton evolution much, as the chiton fauna of
the northeastern Pacific is quite different from that of the
southeastern Pacific, with the exception of some quite deep-
dwelling species in a few genera (e.g., Placiphorella, Tripoplax,
Leptocbiton).
PALEOCLIMATE
The Border localities have a rich fauna of at least 264 molluscan
species (102 bivalve, 136 gastropod, 22 chiton, and four
scaphopod species; Appendix 2). Appendix 2 is mainly compiled
from collections at LACMIP, and in part from the unpublished
manuscript of Hertlein and Grant and from field observations
(M.J.V., C.Z.F., D.J.E., Scott Rugh). Modern ecological data for
these mollusks (e.g., Morris, 1966; Keen, 1971; Rice, 1973;
Abbott, 1974; Keen and Coan, 1975; McLean, 1978; Bernard,
1983; McLean and Gosliner, 1996; Coan et al., 2000) indicate
that most of the fossil species currently live off the San Diego
coast, although a few are extralimital northern or extralimital
southern in their distribution (Figures 18-19). Extralimital
northern species include the bivalves Chlamys hastata (Sowerby,
48 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Figure 19 Modern geographic ranges of other (nonchiton) species that are abundant from the Border localities — LACMIP localities 305, 16862
(305A), and 16817 (305C) — of the San Diego Formation. Dashed line shows current latitude of the San Diego Formation Border beds. Includes 1-17,
bivalves; 18-64, gastropods; 65-66, scaphopods; 67-68, corals; 69, echinoderm; 70, crustacean. 1, Acila castrensis; 2, Barbatia illota; 3, Chama arcana-,
4, Chlamys bastata; 5, Cyclocardia ventricosa ; 6, Ensis myrae ; 7, Gan fucata ; 8, Glycymeris septentrionalis-, 9, Here excavata; 10, Lucinisca nuttalli ; 1 1,
Miltba xantusi; 12, Nuculana taphria; 13, Nutricola tantilla; 14, Panopea abrupta ; 15, Parvilucina approximata; 16, Pododesmus macrochisma-, 17,
Tbracia trapezoides; 18, Acmaea mitra ; 19, Alvania oldroydae-, 20, Ampbissa versicolor, 21, Barbarofusus barbarensis; 22, Calhanax biplicata; 23,
Calliostoma annulatum; 24, C. gemmulatum; 25, C. sitpragranosum-, 26, Cancellaria cooperi; 27, Ceritbiopsis pedroana; 28, Conus californicus; 29,
Crepidula aculeata; 30, C. onyx; 31, Crossata californica; 32, Cylicbnia attonsa; 33, Diadora arnoldi; 34, Epitonium minuticostata ; 35, Epitonium
sawinae ; 36, Eulima raymondi; 37, Glossaulax reclusianus; 38, Haliotis rufescens (as Haliotis sp. cf. H. rufescens); 39, Halistylus pupoides; 40, Hipponix
tumens; 41, Hirtoscala tinctum; 42, Homalopoma radiatum; 43, Kelletia kelletii; 44, Lacuna unifasciata; 45, Ligacalliostoma canaliculatum; 46,
Lirobittium rugatum; 47, Lirularia optabilis; 48, Megastraea turbanica; 49, Megasurcula carpenteriana (as Megasurcula sp. cf. M. carpenteriana); 50,
Megatbura crenulata; 51, Micranellum crebricinctum; 52, Alia (Mitrella) tuberosa; 53, Nassarius perpinguis; 54, Opalia montereyensis; 55,
Opbiodermella inermis; 56, P arviturbo stearnsii (as Parviturbo sp. cf. P. stearnsii ); 57, Pomaulax gibberosa; 58, Pseudomelatoma grippi; 59, Scalina
brunneopicta; 60, Shaskyus festivus; 61, Solariella peramabilis; 62, Tricolia pulloides (as Tricolia sp. cf. T. pulloides); 63, Triphora pedroana; 64,
Turritella cooperi; 65, Caditlus fusiformis; 66, Dentalium neobexagonum; 67, Balanopbyllia elegans; 68, Paracyatbus stearnsii; 69, Eucidaris thouarsii
(as Eucidaris sp. cf. E. thouarsii ); 70, Cancer productus.
1842), Clinocardinm nuttallii (Conrad, 1837), Dermatomya
temiiconcba (Dali, 1913), Ensis myrae Berry, 1953a, Miodontis-
cus prolongatus (Carpenter, 1864), Modiolus sacculifer (Berry,
1953b), Panopea abrupta (Conrad, 1849), Tellina idae Dali,
1891, Thyasira flexuosa (Montagu, 1803), and the gastropod
Haliotis walallensis Stearns, 1899. In addition, some species
occur in the San Diego area and perhaps a bit southward but are
much more common to the north, such as Ligacalliostoma
canaliculatum (Lightfoot, 1786) (McLean and Gosliner, 1996).
Southern extralimital species include the bivalves Barbatia illota
(Sowerby, 1833), Cyclopecten pernomus (Hertlein, 1935),
Dosinia ponderosa (Gray, 1838), Macoma medioamericana
Olsson, 1942, Miltba xantusi (Dali, 1905), and the gastropods
Acirsa cerralvoensis DuShane, 1970, Arcbitectonica nobilis
Roding, 1798, Megastraea turbanica (Dali, 1910), and Scalina
brunneopicta (Dali, 1908). In addition, living Diplodonta
sericata (Reeve, 1850) occur north to Santa Cruz Island,
California, but Coan et al. (2000) indicate that it is permanently
established only as far north as Laguna San Ignacio on the Pacific
coast of central Baja California.
Chitons may be particularly useful environmental indicators, as
their typically fragile, aragonitic shell plates do not withstand
considerable transport or current reworking. Moreover, most of
the recovered chiton plates are remarkably well preserved, without
much abrasion, corrosion, or bioerosion, all indicating rapid burial
near where they lived. Although many of the chiton species from
the Border localities currently range along much of the coastline
from southeastern Alaska to northern Baja California, the
following species indicate a cool-water environment: Mopalia
swanii, M. sinuata, and Amicula. These three taxa currently range
only north of San Diego; in contrast, by far the most commonly
dredged species of Mopalia off of San Pedro (—120 km north of San
Diego) is M. imporcata. Moreover, some common chitons from
the Border locality are more similar to those that today dominate
the central California coast (e.g., Stenoplax fallax, S. beatbiana,
and Tonicella venusta). On the other hand, the collections also
appear to contain the distant extralimital southern Lepidozona
rotbi (as Lepidozona cf. rothi ), as well as Stenoplax circumsenta
(as Stenoplax cf. circumsenta), a species more common south of
San Diego, but these fossils are only provisionally identified as
such. Overall, however, the chiton fauna is most similar to that
presently found off the San Diego coast today. This similarity is
also reflected in a recent faunal survey of chitons from 30-to-2Q0-
m depths off San Diego (Stebbins and Eernisse, 2009).
Microfossils from the Border localities likewise yield evidence
of a mixing of cool- and warm-water taxa, but dominance of taxa
that today occur off the San Diego coast. Mandel (1973)
suggested a temperature range of 22°C to 26°C (subtropical)
based on his study of more than 30 planktonic and benthonic
foraminiferans from localities he referred to as 305A and 305C.
This temperature range is warmer than sea surface temperatures
at the Imperial Beach pier (1 km north of the Border localities),
that ranged between 12°C and 24°C during the period from April
2006 to January 2009 (Scripps Institution of Oceanography
[SIO] ); the maximum temperature at 5-m depth during this same
period was only — 20°C (SIO). However, Mandel’s (1973) faunal
list indicates a mixed warm- and cool-water foraminiferal fauna
and it is unclear if he collected the same beds as Kanakoff.
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 49
We (M.J.V. and C.Z.F.) examined a collection of foramin-
ifers at LACM1P from LACMIP locality 305 and likewise found
some warm-water indicators such as one specimen of Globor-
otalia tumida (Brady, 1877) (Figure 2. 10), a typically warm-
water species that can he found in waters between ~17°C to
29°C but occurs at highest abundances at ~27"C (Be and
Tolderlund, 1971; Hillbrecht, 1996) and abundant Globiger-
inoides ruber (d’Orbigny, 1839) (Figure 2.9), a species that is
commonly found at temperatures between 23°C and 27 C in
the Sargasso Sea off Bermuda (Be, 1960), and only occurs off
Southern California during El Nino events (J. Kennett, personal
communication to M.J.V. , 2006). In addition. Be (1960) found
Orbulina universa d’Orbigny, 1839, another abundant plank-
tonic foraminiferan at LACMIP locality 305, to be most
abundant in the Caribbean Sargasso Sea during the warmer
summer and fall months and preferring water temperatures
between 23°C and 27°C. In contrast to the warm-water plank-
tonic foraminiferans, we confirmed the presence of Globigerina
bulloides d’Orbigny, 1826 (Figure 2.11) from LACMIP locality
305, and this species is very common today in cool, productive
waters (Be and Tolderlund, 1971; Hillbrecht, 1996) off
California.
Unlike the planktonic foraminifera! assemblage, the benthonic
foraminiferal assemblages from the LACMIP lack warm-water
indicators, and instead indicate temperatures similar to those
typical of the San Diego coast today. The overall benthonic
foraminiferal fauna best matches the Hanzawaia nitidula
association of Murray (1991). Four species in this assemblage
also occur in the San Diego Formation: Hanzawaia nitidula
(Bandy, 1953) (Figure 2.12); Quinqueloculina lamarckiana
d’Orbigny, 1839 (Figure 2.13); Cibicides fletcheri Galloway
and Wissler, 1927; and Planulina ornata (d’Orbigny, 1839).
These species prefer sand and are characteristic of some regions
between Nicaragua and Panama, with a temperature tolerance
between 10°C and 30°C. However, there are also similarities
with the Cibicides fletcheri fauna of Murray (1991) that prefers a
fine-grained sand substrate, which is the primary lithology of the
Border beds. Three species, Cibicides fletcheri , Rotorbinella
campanulata (Galloway and Wissler, 1927), and Cassidulina
tortuosa Cushman and Hughes, 1925, occur in the San Diego
Formation and their thermal tolerances are between 13°C and
20°C (Murray, 1991). Although Mandel (1973) and Ingle (1967)
suggested that Hanzawaia nitidula indicates subtropical temper-
atures, it nevertheless lives in modern times along the San Diego
coast (Uchio, 1960).
Page Valentine (1976) identified more than 50 ostracod
species from LACMIP collections associated with locality 305.
Using his data on temperature tolerances (Valentine, 1976),
all but one of the ostracods in the Border beds have an over-
lapping temperature tolerance of 13°C to 20°C. The one slightly
anomalous record, Ambolastracon sp. O, has an inferred tem-
perature tolerance of 13°C to 18°C. This temperature range
falls within sea surface temperatures at the Imperial Beach pier
(see above).
Although the faunas from the Border localities are dominantly
warm-temperate in aspect, and most of the abundant taxa from
these beds currently reside in the Californian biogeographic
province, there are nevertheless a few cases of both extralimital
southern and extralimital northern species. Such a faunal mixture
is relatively common in Pliocene (e.g., Groves, 1991) and
Pleistocene deposits in western North America (Valentine,
1955; Emerson, 1956; Zinsmeister, 1974; Roy et al., 1995).
However, the greatest number of Pleistocene assemblages
previously thought to contain both warm and cool species were
subsequently shown to be from two different terrace levels and
thus to have different ages (Muhs et al., 2002; G. Kennedy,
personal communication, 2010).
An understanding of global, regional, and local climate trends
may help explain faunal mixing. During the early Miocene the
eastern Pacific was overall warmer than today, whereas the
middle Miocene through Pleistocene was a time of oscillating sea
levels and oceanic temperatures, but with an overall cooling trend
(Hall, 2002). Tropical and subtropical mollusks were common in
California during the early and middle Miocene (Marincovich,
1984) — even the upper Miocene Castaic Formation of Los
Angeles County had a distinct warm-water fauna (Stanton,
1966). A subsequent, gradual cooling trend appears to have
begun sometime in the Pliocene between about 4.6 Ma (Leroy et
al., 1999) and 4.15 Ma (Tiedemann et al., 1994), culminating in
the onset of Northern Hemisphere glaciation at 2.7 Ma (Lyle et
ah, 2008). This gradual cooling trend contained dramatic
fluctuations: for example, a warming trend from an anomalously
cold period appears to have occurred from about 3.3 to 3.15 Ma
(Leroy et al., 1999; Ravelo et al, 2004). This mid-Pliocene
warming event has been documented in both the Atlantic and
Pacific oceans and so appears to be a global occurrence (Dowsett
et al., 1996). This warming event was followed by a progressive
cooling leading to late Pliocene/early Pleistocene glaciations
(Tiedemann et al., 1994; Leroy et al., 1999; Ravelo et al., 2004).
By the end of the Pliocene, extralimital southern mollusks had
almost entirely disappeared from California (Addicott, 1970).
Three hypotheses seem most likely to explain the mixture of
northern and southern extralimital taxa in the Border localities:
(1) the Border beds were deposited during the mid-Pliocene
warm period in an area with strong upwelling (Powell et al.,
2009); (2) these beds were deposited at the mouth of a relatively
warm bay in cool surrounding waters (sensu Addicott, 1970),
the latter possibly due to upwelling; and/or (3) the beds are a
mixed assemblage from slightly different time periods while
climate fluctuated. It is also possible that the Border beds were
deposited during the transitional period between the warming
event and the beginning of progressive cooling (—3.15 Ma),
consistent with the age of the formation based on foraminifera
and mollusks.
Upwelling, which is well developed along the marginal eastern
Pacific, can transport cool, deep waters from depth into relatively
shallower, warm surface waters. For example, extralimital
northern species can occur far south of their normal range in
areas of upwelling on the south sides of rocky points along much
of Baja California, Mexico (Hubbs, 1948, 1960; Emerson, 1956;
Stepien et al., 1991). Powell et al. (2009) suggested that the
presence of Architectonica, Miltha xantusi (Dali, 1905), and
other extralimital southern taxa at the Border localities indicated
deposition during the mid-Pliocene warming event, and that the
presence of cool-water species there were due to upwelling.
However, the fossil assemblages from the Border beds are not
dominated by warm-water taxa.
Addicott (1970) noted faunal mixing in Pliocene deposits in
California and suggested the warm-water components likely
occurred there because of warm water maintained in the shallow-
water embayments that occurred in the present-day San Joaquin
Valley, California, with the relatively cooler taxa occurring due
to overall climate cooling in the later Pliocene. A similar shallow-
water bay characterized deposition of the San Diego Formation
(Hall, 2002) and many of the abundant taxa from the Border
localities are most common in bay environments, including
Glossaulax reclusianus (Deshayes, 1839) (see McLean, 1978).
Squires et al. (2006) favored this scenario to explain why
extralimital southern taxa were present in the Pliocene Pico
Formation of Los Angeles County.
50 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Figure 20 Known depth ranges for modern chiton species with
representatives in the San Diego Formation. Dashed line indicates
inferred depth of deposition (25 m, based on analysis of the total fauna).
Key as in Figure 18.
The oxygen isotope record provides clear evidence that there
were many smaller-scale climate shifts related to Milankovitch
cycles throughout the Pliocene (Gradstein et ah, 2004), and thus
it is possible that such shorter time-scale variation in climate
could have contributed to the mixed fauna. Similarly, some
occurrences of mixing of warm- and cool-water molluscan faunas
from Pleistocene marine terraces has been explained by fossils in
those collections having slightly different ages, from both cool
and warm time periods (Muhs et al. 2002).
Perhaps there was a combination of factors. For example,
Ramp et al. (2005) documented the periodic spread of upwelled
waters across the mouth of Monterey Bay, California, a
geographic feature similar in slope to that of the Pliocene San
Diego embayment. Therefore it is possible that the Border beds
were deposited in the mouth of a warm shallow bay with
upwelling nearby. There are many possible explanations for the
presence of these anomalous taxa, and future research may help
determine which is most likely. In any case, the climate was
similar to what occurs today off the San Diego coast.
PALEOBATHYMETRY
Overall, the paleodepth is clearly neritic, or sublittoral, as defined
by Hedgpeth (1957) and Valentine (1961), i.e., from the low-water
line to — 150-m depth. The fossils indicate either continental shelf
or most likely an inner neritic habitat at depths averaging about 20
to 25 m (Figures 20-21).
Figure 21 Known depth ranges for other molluscan (nonchiton) species
depth of deposition (25 m). Key as in Figure 19.
The assemblages of chiton valves from the Border localities are
quite similar to those seen in modern sediments dredged from
~15 to 30 m off the California coast (based on examination of
samples at LACM; Vendrasco, 1999). For example, LACM
station 65-35, from —27 m off San Pedro, California, contains
valves of Callistochiton palmulatus, Leptochiton nexus , Old-
roydia percrassa, and Lepidozona spp., all of which also occur in
the Border beds. This assemblage is also similar to that found in
rock dredges and trawls at similar depths off San Pedro, Los
Angeles County, California (D.J.E., personal observation). The
most conspicuous chitons along the central and Southern
California coast, Nuttallina fluxa, Cyanoplax hartwegii (Car-
penter, 1855), and Mopalia muscosa (Seapy and Littler, 1993;
Liff-Grieff, 2006; MJV and DJE, personal observation), are
missing from this assemblage (except for one specimen of
Nuttallina). This is explained by the relatively deeper-water
deposition of the Border beds.
Nevertheless, there is also a minor shallow-water component to
the assemblage of the Border beds. For example, several of the
chitons in this study are found in the intertidal to shallow subtidal
zones ( Placipborella velata, Lepidozona pectinulata, Stenoplax
fallax, Nuttallina sp., and species questionably identified here such
as S. heathiana, and Mopalia swanii). Likewise, the gastropod
Calliostoma gemmulatum is abundant in the Border beds and
today occurs only in the lower intertidal zone (McLean, 1978). In
addition, the bivalve Penitella penita typically lives in water depths
of less than 10 m and the mussel Modiolus rectus (Conrad, 1837)
lives in depths of less than 15 m (Coan et al., 2000). In addition to
the shallow-water species, a deeper-water (>25-m depth) compo-
nent to the assemblage of the Border beds is also present. For
example, the abundantly occurring Miltha xantusi occurs today no
shallower than 55 m (but see above), and the species Eulima
raymondi Rivers, 1904, Lirobittium rugatum (Carpenter, 1864),
and Solariella peramabilis Carpenter, 1864 have only been
recorded from water depths of more than 30 m.
Overall, overlapping depth ranges of all species in this
assemblage indicate a depth of deposition of the fossils averaging
about 20 to 25 m, with a few species migrating or washing in
from shallower and deeper water.
CHITON VALVE SORTING
Chitons have three distinct types of valves: head, intermediate,
and tail (Figure 4). Normal individuals possess one head valve,
six intermediate valves, and one tail valve. Modern chiton
individuals with fewer or greater than eight valves are known but
are extremely rare. For example, less than half a percent of 3,483
representatives in the San Diego Formation. Dashed line indicates inferred
Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 51
Figure 22 Ratios of valve types in the San Diego Formation (1) and in modern sediments (2-6). 1, Ratios of numbers of intermediate-to-head valves
(filled bars) and intermediate-to-tail valves (unfilled bars) in fossil chiton assemblages from LACMIP localities 305, 16862 (305A), and 16817 (305C).
The expected valve ratio of 6:1 is indicated by the darker dashed line. Only species with 60 or more total valves known from these deposits were included
in this analysis. Abbreviations. Ln = Leptochiton nexus-, Op=Oldroydia percrassa; Cp= Callistochiton palmiilatiis ; Cs=Callistocbiton spbaerae n. sp.;
Lm = Lepidozona mertensii; Lp =Lepidozona pectinulata; Ms=Mopaha sp. cf. M. swanii; T\ = Tonicella sp. cf. T. venusta. 2-6, Ratios of intermediate-
to-end valves of chiton species in specific Flolocene accumulations. Histogram in each case shows the results of a statistical simulation repeated 1,000
times using the same sample size, revealing the expected range of valve ratios if there is no bias. 2, Tonicella lineata , n=302; 3, Mopalia muscosa, n=25;
4, Lepidozona mertensii , n = 32; 5, Cryptochiton stelleri, n=30; 6, Callistochiton palmulatus, n = 61.
individuals of three chiton species examined were aberrant with
an unexpected number of valves (Langer, 1978).
Fossil and modern assemblages of chiton valves typically show
a deviation from the 1:6:1 expected ratio of valve types
(Vendrasco, 1999; Puchalski and Johnson, 2009). A number of
factors may bias chiton valve ratios in fossil assemblages. The
valve types in chiton individuals have physical differences (in
many size and shape parameters; Vendrasco, 1999), they tend to
live in the rocky intertidal or shallow subtidal zones where
currents can be strong and destructive, and their valves are
typically delicate, especially for subtidal species. Valves of all
chitons so far examined are composed of the mineral aragonite
(Carter and Hall, 1990), which is more prone to dissolution than
is calcite (Brenchley and Harper, 1998).
The extensive collection of chiton valves in this assemblage
allows a robust analysis of chiton valve sorting, which shows a
statistically significant deviation from the expected 1:6:1 ratio
(Vendrasco, 1999). The results are shown in Figure 22.1. All
species in this assemblage had a different ratio from the expected,
and in some cases (e.g., Callistochiton spp.) the ratio is
dramatically skewed from the expected. Overall, the deposit is
dominated by Callistochiton valves (which make up more than
80% of the total chiton valves in the LACM1P collections), in
particular C. palmulatus. A similar domination by this species
has been seen in Pleistocene deposits (Chace, 1916a). This
domination is due in part to the robust nature of the tail valve,
which is subsphericai and massive, and so resists degradation far
better than nearly all other chiton valves. The head valve of C.
52 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
palmulatus is also thicker than the central area of the
intermediate valves. The ratio of valve types (head, intermediate,
and tail) in this species from the San Diego Formation is highly
skewed from the expected 1:6:1, biased toward the end valves,
particularly the tail valve, at a ratio of 12.2:1:34.7.
These ratios typically show greater bias than similar assem-
blages of chiton valves from modern sediments (cf. LACM
collections; Figures 22.2-22.6). The modern assemblages were
collected from sediments that lacked clear signs of strong currents
(e.g., no ripple marks) (J.H. McLean, personal communication to
M.J.V., 2009), and so might be expected to have chiton valves in
a ratio closer to the expected 1:6:1. Again, with modern
Callistochiton palmulatus , there is a distinct bias toward the tail
valve (ratio 1:1.43:2; 143 valves from seven localities), indicating
that the unequal dispersal and destruction of chiton valves occurs
soon after the death of individuals. Flowever, in general, the valve
ratios in modern sediments show less deviation from the expected
than the ratios of chitons from the Border beds. This higher level
of deviation in the San Diego Formation was probably not due to
collection bias because bulk matrix samples were processed in a
laboratory setting where volunteers were instructed to “save
everything” (Marincovich, 1974), as evidenced by the high
number of small fragments of shells in the collections at
LACMIP. Flowever, because samples were presorted for us we
cannot be absolutely certain that the biases are neutral with
respect to which valves ended up in the collections. The greater
divergence from the expected 1:6:1 ratio in the Border beds than
in modern sediments is more likely due to exposure to a greater
extent of current activity (for a longer time and/or slightly faster
currents) that caused greater sorting due to different valve shapes
and sizes and greater rates of destruction of the less robust valve
types.
CONCLUSIONS
The San Diego Formation has produced the most diverse and
abundant fossil chiton assemblage known. The LACMIP
collections from the Border localities of this formation contain
three new species ( Callistochiton spbaerae, Lepidozona kana-
koffi, and Amicula solivaga) and 19 additional species in 11
genera in four families. The stratigraphic ranges of six genera in
the eastern Pacific are extended into the Pliocene, helping to fill a
substantial gap in information on the Cenozoic history of chitons.
This assemblage also contains a thermally anomalous record of
the cold-water genus Amicula far south of its current range, as
represented by a new extinct species.
The Border localities of the San Diego Formation are regarded
as Pliocene in age, and evidence discussed here indicates an age
between 3.25 and 2.5 Ma. Data on modern taxa represented here
indicate deposition in a mixed silty/rocky habitat perhaps
averaging about 20-to-25-m depths, possibly near the mouth of
a large bay. There is a mixture of relatively cool- and warm-water
species in the assemblage although most species currently occur
in the nearby shallow marine habitat off of San Diego, and the
average temperature range in which these fossil individuals lived
appears to have been roughly similar to what occurs off of San
Diego now. Upwelling, warm shallow bay habitat, and deposi-
tion of fossils during a time period of fluctuating temperatures
may all have contributed to the faunal mixing.
The massive chiton assemblage allows detailed analysis of
valve ratios, revealing consistent differences from the expected
ratio of 1:6:1 for head:intermediate:tail valves. The divergence
from the expected pattern is on average greater than for chiton
valves in Holocene sediments, providing evidence that tapho-
nomic factors occurring long after valve disarticulation can exert
a strong influence on the proportions of chiton valve types in the
fossil record.
This fossil deposit provides the oldest view of the late Cenozoic
diversification of chitons along the Pacific Coast of North
America. The diversification appears to have intensified from the
middle Miocene to Pleistocene, in part because of regional
increases in productivity and environmental heterogeneity during
that time.
ACKNOWLEDGMENTS
We thank Lindsey Groves (LACM, Malacology Department) for
bringing this collection to our attention, for allowing access to specimens
at the LACMIP collections, and for helpful discussions. Also we thank
Scott Rugh and Thomas Demere (SDNHM) for use of facilities and
collections in their care and for assistance in the field. Harry Filkorn
(Pierce College) and Mary Stecheson (LACM) allowed use of LACMIP
facilities and collections. James Kennett identified numerous foraminif-
eral samples and provided detailed information about their stratigraphic
and environmental significance. George Kennedy (Brian F. Smith &
Associates, Poway, California) provided unpublished consultants’
reports and additional information. John Alderson (LACMIP), Hank
Chaney (Santa Barbara Museum of Natural History; SBMNH), Daniel
Geiger (SBMNH), Lindsey Groves, Patrick LaFollette (LACM, Mala-
cology), Louie Marincovich (California Acacemy of Sciences), James
McLean (LACM, Malacology), LouElla Saul (LACMIP), Richard
Squires (California State University, Northidge), Paul Valentich-Scott
(SBMNH), Robert Stanton, Jr. (LACMIP), and Edward Wilson
(LACMIP, retired) provided helpful information and support. Christo-
pher Peregrine and Therese Muranaka (Border Field State Park)
arranged access to field localities. Lindsey Groves, George Kennedy,
and Timothy Stebhins (City of San Diego Marine Biology Laboratory)
each provided detailed reviews that significantly improved the paper. We
also thank Jody Martin and Vicky Brown (LACM) for their thorough
work in editing the manuscript.
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Received 3 November 2009; accepted 17 December 2011.
Appendix 1
LOCALITY DESCRIPTIONS
Locality data are based on records and original field notes at LACMIP.
Some original landmarks (e.g., a house, ranch) no longer exist and the
extent of fossiliferous exposures may have changed since Kanakoff made
his original collections.
305: Exposure of 18 m, 0.3 to 0.6 m thickness, exactly 89 m from the
international U.S./Mexican border. South of Knox Ranch (as of 1957). 731 m
east and 41 1 meters south of the northwest corner of Section 8, T 19 S, R 2
W, shown on the U.S. Geological Survey (USGS) Imperial Beach, California
7/2' (1:24,000) topographic map. On the hand-drawn map that George
Kanakoff made of the localities, he wrote that the fossil-bearing deposit 305
is 10 feet (3.0 m) above the road. Collectors: William Emerson and George
Kanakoff; collecting dates: July 20, 1956, and December 9, 1957.
16862 (305A): On the west side of a gulley east of 305; 686 m east and
347 m south of the northwest corner of Section 8, T 19 S, R 2 W, San
Bernadino Baseline and Meridian (SBBM), USGS Imperial Beach,
California 7/2' (1:24,000) topographic map, in the Ti|uana River basin.
In Kanakoff’s locality record, he wrote that locality 305 A is at the “same
elevation” as 305. Moreover, Mandel ( 1973) regarded these beds to be “at
the same stratigraphic horizon" as those of 305C. On the hand-drawn map
that George Kanakoff made of the localities, he wrote that the fossil-bearing
deposit 305A is 8 feet (2.4 m) above the road. Collectors: William Emerson
and George Kanakoff (1957); L. Marincovich, P. Oringer, R. Lane, B.
Savic, and F. Wolfson (1959). Collecting dates: December 13, 1957, and
August 3-10, 1959.
16817 (305C): An exposure 18 m long at the base of the hill on the
west side of the gully east of locality 305; same elevation; in the Tijuana
River basin. 30 m west and 1 34 m south of the northeast corner of Section
8, T 19 S, R 2 W, SBBM, USGS Imperial Beach, California 714'
(1:24,000) topographic map. On the hand-drawn map that George
Kanakoff made of the localities, he wrote that the fossil-bearing deposit
305C is 30 feet (9.1 m) above the road. Collectors: George Kanakoff and
others; collecting dates: October 1964; May 11-13, 1965; June 1965.
62 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
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Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation ■ 69
Appendix 2
SPECIMEN NUMBERS FOR CHITON FOSSILS DESCRIBED IN THIS PAPER
Specimen
number
Species
Type specimen
Locality
Valve type (head, interme-
diate, tail)
Figure
13730
Leptochiton rugatus
305
Head
5. 1-5.3
13731
Leptochiton rugatus
305
Head
5.4, 5.7
13732
Leptochiton rugatus
305
Head
5 .5-5.6
13733
Leptochiton rugatus
305
Intermediate
5.8-5.10
13734
Leptochiton rugatus
305
Intermediate
5.11-5.12
13736
Leptochiton rugatus
305
Intermediate
5.13
13737
Leptochiton rugatus
305
Tail
5.14-5.15
13738
Leptochiton rugatus
305
Tail
5.16-5.17
13739
Leptochiton nexus
305
Intermediate
5.18-5.20
13740
Leptochiton nexus
305
Intermediate
5.21
13741
Leptochiton nexus
305
Intermediate
5.22, 5.26
13742
Leptochiton nexus
305
Intermediate
5.23-5.25
13743
Leptochiton nexus
305
Tail
5.27-5.29
13744
Leptochiton nexus
305
Tail
5.30
13745
Leptochiton nexus
305
Tail
5.31-5.32
13746
14294
14295
14296
Leptochiton nexus
Leptochiton nexus
Leptochiton nexus
Leptochiton nexus
305
305
16817 (305C)
16862 (305A)
Tail
3 head, 25 intermediate,
and 60 tail valves
Tail
Tail
5.33-5.34
13747
Oldroydia percrassa
305
Head
6. 1-6.2
13748
Oldroydia percrassa
305
Head
6. 3-6. 4
13749
Oldroydia percrassa
305
Head
6. 5-6. 6
13750
Oldroydia percrassa
305
Intermediate
6.7
13751
Oldroydia percrassa
305
Intermediate
6. 8-6. 9
13752
Oldroydia percrassa
16817 (305C)
Intermediate
6.10, 6.13
13753
Oldroydia percrassa
16817 (305C)
Intermediate
6.1 1-6.12
13754
Oldroydia percrassa
16817 (305C)
Tail
6.14-6.15
13755
Oldroydia percrassa
305
Tail
6.16
13735
14297
14298
14299
Oldroydia percrassa
Oldroydia percrassa
Oldroydia percrassa
Oldroydia percrassa
305
305
16817 (305C)
16862 (305A)
Tail
23 head, 130 intermediate,
and 50 tail valves
2 head, 7 intermediate, and
4 tail valves
1 head and 1 tail valve
6.17
13756
Callistochiton palmulatus
16817 (305C)
Head
7. 1-7.2
13757
Callistochiton palmulatus
305
Head
7.3-7.4
13758
Callistochiton palmulatus
16817 (305C)
Head
7. 5-7.6
13759
Callistochiton palmulatus
16817 (305C)
Head
7. 7-7. 8
13760
Callistochiton palmulatus
16817 (305C)
Intermediate
7.9-7.11
13761
Callistochiton palmulatus
16817 (305C)
Intermediate
7.12-7.14
13762
Callistochiton palmulatus
16817 (305C)
Intermediate
7.15-7.17
13763
Callistochiton palmulatus
16817 (305C)
Tail
7.18-7.19
13764
Callistochiton palmulatus
305
Tail
7.20-7.21
13765
Callistochiton palmulatus
305
Tail
7.22-7.23
13766
1300
14301
14302
Callistochiton palmulatus
Callistochiton palmulatus
Callistochiton palmulatus
Callistochiton palmulatus
305
305
16817 (305C)
16862 (305A)
Tail
-2,500 head, 193
intermediate, and
—6,100 tail
122 head, 12 intermediate,
and 448 tail valves
23 head, 31 intermediate,
and 65 tail valves
7.24-7.25
13767
Callistochiton sphaerae n. sp.
Paratype
305
Head
8. 1-8.2
13768
Callistochiton sphaerae n. sp.
Paratype
305
Head
8. 3-8.4
13769
Callistochiton sphaerae n. sp.
Holotype
305
Intermediate
8. 5-8. 7
13770
Callistochiton sphaerae n. sp.
Paratype
305
Intermediate
8.8-8.10
13771
Callistochiton sphaerae n. sp.
Paratype
305
Intermediate
8.11-8.13
13772
Callistochiton sphaerae n. sp.
Paratype
305
Intermediate
8.14-8.16
13773
Callistochiton sphaerae n. sp.
Paratype
305
Intermediate
8.17-8.18
13854
Callistochiton sphaerae n. sp.
16817 (305C)
Tail
8.19
13774
Callistochiton sphaerae n. sp.
Paratype
305
Tail
8.20-8.22
13775
Callistochiton sphaerae n. sp.
Paratype
305
Tail
8.23, 8.27
13776
Callistochiton sphaerae n. sp.
Paratype
305
Tail
8.24-8.26
14303
Callistochiton sphaerae n. sp.
Unfigured topotype lot
305
33 head, 87 intermediate,
and 83 tail valves
70 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Appendix 2 [Continued]
Specimen
number
Species
Type specimen
Locality
Valve type (head, interme-
diate, tail)
Figure
14304
14305
13777
Callistochiton sphaerae n. sp.
Callistocbiton sphaerae n. sp.
Lepidozona mertensii
16817 (305C)
16862 (305A)
16817 (305C)
3 head, 9 intermediate, and
10 tail valves
2 head and 6 tail valves
Intermediate
9. 1-9.4
13778
Lepidozona mertensii
16817 (305C)
Intermediate
9.5
13779
Lepidozona mertensii
16817 (305C)
Intermediate
9.6
13780
Lepidozona mertensii
305
Intermediate
9. 7-9. 8
13781
Lepidozona mertensii
305
Intermediate
9.9
13782
Lepidozona mertensii
16817 (305C)
Tail
9.10-9.11
13783
Lepidozona mertensii
16817 (305C)
Tail
9.12
13784
Lepidozona mertensii
16817 (305C)
Tail
9.13
13785
Lepidozona mertensii
305
Tail
9.14
13786
Lepidozona mertensii
305
Tail
9.15
14306
14307
14308
13787
Lepidozona mertensii
Lepidozona mertensii
Lepidozona mertensii
Lepidozona pectinulata
305
16817 (305C)
16862 (305A)
305
200 head, 178
intermediate, and 333
tail valves
9 head, 48 intermediate,
and 11 tail valves
2 head, 19 intermediate,
and 8 tail valves
Head
10.1-10.3
13788
Lepidozona pectinulata
305
Head
10.4, 10.7
13789
Lepidozona pectinulata
305
Intermediate
10.5-10.6
13790
Lepidozona pectinulata
305
Intermediate
10.8-10.10
13791
Lepidozona pectinulata
305
Intermediate
10.11
13792
Lepidozona pectinulata
305
Intermediate
10.12
13793
Lepidozona pectinulata
16817 (305C)
Intermediate
10.13
13794
Lepidozona pectinulata
305
Tail
10.14-10.15
13795
Lepidozona pectinulata
305
Tail
10.16, 10.20
13796
Lepidozona pectinulata
305
Tail
10.17-10.19
13797
Lepidozona pectinulata
305
Tail
10.21-10.22
13798
Lepidozona pectinulata
305
Tail
10.23-10.24
13799
Lepidozona pectinulata
16817 (305C)
Tail
10.25-10.26
13800
Lepidozona pectinulata
16817 (305C)
Tail
10.27-10.28
14309
14310
13801
Lepidozona pectinulata
Lepidozona pectinulata
Lepidozonasp. cf. L. rothi
305
16817 (305C)
305
131 head, 498
intermediate, and 293
tail valves
1 head and 9 intermediate
valves
Intermediate
11.1-11.2
13802
Lepidozonasp. cf. L. rothi
305
Intermediate
11.3
13803
Lepidozonasp. cf. L. rothi
305
Intermediate
11.4-11.5
13804
Lepidozona sp. cf. L. radians
305
Intermediate
11.6
13805
Lepidozona sp. cf. L. radians
305
Intermediate
11.7-11.8
13806
Lepidozona sp. cf. L. radians
305
Tail
11.9-11.10
14311
14312
13807
Lepidozona sp. cf. L. radians
Lepidozona sp. cf. L. radians
Lepidozona kanakoffi n. sp.
Paratype
305
16817 (305C)
305
I head, 23 intermediate,
and 9 tail valves
5 intermediate valves
Intermediate
11.11
13808
Lepidozona kanakoffi n. sp.
Paratype
305
Intermediate
11.12
13809
Lepidozona kanakoffi n. sp.
Paratype
305
Intermediate
11.13-11.14
13810
Lepidozona kanakoffi n. sp.
Holotype
305
Intermediate
11.15-11.16
13811
Lepidozona kanakoffi n. sp.
Paratype
305
Intermediate
1 1.17
13812
Lepidozona kanakoffi n. sp.
Paratype
305
Intermediate
11.18-11.20
13813
Lepidozona kanakoffi n. sp.
16817 (305C)
Tail
11.21-11.22
13814
Lepidozona kanakoffi n. sp.
Paratype
305
Tail
11.23-11.24
13815
Lepidozona kanakoffi n. sp.
Paratype
305
Tail
11.25-11.26
13816
Lepidozona kanakoffi n. sp.
Paratype
305
Tail
11.27-11.28
14313
Lepidozona kanakoffi n. sp.
Unfigured Topotype
305
25 intermediate and 22 tail
14314
13817
Lepidozona kanakoffi n. sp.
Stenoplax circumsenta
lot
16817 (305C)
305
valves
1 intermediate and 1 tail
valve
Head
12.1-12.2
13818
Stenoplax circumsenta
305
Head
12.3-12.4
13819
Stenoplax circumsenta
16817 (305C)
Tail
12.5-12.6
13820
Stenoplax circumsenta
16817 (305C)
Tail
12.7
14315
Stenoplax circumsenta
305
1 head, 1 intermediate, and
5 tail valves
Contributions in Science, Number 520
Vendrasco ct al.: Chitons of the San Diego Formation ■ 71
Appendix 2 [Continued]
Specimen
number
Species
Type specimen
Locality
Valve type (head, interme-
diate, tail) Figure
14316
Stenoplax circumsenta
16817 (305C)
1 head, 1 intermediate,
and
13821
Stenoplax fallax
305
1 tail valve
Head
12.8
13822
Stenoplax fallax
305
Head
12.9
13823
Stenoplax fallax
305
Head
12.10-12.11
13824
Stenoplax fallax
305
Intermediate
12.12
13825
Stenoplax fallax
305
Intermediate
12.13
13826
Stenoplax fallax
305
Intermediate
12.14
13827
Stenoplax fallax
16817 (305C)
Intermediate
12.15-12.16
13828
Stenoplax fallax
305
Intermediate
12.17-12.18
13829
Stenoplax fallax
305
Tail
12.19
13830
Stenoplax fallax
305
Tail
12.20
13831
Stenoplax fallax
305
Tail
12.21
14317
Stenoplax fallax
305
5 head, 9 intermediate, and
14318
14319
Stenoplax fallax
Stenoplax fallax
16817 (305C)
16862 (305A)
i 0 tail valves
1 tail valve
1 head and 3 intermediate
13832
Stenoplax sp. cf. S. heathiana
305
valves
Head
13.1-13.2
13833
Stenoplax sp. cf. S. heathiana
305
Head
13.3-13.4
13834
Stenoplax sp. cf. S. heathiana
305
Intermediate
13.5
13835
Stenoplax sp. cf. 5. heathiana
305
Intermediate
13.6-13.8
13836
Stenoplax sp. cf. S. heathiana
305
Intermediate
13.9, 13.12-13.13
13837
Stenoplax sp. cf. S. heathiana
305
Intermediate
13.10
13838
Stenoplax sp. cf. S. heathiana
305
Intermediate
13.11
13839
Stenoplax sp. cf. S. heathiana
16817 (305C)
Tail
13.14-13.15
13840
Stenoplax sp. cf. S. heathiana
305
Tail
13.16
13841
Stenoplax sp. cf. S. heathiana
305
Tail
13.17-13.19
13842
Amicula solivaga n. sp.
Paratype
305
Head
14.1
13843
Amicula solivaga n. sp.
Paratype
305
Head
14.2
13844
Amicula solivaga n. sp.
Paratype
305
Head
14.3
13845
Amicula solivaga n. sp.
Paratype
305
Head
14.4
13846
Amicula solivaga n. sp.
Holotype
305
Head
14.5
13847
Amicula solivaga n. sp.
Paratype
305
Head
14.6-14.7
13848
Amicula solivaga n. sp.
Paratype
305
Intermediate
14.8
13849
Amicula solivaga n. sp.
Paratype
305
Intermediate
14.9
13850
Amicula solivaga n. sp.
Paratype
305
Intermediate
14.10
13851
Amicula solivaga n. sp.
16817 (305C)
Intermediate
14.11-14.12
13852
Amicula solivaga n. sp.
Paratype
305
Intermediate
14.13
13853
Amicula solivaga n. sp.
Paratype
305
Tail
14.14-14.15
13855
Amicula solivaga n. sp.
Paratype
305
Tail
14.16
14320
Amicula solivaga n. sp.
Unfigured Topotype lot
305
3 head, 25 intermediate.
14321
14322
Amicula solivaga n. sp.
Amicula solivaga n. sp.
16817 (305C)
16862 (305A)
and 5 tail valves
1 intermediate valve
1 head, 1 intermediate.
and
13894
Mopalia sinuata
305
1 tail valve
Head
15.1
13895
Mopalia sinuata
305
Intermediate
15.2-15.3
14323
Mopalia sinuata
305
12 head, 42 intermediate.
14324
Mopalia sinuata
16862 (305A)
and 4 tail valves
2 head and 1 intermediate
13857
Mopalia sp. cf. M. swanu
16817 (305C)
valve
Head
15.4, 15.7
13858
Mopalia sp. cf. M. swanii
305
Head
15.5-15.6
13859
Mopalia sp. cf. M. swanu
305
Head
15.8-15.9
13860
Mopalia sp. cf. M. swanii
305
Head
15.10
13861
Mopalia sp. cf. M. swanii
305
Intermediate
15.11-15.12
13862
Mopalia sp. cf. M. swanii
305
Intermediate
15.13
13863
Mopalia sp. cf. M. swanii
305
Intermediate
15.14
13864
Mopalia sp. cf. M. swanii
305
Intermediate
15.15
13865
Mopalia sp. cf. M. swanu
305
Intermediate
15.16
13866
Mopalia sp. cf. M. swanu
305
Intermediate
15.17
13867
Mopalia sp. cf. M. swanii
305
Intermediate
15.18
13868
Mopalia sp. cf. M. swanii
305
Intermediate
15.19
13869
Mopalia sp. cf. M. swanii
305
Tail
15.20-15.21
13870
Mopalia sp. cf. M. swanii
305
Tail
15.22-15.23
13871
Mopalia sp. cf. M. swanii
305
Tail
15.24
13872
Mopalia sp. cf. M. swanii
305
Tail
15.25-15.26
72 ■ Contributions in Science, Number 520
Vendrasco et al.: Chitons of the San Diego Formation
Appendix 2 [Continued]
Specimen
number
Species
Type specimen
Locality
Valve type (head, interme-
diate, tail)
Figure
14325
Mopalia sp. cf. M. swanii
305
139 head, 204
intermediate, and 42 tail
valves
14326
Mopalia sp. cf. M. swanii
16817 (305C)
4 head and 4 intermediate
valves
14327
Mopalia sp. cf. M. swanii
16862 (305A)
1 head, 4 intermediate, and
1 tail valve
13873
Mopalia sp.
305
Intermediate
15.27
13874
Placiphorella velata
16817 (305C)
Head
16.1-16.2
13875
Placipborella velata
16817 (305C)
Intermediate
16.3
13876
Placiphorella velata
16817 (305C)
Intermediate
16.4
13877
Placiphorella velata
16817 (305C)
Tail
16.5-16.6
13878
Placiphorella velata
305
Tail
16.7-16.8
14328
Placiphorella velata
305
1 intermediate valve
14329
Placiphorella velata
16817 (305C)
2 intermediate valves
14330
Placiphorella velata
16862 (305A)
1 head and 1 tail valve
13879
Placiphorella sp. cf. P. mirabilis
305
Intermediate
16.9-16.10
13880
Placiphorella sp. cf. P. mirabilis
305
Intermediate
16.11-16.12
13881
Placiphorella sp. cf. P. mirabilis
305
Intermediate
16.13
13882
Placiphorella sp. cf. P. mirabilis
305
Intermediate
16.14
13883
Placiphorella sp. cf. P. mirabilis
305
Tail
16.15
14331
Placiphorella sp. cf. P. mirabilis
305
3 head, 10 intermediate,
and 4 tail valves
13884
Tonicella sp. cf. T. venusta
305
Intermediate
16.16
13885
Tonicella sp. cf. T. venusta
305
Intermediate
16.17-16.18
13886
Tonicella sp. cf. T. venusta
305
Intermediate
16.19
13887
Tonicella sp. cf. T. venusta
305
Intermediate
16.20-16.22
13888
Tonicella sp. cf. T. venusta
305
Intermediate
16.23
13889
Tonicella sp. cf. T. venusta
305
Intermediate
16.24-16.26
13890
Tonicella sp. cf. T. venusta
305
Tail
16.27-16.28
13891
Tonicella sp. cf. T. venusta
305
Tail
16.29-16.30
14332
Tonicella sp. cf. T. venusta
305
2 head, 49 intermediate,
and 1 tail valve
14285
Dendrochiton sp. indeterminate
305
Intermediate
17.1-17.3
14288
Dendrochiton sp. indeterminate
305
Intermediate
17.4
14286
Dendrochiton sp. indeterminate
305
Intermediate
17.5-17.7
14289
Dendrochiton sp. indeterminate
305
Intermediate
17.8
14287
Dendrochiton sp. indeterminate
305
Intermediate
17.9-17.11
14290
Dendrochiton sp. indeterminate
305
Intermediate
17.12
14292
Dendrochiton sp. indeterminate
305
Intermediate
17.13-17.15
14293
Dendrochiton sp. indeterminate
16862 (305A)
Intermediate
17.16-17.18
14291
Dendrochiton sp. indeterminate
305
Intermediate
17.19
14333
Dendrochiton sp. indeterminate
305
3 intermediate valves
13892
Nuttallina sp. indeterminate
16817 (305C)
Intermediate
17.20-17.22
Contributions in Science, 520:73-93
21 December 2012
Late Pliocene Megafossils of the Pico Formation, Newhall Area,
Los Angeles County, Southern California1
Richard L. Squires2
ABSTRACT. Taxonomic composition and stratigraphic distribution of megafossils in the Pico Formation south of Newhall, northern Los
Angeles County, Southern California, are described in detail. Eighty-three taxa, from 15 localities, were found: one brachiopod, 36
bivalves, 40 gastropods, one scaphopod, one crab, one barnacle, one sea urchin, one shark, and one land plant. All are illustrated here. The
pectinid bivalve Argopecten invalidus (Hanna, 1924) is put into synonymy with A. subdolus (Hertlein, 1925) and A. callidus (Hertlein,
1925). Rare specimens of the gastropods Calliostoma and Ocinebrina might be new species.
The mollusks, which are indicative of a late Pliocene age, lived in waters of inner sublittoral depths and normal marine salinity. Most of
the 41 extant species indicate warm-temperate waters similar to those occurring today off the adjacent coast, although a few species, both
extant and extinct, indicate a southerly warmer water component. The fauna lived predominantly in, or on, soft sands, but a few lived on
other shells or possibly on large rock clasts.
Geologic field mapping done as part of this present study revealed that the Pico Formation south of Newhall was deposited at the site where
a braided river entered the marine environment (i.e., braid delta). Initially, the river gravel and coarse sand interfingered with relatively deep
offshore silts, barren of megafauna, in the lower and middle parts of the formation. Eventually, the delta built up, and the resulting shoaling
conditions in the upper part of the formation were conducive for the megafauna to live in, or immediately adjacent to, the deltaic shoreface
fine sands. Storm waves raked the delta and concentrated the shells of the megafauna, along with cobbles of igneous and metamorphic
basement rocks, into channelized deposits. Postmortem transport distance was short, as evidenced by many paired-valved bivalve shells.
INTRODUCTION
During the Pliocene, the Pico Formation was deposited for a
distance of approximately 92 km along the axis of the Ventura
Basin, which trends parallel to the present course of the modern
Santa Clara River in Southern California (Fig. 1). The formation
has its broadest extent of outcrops in the Ventura area, and the
outcrop pattern narrows significantly eastward toward the
Newhall area. The Pico Formation represents the youngest
marine deposits in the eastern Ventura Basin. Throughout most
of this basin, the Pico Formation is an offshore-marine sequence
consisting of siltstone, mudstone, and claystone with some minor
amounts of sandstone and conglomerate. Megafossils are sparse,
but relatively deep-water benthic foraminifera are common. To
the east, toward Va! Verde and Valencia (Fig. 1), the formation
becomes increasingly sandier and conglomeratic, and shallow-
marine gastropods and bivalves are locally common in the upper
part (Grant and Gale, 1931; Squires et al., 2006). The purposes
of this present study are to 1) determine how far east the shallow-
marine megafossiliferous beds continue beyond the Valencia area
into the stratigraphically and structurally complex Newhall area,
2) tabulate and illustrate the taxonomic composition of the
megafauna, and 3) establish its age, depositional environment,
and zoogeographic implications.
All preexisting geologic maps (e.g.. Winterer and Durham,
1958, 1962; Dibblee, 1991a, 1992a) of the Newhall area are
inconsistent in regard to 1) the differentiation of the Pico
Formation from the other Neogene stratigraphic units in the area
(i.e., Towsley Formation, Saugus Formation, and Sunshine Ranch
Member of the Saugus Formation), 2) the structural geology of
the area, and 3) the depositional environments the Pico
Formation. Also, no previous detailed megafossil investigations
1 URL: www.nhm.org/scholarlypublications
' Department of Geological Sciences, California State University,
18111 Nordhoff Street, Northridge, California, 91330-8266, USA;
Research Associate, Invertebrate Paleontology, Natural History Museum
of Los Angeles County, 900 Exposition Boulevard, Los Angeles,
California, 90007, USA. E-mail: richard.squires@csun.edu
were done. It was necessary, therefore, to do my own geologic
mapping in order to understand the fundamental geologic
relationships of the easternmost Pico Formation in the Ventura
Basin. The outcome is that the Pico Formation in the Newhall
area is recognized for the first time as having been deposited in a
braid-delta environment. This study is important because it
affords the unusual opportunity to observe the complex inter-
fingering between the fluvial and marine components of a
Tertiary-age, predominantly marine formation in Southern
California. The study area encompasses where the two environ-
ments interfinger for a lateral distance of approximately 5 km,
and the lateral-fluvial component extends eastward for an
additional 3 km (Fig. 2).
There might be a few small outcrops of the Pico formation just
south and southeast of the study area in the San Fernando Valley
(e.g., Lopez Canyon) (Chen, 1988) and, possibly, a fault-
bounded, small outcrop approximately 22 km southeast of
Newhall (Berry et al., 2009) in Gold Creek, a tributary of Big
Tujunga Canyon.
PREVIOUS WORK
The earliest work on fossils from the study area was by Gabb
(1869:49), who described a few species of Pliocene mollusks from
an area originally referred to as Fremont Pass, later known as San
Fernando Pass, and now known as Newhall Pass, located just north
of the junction of U.S. Interstate 5 and California State Highway
14. Ashley (1895:338) listed some mollusks from the same general
area. None of his specimens were illustrated nor were they assigned
a museum catalog number; they could not be located.
Eldridge and Arnold (1907:22) used the name “Fernando” for
an enormous section of siliciclastics, largely of Pliocene age, that
crops out over a considerable area of Southern California,
including the study area. Instead of basing the section on
lithology, they improperly based it on three megafossil zones
(collectively of Pliocene age). They erroneously lumped fossils
found in Newhall Pass and Elsmere Canyon, but they listed only
the fossils from Elsmere Canyon. The former beds belong to the
© Natural History Museum of Los Angeles County, 2012
ISSN 0459-8113 (Print); 2165-1868 (Online)
74 ■ Contributions in Science, Number 520
Squires: Pico Formation Paleontology
Figure 1 Index map showing outcrop-distribution map of the Pico Formation (slanted lines) in the Ventura Basin. Newhall-area outcrops (shown in
box) based on this present report; remaining map area based on Dibblee (1987a, b, c; 1988; 1990a, b; 1991a, b; 1992a, b, c, d, e, f; 1993; 1996a, b).
Specific locales: 1 = Holser Canyon; 2 = Pico Canyon, the type section of the Pico Formation; 3 = Valencia; 4 = Running Horse area; 5 = Los Angeles
County Aqueduct (the “cascades”); and 6 = Stetson Ranch Park area.
Pico Formation, and the latter beds are now referred to as the
Towsley Formation of early Pliocene age (Winterer and Durham,
1962; Kern, 1973). English (1914) and Kew (1918) used
“Fernando Group” and “Fernando formation,” respectively,
for outcrops in the eastern Ventura Basin, but these units are
vague, ambiguous, and should not be used.
Kew (1923) was the first worker to use the name “Pico”
(following Clark’s 1921 informal use of this name) for the lower
part of the “Fernando Group.” Kew (1924) formally defined the
Pico Formation by designating a type section area in the vicinity
of Pico Canyon, l I km northwest of Newhall Pass (Fig. 1).
Although he listed megafossils found in the Pico Formation,
none of his localities are from the Newhall area. Kew (1924)
incorrectly correlated beds in Elsmere Canyon to his Pico
Formation. Grant and Gale (1931) over-applied Kew’s (1924)
name “Pico” to include all the Pliocene marine beds in the
Ventura Basin. They failed to recognize that the beds, now
referred to as the Towsley Formation, are lithologically different
from the overlying Pico Formation. They subdivided the so-called
“Pico” unit into three zones and correlated the fossiliferous beds
in the Newhall area just west of Newhall Pass to their “San Diego
Zone.” They mistakenly referred any molluscan species found in
the Newhall area to a “middle” Pliocene age. They mentioned
and illustrated a few fossils from four localities just west of
Newhall Pass (see “Localities” for equivalency to Natural
History Museum of Los Angeles County Invertebrate Paleontol-
ogy Section |LACMIP] localities).
Detailed geologic maps of all or part of the Newhall area were
prepared by Rynearson (1938), Oakeshott (1958), Winterer and
Durham (1958, 1962), Kern (1973), Barrows et al. (1975),
Nelligan (1978), Dibblee (1991a, 1992a, 1996a), and Yerkes and
Campbell (2005). No two maps are in agreement with regard to
the outcrop distribution of the Pico Formation, and there are also
inconsistencies as to which stratigraphic name(s) should be used.
Rynearson (1938), Winterer and Durham (1962:table 4), and
Dibblee (1992a) mentioned a few fossil localities. They are in the
central part of the study area and were recollected by the author (see
“Localities” for equivalency to LACM1P localities). Rynearson was
a student at Caltech, and his senior-thesis fossil collections became
part of the LACMIP collection when Caltech donated its collections
to LACMIP. Winterer and Durham (1962:table 4) provided a
faunal list of some species they collected, but none of their
specimens were illustrated or assigned a museum catalog number
and they could not be located. Winterer and Durham (1962) also
studied the benthic foraminifera fauna of Pico Formation just north
of Gavin Canyon in the southwestern part of the Newhall area.
Dibblee ( 1991a) reported exposures of the Pico Formation just
south of the study area in 1 ) a prominent cliff where the Los
Angeles Aqueduct is aboveground at the “cascades” and 2) in
another prominent cliff approximately 1.8 km to the east, in the
Stetson Ranch area of Sylmar (Fig. 1). Both areas were examined
by the author, and the exposures were placed in the Towsley
Formation because they include greenish-gray sandstones like
those of the Towsley Formation.
Oakeshott (1958:81), Ehlig (1975:14), and Powell (1993:43)
reported that there are outcrops of the Pico Formation along the
trend of the San Gabriel Fault just north of Placerita Canyon and
approximately 1 .5 km northeast of the northeastern corner of the
Newhall area. Dibblee (1996b) mapped these same outcrops as
the Saugus Formation. In order to resolve the issue, the area of
Running Horse Road (Fig. 1), just north of the Placerita Nature
Center, was examined, and these exposures possibly belong to
the Sunshine Ranch Member? of the Saugus Formation.
Squires (2008) studied the geology of the Eocene Juncal
Formation east of Newhall and provided a generalized geologic
map that included the Pico and Saugus formations. Squires et al.
(2006) studied the Pico Formation immediately west of the
western border of the Newhall area. The term “Pico Formation”
is used in this present report because of the historic usage of the
term, thereby reducing further stratigraphic nomenclature
confusion. A more appropriate term would be “marine facies
of the Saugus Formation.”
MATERIALS AND METHODS
Field work was begun in March 2006 but most of field time occurred
during the last half of 2011. The geology was mapped at a scale of
1:12,000, and megafossils and rock samples were collected. Every
available road and trail was hiked, and a considerable amount of cross-
country traversing was done. The field area comprises steep terrain, and
30-m-high or higher vertical cliffs are common, as is dense vegetation that
is impenetrable in many places. The shoreface deposits in the uppermost
part of the formation are especially difficult to access because of these
problems. There is no continuous stratigraphic section to measure the
formation from its base to its top because of faults and local incisement by
overlying stratigraphic units. Thicknesses were derived by means of
graphical techniques: the Elsmere Ridge area was used for the fluvial part
of the formation, and the Gavin Ridge area was used for the marine part
of the formation (Fig. 2).
Fossils were studied from 15 localities: eight previously known and
seven new localities. Some of the previously known localities have been
assigned, over the years, to different but equivalent or approximately
equivalent locality numbers. Approximations had to be made for some of
the previous localities because their word descriptions are inexact and the
localities were never precisely plotted on a map but are in close proximity
to where the present collections were made. In those cases, new locality
numbers based on personal mapping (e.g., LACMIP Iocs. 17917 and
17918) were assigned.
Contributions in Science, Number 520
Squires: I’ico Formation Paleontology ■ 75
Figure 2 Geologic map of the study area south of Newhall, northern Los Angeles County, California.
A total of 2020 specimens were studied, and approximately half of
these specimens were personally collected. The figured specimens, as well
as all the other megafossils collected in the course of this study, were
deposited in the LACMIP collection.
Matrix was removed from the fossils by the use of hammer and chisel,
and, for fine cleaning, a high-speed drill. A systematic treatment for each
megafaunal species is not given here because no new information was
gleaned for most of the species collected during the present study.
Previous synonymies, distinctive morphologic characters, and stratigraph-
ic distributions, etc. are available for most of the species in works such as
Arnold (1903), Grant and Gale (1931), Hertlein and Grant (1972),
Groves (1991), Davis (1998), and Squires et al. (2006). New information
is given here in the “Systematics” section for newly recognized synonyms
of the pectinid Argopecten invalidus and for two potential new species of
gastropods. Figures of the taxa listed in Table 1 are included here in order
to verify this list, and the numerical order of these figures corresponds to
the systematic organization used for the faunal list.
ABBREVIATIONS: Abbreviations used for locality and/or catalog
numbers are CAS (California Academy of Sciences, San Francisco;
includes the Stanford University [SU] collection), and LACMIP (Natural
History Museum of Los Angeles County, Invertebrate Paleontology
Section).
LOCALITIES
All are LACMIP localities in the Pico Formation of upper
Pliocene age, and located relative to the United States Geological
Survey Oat Mountain Quadrangle (7.5 minute), 1952 (photo-
revised 1969), Los Angeles County, southern California.
7725. 118°31'40"W, 34°20'35"N. Elevation 549 m (1800 ft.),
crest of spur at base of power-line tower, 703 m (2300 ft.) north
and 703 m (2300 ft.) west of southeast corner of section 14.
Collectors: H.M. Rice ( circa early 1930s) and R.L. Squires,
October 1, 2011. 7752 [= 5547].' I 18 31'15"W, 34 21'08"N.
Elevation 427 m (1400 ft.), northeast of trailer park in north-
south-trending canyon, on south section-line, 91 m (300 ft.) east
of northeast corner of section 14. Locality represents float
material from a bed located a short distance to the north at the
head of a box canyon with inaccessible vertical cliffs. Collectors:
H.M. Rice ( circa early 1930s); L.G. Barnes and G. Campbell,
April 1965; and R.L. Squires, October 9, November 13, and
December 4, 2011. 7757. 1 18°32'33"W, 34 21'15"N. Elevation
525 m (1725 ft.), on ridgeline, 290 m (950 ft.) north and 1036 m
(3400 ft.) east of southwest corner of section 10. Collectors:
H.M. Rice (circa early 1930s) and R.L. Squires, October 21,
2011. 9659. 1 18°31' 14"W, 34°20'34"N. Elevation 637 m
(2090 ft.), on ridgeline, 655 m (2150 ft.) north and 381 m
(1250 ft.) east of southwest corner of section 24. Collectors: G.A.
Rynearson (1938) and R.L. Squires, September 4, 2011.
Equivalent to loc. 212 of Grant and Gale (1931:102). 17916.
1 18°32'49"W, 34°21'33"N. Elevation 434 m (1425 ft.), south
side of disused road near south end of housing tract south of
Calgrove Blvd., 899 m (2950 ft.) north and 168 m (550 ft.) east
of southwest corner of section 10, T 3 N, R 16 W. Collector: R.L.
Squires, October 21, 2011. 17917 [= 7761 and approximately
7226 and 10339]. 1 18°32'47.5"W, 34 21'30"N. Elevation 480 m
(1575 ft.), east side of power line road east of Gavin Canyon,
747 m (2450 ft.) and 213 m (700 ft.) east of southwest corner of
section 10, T 3 N, R 16 W. Collectors: H.M. Rice (circa early
1930s); G.M. Dorwat, March 22, 1943; C.R. Stauffer, 1949; and
R.L. Squires, October 21, 2011. 17918 |= 7760]. 1 18 32'48"W,
34 21'28"N. Elevation 450 m (1475 ft.), north side of power line
Table 1 Megafossils of the Newhall area Pico Formation listed systematically and with relative abundance vs. localities (arranged west to east).
LACMIP Iocs.
76 ■ Contributions in Science, Number 520
Squires: Pico Formation Paleontology
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Squires: Pico Formation Paleontology
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road east of Gavin Canyon, 701 m (2300 ft.) north and 267 m
(875 ft.) east of southwest corner of section 10, T 3 N, R 16 W.
Collectors: G.M. Dorwat, March 22, 1943, and R.L. Squires,
October 21, 2011. 17919. 118°32'38"W, 34°21'16.5"N. Eleva-
tion 506 m (1660 ft.), on ridgeline just below “0” in “10,” 480 m
(1575 ft.) north and 777 m (2550 ft.) east of southwest corner of
section 10, T 3 N, R 16 W. Collector: R.L. Squires, November 7,
2010, and October 21, 2011. 17920. 118°32'30"W, 34 21'12"N.
Elevation 518 m (1700 ft.), on ridgeline 259 m (850 ft.) north
and 419 m (1375 ft.) west of southeast corner of section 10, T 3
N, R 16 W. Collector: R.L. Squires, December 10, 2011. 17921.
1 18°32'22"W, 34°21',10"N. Elevation 549 m (1800 ft.), on
ridgeline 152 m (500 ft.) north and 129 m (425 ft.) west of
southeast corner of section 10, T 3 N, R 16 W. Collector: R.L.
Squires, December 10, 2011. 17922. 118°32'14"W, 34°21'00"N.
Elevation 479 m (1570 ft.), on east side of power line road just
east of trailer park, 198 m (650 ft.) south and 122 m (400 ft.) east
of northwest corner of section 14. Collector: R.L. Squires,
October 9, 2011. 17923. 118°31'40"W, 34°20'35.5"N. Elevation
610 m (2000 ft.), 739 m (2425 ft.) north and 533 m (1750 ft.)
west of southeast corner of section 14. Collector: R.L. Squires,
September 4, 2011. Equivalent to southernmost loc. of Dibblee
(1992a). 17924. 118°31'38"W, 34°20'53"N. Elevation 632 m
(2075 ft.), on north-south-trending ridgeline, 1204 m (3950 ft.)
north and 488 m (1600 ft.) west of southeast corner of section
14. Collector: R.L. Squires, September 25, 2011. Equivalent to
loc. 213 of Grant and Gale (1931:102) and to the northernmost
loc. of both Rynearson (1938) and Dibblee (1992a). 17933.
118°31'16"W, 34°20'35"N. Elevation 582 m (1910 ft.), small
outcrop north side of road along ridgeline, 671 m (2200 ft.) north
and 183 m (600 ft.) east of southwest corner of section 13.
Collector: R.L. Squires, September 4, 2011. 17934 [= approx-
imately 422, 4720, and 7797], 118°30'22"W, 34°20'15"N.
Elevation 552 m (1810 ft.), on east side of power line road just
north of small concrete building, 30 m (100 ft.) north and 975 m
(3200 ft.) east of southwest corner of section 13. Collectors: G.P.
Kanakoff (date unknown), G.A. Rynearson (1938), and R.L.
Squires, September 4, 2011. In vicinity of Iocs. 211 and 214 of
Grant and Gale (1931:102) and loc. F76 of Winterer and
Durham (1962).
STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS
In the eastern and central parts of the study area (Figs. 2, 3), the
Saugus Formation consists of fluvial (braided-river) deposits that
include siltstone, sandstone, conglomeratic sandstone, and
interspersed lenses of conglomerate. No mudstone was found,
nor were any fossils. The siltstone is green, red, or brown and
crops out mainly in the eastern part of the study area. West of
California State Highway 14, the green siltstones are intercalated
within lighter colored and coarser deposits. The sandstone is
medium to coarse grained and white on fresh surfaces.
Horizontal laminated bedding and low-angle crossbedding are
common. Locally, there can be higher angle, large-scale trough
crossbedding. The conglomerate occurs as channel fills with
erosive bases and sharp tops. Crude fining-upward sequences are
common, and crude imbrication of clasts is less common. Clasts
are matrix supported and poorly to moderately well sorted. Most
of the pebble- to boulder-size (up to 50 cm length) clasts are
commonly rounded to subrounded, but some are flat. They
mostly consist of leucogranite and granite, which together make
up approximately one-half of all the clasts, with the granite
commonly accounting for 30% and leucogranite 20%. Other
clasts, listed in decreasing abundance are gneiss, volcanic
porphyry, quartzite, anorthosite, hornblende-rich diorite, schist,
Contributions in Science, Number 520
Squires: Pico Formation Paleontology ■ 79
°0 conglomerate and • sandstone interfingering gradational LACMIP
Oo- conglomeratic sandstone . siltstone " contact contact ’792° fossil
Figure 3 Schematic cross section of the study area braid delta, with folds and faults removed. Vertical exaggeration X5.5.
and argillite. Up-section, the amount of conglomerate decreases.
Beds in the Saugus Formation commonly weather brown or
orange-brown, and, locally, are oil stained and weather gray,
especially in lower Elsmere Canyon. The sandstone is white on
fresh surfaces. Stratigraphic relationships of the Saugus Forma-
tion with the underlying and overlying rocks are shown in
Figure 3. The lower part of the Saugus Formation in the study
area has many dark-colored deposits (e.g., dark brown, yellow
brown, green, and red) that eventually might prove to belong to
Oakeshott’s (1950) Sunshine Ranch stratigraphic unit, whose
type section is approximately 5.5 km south of the study area.
In the western part of the study area, the Saugus Formation
laterally interfingers with the marine Pico Formation, and the
term “braid delta,” which McPherson et al. (1987) coined for a
gravel-rich delta that forms where a braided river system
progrades into a standing body of water, aptly applies to the
study area. Initially, the fluvial deposits interfingered with
offshore-marine siltstones (barren of megafossils) in the upper
part of the Towsley Formation and in the lower and middle parts
of the Pico Formation. The conglomerates that interfinger with
these relatively quiet-water offshore siltstones are unfossiliferous.
They are also thicker, more wedge-shaped, more laterally
continuous; have much more distinct boundaries; and show
more incisement (up to 3 m) than do the commonly fossiliferous
conglomeratic storm lags that are present higher in the section in
the shoreface deposits. This interfingering continues, but to a
lesser degree, in the adjacent Valencia area to the west.
The offshore-marine siltstone (approximately 450 m thick)
that makes up most of the western part of the Pico Formation in
the study area grades up-section into the sandstones of the
shoreface facies, which consists of a lower fossiliferous part and
an upper unfossiliferous part. The lower part consists of grayish
white, very fine to fine sandstones (approximately 130 m thick)
with scattered channelized lenses and lentils filled with storm lags
of mollusks and associated pebble- and cobble-sized clasts similar
in size and composition to those of the fluvial facies (Figs. 4-8).
Locally, there can be angular clasts in addition to the more
commonly occurring rounded clasts. Locally there are coquinas,
but the shells are unabraded. The shells were transported and
concentrated by storm waves, and distance of transport was
relatively short (see “Taphonomy” for details). These fossilifer-
ous deposits represent a marine transgression that deposited the
shoreface facies as far east as LACMIP loc. 17934, in the
immediate vicinity of California State Highway 14, just north of
the south portal of the Union Pacific Railroad tunnel. The lower
part of the shoreface facies also contains some relatively thick
intervals of unfossiliferous sandstone that locally have intervals
of bidirectional crossbeds (e.g., in the vicinity of LACMIP loc.
7752), probably caused by inflow and outflow of tidal currents.
The lower fossiliferous part of the shoreface facies is equivalent
to the “basal unit” and “middle unit” described by Squires et al.
(2006) for strata immediately west of the Newhall area.
The upper part of the shoreface facies (approximately 35 m
thick) is gradational with the underlying megafossiliferous
shoreface facies and consists of white, unfossiliferous, fine to
medium sandstone that is parallel-laminated and amalgamated.
Minor conglomeratic sandstone beds can also be present. The
upper part of the shoreface facies crops out west of the Beacon
Fault to beyond U.S. Interstate Highway 5 and is the same as the
“upper unit” described by Squires et al. (2006) from strata
immediately west of the Newhall area. The upper unit
interfingers with the overlying Saugus Formation. PHst of this
fault the upper unit has been removed by erosion.
OVERVIEW OF MEGAFOSSILS
The megafossils were collected mostly from localities in the lower
part of the shoreface facies, which trends in a northwest-
southeast direction between Gavin Canyon and California State
Highway 14 (Fig. 2). The locations, whose geographic and
80 ■ Contributions in Science, Number 520
Squires: Pico Formation Paleontology
Figures 4-8 Selected outcrops of the megafossiliferous, shoreface storm-lag deposits in the upper part of the Pico Formation in the Newhall area. 4.
Channel, filled with fossils, vicinity of LACMIP locality 17913, pencil 13 cm length. 5. Channelized lens of fossils, pebbles, and small cobbles, vicinity of
LACMIP locality 7757, hammer 32.5 cm length. 6. Top of channel fill with pectinid fragments, cobbles, and a complete Zonaria ( Neobernaya ) spadicea
(Swainson, 1823) (same specimen shown in Figs. 68, 69), LACMIP loc. 7752, pencil 13 cm length. 7. Part of a lens of Turritella cooperi showing
bimodal-preferred orientation, LACMIP loc. 7752, scale bar 15 mm. 8. Part of a fossiliferous lens with valves of Argopecten invalidus and scattered
pebbles, LACMIP loc. 7757, scale bar 20 mm.
relative stratigraphic positions are shown on Figure 2, are from
an interval approximately 130 m thick in the upper part of the
shoreface facies west of the Beacon Fault. This interval contains
scattered lenses of megafossils. The species and their relative
abundance are listed in Table 1, along with information about
the occurrence of paired valves of the bivalves. The listed
megafauna consists of 83 species: one brachiopod, 36 bivalves,
40 gastropods, one scaphopod, one crab (partial leg), one
barnacle, one sea urchin (spine), one shark (ray tooth), and one
land plant (pine cone). All these taxa are illustrated here (Figs. 9-
106). The ray tooth and pine cone occur together in the same
hand specimen. A few epibionts were also found but are badly
weathered: some small patches of an encrusting bryozoan and
some minute tubes of an encrusting annelid (spirorbid) were
detected on the same brachiopod specimens from LACMIP
loc. 17918. These poorly preserved taxa are not illustrated here
because of their very limited taxonomic information. Boreholes
are scarce. Those made by sponges? or algae? are present on some
oyster valves, those made by predatory gastropods occur on a
few bivalves. Preservation differs greatly among the mollusks.
Calcitic pectinids, oysters, and turritellas are well preserved,
whereas aragonitic mollusks are commonly poorly preserved due
to weathering. Some of the very weathered, small-sized mollusks
are especially prone to disintegration upon touch.
The species found at the greatest number of localities and in
the greatest numbers, are the following: Turritella cooperi
Carpenter, 1864, Argopecten invalidus , Calicantharus bumer-
osus (Gabb, 1869), Glossaulax reclusiana (Deshayes, 1839),
Myrakeena veatchii (Gabb, 1866), and Here excavata (Carpen-
ter, 1857). Paired valves are common, especially for Argopecten
invalidus , Myrakeena veatchii, Tracbycardium ( Dallocardia )
quadragenarium (Conrad, 1837), Callitbaca tenerrima (Carpen-
ter, in Gould and Carpenter, 1857), Saxidomus nuttalli Conrad,
1837, Tresus nuttallii (Conrad, 1837), and Panopea abrupta
(Conrad, 1849).
SYSTEMATICS
Phylum Mollusca Linnaeus, 1758
Class Bivalvia Linnaeus, 1758
Family Pectinidae Rafinesque, 1815
Genus Argopecten Monterosato, 1889
Argopecten Monterosato, 1889:20
Plagioctenium Dali, 1898:696
TYPE SPECIES. Pecten solidulus Reeve, 1853, by subsequent
designation (Monterosato, 1899:193) = Pecten ventricosus G.B.
Sowerby II, 1842, not Pecten circularis G.B. Sowerby I, 1835
Contributions in Science, Number 520
Squires: Pico Formation Paleontology ■ 81
{fide Waller, 1995); Holocene, southern California and Gulf of
California to Peru (Coan et al., 2000:235).
Argopecten invalidus (Hanna, 1924)
Figures 16-19
Pecten ( Plagioctenium ) cooperi Arnold, 1906:124, pi. 49, figs. 2-
4. Not Pecten cooperi Smith, 1903.
Pecten invalidus Hanna, 1924:177, new name for P. cooperi
Arnold, 1906.
Pecten ( Plagioctenium ) subdolus Hertlein, 1925:20, pi. 5, figs. 2,
4, 7.
Pecten ( Plagioctenium ) callidus Hertlein, 1925:22, pi. 5, figs. 1,
3, 5, 6.
Pecten ( Plagioctenium ) invalidus Hanna. Jordan and Hertlein,
1926:441; Minch et al., 1976:table 15.
Pecten ( Aequipecten ) purpuratus Lamarck variety subdolus
Hertlein. Grant and Gale, 1931:211, pi. 5, fig. 1 (west of
San Fernando Pass).
Pecten ( Aequipecten ) purpuratus Lamarck variety callidus
Hertlein. Grant and Gale, 1931:211, pi. 5, fig. 4.
Pecten ( Aequipecten ) deserti Conrad variety invalidus Hanna.
Grant and Gale, 1931:213-214, pi. 5, figs. 5a-c, 6a-c.
Aequipecten callidus (Hertlein). Wilson, 1955:tables 7, 8.
Aequipecten subdolus (Hertlein). Wilson, 1955:table 8.
Argopecten invalidus (Hanna). Vedder, 1960: table 151.1;
Moore, 1984:B37, pi. 10, fig. 5; Squires et al., 2006:11-12,
figs. 15, 16.
Pecten (Argopecten) subdolus Hertlein. Moore, 1968:50, pi. 23,
figs, a, b.
Cblamys ( Argopecten ) callida Hertlein. Hertlein and Grant,
1972:198-199, pi. 32, figs. 9, 11.
Cblamys ( Argopecten ) invalida Hanna. Hertlein and Grant,
1972:200-201, pi. 33, figs. 1, 3, 8.
Cblamys ( Argopecten ) subdola Hertlein. Hertlein and Grant,
1972:201-202, pi. 30, figs. 7, 8; pi. 35, figs. 2, 5, 9.
Argopecten subdolus (Hertlein). Moore, 1984:B37-B38, pi. 10,
figs. 3, 4.
Argopecten callidus (Hertlein). Moore, 1984:B38-B39, pi. 10,
figs. 7, 9.
EMENDED DESCRIPTION. Shell medium size, up to height
1 17 mm; specimens commonly approximately height 45-55 mm.
Valves slightly longer than high on most specimens; smaller
specimens tend to be slightly longer than high, larger specimens
tend to be slightly higher than long. Left valve more convex than
right valve on most specimens; valves nearly equally convex on
few specimens. Hinge line approximately half of disk length.
Umbonal (apical angle) 100°- 105°. Ribs 20-22 in number on
both valves, with lamellae in interspaces. Ribs become obsolete
on anteriormost and posteriormost parts of valves and tend to
flatten out and become more convex in the later stages of
growth. Auricles with prominent radial riblets on both valves;
riblets stronger on anterior auricles of both valves. Left valve:
ribs narrower than on right valve; interspaces wider than ribs
and wider than those on right valve; anterior auricle with very
small notch; posterior auricle slightly truncated; anterior and
posterior auricles, both auricles with seven to nine riblets. Right
valve: ribs wider than on left valve; interspaces narrower than
ribs and narrower than those on left valve; anterior auricle with
small notch; five to seven flattish riblets, strongest one
coincident with notch area and variable in width and elevation;
posterior auricle slightly truncate; six to seven (rarely more)
radial riblets.
COMPARISON. Argopecten invalidus , A. callidus , and A.
subdolus are conspecific based on a comparative study of actual
specimens of each “species” that shows they lack consistent,
reliable morphologic differences separating them from one
another. Their reported differences (see Hertlein, 1925; Hertlein
and Grant, 1972) were based on whether or not the ribs are flat-
topped, rounded, and on the depth of the interspaces. These
differences, however, are attributable to how much weathering
the specimens have experienced. In the study area, for example,
specimens of A. invalidus at any one locality show variation in
the shape and depth of the ribs, with the variation clearly
attributable to the degree of weathering.
In addition to A. invalidus , A. callidus, and A. subdolus. Grant
and Gale (1931:see pages 210, 211, 212, 214) reported three
other argopectinid species in the study area beds: A. percarus
(Hertlein, 1925), A. mendenhalli (Arnold, 1906), and A. imposter
(Hanna, 1924). Argopecten percarus differs from A. invalidus by
having 24-25 ribs on the left valve and an umbonal angle of
118°. Argopecten mendenhalli differs from A. invalidus by
having a much longer hinge line, weak sculpture on the right-
valve anterior auricle, obsolete sculpture on the left-valve
anterior auricle. Argopecten imposter differs from A. invalidus
by having weak grooves along the sides of the major ribs and a
left valve with narrower interspaces.
Argopecten invalidus is similar to A. deserti (Conrad, 1855)
and the extant A. ventricosus (G.B. Sowerby II, 1842).
Argopecten invalidus differs from A. deserti by having larger
size, right-valve interspaces narrower than the ribs, left-valve ribs
narrower than those on the right valve, left-valve interspaces
wider than the ribs, more ribs on the right-valve anterior auricle,
and a shorter hinge line. Argopecten invalidus differs from A.
ventricosus by having a larger maximum height (95 mm), less-
inflated right valve, as well as narrower and generally more ribs
on the right-valve anterior auricle.
In the comparision of the above-mentioned argopectinids, only
the ribs that extend continuously from the beak to the venter
were counted. Specimens with one or two weak, noncontinuous
ribs that are present on both the anteriormost and posteriormost
sides of the specimens were not included. The largest specimen of
A. invalidus in the study area is 70 mm in height.
TYPE MATERIAL. Holotype of Pecten (Plagioctenium)
cooperi Arnold, 1906: CAS 61855.01 [ex CAS/SU 8]; holotype
of Pecten ( Plagioctenium ) subdolus Hertlein, 1925: CAS
61881.01 [ex CAS/SU 51]; holotype of Pecten (Plagioctenium)
callidus Hertlein, 1925: CAS 61882.01 [ex CAS/SU 53].
TYPE LOCALITY. Of Pecten (Plagioctenium) cooperi: Pacific
Beach, San Diego, San Diego County, California; San Diego
Formation, Pliocene. Of Pecten ( Plagioctenium ) subdolus: CAS
loc. 61881 [ex SU loc. 115], San Diego County, California; San
Diego Formation, Pliocene. Of Pecten (Plagioctenium) callidus,
CAS loc. 61882 [ex SU loc. 116], Cedros Island, Baja California,
Mexico, Almejas Formation, Pliocene.
GEOLOGIC AGE. Early to late Pliocene.
STRATIGRAPHIC DISTRIBUTION. LOWER PLIOCENE:
Almejas Formation, eastern Cedros Island and Tortugas Bay,
Baja California Sur, Mexico (Hertlein, 1925; Jordan and
Hertlein, 1926; Minch et al., 1976); Tirabuzon Formation
[formerly Gloria Formation], Baja California Sur, Mexico
(Wilson, 1955). UPPER PLIOCENE: Pico Formation, Holser
Canyon area, Los Angeles County, (Grant and Gale, 1931); Pico
Formation, northern Simi Valley (especially Las Llajas Canyon),
Ventura and Los Angeles counties, California (new information);
and Valencia and Newhall areas, northern Los Angeles County,
California (Grant and Gale, 1931; Squires et al., 2006; present
report); Niguel Formation, San Juan Capistrano, Orange County,
California (Vedder, 1960); San Diego Formation, lower member,
San Diego County, California (Hertlein and Grant, 1972;
82 ■ Contributions in Science, Number 520
Squires: Pico Formation Paleontology
Figures 9-33 Brachiopod (first figure) and bivalves from upper Pliocene Pico Formation in the Newhall area. All specimens coated with ammonium
chloride. 9. Terebratalia occidentalis (Dali, 1871), hypotype LACMIP 14335, LACMIP loc. 17919, brachial valve, height 32.6 mm, X0.7. 10 . jupiteria
tapbria (Dali, 1896), hypotype LACMIP 14336, LACMIP loc. 17917, right valve, height 5.7 mm, X3. 11. Arcopsis sp., hypotype LACMIP 14337,
LACMIP loc. 17917, partial left valve, height 6.8 mm, X3. 12. Anadara trilineata (Conrad, 1856), hypotype LACMIP 14338, LACMIP loc. 7752, partial
Contributions in Science, Number 520
Squires: Pico Formation Paleontology ■ 83
Demere, 1983); and Infierno Formation (Wilson, 1955), Baja
Californa Sur, Mexico.
REMARKS. Argopecten invalidits is one of the most common
megafossils in the study area, and its preservation is excellent.
Specimens range from 3 mm to 67.6 mm in height. Although they
can be weathered, they are unabraded, many have their fragile
auricles intact, and many specimens are paired valves (i.e.,
Table 1).
Class Gastropoda Cuvier, 1797
Family Calliostomatidae Thiele, 1924
Genus Calliostoma Swainson, 1840
TYPE SPECIES. Trochus conulus Linnaeus, 1758, designated
by Herrmannsen, 1846; Holocene, Mediterranean Sea.
Calliostoma sp., aff. C. grantianum Berry, 1940
Figures 53-54
REMARKS. This gastropod is represented by three specimens
from LACMIP loc. 17918. Preservation is very good, but two of
the specimens are incomplete. The illustrated specimen, which
is the most complete one, consists of approximately 3.25
teleoconch whorls and is 5 mm in height. This gastropod is similar
to Calliostoma grantianum Berry (1940:12-13, pi. 2, figs. 4, 5)
from middle Pleistocene strata in San Pedro, Los Angeles County,
California. The Pico Formation specimens differ by having smaller
size, fewer whorls, wider pleural angle, more closely spaced spiral
ribs on the sides of the teleoconch whorls, beads on the spiral rib
adjacent to the suture on the last half turn of the last whorl,
obsolete spiral ribs on the medial part of the flattish base, and three
rather than five ribs in the umbilical region. The immaturity of the
Pico Formation specimens could explain the difference in size and
fewer whorls. Mature C. grantianum have up to 6.5 whorls and
are 15.4 mm in height. There is a possibility that the Pico
Formation specimens represent a new species, but specimens that
are more mature are needed for confirmation.
The Pico Formation gastropod resembles C. canaliculatum
(Lightfoot, 1786), whose chronologic range is late Pliocene to
Holocene (Grant and Gale, 1931:833). This gastropod's species
name stems from Martyn (1784:table 1, pi. 32), but his work was
rejected for nomenclatural purposes by the International Com-
mission on Zoological Nomenclature (1957:Opinion 456). As
noted by Rehder (1967:19), Lightfoot (1786:101, no. 2220) is
regarded by modern workers as the author of this species. See
McLean ( 1 978: 1 9, fig. 7.2) for a description and illustration of it.
The Pico Formation specimens differ by having a much smaller
size, 10° wider pleural angle, lower spire, fewer and more widely
spaced spiral ribs on last whorl, some beading, and fewer and less
well-developed ribs on the base.
According to McLean (1978:19), C. dolarium (Holten, 1802)
is a synonym of C. canaliculatum. Moore (1968:56, pi. 27, fig. b)
illustrated a specimen that she identified as C. doliarium [sic]
from Pliocene strata in San Diego, and this particular specimen
looks very similar to the Pico Formation gastropod in terms of
the spacing of the spiral ribs on the last whorl. The Pico
Formation gastropod differs by having fewer, more widely
spaced, and less well-developed ribs on the base, as well as by
having some beading on the spiral rib next to the suture on the
last whorl.
Family Muricidae Rafinesque, 1815
Genus Ocinebrina Jousseaume, 1880
TYPE SPECIES. Murex corallinus Scacchi, 1836, by original
designation; Holocene, North Atlantic and Mediterranean.
Ocinebrina sp., aff. O. fraseri (Oldroyd, 1920)
Figures 77-79
REMARKS. This gastropod is represented by a single specimen
from LACMIP loc. 17918. Preservation is good, but the tip of its
spire is missing, as well as some of the shell on the dorsal surface
of the last whorl. The specimen, which is 19.3 mm in height, is
similar to the extant Ocinebrina fraseri (Oldroyd, 1920:135, pi.
4, figs. 1-3), from the Pacific Northwest. Northeastern Pacific
species formerly placed in Ocenebra Gray, 1847 were transferred
to Ocinebrina by McLean (1996). The Pico Formation specimen
differs from Oldroyd’s species by having slightly stronger
irregular varices, more and narrower spiral ribs, and reticulate
sculpture on the spire whorls and posterior half of the last whorl.
The Pico Formation specimen is unusual for an Ocinebrina
because it has both an immature-stage open siphonal canal and a
mature-stage outer lip (i.e., outer lip interior with at least four
strong nodes). In Ocinebrina , the siphonal canal remains open
until final maturity and the lip expands and forms labrial
denticles (McLean, 1996:80). Future collecting might show that
this species is new.
left valve, height 23.2 mm, Xl. 13. Limaria sp., cf. L. orcutii (Hertlein and Grant, 1972), hypotype LACMIP 14339, LACMIP loc. 17917, steinkern of
left? valve, height 45.7 mm, X0.5. 14. Myrakeena veatchii (Gabb, 1866), hypotype LACMIP 14340, LACMIP loc. 9659, left valve, height 68.8 mm,
X0.5. 15. Myrakeena veatchii (Gabb, 1866), hypotype LACMIP 14341, LACMIP loc. 9659, right valve (juvenile), height 18.2 mm, Xl.2. 16-19.
Argopecten invalidus (Hanna, 1924). 16. Hypotype LACMIP 14342, LACMIP loc. 9659, left valve (originally paired with following specimen), height
61 mm, X0.7. 17. Hypotype LACMIP 14343, LACMIP loc. 9659, right valve, height 60 mm, X0.7. 18-19. Hypotype LACMIP 14344, LACMIP loc.
9659, height 66.7 mm, X0.7. 18. left valve. 19. right valve. 20. Lyropecten catalinae (Arnold, 1906), LACMIP 14345, LACMIP loc. 7752, right valve,
height 122 mm, X0.4. 21. Swiftopecten parmeleei (Dali, 1898), hypotype LACMIP 14346, LACMIP loc. 17917, left? valve, height 53 mm, X0.6. 22.
Leopecten stearnsii (Dali, 1878), hypotype LACMIP 14347, LACMIP loc. 7752, right valve, height 57.2 mm, X0.6. 23. Patinopecten healeyi (Arnold,
1906), hypotype LACMIP 14348, LACMIP loc. 9659, right valve, height 58.6 mm, X0.7. 24. Pododesmu s macroscbisma (Deshayes, 1839), hypotype
LACMIP 14349, LACMIP loc. 17917, left valve, height 49 mm, X0.5. 25. Epilucina californica (Conrad, 1837), hypotype LACMIP 14350, LACMIP
loc. 7752, left valve, height 26.7 mm, X0.9. 26. Here excavata (Carpenter, 1857), hypotype LACMIP 14351, LACMIP loc. 17920, left valve, height
17.9 mm, Xl.2. 27. Lucinisca nuttalli (Conrad, 1837), hypotype LACMIP 14352, LACMIP loc. 17918, right valve, height 14 mm, Xl.7. 28. Lucinoma
annulatum (Reeve, 1850), hypotype LACMIP 14353, LACMIP loc. 17917, left valve, height 56.4 mm, X0.4. 29. Miltha xantusi (Dali, 1905), hypotype
LACMIP 14354, LACMIP loc. 17934, right valve, height 98.3 mm, X0.2. 30. Cyclocardia occidentalis Conrad, 1855, hypotype LACMIP 14355,
LACMIP loc. 7752, right valve, height 8.2 mm, X2.6. 31. Trachycardium ( Dallocardia ) quadragenarium (Conrad, 1837), hypotype LACMIP 14356,
LACMIP loc. 7752, left valve, height 73.3 mm, X0.4. 32. Chione ( Anomalocardia ) fernandoensis English, 1914, hypotype LACMIP 14357, LACMIP
loc. 17918, left valve, height 11.2 mm, Xl.8. 33. Callithaca tenerrima (Carpenter, in Gould and Carpenter, 1857), hypotype LACMIP 14358, LACMIP
loc. 17918, right valve, height 85 mm, X0.2.
84 ■ Contributions in Science, Number 520
Squires: Pico Formation Paleontology
Figures 34-72 Bivalves and gastropods from upper Pliocene Pico Formation in the Newhall area. All specimens coated with ammonium chloride. 34.
Compsonryax subdiaphana (Carpenter, 1864), hypotype LACMIP 14359, LACM1P loc. 7757, right valve, height 30.6 mm, X07. 35. Amiantis callosa
(Conrad, 1837), hypotype LACMIP 14360, LACMIP loc. 7752, left valve, height 47.5 mm, X0.5. 36. Dosinia ponderosa (Gray, 1838), hypotype
LACMIP 14362, LACMIP loc. 7725, left valve, height 101.7 mm, X0.3. 37. Saxidomus nuttalli Conrad, 1837, hypotype LACMIP 14361, LACMIP loc.
Contributions in Science, Number 520
Squires: Pico Formation Paleontology ■ 85
DISCUSSION
AGE
The chronologic ranges of the Newhall-area species that have the
shortest ranges are depicted in Figure 107. Based on overlap of
these ranges, these species indicate a late Pliocene age, which is in
agreement with the age reported by Squires et al. (2006) for the
Pico Formation in the Valencia area. Their age was based on
mollusks and benthic foraminifera, as well as on paleomagne-
tic studies of the overlying Saugus Formation. Squires et al.
(2006:fig. 23) provided a diagram showing the chronostrati-
graphic framework for the Pliocene and Pleistocene and included
magnetostratigraphy and various biostratigraphic zones/stages.
Their figure, however, is out of date in terms of the age of the
base of the Pleistocene. In 2009, the International Commission
on Stratigraphy (see Gibbard et al., 2009) reported that the
Pliocene ranges from 5.33 to 2.58 Ma. The “early Pliocene”
(Zanciean Stage) ranges from 5.33 to 3.6 Ma, and the “late
Pliocene” (Piacenzian Stage) ranges from 3.6 to 2.58 Ma. The
“middle Pliocene” is no longer recognized.
A late Pliocene age for the Pico Formation in the Newhall area
contradicts a latest Miocene to earliest Pliocene age (5.5 ±
0.4 Ma) reported by Berry et al. (2009:fig. 4) based on strontium-
isotope studies of fragments of oyster and pectinid shells from
Gavin Canyon. Weathered shells might account for the contra-
dictory age report.
Presence of the gastropods Cancellaria hamlini Carson, 1926
and Rictaxis painei grandior Grant and Gale (1931) in the
Newhall area Pico Formation refines their poorly known geologic
age. Carson (1926:51) reported C. hamlini only from strata of
early Pliocene age in Elsmere Canyon, but Kern (1973), in his
detailed study of the fauna there, did not detect this species.
Grant and Gale (1931:444) reported R. p. grandior only from
undifferentiated Pliocene strata in Holser Canyon near Val
Verde, Ventura County, California. These strata are part of an
almost continuous section of Pico Formation that extends from
Newhall Pass to Holser Canyon (Grant and Gale, 1931:33). In
conclusion, the geologic age of both of these gastropods is late
Pliocene.
The taxonomic composition of the megafauna of the Pico
Formation in the Newhall area and adjacent Valencia area is
most similar to the upper Pliocene Niguel Formation at San
Juan Capistrano, Orange County, California (see Vedder, 1960;
Stadum, 1984) and to the upper Pliocene lower member of the
San Diego Formation, San Diego County, California (see
Demere, 1983). There is also similarity to the megafauna of the
upper Pliocene Cebada and Craciosa members of the Careaga
Sandstone, Santa Maria, Santa Barbara County (see Woodring
and Bramlette, 1950).
DEPTH
Table 2 provides the depth-range data for the 41 extant species
found in the Newhall area; the average depth range of these
species is 8 to 144 m. Using Valentine’s (1961 Tig. 2) diagram of
the classification of marine environments, the Newhall-area
megafauna lived predominantly in the inner sublittoral marine
environment.
Winterer and Durham (1962) reported that based on benthic
foraminifera, the marine facies on the north side of Gavin
Canyon shallowed up-section. The extant Epistominella pacifica
(Cushman, 1927) is especially common in beds referred here to
the quiet-water, offshore-marine braid-delta siltstones of the Pico
Formation. They reported that this species lives in waters that
range in depth from 7 to 70 m. Up-section, in the lower part of
the overlying shoreface sandstone, they found sparse benthic
foraminifera, with the extant Nonion scaphum (Fichtel and Moll,
1798) as the best-represented species. They reported that this
species lives in waters that range in depth from intertidal to 16 m.
They found no benthic foraminifera in the stratigraphically
higher deposits in the Pico Formation.
17921, right valve, height 89.7 mm, X0.3. 38. Tresus nuttallii (Conrad, 1837), hypotype LACMIP 14370, LACM1P Ioc. 17918, right valve, height
60 mm, X0.4. 39. Macoma (Rexithaerus) secta (Conrad, 1837), hypotype LACMIP 14364, LACMIP loc. 7752, left valve, height 54.5 mm, X0.4. 40.
Macoma nasuta (Conrad, 1837), hypotype LACMIP 14365, LACMIP loc. 17916, right valve, height 49.4 mm, X0.4. 41. Leporimetis obesa (Deshayes,
1855), hypotype LACMIP 14366, LACMIP loc. 17921, right valve, height 33.3 mm, X0.7. 42. Tellina ( Tellinella ) idae Dali, 1891, hypotype LACMIP
14363, LACMIP loc. 17920, external mold of right valve, height 24.3 mm, XQ.7. 43. Gari sp., hypotype LACMIP 14367, LACMIP loc. 7757, internal
mold of partial left valve, height 62.4 mm, X0.3. 44. Solen ( Ensisolen ) sicanus Gould, 1850, hypotype LACMIP 14368, LACMIP loc. 17917, left? valve,
height 10.5 mm, X0.6. 45. Solen sp., cf. S. perrini Clark, 1915, hypotype LACMIP 14369, LACMIP loc. 17917, right? valve, height 32.6 mm, X0.3. 46.
Panopea abrupta (Conrad, 1849), hypotype LACMIP 14371, LACMIP loc. 17917, left valve, height 65.6 mm, X0.3. 47. }Chaceia ovoidea (Gould,
1851), hypotype LACMIP 14372, LACMIP loc. 7757, right valve, height 42.9 mm, XQ.4. 48. Pandora (Heteroclidus) punctuata Conrad, 1837, hypotype
LACMIP 14373, LACMIP loc. 7757, right-valve interior, height 10.1 mm, Xl.6. 49. iCyathodonta pedroana Dali, 1915, hypotype LACMIP 14374,
LACMIP loc. 7757, partial right valve, height 47.7 mm, X0.5. 50. Haliotis sp., hypotype LACMIP 14375, LACMIP loc. 17921, partial specimen, longest
dimension 57 mm, X0.33. 51-52. Calliostoma sp., cf. splendens Carpenter, 1864, hypotype LACMIP 14376, LACMIP loc. 17918, height 6.7 mm, X3.3.
51. apertural view. 52. umbilical view. 53-54. Calliostoma sp., aff. C. grantianum Berry, 1940, hypotype LACMIP 14377, LACMIP loc. 17918, height
5 mm, X4.2. 53. apertural view. 54. umbilical view. 55-56. Chlorostoma gallina form multifilosa Stearns, 1892, hypotype LACMIP 14378, LACMIP
loc. 7753, height 15.8 mm, Xl.4. 55. apertural view. 56. umbilical view. 57-58. Homoploma paucicostatum ? (Dali, 1871), hypotype LACMIP 14379,
LACMIP loc. 17918, height 5.9 mm, X4. 57. apertural view. 58. ventral view. 59-60. Pomaulax gradata Grant and Gale, 1931, hypotype LACMIP
14380, LACMIP loc. 7752, height 36.4 mm, X0.6. 59. apertural view. 60. umbilical view. 61. Operculum of ? Pomaulax gradata Grant and Gale, 1931,
hypotype LACMIP 14381, LACMIP loc. 7752, interior view, longest dimension 17.5 mm, Xl.3. 62. Lirobittium asperum (Gabb, 1861), hypotype
LACMIP 14382, LACMIP loc. 17918, apertural view of partial specimen, height 5.5 mm, X4.8. 63. Turritella cooperi Carpenter, 1864, hypotype
LACMIP 14383, LACMIP loc. 17917, apertural view, height 31.8, Xl. 64. ICalyptraea (Trochita) sp., hypotype LACMIP 14384, LACMIP loc. 17918,
dorsal view, diameter 7.5 mm, X3. 65-66. Crepidnla aculeata (Gmelin, 1791), LACMIP loc. 17918. 65. Hypotype LACMIP 14385, dorsal view, height
16.7 mm, Xl.4. 66. hypotype LACMIP 14386, two specimens vertically stacked, total height 26.9 mm, X0.5. 67. Grandicrepidula princeps (Conrad,
1857), hypotype LACMIP 14387, LACMIP loc. 17921, dorsal view, height 56.4, X0.5. 68-69. Zonaria ( Neobernaya ) spadicea (Swainson, 1823),
hypotype LACMIP 14388, LACMIP loc. 7752, height 40. 1 mm, X0.6. 68. Apertural view. 69. dorsal view. 70. Glossaulax reclusiana (Deshayes, 1839),
hypotype LACMIP 14389, LACMIP loc. 7752, apertural view, height 46.7 mm, X0.5. 71. Cryptonatica clausa (Broderip and Sowerby, 1829), hypotype
LACMIP 14390, LACMIP loc. 7752, apertural view, height 9.6 mm, X2.4. 72. Sinum scopulosum (Conrad, 1849), hypotype LACMIP 14391, LACMIP
loc. 7757, abapertural view, height 19.6 mm, X0.8.
86 ■ Contributions in Science, Number 520
Squires: Pico Formation Paleontology
Figures 73-106 Gastropods and other megafauna from upper Pliocene Pico Formation in the Newhall area. All specimens coated with ammonium
chloride. 73. Asperiscala sp., cf. A. minuticostata (De Boury, 1912), hypotype LACMIP 14392, LACM1P loc. 7757, apertural? view, base missing, height
8 mm, X3.3. 74. Amaea (Scalina) sp., cf. A. (S.) edwilsoni DuShane, 1977, hypotype LACMIP 14393, LACMIP loc. 17917, apertural? view, base
missing, height 20.2, Xl.l. 75. Gymatium sp., cf. C. ( Reticutriton ) elsmerense (English, 1914), hypotype LACMIP 14394, LACMIP loc. 17917, spire
missing, height 27.5 mm, X 1.3. 76. Ocinebrina atropurpurea (Carpenter, 1865), hypotype LACMIP 14395, LACMIP loc. 7752, height 11.4 mm, X2.4.
77-79. Ocinebrina sp., aff. O. fraseri (Oldroyd, 1920), hypotype LACMIP 14396, LACMIP loc. 17918, height 19.3 mm, Xl.3. 77. apertural view. 78.
Right-lateral view. 79. Abapertural view. 80. Calicantharus humerosus (Gabb, 1869), hypotype LACMIP 14397, LACMIP loc. 7752, height 43.5, X0.7.
81. Calicantharus fortis (Carpenter, 1864), hypotype LACMP 14398, LACMIP loc. 17917, height 33.1 mm, X0.8. 82. Alia tuberosa (Carpenter, 1864),
hypotype LACMIP 14399, LACMIP loc. 17918, height 5.2 mm, X4.2. 83. Amphissa sp., hypotype LACMIP 14400, LACMIP loc. 17918, abapertural
view, height 5.2 mm, X4.2. 84. Barbarofusus barbarensis (Trask, 1855), hypotype LACMIP 14401, LACMIP loc. 17917, height 49.4 mm, X0.7. 85.
Nassarius ( Demondia ) californianus (Conrad, 1856), hypotype LACMIP 14402, LACMIP loc. 17918, height 20.7 mm, Xl.3. 86. Callianax baetica
(Carpenter, 1864), hypotype LACMIP 14403, LACMIP loc. 7752, height 9 mm, X2.6. 87. Californiconus californicusl (Reeve, 1843a), hypotype
LACMIP 14404, LACMIP loc. 7757, height 16.9 mm, XI. 4. 88. Ophiodermella inermis (Reeve, 1843b), hypotype LACMIP 14405, LACMIP loc. 7757,
height 14.3 mm, Xl.9. 89. Cockerella conradiana (Gabb, 1866), hypotype LACMIP 14406, LACMIP loc. 17918, height 6.4 mm, X3.5. 90. Elaeocyma
sp., hypotype LACMIP 14407, LACMIP loc. 7752, height 17.6 mm, Xl.6. 91. Crassispira sp., hypotype LACMIP 14408, LACMIP loc. 17918, height
21.7 mm, Xl.3. 92. Terebra (Strioterebra) martini English, 1914, hypotype LACMIP 14409, LACMIP loc. 17918, height 15.8 mm, Xl.7. 93.
Cancellaria altispira Gabb, 1869, hypotype LACMIP 14410, LACMIP loc. 17934, height 44.3 mm, X0.7. 94. Cancellaria hempbilli Dali, 1909,
hypotype LACMIP 1441 1, LACMIP loc. 7757 , spire missing, height 18.4 mm, XI. 2. 95. Cancellaria tritonidea ? Gabb, 1866, hypotype LACMIP 14412,
Contributions in Science, Number 520
Squires: Pico Formation Paleontology ■ 87
Taxa
late
Mio
early
Plio
late
Plio
early
Pleist
mid
Pleist
late
Pleist
Rec
Sources of Information
Anadara trilineata
Lyropecten catalinae
Swiftopecten parmeleei
Patinopecten healeyi
Argopecten invalidus
Myrakeena veatchii
Pomaulax gradata
Nassorius (0.) californianus
Terebra ( Strioterebra ) martini
Cancellaria altispira
Cancellaria hemphiili
Cyclocar ida occidental is
Lirobittium asperum
Callianax baetica
Crockerella conradiana
Dentalium neohexagonum
Powell et al., 2010
Squires et al., 2006
Hertlein & Grant, 1972
Moore, 1979
Squires et al., 2006
Squires et al.,2006
Grant & Gale, 1931
Addicott, 1965
Grant & Gale, 1931
Grant & Gale, 1931
Grant & Gale, 1931
Powell & Stevens, 2000:
Minor et al., 2009
Grant & Gale, 1931
Grant& Gale, 1931
Grant & Gale, 1931
Grant & Gale, 1931
Figure 107 Chronostratigraphic distribution of the study area species with the most constrained geologic ranges indicating a late Pliocene age.
SUBSTRATE
At least three substrate types are recognized for the study area
deposits: fine-grained offshore sediments, fine- to medium-grained
sandy deltaic sediments, and hard surfaces. The first type was
located immediately seaward of the delta and essentially fringed
the delta; the second occurred on the delta complex itself; and the
third occurred in association with coarse debris on the delta. The
presence of fine-grained offshore substrate is indicated by the very
abundant gastropod Turritella cooperi. Valentine and Mallory
(1965) assigned this species to their Group III Pleistocene offshore
fossil community, along with the bivalve Lucinoma annnlatum
(Reeve, 1850), another megafaunal element, but a rare one, of the
Newhall Pico Formation assemblages. Although details are lacking
about how T. cooperi lives, it is probably like most species of
extant Turritella. Bandel (1976) reported that Turritella variegata
(Linnaeus, 1758) from the Caribbean coast of Colombia lives as a
suspension feeder shallowly buried in soft substrates. Large
populations migrate only at the time of spawning once a year,
and they crawl to more sandy bottoms or bottom covered with
gravel where they can attach their spawn more firmly in coarse
debris than is possible in muddy environments. Allman et al.
(1992) reported that Turritella gonostoma Valenciennes, 1832,
from the northern Gulf of California lives in depths less than 5 m
and, in the winter, migrates into shallow water to reach nutrient-
rich waters and to lay its eggs. It seems very likely that the
specimens of T. cooperi that dominate the fossil assemblages at
most localities in the Newhall area preferred to live in close
proximity to a river delta because the river would deliver nutrients
on which it feeds. During the winter, individuals could migrate,
from silty substrate to shallower water and sandy and gravelly
substrates, in order to lay their eggs.
The fine- to medium-grained sandy delta substrate is indicated
by paired-valved epifaunal bivalves (e.g., Argopecten , Lyropec-
ten, Patinopecten ), epifaunal gastropods (e.g., Glossaulax,
Conus), and paired-valved infaunal bivalves (e.g., Trachycar-
dium, Saxidomus, Tresus, Panopea). Hard-surface biotopes were
very localized. The Haliotis specimen and the Terebratalia
occidentalis brachiopods most likely attached to shell debris or
larger rock clasts. The latter, in a few cases, provided hard
substrate for encrusting bryozoan and spirorbid tubes. Some
individuals of the plicate oyster Myrakeena veatchii lived
attached to each other, based on a cluster of specimens found
attached to each other at LACMIP loc. 9659, where a growth
series of this oyster was also found. The occurrence of the paired-
valved single specimen of the pholadid iChaecia ovoidea (Gould,
1851) is anomalous because this species normally bores into clay
or shale (Coan et al., 2000). Kennedy (1974:39) reported that C.
ovoidea has been known to bore into waterlogged wood, and this
could explain its presence in the study area megafauna.
The above-mentioned three types of substrate are compatible
with the findings derived from Table 2 showing that the majority
of the 41 extant species of the Pico Formation megafauna live in/
on sand or mud; only a few live on hard surfaces (Table 2).
LACMIP loc. 7752, height 23.8 mm, X0.9. 96. Cancellaria hamlini Carson, 1926, hypotype LACMIP 14413, LACMIP loc. 17919, height 21.5 mm,
X0.9. 97. Turbonilla sp., hypotype LACMIP 14414, LACMIP loc. 17918, upper spire missing, height 6 mm, X3. 1 . 98. Rictaxis painei grandior Grant
and Gale, 1931, hypotype LACMIP 14415, LACMIP loc. 7752, height 13.3 mm, Xl.7. 99. Acteocina culcitellai (Gould, 1853), hypotype LACMIP
14416, LACMIP loc. 7760, height 3 mm, X7.5. 100-101. Scaphopod Dentalium neohexagonum Sharp and Pilsbry, in Pilsbry and Sharp, 1897, LACMIP
loc. 7752. 100. Hypotype LACMIP 14417, height 9.8 mm, X2.4. 101. Hypotype LACMIP 14418, diameter 2.3 mm, X3.7. 102. Barnacle Balanus ? sp.,
hypotype LACMIP 14419, LACMIP loc. 17917, side view, height 5.5 mm, X2. 103. Crab leg (partial), hypotype LACMIP 14420, LACMIP loc. 17918,
height 10.2 mm, X2.2. 104. Echinoid spine Eucidaris sp., hypotype LACMIP 144421, LACMIP loc. 17917, height 4.2, X5.4. 105. Ray tooth Myliobatis
sp., hypotype LACMIP 14422, LACMIP loc. 7752, maximum dimension 25 mm, X0.9. 106. Pine cone, hypotype LACMIP 14423, LACMIP loc. 7752,
cross-section, height 50 mm, X0.6.
88 ■ Contributions in Science, Number 520
Squires: Pico Formation Paleontology
Table 2 Depth ranges, substrate preferences, geographic ranges, and faunal provinces of Newhall
Meters
Substrate
Latitudinal range (°N)
Refs.
Terebratalia occidentalis
50-250
On hard surfaces
26-23
1
Jupiteria taphria
10-100
In sand and clay
39.5-28.2
2
Pododesmus macroscbisma
0-90
On hard surfaces
70.6-27.9
2
Epilucina californica
0-80
Sand and gravel of exposed shorelines
41.8-25
2
Here excavata
25-125
In sand or mud
34.4-27.9
2
Lucinisca nuttalli
10 to 75
In sand or muddy sand
36.7-27.8 into Gulf of Califor-
nia to 22.4
2
Lucinoma annulatum
0-665
In sand of exposed shorelines
60.8-25.7
2
Miltha xantusi
20-150
In sand
22.1 into Gulf of California to
Panama (8.3)
3
Trachycardium (D.)
0-50
In sand or mud, bays and offshore
36.6-27
2
quadragenarium
Callitbaca tenerrima
0-30
In gravelly sand
57.1-27.6
2
Compsomyax subdiapbana
2-500
In soft mud
60.8-30.4 + local pop. in Gulf
of California (30.3)
2
Amiantis callosa
0-20
In sand, exposed headlands
34.4-24.8
2
Dosinia ponderosa
0-60
Soft bottoms
27.8 into Gulf of California to
Peru (3.5°S)
3
Saxidomus nuttalli
0-10
In mud or sand, bays and lagoons
40.7-27.7
2
Tresus nuttallii
0-80
In mud, sheltered bays and foreshores
57-24.6
2
Macoma ( Rexitbaerus ) secta
0-100
In silt and sand of bays
54-24.6
2
Macoma nasuta
0-50
In sand or silt, exposed or sheltered
60.2-27.7
2
Leporimetis obesa
subtidal-50
In sand
34.5-24.6
2
Tellina ( Tellinella ) idae
0-100
In sand
34.4-32.7
2
Solen (Ensisolen) sicarius
intertidal
In sand or mud, sheltered bays
54-30.4
2
Panopea abrupta
0-100
In sand or mud
57.6-33.6
2
ICbaecia ovoidea
0-subtidal
Boring into clay, shale, or wood
37.9-27.7
2, 4
Pandora (Heteroclidus)
subtidal-50
In mud
49.9-26.2
2
punctuata
Cyathodonta pedroana
9-114
In mud
36.7-24.6
2
Calliostoma splendens
?
Rocky areas
35-32.5
5
Cblorostoma gallina form
mid tidal
Rocky areas
34-25
6
multifilosa
Turritella cooperi
25-100
On sand
37-24 into W side Gulf of
California to head of Gulf
7
Crepidula aculeata
intertidal
On hard surfaces
42-Chile (30°S)
8
Zonaria (Neobernaya) spadicea
sublittoral
Under overhung rock ledges
35-28
9
Glossaulax reclusiana
0-50
On sand or mud, common in bays
41.8 into Gulf of California to
21.5
60-32.5
10
Cryptonatica clausa
9-970
On soft bottoms
10
Sinum scopulosum
15-171
On sand or mud, common in bays
36.5-27.6
10
Asperiscala minuticostata
18-137
On sand and broken shells
28 into Gulf of California to
Ecuador (0°)
11
Ocinebrina atropurpurea
0-sublittoral
Rocky bottoms
60-30.5
9
Alia tuberosa
sublittoral
In gravel under kelp
60-25
9
Barbarofusus barbarensis
50-350 m
Soft bottoms
36.5-23
7
Calhanax baetica
0-offshore
On sandy bottoms
55-23
9
Calif orniconus californicus
0-30
On rock and sand
37.5-24.5
9
Ophiodermella inermis
0-70
Soft bottoms
53-24.5
7
Crockerella conradiana
24-240
Soft bottoms
34-32
7
Acteocina culcitella
0-offshore
On sand flats and mudflats in bays
55-27.5
9
References: 1 = Hochberg, 1994; 2 =
Coan et al., 2000; 3 =
Coan & Scott, 2012; 4 = Kennedy, 1974; 5 =
Grant and Gale, 1931; 6 = McLean, personal
communication; 7 = McLean, 1996;
8 = Keen, 1971; 9 =
McLean, 1 978; 1 0 = Marincovich, 1977; 11
= DuShane, 1979.
TAPHONOMY
Crepidula aculeata (Gmelin, 1791) (some of which are
vertically
As mentioned earlier, the shoreface-facies megafauna occurs in
channelized, storm-lag deposits. It is striking how the taxonomic
composition of one storm-lag deposit differs so much from one
that is nearby, in either a lateral or vertical stratigraphic sense.
For example, at LACMIP loc. 17918, Turritella cooperi shells are
so abundant that they constitute a coquina bed (with unworn
specimens). In a storm lag a few meters up section, there are
relatively few T. cooperi. Instead, there are concentrations of
both the brachiopod Terebratalia hemphilli and the gastropod
stacked). In addition, both species are represented by juvenile and
adult specimens.
The storm-lag deposits in the upper Pico Formation commonly
represent a mixture of species that lived in different life
associations on different types of substrate. Occasional large
storm waves raked all these shallow waters and thereby mixed
the life associations together. Distance of postmortem transport
was short based on the presence of paired valves of most of the
brachiopods and many of the bivalves (e.g., Panopea, Solena,
Myrakeena, Argopecten, Lyropecten) (see Table 1). None of
Contributions in Science, Number 520
Squires: Pico Formation Paleontology ■ 89
Modern
Molluscan
Provinces
(Valentine,
1966)
Aleutian
Columbian
Mendocinian
Montereyan
Californian
Surian
Panamic
Modern
Marine
Climates
(Hall, 1964)
Cool
Temperate
Mild
Temperate
Warm
Temperate
Outer
Tropical
Inner
Tropical
g
Cl
3
-O
O
o
60°N
c
<5
50°N
40°N
30°N ■
■3 Q.
■Q
O
£
O’
If
!"§
-c
o
cl
N
c
o
p
o
cl
.2
.c
o
Q
c
C5
><
C5
-C
f I
20°N
I
To
To Panama
Peru
Figure 108 Latitudinal distribution of selected mollusks (see Table 2 for details) from the upper part of the Pico Formation, Newhall area vs. modern
molluscan provinces and marine climates. Dashed box shows zone of maximum overlap of mollusk distributions at 31 N to 33.5 N. Solid circle =
latitude of the study area (34°21'N).
these infaunal bivalves were found in their burrows. These
specimens were displaced from their burrows and transported
while alive. Additional evidence of short distance of transport is
based a scarcity of any obvious signs of abrasion. Some examples
are fragile protoconchs of some specimens of Calliostoma sp., aff.
C. grantianum (Fig. 53), Nassarius ( Demondia ) californianus
(Conrad, 1856) and Cancellaria hamlini Carson, 1926 (Fig. 96);
delicate apical tips of many Turritella cooperi ; delicate auricles of
the pectinids, including those of juvenile Argopecten invalidus;
thin varices of Asperiscala minuticostata ? (De Boury, 1921); and
four sets of two vertically stacked specimens of Crepidula
acideata at LACMIP loc. 17918. This is the first report of
vertical stacking of this species. An additional indicator of short
distance of transport is the presence, at LACMIP loc. 9659, of a
growth series of the oyster Myrakeena veatcbii. Specimens range
from 18.5 to 85 mm in height. The smallest specimen is
illustrated (Fig. 15) because no juvenile specimen of this species
has ever been illustrated.
Some of the lentils in the upper Pico Formation storm deposits
consist of dense concentrations of unworn, small-sized, mostly
disarticulated specimens of bivalves. There are also a few lenses
containing abundant Turritella cooperi that show preferred
bimodal distribution (Fig. 8) in the way their shells were oriented
by shallow-marine wave movements. Occasional large storm
waves, which would be more common during the winter, would
move and concentrate the copious Turritella shells, as well as
other offshore shells, in storm-lag deposits on the shoaling parts
of the braid delta.
ZOOGEOGRAPHIC IMPLICATIONS
Squires et al. (2006) reported that the Pico Formation megafauna
in the Valencia area just west of the Newhall area is mostly
indicative of warm-temperate conditions, with a few species
indicative of warmer conditions. This present study corroborates
these findings. Table 2 lists the latitudinal ranges of all the extant
species found in the Pico Formation in the Newhall area, and
Figure 108 shows that the zone of maximum overlap of
representative extant species from this list is between 33.5°N
and 31 N. This zone plots within the “Californian” molluscan
province of Valentine (1966) and the warm-temperate, marine-
climate zone of Hall (1964). There is, however, a warmer water
component (tropical) based on the presence of two extant species
found today considerably south of maximum overlap zone:
90 ■ Contributions in Science, Number 520
Squires: Pico Formation Paleontology
Miltba xantusi (Dali, 1905) and Dosinia ponderosa (Gray, 1838)
live in the southern (tropical) part of the Gulf of California, as
well as much farther south (see Table 2 for references).
Two of the extinct mollusks from the Newhall area are warm-
water indicators found only in fossil deposits of Southern
California and Baja California, Mexico. They are Argopecten
invalidus and Lyropecten catalinae (Arnold, 1906) [= Lyropec-
ten gallegosi (Jordan and Hertlein, 1926)]. Both are known
(Minch et ah, 1976) from as far south as the Pliocene Almejas
Formation just south of Bahia Tortugas on the Vizcaino
Peninsula, Baja California Sur, Mexico.
Another pectinid, Patinopecten healeyi (Arnold, 1906) which
is present at most of the localities in the study area, is also
significant in the interpretation of Neogene zoogeography. This
species, like Lyropecten catalinae , is a giant pectinid (see
Addicott, 1974), because of having a size commonly greater
than 90 mm. Patinopecten healeyi has an early to late Pliocene
chronologic range (e.g., Addicott, 1974; Moore, 1979). It
reached its northernmost occurrence (Cape Mendocino in
northern California), but during the late Pliocene, the species
ranged farther south, with its southernmost occurrence in the
Almejas Formation in Baja California Sur (Moore, 1 979:fig. 1)),
along with the warm-water species Argopecten invalidus and L.
catalinae.
The extinct epitoniid gastropod Amaea (Scalina) edwilsoni
DuShane, 1 977, tentatively identified from the Newhall area, has
been reported (DuShane, 1977) only from the Pliocene Tirabuzon
Formation [formerly Gloria Formation] (Wilson, 1955) near
Santa Rosalia on the Gulf of California, Baja Sur, Mexico.
ACKNO WLEDG MENTS
This study would have been greatly diminished in its scope without the
permission granted to me by the various land owners for access to their
property west of California State Highway 14. James H. McLean (LACM
Malacology) shared his knowledge of vetigastropods, muricids, and
turrids. Lindsey T. Groves (LACM Malacology) provided access to
difficult-to-find literature and shared his knowledge of Pliocene mollusks.
Brian J. Swanson, Pamela J. Irvine, and Jerome Treiinan (all associated
with the California Geological Survey, Los Angeles), shared their
knowledge of the Saugus Formation. Charles L. Powell, II (LISGS, Menlo
Park) shared his knowledge of the fossils from Gold Creek in Big Tujunga
Canyon. The manuscript benefited considerably from critical reviews by
L.T. Groves and C.L. Powell II.
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