Stipatocrinus, a new and unusual camerate crinoid from the lower silurian of western New York

—

Royal Ontario Museum |
[IFE SCIENCES
4~CONTRIBUTIONS

— 146

Stipatocrinus, a New and Unusual
Camerate Crinoid from the
Lower Silurian of Western New York

James D. Eckert and Carlton E. Brett

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LIFE SCIENCES CONTRIBUTIONS 146

Stipatocrinus, a New and Unusual
Camerate Crinoid from the
Lower Silurian of Western New York

James D. Eckert
and
Carlton E. Brett

ROM

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James D. Eckert completed his M.Sc. studies in the Department of Geology at the
University of Toronto in 1981. He is currently continuing graduate studies in the De-
partment of Geological Sciences, University of Rochester, Rochester, New York.

Carlton E. Brett is associate professor in the Department of Geological Sciences, Uni-
versity of Rochester.

Canadian Cataloguing in Publication Data
Eckert, James D., 1952-
Stipatocrinus, a new and unusual camerate
crinoid from the Lower Silurian of western New York

(Life sciences contributions ; 146)

Bibliography: p.

ISBN 0-88854-336-0

1. Crinoidea, Fossil. 2. Paleontology — New York
(State) — Ordovician. 3. Paleontology — New York
(State). I. Brett, Carlton Elliot. If. Royal

Ontario Museum. III. Title. [V. Series.

QE782.E24 1987 563'.91'097479 C87-094782-6

Publication Date: 15 November 1987

ISBN 0-88854-336-0

ISSN 0384-8159

© Royal Ontario Museum, 1987

100 Queen’s Park, Toronto, Canada, M5S 2C6
PRINTED AND BOUND IN CANADA AT THE ALGER PRESS

Stipatocrinus, a New and Unusual Camerate Crinoid from the
Lower Silurian of Western New York

Abstract

Stipatocrinus hulveri gen. et sp. nov. is described from the Upper Llandoverian Reynales
Formation of western New York. Diagnostic characters of this unusual camerate crinoid
include a peculiar cup in which the lowest circlet, consisting of two large and two small
plates designated as basals divided by sutures passing through the AE-interray and C-
ray, possesses a combination of infrabasal, basal, and radial features. Unique t-shaped
radials bridge interrays consisting of numerous small interbrachials irregular in shape and
arrangement. Stipatocrinus probably represents an archaic, previously unrecognized lin-
eage of camerate crinoids that persisted into the Silurian but became extinct in the late
Llandoverian. Thinly plated, flexible interrays of Stipatocrinus reduced metabolic cost
of skeletal growth and possibly aided in respiration.

Introduction

Crinoids are poorly represented in Lower Silurian (Llan-
doverian) strata of eastern North America. This interval
is critical to understanding the evolution of the class, for
it followed major Late Ordovician extinctions that deci-
mated crinoids and other groups of marine invertebrates
and preceded major taxonomic radiation and restructuring
of crinoid assemblages in the Late Silurian (Wenlockian).
One might predict, therefore, that Llandoverian crinoid
assemblages would comprise transitional forms, including
ancestral stocks of certain of the major Wenlockian clades.
Indeed, such precursor taxa have been reported from the
Hopkinton Dolomite (late Llandoverian, C,;—C,) in lowa
(Witzke, Frest, and Strimple, 1979; Witzke and Strimple,
1981), and a slightly older fauna is known from the Brass-
field Formation of Ohio (Ausich, 1985, 1986a, 1986b) in
strata considered to be of late Llandoverian (C,—C,) age
(Berry and Boucot, 1970). Potential ancestors of Wen-
lockian crinoids also occur in the Cataract Group of On-
tario (Eckert, 1984) and in the lower Clinton Group (middle
to late Llandoverian, B,—-C,) of the northern Appalachian
Basin in New York State (Eckert, in prep.). However,
Early Silurian crinoid assemblages of Ontario and New
York State are also distinctly Ordovician in aspect and

characterized by persistence of primitive lineages. For ex-
ample, Ptychocrinus medinensis, a species closely related
to the Late Ordovician crinoid P. splendens, is locally
abundant in the Power Glen Formation (early Llandover-
ian, A,-A,) of New York and the Cabot Head Formation
of Ontario (Brett, 1978; Eckert, 1984). The Reynales For-
mation contains undescribed crinoids very similar to the
Middle Ordovician crinoid Tornatilicrinus from the Leb-
anon Limestone of Tennessee. Stipatocrinus hulveri gen.
et sp. nov. is also inferred to represent a primitive but
persistent Ordovician lineage. These taxa appear to rep-
resent relict lineages that escaped Ashgillian extinction.
Stipatocrinus hulveri formed monotypic, high-density as-
semblages, suggesting that it may have acted as an op-
portunistic species that thrived in physically stressed, un-
crowded environments such as existed in the Early Silu-
rian of the northern Appalachian Basin. These environ-
ments may have provided a refuge for primitive holdover
taxa that became extinct or were displaced coincidentally
with an invasion of diverse Wenlockian echinoderm as-
sociations that may nave evolved in the North American
midcontinent (Witzke, Frest, and Strimple, 1979) or in
presently unknown areas.

Occurrence and Stratigraphy

In 1983, while studying Early Silurian brachiopod com-
munities in western New York, Michael Hulver of the
University of Chicago discovered dolostone slabs covered
with long crinoid stems from talus in the eastern side of
the gorge of the Genesee River at Rochester, New York

(Text-Figs. 1, 2). Subsequent investigation by Brett re-
sulted in discovery of numerous nearly complete individ-
uals of Stipatocrinus hulveri gen. et sp. nov. at this site,
0.3 km north of the lower falls of the Genesee River and
10 to 40 m east of the Rochester Gas and Electric access

Oo km = 30

———————— el,

Toronto

ONTARIO

es

Niagara Rochester

® Falls

Conkey Ave.

TeExtT-Fic. 1. Locality map of southwestern Ontario and western New York State. Arrow in inset at right
indicates occurrence of Stipatocrinus hulveri gen. et sp. nov.

Rochester
lrondequoit

Williamson

Thorold sang

Queenston

TextT-FiG. 2. Upper Ordovician Queenston Formation and Silurian formations exposed in eastern side of
gorge of Genesee River at Rochester, New York. Vertical section is approximately 50 m. Slabs bearing
Stipatocrinus hulveri gen. et sp. nov. were found on talus slope between access road and Reynales Formation
exposed in cliff. Arrows indicate lateral extent of occurrence.

road south of Seth Green Drive, Rochester, Monroe County,
New York (United States Geological Survey, Rochester
West 7.5’ Quadrangle).

Crinoid-bearing slabs appear to comprise parts of a large
rockfall from the Wallington Member of the Reynales For-
mation, exposed in the cliff above the talus (Text-Fig. 2).
Laminated calcisiltite containing crinoids closely resem-
bles that found interbedded with green shales near the base
of the Wallington Member. Crinoid columns and distinc-
tive t-shaped radials were obtained in situ from the lowest
metre of this member, which probably represents the ho-
rizon from which the study material was eroded.

The Reynales Formation, also known as the Reynales
Limestone, consists of complex, time-trangressive, dom-
inantly carbonate strata extending from the Niagara area
eastwards to near Wolcott, New York, where it grades

laterally into the Bear Creek Shale. The Wallington Mem-
ber (Fisher, 1960) is the uppermost unit of the Reynales
Formation in the Rochester area. Approximately 4 m thick
in the Genesee Gorge, the Wallington consists of thin- to
medium-bedded, light grey, cherty, dolomitic limestone
and dolostone with greenish-grey shale partings. Cross-
lamination with a maximum amplitude of 2 cm occurs in
calcisiltite (pelletal grainstone beds). Several horizons of
fossiliferous packstone and grainstone within the Walling-
ton contain abundant specimens of the brachiopods Pen-
tamerus oblongus and Eocoelia hemispherica. On the basis
of these brachiopods, the Wallington was considered to
be of late Llandoverian (C,) age (Berry and Boucot, 1970).
However, further consideration of brachiopod and cono-
dont biostratigraphy led Rickard (1975) to propose an ear-
lier (C,) age.

Materials and Methods

Most specimens of Stipatocrinus hulveri gen. et sp. nov.
are embedded in a hard, dolomitic calcisiltite and proved
difficult to prepare. Attempts to remove matrix, using so-
dium bicarbonate in an airbrasive machine, were not suc-
cessful. Dolomite powder proved to be an effective abrasive
but readily damaged the thin plates of these crinoids. For-
tunately a few specimens, including the holotype, are
embedded in a softer, slightly argillaceous matrix and were
prepared using needles and airbrasion with little damage.

Immersion of specimens in ethanol facilitated morphologic
study. Text-Figures 5, 6, and 7 were prepared by tracing
over photographs. Plate dimensions were measured using
vernier Calipers; orientations of these plates are given in
Table 1:

All study material is deposited in the collections of the
Department of Invertebrate Palaeontology, Royal Ontario
Museum (ROM) in Toronto, Ontario, Canada.

Systematic Palaeontology

Class Crinoidea Miller, 1821
Subclass Camerata Wachsmuth and Springer, 1885
?Order Monobathrida Moore and Laudon, 1943
Superfamily Stipatocrinacea superfam. nov.

DIAGNOSIS

Lowest circlet in cup consisting of four plates (basals?);
two large plates adjacent to one another along C-ray suture
and two small plates directly in line with A- and E-ray
radials. This circlet divided by sutures in AB-, DE-, and
EA-interrays. Radials and fixed brachials narrow, elon-
gate, raised. Primanal and anitaxis absent. Interbrachials
small, exceptionally numerous, irregular in shape and
arrangement.

Family Stipatocrinidae fam. nov.

DIAGNOSIS
Characters of superfamily.

Stipatocrinus gen. nov.

TYPE SPECIES
Stipatocrinus hulveri sp. nov.

ETYMOLOGY

From the Latin stipatus—crowded—in reference to the
numerous interbrachials crowded together in the interrays,
and from the Greek krinon—lily.

DIAGNOSIS

Monotypic genus of Stipatocrinidae with narrow conical
cup and depressed interrays. Radials t-shaped, bridging
interrays. Primibrachials two in each ray, elongate, straight
sided, grooved ventrally. Fixed secundibrachials four to

iA >
Ca

‘acs
o>
oe hs

20,

LIS SY)
rH 2 RT B ree Z <
KORA

TEXT-FiG. 3. Plate diagram of Stipatocrinus hulveri gen. et sp. nov. Note peculiar configuration of proximal
circlet, divided into bilaterally symmetrical halves by sutures in AE-interray and C-ray. The t-shaped radials
(black) enclose suboval interbrachial areas and are smaller in BC- and CD-interrays than in remaining interrays.

six in each ray branch. Fixed pinnule borne by second
secundibrachial. Interbrachials smooth, without ornamen-
tation. Narrow cylindrical anal tube eccentrically located
on tegmen. Arms ten, pinnulate; brachials in immature
biserial arrangement. Column transversely circular.

DISCUSSION

There is little doubt that Stipatocrinus gen. nov. belongs
to the subclass Camerata in view of its densely pinnulate
arms, fixed ray series, fixed pinnules, and numerous in-
terbrachials. However, below this level, classification be-
comes difficult. It is not clear whether Stipatocrinus should
be classified among the Monobathrida or the Diplobath-
rida, or in a separate order altogether, because the peculiar
plate configuration of the base of the cup in this crinoid
renders plate homologies obscure. The problem is com-
pounded, for the column of Stipatocrinus is neither pen-
tameric nor pentagonal, but cylindrical with a round lumen.
Hence, this column does not provide any indication of
orientation of thecal plates relative to the entoneural sys-
tem, as suggested by the “‘Law of Wachsmuth and Spring-
er’ (Warn, 1975).

Even the location of radials in Stipatocrinus 1s somewhat
problematic. The A- and E-rays are each supported by a
single uninterrupted row of plates beginning in the lowest
circlet of the cup (Text-Fig. 3). Thus, plates of this circlet
in the A- and E-rays could be considered to be radials.
However, if this interpretation is followed, the radials of
these rays would lie immediately above the stem facet, a
feature unknown in all other crinoids. In the B-, C-, and
D-rays the lowest plates of the rays are t-shaped and sit-
uated within the second circlet of plates (Text-Fig. 3).
These t-shaped plates are relatively narrow, as in fixed
brachials, and are even grooved ventrally (Pl. 1, figs.
16,20). However, they are differentiated from all other
cup plates by their lateral processes, and they form a dis-
tinctive circlet. We feel fairly confident in designating
plates of the second circlet as radials because a t-shaped
plate of the C-ray overlies a suture between plates of the
lowest circlet. This plate is therefore in typical radial po-
sition. Furthermore, the strong differentiation of these plates
is also suggestive of radials. In other primitive camerate
crinoids, including reteocrinids and xenocrinids, the ra-
dials are always markedly separate from other adjacent
plates (Brower, pers. comm., 1986).

Configuration of the lowest circlet of cup plates in Sti-
patocrinus is unique among camerate crinoids, both in
terms of the shapes and relative sizes of these plates and,
most notably, in their orientation with respect to the ra-
dials. The lowest circlet combines features of infrabasals,
basals, and radials. Three of four sutures dividing this
circlet are interradial (AB-, DE-, and EA-interrays), a
characteristic of infrabasals; the fourth suture is directly
below the C-ray radial as it would be in a normal basal

TEXT-FiG. 4. Stipatocrinus hulveri gen. et sp. nov. Specimens
immersed in ethanol.

A. Individual centred on C-ray. Proximal circlet is divided
by suture in C-ray but not in BC- or CD-interrays. Aborally
directed bifurcation of C-ray ridge continues on basals. Small
suboval interbrachial areas in BC- and CD-interrays, bounded
above by t-shaped radials, are of similar size. Interbrachials,
underlain by black integument, are poorly preserved. Paratype
ROM 44309a, x 4.0.

B. Individual centred on D-ray. Proximal circlet is divided
by suture in C-ray and DE-interray but not in CD-interray. Sub-
oval interbrachial area in DE-interray, bounded above by t-shaped
radials, is smaller than adjacent area in CD-interray. Interbra-
chials are well preserved in this specimen, and proximal portion
of anal tube is visible. Paratype ROM 44309b, x 4.0.

circlet (Text-Figs. 3, 4A,B). Furthermore, two plates in
the lowest circlet resemble radials because they are directly
in line with and support the A- and E-rays.

An unusual and interesting feature of Stipatocrinus is
that the plates of the lowest circlet are dissimilar in size
and shape with respect to each other. Two plates of this
circlet, directly in line with the A- and E-rays, are five-
sided and considerably smaller (narrower) than the larger
six-sided plates that they adjoin laterally (Text-Fig. 3).
Pairing of each larger plate with a smaller one divides the
lowest circlet into bilaterally symmetrical halves, each with
two plates, about a sutural plane passing through the AE-
interray and C-ray. To our knowledge, no other camerate
crinoids, including xenocrinids, possess a basal circlet with
this symmetry.

We emphasize that the peculiar configuration of the
lowest circlet of cup plates in Stipatocrinus is not an ab-
normality. Consistent orientations have been observed in
all seven specimens that have been adequately prepared.
Furthermore, plate organization appears well coordinated
with ray ridge configuration.

an

Homology of the lowest circlet of cup plates in Stipa-
tocrinus is a problem. We have termed these plates basals
because they comprise the only circlet of plates between
the stem facet and inferred radial circlet. However, the
proximal circlet resembles a typical basal circlet only at
the C-ray suture, situated directly below the C-ray radial.
An alternative interpretation is that the lowest circlet of
plates in Stipatocrinus may be homologous with the in-
frabasals of dicyclic camerates, in which the sutures are
invariably interradial in position. However, number and
sutural configuration of plates in the lowest circlet of S1-
patocrinus do not precisely conform to that of a normal
camerate crinoid infrabasal circlet. Nearly all diplobath-
rans possess five equal infrabasals, although the Anthemo-
crinidae possess four. None of these crinoids has a suture
in the C-ray position as in the Stipatocrinus base. Instead,
sutures between infrabasals normally occur in the BC- and
CD-interrays; such sutures are absent in Stipatocrinus (Text-
Figs. 3, 4A).

The origin of the unequal basals in Stipatocrinus 1s un-
clear. The infrabasal circlet of anthemocrinids, a family
unrelated to Stipatocrinus, possesses a large plate presum-
ably derived from fusion of two smaller plates. In contrast,
Stipatocrinus possesses two large and two small plates in
the lowest circlet. The two large plates could have devel-
oped by lateral fusion of two pairs of plates in an infrabasal
circlet that originally possessed six plates. However, this
seems unlikely, for crinoids with six infrabasals are un-
known. A more plausible explanation is that the two larger
plates of Stipatocrinus were derived in two different ways:
one by fusion of two plates, the other by enlargement of
a single plate, so that the sutural position migrated from
an interradial to a radial position. This would imply an
ancestral condition with five plates in the lowest circlet,
for which no evidence exists.

If the lowest cup plates of Stipatocrinus are homologous
with infrabasals, we are faced with the obvious problem
of absence of a basal circlet. Most researchers have implied
that a pseudomonocyclic condition results from loss of
infrabasals (Warn, 1975; Ubaghs, 1978). For example, the
inadunate genus Jocrinus could have evolved from Mer-
ocrinus by loss of infrabasals. Alternatively, certain mon-
ocyclic inadunates including Belemnocrinus may have
evolved from dicyclic forms by loss of the basal circlet
(McIntosh, 1979). The latter process may also have oc-
curred in Stipatocrinus.

The interrays of Stipatocrinus are peculiar in several
respects. Most notably, they are filled with an exceptional
number of small ossicles, more than 400 plates in the CD-
interray of the holotype specimen (ROM 44310a, Pl. 1,
figs. 1,3). Moreover, these plates are irregular in size,
shape, and arrangement and are unusually thin. Unlike the
majority of camerate crinoids, Stipatocrinus has interrays
without a well-developed gradient of progressively smaller

plates distally. Finally, Stipatocrinus lacks a primanal and
anitaxis but possesses a cylindrical anal tube composed of
plates resembling interbrachials.

Moore and Laudon (1943) considered small, irregular,
and numerous interbrachials to be a primitive character.
Brower (1974a) believed this characteristic to be advanced
in xenocrinids, crinoids with interray plating similar to
Stipatocrinus and occurring stratigraphically above sup-
posedly related camerates with fewer and larger interbra-
chials. However, this conclusion was based, in part, on a
misinterpretation of the phylogeny of xenocrinids (Brower,
pers. comm., 1986). Poorly known phylogenies of ca-
merate crinoids do not prove that either of these conflicting
theories is correct. However, we believe that ontogenetic
patterns of growth in primitive pelmatozoans and biostrati-
graphic evidence lend support to the Moore and Laudon
hypothesis.

Ontogeny of interbrachials in most camerate crinoids
was closely integrated and coordinated with increase in
size of the cup (Brower, 1974b). Originating near the
periphery of the tegmen, interbrachials were derived from
tegmen interambulacrals that were modified in size and
shape, becoming regular polygons as they were gradually
incorporated into interrays. Consequently, interrays of most
camerate crinoids typically show a well-developed gra-
dient of progressively smaller and more irregular inter-
brachials towards the tegmen. This gradient apparently
evolved early in the history of camerates, first appearing
in the Lower Ordovician crinoid Proxenocrinus.

Unlike that of most crinoids, ontogeny of interbrachials
in Stipatocrinus and the Late Ordovician crinoid Xeno-
crinus was poorly coordinated and poorly integrated with
overall growth of the cup. In these crinoids, interbrachials
grew more slowly than other calyx plates, necessitating
an intercalatory mode of growth (Brower, 1974a). As a
consequence of this mode of growth, interbrachials in Sti-
patocrinus and Xenocrinus are irregular in shape and ar-
rangement. Interbrachials could have been added anywhere
within interrays of these crinoids. This pattern 1s especially

‘well developed in Stipatocrinus, in which small interbra-

chials adjacent to larger interbrachials are scattered
throughout interrays. Intercalation increased the number
of interbrachials at a given level within the cup as this
crinoid grew. New interbrachials were also added by in-
corporation of interambulacrals. Interbrachials in Stipa-
tocrinus merge smoothly into the tegmen, indicating that
tegmen plates were incorporated into interrays, unaccom-
panied by substantial modification in size or shape of these
ossicles. Because of an intercalatory mode of growth, in-
terrays of Stipatocrinus and Xenocrinus display a poorly
developed gradient of progressively smaller plates distally.

The origin of camerate crinoids and their relationships
to other groups of pelmatozoans is poorly known. How-
ever, biostratigraphic evidence indicates that primitive

Cambrian pelmatozoans, including the probable crinoid
Echmatocrinus, are characterized by thecae possessing a
large number of plates irregular in shape and arrangement.
Moreover, thecae of these echinoderms typically show a
poorly developed gradient of progressively smaller plates
distally, and these plates commonly merge into the tegmen
with little differentiation. We suggest that similar features
in Stipatocrinus represent primitive characters.

The calyces of Stipatocrinus and Xenocrinus are similar
in that both possess large numbers of small irregular in-
terbrachials. However, Xenocrinus has a well-developed
anitaxial ridge, and configuration of the lowest circlet of
plates in Stipatocrinus is unlike that of Xenocrinus. We
conclude that similar morphology of interrays suggests
simply that these crinoids belong to archaic lineages prob-
ably not closely related to each other. In fact, superficial
similarity of these genera could be an example of con-
vergent evolution, although this possibility seems doubt-
ful. It implies repeated development of large numbers of
small interbrachials from ancestors with larger regular in-
terbrachials, which is contrary to evolutionary trends in
camerate lineages of simplifying cup structure by reducing
numbers of interbrachials or eliminating them altogether.

Even the assumption that Stipatocrinus 1s related to di-
plobathran camerates does not provide insight into the
evolution of this genus. Gaurocrinus and Reteocrinus, both
members of the Reteocrinidae, possess large numbers of
irregular interbrachials as in Stipatocrinus. However, these
crinoids have a primanal within the radial circlet and also
possess a prominent, ridged anitaxis. Furthermore, Reteo-
crinus has divergent characters, including interinfrabasal
gaps, spiculelike interbrachials, and apinnulate, branching
arms. None of the more advanced diplobathrans is at all
similar to Stipatocrinus. Thus, Stipatocrinus presently stands
by itself. We follow convention in tentatively assigning
this genus to the Monobathrida because only a single circlet
of plates is situated below the radials. However, we also
emphasize that the present monocyclic-dicyclic schism in
classification of crinoids, discussed by Warn (1975), may
obscure phylogenetic relationships. In fact, Stipatocrinus
may belong to a sister group of the Diplobathrida. Dis-
covery of additional genera related to Stipatocrinus may
readily justify erection of a new order to encompass these
unusual crinoids. We conclude that the several seemingly
primitive features of Stipatocrinus suggest that it may have
been a “‘living fossil’’ in late Llandoverian seas.

Stipatocrinus hulveri sp. nov.
Text-Figs. 1-8; Pl. 1, figs. 1-21; Pl. 2, figs. 1-12

TYPE MATERIAL
Numbered slabs containing approximately 75 calyces and
crowns associated with numerous columnals and columns

of this species are deposited in the collections of the De-
partment of Invertebrate Palaeontology at the Royal On-
tario Museum, catalogue numbers ROM 44309-44344.
Figured specimens: holotype ROM 44310a; paratypes ROM
44309a,b,d; 443 10b-44323.

OCCURRENCE
Reynales Formation, Wallington Member, exposed in the
gorge of the Genesee River, Rochester, New York.

ETYMOLOGY
The species is named in honour of Michael Hulver.

DIAGNOSIS
As for genus.

DESCRIPTION

Calyx steeply conical (height/width = 1.5—1.7), with highly
elevated ray ridges and depressed interrays. CD-interray
about 20 per cent wider than other interrays.

Four plates in lowest cup circlet, here designated as
basals, possibly representing infrabasals. Proximal circlet
comprising approximately I5 per cent of calyx height,
divided by sutures in AB-, DE-, and EA-interrays and in
C-ray, undivided in BC- and CD-interrays (Text-Figs. 3,
4A,B; Pl. 1, figs. 1,5,6,13—15). Basals two large and two
small (Pl. 1, fig. 13). Basals directly underlying A- and
E-ray radials five-sided, smaller (narrower) than larger six-
sided basals occupying AB- through DE-interrays (Text-
Figs. 3, 4A,B, 7; Pl. 1, figs. 5,6). Smaller basals elongate,
widest just above stem facet (PI. 1, fig. 5). Larger basals
expanding in width distally. Sutures passing through AE-
interray and C-ray divide basal circlet into bilaterally sym-
metrical halves (Text-Fig. 3). In AB-, DE-, and EA-
interrays basals meeting along straight suture for about
one-third to one-half of basal height, diverging above
forming concave margins of proximal interrays (Text-Fig.
3; Pl. 1, fig. 5). In BC- and CD-interrays these concave
margins less pronounced, not extending as close to stem
facet (Text-Figs. 3, 4A). Basals in A- and E-rays each
with ridge continuing onto A- and E-ray radials, respec-
tively. Larger basals meeting directly below C-ray along
straight suture for about 80 per cent of basal height, each
possessing two adradially directed ridges. Pair of ridges
divided by suture separating these basals merging up-
wards, forming single ridge on C-ray radial (Text-Figs.
3, 4A).

Radials and higher fixed brachials grooved ventrally (PI.
1, figs. 16,17,20,21), extremely narrow, forming highly
elevated ray ridges extending full width of brachials (Text-
Figs. 3, 4A,B, 8; Pl. 2, figs. 1-5). Radials t-shaped (height/
maximum width = 1.6—1.8). Each radial bisected near
midpoint by pair of short, narrow, laterally directed pro-
jections (Text-Figs. 3, 4A,B; Pl. 1, figs. 5,20). Projections

forming ridges lower in height than ray ridges, crossing
proximal interray areas, narrowly joining radials together.

First primibrachials rectangular, highly elongate (height/
width = 3.0—5.0), straight-sided. Second primibrachials
Y-shaped (height/width = 1.4—1.6), axillary (Pl. 1, fig.
10). Each ray bifurcating near centre of second primibra-
chial, forming two straight ray ridge segments continuing
upwards towards arms. First secundibrachials rectangular
(height/width = 1.5—1.9), each bearing a stout fixed pin-
nule bounded by interprimibrachials (PI. 1, figs. 1,4). Sec-
ond secundibrachials equidimensional (height/width = 1.0).
Succeeding fixed secundibrachials rectangular, wider than
high (height/width = 0.6—0.8). Arms free beyond third
to seventh secundibrachial.

Interrays filled with exceptionally numerous interbra-
chials (more than 400 ossicles in CD-interray of holotype
specimen, ROM 44310a; PI. 1, fig. 1). Interrays of smaller
individuals with fewer plates (Pl. 2, figs. 10,11). Inter-
brachials immediately above basals enclosed in suboval to
subtriangular depressed areas bounded above by lateral
projections of radials (Text-Figs. 3, 4B, 5; Pl. 1, fig. 19).
These enclosed areas smaller in BC- and CD-interrays than
in remaining interrays (Text-Figs. 3, 4A,B; Pl. 1, fig. 6).
Interbrachials irregular polygons, typically five- or six-
sided, varying from four- to seven-sided. Largest inter-
brachials commonly with rounded corners. Interrays dis-
playing poorly developed gradient of progressively smaller
plates distally; smaller plates occurring between larger plates
throughout interrays (Pl. 1, fig. 3). Interbrachials smooth,
without ornamentation, very thin (approximately 0.03 mm
thick), resting on black layer representing degraded or-
ganic matter (Text-Figs. 3, 4A; Pl. 1, fig. 5). Interray
areas loosely sutured to straight-sided ray series.

Primanal and anitaxis absent. Narrow cylindrical anal

1 m m , i

TextT-Fic. 5. Plate diagram of basals and proximal interbra-
chials in AB-interray of Stipatocrinus hulveri gen. et sp. nov.
Paratype ROM 44310b, PI. 2, fig. 19.

tube developed in CD-interray, eccentrically situated near
edge of tegmen (PI. 1, figs. 1,11; Pl. 2, figs. 1,9). Anal
tube incompletely preserved in available specimens, com-
posed of smooth polygonal plates resembling interbrachi-
als (Text-Fig. 6; Pl. 1, figs. 2,4).

Tegmen seen only in cross-section, forming shallow
dome consisting of polygonal plates resembling interbra-
chials in size and shape. Some tegminal plates nodose,
commonly bearing short spines (PI. 1, fig. 12).

Arms ten, pinnulate, relatively long (Table 1). Proximal
brachials in uniserial arrangement (PI. 1, fig. 5), rectan-
gular, wider than high (height/width = 0.4—0.6). Suc-
ceeding brachials cuneate, in immature biserial arrangement
in distal portions of arms (PI. 1, fig. 8). Pinnules incom-
pletely known. Pinnulars attached directly to free brachi-

TEXxT-FiG. 6. Plate diagram of anal tube of Stipatocrinus hul-
veri gen. et sp. nov. Anal plates resemble interbrachials. Dotted
area represents area damaged during preparation. Holotype ROM
44310a, Pl. 1, fig. 2.

als, short, quadrangular, tapering distally (Pl. 1, fig. 7).
Succeeding pinnules lath-shaped (height/width = 2.2—2.7).

Column transversely circular, heteromorphic, tapering
uniformly almost to a point distally (Pl. 2, figs. 4,5,8,10).
Proximal nodals biconcave in longitudinal cross-section
with thickened, rounded epifacets concealing adjacent in-
ternodals (Text-Fig. 7A,B; Pl. 1, fig. 18). Internodals rec-
tangular or slightly biconvex in longitudinal cross-section.

Proximal columnals thin (nodal height/width = 0.25—0.33,
internodal height/width = 0.06—0.13). Columnals becom-
ing successively thicker in distal portion of column (nodal
height/width = 0.28—0.36, internodal height/width = 0.17—
0.22). Noditaxis typically consisting of one nodal, two or
three second-order internodals, a first-order internodal, and
two or three second-order internodals (Text-Fig. 7A—D).
Lumen small, round (PI. 2, figs. 6,7).

TABLE 1. Measurements (in mm) of types of Stipatocrinus hulveri gen. et sp. nov.

Orientation of plate measurements as follows: ROM 44309a—below B- and C-rays (basal), C-ray (radial—
secundibrachial); RoM 44309b and 44310a—below C- and D-rays (basal), D-ray (radial—secundibrachial);
ROM 44310b—below B- and C-rays (basal), B-ray (radial—secundibrachial).

Paratype
Measurements ROM 44309a
Calyx height 13.7
Calyx width ll
Arm length 33.07
Proximal stem diameter Het)
Basal height 2.1
Basal width 2.1
Radial height 37
Radial width Dal
First primibrachial height 2.8
First primibrachial width 1.0
Second primibrachial height 2.4
Second primibrachial width 1.8
Second secundibrachial height 1.4
Second secundibrachial width 1.0
*Specimen crushed. Actual width less than indicated.
tDistal portions of arms not preserved.

1mm
aes |

\

=z
ND
z

Paratype Holotype Paratype
_ ROM 44309b ROM 44310a _ ROM 44310b
14, 1 18. 4 N32
Sa 10.5* a
— ss 18.07
2.8 3.1 Pes)
1.9 DD eS)
1.9 DS) DS)
3.6 3.8 3)-5)
si 2.0 we i)
3.6 3.8 32)
2 2. 0.89
Dell 2.9 DS)
1.9 2.0 IES
1.6 2.0 1.4
0.97 1.0 0.81

a IN Diss IN
‘ alex IN rake “8

C D

TEXT-FiG. 7. Diagrams of longitudinal cross-sections through pluricolumnals of Stipatocrinus hulveri gen.
et sp. nov. Nodals and internodals are indicated, respectively, as follows: N, 1 IN, 2 IN, 3 IN.

A. Pluricolumnal between 9 and 10 mm below cup of paratype ROM 44319, indicated by upper pair of
arrows on PI. 1, fig. 18. Very thin second-order internodals are not visible from exterior of proximal column.

B. Pluricolumnal between 26 and 28 mm below cup of paratype ROM 44319, indicated by lower pair of
arrows on PI. 1, fig. 18. Second-order internodal is incipient nodal. Note prominent, thickened epifacets of
nodals, which partly enclose adjacent third-order internodals.

C. Distal pluricolumnal of paratype Rom 44320, indicated by upper pair of arrows on PI. 1, fig. 9.

D. Distal pluricolumnal of paratype ROM 44320, indicated by lower pair of arrows on PI. 1, fig. 9.

9

Palaeoecology

Limited lateral extent of slabs bearing Stipatocrinus hul-
veri on a talus slope in the gorge of the Genesee River
and apparent absence of similar slabs in the cliff wall above
indicate that these crinoids comprised a highly localized
stand, or “‘garden,’’ on the seafloor. The area of seafloor
occupied by this stand, assuming that the majority of spec-
imens have been discovered, did not exceed 0.2 m?. This
occurrence represents a high-density stand (sensu Brower,
1973) with about 400 crinoids per square metre. Few fos-
sils, including poorly preserved specimens of the brachio-
pod Coolinia? and encrusting bryozoans are associated
with these crinoids (PI. 2, fig. 10). The horizon from which
the Stipatocrinus material was apparently derived is nearly
devoid of fossils, indicating that the seafloor surrounding
this stand was sparsely populated by skeletonized benthic
organisms. Stands of Early Silurian crinoids described by
Brett (1978) and Eckert (1984) also occur in poorly fos-
siliferous strata. Clustering of conspecific crinoids in these
environments may have conferred adaptive advantage by
providing viable breeding populations (Brower, 1973).
Polished slabs obtained by sectioning perpendicular to
bedding planes reveal that well-preserved Stipatocrinus
individuals consisting of nearly complete crowns with long
stems occur in calcisiltite adjacent to a thin encrinite (Text-
Fig. 8). Although it is not possible to demonstrate con-
clusively the sequence of deposition of these layers be-
cause the slabs were not recovered in situ, comparison
with stands of Early Silurian crinoids excavated in situ
(Eckert, 1984) and personal observations of occurrences
of well-preserved crinoids in the Middle Devonian Ham-
ilton Group of western New York and Ontario strongly
suggest that well-preserved Stipatocrinus individuals are
situated immediately above the encrinite. Consisting al-
most entirely of Stipatocrinus columnals, cup plates, and
arm fragments, the encrinite rests with a sharp lower con-
tact on plane-laminated, unfossiliferous calcisiltite. Com-

TeEXxT-Fic. 8. Vertical section through slab containing Stipa-
tocrinus hulveri gen. et sp. nov. Basal encrinite (En) is inferred
to represent lower surface of slab. Calcisiltite layer (Ca) above
encrinite shows well-preserved, sectioned cups and pluricol-
umnals of S. hulveri. Paratype ROM 44322.

plete calyces, typically lacking arms and columns, are
embedded in the lower surface of this encrinite.

In reconstructing the palaeoecology of this occurrence,
we infer that the Stipatocrinus hulveri stand originated
from a chance spatfall on a sparsely populated seafloor.
Most of these pioneer individuals attained maturity, as
indicated by the large size of radials in the encrinite (PI.
1, fig. 20). Death, decay, and subsequent disarticulation
of these crinoids under conditions of generally slow sedi-
mentation gradually formed a carpet of ossicles, repre-
sented by encrinite, below the stand. Resuspension of
ossicles by currents buried decaying, partly articulated,
individuals relatively quickly. Small crinoids, evidently
juveniles, associated with larger individuals indicate that
the stand survived for more than one generation. Even-
tually the stand was completely extirpated by rapid burial,
indicated by excellent preservation of articulated crinoids
in calcisiltite, displaying undulatory laminations. Burial
must have been rapid because modern crinoids exposed
on the seafloor typically decay and disarticulate quickly
after death (Meyer, 1971; Liddell, 1975; Meyer and Meyer,
1986).

In the Reynales Formation at Rochester, beds of Pen-
tamerus, a brachiopod that inhabited relatively shallow,
rough-water environments (Boucot, 1975; McKerrow, 1978)
alternate with sparsely fossiliferous strata deposited in rel-
atively quiescent, probably deeper water conditions. Thus,
occurrence of well-preserved Stipatocrinus specimens in
sparsely fossiliferous strata lacking Pentamerus is con-
sistent with a previous interpretation (Brett and Eckert,
1982) that occurrences of well-preserved crinoids are typ-
ically associated with quiet-water palaeoenvironments near
the limit of normal wave base but within reach of storm-
generated waves and currents. Several slabs bearing S.
hulveri show prominent, subparallel orientation of crowns
and columns suggestive of storm-generated currents during
or immediately preceeding burial (PI. 2, figs. 10,12). After
burial the crinoids rapidly decayed, but disarticulation was
prevented by overlying sediment and absence of biotur-
bation. Internal organs were not preserved in any speci-
mens of Stipatocrinus. However, a black carbonaceous
film representing degraded organic matter commonly cov-
ers inner surfaces of interbrachials (Text-Figs. 3, 4A; Pl.
1, figs. 5,11). A reducing, acidic environment was ap-
parently generated within the calyces as decay proceeded,
inducing formation of syngenetic pyrite on some speci-
mens. Acidic conditions caused dissolution of interbra-
chials in some individuals (Text-Figs. 3, 4A; Pl. 1, figs.
5,11). Dissolution probably occurred before lithification
because the crinoids are not preserved as steinkerns.

Many Stipatocrinus calyces are filled with sparry cal-
cite. These specimens are typically less crushed or flat-

tened than individuals filled with calcisiltite. Precipitation
of calcite within hollow calyces early in diagenesis may
have allowed the crinoids to resist compaction (see Sprin-
kle and Longman, 1982:69). However, it is also possible
that calcite was precipitated late in diagenesis after lithi-
fication. When calcite was absent, thinly plated interrays
of Stipatocrinus made these crinoids susceptible to com-
paction, distorting and flattening them.

Densely pinnulate arms and the flexibility of the prox-
imal portion of the column suggest that Stipatocrinus was
a rheophilic filter feeder. The t-shaped radials that bridge
proximal interray areas helped to strengthen the base of
the calyx. However, narrow brachials and unusually thin
interbrachials that do not interlock with the ray series made
the Stipatocrinus calyx relatively fragile in construction
when compared to most other camerates, perhaps restrict-
ing this crinoid to relatively low-energy environments.
Apparent absence of Stipatocrinus in the Pentamerus com-
munity is consistent with this interpretation.

Extremely narrow fixed brachials and t-shaped radials
made possible incorporation of more interbrachials in Sti-
patocrinus than any other described crinoid of similar size.
Functional morphology of this interray plating is conjec-
tural. The ease with which Stipatocrinus calyces were flat-
tened during compaction of the sediment, without breakage
of plates, demonstrates that the interrays were flexible in
life. Brower (1974a) postulated that large numbers of in-
terbrachials in Xenocrinus aided respiration by diffusion
of oxygen through plate sutures, enhanced by pumping
action of flexible interrays. Perhaps oxygen could diffuse
directly through the unusually thin (0.03 mm thick) inter-
brachials of Stipatocrinus. We note, however, that unlike
certain Ordovician crinoids with pore-bearing calyces, there

is no evidence of auxiliary respiratory structures in Early
Silurian crinoids. Numerous interbrachials in Stipatocrinus
may simply be a scaling phenomenon involving thickness/
width ratios of plates: reduction in plate thickness neces-
sitated smaller plate size in order to retain resistance to
breakage.

Unusually thin interray plating and a thick but very
narrow fixed ray series of the calyx of Stipatocrinus in-
corporated the smallest amount of calcite possible con-
sistent with requirements for sufficient strength and rigidity.
Thus, metabolic cost of calcite secretion in Stipatocrinus
was minimal compared to most other thicker-plated cri-
noids. By reducing metabolic cost, overall growth of Sti-
patocrinus may well have been rapid, perhaps allowing
early reproduction. If Stipatocrinus is assumed to have
colonized environments generally unfavourable to most
crinoids, as occurred during deposition of the lower Wal-
lington Limestone, an r-selective strategy of early repro-
duction may have ensured survival.

The column of Stipatocrinus 1s relatively short, not ex-
ceeding 10 cm in length, and tapers gradually almost to a
point distally. Curvature of the distal portion in paratype
ROM 44314 (PI. 2, fig. 8) and in other specimens suggests
that the column of Stipatocrinus was coiled distally around
other objects for anchorage. This mode of attachment is
characteristic of many camerates with gradually tapering,
heteromorphic columns, including Alisocrinus, Glypto-
crinus, Xenocrinus, and most diplobathrids (Brett, 1981).
Possession of a distally coiled column permitted attach-
ment to a wide variety of substrates (Brett, 1985) and was
probably a contributing factor in the survival of melocrin-
itids, glyptocrinids, dimerocrinitids, rhodocrinitids, and
the lineage leading to Stipatocrinus into the Silurian.

Acknowledgements

Diligent field work by Michael Hulver resulted in discov-
ery of the study material, and we are indebted to him for
making us aware of this occurrence. Additional specimens
were collected by Gordon Baird and Karla Parsons. George
C. McIntosh, James Brower, and James Sprinkle critically
reviewed the manuscript. Janet Waddington of the De-

partment of Invertebrate Palaeontology at the Royal On-
tario Museum provided curatorial services. Darkroom and
preparation facilities were provided by the Department of
Geological Sciences at the University of Rochester. Fi-
nancial support for this study was provided by the Geo-
logical Society of America as grant 3288-84 to Eckert.

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13

PLATE 1, figs. 1—21.

Stipatocrinus hulveri gen. et sp. nov. Reynales Formation, Rochester, New York. Specimens immersed
in ethanol.

1. CD-interray of well-preserved individual. Note absence of primanal and anitaxis. Proximal circlet is
divided by suture in DE-interray but not in CD-interray; t-shaped radials bridge proximal interray areas,
enclosing interbrachials between basals and lateral projections of radials. Narrow, highly raised brachials
enclose thinly plated interrays consisting of numerous, polygonal interbrachials. Distal interbrachials merge
with plates of anal tube and tegmen without differentiation. See also Text-Fig. 6; Pl. 1, figs. 24,10; Pl. 2,
fig. 1. Holotype Rom 44310a, x 3.5.

2. Cylindrical anal tube of above individual showing arrangement of irregular polygonal plates. Distal
portion of tube is missing. See Text-Fig. 6 for a diagram of this specimen. Holotype Rom 44310a, x 8.0.

3. CD-interray detail between first primibrachial and second secundibrachial. Interray, slightly separated
from C-ray in this individual, is composed of numerous polygonal interbrachials irregular in shape and
arrangement. Holotype ROM 44310a, x 7.0.

4. C-ray and adjoining interbrachials showing proximal portion of anal tube and first pinnular of fixed
pinnule borne by second secundibrachial. Holotype Rom 44310a, x 7.0.

5. Anterior view of nearly complete crown. Orientation of rays unknown. Interbrachials, apparently
dissolved during diagenesis, are absent in most of interray area, revealing underlying black layer representing
degraded organic matter. Interray areas below lateral projections of radials are subtriangular in this specimen.
Proximal free brachials are uniserial. See also Pl. 2, fig. 12. Paratype Rom 44311f, x 3.0.

6. Specimen centred on B-ray. Numerous irregular polygonal interbrachials are visible in BC-interray.
Basal circlet is divided by suture in AB-interray but not in BC-interray. See also Text-Fig. 5; Pl. 1, fig. 19;
Pl. 2, fig. 3. Paratype Rom 44310b, x 4.0.

7. Proximal arm detail. Note short pinnules. Paratype ROM 44321, x 5.0.

8. Distal portion of arm with cuneate brachials. Paratype RoM 44309d, x 5.0.

9. Longitudinal cross-section through distal column. Nodals have prominent, thickened epifacets. Typical
noditaxis consists, sequentially, of a nodal, two or three second-order internodals, a first-order internodal,
and two or three second-order internodals. See Text-Fig. 7C,D for diagrams of two noditaxes indicated here
by pairs of arrows. Paratype ROM 44320, x 4.0.

10. Intersecundibrachial detail between bifurcation of D-ray. Holotype Rom 44310a, x 6.0.

11. CD-interray of crown. Incomplete anal tube is outlined by black integument. Most interbrachials are
missing. See also Pl. 2, fig. 12. Paratype ROM 4431la, x 2.0.

12. Longitudinal cross-section through distal fixed secundibrachials and tegmen. Many tegminal plates
possess nodes or short spines. Paratype ROM 44315, x 6.0.

Figs. 13-16. Sequential series of cross-sections through lower portion of cup destroyed by progressive
grinding. C-ray is at upper left of each section.

13. Basals just above stem. Note small opening for lumen. Basal suture at upper left is directly below
C-ray. Two basals below B-, C-, and D-rays are larger than remaining basals.

14. Slightly higher section through basals showing initial development of ridges on rays.

15. Basals sectioned near top of cup with prominent ridges on rays.

16. Section through proximal portions of radials and interrays. Each radial has prominent ventral groove.

17. Cup transversely sectioned just below bifurcation of rays. Cup has been strongly compressed, dem-
onstrating flexibility of thinly plated interrays. Paratype ROM 44316, x 3.0.

18. Longitudinal cross-section through column and proximal portion of cup. One basal and part of adjoining
radial are visible. Proximal nodals are transversely biconcave with slightly thickened epifacets. Internodals
are typically transversely biconvex. See Text-Fig. 7A,B for diagrams of two noditaxes indicated here by
pairs of arrows. Paratype ROM 44319, x 3.0.

19. Proximal AB-interray area enclosed by basals and lateral projections of t-shaped radials. Numerous
irregular, polygonal interbrachials are visible. See Text-Fig. 5 for a diagram of this specimen. Paratype ROM
44310b, x 10.0.

20. Isolated radial showing characteristic lateral projections and deep ventral groove. Left projection is
incomplete. Paratype ROM 44323, x 5.0.

21. Transverse cross-section through three calyces, each sectioned near bifurcation of rays. Fixed brachials
contain prominent ventral groove. Paratype ROM 44313, x 3.0.

PLATE 2, figs. 1-12.

Stipatocrinus hulveri gen. et sp. nov. Reynales Formation, Rochester, New York. Blackened specimens
whitened with ammonium chloride.

1. CD-interray of holotype specimen. Suboval interbrachial area in CD-interray, bounded by a single basal
and t-shaped radials of C- and D-rays, is smaller than adjacent area in DE-interray, bounded below by two
basals. See also Text-Fig. 6; Pl. 1, figs. 14,10. Rom 44310a, X 3.5.

2. Lateral view of nearly complete crown centred on B-ray. See also Pl. 2, fig. 12. Paratype Rom 4431 1d,
x We).

3. Crown centred on B-ray. Suboval interbrachial area of proximal AB-interray is larger than adjacent
suboval area in BC-interray. See also Text-Fig. 5; Pl. 1, figs. 6,19. Paratype Rom 44310b, x 2.8.

4. Partial crown centred on C-ray. Proximal bifurcation of C-ray ridge continues on basals. See also PI.
2, fig. 12. Paratype RoM 44311b, x 2.8.

5. CD-interray view of crown with most of column. See also PI. 2, fig. 12. Paratype RoM 4431le, x 2.0.

6. Pluricolumnal. Two internodals are attached to nodal with prominent epifacet. Paratype ROM 44318b,
x 710:

7. Pluricolumnal. Internodal is attached to nodal displaying broad epifacet. Note small lumen. Paratype
ROM 44317a, X 7.0.

8. Incomplete column coiled distally. Paratype RoM 44314, x 2.0.

9. CD-interray of individual with proximal portion of anal tube. See also Pl. 2, fig. 12. Paratype ROM
443lla, x 3.0.

10. Small slab with nearly complete crown and column near centre of photograph, two additional partial
crowns and numerous pluricolumnals. These small specimens represent juvenile crinoids. Paratypes ROM
44312a—c, X 0.8.

11. Detail of above slab. Lower crown possesses two essentially complete arms. Paratypes ROM 44312a-c,
x 1.6.

12. Well-preserved crinoids on small slab. Specimens are oriented subparallel to each other, suggesting
unidirectional current at time of burial. Paratypes RoM 4431 la—-i, x 0.8.

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