Cacops (Amphibia : Labyrinthodontia) from the Fort Sill Locality, Lower Permian of Oklahoma

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Geology

Published by Field Museum of Natural History

Volume 37, No. 3 June 30, 1977

Cacops (Amphibia: Labyrinthodontia)

From the Fort Sill Locality,

Lower Permian of Oklahoma

John R. Bolt

Assistant Curator, Fossil Reptiles and Amphibians
Field Museum of Natural History

The Library of the

MRRU1978

ABSTRACT at Urbana-ChamP«*

The armored dissorophid (Super family Dissorophoidea ) labyrinthodont amphi-
bian Cacops aspidephorus is unusual in having a large otic notch closed posteriorly
by the tabular. Cacops was previously known only from the "Cacops Bone Bed,"
Lower Permian of Texas. Poor preservation makes this material difficult to study.
Excellently preserved, though disarticulated, Cacops material has now been recov-
ered from the Fort Sill fissure fills, which are probably very close in age to the "Ca-
cops Bone Bed." Identification of the Fort Sill material as Cacops is based on pala-
tines (primarily), armor scutes, and quadrates; the latter are here described for the
first time from Fort Sill. The Cacops quadrate resembles that of other dissorophoids
in having a posterodorsal process, which is unusual in the marked anterior expan-
sion of its dorsal end. Comparison with other dissorophoids having a closed otic
notch shows that Cacops is not unique in this anterior expansion of the process.
Orientation of the process can apparently be used to distinguish trematopsids with
a slit-like, closed (by the tabular) otic notch, from dissorophids. At least one such
trematopsid occurs at Fort Sill, and resembles Cacops in anterior expansion of the
process.

Ontogeny of Cacops is discussed, and it is concluded that: 1. Closure of the otic
notch by the tabular occured early in ontogeny; 2. Exclusion of the laterally-ex-
posed portion of the palatine from the orbital rim, a feature unique to Cacops among
known dissorophids, also developed early in ontogeny; 3. Growth-stages of Cacops
available at Fort Sill were all probably post-metamorphic. All were dentitionally
normal labyrinthodonts, with no trace of the "lissamphibian" dental features found
in the related Doleserpeton. This may be due, however, to the fact that Doleserpet on
is represented by less-mature specimens than is Cacops.

INTRODUCTION

Cacops aspidephorus is a large armored dissorophid amphibian.
Dissorophids belong to the labyrinthodont Superfamily Dissoro-

Library of Congress Catalog Card Number: 77-76917

Publication 1264 61 Uci^QG]£

62 FIELDIANA: GEOLOGY, VOLUME 37

phoidea, consisting of Dissorophidae, Doleserpetontidae, and Trem-
atopsidae (Bolt, 1969), plus Branchiosauridae and Micromelerpe-
tontidae (Boy, 1972). All definitely identifiable Cacops material
comes from the Lower Permian "Cacops Bone Bed" (hereafter
CBB), Baylor County, Texas. The CBB was exhausted long ago,
according to Williston (1911); in any case, it is now inaccessible
beneath Lake Kemp.

Cacops material from the CBB includes three complete and sev-
eral partial skulls. The skull is unusual in having the large otic
notch closed posteriorly by a ventral extension of the tabular ( fig.
1). This tabular extension meets a tall postero-dorsal process
from the quadrate, and overlaps part of the lateral face of the pro-
cess. Presence of a postero-dorsal process (hereafter abbreviated
PDP) on the quadrate is common, perhaps universal, in dissoro-
phoids (Bolt, 1969). In Cacops, however, the PDP is markedly ex-
panded anterodorsally (figs. 1, 3, 4), a feature not known in any
other dissorophoids. This unusual otic region and the skull as a
whole, have never been well described due to the hard matrix of the
CBB and the near-impossibility of tracing sutures in the available
material.

Two localities other than the CBB have been mentioned as pos-
sibly producing Cacops. Olson (1956, p. 320) tentatively referred
two humeri from, his locality FA to Cacops. This identification can-
not be confirmed; the humeri are probably dissorophid, but generi-
cally diagnostic characters in dissorophid humeri are not known at
present. I have suggested the possible presence of Cacops at the
Fort Sill locality, near Lawton, Oklahoma, based on scutes (detailed
description and comparison in Bolt, 1974a) and a highly distinctive
type of dissorophid palatine (briefly described in Bolt, 1974b). Posi-
tive identification was not possible at that time; possible ontoge-
netic changes in taxonomically important characters precluded defi-
nite identification using armor alone, even though the armor resem-
bles that of Cacops quite closely. Evidence for assignment of the
palatines to Cacops was only indirect, and thus inconclusive,
because of the difficulty of tracing sutures in then-available CBB
specimens.

In an effort to find suitable comparative material, preparation of
the last of Williston's CBB collection was undertaken during this
study. Several useful specimens of Cacops (among other genera)
were discovered, including two separated palatines and a quadrate.
Most of the CBB material has now been at least rough-prepared.

BOLT: CACOPS FROM LOWER PERMIAN 63

PDP

0 5 cm

Fig 1. Cacops aspidephorus from the Cacops Bone Bed, FM UC 649. Outline
drawing of skull in left lateral view; based on right side, reversed. Area within otic
notch ( shaded) is roughly cone-shaped, with base of cone directed laterally. Sutures
within the otic notch are unknown, but most of the area anterior to the postero-
dorsal process of the quadrate is occupied by the squamosal. Abbreviations: EN,
external naris; PDP, postero-dorsal process of quadrate; T, tabular; X, location of
distal end of stapes.

In addition to previously-reported material, possible Cacops
quadrates have now been identified at Fort Sill. This paper com-
pares the CBB palatines and quadrates with those from Fort Sill,
and concludes that the evidence supports identification of the Fort
Sill specimens as Cacops. Although all Fort Sill Cacops material
recovered to date is disarticulated, it is very well preserved and
covers a considerable size-range; it can thus make a significant
contribution to our knowledge of osteology and ontogeny in Cacops.

As a dissorophoid, Cacops is part of a radiation that may have
given rise to some or all of the living amphibians (lissamphibians;
this is a collective term which does not imply monophyly). The pos-
sibility of relationship was originally supported mainly by the pres-
sence of bicuspid, pedicellate (sensu Parsons and Williams, 1962)
marginal and fang teeth in Doleserpeton (Bolt 1969). This genus,
sole member of the Doleserpetontidae, is known only from Fort Sill.
Similar dental features have recently been found in some dissoro-
phids (Bolt, in press), and in Doleserpeton itself at least some of the
palatal denticles are now known to be pedicellate (Bolt, ms.). A
survey of dissorophoids for such "lissamphibian" characters is
desirable, but very difficult with most types of preservation. The
fine preservation of Fort Sill specimens has made it possible to
study the palatine denticles of Cacops; and, as explained below, the
morphology of marginal teeth can at least be inferred.

64 FIELDIANA: GEOLOGY, VOLUME 37

"Skull length" in this paper refers to length as measured in the
midline and in the plane of the skull table. Measurements were
taken between the tip of the snout and the posterior end^ of the
postparietals on the skull table.

My thanks to J. Hopson, who critically read the manuscript, and
to Z. Jastrzebski, who did the drawings. I thank Dolese Brothers
Company for permission to collect in the Richards Spur Quarry.

MATERIALS

Specimen repositories are indicated as follows: AMNH— Ameri-
can Museum of Natural History; FM — Field Museum of Natural
History; KU— Kansas University Museum of Natural History;
MCZ— Museum of Comparative Zoology, Harvard University.

The Fort Sill locality is a commercial limestone quarry in SW%
section 31, T4N, R11W, Comanche County, Oklahoma. Quarry
operations periodically expose clay-filled fissures, some of which
contain great numbers of small tetrapod bones. The fissure fills are
discarded as waste by the quarry operators, and most specimens
recorded from Fort Sill have come from the clay dumps. The age of
the fissure fills is unquestionably Lower Permian, and probably
close to that of the Arroyo Formation of Texas (Olson, 1967). Bones
from Fort Sill are usually disarticulated, but otherwise excellently
preserved.

The CBB is on Indian Creek in Baylor County, Texas. The fauna
is of Lower Permian age; according to Olson (1958), the CBB is in
either the upper Arroyo formation or the lower part of the Vale.
The original size of the pocket was about 6 ft. by 10 ft., and 2 ft.
thick (Williston, 1910, 1911).

MORPHOLOGY AND COMPARISON

Palatine— Dissorophid palatines from Fort Sill, tentatively re-
ferred to Cacops, were described and figured previously (Bolt,
1974b, text-figure 8); the figure is reproduced here in Figure 2.
These palatines have a laterally-exposed portion (LEP), as do most
(perhaps all) dissorophoids. A unique feature is exclusion of the
LEP from the orbital rim. This presumably occurred by means of a
secondary union of the lacrimal and jugal dorsal to the LEP. Two
partial skulls from the CBB (FM UR 2431 and UC 900) show a
LEP shaped like that in Figure 1, with a sutural separation between
the LEP and bone dorsal to it. The orbital rim is not preserved in

BOLT: CACOPS FROM LOWER PERMIAN

65

PTC

PTC?

Fig 2. Right palatine of Cacops, from the Fort Sill locality; FM PR 1034. Top, in
dorsolateral view; arrow indicates anterior. Bottom, in palatal view. Large denticles
occur medial and anterior to the fang teeth; small denticles (indicated only schema-
tically) cover most of the palatal surface. Abbreviations: CH, area bordering
choana; EC, contact area for ectopterygoid: LEP, laterally-exposed portion of
palatine; PF, area occupied by fang tooth (two such areas are shown); PTC, contact
area for pterygoid; VC, contact area for vomer.

either case, but the LEP was clearly excluded from it. Similarly,
two parallel cuts 5 mm. apart through the orbital floor of FM UR
2430 show a LEP outlined by sutures and separated from the orbital
rim by bone. Finally, a separated palatine (FM UR 2433) recently
recovered from the CBB collection very closely resembles the Fort

66 FIELDIANA: GEOLOGY, VOLUME 37

Sill palatines in shape of the LEP and its apparent exclusion from
the orbital rim. A second Cacops palatine from the CBB (FM UR
2432) is exposed only in ventral view.

Thirteen Cacops-like palatines are presently known from Fort
Sill. The largest, FM PR 1034, is complete (fig. 2) and about 3.5 cm.
long. This is about the same size as the separated palatines from the
CBB; exact comparison is impossible, since the thin anterior and
posterior portions of both CBB specimens are apparently some-
what damaged. Most of the Fort Sill specimens are broken, some
consisting of little more than the LEP. The smallest measurable
specimen is about 2.3 cm. long, and is considerably smaller in all
dimensions than the CBB palatines. Some of the less-complete
specimens were much smaller, probably about a centimeter long.
The LEP is similarly-shaped in all Fort Sill palatines, and was
clearly not exposed within the orbit.

Most of the ventral surface of each Cacops-like palatine from Fort
Sill is covered with monocuspid denticles (fig. 2); preparation has
necessarily removed denticles from the CBB specimens, so no com-
parison is possible. No trace of pedicely is visible in the Fort Sill
specimens. This was confirmed by examining a small palatine with
the scanning electron microscope. The denticles are largely intact,
but show no trace of pedicely.

The palatal surface shows clear contact areas for the ectoptery-
goid (presumably) and vomer (fig. 2). At least the posterior part of
the pterygoid contact area is coarsely striated; the original descrip-
tion (Bolt, 1974b) concluded that the pterygoid did not extend much
beyond that area, and thus did not reach the vomer. This conclusion
now seems less probable; the very thin medial border of the palatine
suggests that it may have been supported along its length by a nar-
row anterior extension of pterygoid. The CBB specimens are not
well enough preserved to provide a check on this suggestion. If
Cacops does have a pterygoid-vomer contact, it may not be the only
dissorophid with this primitive condition. Only in Tersomius tex-
ensis is it certain that there is no pterygoid- vomer contact (and even
here there is uncertainty as to the exact position of all sutures
around the pterygoid— cf. Carroll, 1964; Bolt, 1974b). The anterior
relationships of the pterygoid are obscure in all other described
dissorophids.

Quadrate— A total of 14 quadrates has been found which prob-
ably pertain to Cacops; all have a strong postero-dorsal process

BOLT: CACOPS FROM LOWER PERMIAN

67

H
5mm

Fig. 3. Cacops quadrate from Fort Sill, FM PR 1032, medial view in plane of pos-
tero-dorsal process. Abbreviations: AB, points between which (maximum) process
length was measured; CD, points between which basal length was measured;/? , the
process angle, is measured between the posterior border of the postero-dorsal pro-
cess, and the line formed by the junction of contact areas for the pterygoid (medi-
ally) and the squamosal + quadratojugal (laterally).

(PDP). In the largest of the quadrates, the PDP is markedly
expanded anteriorly (fig. 3). Some expansion is visible even in the
smallest examples (fig. 4). This type of expanded PDP can be seen
in the Cacops skull ( FM UC 649) figured by Williston ( 1910), and in
a separated quadrate from the CBB (FM UR 2434) which is about

68

FIELDIANA: GEOLOGY, VOLUME 37

0 3mm

Fig. 4. Cacops quadrate from Fort Sill, FM PR, 1033, medial view in plane of
postero-dorsal process.

the same size as that in the skull. The Fort Sill quadrates are consid-
erably smaller with, for example, a process length in the largest
(FM PR 1032; see fig. 3) of 1.2 cm. as compared to about 2.1 cm. in
FM UR 2434. Similarly, FM PR 1032 has a maximum basal length
(see fig. 3) of about 1.5 cm., compared to 2.1 cm., for FM UR 2434
from the CBB. Both the CBB and Fort Sill quadrates have a process

BOLT: CACOPS FROM LOWER PERMIAN 69

angle (see fig. 3) of about 75-85°, as measured in FM PR 1032 and
1033 and UR 2434.

The quadrate is sufficiently well preserved in a number of dis-
sorophoids, to establish the presence of a PDP. It is usually not
possible to be certain whether the process is expanded as in Cacops,
and no similar examples have been reported. Such an expansion is
clearly absent in Doleserpeton which is, however, a much smaller
animal than Cacops and has an open otic notch. Cacops is more ap-
propriately compared with other large dissorophoids having a
closed otic notch. There are only three such species: Longiscitula
houghae, Dissorophus multicinctus (both dissorophids), and
Trematops milleri (a trematopsid). These are also the only dissoro-
phoids known to have a closed otic notch, with the exception of the
Russian dissorophid Zygosaurus lucius which I cannot consider
because there is no useful published information on it and the only
known specimen has been lost. The three dissorophids (including
Cacops ) have very large otic notches closed by a tabular extension
which, in lateral view, stands at about 90° to the skull table. Long-
iscitula (FM UR 430; skull length about 12 cm.) has a PDP, and
there is some indication of expansion, but the area is very poorly
preserved. Dissorophus multicinctus (MCZ 2122-1; skull length
about 13.5 cm.) has an expanded postero-dorsal process, but the
quadrate is so damaged that the process angle and length cannot be
obtained. The process in D. multicinctus seems much thicker than
that of Cacops, and not as high. The latter feature could be partly
due to breakage; however, D. multicinctus has a considerably lower
skull than Cacops, and therefore a lower PDP would be expected.
The process angle in Longiscitula and D. multicinctus is probably
close to that of Cacops, since all have a nearly-vertical tabular
extension. A high process angle may be characteristic of dissoro-
phids, based on these genera plus Tersomius texensis (unexpanded,
relatively low PDP on small skull associated with holotype, AMNH
4719; process angle about 85°, like that in Doleserpeton). In con-
trast to the dissorophids, Trematops milleri (fig. 5) has a slit-like
otic notch and the posterior tabular extension is at about 45° to the
skull roof. The quadrate in such trematopsids should be readily
distinguishable from that in all dissorophids, based only on process
angle. This seems to be the case: the process angle in T. milleri
FM UC 1760 is about 35°. There is apparently no anterior expansion
of the process in T. milleri. Some trematopsids may, however, have
an expanded process: a single quadrate from Fort Sill (KU 34652)

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BOLT: CACOPS FROM LOWER PERMIAN 71

has an anteriorly-expanded PDP with a process angle of 35°, which
suggests trematopsid rather than dissorophid affinities.

DISCUSSION AND CONCLUSIONS

Identification of Cacops. — I believe that the palatine provides
convincing evidence for identification because it is a unique type
on the basis of comparison with most other dissorophoids ( the rela-
tionships and shape of the LEP cannot be determined in some
species). The armor is also good evidence, because it is reasonably
distinctive and can be compared with that of other armored dissoro-
phids (cf. Bolt, 1974a). The quadrate provides the weakest evidence
due to lack of comparative information for other dissorophoids,
although so far as known it resembles that of Cacops most closely.
The quadrate region of dissorophoids and labyrinthodonts in gener-
al will be treated in greater detail in a future paper.

In addition to the comparisons given above, another line of rea-
soning suggests that the isolated bones described are best assigned
to Cacops: The palatine and quadrate are easily distinguished from
those of the unarmored Doleserpeton, the most common dissoro-
phoid at Fort Sill. The next most common dissorophoid elements
(although actually rare) are those here assigned to Cacops. Other
dissorophoid armor scutes, quadrates, and palatines are extremely
rare in collections made to date. It is thus likely that the elements
assigned to Cacops at least belong to the same species. Identifica-
tion of the Cacops palatine makes it virtually certain that the
species is Cacops cf. C aspidephorus.

Ontogeny of Cacops— The Fort Sill specimens, with the exception
of the largest palatine, represent animals considerably smaller and
therefore probably younger than those known from the CBB. Just
as clearly, the Fort Sill animals were not larval-sized; as a rough
estimate, skull lengths probably lay in the range from about 12.5
cm. (the size of most CBB specimens) to 6 or 7 cm.

The shape and (especially) the relationships of the LEP are po-
tentially valuable taxonomic characters, but LEP ontogeny must be
better known before they can be used with confidence. It is inter-
esting that over a considerable size range, these characters are
stable in Cacops. It is therefore most unlikely that any of the
numerous dissorophid species with skull lengths of about 6 cm., and
a LEP which participates in the orbital rim, are juveniles of Cacops.

72 FIELDIANA: GEOLOGY, VOLUME 37

As noted above, a closed otic notch is restricted to the larger dis-
sorophoids. (Not all large dissorophoids appear to have closed otic
notches, but this requires further study.) This may simply reflect
failure to find juvenile skulls of the species with closed otic notches.
On the other hand, it seems at least as likely a priori that otic-notch
closure may have occurred rather late in ontogeny; some of the spe-
cies with open otic notches may thus be represented only by juve-
niles. Two types of evidence suggest that Cacops, at least, devel-
oped otic notch closure at a rather small skull size: direct evidence
comes from FM UR 2435, a partial left half of a Cacops skull from
the CBB discovered in the course of this study. The tip of the snout
is damaged in this specimen, but the position of the orbit and the
posterior end of the postparietal is clear. Skull length can be esti-
mated as about 6 cm., or no more than half the size of the Cacops
skulls described by Williston (1910) which were until now the only
ones available. This skull is thus smaller than that of most other
dissorophoid species (see text-figure 1 in DeMar, 1968; also Olson,
1941). Although the quadrate is missing in this specimen, the pre-
sence of a long ventral extension from the tabular indicates that it
almost certainly had a closed otic notch. Indirect evidence comes
from the Fort Sill Cacops quadrates. All have a rugose area, V-
shaped in outline, on the lateral face of the PDP. This area begins at
the dorsal border of the process and runs less than one-third of the
way down; it probably marks the contact of the tabular extension
with the quadrate. Presence of this area in even the smallest quad-
rates, thus suggests that the otic notch was closed even in small Ca-
cops specimens.

Presence of pedicellate denticles in Doleserpeton may be transi-
tory, and characteristic of a juvenile, early post-metamorphic stage
(Bolt, in press). The non-pedicellate palatine denticles of Cacops do
not indicate whether or not that genus passed through a similar
stage, in as much as the available palatines are all probably from
more mature individuals than are the Doleserpeton specimens.

Isolated marginal tooth-bearing bones of Cacops are not identifi-
able at present in the Fort Sill material. It is virtually certain, how-
ever, that at least some of the labyrinthodont maxillae, premaxillae,
and dentaries at Fort Sill pertain to Cacops. None of the labyrintho-
dont teeth (except those of Doleserpeton) at Fort Sill are either bi-
cuspid or pedicellate. Thus Cacops was probably a dentitionally
normal labyrinthodont, in the growth-stages preserved. This does
not exclude the possibility of a more or less Doleserpeton-\ike mar-

BOLT: CACOPS FROM LOWER PERMIAN 73

ginal dentition at younger stages as observed in Tersomius and
"cf.Broiliellus sp." (Bolt, in press).

REFERENCES

Bolt, J. R.

1969. Lissamphibian origins: possible protolissamphibian from the Lower Per-
mian of Oklahoma. Science, 166, pp. 888-891.

1974a. Armor of dissorophids (Amphibia: Labyrinthodontia): an examination of
its taxonomic use and report of a new occurrence. Jour. Paleontol., 48, pp. 135-
142.

1974b. Evolution and functional interpretation of some suture patterns in Paleo-
zoic labyrinthodont amphibians and other lower tetrapods. Jour. Paleontol.,
48, pp. 434-458.

In press. Dissorophoid relationships and ontogeny, and the origin of the Liss-
amphibia. Jour. Paleontol.
Boy. J. A.

1972. Die Branchosaurier (Amphibia) des saarpfalzischen Rotliegenden (Perm,
SW-DeutschlanH). Abhandl. hess. L.-Amt. Bodenforsch, 65, pp. 1-137.

Carroll, R. L.

1964. Early evolution of the dissorophid amphibians. Bull. Mus. Comp. Zool.,
131, pp. 161-250.

DeMar. R. E.
1968. The Permian labyrinthodont amphibian Dissorophus multicinctus, and
adaptations and phylogeny of the family Dissorophidae. Jour. Paleontol., 42,
pp. 1,210-1,242.

Olson. E. C.

1941. The family Trematopsidae. Jour. Geol., 49, pp. 149-176.

1956. Fauna of the Vale and Choza: 1 1. Lysorophus: Vale and Choza. Diplocaulus,

Cacops and Eryopidae: Choza. Fieldiana: Geol, 10, pp. 313-322.
1958. Fauna of the Vale and Choza: 14. Summary, review and integration of the

geology and the faunas. Fieldiana: Geol., 10, pp. 397-448.
1967. Early Permian vertebrates. Okla. GeoL Survey, Circular 74, pp. 1-111.
Parsons. T. S., and E. E. Williams
1962. The teeth of Amphibia and their relation to amphibian phylogeny. Jour.

Morphol. 110, pp. 373-390.

WlLLISTON, S. W.

1910. Cacops, Desmospondylus; new genera of Permian vertebrates. Jour. Geol.,
21, pp. 249-284.

1911. American Permian vertebrates. Univ. Chicago Press, Chicago. 145 pp.