Colosteus scutellatus (Newberry), a Primitive Temnospondyl Amphibian from the Middle ...

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NoAvMEiRtIaCtANesMUSEUM
PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024
Number 2770, pp. 1-41, figs. 1-14 November 8, 1983
Colosteus scutellatus (Newberry), a Primitive
Temnospondyl Amphibian from the Middle
Pennsylvanian of Linton, Ohio
ROBERT W. HOOK'
CONTENTS
Abstract 2
.....................................................................
Introduction 2
..................................................................
Acknowledgments 2
...........................................................
Abbreviations 3
...............................................................
Methods .................................................................... 3
Review ofPrevious Work .................. 4
....................................
Systematics 6
...................................................................
Description 7
...................................................................
Skull Roof 7
..................................................................
Palate .................................................................... 12
Parasphenoid and Braincase ............... 16
...................................
Mandible ................................................................... 16
Dentition 18
...................................................................
Dermal Sculpture and Lateral Line Canals ..................................... 19
Branchial Arches ............................................................ 20
Postcranial Remains ........................ ................................. 21
Occurrences ofColosteid Remains ............ .................................. 29
Characteristics and Composition ofthe Colosteidae ............................... 29
Shared Derived Characters ofthe Family ...................................... 29
Relationships Within the Family ............ 31
..................................
Relationships ofthe Colosteidae 32
........................................
The Status ofthe Order Temnospondyli ................... ............... 32
The Development ofthe Temnospondyl Otic Notch ............................ 33
Colosteids, Edopoids, and Trimerorhachoids ................................... 34
Systematic Conclusions .................... .................................... 35
Appendix 35
.....................................................................
Literature Cited ............................................................... 37
'Coal Geology Research Group, DepartmentofGeology, University ofKentucky, Lexington, Kentucky.
Copyright © American Museum ofNatural History 1983 ISSN 0003-0082 / Price$3.40
2 AMERICAN MUSEUM NOVITATES NO. 2770
ABSTRACT
Colosteusscutellatus (Newberry), known exclu- (Tatarinov, 1964)isrecommended intheabsence
sively from the classic Coal Measure locality of ofsharedderived characters indicatinga closere-
Linton, Ohio, is the genotype and youngest rep- lationship between the colosteids and any other
resentativeoftheColosteidae, anarchaicgroupof knowntemnospondyls.Thestructureofthestapes
temnospondylsthatalsoincludesPholidogasterand and skull roofsuggests that the colosteoids may
Greererpeton. The colosteids are a monophyletic representtheplesiomorphicsistergroupofalloth-
groupdistinguishedfromothertemnospondylsby er temnospondyls.
massive stapes and no otic notch; elongate pre- AnoverviewofthestatusoftheTemnospondyli
frontal contacting narial border, premaxilla, and indicates that exclusion of the loxommatoids is
maxilla; intertemporal reduced or absent with justified, but that a possible microsaur-temno-
broad postorbital-parietal contact; single pair of spondyl relationship circumvents the possibility
premaxillarytusks;andsingle,elongateMeckelian oftemnospondyl monophyly.
fenestra. The use ofthe superfamily Colosteoidea
INTRODUCTION
The Temnospondyli are the largest and burkemorani Romer, a Colosteus-like form
possibly most diverse order of fossil am- from the Mississippian of West Virginia, it
phibians. Despite an impressive representa- became evident that the colosteids represent
tion of Late Paleozoic and Triassic forms, anarchaiclineagethatmightprovideinsights
temnospondyls older than Pennsylvanian or into the early evolution oftemnospondyls, if
Westphalianagearevirtuallyunknown. Con- not all Paleozoic amphibians. Subsequent
sequently, the astonishing array of temno- study of additional colosteid material (Ro-
spondyls that first appears in the Coal Mea- mer, 1972; Panchen, 1975; Smithson, 1982)
sures of North America and Europe has has identified the need for a more detailed
consistently frustrated paleontologists who understanding ofthe genotype ofthe family.
wish to incorporate at least a modicum of The objective of the present paper is to
phylogenyintheirclassificationsoftheorder. provide a thorough description ofthe genus
The variety and abundance ofPennsylva- Colosteusandanaccuratecharacterization of
nian temnospondyls is nowhere better doc- theColosteidae. Althoughtheaffinitiesofthe
umented than in collections acquired from family are also considered, re-evaluation of
the once-active coal mines ofLinton, Ohio. other primitive temnospondyls is necessary
In addition to a dozen species offishes and before the problem ofinterrelationships can
ascoreofothertetrapods,thisprolificlocality be fully addressed.
has produced seven temnospondyl genera,
four of which are unique to Linton (Hook, ACKNOWLEDGMENTS
1981). The most common of these indige-
nous temnospondyls is Colosteusscutellatus, I amgreatly indebtedto Dr. Donald Baird,
a heavily scaled amphibian with an elongate whose commitment over the past 30 years
body and diminutive limbs. Because similar to the collection, preparation, and identifi-
forms are unknown from younger deposits, cationofLintonfossilsmadethepresentstudy
such as the Texas redbeds (Romer, 1935), possible. I am also grateful to Dr. Robert R.
early workersgenerally considered Colosteus Reisz for support and thoughtful criticism.
as a novel adaptation to the coal swamp en- My thanks are due to Dr. Andrew R. Mil-
vironment. Thus, after a somewhat check- ner, Messrs. John Chom, Stephen Godfrey,
ered taxonomic history, Colosteus and the TimothyR. Smithson, and Carl F. Wellstead
family to which it gives its name, the Colos- for free exchange ofinformation on unpub-
teidae, were removed from the main line lished material; to Dr. Robert L. Carroll for
of temnospondyl evolution (Romer, 1947, initially directing my attention to the need
1966). for a review ofthe Linton colosteids and for
Withthe 1969 description ofGreererpeton making available unpublished drawings by
1983 HOOK: COLOSTEUSSCUTELLATUSNEWBERRY 3
Mrs. Pamela Gaskill; to Drs. Richard Lund YPM, PeabodyMuseum ofNatural History, Yale
andKathy V. Bossy forloans ofpeels ofLin- University
ton specimens; to Dr. Malcolm J. Heaton for
interest in my work and advice on the prep- ANATOMICAL
aration ofspecimens and figures; to Ms. Di- a, angular
ane Scott for helpful suggestions in the pro- a.p.f., anterior palatal fenestra
duction of illustrations; and to Mr. Steven art, articular
Jaunzems for expert photographic services. c, clavicle
I also thank Drs. Anne E. Fry and Dennis cb, ceratobranchial ossifications
Radabaugh ofOhio Wesleyan University for ch, choana
c.r., conical recess
theirassistanceinrecoveringDr. Baird'speels
ct, cultriform process
from the research materials of the late Dr.
cth, cleithrum
JohnN.Chase. Dr. RobertW.MorrisofWit-
co, coronoid
tenbergUniversity and Mr. Michael C. Han- d, dentary
sen ofthe Ohio Geological Survey provided ect, ectopterygoid
valuable guidance in the early stages ofthis eo, exoccipital
work. f, frontal
It is similarly a pleasure to acknowledge h, humerus
the assistance of individuals at institutions hb, hypobranchial cartilage
where I have studied Linton material. These i, interclavicle
ic, intercentrum
include Drs. Eugene S. Gaffney and John G.
im.f., intermandibular fenestra
Maisey, American Museum ofNatural His-
j,jugal
tory; Dr. Angela C. Milner, British Museum
1, lacrimal
(NaturalHistory);Dr. DavidS. Berman, Car- m, maxilla
negie Museum of Natural History; Dr. Mi- n, nasal
chael E. Williams, Cleveland Museum of p, parietal
Natural History; Dr. JohnR. Bolt, Field Mu- pal, palatine
seum ofNatural History; Dr. Donald Brink- pa.f., para-articular foramen
man and Mr. Charles R. Schaff, Museum of pra, prearticular
Comparative Zoology, Harvard University; pc, pleurocentrum
pf, postfrontal
Dr. StigM. Bergstrom, OrtonMuseum, Ohio
pl, pleuracanth shark tooth
StateUniversity; andMs. RuthL. Elder, Mu-
pm, premaxilla
seum ofPaleontology, University ofMichi-
po, postorbital
gan. pp, postparietal
Drs. C. S. Churcher, Thomas S. Parsons, prf, prefrontal
and P. J. Pointing read an early version of pt, pterygoid
the manuscript. The suggestions of Drs. qj, quadratojugal
Baird and Milner improved the final draft. r, radius
sa, surangular
ABBREVIATIONS sp, splenial
spp, postsplenial
INSTITUTIONAL st, supratemporal
t, tabular
AMNH, American Museum ofNatural History
u, ulna
BM[NH], British Museum (Natural History)
u.p., uncinate process
CM, Carnegie Museum ofNatural History
v, vomer
FMNH, Field Museum ofNatural History
I-IV, digits ofmanus
MCZ,MuseumofComparativeZoology,Harvard
University
OSU, Orton Museum, Ohio State University METHODS
PU, Museum ofNatural History, Princeton Uni-
Vertebrateremainsfrom Lintonhavebeen
versity
UMMP, Museum ofPaleontology, University of reducedtovirtuallytwo dimensionsbypost-
Michigan mortem crushing. Early descriptive efforts
4 AMERICAN MUSEUM NOVITATES NO. 2770
werefurthervexed bythepartial orcomplete corded with the description; further dimen-
pyritization oftheoriginal bone material (see sions may be taken directly from the speci-
Moodie, 1915). It was not until the 1950s, men drawings ifnecessary.
when the technique ofacid-etching was fol- The present study considers the morphol-
lowed by the use oflatex as a microcasting ogy ofan animal whose remains present no
compound (Baird, 1955), that detailed study perceivablecharacteristicsfromwhichsexual
ofLinton specimens became feasible. In this maturity or absolute age can be inferred.
innovative manner, Bairdhasprepared most Consequently, the terms subadult and adult
oftheimportantvertebrate materialfrom this are based arbitrarily on absolute size, not de-
locality. Usingthe spray technique described velopmental stage: specimens with an esti-
byHeaton (1980b), I havecasttheremaining mated skull length (measured along the dor-
unpreparedtemnospondyl specimens ofLin- sal midline) less than 15 cm. are considered
toncollections ofNorthAmerican museums. to be subadults. Although semantically in-
These latex "peels" provide detailed casts congruent, this usage provides a means by
fromwhichstudyofColosteusandotherLin- which large, diagnostic materials can be dif-
ton amphibians can proceed. ferentiated from smaller specimens that may
The drawing of significant Linton speci- lack the apomorphic states produced by al-
mens is necessitated by the generally inade- lometricgrowth(A. R. Milner, 1980a). With-
quate representation achieved by photogra- out this discrimination, subadults may form
phyalone. Ratherthanusingstandardcamera the basis of erroneous phylogenetic state-
lucida orgrid ocular techniques (Carroll and ments-the classic example being the infa-
Gaskill, 1978), drawings were traced from mous "order" Phyllospondyli (Romer, 1939).
twofoldphotographicenlargementsontomy-
lardrafting film while thecorresponding peel
REVIEW OF PREVIOUS WORK
wasexamined underhigh magnification. This
method is not only faster than those cited The taxonomic histories of most speci-
above, but also more accurate because it re- mens presently referred to Colosteusare tor-
ducestheamountofperipheral distortion and tuously complex. Since such details are of
allowsfreemovementofthespecimenduring littlegeneral interest, theirtreatmenthasbeen
drawing. relegated to the Appendix. It is appropriate,
Reconstructionsweredraftedonpaperand however, tosummarizepreviousworkbyway
based largely on specimen drawings. Resto- oftracingthepublication historyofthegenus
ration ofthe skull in dorsal view (fig. 1A) is Colosteus and the family Colosteidae.
derived from several nearly complete sub- The first report of fossil vertebrates from
adultskullsofintermediate size(average skull the Ohio Diamond Coal Company Mines at
length of 9 cm.). The reconstruction of the Linton was given by J. S. Newberry in 1856;
palate(fig. 1B)isbasedonfoursubadultspec- it included a briefdescription ofPygopterus
imens whose estimated skull lengths range scutellatus, a supposedly new species of pa-
from 5.5 to 12 cm. Palatal areas not repre- leoniscoidfish. Althoughnofigureswere sup-
sented by actual remains (about 35% ofthe plied or specific specimens adequately de-
composite) were restored with slight modi- scribed, a general picture ofa heavily scaled,
ficationsafter Greererpeton, acolosteidwhose elongate form with flattened head and point-
palatal architecture is reasonably well docu- ed snout was established.
mented (Smithson, 1982). In the absence of In 1869, E. D. Cope erectedthe batrachian
adequate information on the occiput of Co- genus Colosteus on the basis ofLinton ma-
losteus, no reconstruction ofthis region has teriallenthim byNewberry. Copecitedthree
been attempted. species, C. crassiscutatus, C. marshii and C.
Accurate measurement ofLinton fossils is foveatus, and provided measurements by
madedifficult bythecrushed and incomplete which the type specimens can be identified
nature ofspecimens. As such, it is not prac- today. However, Copelateradmitted(1871a,
tical to attempt a conventional tabulation of p. 41) that in describing the type species, C.
dimensions. Incidental measurements arere- crassiscutatus, he had "overlooked" New-
1983 HOOK: COLOSTEUS SCUTELLATUSNEWBERRY 5
berry's original account of P. scutellatus, ropleura, and the familial name lapsed to the
thereby implying that both taxa were inad- Sauropleuridae (Hay, 1902). This oversight
vertently based on the same specimen. Since was amplified by R. L. Moodie, who, in a
Pygopterus was (and is) a valid fish genus, seriesofpapersculminatingina 1916 mono-
andthematerialinquestionwascertainlynot graph, compounded existing taxonomic
piscine (Cope, 1873), Cope recognized the problems with additional errors of his own
proper combination of Colosteus scutellatus invention (see Appendix).
(Newberry, 1856) for the type species. With In an ambitious, ifnot commendable, at-
this synonymy, Colosteus predates Amphi- tempt to obtain "a reduction in the number
bamus ("Raniceps," "Pelion") lyelli (Wy- ofspecies" at Linton, A. S. Romer (1930, p.
man, 1857) as the first tetrapod recorded- 79) resurrected Colosteus but retained only
albeit as a fish-from the Linton deposit. the type species in his redescription of the
Newberry also described (1856) and later genus. Although he corrected many existing
figured (1873, pl. 39, fig. 6) Rhizodus angus- mistakes, Romer "committed some new
tus, a presumed crossopterygian fish from ones" himself(Romer, 1968, p. 67). Partic-
Linton. Romer (1930) noted that the type of ularly unfortunate was his attempt to aug-
this species was unknown and, on the basis ment the postcranially impoverished sample
ofNewberry's figure, recordedR. angustusas ofColosteus with a sizable quantity ofhead-
a synonym of C. scutellatus since the latter less "lepospondyl" material, described orig-
species has page priority. However, because inally by Cope as Molgophisand Pleuroptyx.
the description and figure ofR. angustus are Theimprobable nature ofthisgraftwaselab-
nondiagnostic (there is nothingtobaritfrom orated upon by Steen (1931) and merits no
being any one of the larger Linton labyrin- further consideration.
thodonts) and renewed search for the speci- Romer (1930) also reinstated the family
men has been unsuccessful, it may be thank- Colosteidae in which he associated a second
fullyregardedasa nomendubiumand nomen Linton genus, Erpetosaurus, with the geno-
oblitum. type while transferring Sauropleura to the
In an 187lb summary ofthe "Batrachian Urocordylidae and Amphibamus (as "Pe-
Fauna" ofLinton, Cope erected a new form, lion") to the Peliontidae (subsequently as-
Oestocephalus marshii, without description. signedtotheDissorophidaebyCarroll, 1964).
He later referred this name to Ptyonius Because most of his material consisted of
marshii (Cope, 1874) and revealed that both poorly ossified, branchiosaur-like subadults,
taxa were based on his 1869 description of Romer placed the family among the Phyl-
C. marshii; recent review ofthe urocordylid lospondyli; similarly influenced by the work
nectrideans has upheld this synonymy (Bos- ofWatson (1921), Steen (1931) followed this
sy, Ms). In the same 187lb report, Cope mistakeninterpretation. Upondissolution of
erected another nomen nudum, Colosteus the phyllospondyls, Romer deemed Colos-
pauciradiatus, onlytosupplydescription and teus and Erpetosaurus to be primitive rha-
figures in subsequent papers (1874, 1875). chitomes (1939) that had descended from
The holotype (AMNH 6920, fig. 1 lA) ofthis ichthyostegids (1945), and separated, there-
taxon is an interclavicle that was originally fore, from the main line of temnospondyl
includedin the C. crassiscutatusparatype se- evolution (1947).
ries (Cope, 1869, p. 23; contra 1874, p. 275 Jarvik(1948, 1952) rejectedthepossibility
and 1875, p. 408); however, itdoesnot merit ofa close relationship between Ichthyostega
specific separation because it cannot be dif- and colosteids, but proposed no alternative
ferentiated from comparably sized interclav- placement foreither ColosteusorErpetosau-
icles ofthe type species. rus. This dissent was followed by Lehman
ThefamilyColosteidaewaserectedbyCope (1955), who recognized the "?Colosteidea"
in 1875 to accommodate Colosteus, Sauro- as a superfamily ofthe suborder Rachitomi
pleura, and Amphibamus. However, in one [sic]. Through four volumes of the Bibliog-
ofhislastpapers, Cope(1897) madethe mis- raphy ofFossil Vertebrates (Camp and Alli-
take of synonymizing Colosteus with Sau- son, 1961; Camp et al., 1964, 1968, 1972),
6 AMERICAN MUSEUM NOVITATES NO. 2770
the Colosteidae was included with the Elpis- affinities of Erpetosaurus lie closer to saur-
tostegidae and Otocratiidae in the non-rha- erpetontid trimerorhachoids than to colos-
chitomous suborder Elpistostegalia. More teids (Hook, 1980).
appropriately, Tatarinov (1964) erected the
superfamily Colosteoidea under the Rha- SYSTEMATICS
chitomi andrecognizedtwofamilies, the Co-
CLASS AMPHIBIA
losteidaeandOtocratiidae. Romer, inthelast
ORDERTEMNOSPONDYLI
edition of Vertebrate Paleontology (1966),
SUPERFAMILY COLOSTEOIDEA
questioned his own assignment ofthe colos-
TATARINOV, 1964, SENSUNOVUM
teids to the superfamily Edopoidea, and, at
a later date, indicated further apprehension EMENDED DIAGNOSIS: Primitive tem-
in stating that the two Linton forms "ap- nospondylamphibianscharacterizedbymas-
proach the metoposaurs more closely than sive stapes, extensive tabular-squamosal
the trimerorhachids" (1968, p. 78). contact, and no otic notch; elongate prefron-
The discovery of a Mississippian-age co- tal reaches external naris, contacting pre-
losteid did surprisingly little to clarify the maxilla and maxilla, excluding lacrimal and
phylogenetic position of the family. As the nasalfrom narial opening; intertemporal mi-
first describable non-loxommatoid temno- nute or absent, broad postorbital-parietal
spondyl from the Lower Carboniferous, contact; single pair ofpremaxillary tusks on
GreererpetonburkemoraniRomer(1969)ap- posterolateral palatal flange; single, elongate
pearedtobeidentical inmanyrespectstothe Meckelian fenestra; approximately forty pre-
Pennsylvanian-age Colosteus. Panchen(1975) sacralvertebrae; extensivedorsal andventral
subsequently concluded that two problemat- scalation, ventral scales rhomboidal with
ical labyrinthodonts from the British Lower crenulated posterior margins.
Carboniferous, Otocratia modesta Watson Differentiated from edopoids by well-
(1929) and Pholidogasterpisciformis Huxley developed lateral line system, marginally sit-
(1862), represented a single taxon that was uated external nares, no exposure of septo-
very similarto Greererpeton. Although these maxilla on skull roof, orbital lacrimal, ac-
important discoveries led to the realization cessory tusks on palatine and ectopterygoid,
of the great antiquity ofthe colosteid stock separate sphenethmoid and otico-occipital
(Panchen, 1972, 1973), noattemptwasmade braincase regions, and retention of anterior
toreconcile suchwithexistingclassifications. flangeandentepicondylarforamenonthehu-
Thus, in the most recent comprehensive merus.
scheme of amphibian classification (Carroll Distinguished from trimerorhachoids by
and Winer, 1977), the Colosteidae consisted laterally directed external nares, narrow in-
ofPholidogaster, Greererpeton, Colosteus, and terpterygoid vacuities completely enclosed by
Erpetosaurus, and was assigned to the Tri- pterygoids, thin cultriform process not su-
merorhachoidea. tured to vomers on palatal surface, premax-
As reported by various workers (Romer, illa borders choana, no vomerine tusks, and
1968; Panchen, 1975), the late Dr. John N. dentaryteethmarkedlylargerthanmaxillary.
Chase, in collaboration with Dr. Baird, had
begun a redescription of Colosteus and Er- FAMILY COLOSTEIDAE COPE, 1875
petosaurus. Before his death in 1977, Dr.
DIAGNOSIS: As for the superfamily, which
Chasehadphotographedpeelsofappropriate
is monotypic.
specimens and had initiated drawing efforts
ofimportant material. In 1979, with the as-
GENUS COLOSTEUSCOPE, 1869
sistance of Dr. Baird, I was able to recover
the peels formerly in Dr. Chase's possession TYPE SPECIES: Colosteus scutellatus (New-
and to critically evaluate the association of berry, 1856).
Erpetosaurus with the Colosteidae. On the DIAGNOSIS: Colosteoid temnospondyl
basis ofthis work, which will be reported in characterized by only three bones,jugal, lac-
full at a later date, it is apparent that the rimal, and postfrontal, forming orbital mar-
1983 HOOK: COLOSTEUS SCUTELLATUSNEWBERRY 7
gin; open lateral line system; single row of LeptophractuslineolatusCope, 1877,p. 576;as C.
minute coronoid teeth. Dorsal scalation re- scutellatus, Romer, 1930, pp. 100-101, 106.
sembles gastralia. - Megalocephalus lineolatus (Cope, 1877);
Beaumont, 1977, pp. 73-76.
Anisodexis enchodus Cope, 1885, p. 406; as C.
Colosteus scutellatus (Newberry, 1856)
scutellatus, Romer, 1930, pp. 100-101, 106.
SYNONYMY: - M. lineolatus (Cope, 1877); NEW SYNON-
YMY.
Pygopterus scutellatus Newberry, 1856, p. 98. Diceratosaurus robustus Moodie, 1909b, pp. 67-
Colosteus crassiscutatus Cope, 1869, p. 23. 69, fig. 5; as C. scutellatus, Romer, 1930, pp.
Colosteusscutellatus, Cope 1871a, p. 41; 1874, p. 101, 106, fig. 10.
275; 1875, pp. 407-408, pl. 33, fig. 1, pl. 34, = Erpetosaurus radiatus (Cope, 1874); NEW
fig. 2; 1877, p. 578. Romer, 1930, pp. 100- SYNONYMY.
108,figs.8 (part),9,11.Steen, 1931,pp. 858-
860, figs. 6, 7, p1. 2, fig. 1. SPECIFIC DIAGNOSIS: As for genus.
Colosteuspauciradiatus Cope 187lb, p. 177 (no- HOLOTYPE: AMNH 6916, formerly 8584G
men nudum); 1874, p. 275; 1875, p. 408, pl. and 8666G ofColumbia University, collect-
40, figs. 1, 2. ed by Prof. John S. Newberry (ca. 1855): lat-
Sauropleura scutellata, Cope, 1897, pp. 86, 88. erally compressed anterior portion ofa sub-
Moodie, 1909a, p. 26; 1916, pp. 156-157, pl.
adult individual, including skull, mandibles,
14, fig. 3, pl. 21, fig. 5.
partial ribs, incomplete pectoral girdle and
Sauropleura pauciradiata Cope, 1897, p. 88.
scalation; preserved in counterpart blocks.
Moodie, 1916, pp. 158-160, fig. 34.
HORIZON: Cannel coal below coal seam
SauropleuralongidentataMoodie, 1909b, pp. 74-
76, figs. 18, 19; 1916, pp. 160-161, pl. 16, identified as the Upper Freeport Coal (New-
figs. 2, 3. berry, 1871, 1874), AlleghenyGroup, Middle
Macrerpeton deani Moodie, 1916, pp. 184-185, Pennsylvanian; equivalent to late Westpha-
fig. 40, pl. 21, figs. 1, 2. lian D ofEurope (Baird, 1964).
LOCALITY: Coal mines originally owned by
the Ohio Diamond Coal Company (Murphy,
NON:
1980), Linton, Saline Township, Jefferson
Rhizodus angustus Newberry, 1856, p. 99; as C. County, Ohio; approximately 2.5 km. south
scutellatus, Romer, 1930, pp. 100-101, 106. ofWellsville, Ohio.
= nomen dubium, nomen oblitum. HYPODIGM: See Appendix.
Molgophis macrurus Cope, 1868, pp. 220-221;
questionably assigned to C. scutellatus, Ro-
mer, 1930, pp. 101, 106. DESCRIPTION
= M. macrurus, Romer, 1952, p. 76.
Colosteusfoveatus Cope, 1869, p. 24. SKULL ROOF
= Saurerpeton obtusum (Cope, 1868); NEW The skull is a flat, posteriorly broad struc-
SYNONYMY.
turewithgently slopingcheeks. Indorsal view
Colosteus marshii Cope, 1869, p. 24.
(fig. 1A), the outline ofthe skull and position
= Ptyonius marshii Cope, 1874, p. 265.
Molgophis brevicostatus Cope, 1875, p. 369, pl. of the orbits bear resemblance to the long-
44, fig. 1; questionably assigned to C. scutel- snoutedtrimerorhachoidNeldasaurus(Chase,
latus, Romer, 1930, pp. 101, 106. 1965); smaller skulls show proportionally
= M. macrurus Cope, 1868; NEW SYNONY- larger orbits and shorter snout lengths.
MY (Wellstead, personal commun.). Whether or not the antorbital length of the
Pleuroptyx clavatus Cope, 1875, pp. 370-371, pl. largest skulls would have equaled that of
44, fig. 2; questionably assigned to C. scutel- Greererpeton is not known. The skull width
latus, Romer, 1930, pp. 101, 106. isgreatestjustanteriortothejawarticulation
= P. clavatus; Steen, 1931, p. 860. and is roughly 75 percent ofthe skull length.
Sauropleura newberryi Cope, 1875, pp. 404-405,
Although the posterior margin ofthe skull is
pl. 37, fig. 2; as C. scutellatus, Romer, 1930,
modestly embayed in the area of the post-
p. 100 (only).
- Stegops newberryi (Cope, 1875); Hook and parietal-tabular suture, there is no suggestion
Baird, in press. ofan otic notch. The orbits are directed dor-
8 AMERICAN MUSEUM NOVITATES NO. 2770
A B
C
FIG. 1. Colosteus scutellatus (Newberry). Restoration ofsubadult skull and mandible. A, skull in
dorsal view; B, skull in ventral view; C, skull anddetached mandible in lateral view. Scaleequals 1 cm.
sally with their lateral margins slightly lower act nature ofthe anterior portion ofthe pre-
thanthe medial. Incontrasttocontemporary maxillary-nasalsutureisuncertain. Although
edopoids and trimerorhachoids, the external the evidence is equivocal, rostral fenestrae,
nares are situated near the skull margin and as found occasionally in the loxommatid
have no dorsal exposure. Megalocephalus pachycephalus (Beaumont,
The premaxilla is a robust, tusk-bearing 1977),mayhaveperforatedthedorsalsurface
element that forms the bluntly rounded an- ofthe snout in this region to accommodate
terolateralmarginoftheskull. Becausecrush- the tips ofthe parasymphysial tusks.
inghasfavoredexposureofthemoremassive At about the level ofthe anterior margin
vertical portions ofthis bone at the expense ofthe external naris, the premaxilla contacts
ofthe dorsal and palatalcomponents, theex- the prefrontal. From this point on the dorsal
1983 HOOK: COLOSTEUSSCUTELLATUSNEWBERRY 9
FIG. 2. Colosteusscutellatus(Newberry). Subadultskull,mandible, andanteriorpostcranialskeleton.
Right counterpart block ofholotype specimen, AMNH 6916. Scale equals 1 cm.
surface, the premaxilla gives rise to a wedge- ries, nearly equaling the length of the skull
shaped, posterolateral extension that over- table. It is also the narrowest element in this
lapstheanterioredge ofthe prefrontal before series, with a width less than one-fourth its
passing laterally and downward to the exter- length. At a level slightly posterior to the or-
nalnaris. Theanteriorhalfofthenarialopen- bits, the frontal overlaps the parietal in an
ing is bordered by the premaxilla. Immedi- interdigitating suture.
ately above the premaxillary tusk, a short, PreviousreconstructionsofColosteus(Ro-
unsculptured flange forms the ventral rim of mer, 1945, 1947, 1966) have shown the pre-
the naris; this flange obviously communicat- frontal as not reaching the naris because of
ed with an anterior extension ofthe maxilla, an intervening septomaxilla. However, latex
but the precise configuration is unclear. casts ofAMNH 6916 (fig. 2) and 6945 (fig.
The maxilla occupies about 75 percent of 3A)clearlyindicatethata septomaxillaisnot
the lateral skull margin. It attains its greatest present and that the prefrontal continues an-
height and concomitant dorsal exposure teriorly between the premaxilla and maxilla
where the infraorbital lateral line sulcus in- to comprise about one-sixth ofthe external
tersects the dorsal edge ofthe bone, near the narial border. This uncommon extension of
level of the vomerine tusk. Immediately the prefrontal is identical to that of Greer-
above the marginal tooth row, the external erpeton (Smithson, 1982).
surface ofthe maxilla is nearly vertical and The configuration of the circumorbital
onlyweaklysculptured. Posteriorly, themax- bones is modified from that seen in other
illa appears to contact the quadratojugal, but colosteids to an arrangement that is unique
the evidence for this is equivocal. among all amphibians. In the aforemen-
The nasal is a flat bone that is preserved tioned restorations, a posterolateral exten-
only in subadult specimens (AMNH 6916, sion ofthe prefrontal enters the orbital mar-
fig. 2; 6945, fig. 3A; BM[NH] R.2547, fig. gin. However, close examination of several
3B). Forhalfofitslength, thenasalisabroad well-preserved specimens (AMNH 6916, fig.
elementthatcontactsthepremaxilla laterally 2; 6945, fig. 3A; FMNH UC 2001, fig. 4)
while sharing a common medial suture with indicatesthattheprefrontal isprecluded from
itspartneralongthedorsal midline. Thepos- the orbital margin by an anteriorly directed
teriorhalfoftheboneformsawedgebetween lacrimal-postfrontal suture. In a somewhat
the frontal and prefrontal. similarfashion, abriefpostfrontal-jugal con-
Unlike the frontal ofmost temnospondyls tactontheposteriorsideoftheorbitexcludes
with elongate skulls, the frontal ofcolosteids thepostorbital from the circumorbital series.
is the longest bone ofthe dorsal midline se- The resulting arrangement of only three
10 AMERICAN MUSEUM NOVITATES NO. 2770
B
FIG. 3. Colosteusscutellatus(Newberry). Subadult skull and mandibles ofsingle individual in coun-
terpartblocks. A, holotypeofSauropleura longidentata, AMNH 6945; B, BM[NH] R.2547. Scaleequals
1 cm.
bones-jugal, lacrimal, and postfrontal- gin is formed by the triangular lacrimal. Be-
forming the circumference ofthe orbit is in cause ofthe prefrontal-maxillary suture, the
contrast to the standard five-bone configu- lacrimal fails to reach either the nasal or the
ration of most other primitive labyrintho- external naris. The postfrontal extends an-
donts. teriorlyabovetheorbitandbetweenthefron-
The anterior one-third ofthe orbital mar- tal and lacrimal to meet the prefrontal in a