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BREVIORA

Museum of Comparative Zoology

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US ISSN 0006-9698

CAMBRIDGE, Mass.

4 May 2011

NuMBER 523

THE SMALLER EMBOLOMEROUS AMPHIBIANS (ANTHRACOSAURIA) FROM
THE MIDDLE PENNSYLVANIAN (DESMOINESIAN) LOCALITIES AT LINTON
AND FIVE POINTS COAL MINES, OHIO

RosBeERT HoLMEs! AND DONALD BAIRD2

ABSTRACT.

The remains of small embolomeres (total midline skull length not exceeding 100 mm) from the Middle

Pennsylvanian (Desmoinesian) Linton and Five Points coal mines of southeastern Ohio can be distinguished from those
of Leptophractus found at the same localities by the form and size of the teeth. Its well-ossified condition relative to a
comparably sized juvenile specimen of the embolomere Archeria indicates a much smaller maximum adult size than that
of Leptophractus, the other described embolomere from the Linton Coal Mine. Tooth form and count, shape of the
squamosal and surangular crest, and stratigraphic occurrence all support tentative placement in the family Archertidae.

KEY WORDS:

INTRODUCTION

It has been suggested (Romer, 1963) that
American Carboniferous embolomerous am-
phibians sort into two size groups: a group
comprising taxa that attained a small body
size comparable to that of Archeria from the
Lower Permian of Texas and a group
comprising large-bodied taxa. The anatomy
and systematics of the latter group were
reviewed by Romer (1963).

‘Department of Biological Sciences, University of
Alberta, Edmonton, AB T6G 2E9, Canada: e-mail:
holmes! @ualberta.ca

?24 Ellsworth Terrace, Pittsburgh, Pennsylvania 15213,
U.S.A.

North American embolomeres; Middle Pennsylvanian embolomeres; Five Points Coal Mine; Linton

Although numerous embolomere taxa are
known from the Carboniferous of Europe
(see, e.g., Smithson, 2000), they are relatively
rare in North America. Although some of
the latter material has been described (e.g.,
Carroll, 1967; Holmes, 1984; Klembara,
1985; Holmes and Carroll, 2010), significant
material collected from the Desmoinesian
(“Westphalian D’’) localities of Linton and
Five Points Coal mines in Ohio has not. The
Diamond Coal Mine (Hook and Baird,
1986), located near the abandoned town of
Linton, is arguably one of the most produc-
tive Carboniferous vertebrate fossil localities
in North America. A rich assemblage,
collected from the cannel below the Upper

© The President and Fellows of Harvard College 2011.

D BREVIORA

Freeport coal of the Allegheny Group,
includes nearly 40 genera of fish, amphibians,
and reptiles (see Hook and Baird [1986] for a
review of this fauna and history of the
locality). Aquatic lepospondyls and temnos-
pondyls compose the large majority of the
amphibians, whereas embolomeres are poorly
represented. A few articulated embolomerous
vertebrae and the partial snouts of three large
individuals have been described (Cope, 1873,
1875; Romer, 1963), but an account of
skeletal elements of a small embolomerous
anthracosaur, informally referred to as “Fear-
on’s embolomere”’ in recognition of R. N.
Fearon, who collected the material some time
before 1883, has never been published.

More recently, a second fossil assemblage
has been discovered approximately 42 km
due north at Five Points Coal Mine (Hook
and Baird, 1993). Although slightly older
(early rather than late Desmoinesian) than
the classic Linton locality, the taxonomic
composition of the fossil assemblage at Five
Points shares many similarities with that
from Linton (Hook and Baird, 1993).
Disarticulated remains of embolomeres, al-
though uncommon, are preserved. Since
embolomere remains are rare, not only at
these two sites, but in the North American
Carboniferous as a whole, this material
warrants description despite its fragmentary
and disarticulated condition.

MATERIALS AND METHODS

The specimens described in the paper are
held in the collections of the Carnegie
Museum of Natural History (CM), Pitts-
burgh, Pennsylvania, and Museum of Com-
parative Zoology (MCZ), Harvard Univer-
sity, Cambridge, Massachusetts.

Specimens examined from the Linton locality

MCZ 2161, articulated vertebrae, thoracic
ribs, and a section of articulated ventral

No. 523

armor internal view of a small embolomere
exposed ventrally. After acid etching, verte-
brae, ribs, and posterior part of a lower jaw
and numerous gastralia were also exposed.

MCZ 2293, isolated anterior third of a
lower jaw of a small embolomere exposed
medially. After acid etching, a latex peal of
the lateral aspect was made.

Specimens examined from the Five
Points locality

CM 29599, left femur (part and counter-
part). ;

CM 34605, left squamosal and quadrate
(part and counterpart).

CM 67188, anterior half of right mandible
(part and counterpart).

Although some specimens from Five
Points were recovered during surface collect-
ing, most were discovered by splitting cannel
coal (see Hook and Baird, 1993). The
collecting techniques of R. N. Fearon, who
collected the MCZ specimens over 125 years
ago, are unknown, but were probably
similar. The specimens were acid etched to
remove the poorly preserved bone, after
which a latex peel was made.

Specimens used for comparison

MCZ 1474, Archeria crassidisca. Skull
table and disarticulated caudal vertebrae of
an immature individual from the Archer City
bonebed (Putnam Formation).

DESCRIPTION

Skull. The posterior portion of a lower jaw
(MCZ 2161), exposed in medial aspect, is
preserved in association with numerous
embolomerous centra, ribs, and gastral
scales (Figs. 1, 2A). As in other embolo-
meres, the jaw is deep in the region of the
adductor fossa. The dorsal margin of the
surangular crest is straight, high, and hori-

2011 SMALLER EMBOLOMERES FROM OHIO 3}

Figure 1. Archeriid. Photographs of latex peal (MCZ 2161) taken after acid etching. A, articulated vertebrae,
ribs, and dorsal surface of gastralia. B, disarticulated vertebrae, ribs, gastralia, and posterior portion of mandible in
internal view. Scale bars are divided into 1-cm sections.

4 BREVIORA No. 523

A WES
St = Re . k
SNES

Figure 2. Archeriid. A, drawing of main block (MCZ 2161). B, drawing of anterior end of lower jaw (MCZ
2293), medial aspect. C, drawing of anterior end of lower jaw (MCZ 2293), lateral aspect. D, reconstruction of one
rank of gastralia in internal view showing overlap patterns within the row. Abbreviations: artb, boss on articular;
gast (ext), gastralia, external surface; gast (int), gastralia, internal surface; mand, mandible; na, neural arch; ntc,
notochordal canal; pe, pleurocentrum; pmf, posterior Meckelian fenestra; scr, surangular crest; snc, supraneural
canal; sym, symphyseal surface of lower jaw.

2011

Figure 3.

zontal, as in Archeria. The articular bears a
boss posterior to the glenoid, as in Proter-
ogyrinus (Holmes, 1984) and Archeria
(Holmes, 1989). The posterior portion of a
large posterior Meckelian fenestra is clearly
visible (Figs. 1B, 2A).

The anterior end of a left lower jaw ramus
(MCZ 2293) is preserved in both lateral and
medial view (Figs. 2B, C, 3B, C). Although
not collected with the main block, its small
size and association with embolomerous
centra suggest that it pertains to the same
taxon. It appears to have been from an
individual of about the same size as MCZ
2161; the complete jaws would have been no
more than 100 mm long. This indicates that
the complete skull would have had a
midsagittal length (the postparietal length—

SMALLER EMBOLOMERES FROM OHIO 5)

Archeriid. Photographs of latex peals. A, original surface of main block (MCZ 2161) showing ventral
surface of gastralia. B, anterior end of lower jaw, medial aspect (MCZ 2293). C, anterior end of lower jaw, lateral
aspect, after acid etching (MCZ 2293). Scale bars are divided into l-cm sections.

see Panchen, 1970) of between 85 and
100 mm if skull proportions of embolomeres
such as Proterogyrinus (Holmes, 1984) or
Archeria (Holmes, 1989) are assumed. The
dermal ornamentation, seen on the lateral
surface of the anterior jaw portion (MCZ
2293; Figs. 2C, 3C), is muted as in other
embolomeres. The preserved dentary bears
13 small teeth of equal size. As in Archeria,
the anterior and posterior margins of the
teeth are parallel (i.e., the tooth is not
tapered), and the blunt terminations appear
to be chisel-shaped, although poor preserva-
tion precludes more detailed comparisons.
This morphology is distinct from that seen in
Leptophractus (Cope, 1875; Romer, 1963),
also found at Linton, in which the teeth show
marked variation in size and shape and are

6 BREVIORA

No. 523

pospl prespl

I; iaal

(a A | B

Figure 4. Archertid. Anterior end of jaw ramus (CM 67188) from Five Points in A, lateral and B, medial views.
Abbreviations: ang, angular; d, dentary; pospl, postsplenial; prespl, presplenial.

relatively larger, bullet or cone-shaped, and
distinctly recurved.

The anterior half of a right mandible (CM
67188) is preserved at Five Points (Fig. 4). In
the region of the symphysis, the lateral
surface of the dentary bears closely spaced,
round pits. Posterior to this, it bears more
widely spaced pits, most of which are
extended as shallow grooves. Twenty blunt
teeth are preserved in place. Although
preservation is imperfect, they are clearly
unlike those of Leptophractus but resemble
those of MCZ 2293 from Linton in being
parallel-sided, small, and subequal in size.
There is room for at least 15 additional teeth.
The dentary tapers posteriorly but still
maintains considerable depth at its broken
posterior end, suggesting that a significant
portion (about one-third) of the tooth row
has been lost. If so, a complete dentary
would have contained approximately 55
teeth. The coarsely sculptured splenial (pre-
splenial or anterior splenial) has a limited

exposure along the ventral edge of the ramus.
It terminates directly ventral to the eighth
tooth socket. The anterior ends of two
additional bones are exposed between the
dentary and splenial. The more ventral of the
two, presumably the postsplenial, shares a
long suture with the splenial and terminates
anteriorly directly ventral to the 13th tooth
socket. The more dorsal element, presumably
the angular, shares horizontal sutures with
both the putative postsplenial below and
dentary above, tapering to a wedge between
these bones immediately ventral to the 21st
tooth root. Medial exposure of the jaw is
limited to the region of the symphysis and
the anterior 13 preserved teeth.

A left squamosal from Five Points (CM
34605) is relatively square in proportions. In
contrast to most embolomeres except Arche-
ria (Holmes, 1989: text-fig. 2) and Eoherpe-
ton (Smithson, 1985, fig. 8), the quadrate
lamina of the squamosal is relatively short
(Fig. 5), indicating that the quadrate condyle

2011 SMALLER EMBOLOMERES FROM OHIO 7

Figure 5. Archeriid. Left squamosal and quadrate (CM 34605) in A, lateral and B, medial views. Abbreviations:
j, Jugal; Il, lateral line sulcus; po, facet for postorbital; q, quadrate; ql, quadrate lamina of squamosal; st, facet
for supratemporal.

8 BREVIORA

would not have projected much posterior to
the level of the occiput. Dorsally, the
squamosal bears a relatively long, antero-
posteriorly oriented trough that articulated
with the supratemporal in life. The smooth
edges of the trough show no evidence that an
interdigitating suture was present. Anterior
to the trough, the squamosal bears a fluted
facet that underlapped the postorbital. The
lateral surface of the squamosal bears a
number of pits that radiate from the ante-
rodorsal notch of the squamosal embayment
and, at approximately midheight, a distinct,
horizontal, continuous lateral line sulcus.
The left quadrate remains in articulation
with the squamosal, although postmortem
rotation about its shaft has exposed the
mandibular condyle in anterior view.
Medially, the squamosal bears at its
anteroventral corner an overlapping flange
for articulation with the jugal. A distinct
facet for the quadratojugal is absent. The
ventral end of the quadrate is exposed in
posterior view. The quadrate condyle is
gently saddle shaped, with the medial con-
vexity being better developed than the lateral
condyle, as in Archeria (Holmes, 1989).
Vertebrae. Six articulated but crushed
trunk vertebrae are preserved in dorsolateral
aspect in MCZ 2161 (Figs. 1B, 2A). Disar-
ticulated elements from a more anterior
portion of the column (on the basis of their
proximity to the posterior portion of the
mandibular ramus) are exposed in various
views. The central elements, which have a
notochordal canal of about the same relative
size as that in much larger specimens of
Archeria (Holmes, 1989), are very well
ossified considering their small size (about
10 mm in diameter). One neural arch,
exposed in anterior view 34 mm behind the
mandibular ramus and so presumably from
the anterior trunk region, bears a supra-
neural canal that is relatively smaller than in
anterior trunk arches in much larger sub-

No. 523

adult specimens of Archeria from the Ger-
aldine bonebed (Holmes, 1989).

Ribs. Sixteen ribs of varying states of
completeness are preserved; several are in
close association with the articulated series
of vertebrae (Fig. 1A), the rest scattered
about the block (Figs. 1B, 2A). Their form,
with a well developed capitulum and absence
of a flange, is virtually indistinguishable
from that of other embolomeres such as
Archeria and Proterogyrinus.

Appendicular Skeleton. A left femur 1s
preserved in part and counterpart at Five
Points (CM 29599) in anterodorsal and
posteroventral views (Fig. 6). At approxi-
mately 50 mm in length, it is about 60% and
65% of the length of the femora illustrated
for Proterogyrinus (Holmes, 1984) and Ar-
cheria (Romer, 1957), respectively. Both
proximal and distal expansions are well
developed, and articular surfaces are clearly
set off from the periosteal bone. Neither
proximal nor distal ends are as well ossified
as in a typical Proterogyrinus specimen but
are comparable to those described for
Archeria (Romer, 1957, fig. 8). The adductor
crest and rugosities of the internal and fourth
trochanters are well developed on its ventral
surface. Rugosities for the insertions of the
puboischiofemoralis internus and ischiotro-
chantericus are visible on the dorsal (exten-
sor) surface of the proximal expansion; on
the posterodorsal corner of the distal expan-
sion, deep proximodistal grooves mark the
origins of the peroneus longus and extensor
digitorum longus. On balance, these features
suggest that, although CM 29599 is probably
not from a fully adult individual, it does not
pertain to a juvenile.

Gastral Scales. As originally preserved,
MCZ 2161 comprised a section of articulated
gastralia from the midtrunk exposed in
ventral view (Fig. 3A). Of the approximately
20 ranks exposed, the most complete com-
prise rows of five elements per side. Each

2011 SMALLER EMBOLOMERES FROM OHIO 9

riot ay fe te. ve
SH ipa aa?
wey

Figure 6. Archeriid. Left femur (CM 29599) in A, anterodorsal and B, posteroventral views. Abbreviations: add,
adductor crest; int t, internal trochanter; itr, insertion of the ischiotrochantericus; per long + ext d long, common
origin of the peroneus longus and extensor digitorum longus; pifi, insertion of the puboischiofemoralis internus; tr4,

fourth trochanter.

rank meets its contralateral counterpart
along the midline at an angle of about 90°.
Acid etching has subsequently exposed their
dorsal surfaces, as well as many isolated

gastralia, showing morphology of overlap-
ping surfaces clearly (Figs. 1, 2A). Each
element is asymmetrically tear-drop shaped,
with the tapered end directed anterome-

10 BREVIORA

dially. This conforms to the “spindle-
shaped” gastral scale morphology common
in “labyrinthodonts” (Witzmann, 2007) The
smooth, convex ventral (external) surface
lacks sculpturing like that seen in the
temnospondyl Greererpeton (Godfrey,
1989). The dorsal (internal) surface bears a
longitudinal groove that broadens at the
wider (posterolateral) end to accommodate
the ventral surface of the tapered tip of the
next lateral scute (Fig. 2D). The posterome-
dial edge is thicker than the anterolateral
edge. A very similar morphology and pattern
of overlap is seen in Greererpeton (Godfrey,
1989). However, in MCZ 2161, each element
is remarkably large, having a length equiv-
alent to at least 25% greater than the
diameter of a vertebral centrum. Relatively
large gastralia appear to be characteristic of
embolomeres. Similar proportions are seen
in Proterogyrinus, Archeria (Cope and Mat-
thew, 1915), Pholiderpeton (Clack, 1987),
Eogyrinus (Panchen, 1966, 1972) and embo-
lomeres (probably Calligenethlon) from Jog-
gins, Nova Scotia (Godfrey et al, 1991;
Holmes and Carroll, 2010). In basal tetra-
pods such as Greererpeton (Godfrey, 1989)
and Colosteus (Hook, 1983), they are little
longer than the equivalent of half their
respective centrum diameter. They are rela-
tively larger in the temnospondyl Dendrerpe-
ton (Carroll, 1967), but still distinctly shorter
than the centrum diameter. The paramedian
scales have expanded, spoon-shaped medial
ends to overlap their counterparts on the
opposite side of the median line.

DISCUSSION

Of the 28 and 34 identifiable vertebrate
taxa described from the localities of Five
Points and Linton, respectively, 21 are
common to both localities (Hook and Baird,
1993). Most of the tetrapod taxa at both
localities are small lepospondyls; relatively

No. 523

few specimens (a limited number of “‘laby-
rinthodonts” and reptiles) are large enough
to be included in the same size class as the
material described here. None of the ele-
ments can be assigned to the Temnosponyli,
Baphetoidea (=Loxommatoidea) or to any
reptile known to occur at either locality.
However, the nature of the dermal sculptur-
ing and shape of the teeth, as well as
morphology of the femur and ribs are
consistent with what would be expected for
an embolomere.

Four embolomere specimens have been
described from Linton. Two of _ these,
AMNH 6831 and a “specimen at Columbia
University” (see Romer, 1930:127), compose
the type material of Leptophractus obsoletus.
Except for one partial counterpart, both
have since been lost (Panchen, 1970). A third
skull, originally described as Leptophractus
and later redescribed as Anthracosaurus
lancifer (Romer, 1963), is now considered
to be a large individual of L. obsoletus
(Panchen, 1970; Hook and Baird, 1986). A
few articulated centra not associated with
any of the above are also preserved (Romer,
1963). These specimens indicate that Lepto-
phractus was a large embolomere, with a
midsagittal skull length estimated to have
been between 340 and 355 mm (Panchen,
1977). The Linton material described here
pertains to much smaller individuals with a
midsagittal skull length of no more than
100 mm. Although it is possible that this
material simply pertains to juvenile Lepto-
phractus specimens, this is unlikely. The
preserved dentary teeth are small, close-set,
blunt pegs of uniform size and shape. Up to
55 teeth would have been present in the
complete jaw. Teeth in the same region of
Leptophractus are relatively large, vary con-
siderably in size, and are generally in the
form of recurved, pointed cones (Cope, 1875,
plates XX XVIII, XX XIX; Romer, 1963, figs.
11, 12). The complete jaw would have held

2011

SMALLER EMBOLOMERES FROM OHIO . 11

Figure 7. Archeria crassidisca (MCZ 1474), an immature individual. A, skull table. B, caudal vertebrae,
approximately 30 segments postsacral. Abbreviations: ic, intercentrum; pc, pleurocentrum.

approximately 28 teeth (Romer, 1963). Un-
less there was a drastic change in form,
relative size, and total number of teeth as
adult size was approached, the material
described here cannot be congeneric with
Leptophractus. The relatively advanced state
of ossification of this material also supports
the probability that it represents a taxon
distinct from Leptophractus. The supraneural
canals are small, and vertebral centra are
well ossified, restricting the diameter of the
notochordal canal. The notochord of embo-
lomeres remains an important structural
element in the axial skeleton throughout life.
A small notochordal canal persists even in
the largest known Archeria specimens (centra
of 35 mm diameter and skulls of about
300 mm midsagittal length). In subadults
with a centrum diameter of about 20 mm and
midsagittal skull length of about 170 mm, the
canal is slightly larger (Holmes, 1989).
However, in one juvenile Archeria (MCZ
1474) from the Archer City bone bed, with a
midsagittal length of about 85 mm and a
caudal centrum diameter of about 9 mm
(essentially the same size as the embolomere
described here), the osseous centra are thin

husks and the notochordal canal accounts
for a full half of the diameter (Fig. 7). The
centra in MCZ 1474 are clearly embolomer-
ous, with hemal arch-bearing intercentra
alternating with archless pleurocentra.

The degree of ossification of the centra of
the embolomere described here is more com-
parable to that in subadult and adult Archeria,
suggesting that a full-sized adult would have
been much smaller than Leptophractus. Of the
known embolomeres, only Calligenethlon has
been reported as being smaller, with a mid-
sagittal skull length and centrum diameter of
approximately “two to three inches in length”
(Carroll, 1967:136) and 5 mm (Carroll, 1967,
text-figs. 19, 21), respectively. More recently
discovered embolomere material from Jog-
gins, if assignable to Calligenethion, suggests
that the type material might pertain to a
juvenile individual and that the adult would be
somewhat larger, but its skull would not have
exceeded 100 mm in midsagittal length
(Holmes and Carroll, 2010).

Whether the material from Five Points
pertains to the same taxon present at Linton
is uncertain. Although the two localities are
separated by only 42 km, Five Points is

12

about two million years younger. Neverthe-
less, it is clear that none of it pertains to
Leptophractus. Rather, the relatively well
ossified material from both localities clearly
pertains to more or less adult individuals of
an embolomere of small size. Although the
dentary from Five Points (CM 34605) is
arguably more robust than that from Linton
(MCZ 2161), otherwise in cases where the
same elements occur in both localities, no
differences are apparent, suggesting that the
taxa are likely closely related if not conspecific.

Although the embolomere described here
is probably not Leptophractus, a definitive
taxonomic assignment is problematic. The
high, straight, horizontal, dorsal margin of
the surangular crest and anterior placement
of the jaw articulation, as indicated by the
short quadrate ramus of the squamosal, are
certainly reminiscent of the morphology in
Archeria. A dentary tooth count of about 55
places this taxon at the high end of the range
(from about 24 in Eoherpeton (Smithson,
1985] to 55 in Archeria [Holmes, 1989]) for
embolomeres, and suggests affinities with
Archeria. However, judging from the esti-
mated maxillary tooth counts, the dentary
count in Proterogyrinus probably ap-
proached 50, suggesting that a high tooth
count is not a unique shared character of the
Linton/Five Points embolomeres and Arche-
ria. Tooth morphology resembles that in
Archeria, but a similar tooth morphology
also occurs in Proterogyrinus (Holmes, 1984)
and Pholiderpeton (Clack, 1987), suggesting
the possibility that this tooth morphology is
simply plesiomorphic. Although hardly con-
clusive in itself, it is nevertheless worth
noting that the Linton deposits are Desmoi-
nesian—closer in stratigraphic occurrence to
the Archeria material from the Texas Lower
Permian than any other known embolomere.
With these caveats, the specimens are as-
signed provisionally to the family Archerii-
dae, pending further discoveries.

2 BREVIORA

No. 523

ACKNOWLEDGMENTS

We thank C. Schaff and F. Jenkins Jr. of
the Museum of Comparative Zoology, Har-
vard College, for allowing us to borrow the
material described here, the late P. Gaskill
for drafting some of the figures, M. Brazeau
for discussions over vertebral morphology in
Ectosteorhachis, and A. Milner for sharing
many observations on Carboniferous tetra-
pods. Thanks also to A. Warren and J.
Klembara for extremely helpful reviews of
this manuscript. This study was supported in
part by a grant from Le Fonds Pour la
Formation de Chercheur et L’Aide a la
Recherches (Quebec).

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