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B RE VI 






iVi 11 s e HI m ol v^ omparatt 1 V 




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 

Robert Holmes^ and Donald Baird^ 

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 Leptophractiis 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 Archeriidae. 

Key words: North American embolomeres; Middle Pennsylvanian embolomeres; Five Points Coal Mine; Linton 



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 o^ 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 l@ua!berta.ca 

^24 Ellsworth Terrace, Pittsburgh, Pennsylvania 15213, 

U.S.A. 



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 



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No. 523 



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 tenrnos- 
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 pubhshed. 

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, arliculated vertebrae, thoracic 
ribs, and a section of articulated ventral 



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. I, 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- 



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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. 



BREVIORA 



No. 523 




Figure 2. Archcriid. A, drawing of main block (MCZ 2161). B, drawing of anterior end of lower jaw (MCZ 
229.1), medial a.spect. C, drawing of anterior end of lower jaw (MCZ 229.3), 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; pc, pleurocentrum; pmf, posterior Meckclian fenestra; scr, surangular crest; snc, supraneural 
canal; sym, symphyseal surface of lower jaw. 



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A 








Figure 3. 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 1-cm sections. 



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. IB, 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 — 



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 



BREVIORA 



No. 523 



ang 




Figure 4. Archeriid. 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 splcnial (pre- 
splenial or anterior splcnial) 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 Arclie- 
ria (Flolmes, 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 



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Figure 5. Archeriid. Left squamosal and quadrate (CM 34605) in A, lateral and B, medial views. Abbreviations: 
j, jugal; 11, lateral line sulcus; po, facet for postorbital; q, quadrate; ql, quadrate lamina of squamosal; st, facet 
for supratemporal. 



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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. IB, 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 thai is relatively smaller than in 
anterior trunk arches in much larger sub- 



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. lA), the rest scattered 
about the block (Figs. IB, 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 is 
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. 3 A). Of the approximately 
20 ranks exposed, the most complete com- 
prise rows of five elements per side. Each 



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A 




^^i^iV^'^^^^iP^fli^ pifi 



.^'^ 





intt 



per long |\:y|l:^fe;^; 

+ 
extdl 

1 cm 



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 gastralia, showing morphology of overlap- 
along the midline at an angle of about 90°. ping surfaces clearly (Figs. 1, 2A). Each 
Acid etching has subsequently exposed their element is asymmetrically tear-drop shaped, 
dorsal surfaces, as well as many isolated with the tapered end directed anterome- 



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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 httle 
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 localilics of Five 
Points and Linton, respectively, 21 are 
common to both localities (Hook and Baird, 
1993). Most of the telrapod taxa at both 
localities are small lepospondyls; relatively 



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 XXXVlll, XXXIX; Romer, 1963, figs. 
11, 12). The complele jaw would have held 



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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 
Leptophr actus. 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 CalUgenethlon, 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 



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BREVIORA 



No. 523 



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. 



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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Joggins Formation. Journal of Paleontology 41: 

111-142. 
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amphibian from the Yorkshire Coal Measures. 

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Cope, E. D. 1873. On the Batrachia and fishes from the 

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Academy of Natural Sciences, Philadelphia 1873: 

340-343. 
. 1875. Synopsis of the extinct Batrachia from the 

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, AND W. D. Matthew. 1915. Tertiary Mammalia 



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assemblage from the Alleghany Group (Late 
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