Novitates PUBLISHED by the AMERICAN MUSEUM of NATURAL HISTORY CENTRAL PARK WEST at 79TH STREET NEW YORK, N.Y

Home , Dvinosaurus, Edops, Gerrothorax, Trimerorhachis

AMERICAN MUSEUM Novitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET NEW YORK, N.Y. 10024 U.S.A. NUMBER 2662 NOVEMBER 21, 1978

RONN W. COLDIRON Acroplous vorax Hotton (Amphibia, Saurerpetontidae) Restudied in Light of New Material

AMERICAN MUSEUM

Novitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2662, pp. 1-27, figs. 1-9, table 1 November 21, 1978

Acroplous vorax Hotton (Amphibia, Saurerpetontidae) Restudied in Light of New Material

RONN W. COLDIRON'

ABSTRACT A new individual of Acroplous vorax is described lower jaw characters are an overall dorsoventral and its systematic position within the Saurerpeton- compression and a unique wide exposure of the ar- tidae is reexamined. The new specimen is clearly ticular both laterally and medially. The vertebrae are conspecific with the type as shown by narrow mid- unique among saurerpetontids in having a car- line elements, broad supratemporal and intertem- tilaginous portion of pleurocentrum conspicuously poral, wide but short lacrimal, and nearly identical larger than the intercentrum. pterygoids. A hypothesis of relationships suggests Acroplous The new specimen offers more data on the brain- to be the sister group of Isodectes and brachyopids. case, pterygoid occiput, lower jaw, and humerus. As a result the saurerpetontids are paraphyletic since The internal process of the pterygoid is small and a they exclude the brachyopids. Further, if brachyo- well-developed epipterygoid caps the dorsal process pids are the sister group to "saurerpetontids" and of the pterygoid, indicating a more primitive basal other stereospondyls are more closely related to articulation than that interpreted for Isodectes. Un- eryopids, then stereospondyls would be diphyletic. fortunately, the condition in Saurerpeton is unknown There are many characters, however, that contradict for comparison. Like all other saurerpetontid genera the hypothesis of stereospondyls being diphyletic. (Dvinosaurus, Saurerpeton, Isodectes) the lower jaw Dvinosaurus, long thought to be an aberrant member has a large symphysial tusk and a long retroarticular of the trimerorhachoids, is thought to be the sister process. The new material, however, is primitive in group to "saurerpetontids" and brachyopids. having a small posterior meckelian fossa. Advanced INTRODUCTION In 1971 Orville Bonner and Larry D. Martin Besides the Acroplous material other laby- reopened the quarry at Keats, Kansas, in which rinthodont types, a lungfish, and possible mi- the type of Acroplous vorax Hotton was dis- crosaur remains, were discovered. During the covered. The following year Steven Dart and summer of 1974 I worked the remainder of the Bonner nearly finished quarrying operations. producing layer at Keats. More material of this saurerpetontid amphibian Since Hotton (1959) described Acroplous, was recovered and is described here (fig. 1). Chase (1965) reviewed the known members of

'Graduate Student, Department of Geological Sciences, Columbia University, New York.

na /prefr post fr

A I Pt

It / r pt p

St/ P I pp

1cIa ta

..ang

u cia am cor-

..-14-W4 nfavh VI

FIG. 1. View of main block of new specimen of Acroplous vorax Hotton (KU 28352). x 1.6. Abbreviations: ang, angular; art, articular; bpt, basipterygoid process; bsph, basisphenoid; cl, cleithrum; cla, clavicle; cor, coronoid; cr, cervical rib; d, dentary; dr, dorsal rib; fr, frontal; h, humerus; ic, intercentrum; icl, interclavicle; it, intertemporal; lac, lacrimal; I pt, left pterygoid; max, maxilla; na, nasal; n arch, neural arch; p, parietal; pc, pleurocentrum; postfr, postfrontal; pp, postparietal; prart, prearticular; prefr, prefrontal; r pt, right pterygoid; sp, splenial; st, supratemporal; sur, surangular; ta, tabular. 1978 COLDIRON: ACROPLOUS VORAX HOTTON 3 the Trimerorhachoidea and reclassified the layer. Quite often vertebrate remains are found group. Baird (personal commun.) and Welles in these pockets. A 2-inch iron-stained green and Estes (1969) dealt with the possible relation shale lies above the producing layer followed of Isodectes (Eobrachyops Watson) to the by a 1-foot thick light green shale. brachyopids. Olson and Lammers (1976) have Most recently the Gearyan stage has been described a form, Kourerpeton, also closely re- considered to form the base of the Permian in lated to the brachyopids. The new material Kansas (Zeller, 1968). Dunbar et al. (1960) adds much information about the morphology placed the Speiser Shale near the Putnam-Ad- of Acroplous and suggests that it is more miral Formation boundary, Wichita Group, closely related to Isodectes, Kourerpeton, and Texas. Hotton (1959) preferred to correlate the the brachyopids than to any other known mem- Speiser Shale with the upper part of the Pueblo ber of the Trimerorhachoidea. Formation. The Pueblo Formation lies at the I thank Drs. T. H. Eaton and L. D. Martin base of the Wichita Group, Permian System of for their guidance while this work was first north-central Texas. Thus, Hotton compared undertaken at the University of Kansas. Mr. the Speiser with the lowest vertebrate bearing Orville Bonner was a great help through his beds of Texas. This comparison was based on fine preparation of the new material. Dr. Don- the similarities to Saurepeton and "Pelion" of ald Baird of Princeton University deserves the Pennsylvanian (Upper Freeport) and many thanks for lending his time and advice "Eobrachyops" of the Permian (Arroyo, Clear concerning his recent work on Isodectes. I Fork Group). thank Dr. Eugene Gaffney of the American Baird (in Welles and Estes, 1969) syn- Museum of Natural History for suggestions for onymized "Eobrachyops" from the Texas Per- revision of the manuscript. Ms. Michele Col- mian with Isodectes from the Pennsylvanian of diron was indispensable in typing the manu- Kansas (Bern Limestone, Wabaunsee Group). script. Mr. Chester Tarka and Ms. Lorraine Hotton's attempt to compare the Speiser Shale Meeker helped with the illustrations. Lastly, I to the Texas Permian (Pueblo) on the basis of thank Mr. Raymond Schurle for permission to vertebrate similarities is no longer feasible. Iso- work at the Keats locality. dectes (Eobrachyops) ranges too far strat- igraphically to be of use in correlation. GEOLOGY AND AGE OF THE SEQUENCE Clendening (1971) placed the Gearyan Stage The locality is on the farm of Raymond of Kansas entirely within the upper Pennsylva- Schurle in SE 1/4 NW 1/4, Sec. 36, T9S, R6E of nian Series. He used palynological evidence to Riley County, Kansas. The Speiser Shale forms show that "Gearyan age spores and pollen nearly all of about 20 vertical feet of a steep demonstrate no profound change from the un- bank along Kitten Creek. The exposure runs derlying Virgilian" (Pennsylvanian). Only along the stream for 72 feet just north of Keats. when one reaches the Wymore Shale (Chase The exposure faces S50W. Group-overlies the Speiser Shale, Council The Speiser Shale is bracketed by the Grove Group) does bisaccate pollen increase Funstone Limestone below and the Threemile significantly. Wilson and Rashid (1971) by Limestone above. The Funstone forms the using palynological evidence also reached the stream bed and the Threemile caps the stream same conclusion that the Gearyan stage is bank. The Speiser is a series of alternating 2- Pennsylvanian in age. to 4-feet thick red and green shales. Very thin However, all of these sediments were depos- (2 inches) gray-green limestone sheets lie be- ited in a lowland environment, far away from tween only a few of the red and green shale the Arbuckle highlands in Oklahoma. Lan- facies. The producing layer is gray-green and genheim (1952) stated "lowland plants become lies 4 feet above the Funstone Limestone. Im- known as Pennsylvanian indices in the mid- mediately below the producing layer is a well- western and eastern United States." In that part indurated red facies. The contact between these of the country "during the Pennsylvanian . . . two facies is marked by small pockets of green uplands did not exist . . . as the seas were shale penetrating the topmost part of the red obliterated in the Permian, however, more up- 4 AMERICAN MUSEUM NOVITATES NO. 2662 land plant material found its way to the sites of are displaced slightly away from the midline deposition and was fossilized." Because the elements. This displacement has exposed re- Gearyan sediments in Kansas were far away markably well-developed lappets which ex- from any uplands one might expect only Penn- tended over their midline neighbors. Through- sylvanian pollen assemblages. One is left with out the description of the skull roof these lap- equivocal evidence as to where to place the pets will be described in detail so that a dorsal Permo-Carboniferous boundary in the midconti- view of the skull roof can be reconstructed (fig. nent. 2). The back margin of the skull is broken away from the occiput just anterior to the oc- SYSTEMATIC DESCRIPTION cipital crest. NASAL: The nasals are the most anterior CLASS AMPHIBIA skull roofing bones preserved. The bones end ORDER TEMNOSPONDYLI laterally in a broken edge. Medially a moderate lappet (0.5 mm.) overlies the adjacent (left) SUBORDER RHACH[TOMI nasal in dorsal view. Posteriorly the nasal SUPERFAMILY TRIMERORHACHOIDEA forms a moderately deep wedge between the prefrontal and frontal bones. This wedge marks FAMILY SAURERPETONTIDAE CHASE, 1964 the beginning of the midline elements. Saurer- GENUS ACROPLOUS HOTTON, 1959 peton has a broad posterior wedge but no constriction of the frontals or parietals follows. In AMENDED DIAGNOSIS (largely from Hotton, Acroplous the posterior facing wedge of nasal 1959): A typical saurerpetontid amphibian, hav- interfingers deeply with both frontal and pre- ing a short face, extremely reduced otic notch, frontal. Thus, a strong sutural union is formed well-developed retroarticular process, deep with all adjacent bones that are preserved. The cheek, pronounced ventrally directed quadrate anterior portion of the bone has been lost. process of pterygoid, backward sloping occiput, In both the type and referred specimens the and narrow tabulars. Parasphenoid articulates nasal extends posteriorly to a point level with with broad ventral shelf of pterygoid. The fol- the first one-quarter of the orbital diameter. In lowing characters are unique for Acroplous and distinguish it from all other saurerpetontid gen- -- T- - era: dermal midline elements narrow, large ex- I internal of ternal nares, weak process I - \ pterygoid; tabulars excluded from otic notch by I/ -. \\\ supratemporal; wide lateral exposure of / splenials; larger pleurocentra than intercentra; //. anterior border of interclavicle deeply pectinate.

Acroplous vorax Hotton, 1959 I " II DIAGNOSIS: Same as for genus. I -_ E

MORPHOLOGY \ _ Nearly all the skull roofing bones preserved \ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~II are exposed in ventral view, whereas only the I_ __ ,' _St lacrimal, parts of postparietal, and tabular are exposed dorsally. The parietals, postparietals, supratemporals, intertemporals, prefrontals and postfrontals, tabulars, nasals, and frontals are FIG. 2. A reconstructed dorsal view of the skull all partially articulated with each other. The left roof. Right and left sides of skull are mirror images; side of the skull has been disturbed so that the hatched areas indicate an element is incomplete. Ab- supratemporal, intertemporal, and postfrontal breviations as in figure 1. X1.2. ~~~II 1978 COLDIRON: ACROPLOUS VORAX HOTTON 5 all other saurerpetontids the posterior margin of parietal. The postfrontal-intertemporal suture is the nasal lies ,anterior to the orbital border. In relatively straight where the lappet begins. The Dvinosaurus (Bystrow, 1938) one or both lappet type of suture must also have reinforced nasals reach the anterior level of the orbits. the skull like those of the interfingering type. PREFRONTAL: The prefrontal ends anteriorly Because of the overlapping of frontal by in a break where the orbits begin to turn dor- postfrontal the shape of the postfrontal is some- solaterally. Thus, only a posterior bar is pre- what different from dorsal aspect. From a ven- served around the orbit while its anterior tral view the bone curves posterolaterally widening has been lost. Medially the prefrontal around the dorsal rim of the orbit. The bone interfingers with both nasal and frontal. Parts of steadily increases in width posteriorly as the the suture form a lock-and-key coupling which medial border gently curves posterolaterally. further reinforces the strong suture. Posteriorly When seen from a dorsal view, however, the the bone remains at a fairly constant width (1.5 postfrontal is wider and impinges on the pos- mm.) until the postfrontal boundary is reached. terior half of the frontal. The lappet of the Here, the bone has narrowed to 0.5 mm. and postfrontal reaches its maximum width at its interfingers deeply with the postfrontal. This posterior margin. This causes a posteromedial posterior constriction is typical of all saurerpe- turning of its dorsal margin over the anterior- tontid genera except Isodectes where the pre- most part of the parietal. The exact shape of frontal maintains a constant width. Because of the flange over the parietal cannot be deter- the deep interfingering of this element a large mined. However, the development of the lappet medially directed lappet over the frontal is posteriorly agrees with the appearance of a thought not to be present. The posterior con- flange in the type specimen. These medially striction, then, probably exists in dorsal view directed lappets further contribute to the con- as well. The lateral margin of the bone is thick- striction of midline elements which started at ened to form a rounded ridge under the dorsal the nasals. Also, the portion of lappet overlying rim of the orbit. The anteriormost part of this the parietal indicates a much wider postfrontal- ridge is sheared to show itself in cross section. parietal contact than does the type specimen. In This break is facing slightly ventrally (from a general this new specimen is more typical of dorsal perspective) which shows the face began other trimerorhachoids. This posterior expan- to turn downward at the anterodorsal margin of sion of the postfrontal is similar to other saurer- the orbit. petontids except Saurerpeton. The postero- POSTFRONTAL: The postfrontal is bounded lateral margin of the bone is broken so that a anteriorly by the prefrontal, laterally by the lateral flange in the type cannot be determined frontal and parietal, and posteriorly by the in- for the specimen at hand. The orbital margin is tertemporal. The lateral boundary is taken up swollen to form a ridge around the under sur- almost entirely by the orbit. Farther posteriorly face of the orbit as does the prefrontal. the edge is broken so that the postorbital con- INTERTEMPORAL: The intertemporal-postfron- tact is lost. tal border is straight, and the two bones are The right postfrontal has been displaced to separated by about 0.25 mm. Any interfinger- the left (in ventral view) and the underlying ing of this suture could be masked by a fracture parts of frontal and parietal have been de- along the suture. Medially, there is a well- stroyed by a crack running roughly parallel to developed lappet, 1.5 mm. wide, which is con- the suture between these three bones. The su- tinuous with the more anterior lappet of the ture with the prefrontal has been described postfrontal. Laterally, a lappet is also present above. The anterior one-third of the postfrontal which overlies the postorbital. The edge of this interfingers with the frontal in a complicated lateral lappet is gently concave and agrees with fashion. Posterior to this point a lappet de- a similar convex postorbital-intertemporal velops with increasing width to the juncture border in the type specimen. with the intertemporal. This lappet is well pre- The posterior border is a simple suture but served and consists of parallel posteromedially complicated by fractures and subsequent dis- pointing ridges which fitted over the frontal and placement. A lappet can be seen between the 6 AMERICAN MUSEUM NOVITATES NO. 2662 intertemporal and supratemporal. The displace- peton, and the brachyopids have decreased the ment is small (0.5 mm.) so that neither the otic notch to a greater degree, whereas Saurer- width of the lappet nor which bone it overlaps peton and other trimerorhachoids maintain a can be seen. Also, parts of the posterior margin larger one. of the intertemporal are fractured which ob- TABULAR: The tabulars are broken both lat- scures the shape of its ventrally exposed suture. erally and posteriorly. The anterior and medial Because displacement between the postfrontal sutures with supratemporal and postparietal can and intertemporal is slight no overlapping can be seen only on the surface where the bones be seen if present. abut against each other. The wide medial lappet Like that of the type, the intertemporal in of supratemporal restricts the dorsal exposure dorsal view must be a very large rectangular of tabular to a more lateral position, farther bone with relatively simple borders. Its poste- from the parietals. This condition exists in the rior border runs posteromedially as does the type specimen and is very similar to that seen same border of the type. The posterior suture in Isodectes and Dvinosaurus. However, in trends posteromedially. Because no lappet can both cases the tabular is reduced to a narrow be seen anteriorly, a concave anterior border strip so that the separation from the parietal is (apex pointing anteriorly) cannot be deter- more lateral than posterior as in Saurerpeton, mined. Trimerorhachis, and Neldasaurus. Compared with other saurerpetontids the in- The tabular forms the dorsolateral border of tertemporal is quite large. Its squarish outline the occiput. This part of the bone forms a right resembles only that of Isodectes but the ele- triangle with the apex pointing laterally. A ment in that genus is much smaller. small sheet of bone projects ventrally, anterior SUPRATEMPORAL: The supratemporal is also to the apex of the tabular. Hotton (1959) as- a large rectangular element with a broadly sumed this sheet of bone comprised the anterior pointed anterior border. Among other tri- margin of a posttemporal fenestra. If this part merorhachoids, the element most resembles of the tabular received a cartilaginous paroc- Saurerpeton and Trimerorhachis in its long but cipital process, the posttemporal fenestra would narrow proportions. The supratemporal of lie medial to this tabular process. Posterior to Neldasaurus is also long and narrow but does the ventrally directed process, the tabular is not take up as great a proportion of the skull folded to form a dorsally directed pit. table as in the former genera. Description of In every way, the occipital exposure of the the lateral and medial lappets of the supratem- tabular is comparable with those of Dvino- poral allows an estimation of small otic notch saurus and saurerpetontids. In all these genera size and cheek-skull table kineticism. These the posttemporal fenestra is small and lies me- lappets are well developed and overlie the pari- dial to a ventrally directed tabular process. Un- etal and squamosal. The sutural reinforcement fortunately the condition in Saurerpeton is by the lateral lappet over squamosal would unclear. allow no movement between these two ele- POSTPARIETAL: Both postparietals are nearly ments. Ridging of these lappets is seen clearly complete, with the left attached to the occiput. in ventral view. The lateral lappet is 1.0 mm. The right postparietal is broken at the occiput- wide, whereas the medial lappet is 1.5 mm. skull table juncture. A gentle serrate suture ex- wide. The lappet on the right supratemporal is ists with the parietal and runs at right angles to broken off at the posterior one-third of the bone the midline. The subcutaneous portion forms a length. The right supratemporal shows that the long, thin rectangular element as in the type lappet extended at least to the posterolateral specimen, and unlike any other trimero- edge of the bone. This lateral lappet overlies rhachoid. However, there is no medial expan- the supratemporal along its entire lateral edge. sion anteriorly toward the parietals, which does The otic notch, then, could not have extended occur in Dvinosaurus and Isodectes. farther along the cheek than the anterior margin A prominent ridge separates the skull table of the tabulars (which are thin anteroposte- from the occiput. The ridge expands ventrally riorly). Only Dvinosaurus, Isodectes, Kourer- toward the midline to form an inverted triangu- 1978 COLDIRON: ACROPLOUS VORAX HO1TON 7 lar area of thickened bone. The suture between length. There is slight interfingering between postparietals runs down the center of the tri- parietals posterior to the parietal foramen. This angle and ends at a space occupied by the opening is situated more anteriorly in the new missing supraoccipital. This triangular ridge is specimen. In ventral view an elongate oval pit unique among the saurerpetontids although a (1.5 mm. long) appears to communicate pos- pillar-shaped ridge occurs in Dvinosaurus and teriorly with the parietal foramen. Isodectes. More ventrally and laterally, the FRONTAL: The frontal has a general rec- postparietal overlies the exoccipital in a tangular shape with a swollen lateral margin straight, horizontal contact. where it meets the relatively narrow prefrontal. Immediately above and lateral to the exoc- If the interpretation of the dorsal view of the cipital the postparietal interdigitates with the skull roof is correct, only the posterolateral tabular. This suture runs dorsolaterally toward portion of the bone reaches as far posteriorly as the skull roof. As a result the postparietals it does in the type. Except for the midline occupy most of the dorsal half of the occiput. suture the frontals are united with their neigh- This wide occipital exposure of the postparie- bors by strong sutural contacts (lappets or com- tals is characteristic of trimerorhachoids in gen- plex interfingering) which have been described eral. above. PARIETAL: The parietals are nearly identical Relative to other trimerorhachoids only Tri- in shape with those in the type. Posteriorly, the merorhachis has comparably short prefrontals. parietals are comparable with other saurerpeton- By far, the prefrontals of both the type and the tids in width but converge to form a narrow referred specimen of Acroplous are narrower union with the frontals. In the specimen at than any other trimerorhachoid. hand, the frontal-parietal suture is uncertain. LACRIMAL: The right lacrimal lies alone and Two breaks on either side of the parietals might is exposed in lateral view. Well-developed ran- represent its anterior border. These two are rel- dom pits and ridges present themselves clearly. atively close together and are different from the A deep furrow traverses the orbital margin of frontal-parietal juncture in the type. The new the lacrimal anteroventrally. Nearly all the bone specimen shows this suture tending antero- is present, which is roughly L-shaped. The or- medially rather than at right angles to the mid- bital margin of the bone subtends an angle of line in the type. The bones probably approximately 90 degrees, which is greater than interfingered with one another so that a lappet the exposure in the type. The narial border lies is unlikely. A lappet could change the dorsal only 5 mm. from the anterior end of the orbit, limits of the parietal, but the union between and a wide concave border, although unbroken, parietal and frontal could still be longer and clearly indicates a large narial opening. The somewhat wider. If differences do exist in the lacrimal makes up the entire back margin of the parietal-frontal union they need not be signifi- naris. Although the face is poorly represented, cant because the new specimen is larger than the enlarged naris and its short distance to the the type. orbit point toward an attenuated face with the The parietals extend anteriorly to at least the bones crowded as in the type. Only in posterior one-third of the orbit and possibly Dvinosaurus and Saurerpeton among tri- one-half of its length. The parietals of the type merorhachoids does the lacrimal enter both the extend only to the posterior limit of the orbit. orbit and naris while maintaining its charac- This difference may also be due to the size teristic shortness. In Isodectes the lacrimal re- difference between the two individuals. Only in sembles the brachyopid condition in not Saurerpeton does the parietal extend as far an- reaching the naris. teriorly. This similarity may not be significant A thin smooth shelf on the dorsolateral sur- because of possible changes in relative propor- face marks the area of overlap by the dorsally tions due to comparison of different growth expanded maxilla. This smooth shelf is down- stages. turned so as to point nearly vertically in natural The midline suture is of simple abutment position. The naris lies above this downturning type along most of the parietal and frontal so that most of the orbit, the naris, and most of 8 AMERICAN MUSEUM NOVITATES NO. 2662

the lacrimal lie at about a 45 degree angle to BASISPHENOID: The basisphenoid, although the horizontal midline elements. The bone nar- incomplete, is the only one reported among the rows posteriorly to present only a thin contact saurerpetontids. The element is exposed ven- with the prefrontal. trally so as to show part of the right basi- MAXILLA: The left maxilla is dissociated pterygoid process, a waist immediately behind from the rest of the skull and lies over the right the process, and diverging lateral walls both lower jaw. Twenty teeth are visible with space anteriorly and posteriorly. The bone is 3.0 mm. for 10 to 14 more. The teeth gradually decrease high. The dorsal half of the right lateral wall in size posteriorly. The anterior teeth are ap- extends 3.5 mm. anterior to the basipterygoid proximately 0.9 mm. in height, whereas the process and 2.0 mm. posterior to the broken posteriormost decrease to 0.6 mm. in height. ventral edge. This part of the wall is crushed The maxilla is broken so that the narial border and pushed slightly outward. No foramina are is missing dorsally. The bone as preserved is visible. 22 mm. in length, and is similar in length to The right basipterygoid process points ante- Isodectes but shorter relative to skull length in riorly at a 40 degree angle from the midline. Dvinosaurus and Saurerpeton. If the maxilla The articulating surface is oval and directed ends under the posterior end of the orbit the dorsolaterally. The surface is unfinished so that anterior margin extends just ventral to the the process must have been finished in car- naris. The length of this maxilla agrees well tilage. A groove courses over the process at its with that of the type. Unlike the type, the base dorsally. A ridge runs back from the posterior part of the new maxilla does not basipterygoid process along the lateral edges of curve ventrally as the beginning of the down- the ventral surface. A shallow trough results turned cheek. with the ridges forming the lateral walls. The trough wall is thickened between the basipterygoid processes but the floor thins posteri- BRAINCASE orly. Although crushed and displaced laterally, IMPRESSIONS ON THE SKULL ROOF: There the dorsal half of the lateral wall was more are distinct impressions of the dorsal braincase vertical in life. The part extending past the margins running longitudinally along the parie- basipterygoid process would then bend ante- tal bones. Near the postparietal-parietal bound- romedially. This anterior arm when joined with ary, the braincase impression is widest. From its partner forms the posterior portion of the its posterior end the impression gently curves sphenoid. A vertical break above and slightly anterolaterally to a maximum width of 3.0 mm. behind the basipterygoid process may represent The border then curves sharply medially toward a suture between the sphenoid and the basi- the parietal foramen to form a distinct waist. sphenoid. The edge of the waist forms a right angle. The basipterygoid processes are 6 mm. apart From the waist, the impression runs anteriorly when measured at their lateralmost edges. Up and slightly laterally at a constantly increasing to 4 mm. more in width could be occupied by width in the sphenethmoid region. The impres- the cartilaginous part of the processes. Adding sion disappears toward the anterior border of another 8 mm. for the horizontal shelves of the the parietals. pterygoid (at the internal process), the total The dorsal margin of the braincase appears width allowed for the wings of the para- to be narrow because its borders are totally sphenoid is approximately 18 mm. This meas- confined to the medial half of the parietal urement agrees quite well with the width of width. A narrow braincase is presumed by parasphenoid wings of 20.0 mm. Allowing that Romer (1947) to indicate a primitive condition. the specimen at hand is larger than the type, The platybasic type is characteristic of more the width of the parasphenoid wings agree quite advanced temnospondyls. Unfortunately the well. condition in other saurerpetontids is unknown. OCCIPUT: All the elements of the occiput are 1978 COLDIRON: ACROPLOUS VORAX HOTTON 9 present and in near perfect articulation (fig. 3). The basioccipital is poorly ossified, and this The occiput and posterior part of the skull table portion does not protrude posteriorly from the are crushed on the same plane. The occiput occiput. The supraoccipital is completely unos- could slope more than 50 degrees backward sified, but a broad space wedges between the from the horizontal, which is at least 30 de- postparietals and indicates its presence in car- grees greater than the angle in Kourerpeton. tilage. The occipital angles found in brachyopids are BASIOCCIPITAL: The basioccipital consists of intermediate between Kourerpeton and Iso- two ventrally oriented fingers of bone wrapped dectes (400 to 200 from horizontal). In Acro- around the back of the parasphenoid. These plous the posteriormost extent of the exocci- two processes barely meet at the midline, thus pitals reaches 5 mm. back of the skull table. excluding the parasphenoid from an occipital exposure. Dorsally, the basioccipital is deeply recessed and is of unfinished bone. Exclusion of the parasphenoid from the occiput is a primitive feature among temnospondyls although Isodectes and brachyopids show the advanced condition in which the parasphenoid breaks through to the occipital surface. The condition in Dvinosaurus is unclear. -cult proc In ventral view some of Bystrow's (1938) figures show the basioccipital excluding the parasphenoid from the occiput. In occipital view, Bystrow's figure 5 shows the parasphenoid well pp exposed. EXOCCIPITAL: The exoccipitals form the lateral and ventrolateral borders of the broad oval- shaped foramen magnum. Ventrally, the foramen magnum is open. Two narrow arms of the exoccipitals face each other on the ventral mar- ta gin but do not meet. The basioccipital could have contributed to the ventral margin, or the e x arms of the exoccipital could have met in cartilage. The type specimen is more incomplete in this region and does not help clarify the matter. psphh In occipital view, the exoccipital has a wide contact with postparietal and tabular and narrows ventral to the foramen magnum to form an unfinished posteroventrally directed condylar ex surface. This condylar surface is unfinished so bocc that it must have been continued in cartilage. The posteroventral orientation of the condyle and its long posterior projection indicate that it contributed at least to the dorsolateral part of FIG. 3. Top-back of skull roof, occiput, and the occipital condyle. Because of the poor os- cultriform process of parasphenoid in dorsal view. sification of the basioccipital, it cannot be de- X 1.5. Bottom-ventral view of same block showing the main body of parasphenoid and occiput. X2.1. termined what part it contributed to the Abbreviations: bocc, basioccipital; cult proc, occipital condyle. If the contribution of the cultriform process of parasphenoid; ex, exoccipital; basioccipital was small, the occipital condyle psph, parasphenoid; pp, postparietal; ta, tabular. could have been double. 10 AMERICAN MUSEUM NOVITATES NO. 2662

In ventral view the exoccipital laps over at the anterior edge of the ascending ramus both parasphenoid and basioccipital. The bone (and epipterygoid?). Posterior to this recess the then turns vertically to form a flat lateral wall. ascending ramus rises 3.5 mm. A low broad The XII cranial nerve pierces the lateral wall ridge separates the recess from the higher por- anterodorsally near the contact with the tion of the ascending ramus. postparietal. The nerve may have turned dor- In natural postion the recess would cover sally and posteriorly into a canal which exits only the anterior portion of the basipterygoid the exoccipital ventral to the foramen magnum. process. Because the extent of the epipterygoid No evidence for a vagus foramen can be de- is unclear it is difficult to determine how much tected. The exoccipital is compared more fully it contributes to the basal articulation. How- with other trimerorhachoids in the discussion. ever, the articulation was certainly movable and Opisthotic and prootic bones are missing or the epipterygoid must have played a part. The were not ossified. condition in other saurerpetontids is unknown due either to lack of preservation or ossification. Trimerorhachis presumably maintained PALATE the primitive condition (Romer, 1947). The palate is represented only by the The internal process of the pterygoid proj- pterygoid and parasphenoid. Both right and left ects only 1 mm. medially, below, and slightly pterygoids are present with the left exposed forward of the recess on the dorsal ramus. The laterally and the right medially. Both are essen- maximum width of the horizontal shelf from tially complete. The anterior and posterior ends the internal process to the vertical wall is only of the right pterygoid are buried under the left 3.0 mm. It would be difficult to accommodate pterygoid and left clavicle, respectively. a long lateral wing of the parasphenoid. PTERYGOID: Palatal, quadrate, and ascending However, a horizontal shelf indicates that there rami make up the pterygoid. The palatal ramus was a dorsal covering over the parasphenoid as has only a thin horizontal shelf running from in Dvinosaurus and Isodectes. Therefore, the near its tip to the middle portion of the bone. basal articulation between the dermal elements At its tip the shelf gradually turns ventrally and must be essentially the same. This shelf is cov- points ventrolaterally at 45 degrees. More pos- ered more fully in the discussion below. teriorly the shelf turns abruptly ventrally to The relation of the dorsal and quadrate rami form a vertical wall. The vertical shelf in- to the squamosal, quadratojugal, and quadrate creases steadily in depth posteriorly to just bones is unclear. The thickness and height of below the epipterygoid. The palatal ramus is the dorsal ramus certainly indicates a union 18.1 mm. in length. The quadrate ramus dips with the supratemporal-squamosal area in front steeply to further deepen the vertical shelf. The of the otic notch. The posterodorsal margin of quadrate ramus is short (9.2 mm.) and bends the ascending ramus curves slightly laterally only slightly laterally toward the back margin and could have lapped over the squamosal. Un- of the cheek. The sharp downturning of the like the type specimen, there is no shagreen of quadrate ramus must have made the cheek at palatal teeth on the medially exposed right least moderately deep as in Isodectes, Kourer- pterygoid. peton, and the brachyopids. PARASPHENOID: The parasphenoid is nearly The posterior margin of the pterygoid is complete with the anterior half of the cultriform nearly vertical and extends upward and forward process left as an impression. The cultriform to the epipterygoid. Broken sheets of bone process gradually widens anteriorly to a max- overlap the ascending ramus of the pterygoid imum width of 7 mm. This width is compara- and may represent parts of the epipterygoid. ble to the relatively wide cultriform process The ascending ramus together with the epi- found in other saurerpetontids. At its anterior pterygoid and ascending ramus of the pterygoid expansion, faint grooves cut into the ventral point anteromedially at 45 degrees to the pala- surface which mark the contact with the tal ramus. A posteromedially facing recess lies vomers. In life this contact was probably mova- 1978 COLDIRON: ACROPLOUS VORAX HO1TON 11 ble because of complete separation of the para- teeth forming a shallow U. Posteriorly, the jaw sphenoid and anterior portion of the palate. The is more slender and higher in cross section but cultriform process is marked by a median ridge remains wide. Ornament is present mainly on running along the ventral surface. the ventral half of the lateral surface and is At the base of the cultriform process, the moderately rugose. The lower jaw length af- borders turn abruptly and at right angles later- fords much information about the skull length. ally to form the anterior edge of the para- The distance from the symphysis to the poste- sphenoid wings. This anterior border is slightly rior end of the glenoid fossa is 53 mm. The concave. The wing terminates laterally in a distance from the "occipital crest of postparie- blunt tip 2 mm. wide. The leading edge of the tal to snout" (Hotton, 1959) in Acroplous is 44 wing is of reasonably thickened bone. Rein- mm. All in all, the jaw is typical in general forcement of the leading edge suggests the par- shape to that in any trimerorhachoid. Only in asphenoid wings articulated with the horizontal the anterior dorsoventral compression is it shelf of the pterygoid, and thus contributed to atypical. the basal articulation. The basal articulation, The tooth row in the new specimen is more then, is composed of both pterygoid-para- complete than the tooth row in the type. sphenoid and basisphenoid-pterygoid (plus epi- Twenty teeth are present in the left ramus with pterygoid) parts. This interpretation agrees with space for about 10 more. The teeth increase in Hotton's (1959) for the type specimen. size posteriorly to the ninth tooth (fifteenth if a The posterior border of the parasphenoid complete row were present). Tooth size varies wings runs posteromedially to a broadly only slightly posterior to the ninth tooth. The rounded end. The exoccipitals and basioccipital largest teeth reach a height of 2,0 mm. The flank the entire posterior border. The body of variation in tooth size cannot be studied with the parasphenoid receives the exoccipitals in a respect to replacement. Removal of matrix shallow elongate depression just posterior to the from around the fragile teeth would almost cer- wings. Farther posteriorly, the rounded end of tainly destroy the tooth row. A tusk rises from the body is sutured to the ventrally directed the medial margin near the symphysis. All the wedge-shaped fingers of the basioccipital. The teeth show shallow labyrinthine infolding of the rounded end of the body has no open exposure enamel at their bases. to the occipital surface. DENTARY: The dentary is a long, thin bone which occupied no more than one-third to one- LOWER JAW half of the lateral jaw surface. Acroplous shows the primitive condition of narrow exposure of Both rami of the lower jaw are present. The the dentary relative to Trimerorhachis, Iso- left ramus is exposed in lateral view and is dectes (Chorn, personal commun.), and Saurer- nearly complete and undisturbed. The right peton (USNM 4471). The condition in ramus affords a medial view and is crushed so brachyopids is variable as seen in Watson's that the lateral half is displaced slightly above (1956) figure 2 of Bothriceps and Welles and the medial half. In both rami the bone is frac- Estes's (1969) figure 20 of Hadrokkosaurus. tured badly in places but most sutures can be Ornament is lightly developed with only faint made out. striations present. Posteriorly, the dentary is The ramus is slender anteriorly. Past the broken immediately in back of the tooth row. tooth row the dorsal margin swells to a max- A jagged edge continues posteriorly to the front imum height near the dentary-coronoid junc- of the adductor fossa. This missing portion of ture. Farther posteriorly the jaw narrows the dentary begins to rise gently toward the gradually dorsoventrally. A long, strongly de- coronoid process but wedges out below it. Me- veloped retroarticular process (7.5 mm.) ex- dially, the bone is exposed only slightly. tends past the glenoid fossa. SPLENIALS: The splenials have a noticeably In cross section the anterior portion of the pitted surface unlike the dentary. The bones are ramus is rounded with the bones below the laterally exposed for about one-half the height 12 AMERICAN MUSEUM NOVITATES NO. 2662 of the ramus. This wide exposure is primitive The splenials take up the rest. More posteriorly and its analysis is covered above in the descrip- the coronoids bear a large number of closely tion of the closely associated dentary. The ori- packed denticles which run anteriorly to at least entation is nearly flat ventrally and only takes a the middle of the tooth row. Toward the ante- shallow dorsal turn to meet the dentary. The rior end no denticles appear. The presence of result is a compressed anterior half of the jaw. denticles is a primitive rhachitomous feature The anterior splenial most probably shared in which persists into the brachyopids (cf. the jaw symphysis with the dentary. There is Hadrokkosaurus). no sign of narrowing anteriorly. Both splenial ARTICULAR: If the interpretation of the artic- and postsplenial are of equal length. The ular is correct, Acroplous would be unique postsplenial meets the angular under the third among rhachitomous amphibians in having a tooth from the end of the tooth row. The wide lateral exposure. The articular meets the splenials occupy one-third of the medial wall surangular dorsally about 3 mm. anterior to the and lie under the coronoids. This is a relatively glenoid fossa. Laterally, the suture runs post- advanced condition and Saurerpeton (AMNH eroventrally, the articular meeting the angular 6935), Trimerorhachis, and Isodectes (Chorn, below the anterior rim of the glenoid fossa. In personal commun.) have broad medial expo- medial view the suture runs vertically just pos- sures as well. On the other hand, Dvinosaurus terior to the foramen chorda tympani. This fo- shows the primitive condition. ramen lies just anteroventral to the glenoid ANGULAR AND SURANGULAR: The posterior fossa. half of the jaw is badly fractured in lateral The rim of the glenoid fossa forms a ridge view. Parts of the sutures are obscured, and of thickened bone dorsally and laterally extend- some of the bone surface is worn away. The ing back to the end of the retroarticular proc- surangular is restricted ventrally by a deep an- ess. The fossa faces slightly laterally so that, gular. The angular takes up approximately articulated, the angular-surangular wall and ad- three-quarters of the lateral surface. In tri- ductor fossa lie vertically. merorhachoids such as Trimerorhachis the an- The retroarticular process is long and stoutly gular is equally advanced in its dominance over developed, as in all saurerpetontids and the surangular. However, Dvinosaurus, Saurer- brachyopids. A groove runs dorsally along its peton, and Isodectes are more primitive in hav- entire length which must serve for insertion of ing only a thin lateral exposure of the angular. part of the depressor mandibuli muscle. The The condition in brachyopids is variable as well-developed retroarticular process, and long, seen in Bothriceps (Watson, 1956) or Hadrok- deep adductor fossa point to an extremely kosaurus (Welles and Estes, 1969). Medially, strong jaw apparatus. The presence of reinforc- the angular covers a narrow longitudinal strip ing lappets of the dermal skull roofing bones below the adductor fossa, like all trimero- goes in hand with the well-developed trigemi- rhachoids for which the medial surface of the nal musculature. As far as can be determined, jaw is known. Dorsally, the surangular shares nearly all bones of the lower jaw abut against the anterior one-quarter of the coronoid process or overlap their neighbors. with the posterior coronoid. Medially, the surangular covers all but the anteriormost lateral VERTEBRAE wall of the adductor fossa. PREARTICULAR: The prearticular covers the The vertebral column is very fragmentary. medial surface of the adductor fossa. Ante- Only a few vertebrae are present but all are riorly, the prearticular extends past the small well preserved and afford different views of the posterior meckelian foramen. Anterior to the separate elements. meckelian foramen the element is obscured. NEURAL ARCH: The neural arch (fig. 4a) CORONOIDS: Only parts of the coronoids and measures 11 mm. in height and 5 mm. in width splenials of the right ramus are exposed under from a line running horizontally through the overlying bone fragments. The coronoids oc- anterior zygapophysis. Immediately dorsal to cupy fully two-thirds of the medial jaw surface. this process the arch constricts to a waist 2.5 1978 COLDIRON: ACROPLOUS VORAX HOTTON 13

mm. wide. The dorsal edge of the spine slopes downward anteriorly and is 3.5 mm. wide. The pedicel is a broad triangular element. The posterior surface runs nearly directly vertically. The anterior margin is wavy and runs anterodorsally at 45 degrees. There is no trans- narch n arc verse process on the pedicel. The bone is narnnrsmooth with very little relief. Only a small notch separates the zygapophysis from the pedicel. The anterior zygapophysis extends forward nearly 3 mm. from the anterior border of the arch. The posterior zygapophysis is poorly pre- pc\' / \ served but forms a flat articulating surface at iC \', pC least 1.4 mm. long. This surface leads into a notch that forms the posterior part of the waist. 7 ~~~Dorsally, the zygapophysis is set off from the 7 ~~~spine as a low bump. The neural arch resem- A l' J Jbles the dorsals of Neldasaurus and Dvino- saurus in having fairly well-developed posterior zygapophyses and simple rectangular neural spines. These features seem to be primitive for rhachitomes. In end view the pedicels expand ventrally, A1: {posteriorly, and laterally to form two triangular shaped areas of bone. This posterior expansion /:'.'.Q/.;\,.. must have reinforced the rib articulation. Ante- riorly, the pedicel wedges out to a sheet of bone. Posteriorly, there is only a small indentation for the nerve cord. Dorsal to the pedicel the arch narrows rapidly to form a narrow spine. Just dorsal to the posterior zygapophysis lies a shallow pit which must have served as an ...t..*@.1,.5s.i-twi , origin for an interspinous ligament. INTERCENTRUM: The intercentrum is a broad

- . /..U-shaped, jt.....element, as in most rhachitomes. It is 3.2 mm. long ventrally. Dorsally, the bone constricts slowly to a narrow wedge. The element is 6.9 mm. high and the ascending processes barely point toward one another. The external surface is featureless except for two ridges running dorsoventrally along the borders. There is no indentation for reception of the rib capitulum. PLEUROCENTRUM: The pleurocentra appear very much like the type. They are 4.0 mm. D high and 1.5. mm. wide. Very little surface FIG. 4a, b. a. Reconstruction of vertebrae. Dotted relief is present with only a very slight indenta- line indicates probable cartilaginous extension of tion on the posterior edge for articulation with pleurocentrum. Abbreviations as in figure 1. x 3.5. the rib capitulum. The bone is of only moder- b. Scales reconstructed from fragments. One os- ate thickness unlike the relatively stout inter- teoderm shown at right. x 14. centrum. The anterior and posterior edges are 14 AMERICAN MUSEUM NOVITATES NO. 2662

parallel. Both dorsally and ventrally, the edges bone length so as to form broad wings. The converge to a point. Overall, the element re- anterior border is not present, but there is no sembles a long parallelogram. indication of any anterior constriction. The an- Nearly all the vertebral elements are disar- terior edge was probably broad and straight. ticulated, but reconstruction is not difficult Ridge impressions indicate that there may have because of the excellent preservation. Three been a pectinate extension of the anterior mar- nearly complete neural arches are exposed in gin as in the type. lateral view. Two lie adjacent to each other and The interclavicle clearly shows wide, low- a third is far removed. Two fully exposed inter- ridged impressions for the clavicles on its centra, one in lateral and the other two in end wings and anterolateral margins. These impres- view, are used for the reconstruction. Only one sions become narrow and pinch out altogether pleurocentrum is adequately preserved to assist at least 5 to 7 mm. from the anterior margin. in the reconstruction. Anteromedially, there is a broad ornamented The neural arch points backward at an angle space (6 mm.) that separated the two clavicles. of approximately 27 degrees from the vertical. CLAVICLE: The clavicles, also, are unre- At this angle, the anterior and posterior markable, exhibiting no marked differences zygapophyses lie horizontal and are in wide from other trimerorhachoids with the exception contact (1.4 mm. overlap). The pedicel forms a of a large foramen that punctures the element at wide ventrally pointing wedge and abuts its anterior tip. The elements are anteriorly oval against the anterior surface of the pleuro- in outline. The posterior border is wide and centrum. A slight concavity in the anteroventral excavated. The lateral and medial borders are edge of the pedicel receives the ascending proc- convex with a sharp convergence anteriorly. ess of the intercentrum. Posterolaterally, the dorsal process rises at a The ossified portions of the central elements sharp angle from the body of the clavicle. are of unequal size, with the intercentrum con- Both clavicles have their internal surface ex- spicuously larger than the pleurocentrum. posed. Striations run parallel to the ante- However, because of the great width of the romedial edge that mark the area overlapping pedicel and backward pointing neural arches, the interclavicle. The anterior end is thickened the pleurocentrum must have been continued in and elevated above the rest of the bone which cartilage to a greater overall size than the inter- forms a shelf. This shelf continues along the centrum (fig. 3). When in natural position the lateral border to the posterolateral upwelling for two elements contribute to supporting the arch the dorsal process. This upwelling indicates very much like some dissorophids (Doleser- that the anterior tip of the bone was lateral to peton) and unlike other trimerorhachoids. the interclavicle border. The posterior border extends about 2 mm. past the dorsal process. PECTORAL GIRDLE The length of the entire bone is about 24 mm. CLEITHRUM: Only the descending stem (6 A nearly complete interclavicle, two partial mm. with 2 mm. more as an impression) of the clavicles, and a fragment of a cleithrum repre- cleithrum lies open to view. The stem increases sent the pectoral girdle. in diameter until it plunges into matrix below INTERCLAVICLE: In every respect except its the overlying right clavicle. A prominent anterior margin the interclavicle is typical of groove runs longitudinally for the reception of the rhachitome type. The element is strongly the anterodorsal edge of the scapula. The extent ornamented ventrally and has a dorsally shal- of the dorsal expansion over the scapula cannot low concave curvature. The posterolateral bor- be determined. ders are gently concave, whereas the antero- The large, shallowly curved interclavicle and lateral borders are straight and converge at a clavicle and the sharp angle between the dorsal very shallow angle. The lateral corners are stem and main body of the clavicle indicate wide transversely over about one-third of the quite clearly a flat-bodied animal. 1978 COLDIRON: ACROPLOUS VORAX HOTTON 15

APPENDICULAR SKELETON oped supinator process. The degree of twist in Acroplous is comparable to that in Dvinosaurus The appendicular skeleton is meagerly repre- but less than in Trimerorhachis. The humerus sented. Only a right humerus and one phalanx of Isodectes is unknown, whereas the Saurer- are present. peton humerus is preserved but all features are HUMERUS: The humerus is complete and is obscured. exposed dorsally. Both proximal and distal The only phalanx preserved is dorsoventrally ends are expanded and completely developed. compressed with the ends slightly expanded. The two ends are twisted 46 degrees to one another. A similar degree of twist occurs in Eryops (KU 762). The type humerus has only a RIBS 10 to 15 degree twist. In the referred specimen Eight ribs are scattered over the block and most crests and processes are only slightly de- none are in direct association with vertebrae. veloped. There is no distinguishable supinator Five cervicals and three dorsal ribs are present. process. The pectoral crest tums sharply down- Neither of the two series is remarkable in any ward and curves moderately ventral to end in way. Neldasaurus shows similar dorsal ribs, matrix level with the humerus waist. The sharp whereas the cervicals resemble closely those downward turn sets off the pectoral crest from described for Gephyrostegus (Carroll, 1970). the rest of the head. The long length and mod- The cervical ribs are broad, anteroposteriorly erate curvature points toward a crest as strongly compressed, and short. The head is differenti- developed as in Eryops. ated into two distinct capitular and tubercular The articulating portion of the head is short, facets. The tuberculum is a long (4 mm.) nar- thin, and nearly straight, ending in a slightly row process which is a continuation of the curved knob. This knob must be the sub- dorsal margin of the rib. The capitulum in one coracoscapularis process. It is developed to a rib is well developed (1.8 mm. long) and runs similar degree in Eryops. roughly parallel to the tuberculum. In other The proximal expansion constricts to a waist cervicals the capitulum projects only as a boss and then immediately expands distally. There is separated from the tuberculum base by a slight no shaft unlike the moderate one seen in the concavity. The capitulum articulated on the type. Slight ridges run distally from the waist lower one-third of the posterior face of the toward the ectepicondyle and entepicondyle. A intercentrum with the tuberculum lying just slight bump forms the end of the ectepicondyle. above the angle of the pedicel. The distal end is triangular in shape with the The total length of 14.1 mm. is only one and anterior and posterior halves converging at right one-third times greater than the height of the angles. Their intersection is emarginated to ac- neural arch. The shaft is wide proximally (3.0 commodate the olecranon process of the ulna. mm.) but constricts at mid-length to a width of The entepicondyle extends much farther distally 2.1 mm. The shaft expands distally to a width than the ectepicondyle as in Eryops. of 2.8 mm. Part of the distal expansion forms a The general outline of the humerus resem- dorsally directed blade. The distal end is un- bles that of Eryops except most areas for mus- finished bone and presumably continued in car- cular attachment are not nearly so well tilage. A low, narrow ridge traverses the developed. The poor development of muscle ventral surface from the tubercular process attachments indicates an animal adapted to an down across the posterior face to the distal end aquatic life. This agrees with the aquatically of the bone. The anterior face of the rib is shaped flat clavicle and abruptly upturned dor- smooth with no irregularities. sal process. However, the humerus is stout and The cervical ribs most likely ran postero- relatively long compared to skull length. ventrally with the anterior surface facing later- Dvinosaurus and Trimerorhachis are more ally. This orientation would allow the anterior primitive in still maintaining a weakly devel- surface to front the internal surface of the 16 AMERICAN MUSEUM NOVITATES NO. 2662

scapula. The ribs may have overlain one an- The similarities of the referred specimen to other distally as evidenced by the longitudinal the type leave no doubt that they are the same ridge and the small dorsal expansion at the species. The skull roof is nearly identical with distal end. that of the type (fig. 2). The wide overlap of Where along the vertebral series the dorsal some of the skull roof elements could easily ribs belong cannot be determined. These are account for the small differences seen in ventral more like typical rhachitomous dorsal ribs with and dorsal views. The humerus exhibits the the capitulum and tuberculum forming a single, largest difference between the specimens but undivided head. The head is shaped so that the this is due to increased maturity. Hotton (1959) tuberculum is set off at an angle from the stated that "ossification in most of the ... capitulum. Like the ribs, the shaft is anteropos- limb bones is restricted to perichondral layers teriorly compressed. The shaft remains fairly ." Because the new specimen is more ma- constant in width (2.4 mm.) up to the distal ture, more periosteal bone is deposited, giving third of the bone where it gradually tapers. A the bone its larger size and better developed groove runs along the dorsal edge of the proxi- articular surfaces and processes. mal one-half of the rib. The largely cartilaginous pleurocentra are Both dorsal ribs are incomplete and have a probably larger than intercentra in the referred minimum length of 16.0 mm. so that they are specimen. The vertebrae as preserved only rep- slightly longer than the cervical ribs. The shaft resent the ossified portions of the column. Pre- is only slightly curved so that the ribs extend sumably, the type pleurocentra were also far laterally. The result is a dorsoventrally com- continued in cartilage to a greater overall size pressed body form. The ventral body width than the intercentra. The neural arches lie at a across the pectoral girdle is at least 35 mm. flatter angle on the centra as indicated by the This figure agrees well with the rib length plus poorly developed posterior zygapophyses. vertebral width (8 mm.) of 40 mm. Comparison to the type in this regard is difficult because only two partial neural arches are SCALES exposed. Nothing of its structure contradicts the Pitted new interpretation. Two types of scales are preserved. The pterygoid of both specimens is identical subround osteoderms fit well with similar struc- of tures on the type. Only isolated pieces are except for size. The dorsal margin epi- of the matrix. pterygoid, conical recess, and deep vertical found throughout different layers shelf of palatine ramus agree completely. The A series of articulated scales lie on one small anteriormost of the ramus has a shale fragment (fig. 4b). The scales are much part palatine 2 with slightly wider horizontal shelf in the type. longer than wide (6 mm. to mm.) gently However, the anterior part of the vertical shelf convex longitudinal borders. Each scale appears could have been crushed into the horizontal to overlap one-half of its neighbor. Very low ramus in run down the scales. The plane. The ventral half of the quadrate ridges longitudinally the type is missing. scales are very thin. The clavicles prove to be more broad than illustrated for the type. This may be due to DISCUSSION differences in relative growth of the larger (re- In this section I summarize the similarities ferred) specimen. between the type and referred specimens of Both lower jaws, basisphenoid, cervical Acroplous vorax so as to establish that they are ribs, and neural arches add more information conspecific. Further, and more importantly, I about Acroplous vorax. However, these struc- attempt (1) a precise placement of Acroplous tures are either not present or incomplete in the within the saurerpetontids; (2) the relation of type and do not invite comparison between the this group to the brachyopids; and (3) an analy- specimens. sis of all characters used in a hypothesis of Placement of Acroplous within the Tri- relationships with respect to other rhachitomous merorhachoidea has been established by Chase amphibians. (1965). Advanced characters used by Chase are: 1978 COLDIRON: ACROPLOUS VORAX HOTTON 17

(1) antorbital flattening; (2) small otic notch; (3) which unite trimerorhachids, Dvinosaurus, sau- "postorbital segment of skull expanded"; (4) rerpetontids, and brachyopids as a monophy- short faced; (5) "quadrate close to the level of letic group (however, see discussion of the occipital condyle"; (6) "broad cultriform character 4, below). It is not known whether or process of the parasphenoid"; (7) "anterior pal- not trimerorhachoids are monophyletic but are atal fenestrae"; (8) "modest retroarticular proc- shown to be such in figure 5. It is beyond the ess in the lower jaw." scope of this paper to attempt to test the hy- Previous to Chase's work other workers pothesis that they are monophyletic. Character were led astray by an earlier interpretation of 1 (otic notch poorly developed) occurs in the Saurerpeton in which its synonym "Pelion" group listed in figure 5 and in Otocratia (Wat- was thought to be a valid genus. Steen (1931) son, 1929), Colosteus (Romer, 1930), Er- and Watson (1956) had misinterpreted the ante- petosaurus (Romer, 1930), Tertrema (Romer, rior palatal fenestrae of "Pelion" for internal 1947), Cyclotosaurus (Fraas, 1889), and meto- nares. As a result Hotton (1959) followed Steen posaurs (Sawin, 1945). Tertrema and and hypothesized two parallel lineages of tri- Cyclotosaurus secondarily close the otic notch merorhachoids. He attempted to place Acro- but an opening is still present. The condition is plous in a line between Saurerpeton and not comparable to trimerorhachoids. The Dvinosaurus largely on the presence of sym- metoposaurs may be closely related to the physeal tusks and anterior palatal fenestrae. brachyopids (Romer, 1947) and this is not a Hotton's other line consisted of "Pelion"- valid outgroup. The other genera are unrelated "Eobrachyops" brachyopids. Hotton thought to one another, and presumably do not repre- these three genera lacked symphyseal tusks and sent the primitive condition for temnospondyls. anterior palatal fenestrae, and thus were closely Character 2 (expanded postorbital region) related. Chase established that symphyseal occurs in the groups listed in figure 5, Co- tusks and accompanying palatal fenestrae are losteus (Romer, 1930), Erpetosaurus (Romer, present in all adequately known trimero- 1930), various trematosaurs (Meyer, 1858; rhachoids. Therefore, no dichotomy between a Huene, 1920), plagiosaurs (Watson, 1956), and Trimerorhachis-Acroplous line and "Peli- metoposaurs (Fraas, 1889; Case, 1922; Branson on"-"Eobrachyops" line existed. Instead, Ac- and Mehl, 1929). We see that only two primi- roplous, "Eobrachyops," and Saurerpeton were tive types possess an expanded postorbital re- placed in a new family, the Saurerpetontidae. gion. Trematosaurs are not primitive laby- This study corroborates Chase's hypothesis that rinthodonts and their systematic position within these three genera, including the newly de- the group is uncertain. Metoposaurs and pla- scribed Kourerpeton (Olson and Lammers, giosaurs (Romer, 1947; Watson, 1956) may be 1976) and the brachyopids, are more closely close relatives to the brachyopids. These related to one another than to any other tri- groups, then, do not constitute valid outgroups. merorhachoid. Further, this study hypothesizes Character 3 (broad cultriform process) oc- that Dvinosaurus, which Chase (1965) placed in curs in many other labyrinthodonts besides a separate family, is the sister group to the those in figure 5. The only primitive type with Saurerpetontidae. a broad cultriform process is Eugyrinus (Wat- Figure 5 shows a hypothesis of relationship son, 1921). Various eryopids such as Eryops for Trimerorhachis, Dvinosaurus, the saurerpe- (Sawin, 1941), Platyrhinops (Steen, 1931), tontids, and the brachyopids. One can see from Stegops (Romer, 1930; Steen, 1931) have a figure 5 that the saurerpetontids are paraphylet- moderate to broad cultriform process. It also ic, for they exclude their sister group, Kourer- occurs in more advanced rhachitomes such as peton plus the brachyopids. The numbers at the the trematosaurs Lyrocephalus (Save-Soder- nodes of the cladogram refer to characters bergh, 1935), and Peltostega (Wiman, 1916), which appear in table 1. Each character is the neorhachitomes Lydekkerina (Watson, 1919) thought to be apomorphic at the level in which and Sclerothorax (Huene, 1932), and various it appears. The characters are discussed sepa- capitosaurs (Meyer, 1858; Welles and Cosgriff, rately below. Characters 1-6 are apomorphies 1965). Again, the metoposaurs (Case, 1922; 18 AMERICAN MUSEUM NOVITATES NO. 2662

. A \t\fP,\7 ;,\00 H°\° Of ~~o(~~O050 °'(e(pe (~~09 dejSe(9e0 0O\ \ 0~~22,28 C<3 R1,32 CS1 \/ 30

\ \ \ 22,~~~~~23,24

\ \ ~~~~19,20,21

FIG. 5. A hypothesis of relationships that unite trimerorhachids, Dvinosaurus, saurerpetontids (Saurerpeton, Acroplous, and Isodectes), Kourerpeton, and brachyopids as a monophyletic group. The numbers refer to derived characters listed in table 1.

Branson and Mehl, 1929) and plagiosaurs natural group. Brachyopids, however, show (Huene, 1922) show this character. Because what looks like the primitive condition of me- only one primitive form (Eugyrinus) possesses dian unpaired fenestrae. To maintain the pres- the broad cultriform process it is thought to be ent hypothesis one must argue that brachyopids derived for the trimerorhachoids. These other secondarily fused the fenestrae independently of advanced groups which show it could be other groups that also show the character. This argued to be closely related to tri- ad hoc hypothesis weakens the hypothesis of merorhachoids, but this would rely on a par- relationships shown in figure 5. simony argument. All that can be shown here Character 5 (retroarticular process moderate is that character 3 tends to unite the groups in in length) occurs in every taxon of figure 5 in figure 5 as a monophyletic group. which the lower jaw is well enough known. Character 4 (paired anterior palatal fenes- The character appears in few other temnospon- trae) occurs in very few labyrinthodont genera dyls except most stereospondyls (Nilsson, besides those appearing in figure 5. Genera 1944). Among more primitive rhachitomes the such as Trematosuchus (Haughton, 1925), character occurs in Cacops (Case, 1911) and Platystega (Wiman, 1915), Tertrema (Wiman, Eugyrinus (Nilsson, 1944). Most primitive 1917), Trematosaurus (Watson, 1919), Kes- forms lack any retroarticular process such as trosaurus (Haughton, 1925), and Mastodon- the ichthyostegids, loxommids, and colosteids saurus (Fraas, 1889) also show character 4. All (where known). Regardless of the condition in other genera that show anterior palatal fenestrae stereospondyls, the character is considered to have median unpaired vacuities. The character be derived. as it appears in the latter two genera is proba- Character 6 (moderately developed medial bly not homologous on grounds of topographic exposure of angular) is found in only one prim- dissimilarity. Metoposaurs show paired anterior itive rhachitome, Megalocephalus. Nilsson palatal fenestrae and may be closely related to (1943) stated that this condition is advanced for the trimerorhachoids. Because only a few other the stegocephalia. Advanced taxa, besides those genera show character 4, the character is proba- in figure 5, which also show the character are bly advanced and unites trimerorhachoids as a Sassenisaurus (Nilsson, 1943), a capitosaur, 1978 COLDIRON: ACROPLOUS VORAX HOTTON 19 and Aphaneramma (Nilsson, 1943), a trema- unite Dvinosaurus, saurerpetontids, and brachy- tosaur. Within the trimerorhachoids, the condi- opids as a monophyletic group. tion is unknown in Kourerpeton. Saurerpeton Character 7 (antorbital flattening) is very (AMNH 6935) shows very clearly a narrow marked in these forms. A relatively deep snout medial exposure of the angular. The contribu- occurs in primitive rhachitomes such as Ich- tion of angular in Isodectes is similar, but from thyostega (Save-Soderbergh, 1932), Colosteus Watson's (1956) figures it could have been no (Romer, 1930), Macrerpeton (Romer, 1930), more than is seen in brachyopids. This study and Dendrerpeton (Steen, 1934). The status of shows the same condition in Acroplous. Among this character as being derived depends on the brachyopids, Blinosaurus (Cosgriff, 1969), meager reconstructions available being both ac- Hadrokkosaurus (Welles and Estes, 1969), and curate and representative. Boreosaurus (Nilsson, 1943) also show the Character 8 (broad parabolic outline of skull character. A narrow medial exposure of the in dorsal view) occurs in very few other angular seems to be derived for trimer- rhachitomes other than those of figure 5. Am- orhachoids. phibamus ( vPotamochaston Steen, 1938) and Characters 7 through 15 are used here to Stegops (Romer, 1947) have similar skull roof

TABLE 1 Apomorphous Characters Appearing in Figure 5 1. Otic notch poorly developed. 2. Expanded postorbital region. 3. Broad cultriform process. 4. Paired, anterior palatal fenestrae. 5. Retroarticular process moderate in length. 6. Moderately developed medial exposure of angular. 7. Antorbital flattening. 8. Broad parabolic outline of skull in dorsal view. 9. Modest ventrally directed flange of quadrate process of pterygoid. 10. Space separating pterygoid from squamosal in occipital view. 11. Narrow lateral exposure of splenials. 12. Squamosal and quadratojugal cover the posterior surface of quadrate. 13. Occiput projects posterior to skull roof. 14. Double occipital condyle. 15. Lateral wing of parasphenoid articulates on ventral shelf of pterygoid. 16. Small palatal teeth absent. 17. Maxilla fails to reach level of anterior border of subtemporal fossa. 18. Quadrate anterior to occipital condyle. 19. Cheek deep posteriorly with quadrate well below parasphenoid. 20. Palatine enters border of interpterygoid vacuities. 21. Well-developed coronoid process. 22. Pronounced ventrally directed flange of quadrate process of pterygoid. 23. Further reduction of otic notch. 24. Vagal foramen completely enclosed by exoccipital. 25. Palatine-vomer contact lateral to choanae. 26. Otic notch lost. 27. Antorbital flattening more pronounced. 28. Intertemporal lost. 29. Fusion of braincase and palate. 30. Posterior coronoid forms distinct pillar like coronoid process. 31. Tabulars reduced to narrow strips. 32. Wide lateral exposure of both splenials. 20 AMERICAN MUSEUM NOVITATES NO. 2662 outlines. Because these genera are not closely To accept Dvinosaurus as the sister group to related to the taxa under study, the character is the saurerpetontids, Kourerpeton, and brachy- considered derived. opids requires the ad hoc hypothesis that the Character 9 (modest ventrally directed quad- intertemporal was lost independently in rate process of pterygoid) occurs in no other Dvinosaurus. Bystrow (1938) suggested that the group of labyrinthodonts. Some temnospondyls postorbital may be a compound element. have a stout and deep quadrate process of the However, in all of Bystrow's illustrations the pterygoid (Megalocephalus, Eryops, Edops, ornament pattern radiates from the center of the Romer 1947), but in none of these does the postorbital out to its periphery. One sees no process form a sharp angle with the rest of the hint of two centers of ornament radiation or pterygoid. This character, then, is thought to be any other sign that the element may be com- derived for Dvinosaurus and its more ap- pound. omorphous sister groups. Chase (1965) mentioned other special char- Character 10 (space separating pterygoid acters in which Dvinosaurus is presumed to be from squamosal in occipital view) is used here advanced over most other trimerorhachoid gen- only tentatively. The character is unknown in era. The exoccipital completely surrounds the Saurerpeton, Acroplous, and Kourerpeton. vagal foramen as in Isodectes and Kourerpeton. However, it does occur in Dvinosaurus (Bys- The condition is unknown in Saurerpeton and trow, 1938), Isodectes, and brachyopids (Wat- its position is only guessed at in Acroplous. son, 1956). Among other temnospondyls Another supposed advanced character is the Platystegos (Watson, 1956), Platyops (Efre- tabular contributing to the paroccipital bar. The mov, 1933), and Trematosaurus (Jaekel, 1922) new specimen of Acroplous shows the same show the character. Except for Platystegos and condition. Again, however, the condition is un- primitive forms well enough known (loxom- known in Saurerpeton. Because of our spotty mids, Edops, Romer and Witter, 1942) the knowledge of the distribution of these features pterygoid is closely appressed against the squa- they cannot contradict the present hypothesis of mosal. relationships. Character 11 (narrow lateral exposure of Character 12 (squamosal and quadratojugal splenials) is found in only one primitive form, cover posterior surface of quadrate) occurs in Eugyrinus (Watson, 1940) besides those taxa only one other genus (Platystegos, Watson which share it in figure 5. Other temnospondyls 1956) besides Dvinosaurus (Watson, 1956) and which show the character are Eryops (Sawin, its more apomorphic sister taxa. However, the 1941) and stereospondyls (Nilsson, 1943). Acro- condition is unknown in both Saurerpeton and plous, as can be seen in figure 1, has a wide Acroplous. Olson and Lammers (1976) stated lateral exposure of both splenials (character that in Kourerpeton "the quadratojugal and 32). This is a clear contradiction to the hypoth- squamosal carry around the quadrate posteri- esis of relationships of figure 5. Because this is orly, but only slightly . . ." Regardless of its the only taxon that does not share the derived degree of expression, I regard the character as state it is considered to be a character reversal present in this genus. and hence an autapomorphy. However, consid- Character 13 (occiput projects posterior to ering the wide lateral exposure of splenials in skull rooF) is found only in those taxa in figure Acroplous as an autapomorphy is an ad hoc 5 except possibly Kourerpeton (Olson and hypothesis used to save the general hypothesis Lammers, 1976). The character is also ques- of relationships. Hence, regardless of what one tionable in Saurerpeton, although Watson calls the condition in Acroplous, the general (1956) illustrated the occiput of "Pelion" slop- hypothesis is weakened. ing posteriorly away from the skull table. Dvinosaurus has no separate intertemporal Metoposaurus (AMNH 1832) and Gerrothorax (character 28). This would tend to unite (AMNH 3868) also show the character. Be- Dvinosaurus with Kourerpeton and the cause the metoposaurs and plagiosaurs are brachyopids since this is a derived character. probably closely related to the brachyopids 1978 COLDIRON: ACROPLOUS VORAX HOTTON 21

(Romer, 1947), they do not constitute a valid plainly seen in Dvinosaurus (Amalitsky, 1921; outgroup. Therefore, the character is judged to Bystrow, 1938), Saurerpeton (AMNH 6928, be derived for Dvinosaurus and its sister group. USNM 4471, PU 19298) and Isodectes (AMNH Character 14 (double occipital condyles) oc- 2455). In all of these specimens the anterior curs in Dvinosaurus, brachyopids, and probably margin of the parasphenoid body abuts against Acroplous. The condition is unknown in a posteriorly facing wall of the internal process Kourerpeton (Olson and Lammers, 1976). It of the pterygoid. Dorsally, a shelf covers the was always assumed that Saurerpeton showed anterolateral portion of parasphenoid. In Acro- the primitive condition. However, specimen plous, Hotton (1959) has reconstructed the par- USNM 4471 shows what may be a ventrally asphenoid and pterygoid in an identical fashion. exposed exoccipital which carries a fairly wide Only the dorsal view of the internal process of posteriorly facing surface. It cannot be seen the pterygoid can be seen in the present speci- whether this surface is finished or was contin- men (KU 28352). Both Kourerpeton and ued in cartilage. At any rate the element looks brachyopids fused the parasphenoid with the very much like the exoccipital of Acroplous. pterygoid. The complete fusion of the palate to The condyle may have been double. Other the braincase in these two taxa in no way con- specimens give further suggestive evidence of a tradicts the hypothesis of relationships given in double condylar condition. A specimen of Sau- figure 5. On the other hand, because different rerpeton (AMNH 6837) shows a smooth occip- character states are involved, they cannot cor- ital surface, but to one side of the midline a roborate the hypothesis either. boss raises up toward the ventral surface of the Among different forms Dendrerpeton (Wat- occiput. This boss faces posteriorly and ends in son, 1956; Carroll, 1967) and Erpetosaurus unfinished bone. (Romer, 1930; Watson, 1956) share this char- These two specimens are very suggestive of acter. Among more advanced forms Actinodon the condition in Acroplous. It is entirely possi- (Watson, 1962) shares this character. Er- ble that the unfinished surfaces in the latter petosaurus is a colosteid and if that taxon con- specimen were completed in two separate car- stitutes the sister group to the trimerorhachoids tilaginous condyles. In no specimen of Saurer- then character 15 may be primitive within the peton was there any suggestion of a single saurerpetontids. However, because it is not occipital condyle. seen in all other primitive temnospondyls, and Watson (1956) stated positively that Iso- its distribution is not well known within the dectes possesses a single "large, concave con- colosteids, the character is used as a syn- dyle." After reexamination of the type (AMNH apomorphy. Obviously, in light of its distribu- 2455) all one can say of the basioccipital area tion in other temnospondyls, its assignment as is that a fairly large area of fractured and possi- being derived can only be tentative. bly unfinished bone exists. Dorsally, the exoc- Characters 16 through 21 unite Saurerpeton, cipitals form raised pillars that support large Acroplous, Isodectes, Kourerpeton, and brachy- unfinished and posteriorly facing bosses on lat- opids as a monophyletic group. Character 16 eral sides of the foramen magnum. Exactly as (small palatal teeth lost) is a weak character in in Acroplous and Saurerpeton these bosses that its distribution throughout the rhachitomes could have supported double cartilaginous con- makes its derived status questionable. In nearly dyles. However, given the relatively large area all primitive rhachitomes, palatal teeth (exclu- presumably filled by the basioccipital, a single sive of the shagreen of very small denticles) are condyle could also have been present. Because restricted to tusk pairs on the palatal elements. we simply do not know what the condition is in In Neldasaurus, Trimerorhachis, and these three genera this character must be con- Dvinosaurus a large number of small teeth sidered primitive. grow in line with the larger tusks. One cannot Character 15 (lateral wing of the para- use character 16 to corroborate the hypothesis sphenoid articulates on the ventral shelf of the in figure 5 with the present knowledge of its pterygoid) is a distinct character which is distribution within the trimerorhachoids. The 22 AMERICAN MUSEUM NOVITATES NO. 2662 character can only be derived if Tri- Dvinosaurus (Bystrow, 1938) have ratios of merorhachis, Neldasaurus, and Dvinosaurus 70.0 and 7.9, respectively. In Neldasaurus are primitive sister groups. Obviously, by using (Chase, 1965) the quadrate is actually above the these three genera as an outgroup, character 16 parasphenoid. If these three genera are more must be derived and hence corroborate the hy- primitive sister groups of Saurerpeton and its pothesis of relationships. If these three genera close relatives, then this character is derived. are more closely related to any of the "saurer- However, primitive rhachitomes in general petontids" or brachyopids, then character 16 have low ratios such as Megalocephalus would be primitive and could not corroborate (Romer, 1947) and Dendrerpeton (Romer, the present hypothesis. 1947). As for character 19 the distribution of Character 17 (maxilla fails to reach level of high ratio taxa within nonsaurerpetontid tri- anterior border of subtemporal fossa) is found merorhachoids would have to be known in in specified taxa in figure 5 and in che- order to assign the character as derived. noprosopids (Romer, 1947). The character also Character 20 (palatine enters border of inter- occurs in the capitosaur Stenotosaurus (Romer, pterygoid vacuities) occurs in nearly every 1947). The maxilla in the brachyopid Both- group of advanced temnospondyls besides those riceps just reaches the anterior margin of the of figure 5. There is no doubt that it is an subtemporal fossa. The metoposaur Metopo- advanced character for in no primitive form saurus also shows the condition seen in Both- does the palatine enter the vacuities. riceps. Because primitive rhachitomes do not Character 21 (well-developed coronoid proc- show the character (Ichthyostega, Save-Soder- ess) is discussed at this point only tentatively. bergh, 1932; Erpetosaurus, Romer, 1930; lox- One specimen of Saurerpeton (AMNH 6935) ommids, Watson, 1929; Edops, Romer and shows a well-developed coronoid process. This Witter, 1942; Dendrerpeton, Carroll, 1967; Eu- bulge behind the dentary, however, could be gyrinus, Watson, 1940; Eryops, Sawin, 1941) due to post-mortem crushing and flattening. Ac- as well as some advanced forms such as tre- roplous, Isodectes (Watson, 1956), and matosaurs and capitosaurs (just mentioned), the brachyopids have moderate (Hadrokkosaurus, character is thought to be derived. This judg- Welles and Estes, 1969) to well-developed ment is made in spite of some brachyopids and (Blinosaurus, Cosgriff, 1969) coronoid pro- metoposaurs showing an intermediate condi- cesses. The condition in Kourerpeton is un- tion. known. Dvinosaurus also has a pronounced Character 18 (quadrate anterior to occipital coronoid process but it is formed in a different condyles) occurs in no known primitive way. The posterior coronoid forms a distinct rhachitome. Besides those taxa in figure 5, pillar-like coronoid process (character 30). It is metoposaurs (Fraas, 1889 Case, 1922; Branson judged to be nonhomologous with character 21 and Mehl, 1929), some trematosaurs (Lyro- and, thus, cannot contradict the hypothesis of cephalus and Aphaneramma, Romer 1947) and relationships. the capitosaurid Cyclotosaurus (Meyer, 1858; Characters 22 through 24 unite Acroplous, Fraas, 1889; Welles and Cosgriff, 1965) show Isodectes, Kourerpeton, and brachyopids as a the same condition. Because these latter taxa natural group. Character 22 (pronounced ven- do not constitute the primitive sister taxa to trally directed flange of quadrate process of those listed in figure 5, the character is con- pterygoid) can be seen clearly in brachyopids, cluded to be derived. Acroplous, and Isodectes. The quadrate flange Character 19 (cheek deep posteriorly with of pterygoid in Kourerpeton does not bend ven- quadrate well below parasphenoid) can be seen trally to the same degree as in the former taxa. quite clearly in saurerpetontids, Kourerpeton, The condition in Kourerpeton, then, contradicts and brachyopids. These taxa have ratios of the hypothesis of relationships. It is required to quadrate width vs. height of parasphenoid erect an ad hoc hypothesis that Kourerpeton above the base of the quadrate of 5.6 or secondarily lost the more pronounced condi- less. Trimerorhachis (Watson, 1956) and tion. 1978 COLDIRON: ACROPLOUS VORAX HOTTON 23

Character 23 (further reduction of otic nounced) as seen in Watson's (1956) and notch) is very distinct in Acroplous and its Welles and Estes' (1969) figures shows that apomorphous sister groups. Dvinosaurus (Bys- Isodectes and brachyopids are very distinct. trow, 1938) shows the same condition. Again, However, Kourerpeton has as deep a snout as it is necessary for the current hypothesis to Acroplous. Also, capitosaurs, metoposaurs, and hold, to assume that Dvinosaurus secondarily trimerorhachids such as Neldasaurus and Tri- lost a deeper embayment of the otic notch. merorhachis exhibit character 27 as well. This Very few forms approach the condition seen in character, then, can be used only tentatively to Acroplous and its close relatives. Cyclotosaurus unite Isodectes, Kourerpeton, and brachyopids. (Fraas, 1889) and some other cyclotosaurs sec- A possible contradiction of the present hy- ondarily close the notch from behind. Panchen pothesis must be dealt with here. Saurerpeton, (1972) argued that an unnotched skull roof may Acroplous, and Isodectes have tabulars reduced be primitive for the tetrapods. However, the to narrow strips (character 31). This character is otic notch surely must be primitive for the tem- not seen in brachyopids (the condition in nospondyls as a whole because nearly every Kourerpeton is unknown). If the present hy- taxon possesses it. In that case, its absence or pothesis of relationships were true, one would reduction would be a derived condition. expect Kourerpeton and brachyopids to inherit Character 24 (vagal foramen completely en- the character from the common ancestor of closed by exoccipital) is used with uncertainty Saurerpeton and brachyopids. To maintain the to unite Acroplous, Isodectes, Kourerpeton, present hypothesis one must argue that narrow and brachyopids. The condition is unknown in tabulars are either evolved independently in Acroplous, and Hotton (1959) restored the Saurerpeton, Acroplous, and Isodectes, or that vagal foramen between the exoccipital and the character was lost in brachyopids. Both opisthotic. Given the evidence at hand, the alternatives are nonparsimonious and tend to vagal foramen could very well have laid en- contradict the present hypothesis. One could tirely within the exoccipital. If Acroplous does abandon the hypothesis as shown in figure 5 not show this derived condition, then character and unite Acroplous, Saurerpeton, and Iso- 24 can be used to unite only Isodectes, Kourer- dectes as a monophyletic group (fig. 6). peton and brachyopids. As with many other Characters 28 and 29 unite Kourerpeton and characters in this study, character 24 occurs in brachyopids as a natural group. Unfortunately, other groups of stereospondyls (Romer, 1947). the loss of the intertemporal (character 28) and This type of character distribution will be dis- fusion of the braincase and palate (character cussed at the end of this section. 29) occur in many other advanced temnospon- Characters 25 through 27 unite Isodectes, dyls (Romer, 1947). Kourerpeton, and brachyopids as a monophy- There are no known derived characters unit- letic group. Character 25 (palatine-vomer con- ing brachyopids exclusive of Kourerpeton as a tact lateral to choana) occurs in only two natural group. Therefore, some brachyopids genera (Platyrhinops, Steen 1931; Metopo- may be the sister taxa to both Kourerpeton and saurus, Case 1922) besides those taxa men- the remainder of the brachyopids. In other tioned in figure 5. The maxilla forms the words Kourerpeton may be more closely re- external border of the choana in primitive lated to a subunit of the brachyopids than to the forms. This character, then, must be derived. brachyopids as a whole. Character 26 (otic notch lost) is unique among the group including Isodectes, Kourer- SUMMARY peton and brachyopids. As mentioned before, capitosaurs such as Cyclotosaurus (Fraas, 1889) A concise, testable hypothesis of saurerpe- have no posterior emargination of the skull roof tontid and brachyopid relationships has been but this condition is fundamentally different presented. As one must have noticed, many than in taxa of figure 5. characters (i.e., 2, 3, 4, 5, 6, 10, 11, 14, 17, Character 27 (antorbital flattening more pro- 18, 20, 23, 24, 27, 28, 29) are not seen only in 24 AMERICAN MUSEUM NOVITATES NO. 2662

FIG. 6. Same hypothesis of relationships as in figure 5 except the saurerpetontids are considered to be a monophyletic group. This hypothesis is contradicted by the distribution of derived characters 22 through 27 and is thus contradicted more times than the hypothesis shown in figure 5. The numbers refer to derived characters listed in table 1.

FIG. 7. A hypothesis of relationships uniting all stereospondyls with trimerorhachids, Dvinosaurus, Saurer- peton, Acroplous, Isodectes, and Kourerpeton as a monophyletic group exclusive of the eryopoids. those taxa appearing in figure 5 but in other eospondyls are more closely related to the taxa advanced temnospondyls (Romer, 1947). Given in figure 5 than to eryopoids (fig. 7). Second, this distribution of characters, three alternative Kourerpeton and brachyopids could be more hypotheses of relationship exist. First, all ster- closely related to eryopoids than to tri- 1978 COLDIRON: ACROPLOUS VORAX HOTTON 25 merorhachids (fig. 8). Third, the characters related to saurerpetontids, whereas other ster- listed above could be derived in parallel which eospondyls are more closely related to implies that stereospondyls are not monophy- eryopoids (fig. 9). Given the preponderance of letic. That is, brachyopids are more closely characters linking saurerpetontids, Kourerpeton

FIG. 8. A hypothesis of relationships uniting Kourerpeton and all stereospondyls with eryopoids as a monophyletic group exclusive of trimerorhachids, Dvinosaurus, Saurerpeton, Acroplous, and Isodectes.

,HOtfef|QAseG~~~~PS. ,1°P ,,,>e f\f5 j

FIG. 9. A hypothesis of relationships showing stereospondyls to be polyphyletic. 26 AMERICAN MUSEUM NOVITATES NO. 2662 and brachyopids as a natural group, the first or Lower Permian. Bull. Mus. Comp. Zool., third phylogeny (figs. 7 or 9) seems to hold. Harvard, vol. 133, no. 3, pp. 156-225. For the phylogeny in figure 9 to hold, one Clendening, J. A. would have to derive independently every char- 1971. Palynological evidence for assignment of acter (except 28 and 29) between brachyopids the Gearyan Stage of Kansas to the Penn- and other stereospondyls and in trimero- sylvanian. Geol. Soc. Amer., South Cent. Sec., 5th Annual Meeting, vol. 3, no. 3, rhachids, Dvinosaurus and saurerpetontids. pp. 234-235. Given the present character distribution the hy- Cosgriff, J. W. pothesis of relationships shown in figure 9 has 1969. Blinosaurus, a brachyopid genus from been refuted. The conclusion that brachyopids Western Australia and New South Wales. are more closely related to saurerpetontids than Jour. Roy. Soc. Western Australia, vol. to stereospondyls agrees with Watson (1956), 52, no. 3, pp. 65-88. Hotton (1959), Chase (1965), and Olson and Dunbar, C. O., et al. Lammers (1976). Romer (1947) suggested that 1960. Correlation of the Permian formations of a close relationship might exist. North America. Bull. Geol. Soc. Amer., Unlike the authors just mentioned, I have vol. 71, no. 22, pp. 1763-1805. tried to place Dvinosaurus, Saurepeton, and Efremov, J. A. Acroplous in a clearer phylogenetic scheme. 1933. Neubeschreibung des Labyrinthodonten However, I have had no more success than Platyops stuckenbergi aus den oberper- mischen Ablagerungen des Flusses Kitjak, Olson and Lammers (1976) concerning the po- eines Nebenflusses der Wjatka. Trav. Inst. sition of Kourerpeton. Pal. Acad. Sci. URSS, vol. 2, pp. 117-164. Fraas, E. 1889. Die Labyrinthodonten der schwabischen LITERATURE CITED Trias. Paleontographica, vol. 36, pp. 1-158. Amalitsky, V. P. Haughton, S. H. 1921 Dvinosauridae, North Dvina excavations 1925. Descriptive catalogue of the Amphibia of of Prof. V. P. Amalitsky, I, Petrograd the Karoo System. Ann. S. African Mus., Akad. Nauk, pp. 1-16. vol. Branson, E. B., and M. Mehl 22, pp. 227-261. 1929. Triassic amphibians from the Rocky Hotton, N. Mountains region. Univ. Missouri Studies, 1959. Acroplous vorax, a new and unusual laby- vol. 4, no. 2, pp. 155-255. rinthodont amphibian from the Kansas Bystrow, A. P. Permian. Jour. Paleo., vol. 33, no. 1, pp. 1938. Dvinosaurus als neotenische Form der 161-178. Stegocephalen. Acta Zool., vol. 19, pp. Huene, F. von 209-295. 1920. Gonioglyptus, ein alttriassischer Stegoce- Carroll, R. L. phale aus Indien. Acta Zool., vol. 1, pp. 1967. Labyrinthodonts from the Joggins Forma- 433-464. tion. Jour. Paleont., vol. 41, no. 1, pp. 1922. Beitriige zur Kenntnis der Organisation 111-142. einiger Stegocephalen der schwabischen 1970. The ancestry of reptiles. Philos. Trans. Trias. Ibid., vol. 3, pp. 395-460. Roy. Soc. London (B), vol. 257, pp. 1932. Ein neuartiger Stegocephalen-Fund aus 267-308. dem oberhessischen Buntsandstein. Pal- Case, E. C. aeont. Zeitschr., vol. 14, pp. 200-229. 1911. Revision of the Amphibia and Pisces of Jaekel, 0. the Pennian of North America. Publ. Car- 1922. Neues uber Hemispondyla. Palaeont. negie Inst. Washington, vol. 146, pp. Zeitschr., vol. 5, pp. 1-25. 1-179. Langenheim, R. L. 1922. New reptiles and stegocephalians from the 1952. Pennsylvanian and Permian stratigraphy of Upper Triassic of Western Texas. Ibid., the Crested Butte Quadrangle, Gunnison vol. 321, pp. 1-84. County, Colorado. Amer. Assoc. Petrol. Chase, J. N. Geol., vol. 36, pp. 543-574. 1965. Neldasaurus wrightae, a new rhachit- Meyer, H. von omous labyrinthodont from the Texas 1858. Labyrinthodonten aus dem bunten Sand- 1978 COLDIRON: ACROPLOUS VORAX HOTTON 27

stein von Bernburg. Palaeontographica, 1934. The amphibian fauna from the South Jog- vol. 6, pp. 221-245. gins, Nova Scotia. Ibid., vol. 104, pt. 3, Nilsson, T. pp. 465-504. 1943. On the morphology of the lower jaw of 1938. On the fossil Amphibia from the Gas Coal Stegocephalia with special reference to of N'rany and other deposits in Czecho- Eotriassic stegocephalians from Spitsber- slovakia. Proc. Zool. Soc. London (B), gen. I. Descriptive Part. K. Svenska Vet- vol. 108, pp. 205-283. enkapsakad. Handl., vol. 20, no. 9, pp. Watson, D. M. S. 1-46. 1919. The structure, evolution and origin of the 1944. On the morphology of the lower jaw of Amphibia. -The "orders" Rhachitomi Stegocephalia with special reference to and Stereospondyli. Philos. Trans. Roy. Eotriassic stegocephalians from Spitsber- Soc. London (B), vol. 209, pp. 1-73. gen. II. General part. Ibid., vol. 21, no. 1921. On Eugyrinus wildi (A.S .W.), a branchio- 1, pp. 1-70. saur from Lancashire coal-measures. Geol. Olson, E. C., and G. E. Lammers Mag., vol. 58, pp. 70-74. 1976. A new brachyopid amphibian. In C. S. 1929. The Carboniferous Amphibia of Scotland. Churcher (ed.), Athlon, Essays on Palae- Pal. Hungarica., vol. 1, pp. 219-252. ontology in honour of Loris Shano Rus- 1940. The origin of frogs. Trans. Roy. Soc. sell. Roy. Ontario Mus. Life Sci. Misc. Edinburgh, vol. 60, pp. 195-231. Publ., pp. 45-57. 1956. The brachyopid labyrinthodonts. Bull. Panchen, A. L. Brit. Mus. Nat. Hist. (Geol.), vol. 2, no. 1972. The interrelationships of the earliest 8, pp. 318-391. tetrapods. In Joysey, K. A. and Kemp, T. 1962. The evolution of the labyrinthodonts. Phil. S. (eds.), Studies in Vertebrate Evolution, Trans. Roy. Soc. London (B), vol. 245, Winchester Press, New York, pp. 65-87. no. 723, pp. 219-265. Romer, A. S. Welles, S. P., and J. Cosgriff 1930. The Pennsylvanian tetrapods of Linton, 1965. A revision of the labyrinthodont family Ohio. Bull. Amer. Mus. Nat. Hist., vol. Capitosauridae and a description of Par- 59, no. 2, pp. 77-147. otosaurus peabodyi, n. sp. from the 1947. Review of the Labyrinthodontia. Bull. Wupatki member of the Moenkopi Fonna- Mus. Comp. Zool., Harvard, vol. 99, no. tion of Northern Arizona. Univ. Calif. 1, pp. 7-368. Publ. Geol. Sci., vol. 54, pp. 1-148. Romer, A. S., and Witter, R. V. Welles, S. P., and R. Estes 1942. Edops, a primitive rhachitomous amphib- 1969. Hadrokkosaurus bradyi from the Upper ian from the Texas red beds. Jour. Geol., Moenkopi Fornation of Arizona, with a vol. 50, no. 8, pp. 925-960. review of the brachyopid labyrinthodonts. Save-Soderbergh, G. Univ. Calif. Publ. Geol. Sci., vol. 84, pp. 1932. Preliminary note on Devonian stegoce- 1-56. phalians from East Greenland. Meddel. Wilson, L. R., and M. A. Rashid om Gr0nland, vol. 94, no. 7, pp. 1-107. 1971. Palynological evidence for Pennsylvanian 1935. On the dermal bones of the head in laby- age assignment of the Gearyan Series in rinthodont stegocephalians and primitive Kansas and Oklahoma. Geol. Soc. Amer., Reptilia with special reference to South Cent. Sec., 5th Annual Meeting, Eotriassic stegocephalians from East vol. 3, no. 3, p. 248. Greenland. Ibid., vol. 98, no. 3, pp. Wiman, C. 1-211. 1915. Ueber die Stegocephalen aus der Trias Sawin, H. J. Spitzbergens. Bull. Geol. Inst. Univ. 1941. The cranial anatomy of Eryops mega- Uppsala, vol. 13, pp. 1-34. cephalus. Bull. Mus. Comp. Zool., Har- 1916. Neue Stegocephalenfunde aus dem vard, vol. 86, no. 5, pp. 407-463. Posidonomyaschiefer Spitzbergens. Ibid., 1945. Amphibians from the Dockum Triassic of vol. 13, pp. 209-222. Howard County, Texas. Univ. Texas 1917. Ueber die Stegocephalen Tertrema und Publ. no. 4401, pp. 361-399. Lonchorhynchus. Ibid., vol. 14, pp. Steen, M. 229-240. 1931. The British Museum Collections of Am- Zeller, D. E. phibia from the Middle Coal Measures of 1968. The stratigraphic succession in Kansas. Linton, Ohio. Proc. Zool. Soc. London, Bull. Geol. Surv. Kansas, vol. 189, pp. vol. 100, pt. 4, pp. 849-891. 1-81.