The Coal Measures Amphibia of North America

by Roy Lee Moodie

The skull roof is sculptured with pits much like those of Archegosaurus. The larger the bones, the rougher the sculpture. The bones of the middle of the skull (that is, the parietals, frontals, premaxillæ, nasals, and postparietals) are of the normal form and only show an unusual difference in that they are large in the inverse order. The pineal foramen lies in the anterior third of the parietals; that is the primitive condition which occurs in the young forms of the Branchiosauridæ. The nostrils are inclosed by the premaxillæ in front, in the median line by the nasals and laterally by the maxillæ. The jugals, by their backward prolongation, form, behind the maxillæ, the border of the skull, and only attain to some size on the upper side of the cranium.

Jaekel's "perisquamosal" (see [plate 15]), which is of a doubtful nature, is not indicated in the type specimen nor in the specimens of the other two species ([462]) assigned to this genus. In D. robustus and D. lævis the "perisquamosal" region is easily separable into its component elements. The sutures between the elements may have been indistinct in his specimen, but it is hardly conceivable that a union of the skull bones would occur in one species and not in another of the same genus. Jaekel's suggestion ([347]) that "Etwas mehr Wahrscheinlichkeit möchte ich der Vorstellung beimessen, dass diese Ausbreitungen zum Schutz freier Kiemen dienten, wie sie z. B. bei den Perennibranchiaten als baumförmige Organe weit am Halse herausragen" can hardly find acceptance with students of the Paleozoic Amphibia, since there is not the slightest evidence that the Microsauria ever possessed external gills and considerable presumptive evidence that they did not. His comparison of the "perisquamosal" to the "Kiemendeckel" of the fishes is also very unhappy on morphological grounds, since the elements of his "perisquamosal" form constituent parts of the skull roof, which the operculum never does.

The palate of the skull ([plate 15, fig. 2]) has been determined by removing the skull bones of one specimen. Anteriorly the premaxillæ and maxillæ are clearly recognizable as large dentiferous elements. The premaxillæ have 4 to 7 teeth, the short maxilla has 3 to 4. All the teeth are of nearly equal size. Smaller teeth seem to be indicated by impressions found between the larger ones. The vomers, which are tolerably large, unite with the premaxillæ behind and inclose at least half of the palatine foramen on the inner side. They are furnished with small teeth, which in the anterior part are very irregularly placed, but they are more regular posteriorly.

The palatines and transverse bones are questionably identified. They seem to lie posterior and lateral to the vomers, but the sutures are indistinct. The large parasphenoid seems well displayed and is more or less heart-shaped. There would seem to be a slight indication of double occipital condyles. The pterygoids are broad plates which inclose the parasphenoid and form the lateral boundary of the palate. The cotyli are very indistinct, but appear as elongate grooves.

The pectoral girdle ([plate 15, fig. 3]) consists, apparently, of seven elements, three paired and one unpaired. The unpaired element (the interclavicle) is truncate posteriorly and acuminate in front, with its surface radially grooved and the anterior borders beveled for articulation with the clavicles. The clavicles are triangular, as is usual with the Microsauria. They are sculptured with radiate grooves and ridges, with decided inosculations at the ossific center. The coracoids have only part of their surface ornamented; most of their surface is smooth for articulation with the interclavicle and scapula. A long spine projects from the inner surface of the coracoid. A pair of small elements lie one on either side of the clavicles and Jaekel ([347]) interprets them as the cleithra. If they are cleithra they are unique among the Microsauria. The pectoral girdle does not, however, indicate that Diceratosaurus is "unique among all known quadrupeds."

Jaekel regards the limb which is preserved with the material as an arm ([plate 15, fig. 4]), but there is no reason stated for his conclusion. It has all of the characters of the leg and may be regarded as such. Only a part of the lower end of the femur is preserved. The tibia and fibula are preserved as separate rod-like elements with one of the bones longer and larger, probably the tibia. There are 5 toes which have the customary phalangeal formula for a microsaurian foot of 2-3-3-4(?)-3. The tarsals are unossified.

The vertebræ ([plate 15]) were perforated for the notochord, and are hour-glass-shaped, with the neural arch thickened to support a heavy spine which bore a sculptured plate. These apical plates occur in the dorsal region, but diminish toward the caudal vertebræ. The number of the vertebræ in the dorsal region is very small and in the tail very large. There are possibly 2 vertebræ in the cervical, 11 in the dorsal series; the thirteenth carries the pelvis. There are over 100 vertebræ in the tail.

The ribs have an expanded head and the transverse processes of the vertebræ are long.

The following account is based on the writer's study of the type specimen and he is able to add several points of interest to a knowledge of the anatomy of the type of this interesting microsaurian.

The type specimen consists of 11 consecutive vertebræ with a portion of the skull, the greater portion of the pectoral girdle, parts of both fore limbs, ribs, and ventral scutellæ ([plate 14, fig. 4]). The species is represented in the collection by yet another specimen, on which Cope based his Tuditanus mordax ([plate 22, fig. 5]), of which he himself says: "Further examination of the specimen on which the latter (T. mordax) was founded leads to the belief that it is an imperfect cranium of Ceraterpeton (Diceratosaurus) punctolineatum Cope." The plates referred to are rather to be regarded as elements of the pectoral girdle and I believe they represent the clavicle and a portion of the interclavicle.