Part 2

Key:

A. Anterior height of fragment B. Posterior height of fragment C. Length of fragment at tooth-row D. Dorsal length of fragment E. Mean length of teeth F. Anterior width of naris

============================================================ CATALOGUE NUMBER | A. | B. | C. | D. | E. | F. AND MEAN | | | | | | -----------------+------+------+------+------+------+------ KU 11117 | 6.0 | 8.0 | 6.0 | 8.0 | 3.0 | 3.0 KU 11118 | 6.0 | 6.0 | 9.0 | 8.0 | 2.0 | 3.0 KU 11119 | 6.6 | 8.0 | 10.0 | 11.0 | ? | 4.6 -----------------+------+------+------+------+------+------ Mean | 6.2 | 7.3 | 8.3 | 9.0 | 2.5 | 4.5 -----------------+------+------+------+------+------+------

Discussion.--The Nitosauridae are small primitive edaphosaurs with a moderately elongate face, sharp subisodont teeth, little development of canines and few specializations. The jaw is of a primitive type and articulates on a level with the tooth-row. The palatal dentition is primitive (Romer, 1956:280). The nitosaurids are thought to be related to the later Caseidae, and the most obvious structural similarities are found in the postcranial skeleton (Vaughn, 1958:989). Cranial resemblances between the families are fewer, but nevertheless indicate that a nitosaurid-caseid relationship exists.

Vaughn (1958) described a small pelycosaur, Colobomycter pholeter (Eothyrididae, Ophiacodontia) that structurally resembles the Caseidae. This individual also was obtained from the Fort Sill locality. In Vaughn's opinion the features of Colobomycter indicate a close relationship between eothyridids and caseids and the possibility that the caseids may well have been of eothyridid rather than nitosaurid derivation.

In view of this historical uncertainty of the relationships between the Nitosauridae, the Eothyrididae and the Caseidae, it is well to consider how the maxillary fragments described above differ from and resemble representatives of each of these three families as reported in the literature.

Delorhynchus resembles Colobomycter in size. The mean extra-maxillary length of the undamaged teeth of the three fragments is 2.5 mm., equal to that reported by Vaughn (1958:985) for teeth about midway in the postcanine series of Colobomycter. None of the teeth of Delorhynchus extends beyond the maxillary rim as far as does the canine of Colobomycter (3.5 mm.).

The teeth in both genera are conical and sharply pointed. The naris in each is enlarged, and the lacrimal is excluded from the narial margin in each (by inference in Delorhynchus.)

The differences between the maxillae of Colobomycter and Delorhynchus are most striking in the lack of canines in the latter and the correlated absence of modifications of the maxillary for support of canines. Additionally, Delorhynchus bears an infraorbital canal in contrast to the groove in similar position in Colobomycter. The recurvature of the four teeth present in the fragments of Delorhynchus differs from that in the teeth of Colobomycter in which only the canine and precanine are recurved. Vaughn implies that anterior and posterior cutting edges extend the length of the teeth in Colobomycter; these are restricted to the distal third of the teeth in Delorhynchus. The external surfaces of the maxillae of Delorhynchus are pitted and ridged; Vaughn was unable to discern sculpturing of the corresponding surfaces in Colobomycter.

Delorhynchus resembles the nitosaurids in size, the shape and sharpness of the teeth, their recurvature and the slight enlargement of their bases, the exclusion of the lacrimal bone from the narial margin (in Mycterosaurus) and the apparent lack of a special canine pair of teeth. Resemblances to the caseids are to be noted in the enlargement of the naris (4.5 mm. in height as opposed to 1.7 mm. in Colobomycter), lack of development of canines, presence of an infraorbital canal (in Cotylorhynchus) and absence of many replacement gaps in the marginal row of teeth.

The absence of caniniform enlargement and the extension of the maxilla dorsad of the naris exclude Delorhynchus from the Eothyrididae (Ophiacodontia) but are no bar to its inclusion in the Nitosauridae (Edaphosauria). The marginal teeth of Delorhynchus are simple and primitive, being much like those of the nitosaurids that are described in the literature.

The large narial opening and its posterior, dorsal and ventral enclosure by the maxilla, the infraorbital canal, and the sculptured external surfaces of the maxillary fragments indicate that Delorhynchus, in these features at least, is close to achieving the caseid grade.

Family SPHENACODONTIDAE

=Thrausmosaurus serratidens= new genus and new species

(Thrausmosaurus is formed from the neuter Greek noun, thrausma, meaning fragment, and the masculine Greek noun, sauros, meaning reptile. The specific name, serratidens, is formed from the Latin serratus, meaning serrate, and the masculine Latin noun, dens, meaning tooth. The specific name is used as a substantive in apposition with the generic name.)

Type specimen.--Fragmentary left dentary, bearing five teeth, the most posterior of which is broken at the base, KU 11120.

Referred specimens.--Fragmentary ?left maxilla, having two teeth, KU 11121; fragmentary left dentary having two teeth, KU 11122.

Horizon and locality.--From the early Permian fissure deposits in the Arbuckle limestone of the Dolese Brothers Limestone Quarry, approximately 6 miles north of Fort Sill, in sec. 31, T. 4N, R. 11 W, Comanche County, Oklahoma.

Diagnosis.--Small; teeth thecodont, compressed laterally, recurved distally, and bearing anterior and posterior cutting edges; anterior serrations limited to recurved portions of teeth, posterior serrations extending nearly entire length of teeth; lateral compression of teeth more pronounced medially than laterally; bases of teeth expanded.

Description.--The type specimen is 16 mm. long. It bears five teeth that are implanted in a straight row. Empty sockets are present between the first and second teeth, and the third and fourth teeth. The first tooth is 3.0 mm. long, the middle two are each 2.5 mm. long, and the fourth tooth is 2.0 mm. long. The fifth tooth is broken off at its base.

The empty sockets are large. The mouth of each is circular and approximately 2.0 mm. in diameter. Both sockets are 1.25 mm. deep. The bases of the teeth are expanded to fill the sockets, although the blades of the teeth arise from only the lateral portions of the bases. The edge of the dentary rises above the bases of the teeth medially, thereby producing a small depression at the junction of each base with the dentary bone.

The lateral compression of the teeth is pronounced but asymmetrical, in that the lateral surface of each blade is more convex than the medial surface.

FIG. 4. KU 11120 (type specimen), lateral view of left dentary. FIG. 5. KU 11121, lateral view of ?left maxilla. FIG. 6. KU 11122, lateral view of left dentary.]

The recurvature of the anterior cutting edges is much more severe than that of the posterior edges, but the recurvature of both is limited to the distal half of each tooth.

The serrations of the cutting edges are not visible to the naked eye and are limited on the anterior edges of the teeth to those portions of the blades that are recurved. The posterior serrations extend nearly to the junction of the blade of each tooth with its base. The serrations tend to be more nearly crenulate than cuspidate.

A portion of the lateral wall of the dentary surrounding the Meckelian canal is present. The external surface of the wall is gently convex and smooth, without sculpturing. The internal surfaces of the canal are unmarked either by muscle scars or foramina.

The fragment is a piece from the posterior portion of the dentary, since the decrease in height from the first tooth to the fourth is pronounced.

KU 11122, a fragment of the left dentary bearing two teeth, is 7.5 mm. long. The anterior tooth is 3.0 mm. long; the posterior tooth is 3.5 mm. long. The shape of the teeth and their implantation conform to the description of the type specimen. The lateral surface of the fragment is smooth and gently convex. What little is present of the surface bordering the Meckelian canal is unmarked.