The Coal Measures Amphibia of North America

by Roy Lee Moodie

Moodie, Jour. Geol., XVII, No. 1, p. 63, figs. 13, 14, 1909.

Type: Specimen No. 102 (8680 G), American Museum of Natural History, where it forms part of the Newberry collection.

Horizon and locality: Linton, Ohio, Coal Measures.

The species is represented by an almost complete skull, which had been identified previously by Cope as Tuditanus radiatus. The specimen consists of the impressions of the bones of the cranial roof, the bones themselves having disappeared. It is not probable that the dorsum of the skull was smooth. The details in the structure of the skull have been ascertained quite definitely. There can be no doubt that the arrangement of the elements is accurate, as shown in [figure 24 A]. The supratemporal, as in Erpetosaurus tabulatus Cope, is excluded from the parietal.

The form of the skull at once recalls that of the species D. punctolineatus, as figured by Jaekel (see [plate 15]). The orbits are located in nearly the same region of the skull and the sutures separating the cranial elements are quite similar in the anterior portions. The species D. lævis is based on the divergent character of the horn-like protuberances which project from the squamosals. The horns of D. punctolineatus are convergent. The present skull is also smaller and the parietals in D. lævis are much larger than in the type species. In the type species, also, the pineal foramen is located well forward in the parietal, while in the present form the foramen is located well posterior.

The skull is almost rectangular. The nostrils are elongate ovals. The orbits are circular and the distance between them is equal to two-thirds of the dimensions of the orbit. They are located well forward in the skull and are bounded laterally by the maxillaries. The nostrils have much the same character as in the type form, being broadly oval.

The premaxillæ are elongate transversely, being about twice as long as wide. They are identical in shape and relations with the same elements in D. punctolineatus Cope. The nasal is nearly square and forms the interior boundary of the nostril. The frontal is elongate in the median length of the skull and it is acuminate posteriorly, where the acumination is inclosed by the parietal and postfrontal. The parietals are by far the largest elements in the cranium. They form together an oval which is elongate in the longitudinal diameter of the skull. They inclose between them, in the median suture, the small pineal foramen. They are acuminate in front, with a broad truncate posterior base, where they are bounded by the postparietals. The postparietal is nearly square, being somewhat wider than long. It joins the tabulare and the parietal. The tabulare is elongate in the long diameter of the skull. It ends anteriorly in a point which is inserted between the postorbital and the parietal, and bears a short protuberance posteriorly, much as does the same element in the type species.

There are four elements which take part in the formation of the posterior border of the skull. These are the postparietal, the tabulare, the squamosal, and the supratemporal. It is very unusual for the supratemporal to reach the posterior edge of the cranium. The pref rental lies anterior to the orbit, of which it forms the anterior border. The lacrimal has not been detected, although Jaekel ([347]) has indicated it in his drawings of the skull of the type species. The maxilla is elongate and forms the lateral border of the skull. No teeth have been detected, although they were doubtless the same as Jaekel has figured in D. punctolineatus. The jugal is an elongate element joining the maxilla posteriorly. Jaekel included this element in his "perisquamosal," but the sutures are clearly evident in the present specimen and there is no evidence of a structure at all similar to a "perisquamosal." The postorbital is fully as large as the jugal which it joins, forming a part of the posterior border of the orbit and ending posteriorly in a point which is inclosed by the tabulare and the squamosal. The postfrontal with the foregoing element forms the entire posterior border of the orbit and it likewise ends in a point inclosed by the parietal and the postorbital. The quadratojugal has much the same shape and relations as in D. punctolineatus, although it is located further back. The squamosal is also elongate, as are most of the posterior cranial elements, and it also has an acumination which is directed forward and is inclosed by the postorbital and jugal. The anterior suture of this element is rather indistinct, but it is, I believe, as represented ([fig. 24]). The element is elongate and is prolonged posteriorly to form the horn, which ends in a blunt point and is not sharp, as in the type species.

Jaekel ([347]) regards the species Diceratosaurus punctolineatus Cope as being unparalleled among known vertebrates in the possession of a "perisquamosal" element. In closely allied species the "perisquamosal" is easily separated into its component elements, and the morphology of the present skull would throw considerable doubt on Jaekel's interpretation of the skull of the type species. Another specimen, described below as another species of this genus, shows no evidence of this fusion. So far as I can learn, there have been no cases of true fusion of cranial elements correctly reported, unless it be that which possibly exists between the two frontals in the skull of Diplocaulus. It was on the basis of such fusions that Maggi ([397]) proposed to derive the interparietals of the primates from the tabulare of the stegocephalians.