Laelaps Cope, 1866

Cope, E. D., 1876, On some extinct reptiles and batrachia from the Judith River and Fox Hills beds of Montana, Proceedings of the Academy of Natural Sciences of Philadelphia 28, pp. 340-359 : 340-341

Laelaps Cope .

Proceed. Acad., Phila., 1866, p. 275. Extinct Batr. Rept. N. Amer., 1869, p. 100.

Two species of this genus were described in the latter memoir above cited, the L. aquilunguis , Cope, and L. macropus , Cope, both from the greensand or Fox Hills group of the cretaceous of New Jersey. A considerable portion of the skeleton of the former was described, including the peculiarities of the ankle-joint, which led me to the conclusion, previously unsuspected by naturalists, that the Dinosauria present affinities to the cursorial birds. The teeth of this species were described and figured, but in the L. macropus they were, and still remain, unknown.

In a preliminary report on the extinct Vertebrata obtained by the writer on the Upper Missouri the present year, three addititional species were referred to this genus, viz. the Laelaps incrassatus ; L. explanatus , and L. falculus . Their characters were ascertained from teeth alone, so that their pertinence to the genus Laelaps is not fully assured. A fourth species of carnivorous dinosaurian was described under the name of Aublysodon lateralis .

One of the most valuable specimens obtained hy my expedition of 1876, is the nearly entire left dentary bone of the Laelaps incrassatus , which exhibits the teeth of its two extremities. The different forms of the teeth of the carnivorous Dinosauria graduate into each other by such easy stages, as to have given rise to question in reference to their proper interpretation; whether they indicate different species or only different positions in the dental series. In describing the Aublysodon horridus , the first known of the species of the Judith River beds, Dr. Leidy expressed the suspicion that a certain form characterized the teeth in the position of incisors,another those in the position of canines. and another form the remainder of the series. The teeth of the last kind have the form of those of Laelaps ; in others the posterior serrulate cutting edge is latero-posterior, the posterior aspect being thickened, and either transverse or convex in section. In the supposed canines the anterior scrrulate edge is wanting, or represented by a second posterior edge parallel with the original one, thus forming a compressed chair-shaped crown. Numerous specimens of all these forms were obtained by the expedition.

Examination of the dental series of the Laelaps incrassatus shows that the antero-posterior diameter of one or two teeth in the position of canine, becomes oblique in the curved long axis of the dentary bone. The transverse diameter is also greatly increased so as to equal or even exceed the antero-posterior; the serrate edges are opposite to each other. A tooth of this type was the first of this species which I observed, and the name has reference to its peculiar form. A tooth in the position of first or anterior incisor, differs in having the anterior serrate crest removed to the middle of the inner aspect of the apical portion of the crown, while the posterior edge retains its usual position. Further posterior transfer of the anterior cutting edge and a grooving of the posterior face, would produce a tooth of the form suspected by Leidy to be the canine of Aublysodon horridus , while the canine just described is different from any tooth referred by Leidy to the same species. But a large tooth found in immediate association with the jaw, but separated from it, has the posteriorly truncate form described by Leidy as typical, and is very probably the tooth of the maxillary bone, near the position of the superior canine of a mammal.

It may he observed in conclusion, that if the teeth suspected by Leidy to be canines of Aublysodon horridus , but which l suppose to be incisors, are really such, Aublysodon must he regarded as a genus distinct from Laelaps ; while, on the other hand, should such determination prove to be inadmissible, and the two genera be the same, the name Laelaps must be preserved as the older; it was published in 1866, while Aublysodon bears date 1868.

In examining the very numerous teeth discovered by the expedition, I find four species in addition to those already named. A list of all the species is now given.