On The Affinities of Leptarctus primus of Leidy

On The Affinities of Leptarctus primus of Leidy - American Museum of Natural History, Vol. VI, Article VIII, pp. 229-331.

Up to the present time but very little has been known of the existence of the peculiarly American family Procyonid in any deposits older than the very latest Quaternary. Leidy has described and figured[1] an isolated last upper tooth, from the Loup Fork deposits of Nebraska, under the name of Leptarctus primus, which has been referred to this family. The Museum Expedition of last year into this region was successful in obtaining additional material, which we provisionally refer to Leidys species. The specimen consists of the right ramus of the lower jaw, carrying the third and fourth premolars and the canine. The condyle is broken away, but the coronoid process and the angle are preserved. The specimen is from a young individual in which the last premolar had just cut the gum. The alveoli of all the other teeth are present and in a good state of preservation. The dental formula is as follows: I.3, C.1, Pm.3, M.2. The incisors are not preserved, but their alveoli indicate that they were much crowded, the outside one being placed almost directly in front of the canine, and the middle one pushed back considerably out of position. This series is in marked contrast with that of the Raccoon, in which the crowns of the incisors form almost a straight line across the jaw, and the middle one is crowded backwards to a very slight extent. The canine is peculiar and differs markedly from that of the Raccoon. It is rather robust, very much recurved and grooved by a deep vertical sulcus upon its antero-internal face. This sulcus is but faintly indicated in the Raccoon. The postero-external face of the crown is marked by a sharp ridge which becomes more prominent near [Pg230]the apex. The first premolar is not preserved, but its alveolus indicates that it was a single-rooted tooth, placed behind the canine after the intervention of a very short diastema. The second premolar is bifanged; its crown is composed of a principal cusp, to which is added behind a small though very distinct second cusp. There is in addition to these cusps a distinct basal cingulum, most prominent in the region of the heel. The third premolar, like the second, is double rooted; its crown moreover is made up of two cusps, the posterior being almost as large as the principal one. These cusps do not stand in the line of the long axis of the jaw, but are placed very obliquely to it. The heel is not very prominent, but the basal cingulum is well developed, both in front and behind. As compared with the Raccoon, the second premolar is more complex in that it has two cusps instead of one. In the third premolar the posterior cusp is much better developed, and placed more obliquely than in the corresponding tooth of Procyon; the heel is moreover not so broad. ......Buy Now (To Read More)

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Ebook Number: 26542
Author: Wortman, Jacob Lawson
Release Date: Sep 5, 2008
Format: eBook
Language: English