An Apternodontid (Insectivora) from the Chadronian Oligocene of Northeastern Colorado

Abstract

Part of a skull and endocranial cast of an apternodoneid was found in Charonian age beds of the Horsetail Creek member of the White River Oligocene at the lliff Locality (W% Sec. 16, T 10 N, R 51 W, Logan County) in northeastern Colorado. The anterior part of the skull differs from described species of Apternodus in having the large lacrimal foramen excluded from the orbit and absence of a lateral crest on the maxillary. The endocranial cast is described. Trans. Kansas Acad. Sci., vol. 81:4, 1978. Circumstances of Discovery The specimen was found in the floor of a rill in the weathered surface of grayish-white silts near the top of unit no. 1 of measured section XVli (page 26, Galbreath, 1953). The snout, endocranial cast, and a few fragments of cranial bone were found ventral side up and oriented in the same axis thus indicating that a relatively complete skull had been bu ried. Description of Skull Fragment Figure 1 shows the extent of damage to the skull fragment but does not show the slight distortion due to crushingj Comparison of the three views should not leave any do ubt about the identity of the matrix that was deliberately preserved at the rear of the fragment during cleaning. Using the overall length of Apternodus brevirostris Schlaikjer as a guide, the dimensions (TabJe 1) of the skull fragment and the endocranial cast indicate a minimal length of 45 mm and a probable length of 50 mm for the skulil i.e, about the size of A. brevirostris or A. gregoryi Schlaikjer. Some traces of the naso-maxillary and maxillo-palatine sutures are visible. There are no sutures indicating the posterioror lateral borders of the frontal bone but on the right side of the fragment there are seven mm of dorsal and lateral walls posterior to a transverse plane marking the anterior border of the internal nares. The sagittal crest is strong and divides anteriorly into strong ridges that extend to the orbital processes. The recessed area for origin of the superior labial levator muscle extends back to be in line with the M1.