New Mexico Geological Society Annual Spring Meeting — Abstracts

A partial skull and skeleton (NMMNH P-27844) from the Mixodectes pungens Zone of the early Paleocene (Torrejonian) Ojo Encino Member, Nacimiento Formation (NMMNH locality L-2701) represents a juvenile of the pantodont mammal Pantolambda bathmodon. The skull includes much of the upper dentition (Dp¹?, Dp^2-4, M^1-2), parts of both maxillae, portions of the skull roof (frontal and parietal) and the glenoid area. The preserved upper deciduous dentition is relatively unworn. The postcranial skeleton includes several partial vertebrae, ribs, part of a left scapula, part of the right ilium, and portions of the front and hind limbs including a nearly complete manus (several carpal bones, partial metacarpals, and several phalanges). This specimen is significant in that it is the first reported juvenile specimen of P. bathmodon and provides information on the deciduous dentition of Pantolambda.

This juvenile specimen of P. bathmodon allows study of certain aspects of its ontogeny by placing constraints on the tooth eruption sequence and by providing information on relative times of fusion between various elements. There are unfused sutures between the frontals. The parietals are probably only partially fused. The frontals are fused to the parietals, but a digitating sutural contact between these elements is still readily visible between them. All the limb elements have unfused epiphyses, excpet possibly for the distal end of the humerus that may be only partially fused. The distal ends of the scapula and the metacarpals are unfused. The size of limb articular ends approach adult size and the lengths of the ulna and radius are approximately 75% of adult length (based on shaft length) and so fusion of the epiphyses evidently did not commence and the toss of the deciduous dentition did not begin until the animal had attained near-adult size. In these respects, P. bathmodon resembles the early Eocene (Wasatchian) pantodont Coryphodon.