Puercolestes

Puercolestes lived during the early recovery of North American mammal faunas after the end-Cretaceous extinction. Its type species, P. simpsoni, rests on a damaged partial skull and teeth from New Mexico. Later upper teeth from Montana provide additional comparisons, but no complete skeleton establishes the animal's exact living appearance.

The genus belongs in the ancient mammal catalogue. Litaletes is another Paleocene mammal frequently studied from teeth, while Promioclaenus represents a different early placental lineage. Occurrence near the same broad boundary does not make them one family.

Quick facts

Reynolds's name and the type fossil

T. E. Reynolds named Puercolestes simpsoni in 1936 from the San Juan Basin of New Mexico. The type comes from the Pu2 interval of the Nacimiento Formation. Modern catalogues list its damaged partial skull as UCMP 36658. It retains part of the upper dentition, but neither a complete cranium nor the postcranial skeleton.

The original label of an insectivorous mammal reflects the classification used at the time. Later researchers compared it with other cimolestids, early placental mammals whose wider relationships have been debated. Taxonomic changes do not alter the physical identity of the type; the premolars and molars remain the basis for testing referrals.

Montana's associated upper teeth

At Kerr Butte in northeastern Montana, UCMP 218933 preserves an associated upper fourth premolar and first two molars, P4 and M1–M2. Their association reveals how characters change along one tooth row. Other Garbani Channel Complex localities produced mostly isolated crowns; a similar size alone cannot place every crown in the same species.

William Clemens referred these fossils as Puercolestes sp. cf. P. simpsoni in 2019. The abbreviation cf. marks comparison, not a fully confirmed identification. The Montana material is from the Pu3 interval in the Tullock Member of the Fort Union Formation, later than the Pu2 New Mexico type. The two assemblages should not be combined into one imagined skeleton.

What the molars can and cannot distinguish

On upper molars, palaeontologists compare the relative height and spacing of major cusps, the shape of the chewing basin and the development of marginal shelves. Tooth position matters: P4, M1, M2 and M3 have different roles and shapes. Heavy wear can hide a small cusp, and distinct cimolestids may overlap in crown size.

Isolated lower p4s and molars from the Montana beds have not yet been tied securely to the associated upper teeth by dentaries preserving several positions. That limits attempts to separate Puercolestes from the somewhat smaller Betonnia. A future jaw with linked upper and lower material could test both the generic and species referrals.

A rare member of recovering faunas

The Garbani Channel Complex preserves river-channel deposits and diverse small vertebrates from approximately the first million years of the Paleocene. Cimolestids are relatively rare within these faunas. The Pu2 and Pu3 labels refer to local mammal intervals rather than exact dates of the genus's appearance or extinction.

Teeth allow discussion of food processing, but no stomach contents identify a precise diet. No limb skeleton establishes whether this particular mammal ran, climbed or dug. Body length, mass, fur colour and ear shape in the cover are artistic choices. The fossil record supports an early Paleocene cimolestid from New Mexico and provisionally similar Montana teeth.