Evolution of Paleocene and Eocene Phenacodontidae (Mammalia:Condylarthra).

Abstract

Phenacodontidae is a family of Paleocene and Eocene placental mammals known from North American and Europe. North American phenacodontids are among the most abundant mammals during their range from middle Torrejonian (63 Ma) through Bridgerian l and -mammal ages (49 Ma). In Europe, phenacodontids are rare and known only from the early and middle Eocene. This study evaluates: (1) patterns of dental variability in phenacodontids; (2) evolution, geographic and chronologic distribution, and phylogenetic relationships of phenacodontid taxa; and (3) the relation of phenacodontids to the phylogeny of condylarths and other ungulates. Different teeth in the tooth row and different dimensions within a tooth are not all equally variable. Overall dental variability of a population of Ectocion is similar to that of a population of extant Procyon. The pattern of phenacodontid evolution is analyzed on the basis of more than 6,000 dental phenacodontid specimens. Torrejonian phenacodontids are Tetraclaenodon puercensis and T. septentrionalis new. Phenacodontids restricted to the Tiffanian are: Ectocion collinus, E. pinus (new), E. mediotuber (new), Phenacodus matthewi, P. bisonensis, P. grangeri, and P. magnus (new). Phenacodus vortmani ranges from late Tiffanian through Wasatchian. Ectocion major is restricted to the Clarkforkian. Ectocion osbornianus, E. parvus, Copecion brachypternus, and P. intermedius occur in Clarkforkian and Wasatchian. C. davisi and P. trilobatus are only known from the Wasatchian. E. superstes and P. intermedius are known from the Bridgerian. European Eocene phenacodontids are P. teilhardi, P. lemoinei (new), and P. condali. Ectocion and Copecion are monophyletic, while Tetraclaenodon and Phenacodus are probably paraphyletic. The distribution of phenacodontid taxa is partly determined by the sedimentary facies in which fossils occur which suggests habitat specialization. This is most obvious in the late Tiffanian: E. pinus and P. magnus dominate poorly-drained environments, while E. mediotuber, P. vortmani, and P. grangeri dominate well-drained environments. Cladistic analysis of dental, cranial and postcranial remains suggests that Meniscotherium and Perissodactyla are closely related, and that Phenacodontidae is the sister group to combined Meniscotherium and Perissodactyla.