Palaeanodonta and pholidota

INTRODUCTION During the Cenozoic, North America served as homeland to a diversity of what might be broadly called “edentate” mammals. True Xenarthra, largely confined to South America, did not arrive in North America until the late Miocene (Hemphillian). Earlier in the Tertiary, the resident “edentates” belonged to the Palaeanodonta and the Pholidota. Palaeanodonts were a moderately successful radiation of small, robust, fossorial mammals known mainly from early Paleocene (Torrejonian) through latest Eocene (Chadronian) rocks of the Rocky Mountain region. In recent years, a few specimens have been found in lower Eocene sediments of China and lower Oligocene beds of Europe (Heissig, 1982; Tong and Wang, 1997; Storch and Rummel, 1999). Most representatives show dental reduction and modifications of the jaws and palate believed to be associated with myrmecophagy, or at least a diet of small invertebrates. Although never abundant or diverse, palaeanodonts are well represented in some early and middle Eocene faunas, and their highly distinctive anatomy is at once recognizable. Jaw fragments are common in some deposits, but the teeth are reduced or vestigial in most species and are practically never found isolated. By comparison, skulls and partial skeletons – typically rare in the fossil record – are not unusual for palaeanodonts, perhaps because they died and were buried in burrows. Despite relatively complete osteological knowledge of several species, the relationships of palaeanodonts remain controversial. They are usually considered to be related to either Xenarthra or Pholidota (or both), but conclusive evidence of their affinities is lacking.