The first North American mammoths: Taxonomy and chronology of early Irvingtonian (early Pleistocene) Mammuthus from New Mexico

Abstract

In North America, some of the most complete and well-dated records of primitive mammoths are from lower Pleistocene deposits in the Rio Grande rift of central and southern New Mexico. The oldest of these mammoths are early Irvingtonian in age (1.3–1.4 Ma) and are assigned to Mammuthus meridionalis, based on their primitive jaw morphology and relatively broad, low-crowned molars, with low plate ratios and thick enamel. The somewhat younger, primitive New Mexican mammoths are also early Irvingtonian (0.8–1.3 Ma) but are more advanced morphologically, so we refer them to M. imperator. The primitive mammoths from the early Irvingtonian Leisey Shell Pit in Florida are morphologically similar, and we refer them to M. imperator. The recent suggestions that North American Mammuthus is derived from Eurasian M. trogontherii and that all North American mammoths (except the late arriving M. primigenius) belong to one species, M. columbi, are rejected because they are based on internal inconsistency, incorrect data, and inadequate analysis of the North American mammoth record. The New Mexican mammoths confirm the presence of M. meridionalis-grade Mammuthus in North America before 1.3 Ma and the rapid evolution of an M. imperator-grade mammoth by 1.2 Ma.