Mammals of New Mexico

New Mexico possesses a rich diversity of native mammals: 148 species have been recorded in the state. This diversity results from the state's geographic position, great topographic relief, and dynamic history. The Southwest is the meeting ground of the Great Plains grasslands, three regional deserts, and the Rocky Mountains, and contains mammals from each region. Western North America is a jumbled mix of mountain peaks, desert-grassland basins, and riverine corridors. This diversity stands in stark contrast to more continuous habitats in the rest of North America.

Glacial advances ("Ice Ages") during the last three million years brought waves of plants and animals that were adapted to cool, wet conditions into the region, pushing out warm, dry-adapted forms. With each glacial retreat, desert forms returned, and the initial invaders were themselves forced to retreat northward and into isolated mountains.

Oldest mammal skull

World's Oldest Mammal

Mammals have lived in the Southwest since their emergence in the reptile-dominated world of the Triassic Period, 220 million years ago. In 1990, NMMNH curator Spencer Lucas and his students discovered the world's oldest mammal in West Texas. New Mexico's rocks hold a rich history of the evolution of mammals. Late-Cretaceous-age (80-66 million years before present) beds in the San Juan Basin of northwest New Mexico preserve a diverse fauna of Mesozoic mammals, including some of the earliest marsupials.

Tertiary Mammals

New Mexico is famous for its Tertiary mammals. Early Tertiary (66-34 million years ago) deposits in the San Juan Basin contain some of the most abundant fossils of primitive mammals. Deposits along the Rio Grande Valley contain a treasure trove of late Tertiary (25 million years ago to recent) mammals.

A Coryphodon from the Tertiary

Pleistocene Mammals

Caves throughout New Mexico have served as traps during hundreds of thousands of years, preserving a rich record of changing conditions in the Ice Ages. These fossil deposits, studied by Art Harris (University of Texas, El Paso) and former NMMNHS director and curator Richard Smartt, have yielded not only fantastic creatures such as giant ground sloths, dire wolves, and camels, but also tiny mammals that provide clues about the specific environment of the time.

A pika

NMMNHS curator David Hafner attempts to reconstruct the past history of New Mexico's mammals by studying genetic relationships among living populations. They study species that were trapped on mountaintops following the last glacial retreat, such as pikas. Using modern genetic techniques as well as the fossil record, researchers can "rewind the film" that shows us the changing distributions of these mammals during the last 50,000 years.

Changing Times

Since the arrival of Europeans to New Mexico, at least four native mammals have been driven to extinction in this state: Mexican gray wolf, Mexican grizzly bear, river otter, and jaguar. The black-footed ferret is probably extinct in the state. Bison, which once roamed the eastern plains, are restricted to a single captive herd. Reintroduction of the Mexican gray wolf has recently occurred in New Mexico.

Europeans brought a number of mammals with them, or later introduced species for game. These now-free-living species include: house mice and rats; nutrias; feral pigs, goats, burros and horses; and barbary sheep and ibex. Feral dogs and cats often create a "no-man's-land" around human communities where few, if any, native mammals survive.

A Mexican gray wolf

The general drying trend that followed the last glaciation has been hastened by man, through overgrazing, suppression of natural fire cycles, and overuse of water. Deserts and piñon-juniper woodland are replacing grasslands in the state, and native mammals are changing their distributions. Species that depend on wetlands or grasslands are suffering extensive range reduction.

Discovery continues in New Mexico. In the past 10 years, two species (least shrew and meadow jumping mouse) thought to be extinct were discovered. Two other species (another shrew and a grasshopper mouse) have been added to the state's list. Continuing research on mammals may provide better information on the effects of past climatic changes in the region, and allow more accurate predictions of future changes.