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Evolution in the Southwest

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Notable Fossil Finds:

  • In 1996, the oldest-known horned ("ceratops") dinosaur in North America was discovered in the high desert of western New Mexico. The animal lived about 90 million years ago, when oceans covered much of the region. Dinosaur fossils from this time are very rare.

  • In 1927, giant bison fossils were found in Folsom, N.M., with spear points embedded in the bones. The bison date to about 11,000 years ago. In 1935, near Clovis, N.M., more points, this time with mammoth bones, were discovered. These dated to about 13,000 years ago. The two finds revised early estimates as to when humans arrived in North America from Asia.

  • In 1979, a Seismosaurus, considered to be the longest dinosaur that ever lived (more than 120 feet), was discovered in San Ysidro, N.M. Its name translates to "ground-shaking dinosaur." (See an exhibit about its discovery at the New Mexico Museum of Natural History.)

  • In 1947, near-complete dinosaur skeletons were found sticking out of the shale at Ghost Ranch, N.M., including what is now the state fossil, a three-foot-tall, long-tailed carnivore. Fossils from this find are in the American Museum of Natural History in New York. The Ghost Ranch Visitor Center has similar fossils from other local finds.

  • In 2001, two feathered dinosaur species previously unknown in North America were found in New Mexico's Zuni Basin. One was a long-necked plant-eater, the other a two-legged meat-eater that stood about three feet tall.

  • The skull of a "terrible crocodile," which grew to some 50 feet long, was found near the Rio Grande in Texas. This largest-known crocodile is thought to have preyed on dinosaurs that drank from lakes and rivers. (See it at the Oklahoma Museum of Natural History.)

  • In 1971, a species of Quetzalcoatlus, the largest-known flying reptile, was discovered in Big Bend National Park, Texas. It had a 40-foot wingspan and lived until the dinosaur extinction 65 million years ago.

  • In 2000, researchers in Big Bend National Park, Texas, discovered neck bones of a 65-million-year-old, 100-foot-long Alamosaurus, one of the largest dinosaurs known in North America.

  • First discovered in 1958, the well-preserved Elephant Hill trackways near Camp Verde, Ariz., feature footprints of mastodons, a camel, sloths, and a what might be a mountain lion, all no more than 2 million years old.

  • In 1988, scientists found a new seven-foot plant-eating dinosaur from the Triassic period near Tucumcari, Ariz.

  • The Barringer Meteor Crater, located on a limestone desert plain in Arizona, stretches nearly a mile across and is nearly 600 feet deep. The meteorite that formed the crater crashed to Earth just 50,000 years ago. (Not a fossil, but nonetheless fascinating!)

Endangered Species:

Photo of Ocelot The following animal and plant species are among those listed in the federal government's register of endangered species in this region.


Ocelot (land mammal)

  • Appearance: This small cat's coat is short and marked by rosettes and spots that run in parallel along both sides of its body (3 feet long, 15-30 pounds)
  • Habitat: Dense, thorny scrub brush
  • Threat: Human hunting, habitat loss to farming and development
  • Fast fact: In 1995, only 80-120 individuals were counted; ocelot litters number only 1-2 kittens.

Southwestern willow flycatcher (bird)

  • Appearance: Brownish-olive body with yellowish belly (less than six inches)
  • Habitat: Breeds in thickets and woodland alongside streams and rivers
  • Threat : Habitat loss, nest predation, and egg parasitism
  • Fast fact: Its Latin genus name, Empidonax, means "mosquito king."

Greater long-nosed bat (land mammal)

  • Appearance: Three to four inches long with distinctive noses
  • Habitat: Roost in caves and feed by night on plant nectar and pollen
  • Threat: Often killed by humans fearing diseases spread by vampire bats; loss of agave plants to clearing or exportation
  • Fast fact: Their long noses and tongues are well adapted for getting to nectar in desert plants; they help plants reproduce by spreading pollen.

Kemp's ridley sea turtle (reptile)

  • Appearance: Its dark, mottled-green shell is broad and flat, and front limbs are flipperlike (2-3 foot shell, 90 pounds)
  • Habitat: Tropical and temperate Atlantic waters; this sea turtle feeds on crabs and other bottom-dwelling marine animals
  • Threat: Shrimp trawler nets entangle turtles at sea; coyotes and people dig up and eat their eggs
  • Fast fact: While Kemp's ridleys normally breed exclusively on one stretch of beach in northeast Mexico, eggs are now being transported to Padre Island, Texas, to establish as second breeding site.

Texas blind salamander (amphibian)

  • Appearance: Short, slender body with a long tail, spindly legs, a large head, and a flattened snout; its skin is whitish to transparent
  • Habitat: Feeds on snails, shrimps, and amphipods in watery caves
  • Threat: Deteriorating water quality, and a decline in water levels due to increased human consumption and irrigation
  • Fast fact: An effort to protect these salamanders from collectors backfired when the cave they inhabit was sealed, killing a population of bats and altering the overall health of the ecosystem.

Black-capped vireo (bird)

  • Appearance: Black- or gray-headed, with yellowish-green feathers (4.5 inches)
  • Habitat: Open rangelands with low-growing shrubs
  • Threat: Land development, overgrazing by livestock, strict fire-management policy
  • Fast fact: The males sing to attract mates and to defend their territories.


The Southwest region, known for its unique mix of mountain, plain, and coastal geographies, didn't begin to emerge from the oceans until about 300 million years ago. The Ouachita Mountains were first to peek through. The organic remains of lush plants and animals that lived on dry land were the foundation for coal beds that underlie the eastern part of the region.

The Carlsbad Caverns are the eroded insides of a 250-290 million-year-old tropical reef. During this time, the Permian period, all the world's lands were united in a supercontinent, Pangaea. North America was situated near the equator, and what is now Texas was part of Pangaea's west coast. Another fossil fuel, oil, has its origins in marine creatures that lived at this time.

Over the next 200 million years, sea levels fluctuated and several large areas were again covered by shallow seas. As mountains to the east and west weathered, massive amounts of sediment were carried by wind and rivers and deposited over the Great Plains. The remains of many an ancient dinosaur lie buried here. In the years following the dinosaur extinction, the Southwest was geologically stable. Sea levels receded to about where they are today. Beginning about 50 million years ago, however, and lasting several million years, volcanoes spewed lava and ash over much of the region.

From fossils, we know giant ground sloths, camels, and bison later roamed the Southwest, some as recently as 10,000 years ago. While the region was spared the land-changing effects of glaciation, it was during the last Ice Age that one famous meteor left an indelible mark on its landscape: Barringer Meteor Crater, which struck Earth 50,000 years ago, is among the best-preserved meteor craters in the world.

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