Wyoming's Garden of Eden

Natural History, April, 2001 by Kenneth D. Rose

<< Page 1 Continued from page 2. Previous | Next

Remains of odd-toed ungulates are among the most common Eocene fossils found in the Bighorn Basin. Jaws of Hyracotherium (or Eohippus, the dawn horse) have emerged by the thousands, and its skeletons are more numerous than those of any other mammal. Less common, and found only recently, are skeletons of Homogalax and other ancient relatives of the present-day tapirs of South America and Asia. The tapiroids were generally larger than dawn horses, the biggest being sheep-sized. Both Hyracotherium and Homogalax were well adapted for running, but the tapiroid was more primitive in this regard, suggesting that it more closely resembled the ancestor of all odd-toed ungulates than does Hyracotherium. The hind feet of both animals bore just three toes; the front feet had three plus a greatly reduced fourth digit. All the toes were equipped with a small, broad hoof.

Most Popular: 5 Super Tips To Get Rid Of Your Public Speaking Fear: How To Overcome Public Speaking Anxiety; 10 Cheap Ways To Build Your Brand: Learn Why Branding Reinforcement Is Important For Your Business; 13 Job Interview Mistakes To Avoid; Conflict Resolution & the Project Manager; 3 Questions No Job Seeker Ever Wants To Be Asked?

The molars of Hyracotherium and Homogalax were low-crowned, like those of Diacodexis, but had multiple shearing crests, a specialization for processing vegetation. Unlike many of their hoofed descendants, neither they nor any other early Eocene ungulate was a grazer. Grassland habitats were not to become widespread for millions of years. The teeth of early Eocene ungulates lacked the high crowns and elaborate chewing surfaces that allow grazers to grind grasses, which contain abrasive silica. These animals were probably browsers that fed on softer plant material, leaves, and shoots.

Not all the plant eaters in the Bighorn Basin Eocene mammal community were related to present-day ungulates. The most abundant large herbivore was Coryphodon, a ponderous, cow-sized member of an extinct group known as pantodonts. Like tapirs and pygmy hippopotamuses today, Coryphodon probably preferred wet forests or swamps, where it used its tusklike canines and broad, crested molars to feed on vegetation.

The newcomers that arrived in association with the warming at the end of the Paleocene--especially primates and ungulates--significantly altered the composition of the Bighorn Basin's mammal communities. Paleocene faunas were dominated by what we refer to as archaic mammals: condylarths (archaic ungulates), archaic primates, small rodent-like multituberculates, pantodonts, and others. While all these groups survived into the Eocene, most were substantially reduced in numbers and diversity. The change in mammal life was not only abrupt, it was profound: fossil evidence shows that in the early Eocene, half the individuals in many mammal communities belonged to immigrant species. This faunal turnover at about 55 million years ago took place not just in the Bighorn Basin but across all the northern continents. The results have been long lasting. Even- and odd-toed ungulates are the predominant large mammalian herbivores in most of the world today, and primates populate rainforests from South America to Africa and Asia. One thing seems clear: the immigrations were tied to global warming. But had we been there 55 million years ago, we could hardly have predicted the eventual ecological impact of that warming event. Only through paleontology have we gained the hindsight to appreciate the potential consequences of widespread climate change.

Featured White Papers

Wyoming's Garden of Eden

Natural History, April, 2001 by Kenneth D. Rose

Find Research Guides for:

Find Featured Titles for: Business

Most Popular Articles in Reference

Most Popular Publications in Reference