Fossil Implies Our Early Kin Lived in Trees, Study Says

Hillary Mayell
for National Geographic News
November 21, 2002

The discovery of a fossil skeleton of a 56-million-year-old tiny mammal indicates that our early ancestors were tree-living fruit eaters, and is helping scientists to understand the early evolution of primates.

"One of the big unanswered questions in mammalian vertebrate paleontology is what did primates evolve from, where, and why," said Jonathan Bloch, a paleontologist at the University of Michigan Museum of Paleontology.

The earliest true primates, called euprimates, first appear in the fossil record 55 million years ago in North America, Asia, and Europe. Euprimates as a group includes humans, monkeys, and apes. The question is what happened during the 10-million-year stretch between the extinction of the dinosaurs, roughly 65 million years ago, and the first appearance of primates.

The nearly complete fossil skeleton of a Carpolestes simpsoni, found in the Clarks Fork Basin of Wyoming, may begin to answer some of those questions.

Carpolestes is a member of an archaic group of primates called plesiadapiforms. Plesiadapiforms lived from about 65 to 45 million years ago.

The characteristics that separate primates from other mammals are a large brain; the ability to grasp, which requires opposable thumbs and big toes; the ability to leap; eyes in the front of the face rather than on the side; and nails instead of claws.

Because Carpolestes combines features of the earlier plesiadapiforms with primate-like features, it begins to answer the question of what order these traits evolved, and for what purpose. The study is published in the November 22 issue of the journal Science.

Evolution of Primates

There have been three hypotheses to explain why and how primates evolved.

In one view, grasping ability with nails, and forward facing eyes evolved together to enable the animals to prey on insects found at the base of trees.

A second hypothesis is that grasping with nails, forward facing eyes, and the ability to leap evolved together in order to move through the branches of trees rapidly.

It has also been suggested that grasping evolved first to allow the animals to eat the fruit on small branches, and forward facing eyes evolved later to enable them to prey on insects.

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