A team of anthropologists said their study of South Texas fossil deposits revealed evidence including ancient teeth that shows the area was home to numerous types of primates 42 million years ago.
Lamar University Professor Jim Westgate and two colleagues announced the discovery of three new genera and four new species of primates based on their examination of material removed from Lake Casa Blanca International State Park near Laredo and the Mexican border.
Westgate said the Laredo area was a coastal lagoon during the stage of geologic history known as the Eocene Epoch, which was when primates were becoming extinct on much of the continent.
"It was kind of the last gasp for the primates in North America," said Westgate, a professor of earth and space sciences.
The researchers presented their findings last week at a conference of the American Association of Physical Anthropologists in Philadelphia.
Westgate and others are still studying the 15 tons of material excavated from the park's fossil deposits between 1983 and 1996. Researchers recovered 1,800 mammal teeth, including 50 from primates.
Dana Cope, a co-author of the study and associate professor of anthropology at College of Charleston in South Carolina, compared the teeth with other primate teeth from the same era. He said the newly discovered teeth, which measure about 4 millimeters (0.16 inch), were not from known primates.
"This is a very important locality," Cope said. "Not much is known about Eocene mammals outside the Rocky Mountains."
Cope said the genus the researches have focused on likely had a diet of leaves and foliage and weighed about 2 pounds (1 kilogram). Its closest living relative would probably be the tarsier primate that lives in the Philippines.
Westgate said one of the project's main goals was to excavate the material and protect it for study and documentation.
"We knew way back we had something important," he said. "Now we're targeting areas that needed more research."