UF: 'Terror bird' made early appearance

Published: Tuesday, January 23, 2007 at 6:01 a.m.
Last Modified: Monday, January 22, 2007 at 11:49 p.m.

University of Florida researchers have used a little-known method for dating fossils to help them discover that a prehistoric "terror bird" came to North America earlier than was first believed, according to a UF news release.

The Titanis walleri, a flightless, carnivorous bird that stood 7 feet tall and weighed about 330 pounds, was first thought to have migrated to North America from South America via the Panamanian land bridge that formed about three million years ago.

Using a process that analyzes the rare earth elements present in the fossils, UF paleontologist Bruce MacFadden and his team were able to date a Titanis walleri bone found in Texas to about 5 million years ago, making the land bridge theory impossible.

MacFadden and his team now believe the birds probably used islands to make their way north — islands that now form the Isthmus of Panama.

"We used rare earth elements because they're highly specific to certain time periods and different groundwater conditions," MacFadden said. "This is the first time that the uptake of rare earth elements during the early stage of fossilization has been used to determine the age of fossils in North America."

MacFadden explained that when an animal dies, the pores in the bones absorb groundwater, leaving a distinct pattern of specific rare earth elements in the fossilized bone. As time passes, the groundwater conditions and the rare earth elements change.

The process has been widely used to study igneous and metamorphic rocks, but has only been applied to fossils by one other researcher: Clive Trueman of the University of Southampton in England.

"It is very difficult to assess the age of fossil bones directly as they are too old to be carbon dated," Trueman wrote in an e-mail to UF. "Bones can also be moved after death, further confusing their true age. MacFadden's approach compares bones of disputed age with those of known age. If the chemistry matches, the bones are the same age irrespective of their final resting place."

Titanis walleri fossils have only been found in Texas, where a single toe bone was located, and in Florida, where about 40 bone fragments have been found, according to UF.

When MacFadden's team analyzed fossils found in the Santa Fe River in North Central Florida, they determined them to be 2 million years old.

"This also shows the last known occurrence of Titanis in the fossil record and reflects its extinction," MacFadden said.

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