Scientists no longer have to date the rocks that a fossil is found in to determine its age—new techniques allow for direct determination of its age.
Art © DK
From the U Florida press release:
Scientists have shown that Titanis walleri, a prehistoric 7-foot-tall flightless “terror bird,” arrived in North America from South America long before a land bridge connected the two continents using analysis of rare earth elements.
“It was previously thought that Titanis immigrated to Texas across the Panamanian land bridge that formed about 3 million years ago connecting North and South America,” said MacFadden. “But the rare earth element analysis of a fossil Titanis bone from Texas determines its age to be 5 million years old. This shows that the bird arrived 2 million years before the land bridge formed, probably across islands that formed what today is the Isthmus of Panama.”
The terror bird was carnivorous, weighed about 330 pounds, had powerful feet and a head larger than a man’s. It is known in the fossil record from a single toe bone in Texas, and in Florida by about 40 bone fragments from different skeletal regions. MacFadden’s team also analyzed six specimens from the Santa Fe River in north Central Florida.
“We found that the Titanis fossils were 2 million years old and not 10,000 years old as had been suggested,” MacFadden said. “This also shows the last known occurrence of Titanis in the fossil record and reflects its extinction.”
Illustration Credit - Scientific American / Feb.1994
Geologists have used the technique to study igneous and metamorphic rocks, but only one other researcher worldwide has applied this technique to date the age of fossils: professor Clive Trueman from 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. “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 of the same age irrespective of their final resting place.”
The study will be published Jan. 23 in the online version of the journal Geology and featured in its February print edition. I’ll add the link once it is posted.