Tuesday, January 23, 2007
Titanis walleri: 'Terror bird' arrived in North America before land bridge
A University of Florida-led study has determined 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.
UF paleontologist Bruce MacFadden said his team used an established geochemical technique that analyzes rare earth elements in a new application to revise the ages of terror bird fossils in Texas and Florida, the only places in North America where the species has been found. Rare earth elements are a group of naturally occurring metallic elements that share similar chemical and physical properties.
"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, a curator of vertebrate paleontology at the Florida Museum of Natural History at UF. "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 study will be published* January 23 (2007) in the online version of the journal Geology and featured in its February print edition.
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."
When an animal dies, its porous bones absorb groundwater as they fossilize. As the local groundwater conditions change, the rare earth elements' concentrations change, resulting in a unique chemical signature.
"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."
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."
David Gradstaff, a professor and chairman of the geology department at Temple University, said the technique is timely and important.
"If a fossil gets moved or reworked from its place of formation, it will have a fingerprint that is different from the others nearby," Grandstaff said. "Who knew that all these fossils essentially have a tag that says 'hey, I'm from over here!' "
Co-authors of the study include Richard Hulbert Jr. of the Florida Museum of Natural History; Joann Labs-Hochstein, who at the time of the study was a postdoctoral student of MacFadden's; and Jon Baskin of Texas A and M University.
Source: University of Florida News Release "'Terror bird' arrived in North America before land bridge, study finds" (Tuesday, January 23, 2007.)
Based on the Geology paper:
Revised age of the late Neogene terror bird ( Titanis) in North America during the Great American Interchange
Bruce J. MacFadden, Joann Labs-Hochstein, Richard C. Hulbert Jr, Jon A. Baskin
Volume 35, Issue 2 (February 2007) pp. 123 - 126
The giant flightless terror bird Titanis walleri is known from Florida and Texas during the late Neogene. The age of T. walleri is problematic because this taxon co-occurs with temporally mixed (i.e., time-averaged) faunas at two key sites. Thus, prior to this study, T. walleri from the Santa Fe River, Florida (type locality), was either as old as late Pliocene (ca. 2.2 Ma) or as young as latest Pleistocene (ca. 15 ka). Likewise, T. walleri from the Nueces River, Texas, was either early Pliocene (ca. 5 Ma) or latest Pleistocene (ca. 15 ka). In order to better resolve this age range, the rare earth element (REE) patterns of T. walleri from the Santa Fe River, Florida, were compared to two biochronologically distinctive groups (late Pliocene versus late Pleistocene) of fossil mammals from the same locality. Similarly, the REE patterns of T. walleri from Texas were compared to two groups (early Pliocene versus latest Pleistocene) of fossil mammals from the same locality. The REE patterns of T. walleri from Florida are indistinguishable from those of the co-occurring late Pliocene mammals. Likewise, the REE pattern of T. walleri from Texas is indistinguishable from those of the co-occurring early Pliocene mammals. Given these REE constraints, the revised age of T. walleri is early Pliocene in Texas (ca. 5 Ma) and late Pliocene (ca. 2.2-1.8 Ma) in Florida. As such, T. walleri is interpreted as an early immigrant during the Great American Interchange prior to the formation of the Isthmian land bridge. No evidence currently exists for Pleistocene T. walleri in North America.
Brodkorb, Pierce (1963): A giant flightless bird from the Pleistocene of Florida. Auk 80(2): 111-115.
The large, flightless birds of the superfamily Phorusrhacoidea have had a known history confined, until now, to Argentina and Uruguay, and, in time, to the period from the Oligocene to the early Pleistocene. This paper extends the known geographic occurrence of the group to North America and its known geologic range into the late Pleistocene. The fossil here described from a fluvial deposit in northern Florida, is a bird of tremendous size, larger than the African ostrich and more than twice the size of the South American rhea.
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Technorati: titanis, walleri, prehistoric, terror, bird, flightless, north, america, south, land, bridge, fossils, texas, florida, paleontology, vertebrate, museum, natural history, isthmus, panama, geology, carnivorous, fossil, record, bones, giant, pleistocene, ostrich, rhea, birds, dinosaur, tarbosaurus