Titanis walleri: The elusive Terror Bird

Aves; Phororachoidea; Phorusrachidae;Titanis walleri

Titanis walleri, more commonly known as the Terror Bird, is the largest predatory bird known to have existed. It was also flightless. Fossil material of this bird has been recovered from two-million year old sediments in Florida and the Gulf Coast of Texas, Titanis is a member of a South American group of birds called Phororachoidea, which all went extinct during the Pleistocene, approximately a million years ago. The fossil record for this group of birds is almost exclusively South American, where they have been recovered from late Oligocene to Pliocene deposits in predominantly Argentina and Uruguay (Baskin, 1995). Phorusrachids arrived in North America subsequent to the Panamanian land bridge connection between North and South America, which occurred approximately 2.3 million years ago.

Since their first discovery in Patagonia by the Chicago Field Museum paleontologist in the 1890s, paleontologists have believed that these flightless predatory birds evolved in situ on the island continent of South America as the dominant carnivores on land. Their closest relatives are an extant group of volant birds, Cariamas, that live in Argentina and Brazil (Riggs, 1939). Recent discoveries of phorusrachid fossil material in older sediments (Eocene-Oligocene) in Europe challenge the notion that these birds were exclusively from South America, suggesting that they evolved from an earlier group of birds that diversified on the continent of Gondwana (Mourer-ChauvirŽ, 1981).

Phorusrachids ranged in size from 5 feet to 9 feet tall (Marshall, 1994), with Titanis being the largest of these birds known. Because very little material of Titanis has been discovered its exact size is unclear, estimates range from 6 to 7 feet tall (Brodkorp, 1963; Chandler, 1994; Marshall, 1994). Recovered material from Northern Florida includes; two quadratojugal bones (cheek bones), two cervical vertebrae, a thoracic vertebra, two hands, and portions of the foot bones (Brodkorp, 1963; Chandler, 1994). From Texas, only a single element from a toe bone is known (Baskin, 1995).

The Florida Museum of Natural History is planning to mount a to-scale steel sculpture rendering of Titanis walleri for the Hall of Florida Fossils: Evolution of Life and Land, exhibit. The concept and construction of this sculpture is by Richard Webber of Museum Productions in New York City.

In order to more acurately estimate its size of Titanis, FLMNH's researchers, Gina Gould and Irv Quitmyer, along with Richard Webber and Julia Clarke, have been collecting measuremnts of phorurachid elements, as well as those from their sister group the cariamids, in preparation for a regression analysis to best estimate the length of the skull and the total height of the bird.