Avian infection could have killed T. rex

Published in The Hindu on October 1, 2009

Contrary to popular belief that bacterial bone infection or bite wounds from other tyrannosaurids could have killed Tyrannosaurus rex, a study suggests that they were killed by a common avian infection (Trichomonas gallinae).

This study provides evidence for the “ancient evolutionary origin of an avian transmissible disease in non-avian theropod dinosaurs,” notes the paper published in PLoS One journal. The study shows that cross-species infection is not a modern phenomenon but was present even millions of years ago.

The paper is based on a study of ‘Sue’ — the Tyrannosaurus rex that is exhibited at the Field Museum in Chicago, and a few other specimens.

Ewan D.S. Wolff from the University of Wisconsin, Madison, the first author of the paper, found similar lesions in 15 per cent of the 61 T. rex individuals examined.

Though concrete evidence of how the infection killed the tyrannosaurids is not available, the authors note: “These animals died as a direct result of this disease, mostly likely through starvation.”

Tell-tale marks

Most predatory dinosaurs exhibit bone traumas on the head. They also show cranial abnormalities that are very different from injuries caused by biting. The lesions have a very distinct shape — smooth-edged erosive lesions that are commonly seen in the mandible.

Similar abnormalities in the mandible are seen in modern birds that are infected by the avian parasitic infection. It is commonly seen in both wild and domestic pigeons, and even in turkeys and chickens.

Possible causes of infection

They suggest five possible scenarios for transmission: water-borne transmission, feeding of tainted prey to nestlings, consumption of infected prey, cannibalism, or snout to snout contact between two individuals. However, little proof is available for most of the scenarios.

“Evidence supports the possibility of transmission via snout-to-snout contact in a modification of the bill-to-bill transmission that can occur in living birds,” they write.

The study of the dinosaurs makes one thing clear: T. gallina-type infection followed the same route of disease development. Immaterial of the route of infection, the infection within the oropharynz could have spread to other tissues by invading the mucosal surface. This is what is seen in modern birds.

The infection could have then become chronic in the mandible, which in turn could have made feeding very difficult, as is the case with modern birds infected by the bacteria. The Tyrannosaurus could have ultimately died of starvation.

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