Which came first, the chicken or the alligator? When it comes to the Tyrannosaurus rex family tree, it turns out that both modern-day chickens and alligators can call the T. rex “cousin.”
A group of researchers, including North Carolina State University paleontologist Dr. Mary Schweitzer, have used protein sequences from 68 million-year-old bone-derived collagen to determine the evolutionary relationships of T. rex. The results appear in the April 24 edition of Science.
Schweitzer, associate professor of paleontology at NC State with a joint appointment at the N.C. Museum of Natural Sciences, had previously discovered soft tissue in the leg bone of a T. rex recovered in 2003 from the Hell Creek formation in Montana. She provided samples of collagen from the bone to her colleagues Dr. John Asara at Harvard Medical School and Beth Israel Deaconness Medical Center, and Dr. Chris Organ of the department of organismic and evolutionary biology at Harvard. Asara sequenced the protein, and found similarities between the peptides extracted from T. rex collagen protein fragments and those of modern-day chickens. However, these initial sequences were not analyzed phylogenetically, or in terms of where they might place T. rex within the evolutionary “family tree.”
The researchers then conducted multiple phylogenetic analyses by comparing the sequence data from T. rex and a mastodon fossil, to a database of sequence data from 19 animals, including living animals. The results place the non-avian T. rex within the class Archosauria between the ancestors of modern-day alligators and their avian relatives, the modern-day chicken. The mastodon, as expected, was found to be a relative of modern elephants, proving that the genetic material was authentic, and that trait evolution can be traced at the molecular level.
“The really interesting thing here is that we have hard evidence that it is possible to trace evolutionary traits of extinct animals through molecular analysis,” Schweitzer says. “This will give us greater insight into the ways in which species evolve over time.”
– peake –
Note to Editors: An abstract of the paper follows.
“The Molecular Phylogenetics of Mastodon and Tyrannosaurus rex”
Authors: Chris L. Organ and John Asara, Harvard University; Mary Schweitzer, North Carolina State University, et al.
Published: April 24, 2008 in Science
Abstract: Protein sequences from bone-derived collagen as old as 68 million years have been detected using mass spectrometry (1, 2). A BLAST search of the resulting peptides found similarities between the peptides extracted from Tyrannosaurus rex collagen protein fragments and those of birds (Gallus gallus) and between mastodon (Mammut americanum) and other mammals. However, the sequences were not subjected to phylogenetic analysis. Here, we perform a Bayesian phylogenetic analysis to infer the evolutionary relationships of the T. rex [Museum of the Rockies (MOR) 1125] and mastodon (MOR 605) material. The primary goal for this analysis was to: 1. Determine if short and fragmented collagen sequences contain a phylogenetic signal and to 2. Evaluate the authenticity of the protein sequences through multiple phylogenetic analyses. Our results support the endogenous origin of T. rex and mastodon protein fragments because they correctly place the non-avian dinosaur within Archosauria between alligator (Alligator mississippiensis) and avian dinosaurs (Gallus gallus and Struthio camelus). The results also group mastodon with elephant (Loxodonta africana) over other vertebrates, thereby supporting the claim that this material is genuine as well. This result is the first molecular phylogeny for a non-avian dinosaur, extending our knowledge of trait evolution within non-avian dinosaurs into the macromolecular level of biological organization.