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Phylogenetics Support Tyrannosaurus Rex's Evolutionary Relationship with Birds

NEW YORK (GenomeWeb News) – Tyrannosaurus rex peptide sequences are more similar to modern-day birds than to reptiles, according to new research, providing added evidence for a relatively close evolutionary relationship between dinosaurs and birds.
About a year ago, researchers from Harvard University and elsewhere first reported that they could tease minuscule amounts of protein from mastodon and T. rex bone samples that were up to 600,000 and 68 million-years-old, respectively, and analyze them by mass spectrometry.
Now, members of the same team report using molecular phylogenetics to group mastodon and T. rex based on their collagen protein peptide sequences. These latest results, appearing in today’s issue of Science, suggest T. rex is more closely related to chickens and ostriches than to alligators and seem to confirm the long-held suspicion that dinosaurs and birds have a common ancestor. They also corroborate a relationship between mastodons and modern day elephants.
“We determined that T. rex, in fact, grouped with birds — ostriches and chickens — better than any other organism that we studied,” senior author John Asara, director of Beth Israel Deaconess Medical Center’s Mass Spectrometry Core, said in a statement. “We also show that it groups better with birds than modern reptiles, such as alligators and green anole lizards.”
Asara and his team compared collagen alpha one and two peptide sequence from T. rex and mastodon with those from 21 modern species, including elephant, green anole lizard, and alligator. Most of the peptide sequences were from the NCBI and Ensembl databases or previous studies. But the team also did microcapillary liquid chromatography tandem mass spectrometry with an ion mass spectrometer to get collagen alpha one and two peptide sequences from American alligator bone samples.
They then generated evolutionary trees by Bayesian, likelihood, parsimony, and distance methods. Though there were slight differences in the groupings depending on the type of analysis used, the same general patterns held: T. rex grouped with birds, particularly chickens and ostriches, while mastodon fell into the mammalian group and was apparently most closely related to elephant.
“These results match predictions made from skeletal anatomy, providing the first molecular evidence for the evolutionary relationships of a non-avian dinosaur,” lead author Chris Organ, a post-doctoral organismic and evolutionary biology researcher at Harvard University, said in a statement.
More data is needed to refine the phylogenetic tree, particularly T. rex’s precise branching position with respect to birds and alligators. Even so, the molecular data supports hypothetical relationships presumed from skeletal evidence. And, the team says, it demonstrates the power of molecular techniques to probe evolutionary events in the distant past.
“Our findings suggest that molecular data from long-extinct organisms may have the potential for resolving relationships at critical areas of the vertebrate evolutionary tree that have, so far, been intractable,” the authors wrote.

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