Tyrannosaurus rex

We sequenced collagen protein fragments derived from fossilized bones of two extinct taxa: a 160,000- to 600,000-year-old mastodon [specimen number Museum of the Rockies (MOR) 605] (9) and a 68-million-year-old dinosaur (Tyrannosaurus rex,

MOR 1125) (10),

results that are supported by immunological and molecular analyses published in this issue by Schweitzer et al. (11). We first looked for tryptic peptide fragments from extracts of fossilized bone that matched identically with sequences from an orthologous protein or proteins from extant taxa, thereby identifying the protein(s) of interest. This is a common procedure for conserved proteins from taxa that share genomic information. Next, we generated a protein sequence database of likely drifts in amino acids in other tryptic peptides by comparing amino acid sequences ofthe orthologs from multiple related extant taxa. This approach produced a manageable number of theoretical protein sequences. The predicted peptide fragmentation pattern from these theoretical protein sequences were then compared with the fragmentation patterns of additional peptides derived from extracts of fossilized bone that did not match peptides in public sequence databases (fig. S1).