Comment on "Protein sequences from mastodon and Tyrannosaurus rex revealed by mass spectrometry"

Abstract

We used authentication tests developed for ancient DNA to evaluate claims by Asara et al. (Reports, 13 April 2007, p. 280) of collagen peptide sequences recovered from mastodon and Tyrannosaurus rex fossils. Although the mastodon samples pass these tests, absence of amino acid composition data, lack of evidence for peptide deamidation, and association of alpha1(I) collagen sequences with amphibians rather than birds suggest that T. rex does not.

Figure 1

Plot of radiocarbon age versus estimated effective collagen degradation temperature for radiocarbon dated bones from laboratory databases (principally Oxford and Groningen). The line represents the expected calendar age at which 1% of the original collagen remains following a zero-order reaction; almost no bone collagen survives beyond this predicted limit. Inset. 99% confidence intervals of amino acid compositions by first two principal component analyses (48% of total variance) for < 11 ka (n = 324), 11-110 ka (n = 210), 110-130 ka (n = 26) and 130-700 ka (n = 31) bones from NW Europe. Pliocene samples are not plotted, as their composition (n = 8) is highly variable and yields of amino acids are low. The orange line indicates a compositional trend observed when compact bone is heated for 32 days at 95 °C, which reduces collagen to 1% of initial concentration, each inflection representing a separate analysis (n = 32). The composition becomes more similar to mixed tissues samples (meat and bone meal, n = 32) principally due to the depletion of Gly. An amino acid profile for mammoth (m) is consistent with collagen, unlike the associated sediment sample (s) (data from ​11).

Figure. 2

Phylogenetic networks of α1(I) sequences using Neighbor-Net analysis (A) with the original assignments (2) and (B) following reinterpretation of the mass spectrometric data (12). T. rex does not group with bird/reptile using either set of sequence alignments. More sequence is required for a full, model-based phylogenetic analysis