Ancient Proteins Demonstrate South American Ungulates are Laurasiatheres, not Afrotheres

WELKER, F; COLLINS, M. J. ; THOMAS, J; WADSLEY, M.; BRACE, S.; CAPPELLINI, E.; TURVEY, S.; REGUERO, M.; GELFO J. N.; KRAMARZ, A.; BURGER, J. ; THOMAS-OATES, J.; ASHFORD, D. A. ; ASHTON, P.; ROWSELL, K.; PORTER, D. M.; KESSLER, B.; FISHER, R.; BAESSMANN, C.; KASPAR, S. ; OLSEN, J.; KILEY, P.; ELLIOT, J.A.; KELSTRUP, C. ; MULLIN, V.; HOFREITER, M.; WILLERSLEV, E.; HUBLIN, J. J. ; ORLANDO, L.; BARNES, I; MACPHEE, R.

NATURE

NATURE PUBLISHING GROUP

Lugar: Londres; Año: 2015 vol. 522 p. 81 - 84

0028-0836

No large group of recently-extinct placental mammals remains as evolutionarily cryptic as the ~280 genera grouped as ?South American native ungulates? (SANUs). To Darwin1,2, who first collected their remains, they included perhaps the ?strangest animal[s] ever discovered?. Today, much like 180 years ago, it is no clearer whether they had one origin or several, arose before or after the Cretaceous/Palaeogene (K/Pg) transition 66.2 Ma (million years ago)3, or are more likely to belong with the elephants and sirenians of superorder Afrotheria than with the euungulates (cattle, horses, and allies) of superorder Laurasiatheria4?6. Morphology-based analyses have proven unconvincing because convergences are pervasive among unrelated ungulate-like placentals. Ancient DNA approaches have also been unsuccessful, probably due to rapid DNA degradation in semitropical and temperate deposits. Here we apply proteomic analysis to screen bone samples of the late Quaternary SANU taxa Toxodon(Notoungulata) and Macrauchenia (Litopterna) for phylogenetically informative protein sequences. For each SANU we obtained ≈90% direct sequence coverage of collagen (I) α1 and α2 chains, representing approximately 900 of 1140 amino acid residues for each protein. A phylogeny was estimated from an alignment of these fossil sequences with collagen (I) gene transcripts from available mammalian genomes or mass spectrometrically (MS/MS) derived sequence data obtained for this study. The resulting consensus tree agrees well with recent higher-level mammalian phylogenies7?9. Toxodon and Macrauchenia form a monophyletic group whose sister taxon is not Afrotheria or any of its constituent clades as recently claimed5,6, but instead crown Perissodactyla (horses, tapirs, and rhinos). These results are consistent with the origin of at least some SANUs4,6 from ?condylarths,? a paraphyletic assembly of archaic placentals. With ongoing improvements in instrumentation and analytical procedures, proteomics may produce a revolution in systematics like that achieved by genomics, but with the possibility of reaching much further back in time.