IMGT Lexique

Phylogeny

Separation of the monotremes from the therian : 170 million years ago [1].
Separation of the mammalian ancestors from the reptilian lineage: 310 million years ago [2].

References:
[1]	Retief, J. D. et al. Eur. J. Biochem. 218, 457-461 (1993). PMID: 8269934
[2]	Kumar, S. and Hedges, S. B. Nature 392, 917-920 (1998). PMID: 9582070