The molecular clock was calibrated using the well documented fossil-based estimate of 255 My (252 My - 257 My) for the reptile-avian split [ 27] and the human sequence was used as an outgroup.
Similarly, phylogenetic analysis strongly indicated that TLR2A to be orthologous to the functional TLR2 gene in mammals, sharing a common ancestor with TLR2B 341-356 Mya, prior to the split of reptiles and mammals 310-325 Mya.
It has been proposed that KRAB domains were recruited into Zn-finger containing proteins in the early vertebrates, whereas SCAN domains appeared later on, just before the split of reptiles and birds [ 27].
Instability of tree nodes at the split of reptile, mammalian and fish CXCL8_L2 clusters, using NJ or ML as tree construction method, render the respective evolutionary distances of fish CXCL8_L1 and fish CXCL8_L2 to mammalian CXCL8 difficult to assess precisely.
No fewer than 51 alien taxa – the technical term for species and sub-species counted together – have been observed, split between 30 reptiles, ranging from snapping turtles to red-eared terrapins, and 21 amphibians, from American bullfrogs to midwife toads.
Based on the results, the authors say, hair-keratin genes likely evolved before the split between mammals and reptiles.
Class I genes are not found in the orthologous region in Anolis, suggesting that a class I MHC gene was translocated to this region after the split of Rhynchocephalia from other reptiles and then duplicated here.
This shows that the diversification of the KRTAP gene family occurred early in mammalian evolution, likely starting after the split of sauropsids (leading to birds and reptiles) and synapsids (leading to mammals-like reptiles) around 350 Myr ago [ 58, 55].
The majority of these gain or loss events correlate with the split between Synapsida (mammals) and Sauropsida (reptiles and birds).
Descendants of the last common ancestor of mammals and reptiles (which appeared around 310 Ma in the Late Carboniferous) are therefore split into two clades: Synapsida, which includes Dimetrodon and mammals, and Sauropsida, which includes living reptiles and all extinct reptiles more closely related to them than to mammals.
