Phylogenetic position of turtles among reptiles: Evidence from immunological comparisons of eggshell matrices

The phylogenetic affiliation of turtles among major groups of reptiles is a controversial issue. Since turtles have no temporal fenestra unlike other reptiles and birds, turtles have been traditionally considered as the only survivors of anapsids, which have no fenestra, and as the most basal reptiles. Recent molecular studies, however, posit an archosaurian (crocodiles and birds) affinity of turtles and the earliest branching of squamates (lizards and snakes) instead of turtles. To address this issue, we performed enzyme linked immunosorbent assays (ELISA) on the extracts from eggshells of a total of 25 reptiles and birds. Antiserum raised against eggshell extracts from chicken (Galius gallus domesticus) reacted with those from crocodiles and turtles stronger than those from squamates, and the other antiserum raised against eggshell extracts from a soft-shelled turtle (Pelodiscus sinensis) reacted with those from birds and crocodiles stronger than those from squamates. These results support the archosaurian affinity of turtles and the scheme of recent molecular phylogeny.