Convergence is inferred when two groups share a similar characteristic that is thought to be not due to common ancestry. Convergence confuses the evolutionary interpretation of shared features, causing inconsistencies in the pattern. But convergence is a common problem in evolutionary studies, often producing numerous inconsistencies in proposed evolutionary trees. Reptiles have been divided into subgroups, one of which is Diapsida. This group includes lizards, snakes, crocodilians, sphenodontids, dinosaurs, and several other extinct groups.
Diapsids first appear in Upper Carboniferous strata, but are relatively rare in Paleozoic sediments.
The number of groups of diapsid fossils increases as one moves upward through the geologic column. As additional groups are included, the number of uniquely shared characteristics decreases, apparently due to convergence. This means that only a minority of character traits show patterns consistent with the hypothesis of common ancestry for this group. Ratite-like neoteny induced by neonatal thyroidectomy of European starlings, Sturnus vulgaris . Journal of Zoology, London.