The genesis of reptiles and the amniotic egg - This is Gephyrostegus watsoni (Brough and Brough 1967), a basal reptile from the Westphalian (310 mya, with origins in the Viséan, 340 mya). Formerly considered a non-reptile tetrapod, G. watsoni had a deep pelvis, deep enough to lay large amniote eggs. It lacked posterior dorsal ribs, so gravid females could carry a large cache of amniote eggs. And it was found with at least seven large crushed sphere-shapes, perhaps the most primitive examples of amniote eggs (light blue above hips). No eggshell was present here, but each egg had an amniotic membrane, a trait shared by all living amniotes, including reptiles and their descendants the birds and mammals.

Welcome to the study of reptile evolution - Here you'll be able to trace the lineage of major clades, including the line that ultimately led to humans. You'll see where and when body parts (= traits) became added, substracted and modified. Most of the evolutionary links have been made and many of the mysteries and mistakes of the past have been solved and corrected with the present tree. The difference, in this case, is that many more genera were included than ever before (originally 224, now 500+), but the current tree can be recovered with as few as 60 carefully chosen taxa). Prior studies assumed certain relationships, several of which turned out to be mistakes when seen in a larger, more complete context. References and links are provided at the bottom of each page.

Every taxon listed here, unless it represents the last of its lineage or still survives, can be considered a transitional taxon. Notably, smaller, plainer specimens are typically found at the bases of major clades. Larger spectacular specimens are usually evolutionary deadends.

By definition, the Reptilia includes turtles, lizards, snakes, crocodilians and birds, their last common ancestor and all of its descendants. That last common ancestor is Gephyrostegus, according to the large reptile tree. Here, distinct from all prior studies, all known reptiles nest in two major branches with turtles and lizards on one branch and crodilians, birds and mammals on the other.

The new Lepidosauromorpha, are all those sharing a more recent common ancestor with living lizards, the Lepidosauria, than with Archosauria (Gauthier 1986). The new Archosauromorpha share more traits in common with living archosaurs (birds and crocs) than with Lepidosauria. This primitive division has not been reported before because all prior studies were more limited in scope. For those interested in obtaining the MacClade data file, click here and make your request.

The term Amniota is commonly and scientifically used to encompass all reptiles, birds and mammals, but in the present tree, the inclusion set of taxa within the Amniota is redundant with the Reptilia. Hence the more recent term, Amniota, can now be dropped from usage.

Ichthyostega is at the base of the Tetrapoda here. Reptilomorphs are tetrapod taxa leading toward reptiles (not including Eryops and Amphibians). Silvanerpeton and Gephyrostegus are basal reptiles/amniotes here.

In other studies Diadectes, Chroniosuchus and Solenodonsaurus were also considered reptilomorphs. That is an error resulting from a small taxon list. Here those taxa nest deep within the reptiles.

A similar study of large scope looked at pre-amniote tetraopds (Ruta, Jeffery and Coates 2003). It was not accurate near and within the Reptilia (= Amniota) due to the short and resricted amniote taxon list employed.