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 most 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 false when seen in a larger, more complete context. As time goes by, new taxa will be featured, more lineages will be added and the inevitable corrections will be made. 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.

If you want to read the book, "From the Beginning - The Story of Human Evolution" by David Peters (Little, Brown 1991), which is where the above image was first published, click here for the PDF.

Learn more about the genesis of reptileevolution.com. Comments are always welcome.

Recently a few well-meaning, but seriously misguided paleontologists have railed against this website. I encourage you to read their work, read my 7-part reply to their largely bogus arguments and read whatever interests you on this site. Then decide for yourself whether or not ReptileEvolution.com contains work of value.

The reptile family tree begins with Gephyrostegus because, 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 present study. In the present study, 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.

Gephyrostegus bohemicus itself was probably too large to produce embryos enclosed within an amniotic membrane, the defining character of the Amniota (= Reptilia in this study). Gephyrostegus watsoni is a more likely candidates.

The first reptile invented the amniotic membrane, which surrounds and protects the developing embryo in all reptiles (including birds and mammals). The eggs of Cephalerpeton and Cassineria were more or less protected from desiccation and so could be laid away from water, but probably in damp leaf litter and moss rather than any hot and arid place. There is no fossil evidence that an eggshell was created at this node.

Shortly after a very early sister to Cephalerpeton members of the Reptilia split into two clades represented at their bases by Westlothiana and Cephalerpeton. 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, without the benefit of an umbrella study like this one.

The more complete reptile family tree with archosauromorph and lepidosauromorph branches is found here. See a (slightly outdated) chronological phylogram of the same tree below. 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.

Earlier, with just two microsaurs included, the large study found Utaherpeton and Tuditanus to nest within the Reptilia with Westlothiana. The addition of several other microsaurs clarified the situation and moved all microsaurs out of the reptilia.

Ichthyostega is at the base of this tree. Reptilomorphs are tetrapod taxa leading toward reptiles (not including Eryops and kin). Silvanerpeton and Gephyrostegus are reptile sister taxa with the latter considered a protoreptile.

In other studies Diadectes, Chroniosuchus and Solenodonsaurus were also considered reptilomorphs. That is an error resulting from a too 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.