As we learned earlier, hypotheses on snake origins have suffered by not recognizing that living snakes are diphyletic. The tiny burrowing snakes (Scolecophidia, Aniliidae, Uropeltidae), like Cylindrophis, have a separate lineage through ancestors like Heloderma. The larger non-burrowing snakes (Macrostomata), like Pachyrhachis, have a lineage through Adriosaurus and Ardeosaurus (Fig. 1) according to the large reptile tree.
Wiki reports, “Based on comparative anatomy, there is consensus that snakes descended from lizards.”
Wiki also reports, “The origin of snakes remains an unresolved issue. There are two main hypotheses competing for acceptance. 1) Burrowing lizard hypothesis; 2) Aquatic mosasaur hypothesis.”
As it turns out, based on the results of the large reptile tree, both are correct.
Wiki notes that Anilius is the most primitive known snake and the large reptile tree nests it closest to Lanthanotus, a sister to the ancestor of burrowing snakes. These are not directly related to boas, cobras and king snakes.
How far back can we trace the origin of snakes?
With the large reptile tree we can trace the origin of snakes back to Ichthyostega, but here (Fig. 1) we go back to the most primitive known reptile, Cephalerpeton. Because snakes are at one end of the lepidosaurormorph branch to get to snakes you pass through the basal taxa of all the other lepidosauromorphs, including diadectids, caseids, pareiasaurids, chelonians, gliding lepidosauriforms, lepidosaurs, tritosaurs (including pterosaurs and drepanosaurs) and squamates (including squamates). So, what we have are a series of mostly small lizardy forms (Fig. 1) that ultimately gave rise to a wide variety of derived forms. Several lizardy squamates lost their limbs. Snakes are just the most successful version of these.
What is Najash?
Described as a terrestrial Cretaceous protosnake with legs, Najash (Apesteguía and Zaher 2006) appears to share more pelvic traits with Heloderma than Adriosaurus, confirming our tree topology separating burrowers from the others, including swimmers.
All it takes is another study with a similar gamut to confirm the diphyletic origin of living snakes.
Apesteguía S and Zaher H 2006. A Cretaceous terrestrial snake with robust hindlimbs and a sacrum. Nature 440: 1037-1040.