Turtles are closer kin to birds and crocodiles than to lizards
Genetic studies keep reaching the same surprising verdict: a turtle's nearest living relatives are birds and crocodilians, not lizards and snakes. Biologists named that grouping Archelosauria in 2015. Skeletons, however, told a different story for decades, and only recently have anatomical studies started to agree with the DNA.
The clade unites turtles with archosaurs, the lineage that survives today as birds and crocodilians, and leaves out the lepidosaurs: lizards, snakes and the tuatara. Most analyses built on DNA and protein sequences back this arrangement. One striking signal sits in the genome itself, where about 1000 ultra-conserved elements are shared by turtles and archosaurs yet missing from lepidosaurs, and other genome-wide studies point the same way.
Crawford and colleagues coined the name in a 2015 paper, fusing archosaurs with chelonians, the formal word for turtles. They pinned the definition to two species, covering everything descended from the latest common ancestor of the Nile crocodile and the Greek tortoise. In 2021 Joyce and co-authors revised the wording so that a lizard, Lacerta agilis, is explicitly shut out.
Bones had long pointed elsewhere. Anatomical studies variously put turtles among the parareptiles, an early reptile group whose span ran from the Carboniferous into the Triassic, among early diapsids outside Sauria, or beside the lepidosaurs in a proposed group called Ankylopoda. In 2022 Simoes and colleagues became the first to recover Archelosauria from anatomy alone, although not in most of their runs. They identified two shared derived features: a sagittal crest on the supraoccipital bone, and the absence of an entepicondylar foramen on the humerus.
Jenkins and colleagues strengthened the anatomical case in 2026, placing the turtle lineage inside Archosauromorpha, nearer to modern archosaurs than to the early form Protorosaurus, and suggesting the turtles' ancestor looked rather protorosaur-like. The same study reassigned Eunotosaurus, a Permian reptile sometimes treated as an early turtle cousin, to the millerettids, with no close tie to turtles. A 2023 study by Wolniewicz and colleagues went further and proposed widening the clade to take in three Mesozoic marine reptile groups, but that result had only weak support.
Source: Archelosauria
