Vancleavea is a genus of extinct, armoured, non-archosaurian archosauriforms from the Late Triassic of western North America.

Vancleavea individuals had short snouts with large, fang-like teeth, and long bodies with small limbs.

Phylogenetic analyses by professional paleontologists have shown that Vancleavea was an archosauriform, part of the lineage of reptiles that would lead to archosaurs such as dinosaurs and crocodilians.

Vancleavea lacks certain traits which are present in most other archosauriforms, most notably the antorbital, mandibular and supratemporal fenestrae, which are weight-saving holes in the skulls of other taxa.

However, other features clearly support its archosauriform identity, including a lack of intercentra, the presence of osteoderms, an ossified laterosphenoid, and several adaptations of the femur and ankle bones.

GR 138 is particularly notable due to being a nearly complete and articulated skeleton preserving a variety of osteoderms in the positions they would have been in during life.

[9] Imbricating osteoderms cover the entire body, the limbs are relatively short, and the skull is highly ossified.

A distinguishing feature of Vancleavea is the lack of an antorbital fenestra, a hole in front of the eyes which is typical for archosauriforms.

At the level of the eyes, the nasals are divided by another feature unique to Vancleavea: a single narrow bone likely acquired by a neomorphic mutation.

[2] Similar to proterochampsians and a few types of archosaurs (crocodylomorphs, dinosaurs, and shuvosaurids), Vancleavea does not possess a postfrontal, a small wedge-like bone which sometimes occupies the rear upper corner of the orbit.

The quadrate bone, which forms the cranium's contribution to the jaw joint, is located inwards from the squamosal's ventral process.

In most archosauriforms, the exoccipitals form the upper surface of the occipital condyle, but Vancleavea is unique in lacking this contact.

It is plausible that it was lost through evolution (as is the case with the antorbital and supratemporal fenestrae), but there is also the possibility that it was too small to be noticeable in the preserved Vancleavea skull.

Some dorsals of Vancleavea are also characteristic in the possession of a shallow groove which extends down the underside of each centrum, bordered by a pair of keels.

Rather than possessing the pinched sides of dorsals, they instead have massive facets for sacral ribs which connect the spinal column to the hip bones.

[4] They possess tall and thin neural spines as well as chevrons, similar structures which extend from the underside of the centra.

[2] The humerus (upper arm bone) is rather simple, with a rounded head that forms the "ball" part of a ball-and-socket joint with the glenoid socket.

[4] The ulna and radius (lower arm bones) are also rather simple, although certain features (such as convex outermost joints) are shared with other archosauriforms.

However, the ilium of Vancleavea is short in this direction, instead slanting upwards and slightly backwards to form a leaf-shaped blade on top of a pinched "neck".

This branch contacts the ischium along a straight edge, although part of their connection is left open as a notch which partially or completely enclosed the obturator foramen.

This ridge, which is not present in every femur referred to Vancleavea, is believed to be an area for the attachment of the powerful caudofemoralis muscle which helps to pull the leg back.

Although this spur (formally known as a calcaneal tuber) is common in many archosauriforms, that of Vancleavea is unique in having a 'squashed' shape, with the upper/front and lower/rear surfaces meeting each other at a rounded outer apex.

Similar to advanced archosauriforms, Vancleavea only possessed two distal tarsal bones in the ankle (apart from the calcaneum and astragalus), rather than four as in more basal members of the group.

Hunt, Lucas, & Spielmann (2005) were the first paleontologists to use morphotypes to describe Vancleavea osteoderms,[6] but their designations differed from those in later studies such as Nesbitt et al. (2009), which are used here.

The throat region, between the shoulder and jaws, possesses "morphotype A" osteoderms, which are teardrop-shaped and sometimes keeled, with a pointed front tip and rounded rear edge.

They all tightly overlap and possess front spurs and low keels, but the osteoderms that form several rows on the back are more symmetrical and diamond-shaped.

[2] Mesosuchus Proterosuchus Erythrosuchus Euparkeria Chanaresuchus Leptosuchus Postosuchus Desmatosuchus Vancleavea Doswellia Turfanosuchus Megalancosaurus Prolacerta Before the genus was described 1995, an additional specimen consisting of fragmentary skull material found by Charles Camp in 1923 was suggested to belong to a proterochampsid.

[1] A 2008 phylogenetic study tentatively suggested that Vancleavea was a basal archosauriform more derived than Erythrosuchus, Proterosuchus, and possibly even Euparkeria.

[2] Claims of a close relation between Vancleavea and thalattosaurs have been thoroughly debunked by paleontologists such as David Marjanovic and Jaime Headden.

Vancleavea is unique among archosauriforms and tetrapods in general in that the fin-like tail is deepened by elongated osteoderms rather than tall neural spines.