page_title: Vancleavea
section_title: Postorbital region
hierarchical_section_title: Vancleavea / Description / Skull / Postorbital region
caption_attribution_description: English: The skull of Vancleavea campi in left lateral view, based on GR 138. Bones are individually color-coded almost identically to those of https://commons.wikimedia.org/wiki/File:Dromaeosaurus_skull_en.svg by AS. The exception to this rule is that the unique neomorphic bone between the nasals of Vancleavea is colored red rather than the sclerotic ring, which is not depicted. Legend: &#160;&#160; Premaxilla &#160;&#160; Maxilla &#160;&#160; Nasal &#160;&#160; "Neomorphic bone" &#160;&#160; Prefrontal &#160;&#160; Frontal &#160;&#160; Jugal &#160;&#160; Postorbital &#160;&#160; Parietal &#160;&#160; Squamosal &#160;&#160; Quadrate &#160;&#160; Quadratojugal &#160;&#160; Surangular/articular &#160;&#160; Angular &#160;&#160; Dentary
context_page_description: Vancleavea is a genus of extinct, armoured, non-archosaurian archosauriforms from the Late Triassic of western North America. The type and only known species is V. campi, named by Robert Long & Phillip A Murry in 1995. At that time, the genus was only known from fragmentary bones including osteoderms and vertebrae. However, since then many more fossils have been found, including a pair of nearly complete skeletons discovered in 2002. These finds have shown that members of the genus were bizarre semiaquatic reptiles. Vancleavea individuals had short snouts with large, fang-like teeth, and long bodies with small limbs. They were completely covered with bony plates known as osteoderms, which came in several different varieties distributed around the body. 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.
context_section_description: The jugal (cheek bone) is complex. It has a tapering front edge that extends under the eye to contact the prefrontal, thereby excluding the maxilla from the orbit. A triangular upward projection rises up behind the eye and splits the lower part of the postorbital bone (which forms the rear edge of the eye) in half. Both the jugal and postorbital have very long rear extensions which nearly reach the back of the skull. A massive open space (about a third the length of the skull) lies in the area between these two extensions. This hole is known as a lateral temporal fenestra. Reptiles of the group Diapsida are typically characterized by having two temporal fenestrae at the back of the skull: a lower one on the side of the skull (the lateral temporal fenestra) as well as a larger one on the top of the skull (the supratemporal fenestra). Vancleavea breaks away from this standard, as its supratemporal fenestra has completely closed up during evolution, leaving only the huge lateral temporal fenestra.
  The flat and heavily sculptured skull roof is formed by the paired frontal bones above the eyes and the parietal bones above the temporal fenestra. The connection between the frontal pair and the parietal pair is W-shaped, with each parietal having a triangular forward point which penetrates each frontal. A similar connection is also present at the front edge of the frontals, where each frontal is bisected by the rear tip of each nasal bone. 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 rear edge of the skull is somewhat difficult to interpret even in well-preserved specimens such as GR 138. The upper rear corner of the temporal fenestra is formed by the squamosal bone, which connects to the back of the postorbital bone and the parietal bone, as well as the braincase. The front edge of the squamosal possesses a deep 'pocket', while the lower portion of the bone expands into a large downward-pointing 'hood'. A thin structure known as a ventral process stretches downwards, forming the rear edge of the temporal fenestra. This ventral process connects to the quadratojugal bone, which itself contacts the rear branch of the jugal and forms the rear lower corner of the temporal fenestra. The quadrate bone, which forms the cranium's contribution to the jaw joint, is located inwards from the squamosal's ventral process. The quadrate not only contacts the lower jaw, but also connects to the inner face of the quadratojugal and is overlapped by the 'hood' of the squamosal. The appearance of the quadrate is yet another unique aspect of Vancleavea. In most basal archosauriforms, the quadrate is tall and straight, but in Vancleavea it is short, stout, and arched forwards.
caption: A color-coded diagram of the skull
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