The Procolophonidae are a group of small parareptiles (sensu Laurin and Reisz 1995) with a widespread distribution in the Triassic whose remains have been found on every continent. Erected by Owen (1876), Procolophon, from the Lower Triassic of South Africa (Watson 1914; Broili and Schröder 1936) and Antarctica (Colbert and Kitching 1975), is the best-known taxon and its skull has been described in detail (Kemp 1974; Carroll and Lindsay 1985). The first member of the clade to be named was Leptopleuron from the Upper Triassic Lossiemouth Sandstone (Owen 1851) but at the time its affinities were poorly understood. Preserved as natural molds in the Lossiemouth Sandstone, the material has proved difficult to work with and as a consequence details of the skeletal structure have remained somewhat obscure. Recently, Spencer, working with latex casts taken from the original molds, has begun to elucidate some of the details of the skull, in particular the braincase (Spencer 2000). Whereas a number of different taxa have been described from the Triassic of Russia, most of them have been based solely on jaw elements, with only the skull of Tichvinskia (Ivakhnenko 1973) being described in any detail.
Hypsognathus from the Newark Supergroup of eastern North America was first described by Gilmore (1928). This characteristic procolophonid, closely related to Leptopleuron, is now known from several localities and has been described in some detail (Colbert 1946; Sues et al. 2000). In recent years, additional procolophonid taxa have been described from the Newark Supergroup (Baird 1986; Sues and Olsen 1993; Sues and Baird 1998), including the leptopleuronine Scoloparia, that is represented by two partial skulls and other isolated elements. Isolated jaw material has also been recognized within the Triassic fissure assemblages of southwest Britain (Fraser 1986; Walkden and Fraser 1993), and although more complete specimens are known, this taxon has yet to be fully described (Walkden and Fraser 1993). Together this material appears to comprise at least three separate taxa.
Here we describe a single small procolophonid skull from the Owl Rock Member of the Chinle Formation of Utah. This specimen represents the first described associated cranial material of a procolophonid from the Chinle Formation. Sues et al. (2000) mention the occurrence of several partial skulls of procolophonids together with postcranial remains from the Owl Rock Member of Arizona that are very similar to Hypsognathus. However, these are distinct from the new specimen from Utah (H.-D. Sues, personal commun., 2003). Libognathus sheddi (Small 1997) is a procolophonid taxon from the Upper Triassic Dockum Group of Texas. Unfortunately, because it is based exclusively on lower jaw material, Libognathus cannot be compared to the present specimen. Originally described as a species of Trilophosaurus by Murry (1987), Chinleogomphius jacobsi was moved to the Procolophonidae by Sues and Olsen (1993) based on similarities in the dentition. This taxon is known from the Placerias Quarry in Arizona, in the lower part of the Chinle Formation. The maxillary teeth are known, but differ greatly from the Utah specimen described here. Heckert (2004) described isolated fragmentary procolophonid material from Arizona and New Mexico that is not comparable with the present specimen.
This specimen was prepared by the late Will Downs and is deposited in the collections of the Museum of Northern Arizona, Flagstaff, Arizona (MNA).