Lucasuchus
Introduction '''''Lucasuchus''''' is an extinct genus of aetosaur. Fossils have been found from the Bull Canyon Formation of the Dockum Group outcropping in the Revuelto Creek locality in Quay County, New Mexico. All specimens date back to the Norian stage of the Late Triassic. The genus was named in 1995 after the American paleontologist Spencer G. Lucas. ''Lucasuchus'' was first proposed to be a junior subjective synonym of ''Longosuchus'' in 1999, and several other studies have also considered it to be an invalid genus. However, more recent studies concluded that ''Lucasuchus'' is not congeneric with any other known aetosaur genus, and is likely to be more closely related to ''Desmatosuchus'' and ''Acaenasuchus'' than to ''Longosuchus''. The presence of elongate lateral osteoderm horns is shared by all of these genera, which make up the subfamily Desmatosuchinae.It has been suggested that ''Lucasuchus'' is either a sexual dimorph belonging to the same species as ''Longosuchus meadei'' or an ontogenetic stage of the species (meaning that it represents one particular age group). However, several characteristics of ''Lucasuchus'' may indicate that it is indeed distinct from ''L. meadei'' rather than an example of morphological variation. For example, ''Lucasuchus'' has a clear radial pattern of pits and grooves on the paramedian osteoderms of the back while ''Longosuchus'' has only a random pattern of pits on the paramedians. In ''Lucasuchus'', the paramedians have large conical eminences, or projections, while in ''Longosuchus'' these projections are only present in the form of low pyramidal bosses. ''Lucasuchus'' also lacks the emarginations (or notches) on the spikes of the lateral osteoderms that are seen in ''Longosuchus''.
References