''Lucasuchus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

aetosaur Aetosaurs () are heavily armored reptiles belonging to the extinct order Aetosauria (; from Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs ...

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s have been found from the

Bull Canyon Formation The Cooper Canyon Formation is a geological formation of Norian age in Texas and New Mexico.Weishampel, David B; et al. (2004).Dinosaur distribution (Late Triassic, North America)" In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (ed ...

of the

Dockum Group The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Color ...

outcropping in the Revuelto Creek locality in

Quay County, New Mexico Quay County () is a county in the state of New Mexico. As of the 2010 census, the population was 9,041. Its county seat is Tucumcari. The county was named for Pennsylvania senator Matthew Quay, who supported statehood for New Mexico. Its easter ...

. All specimens date back to the

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

stage of the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

. The genus was named in 1995 after the American

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Spencer G. Lucas Spencer George Lucas is an American paleontologist and stratigrapher, and curator of paleontology at the New Mexico Museum of Natural History and Science. His main areas of study are late Paleozoic, Mesozoic and early Cenozoic vertebrate fossils ...

. ''Lucasuchus'' was first proposed to be a

junior subjective synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linn ...

of ''

Longosuchus ''Longosuchus'' (meaning "Long's crocodile") is an extinct genus of aetosaur from the Late Triassic of North America and Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of Nort ...

'' 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 ''Desmatosuchus'' (, from Greek δεσμός ''desmos'' 'link' + σοῦχος ''soûkhos'' 'crocodile') is an extinct genus of archosaur belonging to the Order Aetosauria. It lived during the Late Triassic. Description ''Desmatosuchus'' was a ...

'' and ''

Acaenasuchus ''Acaenasuchus'' (meaning "thorn crocodile") is an extinct genus of pseudosuchians, endemic to what would be Arizona during the Late Triassic, existing for approximately . Discovery and naming The holotype, UCMP 139576 (a left(?) dorsal paramedi ...

'' than to ''Longosuchus''. The presence of elongate lateral

osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amp ...

horns is shared by all of these genera, which make up the

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

Desmatosuchinae Desmatosuchinae is a major subfamily of aetosaurs within the clade Desmatosuchia. It is a stem-based taxon defined as all aetosaurs more closely related to ''Desmatosuchus'' than to ''Stagonolepis,'' ''Aetosaurus'', or '' Paratypothorax''. Th ...

.Sereno, P. C. (2005)
Desmatosuchinae
. Stem Archosauria ''TaxonSearch ersion 1.0, 2005 November 7'. Retrieved on 2009-07-18. It has been suggested that ''Lucasuchus'' is either a sexual dimorph belonging to the same species as ''Longosuchus meadei'' or an

ontogenetic Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the st ...

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

{{Taxonbar, from=Q4162514 Aetosaurs of North America Triassic reptiles of North America Fossil taxa described in 1995 Prehistoric pseudosuchian genera