''Lucasuchus'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

aetosaur Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...

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 preserve ...

s have been found from the

Bull Canyon Formation The Bull Canyon Formation is a geological Formation (geology), formation of Late Triassic (Norian) age in eastern New Mexico and the Texas Panhandle. It is one of several formations encompassed by the Dockum Group. The Bull Canyon Formation prese ...

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 2020 U.S. census, the population was 8,746. Its county seat is Tucumcari. The county was named for Pennsylvania senator Matthew Quay, who supported statehood for New Mexico. Its ...

. All specimens date back to the

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

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 a ...

. The genus was named in 1995 after the American

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

Spencer G. Lucas. ''Lucasuchus'' was first proposed to be a

junior subjective synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...

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 ''Desmatosuchus'' (, from Greek language, 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 ''Desma ...

'' and '' Acaenasuchus'' 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 amph ...

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 botanical subfamily names with "-oideae", and zo ...

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''. The ...

.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 stu ...

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