Lucasuchus
Encyclopedia
Lucasuchus is an extinct genus
of aetosaur
. Fossil
s 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 Longosuchus, 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of aetosaur
Aetosaur
Aetosaurs are an extinct order of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scutes. All aetosaurs belong to the family Stagonolepididae...
. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found from the Bull Canyon Formation of the Dockum Group
Dockum Group
The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much...
outcropping in the Revuelto Creek locality in Quay County, New Mexico
Quay County, New Mexico
-2010:Whereas according to the 2010 U.S. Census Bureau:*86.1% White*1.1% Black*1.2% Native American*1.0% Asian*0.0% Native Hawaiian or Pacific Islander*3.4% Two or more races*7.2% Other races*42.4% Hispanic or Latino -2000:...
. All specimens date back to the Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...
stage of the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
. The genus was named in 1995 after the American paleontologist Spencer G. Lucas
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, stratigraphy, and continental deposits,...
.
Lucasuchus was first proposed to be a junior subjective synonym
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
of Longosuchus
Longosuchus
Longosuchus is an extinct genus of aetosaur from the Late Triassic of North America. It measured about 3 metre in length....
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
Desmatosuchus is an extinct genus of archosaur belonging to the Order Aetosauria. It was one of the largest aetosaurs, being long and about 1.50 m high. It lived during the Late Triassic in Texas....
and Acaenasuchus
Acaenasuchus
Acaenasuchus is an extinct member of the order Aetosauria, endemic to what would be North America during the Triassic, existing for approximately .It was a heavily armored aetosaur with thorn-like spikes on its back....
than to Longosuchus. The presence of elongate lateral osteoderm
Osteoderm
Osteoderms are bony deposits forming scales, plates or other structures in the dermal layers of the skin. Osteoderms are found in many groups of extant and extinct reptiles, including lizards, various groups of dinosaurs , crocodilians, phytosaurs, aetosaurs, placodonts, and hupehsuchians...
horns is shared by all of these genera, which make up the subfamily Desmatosuchinae
Desmatosuchinae
Desmatosuchinae is one of the two subfamilies of aetosaurs, the other being Aetosaurinae. It is a stem-based taxon defined as all aetosaurs more closely related to Desmatosuchus than the last common ancestor of Desmatosuchus and Stagonolepis. All synapomorphies that diagnose the clade can be found...
.
It has been suggested that Lucasuchus is either a sexual dimorph
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
belonging to the same species as Longosuchus meadei or an ontogenetic
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
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 Longosuchus, 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.