extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
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 ...
of
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 ...
from 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 ...
of the
North Carolina
North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and So ...
, represented by the
type species
In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
''Gorgetosuchus pekinensis''. It is mainly known from
osteoderms
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 ...
, including the front half of an articulated
carapace
A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
. ''Gorgotesuchus'' is typically considered a basal desmatosuchin, though alternative interpretations exist.
Discovery
''G. pekinensis'' was named and described by Heckert ''et al.'' (2015) on the basis of ten rows of bony plates called
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 ...
s, representing the front part of an armored
carapace
A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
that would have covered the back of the animal. These plates were found embedded in
sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates) ...
Pekin Formation
The Pekin Formation is a Late Triassic (Carnian) geological formation in North Carolina. The Pekin Formation is specific to the Sanford Sub-Basin of the Deep River Basin of North Carolina, although it may be equivalent to the Stockton Formation o ...
. (The Pekin Formation consists of interbedded red
mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
s,
siltstone
Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...
s, sandstones and conglomerates; it was the fine-grained mudstones and siltstones that the mining operation was targeting for
brick-making
A brickworks, also known as a brick factory, is a factory for the manufacturing of bricks, from clay or shale. Usually a brickworks is located on a clay bedrock (the most common material from which bricks are made), often with a quarry for cl ...
, so coarser-grained blocks were removed from the pit). ''Gorgetosuchus'' was part of a diverse faunal community in a continental
rift valley
A rift valley is a linear shaped lowland between several highlands or mountain ranges created by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear dep ...
system during the Late Triassic, which also included
traversodontid
Traversodontidae is an extinct family of herbivorous cynodonts. Traversodonts were primarily Gondwanan, with many species known from Africa and South America. Recently, traversodonts have also been found from Europe and eastern North America. Tra ...
s,
phytosaur
Phytosaurs (Φυτόσαυροι in greek) are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. Phytosauria and Phytosauridae are often considered to be equivalent ...
s,
dicynodont
Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typicall ...
s, and
temnospondyl
Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...
s. ''Gorgetosuchus'' coexisted with two other aetosaurs, ''
Lucasuchus
''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 ...
''Gorgetosuchus'' is unique among aetosaurs in having cervical (neck) osteoderms that nearly wrap around the entire neck and are strongly angled to give the neck a hexagonal shape in cross-section. The lateral (side) and paramedian (upper) osteoderms each bear prominent spines. Other aetosaurs such as ''
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 ...
'' also have neck spines, but only on the lateral osteoderms. The cervical osteoderms are wider than they are long, a feature that unites ''Gorgetosuchus'' with basal "
aetosaurine
Aetosaurinae is one of the two main clades of aetosaurs, the other being Desmatosuchia. It is a stem-based taxon defined as all aetosaurs more closely related to ''Aetosaurus'' than ''Desmatosuchus''. Aetosaurinae currently comprises ''Aetosaurus ...
" aetosaurs. However, several features of the osteoderms (such as a flange on the lateral cervical osteoderms that overlaps the paramedian osteoderms) link it with the
desmatosuchine
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 ...
s, a more
derived
Derive may refer to:
* Derive (computer algebra system), a commercial system made by Texas Instruments
* ''Dérive'' (magazine), an Austrian science magazine on urbanism
*Dérive, a psychogeographical concept
See also
*
*Derivation (disambiguatio ...
group of aetosaurs.
Classification
Among aetosaurs, ''Gorgetosuchus'' closely resembles ''Lucasuchus'' and ''Longosuchus'', both of which are desmatosuchines. A
phylogenetic analysis
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
conducted by Heckert ''et al.'' (2015) placed ''Gorgetosuchus'' close to these taxa as the most basal desmatosuchine, but the results were not statistically well supported. Below is a strict consensus tree from their analysis showing the placement of ''Gorgetosuchus'':
''Gorgetosuchus'' was also placed as the basal-most member of
Desmatosuchini
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 ...
(traditional desmatosuchines) in an analysis by Parker (2016). However, an analysis by Hoffman ''et al.'' (2018), based on an earlier analysis by Schoch & Desojo (2016), placed it within Typothoracinae, closely related to ''
Typothorax
''Typothorax'' is an extinct genus of typothoracine aetosaur that lived in the Late Triassic. Its remains have been found in North America. Two species are known: ''T. coccinarum'', the type species, and ''T. antiquum''.
Description
''Typothor ...
'' and ''
Redondasuchus
''Redondasuchus'' is an extinct genus of aetosaur. It may be a junior synonym of '' Typothorax coccinarum'', another aetosaur. ''Redondasuchus'' is a member of the clade Typothoracisinae within the subfamily Aetosaurinae, and lived during the mi ...
''. Typothoracines and desmatosuchins are known to have a large degree of
homoplasy
Homoplasy, in biology and phylogenetics, is the term used to describe a Phenotypic trait, feature that has been gained or lost independently in separate lineages over the course of evolution. This is different from Homology (biology), homology, w ...
(convergent evolution) in certain osteoderm traits observed in ''Gorgetosuchus''. On the other hand, other skeletal traits strongly diverge between the two groups, so the position of ''Gorgetosuchus'' would likely stabilize if more non-osteoderm bones were discovered.