Aetosaurinae is one of the two main clades 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 ...

s, the other being

Desmatosuchia 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, herbivoro ...

. It is a

stem-based taxon Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a '' type'', which ...

defined as all aetosaurs more closely related to ''

Aetosaurus ''Aetosaurus'' is an extinct genus of pseudosuchian reptile belonging to the order Aetosauria. It is generally considered to be the most primitive aetosaur. Three species are currently recognized: ''A. ferratus'', the type species from Germany a ...

'' than ''

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 ...

''. Aetosaurinae currently comprises ''Aetosaurus,'' similar forms such as '' Coahomasuchus'' and '' Stenomyti'', and the widespread and successful aetosaur clade Typothoracinae.

Previous usage

Aetosaurinae was originally named in 2000, as a

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 ...

solely including ''Aetosaurus'', which was assumed to be the earliest-diverging aetosaur. In 2007, it was extended to include the subfamily Typothoracinae as well as various basal aetosaurs which were not clearly within

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 c ...

. These proposed non-typothoracine aetosaurines included ''Coahomasuchus'', ''

Neoaetosauroides ''Neoaetosauroides'' is an extinct genus of primitive aetosaur. Its type and only species is ''N. engaeus''. Fossils have been found in Los Colorados Formation outcropping along the Sierra Morada River in the Ischigualasto-Villa Unión Basin in ...

'', ''

Aetosauroides ''Aetosauroides'' (meaning "''Aetosaurus''-like") is an extinct genus of aetosaur from the Late Triassic of South America. It is one of four aetosaurs known from South America, the others being ''Neoaetosauroides'', '' Chilenosuchus'' and ''Aetob ...

'', ''

Stagonolepis robertsoni ''Stagonolepis'' is an extinct genus of stagonolepidid aetosaur known from the Late Triassic (Carnian stage) Hassberge Formation of Germany, the Drawno Beds of Poland, and the Lossiemouth Sandstone of Scotland. Supposed fossils from North and So ...

,'' and ''"Stagonolepis"'' (''

Calyptosuchus ''Calyptosuchus'' (meaning "covered crocodile") is an extinct genus of aetosaur from the Late Triassic of North America. Like other aetosaurs, it was heavily armored and had a pig-like snout used to uproot plants. Description ''Calyptosuchus'' ...

'') ''wellesi''. As a subfamily containing practically all non-desmatosuchine aetosaurs, Aetosaurinae was poorly-supported. It was diagnosed by a singly

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

: the dorsal eminence of each paramedian

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 ...

was offset medially. A phylogenetic study in 2012 found that this widest usage of Aetosaurinae was

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

. ''Aetosaurus'' was recovered as the basal-most stagonolepidid, with other non-typothoracisine aetosaurines placed as successively 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 ...

taxa leading up to a clade containing Desmatosuchinae and Typothoracisinae. In this phylogeny, all aetosaurines except for ''Aetosaurus'' were more closely related to ''Desmatosuchus'' than they are to ''Aetosaurus.'' As a result, the clade Aetosaurinae would only include ''Aetosaurus''.

Current usage

More recent data and phylogenies have brought Aetosaurinae back into usage, albeit in a more restricted form. A 2016 study once again considered Typothoracinae to be closer to ''Aetosaurus'' than to desmatosuchines. Therefore, Typothoracinae would lie within Aetosaurinae, making Aetosaurinae a valid and non-

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

clade once more. Newly described or redescribed genera such as ''Stenomyti'' and ''Coahomasuchus'' have also been incorporated into Aetosaurinae. Aetosaurinae is the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

to Desmatosuchia, a new clade including desmatosuchines and their relatives, such as ''Stagonolepis''. Relative to desmatosuchians, aetosaurines have proportionally shorter and more lightly built skulls, as well as several other distinctive traits. The

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

is large and circular, while the

supratemporal fenestrae The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

are fairly small. This also means that the parietals are wider than the frontals on the skull roof, at least in early-diverging genera such as ''Aetosaurus'' and ''Stenomyti''. The nares are similar in size or smaller than the orbit. The snout tapers to a point, without the "shovel-shaped"

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

extensions found in ''Stagonolepis'' and ''

''.

References

Aetosaurs {{triassic-reptile-stub