''Aetosauroides'' (meaning "'' Aetosaurus''-like") is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

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 ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

. It is one of four aetosaurs known from South America, the others being '' Neoaetosauroides'', '' Chilenosuchus'' and '' Aetobarbakinoides''. Three species have been named: 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( ...

''A. scagliai'', ''A. subsulcatus'' and ''A. inhamandensis''. Fossils have been found in the Cancha de Bochas Member of the Ischigualasto Formation in the

Ischigualasto-Villa Unión Basin The Ischigualasto-Villa Unión Basin ( es, Cuenca de Ischigualasto-Villa Unión) is a small sedimentary basin located in the Argentine Northwest, Argentina. It is located in the southwestern part of La Rioja Province and the northeastern part o ...

in northwestern Argentina and the

Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age ( Late Triassic), and is notable for its fossils of cynodonts, " rauisuchian" pseudosuchians, and early dinosaurs an ...

in the

Paraná Basin The Paraná Basin ( pt, Bacia do Paraná, es, Cuenca del Paraná) is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande ...

in southeastern Brazil. The strata date to the late

Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followe ...

and early

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 ...

stages, making ''Aetosauroides'' one of the oldest aetosaurs.

Description

Most individuals of ''Aetosauroides'' measured around in length, with one large individual reaching (with

histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vi ...

suggesting an age of 23 years).

Sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definit ...

was probably reached at in length, although these individuals were not yet fully grown.

Sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

has been suggested for ''Aetosauroides'', with males reaching the size range. ''Aetosauroides'' was proposed to be synonymous with the genus '' Stagonolepis'' in 1996 and 2002. Smaller specimens of both species were placed with ''Stagonolepis robertsoni'', and larger specimens were considered to be ''S. wellesi''. This synonymy is not accepted, with several studies identifying unique features that distinguish ''Aetosauroides'' from ''Stagonolepis''. Among these are

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The ...

e that do not touch the nostrils, oval-shaped holes on the centra of the

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characterist ...

e, and a convex margin of the lower jaw. In a 2011 study, ''A. subsulcatus'' and ''A. inhamandensis'' were proposed to be synonymous with ''A. scagliai''. Additionally, a contemporary aetosaur named from a juvenile specimen in 2014, '' Polesinesuchus aurelioi'', was found to be similar in its vertebrae and the basioccipital of its braincase to juvenile specimens of ''Aetosauroides'' in two 2021 studies, and it was proposed as a junior synonym of the latter.

Classification

phylogenetic 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 ...

analysis presented by Julia B. Desojo, Martin D. Ezcurra and Edio E. Kischlat in 2012 found that ''Aetosauroides'' lies outside Stagonolepididae. If this phylogeny is correct, Stagonolepididae and Aetosauria would not be equivalent groupings, and ''Aetosauroides'' would be the first non-stagonolepidid aetosaur.

References

{{Taxonbar, from=Q4688774 Aetosaurs Prehistoric pseudosuchian genera Carnian genera Norian genera Late Triassic reptiles of South America Triassic Argentina Fossils of Argentina Ischigualasto Formation Triassic Brazil Fossils of Brazil Santa Maria Formation Fossil taxa described in 1960