Typothoracinae is a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

of aetosaurs within 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 subfamily botanical names with "-oideae", and zoologi ...

Aetosaurinae. It was originally defined as a stem-based taxon including all aetosaurs closer 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 ...

'' than to '' Stagonolepis'' or '' Desmatosuchus''. This definition was later expanded to specifically exclude '' Aetosaurus''; as of 2016, Typothoracinae is defined as the least inclusive clade containing ''Typothorax'' and ''

Paratypothorax ''Paratypothorax'' is an extinct genus of aetosaur, known from a single species, ''Paratypothorax andressorum''. It was a broadly distributed member of the group found in Germany, North America, and possibly parts of Gondwana. The best specimen ...

'', but not ''Aetosaurus,'' ''Stagonolepis'', or ''Desmatosuchus''. The clade was first named in 2007 under the spelling Typothoracisinae, after its namesake ''Typothorax''. However, this spelling was based on incorrect taxonomic nomenclature, and the clade's name was corrected to Typothoracinae in 2016. Typothoracines can be distinguished by their wide bodies. The

transverse processes 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 characteristic i ...

of the dorsal (trunk) vertebrae are reinforced and elongated, more than twice the width of the centrum. Their

neural spines 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 characteristic ...

, on the other hand, are short. The overlying

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 ...

of osteoderms has a very broad, discoidal shape, distinct from the narrower carapace seen in other aetosaurs. The widest dorsal paramedian osteoderms have a width-to-length ratio exceeding 3.5. They also tend to possess a strong keel running along their underside, as well as a sigmoid lateral edge which appears to have a "clipped" posterolateral corner. Though typothoracines lack the massive neck spines of certain desmatosuchines, their cervical (neck) lateral osteoderms do bear moderately large curved spines with a flattened cross section. The dorsal lateral osteoderms have a strongly bent shape: there is an acute angle of flexion between the dorsal (upper) flange and the lateral (outer and lower) flange, which meet along a low blade-like surface or short spine on the outer edge of the osteoderm. In the lateral osteoderms above the hip and the front part of the tail, the lateral flange is triangular and concave, leading up to a hooked eminence.

References

Aetosaurs Late Triassic first appearances Late Triassic extinctions {{triassic-animal-stub