Typothoracisinae is a clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 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...

s within the subfamily Aetosaurinae

Aetosaurinae

Aetosaurinae is one of the two subfamilies of aetosaurs, the other being Desmatosuchinae. It is a stem-based taxon defined as all aetosaurs more closely related to Aetosaurus than to the last common ancestor of Aetosaurus and Desmatosuchus. The only synapomorphy that diagnoses the clade...

. It is a stem-based taxon defined as all aetosaurs closer to Typothorax

Typothorax

Typothorax is an extinct genus of 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:...

than to Stagonolepis

Stagonolepis

Stagonolepis is an extinct genus of aetosaur. It was about long.An aetosaur, Stagonolepis was a quadrupedal animal covered in thick armoured scales that ran down the length of the its body. A slow-moving browser, it would have used this heavy body armour to repel attacks from contemporary...

or 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....

. As with many aetosaur taxa, most of the synapomorphies that diagnose the clade are found in the 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...

s. These include a strongly acute angle of flexion between the dorsal and lateral flanges of the dorsal and lateral plates and triangular-shaped pelvic and anterior caudal dorsal lateral plates possessing semicircular borders and hook-like eminences.