The type and only known species Australosuchus clarkae lived during the Late Oligocene and the Early Miocene in the Lake Eyre Basin of South Australia.

Australosuchus is among the mekosuchines with the southernmost distribution, being found exclusively at a latitude below 27°S, which is the basis for its scientific name meaning "southern crocodile".

One explanation suggests that Australosuchus was especially cold-resistant compared to contemporary forms like Baru and was thus able to inhabit freshwater systems too cold for its relatives.

This makes it only the fourth mekosuchine to have been formally described and one of the species that first lead to the recognition of an endemic Australian Cenozoic group of crocodilians.

The holotype of Australosuchus is specimen QM F16788, a partial skeleton collected in 1975 that includes a nearly complete skull and lower jaw, various vertebrae, parts of the forelimbs and the dorsal armor.

Some fossils were initially described as stemming from the Mampuwordu Sands, which has been interpreted to be Late Pliocene to Early Pleistocene in age, but this is generally deemed unlikely.

However, while in most genera this is achieved through a marked constriction in the form of the rostrum, in Australosuchus the dentary teeth slide into a semi-enclosed pit.

This renders the fourth dentary less visible when the jaws were closed, which in turn gives Australosuchus an appearance more similar to alligators than to crocodiles.

The dentition of the upper jaw is described as pseudoheterodont, the teeth feature prominent, but unserrated, cutting edges and the tooth sockets are rounded in the front of the snout before becoming more ovate further back.

The prefrontals connect directly from the lacrimal and form a W-shaped suture together with the nasals and the anterior process of the frontal bone.

The anterior process is especially long and slender in Australosuchus and extends in-between the two nasal bones, while the posterior region is robust and concave due to the raised eye sockets.

[4] Australosuchus was described during the early stages of mekosuchine research, when an endemic Australian crocodilian radiation had just been proposed and before the family was officially named.

In a 2018 study using a combination of morphological, genetic and stratigraphic data, Lee and Yates recovered Australosuchus as the earliest diverging member of the family.

In the purely morphology based analysis by Rio and Mannion (2021), Australosuchus was found outside of Mekosuchinae as the sister taxon to the Crocodylidae.

Krabisuchus siamogallicus Orientalosuchus naduongensis Jiangxisuchus nankangensis Eoalligator chunyii Dongnanosuchus hsui "Baru" huberi Volia athollandersoni Trilophosuchus rackhami Mekosuchus spp.

This renders Australosuchus relatively isolated from the diverse crocodilian fauna found in more northern parts of Australia at the time, notably that of the Riversleigh World Heritage Area which was inhabited by another semi-aquatic generalist, Baru.

Yates further highlights that plenty of freshwater systems would have been present between the two basins, theoretically allowing even semi-aquatic forms to travel between them.

Furthermore, while this is a great latitude already by modern standards, Yates additionally notes that the Oligocene represents a cold period within Australia's history, putting further emphasis on how unusual the range of Australosuchus was.