Koolasuchus

Credit: Tim Bertelink on the Wikimedia Commons.

*Koolasuchus* is an extinct genus of Brachyopoid Temnospondyl that lived in Australia during the Early Cretaceous.

## History

The first temnospondyls from the Strzelecki Group was NMV-PI56988, a posterior mandibular fragment, collected in ~1980. This was first mentioned by Anne Warren and R. Jupp (1986) in a publication, but did not give a concrete identification since it was Cretaceous-aged, which is much younger than any temnospondyl known at this time. In 1991, NMV-PI86040, an intercentrum, and NMV-PI86101, an isolated skull roof (a frontal, supratemporal or parietal) were reported, The intercentrum confirmed that temnospondyls were present in this time and place, with the morphology of the skull roof leading authors to believe it was a plagiosaurid or brachypoidean. This is now seen as incorrect.

*Koolasuchus*, named in 1997 from the Aptian-aged Strzelecki Group, Wonthaggi Formation, Victoria, is known from 4 mandibular fragments and several postcrania (including ribs, vertebrae, a fibula, and a partial pectoral girdle). A mandible was found in 1978 in the Punch Bowl foossil site, near San Remo. Later specimens were recovered in 1989, on the nearby Rowell's Beach site. A partial cranium is also known, but has not been fully prepared yet. It was named after Lesley Kool, but also being a pun on the word English word "cool", referencing the cold climate of its paleoenvironment. The type is *K. cleelandi* - named after Mike Cleeland. In 2022, it was made the state fossil of Victoria after 11,650 were cast.

## Description

*Koolasuchus* was an aquatic temnospondyl, being ~4-5 meters (13‐16 feet) long and up to 500 kilograms (1,100 pounds) in mass. Although erected from incomplete material, the skull was likely 65 centimeters (26 inches) long. Like other Chigutisaurids, *Koolasuchus* had a wide and rounded head and tabular horns that projected from the posterior of the skull.

*Koolasuchus* is differentiated from related temnospondyls, not including *Siderops* and *Hadrokkosaurus*, by including the mandibular ramus' "articular is excluded from the dorsal surface of the postglenoid area by a suture between the surangular and the prearticular", being differentiated from the latter two by a lack of coronoid teeth.

## Paleoecology

   *Koolasuchus* lived in rift valleys in southern Australia during the Early Cretaceous. During this time, this area was below the Antarctic Circle, and temperatures were cool for the Mesozoic, meaning *Koolasuchus* lived in a very cool environment. Based on the coarse-grained rocks where material was extracted, *Koolasuchus* likely inhabited fast-moving streams, possibly having a similar in lifestyle to crocodilians. Although eusuchians and related were common during the Early Cretaceous, they did not occur in southern Australia about 120 million years ago, possibly due to the climate. By 110 million years ago, known from rocks of the Dinosaur Cove site, the temperature had warmed, with crocodilians returning to the area. These crocodilians probably displaced *Koolasuchus*; leading to its exclusion in younger rocks and probable extinction.

## References

* https://en.wikipedia.org/wiki/Koolasuchus
* https://museumsvictoria.com.au/article/victorias-new-state-fossil-emblem-koolasuchus-cleelandi/