Quinkana

Extinct genus of reptiles
Automatic taxobox
| fossil range = Late Oligocene Late Pleistocene,

Additional discoveries were made in the years following this event, with a second ziphodont crocodilian being recovered from the Texas Caves in southern Queensland in 1975 by Michael Archer. The Texas Cave crocodile, as it was referred to in later publications, consisted of a partial maxilla with some additional bone fragments that would be described in 1977 by Max Hecht and Michael Archer. Several further discoveries followed, many of which were eventually listed and briefly discussed once Quinkana was described. These early finds include not just the Texas Cave crocodile but also the Croydon specimens, the Rosella Plains teeth (originally identified as Megalania), the Darling Downs teeth and the Chinchilla jugal (named so after the town of Chinchilla, Queensland). Generally, these remains were isolated elements dating to the Pliocene and Pleistocene. Some remains have even been found near Lake Palankarinna in South Australia, though like the Texas Cave material they too were originally considered to have belonged to a sebecosuchian. These discoveries caught the attention of paleontologist Ralph Molnar, who described Quinkana as a genus in 1981 based primarily on the rostrum from the Chillagoe caves, though he also dealt with much of the more fragmentary material including the Chinchilla jugal and teeth from the Darling Downs region. Molnar also assigned the Texas Cave crocodile to the genus, but was hesitant to make an identification on a species level given some slight differences that may or may not be the result of ontogeny. The same is the case with most of the other material examined in this work, though the similarities to Quinkana were clear, the material was generally too fragmentary to be assigned to Quinkana fortirostrum specifically. In this early work, Molnar sets up several discussions regarding this taxon that would receive a lot of focus later on, in particular its relationship to other crocodilians and its ecology. Based on its unique cranial anatomy, Molnar cautiously proposed that that Quinkana could have been a terrestrial predator, though he himself acknowledged several counterarguments to this hypothesis. Based on the same information, he also tentatively suggested a relationship between Quinkana and the European Pristichampsus.

The ecology and lifestyle of Quinkana has long been a matter of debate as far back as the type description by Molnar, who lists several points in favour of terrestrial habits while also highlighting potential counterarguments. For instance, the discovery of the holotype of Quinkana fortirostrum in cave deposits is assumed by him to be a strong indicator that the animal traveled over land before falling to its death, but at the same time Molnar highlights that even modern crocodilians will occasionally travel distances over land. Likewise the depositional environment does not give any clear evidence for terrestrial habits either. Many of the localities that yielded Quinkana remains show a mix of terrestrial and semi aquatic fauna, as is the case for the deposits that yielded the fossil remains of unambiguously terrestrial crocodylomorphs elsewhere in the world. Another study dealing with the postcranial anatomy of mekosuchines was published by Stein and colleagues in 2017, specifically examining the shoulder girdle and hips of these animals based on fossils found across Australia. Among these fossils were various elements discovered in regions that also yielded remains of Quinkana, specifically the Riversleigh WHA. Four morphotypes are identified by the team, with "pelvic form four" having possibly belonged to Quinkana meboldi due to the highly derived state of the ilium and ischium, which differ greatly from "pelvic form one" (associated with Kambara) and "pelvic form three" (associated with Baru darrowi). "Pelvic form four" shows several aspects that are convergent with the hip of sebecosuchians and thus could have supported a pillar erect stance while limiting a sprawling gait. Stein and colleagues note that this derived state, primarily achieved by the more enclosed accetabulum and expanded iliac crest, would match the cursorial habits and terrestrial lifestyle often inferred based on the cranial material. However, until more material showing a clear relation between this pelvic form and Quinkana skull material is found, it cannot be ruled out that the hip fossils belonged to a different mekosuchine. One suggestion made by Molnar is that Quinkana, together with Megalania, could have been one of the dominant terrestrial predators of Pleistocene Australia, given the relative lack of large mammalian land predators compared to other continents. However, not all of Wroe's counterarguments hold up. Crocodilian specialist Christopher Brochu for example maintains that the hooves of planocraniids were an anatomical feature rather than the result of taphonomy, with members of said group still being considered to have been largely terrestrial. Naturally Wroe's writings also do not account for later discoveries regarding the pelvic adaptations of mekosuchines. Both of these crocodilians may have preferred different habitats from one another and Quinkana, with Baru frequenting shallower waters and Harpacochampsa possibly living in slow moving waters like ponds and billabongs. While many of the prey animals at Bullock Creek do show signs of having been attacked by crocodilians, the more flattened punctures that would have been left by Quinkana'''s ziphodont teeth are noted to be much rarer than those of Baru. During the Pliocene an indetermined species of Quinkana coexisted with Kalthifrons in the Lake Eyre Basin, specifically the Mampuwordu Sands. Q. babarra appeared in the Bluff Downs Local Fauna alongside an indetermined species of Crocodylus and a mekosuchine possibly referrable to Paludirex, while non crocodilian predators include the marsupial Thylacoleo, giant snakes and large monitor lizards. Even more recent rock layers of the late Pliocene to middle Pleistocene saw Quinkana coexist with the gharial Gunggamarandu, both Paludirex vincenti and Paludirex gracilis, a possible third Paludirex species and an indeterminate species of Crocodylus. According to Rio and Mannion (2021) Quinkana finally died out around 10.000 years ago. The idea that Quinkana was driven to extinction by the gradual drying of Australia, destroying forest habitats and freshwater systems, is also supported by other publications on the matter. Sobbe, Price and Knezour for example describe the process of aridification as destroying the closed woodlands and vine scrublands that previously covered the landscape and leading to an expansion of open grasslands, which were oftentimes subject to prolonged periods without rain. They argue that this progress may have begun as early as the beginning of the Pleistocene, with the team noting a marked decline in Quinkana'' material in the eastern Darling Downs following the end of the Pliocene.