Quinkana

As one of the first fossil crocodilians to be recognized from Australia, Quinkana has a long history. Some of the earliest fossil finds now attributed to this genus date as far back as 1886, when Charles Walter De Vis found a variety of fossil bones, including those of Quinkana, in the Darling Downs region of Queensland, which he informally dubbed Pallimnarchus pollens (now considered to be a nomen dubium). The research history of Quinkana began in earnest in 1970 with the discovery of fossil material in the Tea Tree Cave (part of the Chillagoe caves of Northern Queensland) by Lyndsey Hawkins, a member of the Sydney University Speleological Society. The fossil specimen (AMF.57844) consisted of a partial rostrum, lacking the very tip of the snout and its teeth. This rostrum was noted for its unusual form, with a much deeper snout compared to extant crocodilians and toothsockets indicative of ziphodont teeth, a combination of traits previously unknown from Australia. Preliminary comparisons were made with modern crocodylids as well as extinct groups that shared similar morphology, namely pristichampsines and sebecosuchians. 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 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. Etymology Its generic name was derived from the Quinkans, a type of spirit of the Northern Queensland aboriginal Gugu-Yalanji people. Molnar explains that part of the reason for this choice in name was that Quinkans were represented by crocodiles in at least one instance at a southeastern Cape York rock painting location. == Species ==

• Quinkana fortirostrum :The second species of Quinkana to be named, Q. timara is known from the Bullock Creek Locality near Camfield Station in Australia's Northern Territory, dating to the middle to late Miocene. :Named in 1996, this species is known from the early Pliocene Allingham Formation of Queensland, but only preserved through a fragment of the maxilla and a few isolated teeth. Q. babarra can be differentiated from Q. fortirostrum and Q. timara by likely having a wider and shorter snout. The name is derived from the Gugu-Yalanji word babarr meaning "older sister" in reference to it being older than the type species. • Quinkana meboldi :This species was found at the White Hunter Site in Riversleigh, northwestern Queensland which is a late Oligocene deposit (ca. 25 Ma), Another notable discovery is the "Floraville taxon", which according to Jorgo Ristevski and colleagues could represent a second ziphodont genus in addition to Quinkana. Given the large quantity of ziphodont crocodilians likely to be distinct from Quinkana, Ristevski and colleagues have argued that many isolated teeth traditionally referred to the Quinkana could also belong to these other forms. Another instance of possible postcranial material is noted in Stein et al. 2017, who describe pelvic material from the Golden Steph Site and Price is Right Site of the Riversleigh WHA. Though much like with the metatarsal there is no associated skull material to confirm the fossils actually belonged to Quinkana, the terrestrial adaptations suggested by the anatomy of the material would match what is commonly inferred for the genus. == Description ==

Quinkana is best distinguished from other mekosuchines by the proportions of its snout and its highly specialised dentition, both of which are oftentimes cited as evidence for a more terrestrial lifestyle. The snout of Q. fortirostrum is noticeably deep and angular, its proportions somewhat resembling much older fossil crocodylomorphs such as the planocraniids that existed during the Paleogene across the Northern Hemisphere and the sebecosuchians that were primarily found in South America from the Cretaceous to the Miocene. Molnar describes the skull of Q. fortirostrum as being broader than that of members of the aforementioned groups, yet also distinctly deeper (higher) than those of any modern crocodilians with a distinct trapezoid cross-section. However, information on this specimen is sparse, as it is not only fragmentary but only discussed in a singular abstract before being mentioned by Molnar in his 2004 book "Dragons in the Dust". ==Phylogeny==

Given that Quinkana predates most of the research done on the Mekosuchinae, early research was uncertain about its relationship to other crocodilians. The type species Q. fortirostrum was originally classified under Crocodylidae in 1981 through comparison against other Eusuchian genera Pristichampsus, Paleosuchus, and Osteolaemus and against the sebecosuchian genus Sebecus. The most similarities were found with Pristichampsus and it was determined that the genus should fall under Eusuchia, whereas similarities to Sebecus were dismissed as the result of convergently acquiring the ziphodont condition. At the same time, the snout form and ziphodont dentition clearly set apart Quinkana from most other crocodilians with the exception of members of the Pristichampsinae. Though Molnar did not definitively assign the genus to said family (which has since then been changed to Planocraniidae), he argued that future discoveries were likely to confirm his suspicion that Quinkana was related to these Paleogene animals. The Mekosuchinae classification was contrasted in the 1994 description of Q. timara, in which Dirk Megirian suggested that further research into the phylogeny of Pristichampsus and Quinkana was necessary because of the similarities in the snout when compared to other Crocodylidae. However, at the time of Megirian's writing he was unaware of the work by Molnar, Willis and Scanlon, only briefly addressing the existence of Mekosuchinae in a note added later on. Another study headed by Jorgo Ristevski, the results of which are shown on the right, found results that differed significantly, suggesting that Quinkana was in fact not related to these other terrestrial forms, but instead most closely allied to large-bodied generalists like Paludirex and Baru. Yet another alternative was recovered by Yates and colleagues in their description of Baru iylwenpeny, which positioned Quinkana between Kalthifrons and a clade composed of Mekosuchus, Paludirex and Baru. Though the position of Quinkana as a mekosuchine is generally accepted as consensus, some research has proposed an alternative placement outside of the clade. In 2021, Rio and Mannion published a paper on the phylogeny of crocodilians utilizing a new dataset based purely on morphological traits, in contrast to the work of Lee and Yates which unified various different fields for their phylogenies. While the majority of Mekosuchinae remains intact, this resulted in some taxa as being recovered much closer to today's crocodiles. In addition to Australosuchus, this also affected Quinkana, which nested closely to "Crocodylus" megarhinus just outside of the genus Crocodylus. However, these results are generally not followed by mekosuchine researchers. }} == Paleobiology ==

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 Q. 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 Q. 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 acetabulum 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 undetermined 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 undetermined 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. == References ==