Quinkana is an extinct genus of mekosuchine crocodylians that lived in Australia from about 25 million to about 20,000 years ago, with the majority of fossils having been found in Queensland. Four species are currently recognized, all of which have been named between 1981 and 1997. The two best understood species are Q. fortirostrum, the type species, and Q. timara, a more gracile form from the Miocene. The other two species, Q. babarra and Q. meboldi, from the Pliocene and Oligocene respectively, are only known from a few poorly preserved bone fragments. The name Quinkana comes from the "Quinkans", a legendary folk spirit from Gugu-Yalanji mythology.
Quinkana is primarily known for its ziphodont teeth, meaning they were recurved, serrated and possessed flattened sides that gave them a blade-like shape. However, technically such teeth are only known from two species, as the basal-most form lacked serrations while the holotype of Quinkana fortirostrum did not preserve teeth in its alveoli. The genus is distinguishable by the combination of these ziphodont teeth and a deep, altirostral skull that is sometimes compared to those of sebecosuchians and planocraniids, leading some early researchers to mistakenly assign Quinkana to said groups. Quinkana is typically estimated to be around in length and to weigh around , though some remains from the Pliocene could suggest an even greater size. However, these estimates are based on fragmentary specimens and dimensions of related genera as there have been no complete Quinkana specimens found.
The genus has been argued amongst paleontologists to be either terrestrial or semi-aquatic, with both sides providing a variety of arguments. Academic analysis cites comparative morphologies as indicators of Quinkana's habitation to be terrestrial, commonly comparing the anatomy of the crocodilian to other, more definitively terrestrial crocodylomorphs from the Mesozoic and early Cenozoic. The discovery of pelvic bones that belonged to a crocodilian with a pillar-erect stance in the same strata as Quinkana also support this line of thinking, even though no clear overlap to confirm this hypothesis exists. While the majority of mekosuchine researchers support the idea that Quinkana was terrestrial, some counter arguments have been raised in the past, especially highlighting that Quinkana is still consistently found to have lived near freshwater. The role Quinkana filled in the ecosystems of Late Pleistocene Australia has also been a matter of debate, with older literature in particular often claiming that the continent was dominated by reptilian predators. Opponents of this hypothesis meanwhile highlight how Quinkana was relatively rare, whereas large marsupial predators like Thylacoleo were much more common.
Regardless of its lifestyle and behavior, Quinkana is predominantly found in sediments preserving various types of woodland in proximity to bodies of water such as ponds, streams and billabongs. Though successfully surviving a drastic arid period that marked the transition from the Late Miocene to the Early Pliocene, Quinkana would eventually die out towards the end of the Pleistocene, with estimates suggesting that it died out somewhere between 40,000 and 20,000 years ago. The precise reasons for Quinkanas disappearance are unknown, but it is hypothesized that another period of intense aridification gradually dried up the river basins and destroyed the forests that the crocodilian inhabited, leading it to go extinct alongside much of Australia's megafauna.
History and naming 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 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 tooth sockets 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.
Subsequent years saw a noticeable improvement in the scientific understanding of Australasian fossil crocodilians, with various species being described and finally being placed in the subfamily Mekosuchinae in 1993. Shortly after this, in 1994, Quinkana timara was named by paleontologist Dirk Megirian as a second species within the genus, although the timing of events meant that he could not properly address the newly erected Mekosuchinae in the main text of his publication. The holotype of Q. timara (NTM P895-19) consists of various snout fragments discovered within limestone found in the Bullock Creek Locality in the Northern Territory. In the same paper, Megirian also attributes multiple other fossils from the same site to this species.
Only two years later a third species of Quinkana, Quinkana babarra, was described, this time by Brian Mackness and Paul M.A. Willis. The holotype (QM F23220), a fragment of the maxilla, was uncovered in 1991 by Mackness at the Dick's Mother Lode Quarry in the Charters Towers Region of northeast Queensland, a locality that would have been intermediate in time between those of the two previously named taxa. However, Quinkana babarra proved to be much more fragmentary than either of the two established species. Partly for this reason, the diagnosis that had been established by previous works for Quinkana was altered the most significantly by Willis and Mackness, removing features such as the prominent knobs before the eyes as they are not preserved in their taxon. The final species to be named was Quinkana meboldi, discovered the same year as Quinkana babarra by Willis. It was described only a year later in 1997 on the basis of multiple maxillary fragments and a partial dentary alongside multiple other mekosuchines from the White Hunter Site of the Riversleigh World Heritage Area, namely Baru wickeni, "Baru" huberi and Mekosuchus whitehunterensis.
After these early descriptions, things became relatively quiet in terms of fossil material, with far fewer notable discoveries being made. During this period the ecology and habits of Quinkana gained more attention, with repeated debate on its role in Australia's prehistoric ecosystems and whether or not it was terrestrial. Among the more notable later finds was the discovery of a ziphodont tooth in the Late Pleistocene King Creek catchment of the eastern Darling Downs, an otherwise well sampled locality known for its abundant material of Megalania. This marked the first Late Pleistocene Quinkana material of the region since the teeth mentioned by Molnar in 1981.
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. However, it has been noted that though the Quinkans serve as inspiration for the name, no rock art from Australia is actually inferred to depict any mekosuchines, but usually inferred to show the two modern Australian crocodile species.