Paludirex

Early history of Pallimnarchus Although only named in 2020, Paludirex has a long and rich history thanks to its ties to the historic genus Pallimnarchus. Pallimnarchus pollens was informally described in 1886 by Charles Walter De Vis, who based the genus on skull remains and osteoderms discovered around 1860 that was mineralised by apatite. De Vis' collection lacked cohesion and not only consisted of material that belonged to different individuals, but even to different species, as one bone was later proven to have belonged to a species of Quinkana. Their exact origin is likewise not well recorded by De Vis, with the type locality of the remains being unknown beyond the fact that they stem from the Darling Downs region of Queensland. While the nomenclature used by Sill was incorrect, this would not be the only time a link between Pallimnarchus and the genus Crocodylus was made. In 1982 Australian paleontologist Ralph Molnar proposed that the "Lansdowne Snout" actually belonged to a saltwater crocodile, Revisions and second species Molnar however did not follow through on that, instead publishing a formal redescription of Pallimnarchus later that same year. Molnar tentatively accepted the validity of Pallimnarchus as a genus but recognized the highly flawed nature of De Vis' work. Given the fact that De Vis' material consisted of fragmentary remains of multiple individuals, Molnar established a lectotype, the anterior portion of a lower jaw (specimen QMF1149) that was part of De Vis' original collection. Beyond being labeled as the holotype in collections already, this immature specimen was chosen as it was significantly more complete than the other material the genus had previously been based on. However, Molnar's description was still limited in comparison, with only four other Australasian crocodilians being known at the time: the saltwater crocodile, freshwater crocodile, New Guinea crocodile and Quinkana. Paludirex Things once again fell silent around Pallimnarchus during the 2000s, with publications on this genus only appearing occasionally. This was not helped by the fact that Molnar's lectotype was lost following his initial redescription, with Jorgo Ristevski and colleagues suspecting that the material disappeared sometime during the late 90s or early 2000s. The fate and current whereabouts of the lectotype are unknown and even a thorough search of the collection of the Queensland Museum in 2004 only yielded a singular, non-diagnostic fragment of said specimen with the remainder of the mandible nowhere to be found. This means that the only source for information on the lectotype are the illustrations and photographs provided by Molnar in the 1982 paper. In 2008, "Geoff Vincent's specimen" was returned to Dot Vincent, the wife of the late Geoff Vincent, who subsequently donated it to the Chinchilla Museum. In the process one skull fragment was accidentally left behind in Brisbane, which led to different parts of the skull now having different specimen numbers. By then it had become clear that Pallimnarchus had once again entered taxonomic limbo in spite of the previous efforts by Willis and Molnar, as the attempts at redefining the genus were insufficient to differentiate it from the surge of new mekosuchines and the lectotype itself disappeared. Ristevski et al. published a third and final revision of the genus in 2020, declaring it dubious based on the fact that no distinguishing features could be found in the small piece of the lectotype that still remained. The team, which included Ralph Molnar, instead established a new name for the material previously assigned to Pallimnarchus. The result of their work was Paludirex vincenti, a taxon not based on mandibular remains as Pallimnarchus was but based on the skull fragments that compose "Geoff Vincent's specimen". While this decision finally established a well preserved holotype and provided a detailed diagnosis, it also meant that the vast quantity of material previously assigned to Pallimnarchus had to be reevaluated, with mixed results. Some specimens, notably those that preserve elements of the cranium, could confidently be assigned to the newly erected genus. A premaxilla and maxilla found near the Condamine River near Warra were attributued to Paludirex vincenti and the "Mirani Shire skull" could at least be tentatively assigned to the species. Additionally, the "Lansdowne Snout" was referred to P. vincenti three years later. Furthermore, the validity of the material previously dubbed Pallimnarchus gracilis was confirmed, creating the new combination Paludirex gracilis. However, Paludirex gracilis was now restricted to the type material, the premaxilla and the associated dentary fragment. The switch to "Geoff Vincent's specimen" as the holotype did have one big drawback, which is that the specimen has no associated mandibular remains. This means that the only lower jaw remains currently referable to Paludirex are those directly associated with the premaxilla of P. gracilis, meaning that the validity of many of the mandibles previously referred to Palimnarchus is up in the air. Although it is deemed likely that some, although not all, of these lower jaws did belong to Paludirex, they cannot be confidently assigned to the new genus until fossils are found that preserve both the upper and lower jaws in association with one another. Until such a fossil is found, these remains can only be identified as Crocodilia indet. and nothing more specific. Ristevski and his team further highlight various possible scenarios for the future of Pallimnarchus. Should the lectotype be rediscovered, there is the possibility that Paludirex may eventually become a junior synonym of Pallimnarchus. At the same time, it is just as likely that future research finds the two to be different animals altogether, as the presence of multiple broad-snouted crocodilians in the Pliocene of Australia is not only possible but very likely. However, both of these possible scenarios hinge on the lectotype being rediscovered, it preserving previously unrecognized diagnostic features and finally for there to be sufficient overlapping material of other crocodilians to compare it to. Until then, Pallimnarchus is treated as a nomen dubium and Paludirex as valid and distinct taxon. Etymology Paludirex is derived from the Latin words "paludis" and "rex", translating to "swamp king". This etymology was deliberately chosen to maintain a connection with its predecessor, as it serves as a rough equivalent to the etymology of Pallimnarchus, whose name translated to "ruler of all swamps". ==Species==

• Paludirex gracilis :The larger and more robust of the two species, P. vincenti is also the older of the two, although the age records are muddy. The type specimen is confirmed to have been collected from Pliocene strata, but the Condamine material was found in a region that preserves both Pliocene and Pleistocene fossils. The origin of the "Mirani Shire skull" is also not fully understood, but it may have come from the Pleistocene deposits near South Walker Creek. Assuming that the "Mirani Shire skull" did indeed belong to P. vincenti, the species would have ranged from Darling Downs in the south to the Nebo district in the north and existed from the Pliocene to Pleistocene. Paludirex vincenti derives its name from Geoff Vincent, who discovered the holotype skull. Although few remains have been assigned to each species respectively, there are several specimens previously referred to Pallimnarchus that may represent additional species distinct from either Paludirex gracilis or Paludirex vincenti. For example, QMF1152, one of De Vis' Pallimnarchus fossils, and QMF1154, a snout fragment from the same deposits as Paludirex vincenti. Both share some aspects with the two recognized Paludirex species while differing in others, and based on this they may represent an additional third species of Paludirex that lived during the Pliocene in Queensland. Until further research is conducted and a name is coined, the taxon is referred to as the Darling Downs taxon by Risevski and colleagues. ==Description==

Paludirex was a large-bodied mekosuchine that bears all the hallmarks of a semi-aquatic ambush predator, possessing a platyrostral (flattened) skull as well as nostrils that were directed upwards like in many modern crocodilians. On the surface, Paludirex is best distinguished from other mekosuchines not just in size but also in the proportions of its skull. In Paludirex vincenti the skull was robust and deep like in Baru, but not to the same degree as in altirostral forms like Quinkana. This applies even moreso to Paludirex gracilis, which had a much shallower snout compared to its older relative. More importantly, the skull of both species of Paludirex was proportionally very wide. This is especially prominent in Paludirex vincenti, which had a rostrum that is around half as wide as the entire skull is long. ==Phylogeny==

Although Pallimnarchus, as the earliest discovered fossil crocodilian of Australia, was crucial in establishing the presence of the "Australian tertiary radiation" (later known as Mekosuchinae), its precise position within this group remained unclear for a long time. Given the poor description of the remains assigned to Pallimnarchus and the rapid increase in research on this group, its placement shifted multiple times throughout the 90s and 2000s. In this time period, Pallimnarchus commonly claded with other generalist platyrostral members of the group, such as Australosuchus in Willis (1997), alongside Australosuchus and Kambara in Mead et al. (2002) and with Kalthifrons and Baru in Lee and Yates (2018). }} The erection of Paludirex by Ristevski et al., establishing a proper diagnosis for the genus, paved the way for thorough and more reliable phylogenetic results. The phylogenetic analysis conducted as part of this paper yielded two results. The first, which was run without implied weighting, only yielded a poorly resolved paraphyletic Mekosuchinae, leading to the team conducting a second analysis with clearer results. Under implied weighting Paludirex was found at the base of a clade that contained both Quinkana and Kalthifrons as well as Mekosuchus and Baru. ==Paleobiology==

. Paleoecology Given the uncertain state of much of the material previously assigned to Pallimnarchus, little is known for certain about the ecology and paleobiology of Paludirex. Based on the anatomy of its skull, Paludirex would have most likely been a semi-aquatic ambush predator, a lifestyle consistent with that previously suggested for Palimnarchus and seen in modern crocodilians. From these similarities it has been further interpreted that Paludirex was a generalist, capable of preying on a wide range of prey items. A similar paper was published by Mackness and colleagues ten years later, this time reporting on a pathological femur from the Pliocene Chinchilla Sands. Much like with Mackness' previous work, there is no direct evidence that this fossil actually belonged to Pallimnarchus or Paludirex. Akin to their previous study, the referral was based on clear differences with Crocodylus and a size that was deemed too large to have come from Quinkana, leaving Pallimnarchus. The femur shows signs of trauma followed by osteitis and infection, which, like the pathology of the Bluff Downs bone, was most likely the result of an attack by another crocodile. Sympatric crocodilians While mekosuchines were already on the decline in Australia by the Pliocene, Paludirex nonetheless coexisted with other crocodilians. The most famous of its contemporaries was Quinkana, an animal with serrated teeth often thought to have been terrestrial in nature. Given the likely terrestrial habits of Quinkana and the semi-aquatic habits of Paludirex, the two animals likely did not compete for the same resources, explaining how they coexisted. While Paludirex and Quinkana are thought to have led different lifestyles, the former may have still had to share its habitat. Fossil evidence from Darling Downs suggest that there was at least one other semi-aquatic crocodilian native to the region, possibly an as of yet unnamed species of Paludirex. This is based on the discovery of remains from the same Pliocene localities as P. vincenti that differed from the anatomy of either named species, having slightly different proportions and tooth arrangements. This form, at times referred to as the Darling Downs taxon, shared the robust skull of P. vincenti, but seemingly grew no larger than P. gracilis. Whether Paludirex also coexisted with saltwater crocodiles is less clear. Although there is ample material that has been historically assigned to saltwater crocodiles, recent research casts doubt over the correctness of these interpretations. Ristevski and colleagues argue that saltwater crocodiles only arrived in Australia comparatively recently, showing no confirmed overlap in their distribution with the last individuals of Paludirex. However, there are as of yet unidentified Crocodylus remains dating as far back as the Pliocene, which may have belonged to an animal that could have encountered Paludirex. Widespread aridification greatly affected the various freshwater basins that this crocodilian was native to while also affecting other freshwater megafauna. Hocknull et al. suggest that species of Crocodylus may have avoided the brunt of these events by retreating into more coastal waters, whereas the native mekosuchines may have been more dependent on freshwater. Loss of terrestrial megafauna prey may also have been a factor in the extinction of Paludirex. It has also been suggested that competition with saltwater crocodiles may have factored into its extinction. Saltwater crocodiles were probably present in Australia by 47,700-40,100 years ago, based remains found at South Walker Creek in northeast Queensland, close in time to the youngest records of Paludirex. ==References==