User:Armin Reindl/sandbox

Armin Reindl/sandbox Temporal range: Eocene - Holocene,
Restoration of the skull of Quinkana timara at the Central Australian Museum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauromorpha
Clade:	Archosauriformes
Order:	Crocodilia
Clade:	†Mekosuchinae Willis, Molnar & Scanlon, 1993
Type species
†Mekosuchus inexpectatus Balouet & Buffetaut, 1987
Genera
Australosuchus Baru Kalthifrons Kambara Mekosuchus Paludirex Quinkana Trilophosuchus Ultrastenos Volia

Mekosuchinae is an extinct clade of crocodilians from the Cenozoic of Australasia. They represented the dominant group of crocodilians in the region during most of the Cenozoic. They first appear in the fossil record in the Eocene in Australia, and survived until the arrival of humans: in the Late Pleistocene in Australia and within the Holocene in the Pacific islands of Fiji, New Caledonia and Vanuatu.

Mekosuchine crocodiles are a diverse group. Another mekosuchine fossil, currently undescribed, has been found in Miocene deposits from New Zealand. One genus, Mekosuchus, managed to spread to the islands of the Pacific; it is believed to have island-hopped across the Coral Sea, moving first to a now submerged island known as Greater Chesterfield Island, then New Caledonia and onwards. In the Pleistocene, Quinkana was one of the top terrestrial predators of the Australian continent.

Mekosuchines underwent a drastic decline in post-Miocene Australia, with all genera, except for Quinkana and Paludirex (both perishing during the Quaternary extinction event) becoming extinct in Australia by the end of the Pliocene. After the demise of Quinkana and Pallimnarchus, the group survived on Vanuatu and New Caledonia until the arrival of humans, who are presumed to have driven them to extinction.

While historically considered to be true crocodiles (of the family Crocodylidae), modern research places them as an independent group within or closely related to Longirostres, which contains both crocodiles and gavialids.

Species

Genus	Species	Age	Location	Notes	Image
Australosuchus	Australosuchus clarkae	Late Oligocene - Early Miocene	Australia
Baru	Baru darrowi	Middle Miocene	Australia
	Baru iylwenpeny	Late Miocene	Australia
	Baru wickeni	Late Oligocene	Australia
Kalthifrons	Kalthifrons aurivellensis	Pliocene	Australia
Kambara	Kambara implexidens	Eocene	Australia
	Kambara molnari	Eocene	Australia
	Kambara murgonensis	Eocene	Australia
	Kambara taraina	Eocene	Australia
Mekosuchus	Mekosuchus inexpectatus	Holocene	New Caledonia
	Mekosuchus kalpokasi	Holocene	Vanuatu
	Mekosuchus sanderi	Early Miocene	Australia
	Mekosuchus whitehunterensis	Late Oligocene - Early Miocene	Australia
Paludirex	Paludirex gracilis	Late Pleistocene	Australia
	Paludirex vincenti	Pliocene - Pleistocene?	Australia
Quinkana	Quinkana fortirostrum	Pleistocene	Australia
	Quinkana babarra	Early Pliocene	Australia
	Quinkana meboldi	Late Oligocene	Australia
	Quinkana timara	Middle Miocene	Australia
Trilophosuchus	Trilophosuchus rackhami	Oligocene - Miocene	Australia
Ultrastenos	Ultrastenos huberi	Late Oligocene	Australia
Volia	Volia athollandersoni	Pleistocene	Fiji

Phylogeny

External relationships

Mekosuchinae is cladistically defined as a node-based taxon composed of the last common ancestor of Kambara implexidens, Mekosuchus inexpectatus, and all of its descendants.

Mekosuchinae is traditionally thought to be included as a basal member Crocodyloidea, although this is disputed. A 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data established the inter-relationships within Crocodilia, which was expanded upon in 2021 by Hekkala et al. using paleogenomics by extracting DNA from the extinct Voay.

The below cladogram shows the results of the Lee and Yates study (2018), which placed Mekosuchinae outside of Crocodyloidea, as more basal than Longirostres (the combined group of crocodiles and gavialids).

Paleobiology

Ecology

Being the dominant group of crocodilian throughout the vast majority of the Cenozoic in Australia, mekosuchines largely went without much competition from other groups and thus filled a wide range of nisches. Broadly speaking, mekosuchines may be divided into three main ecomorphs: semi-aquatic generalists, more terrestrial altirostral dwarf forms and terrestrial ziphodonts. Though a longirostrine ecomorph has been proposed at one point, later studies have proven this assumption to have been based on insufficient and missinterpreted material.

Semi-aquatic Forms

A vast majority of mekosuchines falls within the first category, generally resembling other generalist crocodilians of today in their skull shape and subsequently their inferred behavior. Australosuchus, Kalthifrons, Ultrastenos, the four species of Kambara and Paludirex all share the hallmarks of semi-aquatic ambush predators, having flattened skulls of medium length and eyes positioned high up on the skull, allowing them to keep their eyes above the water surface while most of their bodies remain hidden. Baru, although also semi-aquatic, did differ significantly in its unique skull morphology, leaning closer to altirostry. These semi-aquatic forms can further be divided by prey preference and size, although the former remains largely speculative for many of them.

For instance, Ultrastenos, the smallest mekosuchine to feature a generalized skull shape, was once speculated to have potentially fed on small reptiles and amphibians. However, this hypothesis was largely based on the now incorrect assumption that it had narrow, elongated jaws, and was established in order to explain such morphology despite the apparent lack of fish typically associated with longirostrine forms. Less is known about both Australosuchus and Kalthifrons from the Lake Eyre Basin, tho both are considered medium-sized for mekosuchines, the former reaching 3 m (9.8 ft).

Kambara meanwhile is better studied, with researchers having spent more time on its potential feeding habits and even some direct fossil evidence. Like the afforementioned taxa, Kambara had a flattened skull indicative of semi-aquatic habits, but was surprisingly diverse in the details of the skull shape. The fact that dentition between species differs in whether or not it forms an overbite or interlocks has been suggested to be of ecological significance, with an overbite possibly useful in breaking and slicing while interlocking teeth are more apt to grip and hold. This, coupled with differently pronounced muscle attachments suggesting differences in grip strength, has been used to suggest that some species of Kambara were more adept at feeding on smaller prey while others, in particular Kambara taraina, were capable of hunting even larger mammals. However, the only direct evidence for the specific diet of Kambara comes in the form of turtle shells that bear crocodilian bitemarks. The specific patterns of bites show that Kambara engaged in behavior known as "juggling", i.e. repeated bites meant to allign the prey with the teeth or with the throat, either to crush or swallow it.

While Paludirex gracilis overlaps in size with Kambara and is assumed to be similarily generalist, the larger Paludirex vincenti is thought to have been able to tackle much larger prey by simple virtue of its size alone, reaching a length of around 5 m (16 ft). This was only aided by a noticably more robust skull, leading some researchers to suggest that it could have even preyed on the larger marsupials of its time.

Though not quite as large as Paludirex, Baru may display the greatest degree of specialisation towards hunting large prey. It's skull is much deeper than that of other semi-aquatic mekosuchines and its teeth were highly elongated, recurved and in some species feature small crenulations. It is hypothesized that the cleaver-like head served to deliver an strong, incapacitating blow to its prey, possibly even piercing armour or tough hide. The curvature of the teeth would then be able to restrain the prey while the serrations may have been used to cut through flesh. Willis and colleagues speculate that through this method it may have hunted animals as large as 300 kg (660 lb), while fossil evidence shows bitemarks, likely those of Baru, left on the bones of Dromornis, Emuarius and Neohelos. It is possible that this stark contrast to other semi-aquatic mekosuchines could be rooted in habitat preferences. Baru may have inhabited relatively shallow bodies of water, which would render it much more difficult to drown prey and thus may have required the animal to dispatch of prey in a quicker manner.

Altirostral dwarf taxa

In stark contrast to the medium to large sized semi-aquatic taxa stand the two genera of altirostral dwarf forms, namely Trilophosuchus and Mekosuchus.

Terrestrial ziphodonts

Perhaps the most enigmatic mekosuchine morphotype concerns those with ziphodont dentition, traditionally interpreted as terrestrial predators. The best known and only named representative of this type is Quinkana, which has been the center of much speculation ever since its discovery.

References

• Mead, J. I.; Steadman, D. W.; Bedford, S. H.; Bell, C. J.; Spriggs, M. (August 2002). Guyer, C. (ed.). "New extinct mekosuchine crocodile from Vanuatu, South Pacific" (PDF). Copeia. 2002 (3): 632–641. doi:10.1643/0045-8511(2002)002[0632:NEMCFV]2.0.CO;2. S2CID 86065169.