#indosinosuchus

[berensreverie]

Indosinosuchus A teleosaurid from Late Jurassic or Early Cretaceous Thailand :)

[justgoji]

Junggarsuchus (with a healed limb) and Indosinosuchus for croctober!!

[paleonativeart]

Day 14: Indosinosuchus

An teleosaurid neosuchian that swim throughout the shallow rivers during the wettest season of late Jurassic or Early Cretaceous period.

[sinasinasinas]

Croctober day 14:

Indosinosuchus

[arminreindl]

Indosinosuchus the freshwater Teleosaur

Ignoring the fact that I skipped out on posting about my recent deepdives on Armadillosuchus and Odobenocetops (besides that one figure I made) on Tumblr, let me catch up by talking about Indosinosuchus.

Indosinosuchus (Indochinese Crocodile, after the Indochinese Tectonic Block) is a type of teleosaurid from the Late Jurassic Phu Kradung Formation of China. First of all the Phu Kradung is a fascinating formation with a long and somewhat convoluted dating history. For quite some time researchers argued whether or not its Late Jurassic (based on fauna) or Early Cretaceous (based on pollen). Recent papers seem to argue that both can be true, with the lower parts being Jurassic and the upper Cretaceous, which also accounts for a faunal turnover visible throughout the record. Related to Indosinosuchus, we have classically Jurassic teleosaurs in the lower levels and pholidosaurids in the upper.

artwork by Kmonvish Lawan and Sakka Weerataweemat

Whats far more interesting however is that the Phu Kradung Formation is continental in nature, preserving floodplanes dominated by lakes and rivers. This is quite the unusual habitat for a teleosaur, which are traditionally marine animals, living in the coastal or even open waters of the Tethys. In fact the only other known example of a freshwater teleosaur is an unnamed animal from China that sometimes clades closely to Indosinosuchus.

Indosinosuchus is known from a total of 10 fossil individuals, largely consistsing of skulls and mandibles with the occasional postcrania, which were all found in a single locality and have been determined to represent at least two different species: I. potamosiamensis (Thai River Indochinese Crocodile) and I. kalasinensis (Indochinese Crocodile from the Kala Province).

Now overall, Indosinosuchus had a pretty long and narrow snout compared to most modern crocodilians. However, among teleosaurs, this animal was actually among the more robust genera. Even more so when you consider that within teleosaurs, it falls within the teleosaurid family, not the overall more robust machimosaurids that would eventually become durophages and macropredators, cracking turtle shells.

Analysing the biomechanics of Indosinosuchus did show some cool things. The snout was pretty average at resisting stress and force, at least for teleosaurs, but the bite force was respectably high. The force that could be transferred to the tip of the snout in particular is among the highest in this group and the maximum force it could excert was the single highest among all teleosaurs.

The two species however begin to differ in how fast they could close its jaws. I. potamosiamensis follows what would be expected. A teleosaur with a massive bite but only closing its jaws slowly as in teleosaurs with similar mechanical advantage values. I. kalasinesis however could close its jaws surprisingly fast, something you'd otherwise expect from animals with a much lower bite force that needed to strike a lot more swiftly in order to catch prey.

While we don't quite know the precise ecology of the two species, scientists could deduce a few things. For one, obviously the difference in the jaw closing/opening speed is a good sign that they had somewhat different lifestyles, which could explain why two so similar species coexisted at the same time in the same place. Secondly, although its bite force was notably high, it does not appear like Indosinosuchus went after especially large prey. Sure, it could bite hard and had a relatively robust rostrum, but its teeth were not particularily specialised like in Machimosaurus. So it has been suggested that it was a generalist, not a specialist as shown in this figure by Johnson, Young and Brusatte.

Last but certainly not least is the way these animals died. It does seem rather odd that 10 specimens all seemingly died in the same place at the same time, with most preserving the skull and not much else. Well there may be a reason. One clue stems from the most complete non-skull we have, which is a remarkably well preserved spinal column preserved in articulation, but missing the skull. So the idea is that the carcass may have floated in rather still waters (like an oxbow lake) and the weight of the head would eventually separate the two pieces. The spine must have been burried rather quickly afterwards so that it wouldn't just fall apart. Well the hypothesis continues that this could have been during a drought, when water levels were gradually receeding. We know that modern crocodiles will amass in great numbers during droughts until bodies of waters are nothing but mud and crocs, so it makes sense here. The full drying out of their sanctuary would then contribute to preservation and we even have evidence that they spend a minimum of 8 weeks in the dry thanks to the feeding traces of scavenging beetle larvae.

There is also a second hypothesis that suggests that the bodies may have been washed on land during a flashflood, but I personally think the drought hypothesis is a lot more interesting. Plus I managed to get @knuppitalism-with-ue to draw something akin to the later, with an unfortunate group of Indosinosuchus being stuck in a dried up lakebed as a local mamenchisaur approaches in the search for water.

Obligatory link to the Wikipedia page post-overhaul: Indosinosuchus - Wikipedia and the before and after, wondering if I should do the same with Armadillosuchus and Odobenocetops or if I should just come back once I got the next project done (Doratodon)