Tag: ichthyosauria

Kyhytysuka

The first definite ichthyosaur fossil found in Colombia was a single well-preserved skull, found in Early Cretaceous deposits dating to between 130 and 112 million years ago.

Although first discovered in the 1970s, this marine reptile wasn’t described until the late 1990s, at the time being named as a species of Platypterygius. But since then more pieces of the skeleton have been recovered, and the Platypterygius genus has been found to be a wastebasket taxon in need of revision, so in 2021 the Colombian ichthyosaur got a more detailed redescription and its own distinct name: Kyhytysuka sachicarum.

Kyhytysuka was a mid-sized ichthyosaur, about 5.5m long (18′) – about the size of a small modern orca – with a large head and a long robust snout. Its teeth varied in size, shape, and spacing along its jaws, with several different regions that were specialized to catch, slice, and crush its prey.

It could also open its jaws very widely, possibly up to an angle of 75°, suggesting it was able to tackle particularly large prey such as other marine reptiles. Possible soft tissue preservation around its lower jaw might also be evidence of elastic connective tissue that would have allowed its throat to expand out while swallowing big prey items.

This makes Kyhytysuka the first known example of a Cretaceous-aged ichthyosaur with an apex predator lifestyle, convergently evolving a similar ecological role to some earlier Triassic and Jurassic species.

Guizhouichthyosaurus

In the mid-Triassic seas, covering what will one day be part of southwestern China, an ichthyosaur flails at the surface desperately trying to deal with an ambitiously large meal.

240 million years later human paleontologists will name their kind Guizhouichthyosaurus tangae, and initially assume that their narrow snout and small peg-like teeth are suited only for a diet of small soft-bodied fish and cephalopods.

In reality they eat a much wider range of prey – including other marine reptiles.

But for a 5m long (16’5″) Guizhouichthyosaurus, perhaps this particular catch is a little too much. The unlucky thalattosaur was a rather large example of a Xinpusaurus xingyiensis – nearly matching the ichthyosaur in length at around 4m long (13’2″), although much less bulky – and after biting off the head and tail the predator is still struggling to actually eat the sizeable carcass.

Even with a gravity assist from holding their prize vertically up above the water, swallowing is proving difficult and the Guizhouichthyosaurus can’t breathe around it.

They’re slowly suffocating.

They’ll eventually get it down their gullet, but by then it’ll be too late. Weak and dizzy from asphyxiation, they’ll soon sink to the sea floor and never resurface, their body settling not very far from where their prey’s severed tail fell.

Mixosaurus

Mixosaurus cornalianus here was a small early ichthyosaur, only about 0.8-1m long (2’7″-3’3″) and generally considered to be transitional between the eel-like swimming style of basal forms and the more dolphin-like later forms. Living during the Middle Triassic, about 242 million years ago, it inhabited a shallow tropical sea that covered what is now the modern border between Switzerland and Italy.

It was previously thought to be a slow swimmer with a low and poorly-developed tail fin, and whether it even had a dorsal fin or not was unclear. But now new specimens with soft tissue impressions have given us a big surprise.

Not only did it actually have a fairly well-developed semilunate tail fin, but it also had a dorsal fin positioned much further forward on its body than expected, giving it a shape similar to some small sharks and representing the current earliest known dorsal fin of any amniote.

Bundles of stiffening collagen fibers inside its fins were very similar to those known from later Jurassic ichthyosaur species, indicating that this adaptation evolved much earlier in the lineage than previously thought. Along with stomach contents showing it mainly ate both cephalopods and small fish – fairly fast-moving prey – this suggests it was a capable open-water swimmer. It wouldn’t have been quite as speedy as its much more specialized Jurassic relatives, but it may have still been about as efficient as the small modern sharks it resembled.