ichthyosauromorpha – Nix Illustration

Hupehsuchus

Hupehsuchians were small marine reptiles closely related to ichthyosaurs, known only from the Early Triassic of southwestern China about 249-247 million years ago. They had toothless snouts, streamlined bodies, paddle-like limbs, and long flattened tails, along with a unique pattern of armor along their backs made up of overlapping layers of bony osteoderms.

Hupehsuchus nanchangensis was a mid-sized member of the group, about 1m long (3’3″). Newly-discovered fossils of its skull show that its long flattened snout had a distinctive gap between the bones (similar to the platypus-like snout seen in its relative Eretmorhipis) with an overall shape surprisingly convergent with that of modern baleen whales – suggesting that this hupehsuchian may have been a similar sort of filter-feeder.

A diagram comparing Hupehsuchus' skull to that of a modern baleen whale. — *Hupehsuchus skull compared to a modern minke whale*
From fig 2 & fig 3 of Fang et al (2023). First filter feeding in the Early Triassic: cranial morphological convergence between *Hupehsuchus* and baleen whales. *BMC Ecol Evo* 23, 36. https://doi.org/10.1186/s12862-023-02143-9

Grooves in the bones along the outer edges of its upper jaws may be evidence of filtering structures similar to baleen, although with no soft-tissue preservation we don’t know exactly what this would have looked like. Its slender flexible lower jaws probably also supported a large expandable throat pouch, allowing it to filter plankton out of larger volumes of water.

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.

Retro vs Modern #05: Ichthyosaurus communis

Fossilized ichthyosaur bones have been found for centuries, but were initially misidentified as being the remains of fish, dolphins, and crocodiles. More complete skeletons began to be discovered in the early 19^th century – particularly by pioneering paleontologist Mary Anning – and Ichthyosaurus communis was one of the first species of these ancient “fish lizards” to be scientifically recognized.

1830s-1870s

Early reconstructions of ichthyosaurs in the 1830s depicted flippered crocodile-like animals with long straight eel-like tails and strangely shrinkwrapped features, showing the sclerotic rings of their eyes and the internal bones of their flippers as highly visible externally. They were also frequently portrayed as being amphibious, hauling themselves out of the water to bask.

By the late 1830s impressions of smooth scaleless skin had been found, and specimens with tail-tips that were always “broken” in the exact same place were interpreted as evidence of the presence of some sort of paddle-like tail fin. The 1850s Crystal Palace Ichthyosaurus statues show this slightly updated version, along with a low dorsal ridge on their backs reminiscent of a beluga whale.

2020s

From the 1880s onwards the discovery of exceptional ichthyosaur specimens preserving whole body outlines revealed a fully aquatic streamlined shape, a triangular dorsal fin, and a crescent-shaped vertical tail fluke. Numerous examples of fossilized pregnant females also showed that ichthyosaurs gave live birth rather than laying eggs.

This highly dolphin-like version of ichthyosaurs quickly caught on and became the standard depiction into the early 20^th century, frequently showing them as highly active animals – swimming in groups, chasing fish and ammonites, and leaping dramatically out of the water like their modern cetacean counterparts. While we don’t actually know if they were social or acrobatic like dolphins, it was still a surprising and refreshing contrast to the increasingly lumpy and sluggish depictions of non-avian dinosaurs that were happening around the same time.

Actual further paleontological study on ichthyosaurs was scarce for decades, however, with a general attitude that the group was already scientifically “complete” and there wasn’t much new or interesting left to learn about them anymore. It wasn’t until the late 20^th century that they began to have their own “ichthyosaur renaissance” alongside the dinosaurs, with a sharp rise in research in the last few decades bringing us a lot of new information about their diversity and biology.

Ichthyosaurus communis was just one of several species in the Ichthyosaurus genus, living during the Early Jurassic, about 196-183 million years ago, in the shallow tropical seas of what is now Europe. About 3.3m long (~11′), it was adapted for high-speed long-distance swimming like a modern tuna, and it probably had a large keeled peduncle on the sides of its tail.

Bone structure and isotope analysis show that ichthyosaurs were all warm-blooded. One exceptional specimen also preserves an insulating layer of cetacean-like blubber, along with some evidence of its coloration: overall darker on the top and lighter on the underside in a countershaded pattern.

(I’ve given this reconstruction some speculative disruptive camouflage, too.)

Some of the preserved pigmentation has enough microscopic detail to show what appear to be branched melanophore cells associated with the ability to change color – suggesting that ichthyosaurs may have been able to actively darken and lighten their coloration like some modern lizards.

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.

Shonisaurus

Most ichthyosaurs were similar in size to the modern dolphins they convergently resembled, but during the Late Triassic some of them got much much bigger.

Shonisaurus popularis lived about 222-212 million years ago, in Nevada, USA — a region that’s currently made up of dry deserts, but which was submerged under a tropical inland sea at the time.

At around 15m long (49′) it was roughly the same size as a modern humpback whale, with a long narrow snout, a fairly deep fusiform body, and four equally-sized flippers. Unlike many other ichthyosaurs it doesn’t seem to have had a dorsal fin, and its tail fluke shape was rather “primitive” indicating it was probably a slow cruising swimmer.

Juveniles had a few small teeth at the tips of their jaws, but larger adults were entirely toothless, suggesting that they may have specialized in different ecological niches at different stages of their lives. Fully-grown Shonisaurus probably mostly fed on prey such as soft-bodied cephalopods and small fish, which must have been incredibly abundant in the ancient Nevadan sea to support a population of such huge marine reptiles.

But Shonisaurus popularis wasn’t even the biggest of the Late Triassic giant ichthyosaurs. Further north in British Columbia, the closely related species Shonisaurus sikanniensis reached lengths of up to 21m (69′), and fragmentary remains from England hint at something even larger still, estimated at around 25m (82′) – close in size to the modern blue whale, and potentially being the largest non-dinosaurian reptile to ever live.

Eons Roundup 4

Some more recent commission work for PBS Eons!

An illustration of an extinct entelodont, an omnivorous hoofed mammal. It has a hippo-like head and a body proportioned rather like a hyena, with high shoulders and long slender legs. It has cloven-hoofed feet and a short tail, and its body is covered in a coat of short bristly fur. — Eoentelodon

The entelodonts Eoentelodon and Brachyhyops, from “The Hellacious Lives of the Hell Pigs”
https://www.youtube.com/watch?v=trJpxwMGoCw

An illustration of an extinct ichthyosaur, an ancient marine reptile. It has a short narrow snout full of rounded teeth, large eyes, a long tapering body, four flippers, and a long tail ending in a vertical fin. — Tholodus

An illustration of an extinct mosasaur, an ancient marine reptile. It has long triangular jaws full of many small sharp teeth, a long lizard-like body, four paddle-like flippers, and a long tail ending in a vertical fin. — Tholodus

The early ichthyosaur Tholodus and the mosasaur Pluridens, from “When Ichthyosaurs Led a Revolution in the Seas”
https://www.youtube.com/watch?v=V342aXQs9XY

An illustration of an extinct early bat in flight. It has claws on all five fingers on each wing, along with small ears and a long tail. — Onychonycteris

An illustration of an extinct early bat in flight. It has claws on both its thumb and the first wing finger one each wing, along with small ears and a long tail. — Onychonycteris

The early bats Onychonycteris and Icaronycteris, from “When Bats Took Flight”
https://www.youtube.com/watch?v=zWeYCULC0UQ

Eretmorhipis

Eretmorhipis carrolldongi, a hupehsuchian marine reptile from the Early Triassic of China (~247 mya).

This species was originally named back in 2015, but at the time the only known specimens were missing their heads. It was assumed that its skull would have looked similar to those of other hupehsuchians… but now new fossils have been found, and it seems to have actually been much much weirder!

Eretmorhipis’ head was surprisingly tiny in proportion to its body – sort of like a marine version of Cotylorhynchus – and its shape convergently resembled the modern platypus, with a wide “duck bill” and very small eyes. It may have hunted for food along the seafloor in a similar manner to the platypus, using either a highly sensitive sense of touch or possibly even electroreception to locate small invertebrates like worms and shrimp.

It also had much larger bony osteoderms than its other known hupehsuchian relatives, forming a distinctive protruding spiky ridge down its back. At about 85cm in length (2′9″) it was one of the largest marine animals around at the time, so this structure probably wasn’t needed for defense – but as with other hupehsuchians its actual function is still unknown.

Ichthyosaur Blubber

In early 2017 evidence of blubber was found in plesiosaurs, indicating that they were probably much more chubby than they’re usually reconstructed, and now in late 2018 it’s been found in an ichthyosaur, too!

Living during the Early Jurassic (~183-179 mya) in the shallow seas that covered most of Europe at the time, Stenopterygius was an average-sized ichthyosaur growing up to about 4m in length (13′). A fossil found in Germany has some incredibly good soft-tissue preservation, showing smooth flexible scaleless skin, a layer of insulating blubber very convergently similar to that found in cetaceans, and even evidence of countershaded coloration.

While the confirmation of blubber is amazing, and gives further evidence that ichthyosaurs were warm-blooded, the color preservation might actually be even more interesting. The skin pigmentation is preserved in enough fine detail for branched melanophores to be visible under a microscope – a type of cell associated with the ability to change color. So there’s a possibility that ichthyosaurs could actively darken or lighten their color patterns, for purposes such as better camouflage, UV protection, or temperature regulation.

Grendelius

Grendelius mordax, an ichthyosaur from the Late Jurassic of England (~155-150 mya).

Named after the monster Grendel from the epic poem Beowulf, this 4m long (~13′) marine reptile had a big robust skull with large teeth, proportionally short flippers, and smaller eyes than some of its other relatives. It also had an unusual bony “hump” on its snout above its nostrils.

(About 20 years ago Grendelius was reassigned into Brachypterygius on the basis of the two not being distinct enough from each other to justify having separate genus names – but a more recent study suggests that that they actually were different after all, and the name may be valid again.)