Result of the Jialingjiang Formation #paleostream! This might be one of my favorite Triassic formations, although I might be biased because I love hupehsuchians and this formation just manages to hold all of them.
This formation preserves the contents of a large, very salty and very warm lagoon during the early Triassic in China. Tidal zones with mudflats and stromatoliths would be common here but it was certainly no easy place to live. The diversity of organisms we have isn't very high...
But what we have is largely endemic. This part of China was quite isolated from the rest of the world and being the hostile environment made the animals that evolve here rather unique. However one should also mention that we deal with quite a bit of taphonomic bias here...
...because, while we have the well ossified marine reptiles often times preserved as complete, stunning specimens the rest leaves much to be desired. Not a single fish has been found up to this point but trace fossils attributed to fish make their presence likely.
The stars of this assamblage are certainly the already mentioned hupehsuchians, an enigmatic, endemic clade of weirdos. They range for 2 m long bony tubes, over filter feeding armored blimbs to tiny eyed swimming plush stegosaurs that would rummage through the sediment.
Most of the animals living here were rather small by marine reptile standards, probably because of the conditions they lived in, and yet this formation gave us, in my eyes, one of the most charming collections of Triassic goofballs.
Size chart by me this time, did this a while ago.
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.
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.
Sketches from last night´s #paleostream Hupehsuchus duo dancing in a shallow lagoon. sleepy Bobosaurus with a swarm of ammonites. Carolowilhelmina swimming around at night.
Eucoelophysis been attacked by a metoposaurid
Carolowilhemina swimming around at night
Click on the above links to refresh your memory about these animals! And feel free to use this post to debate and argue on what people should vote for!
The Official Tag for Triassic Madness is “#Triassic March Madness”! Be sure to look there for posts!
Time and Place: Between 248 to 247 million years ago, in the Olenekian of the Early Triassic
Hupehsuchus is known only from the Jialingjiang Formation in the Hubei Province of China.
Physical Description: At first glance, Hupehsuchus looks a lot like what you’d expect a primitive ichthyosaur to look like, and indeed they are related. Only around 1-2 metres (3-6 feet) long, its body is long and streamlined, with a long, pointed snout lacking teeth, limbs evolved into large rounded paddles, and a long flattened tail without a fluke. However, on closer inspection Hupehsuchus turns out to be much more bizarre.
Like other hupehsuchians, Hupehsuchus is heavily armoured with vertically layered rows of osteoderms running down its back over the vertebrae (you read that right, they’re on top of each other). These osteoderms interlock with each other, which may have stiffened the body and/or provided ballast. The vertebrae themselves have tall neural spines, giving Hupehsuchus an almost humpbacked appearance, and the neural spines appear to be made up of two separate pieces, one attached to the vertebra, the other seemingly attached to the osteoderms. Only hupehsuchians have vertebrae like that. Its body was probably compressed from side to side, taller than it was wide, and was only flexible around the hips and tail. The armour on its back is complemented by a robust, thick ribs that almost create a shield around its sides, and it even has heavily built, interlocking gastralia on its underside complete with another row of smaller osteoderms on the underside.
The skull of Hupehsuchus is also very unusual. The jaws are long, pointed, and the skull was seemingly quite broad and flat from above, resembling a duck’s bill. The lower jaws were incredibly thin and loosely attached to each other, and were probably capable of bending and bowing outwards like a pelican or baleen whale. The lower jaw may even have supported a large gular pouch, and large hyoid bones imply it had a powerful tongue. Furthermore, several parallel grooves in the upper jaw suggest the presence of a baleen-like structure in its mouth, making it even more uncannily similar to baleen whales. The neck, though, is relatively long and slender compared to a whale.
Diet: The bizarre adaptations of Hupehsuchus suggest it may have been a filter-feeder, sifting small particles and animals out of the water column or near the sea bed.
Behavior: Hupehsuchus was likely a lunge-feeder, in spite of its relatively long neck. The laterally compressed body and flexible hips and tail indicate that it swam by undulating through the water, likely lunging forwards suddenly through swarms of plankton and other small organisms to feed. The flexible jaws of Hupehsuchus imply that it engulfed large amounts of water as it fed, like whales, and would have strained it out through its filtering structures using its tongue.
Hupehsuchus almost certainly gave birth to live young, like ichthyosaurs. Partly because its anatomy was totally unsuited for crawling onto land to lay eggs, but also because one of the oldest ichthyosaurs, Chaohusaurus, is known to have given birth to its babies head-first, the opposite of the tail-first birth in other ichthyosaurs. Babies born head-first in water are at risk of drowning during birth, so this implies that live birth evolved in the ancestors of ichthyosaurs while they were still on land, which would mean that Hupehsuchus likely would have inherited this trait too.
Ecosystem: Hupehsuchus, and indeed all other hupehsuchians for that matter, are known only from a single locality in China. Here Hupehsuchus coexisted with its fellow hupehsuchians Nanchangosaurus, little short-necked Eohupehsuchus, the tubular Parahupehsuchus (I’m sensing a pattern here) and the truly bizarre platypus-faced Eretmorhipis (along with an undescribed polydactylous species!).
The diversity of hupehsuchians in this one habitat likely lead to diverse niche partitioning between them. Hupehsuchus was one of the largest, and seemingly occupied a more active lifestyle, lunge-feeding on organisms in the water. Nanchangosaurus had a similar skull to Hupehsuchus, and so may have had a similar diet, but it was smaller and had a body shape more suited for swimming along the sea bed. Parahupehsuchus was so heavily encased in armour that its body was practically a bony tube, and rather than round paddles it had pointed flippers, suggesting a different swimming style (for what, we don’t know). The bizarrest of them all, Eretmorhipis, may have specialised in grubbing blindly through the seabed, sensing prey with its bill like a platypus, possibly even at night.
The habitat is believed to have been a shallow lagoonal environment, perhaps sheltered from larger predators that could have preyed upon them, like giant nothosaurs. However, they nonetheless coexisted with the primitive ichthyosaur Chaohusaurus and two species of pachypleurosaur (sauropterygians related to nothosaurids), Keichousaurus and Hanosaurus, as well as an undescribed large sauropterygian 3-4 metres (10-13 feet) long. Strangely, no fish have been discovered in this formation, so it’s quite possible that the smaller hupehsuchians were the main food source for some of these larger marine reptiles (as evidenced by a bite taken out of one Eohupehsuchus paddle!). These conditions may have also prompted the strange dietary adaptations of the hupehsuchians, with no smaller fishes to eat, they specialised in eating tiny marine invertebrates and other plankton.
Other: Hupehsuchians are very mysterious marine reptiles, they are known from only one location in the whole world and from a very narrow range of time in the earliest Triassic. Hupehsuchus was once suggested to be a missing link between the ichthyosaurs and their as-yet-unknown terrestrial ancestors, although as more early ichthyosauromorphs have been discovered it is clear that is not the case, and that hupehsuchians are a bizarre offshoot of their own.
Hupehsuchus is part of a surprisingly diverse range of early-derived ichthyosauromorphs that lived in China during the Early Triassic, just a few million years after the Permian Mass Extinction, including the first proper ichthyopterygians and the peculiar (possibly amphibious) nasorostrans like Cartorhynchus. These marine reptiles were very quick to diversify in the wake after the extinction, as the strange filter-feeding lifestyle of Hupehsuchus testifies, quite the opposite of the predicted slow recovery for marine ecosystems. However, it remains a mystery why only the ichthyosaurs prevailed, and all the other strange and diverse ichthyosauromorphs like Hupehsuchus never even made it into the Middle Triassic. Perhaps they were just too strange and specialised even for the Triassic.
~ By Scott Reid
Sources under the Cut
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Chen X. H., Motani, R., Cheng, L., Jiang, D. Y., Rieppel, O. (2014) “The Enigmatic Marine Reptile Nanchangosaurus from the Lower Triassic of Hubei, China and the Phylogenetic Affinities of Hupehsuchia”. PLoS ONE 9(7): e102361.
Chen, Xiao-hong; Motani, Ryosuke; Cheng, Long; Jiang, Da-yong; Rieppel, Olivier (May 27, 2015). "A New Specimen of Carroll's Mystery Hupehsuchian from the Lower Triassic of China". PLoS ONE. 10 (5): e0126024.
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