A large number of Triassic marine reptiles have similar body plans: A barrel-shaped body, large flippers, short but slender neck, and moderate to small head. This bauplan is useful for many pelagic animals, although most Triassic sediments preserving these are near-shore shallow continental shelf regions.
This has led many observers, both past and present, to refer these animals into a few, small groups, even classically as few as one. Today, these groups are diverse and split amongst a radiation of sauropsids from the base (such as mesosuchids) to deep into stem-crocodiles (thalattosuchians), and a range amongst the nodes between (ichthyosaurs, plesiosaurs, choristoderes, placodonts, saurophargids, pachypleurosaurs, etc.).
Today’s taxon belongs to a small group of tiny headed, barrel-bodied, deep pelagic group known as Hupehsuchia, an early radiation related to Ichthyosauria. It’s perhaps the oddest of the bunch, but due solely to its cranial features, whereas otherwise it’s less remarkable. Hupehsuchians have pachyostotic ribs and gastralia, aquatically adapted limbs ill-suited for terrestrial navigation (lacking developed elbow and knee joints), tiny heads atop slender and moderate necks, deep and long tails, and a row of dermal armor resembling sturgeon midline osteoderms atop their vertebrae. Today, I present Eretmorhipis carrolldongi (Carroll and Dong’s fan oar – there are issues with the etymology, but this is the intention).
Special bonus, no armor Eretmorhipis.
The notable feature for this animal is the toothless and extraordinarily slender jaws, forming a U-shaped loop as in a few whales and crocs attributed to a ram-based engulfing feeding style. This might lead to speculation regarding extra oral tissues for filtration (a topic broached by Carroll and Dong themselves), but is likely not necessary, as these animals seem to present the ability to filter out salt from engorged water. This is not presented here.
Carroll, R. L. & Dong Z.-m. 1991. Hupehsuchus, an enigmatic aquatic reptile from the Triassic of China, and the problem of establishing relationships. Philosophical Transactions of the Royal Society of London B 331(1260): 131-53.
Chen X.-h., Motani R., Cheng L., Jiang D.-y. & Rieppel, O. 2015. A new specimen of Carroll’s mystery hupehsuchian from the Lower Triassic of China. PLoS ONE 10(5): e0126024.