Tag: marine reptiles

Alienochelys

Alienochelys selloumi, a sea turtle from the Late Cretaceous of Morocco (70-66 mya). Although only known from a single skull, it was probably around 2-2.5m long (6′6″- 8′2″), and was closely related to both the modern leatherback turtle and the giant Archelon – and so it wouldn’t have had a solid shell but instead a leathery skin-covered carapace.

But that one skull was also incredibly weird. While most turtles have pointed beaks, Alienochelys had a blunt squared-off face, sort of “pug-nosed”, with its nostrils set high up between its eyes. It seems to have been specialized for crushing hard-shelled prey between the wide flat grinding surfaces of its beak, more similar to the jaws of rays than those of other turtles.

It also lived alongside another bizarre-jawed turtle, but that’s a subject for another time.

Sclerocormus

Sclerocormus parviceps, an unusual ichthyosauriform from the Early Triassic of China (~248 mya).

Its short toothless snout suggests it was a suction feeder, using water pressure differences to pull small soft-bodied prey straight into its mouth like a syringe.  Along with a heavily built body similar to those of hupehsuchians, and a very long tail that made up over half of its 1.6m length (5′3″), it was probably a fairly slow swimmer living in shallow coastal waters.

It was a close relative of Cartorhynchus, and may have been similarly capable of hauling itself onto land like a modern pinniped.

Mauriciosaurus

Mauriciosaurus fernandezi, a polycotylid plesiosaur from the Late Cretaceous of Mexico (~94-89 mya). About 1.9m long (6′3″) with a flipper-span of 1.5m (4′11″), it’s known from a near-complete skeleton with preserved soft tissue impressions. The fossil shows evidence of rows of very tiny scales, the skin outlines of the flippers, and also a thick layer of insulating blubbery fat.

Its body shape in life would have been similar to modern leatherback turtles, roughly teardrop-shaped and hydrodynamic – much chubbier than most plesiosaur reconstructions had been previously depicting!

Unsolved Paleo Mysteries Month #12 – Muddled Mosasaurs

Numerous groups of reptiles have “returned to the water” and become aquatic over the last three hundred million years, but tracing their direct ancestry can be surprisingly difficult. Highly modified and specialized anatomy, lack of transitional forms, and similar features convergently evolving multiple times can all obscure relationships, making it hard to properly classify them.

We’re only just starting to figure out the true origin of turtles (they’re probably archosauromorphs), and they’re a marine reptile group with living members.

Some of the completely extinct ones are even more uncertain. For example: mosasaurs. (Represented here by the eponymous Mosasaurus.)

While some semi-aquatic early mosasaurs are known, and they seem to be closely related to aigialosaurs and dolichosaurs, their exact placement within the squamates is a lot less clear. Traditionally they were regarded as the sister group to snakes, but some studies have found them to be closer to monitor lizards instead, and others have even placed them as much more basal scleroglossans. Their classification in phylogenetic analyses is “highly unstable”, changing depending on what other reptile groups are included, so there’s no real current consensus.

(And even if they are most closely related to snakes, that doesn’t necessarily help much – the exact origin and evolution of snakes is still very poorly known, too!)