Leivanectes

Elasmosaurids are often depicted with noodly snake-like or swan-like necks, but they were probably actually quite stiff and inflexible in life. And while we know from fossilized gut contents that they ate relatively small prey like fish, crustaceans, and cephalopods, exactly how they used their distinctive long necks is still uncertain.

There’s some variation in the sizes and shapes of their teeth, so it’s likely each species was specialized for slightly different feeding styles – we’ve even found a filter-feeding one! – and the recently-named Leivanectes bernardoi here adds in a little more diversity, too.

Living about 115-112 million years ago during the mid-Cretaceous of Colombia, Leivanectes would have been fairly large at around 9m long (29′6″), slightly bigger than the other elasmosaurid species known from the same ancient marine deposits. It had a reduced number of teeth in its jaws, but these teeth were also proportionally larger, suggesting that it may have been tackling bigger tougher prey than its relatives.

Unfortunately it’s currently only known from a single partial skull, so we don’t have any other clues about its ecology.

Panzhousaurus

Panzhousaurus rotundirostris, a sauropterygian marine reptile from the mid-Triassic of southwestern China (~245 mya), living just a few million years after the devastating Permian-Triassic mass extinction. This small marine reptile was only about 40cm long (1′4″) and is known from a single near-complete skeleton.

Although it was a distant evolutionary cousin to plesiosaurs (and even more distantly to modern turtles), it was actually most closely related to an early sauropterygian lineage known as the pachypleurosaurs – a group of small lizard-like aquatic reptiles with tiny heads, long necks, and paddle-like limbs.

It had an unusually short and rounded-off snout compared to its relatives, and since it would have lived alongside many other diverse marine reptiles it was probably specialized for a slightly different ecological niche.

Paludidraco

Paludidraco multidentatus from the Late Triassic of Spain (~237-227 mya).

This 3m long (9′10″) animal was a member of the nothosaurs, a group of semi-aquatic seal-like marine reptiles that were closely related to plesiosaurs (and both were also evolutionary cousins to modern turtles).

It had long slender jaws full of numerous tiny teeth, creating an interlocking comb that was probably used for filter feeding – scooping up mouthfuls of fine-grained sediment from the seafloor and filtering out small invertebrates or soft plant matter.

The bones of its skeleton were also highly thickened and dense, a condition known as pachyostosis that provided ballast to weigh it down in the water. This would have made it a slow and unmaneuverable swimmer, but a very energy-efficient one, using its natural neutral buoyancy to hover or walk along the seabed.

It was essentially a reptilian manatee, filling a similar sort of ecological niche.