Marine Reptile Month #25 — Vancleavea
Late Triassic period (228-203 mya)
Vancleavea was an unusual late-surviving “non-archosaurian archosauriform”, which basically means it was about as closely related to the archosauria as it’s possible to get without actually being one. 1.2m long (3ft 11in) and covered in overlapping armored scales, its short limbs, deep tail, and upwards-facing nostrils suggest it was a semi-aquatic swimming animal.
Uniquely among all known tetrapods, it also formed its vertical upper tail fin from a row of highly elongated ostederms.
Color palette used: “Shirley the Medium”
Marine Reptile Month #24 — Askeptosaurus
Middle Triassic period (247-242 mya)
The askeptosaurids had longer necks and narrower snouts than other thalattosaurs, and appear to have been adapted to hunt fish in deeper water.
Askeptosaurus was very thin and elongated, with a flexible eel-like tail making up around half of its 2m length (6ft 6in). Its relatively large eyes, supported by a bony sclerotic ring much like those of ichthyosaurs, would have allowed it good vision in low light levels.
Color palette used: “Aftermath”
Marine Reptile Month #23 — Hupehsuchus
Early Triassic period (~251-247 Ma)
The hupehsuchians were icthyosaur-like marine reptiles which may or may not be a sister group to early icthyopterygians like Utatsusaurus. They had long narrow snouts, flipper-like limbs (some displaying polydactyly), and bony armor along their spines. One genus named earlier this year, Parahupehsuchus, even modified its entire ribcage into a rigid bone “body tube”.
Hupehsuchus itself was about 1m long (3ft 3in), and its toothless beak-like snout may have been an adaptation for ram feeding.
Color palette used: “[1LP] Tylee”
Marine Reptile Month #22 — Pachypleurosaurus
Middle Triassic period (~242-235 mya)
Despite having an incredibly similar name, Pachypleurosaurus doesn’t have anything to do with yesterday’s Pleurosaurus. This 1m long (3ft 3in) marine reptile was a basal sauropterygian, closely related to both nothosaurs and plesiosaurs. Unlike the highly adapted flippers of the later plesiosaurs, the limbs of pachypleurosaurs were still very similar to those of terrestrial reptiles, and they probably swam with undulating motions rather than paddling.
Color palette used: “Laced Pastries”
Marine Reptile Month #21 — Pleurosaurus
Late Jurassic to Early Cretaceous period (~152-140 mya)
The pleurosaurs were aquatic members of the rhynchocephalians, a once-widespread group of lizard-like reptiles represented today by just a single genus, the tuatara.
About 60cm long (2ft), Pleurosaurus had a highly elongated body with short limbs and a powerful tail, and was probably capable of fast swimming with an undulating eel-like motion.
Color palette used: “50 Shades of Baby Food”
Marine Reptile Month #20 — Trinacromerum
Late Cretaceous period (~100-89 mya)
With short necks and elongated heads, the polycotylid plesiosaurs look very similar to the pliosaurs — but they were actually members of the mostly long-necked plesiosauroids instead.
Trinacromerum’s streamlined shape and long flippers would have allowed it to swim at high speeds. At around 3m in length (9ft 10in), its life appearance had been likened to a giant “four-flippered penguin”.
Color palette used: “Blood Orange”
Marine Reptile Month #19 — Qianosuchus
Middle Triassic period (~247-242 mya)
The oldest archosaur known to have taken up a semi-aquatic lifestyle, the 3m long (9ft 10in) Qianosuchus was a member of the poposauroids, an unusual group of stem-crocodyllians that also included sail-backed forms and dinosaur-mimics. It had a deep vertically-flattened tail adapted for propulsion, and dagger-like teeth to keep hold of slippery marine prey, but also retained long erect limbs well-developed for running on land.
I’ve reconstructed it here with a very speculative coating of otter-like fuzz (obscuring the small rows of reduced osteoderms in the skin along its back), because I like to do that kind of thing.
Color palette used: “Portal”
Marine Reptile Month #18 — Plotosaurus
Late Cretaceous period (72-66 mya)
Plotosaurus was one of the most “advanced” mosasaurs in terms of anatomical adaptations, with a highly streamlined body and a large tail fin enabling it to swim at high speeds as a pursuit predator. It grew to lengths of between 9 and 13m (25’6”-42’8”), and probably fed on fish, ammonites, smaller marine reptiles, and aquatic birds — swallowing them almost whole thanks to snake-like flexible jaws.
And, yes, mosasaurs almost certainly had forked tongues. Based on their evolutionary relationships to varanoids and snakes, it’s also possible that they might have been venomous, too.
Color palette used: “Poesie”