marine reptile month 2014

August on this blog is Marine Reptile Month! Every day (except Sundays) there’ll be a new art post featuring an extinct example of these diverse animals. “Marine reptiles” don’t form any sort of distinct taxonomic clade – and none of them were dinosaurs – but they all represent a huge range of unrelated groups that each evolved their own adaptations for aquatic environments throughout geologic history.

Also each one will be done using a randomly picked color scheme from Colourpod, because that’s what all the cool kids are doing right now it seemed like a fun challenge.

#1 – Utatsusaurus

Early Triassic period (245–250 mya)

The earliest known ichthyopterygian, Utatsusaurus was about 3m (9ft) long and showed several transitional features between its terrestrial ancestors and the more advanced members of the group. It had a broader skull with a less pointed snout, no dorsal fin, and the shape of its vertebrae suggest it swam by undulating its whole body with an eel-like motion instead of concentrating thrust in the tail like later true ichthyosaurs.

Color palette used: “Future Bell

Marine Reptile Month #6 – Nectosaurus

Late Triassic period (235-228 mya)

During the latter half of the Triassic, a group of lizard-like reptiles known as the thalattosaurs thrived in coastal waters. With short stocky limbs and long paddle-shaped tails they somewhat resembled the modern marine iguana – until you look at their heads, at least. Some types had long toothy jaws and were clearly predators, but others had much stranger skulls.

The 1m long (3ft 3in) Nectosaurus was one of the weird ones. The tip of its upper jaw was downturned so sharply it nearly formed a right-angle with the rest of its mouth, creating a bizarre toothy “hook snout”. It’s not clear what this creature was even doing with such a strange nose – but it was obviously a useful adaptation for something, since at least two other thalattosaurs (Hescheleria and Paralonectes) are known to have had very similar snouts.

Color palette used: “Windshield

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

Marine Reptile Month #2 – Tchoiria

Early Cretaceous period (125-112 mya)

Although technically a freshwater reptile, Tchoiria is a member of an interesting yet often-overlooked group known as choristoderes. Despite its rather gharial-like appearance this 1.5m long (~5ft) animal wasn’t related to any of the crocodyllians – it was fully aquatic, spending its entire life in the water, and probably gave birth to live young.

Choristoderes actually lived through the K-Pg extinction event, with some forms surviving until the end of the Oligocene epoch 34 million years ago. One species, the small lizard-like Lazarussuchus, made it even further, with fossils known from just 20 million years ago in Europe.

Color palette used: “Christmasy

Marine Reptile Month #4 – Tanystropheus

Middle Triassic period (245–228 mya)

The Triassic was sort of weird. In the wake of the most devastating extinction event in Earth’s history, life re-diversified in a great “Triassic explosion” of new body plans and evolutionary experiments. Many recognizable groups arose in this time – including plesiosaurs, ichthyosaurs, pterosaurs, dinosaurs, crocodyllians, frogs, modern types of corals, and the first true mammals – but there were also a whole host of other oddball animals that don’t always seem to make sense.

Like Tanystropheus. Half of this semi-aquatic 6m (20ft) protorosaur was made up entirely of neck, but with only a few extremely elongated cervical vertebrae it would have been rather stiff and inflexible.  Soft tissue remains in one fossil show a large muscle mass behind Tanystropheus’ hips, evidence of very powerful hind limb muscles – and also giving enough weight in its rear body to counterbalance and stabilize that massive neck.

Although often depicted as a “living fishing pole”, sitting on the shoreline and snatching up aquatic prey with its neck, the lifestyle of this animal is still poorly understood. Complicating matters is that fact that juvenile specimens have differently-shaped teeth to adults, suggesting that Tanystropheus exploited different ecological niches at various stages of its life.

Color palette used: “Emotional

Marine Reptile Month #9 – Metriorhynchus

Middle-Late Jurassic period (167-155 mya)

The “sea crocodiles”, or thalattosuchians, were crocodyllians highly adapted to marine life – and the metriorhynchids took this to the extreme. They completely lost their osteoderm “armor” to become more streamlined, developed paddle-like limbs, and even had shark-like vertical tail fluke.

How Metriorhynchus and its kin reproduced is still unknown, as no fossil eggs or embryos have ever been found. Their fully-aquatic anatomy makes it seem unlikely that they were capable of hauling out onto land to breed, so it’s possible they evolved the ability to give birth to live young, much like several other lineages of marine reptiles. However, no other archosaurs are known to have ever developed viviparity, so if these animals were capable of it they would be unique amongst the entire group.

Color palette used: “Galactica

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 #12 – Hydrotherosaurus

Late Cretaceous period (72-66 mya)

One of the larger elasmosaurid plesiosaurs, Hydrotherosaurus reached lengths of around 13m (42ft 7in). And, like the unrelated Tanystropheus, about half of that was neck – although Hydrotherosaurus had 60 cervical vertebrae compared to Tanystropheus’ 10-12.

Although often depicted with swan-like or snake-like highly flexible necks, elasmosaurs weren’t actually capable of such extreme postures. Their necks seem to have been relatively stiff, and may have functioned as rudders – turning the head towards something would cause the whole body to move in that direction.

The lifestyle of these animals is still a little unclear. They’ve been proposed as “spear fishers”, sticking their long necks and heads into schools of fish to snatch up prey before the main bulk of their bodies became visible. Stomach contents of seafloor crustaceans and molluscs, along with trace fossils of odd gutter-like gouge marks, however, raise the possibility of elasmosaurs instead scooping up mouthfuls of prey-rich sediment.

There’s also some fun speculation about the necks being electric organs.

Color palette used: “Revenge of the Sunfish

Marine Reptile Month #13 – Pliosaurus

Late Jurassic period (~156-147 mya)

There were two main body shapes for the plesiosaurs: the long-necked small-headed forms, and the short-necked large-headed forms like Pliosaurus. The pliosaurids were apex predators, feeding on fish, cephalopods, and other marine reptiles, with the largest genera reaching lengths of around 10-13m (~33-43ft). There’s no current evidence for any of them growing significantly bigger than that – the 25m (82ft) Liopleurodon depicted in Walking With Dinosaurs was a complete fabrication.

This Pliosaurus looks familiar…

Color palette used: “Shiny Giratina

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 #7 – Nothosaurus

Early to Late Triassic period (240-210 mya)

Nothosaurus was about 4m long (14ft) and probably had a semi-aquatic lifestyle similar to modern seals, hunting in the water but still regularly coming ashore. Along with the more famous plesiosaurs, the nothosaurs were members of the sauropterygia – but while their plesiosaur cousins became fully adapted to marine life and went on to be successful throughout the rest of the Mesozoic, the nothosaurs were wiped out at the end of the Triassic.

Color palette used: “Same Old Song

Daily Paleo Art Month #10: Henodus

Much like the not-a-rabbit from a couple of days ago, this creature wasn’t a turtle. It was actually a member of a Triassic marine reptile group known as placodonts, which were closer related to plesiosaurs than anything resembling a chelonian. Henodus here came from the Late Triassic of Germany, around 225 million years ago, and reached lengths of about 1m (3.3ft).

Henodus is the only placodont found in non-marine deposits, living in brackish lagoons or perhaps even freshwater. There’s also evidence for keratin structures in its mouth that resemble baleen, which suggest it was some sort of filter-feeder.