Bipedal running has convergently evolved multiple times in squamate reptiles, known in over 50 modern species – and fossil evidence shows this is nothing new, with lizards repeatedly developing the ability to sprint on their hind legs for well over 100 million years.
Its limb proportions indicate it would have been a bipedal runner, making it one of the earliest known examples of this type of locomotion in lizards. Its skull also had some features convergent with varanids, suggesting it may have had a similar sort of active-pursuit-hunting ecology.
The modern tuatara is the only living representative of an entire major lineage of reptiles known as sphenodontians – an evolutionary “cousin” group to all lizards and snakes, last sharing a common ancestor with them over 240 million years ago.
And during the Triassic and Jurassic these lizard-like animals were a widespread and diverse bunch, found worldwide and occupying many of the ecological roles that were later taken over by true lizards. They ranged from tiny insectivores to omnivores, relatively large herbivores, and specialized shell-crushers – and some even adapted to a fully aquatic fish-eating lifestyle.
Pleurosaurus ginsburgi here lived during the Late Jurassic, about 150-145 million years ago, in the warm shallow seas and lagoons that covered most of Europe at that time. Fossils of this particular species are known from southern France, with the closely related Pleurosaurus goldfussi found in both the same region and the German Solnhofen Limestone.
These swimming sphenodontians could grow to around 1.5 in length (~5′), with elongated bodies, pointed triangular snouts with retracted nostrils, short flipper-like forelimbs, and especially long eel-like tails. Soft tissue impressions also show scaly skin covering their bodies and a “frill” running along the top of the tail.
Fossils of at least a dozen different species of these predatory marine reptiles have been found in the area, and they seem to have all been occupying different ecological roles to avoid being in direct competition with each other. Many had conical piercing teeth adapted for gripping onto slippery soft-bodied prey, but others had rounded blunt teeth for crushing hard shells, and some even had sharp shark-like teeth for tearing flesh.
This 7m long (23′) mosasaur was part of the plioplatecarpine lineage, but it had uniquely long and narrow jaws with pointy interlocking teeth and highly retracted nostrils. Its snout shape resembled that of a crocodilians like modern gharials more than any of its short-skulled close relatives, and it was probably specialized for a similar diet of small fast-moving fish.
Along with its uniquebirds, Mauritius was also home to many endemic reptile species. In the absence of terrestrial mammals giant tortoises were the largest herbivores on the island, and various geckos, skinks, and snakes helped to fill out the rest of the vertebrate ecosystem.
Leiolopisma mauritiana was a very largeskink, one of the biggest ever known to have existed with a total length of around 80cm (2′7″). Its ancestors originated in Australasia, over 5600km away (~3500 miles) at least 3-4 million years ago – and they must have endured a particularly long ocean rafting journey without any island hopping stops, since none of the other islands along that route seem to have ever had populations of similar skinks.
It probably lived in rocky areas, possibly also being capable of digging burrows, and would have eaten an omnivorous diet of seeds, fruits, invertebrates, and smaller lizards and birds.
By the early 1600s it was already extinct, very soon after the arrival of humans, probably due to predation from invasive mammals like rats. However, its half-sized close relative Leiolopisma telfairii does still survive on rat-free Round Island a short distance to the north of Mauritius, and recent conservation efforts have been rebuilding its population and setting up new colonies on other nearby small islands.
Barbaturex morrisoni, a large herbivorous lizard which lived about 40-37 million years ago during the Eocene. Known from Myanmar in Southeast Asia, it’s estimated to have reached lengths of 1.4-1.8m (4′7″-5′10″) and was closely related to modern spiny-tailed lizards.
It had a row of bony knobs along the edges of its lower jaw, which may have supported some sort of display structure. I’ve given it some fleshy double-dewlaps here, and a spiky tail similar to its relatives, but since it’s only known from fragmentary fossils these features are pretty speculative.
Surprisingly Barbaturex was much bigger than a lot of the herbivorous ungulate mammals around at the time, and was also larger than most of the local carnivores – a very different situation to modern ecosystems, where even the biggest plant-eating lizards are still smaller than ungulates.