Huehuecuetzpalli

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.

Huehuecuetzpalli mixtecus here lived in east-central Mexico during the mid-Cretaceous, about 105 million years ago. About 25cm long (10″), it was part of an early branch of the iguanomorph lineage, related to the ancestors of modern lizards like iguanas, chameleons, and agamids.

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.

Eons Roundup 4

Some more recent commission work for PBS Eons!

The entelodonts Eoentelodon and Brachyhyops, from “The Hellacious Lives of the Hell Pigs”
https://www.youtube.com/watch?v=trJpxwMGoCw


The early ichthyosaur Tholodus and the mosasaurPluridens, from “When Ichthyosaurs Led a Revolution in the Seas”
https://www.youtube.com/watch?v=V342aXQs9XY


The early bats Onychonycteris and Icaronycteris, from “When Bats Took Flight”
https://www.youtube.com/watch?v=zWeYCULC0UQ

Island Weirdness #26 – The Mauritian Giant Skink

Along with its unique birds, 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 large skink, 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

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.