June 2017 – Nix Illustration

Chinlestegophis

The newly-named Chinlestegophis jenkinsi, in the style of last year’s Amphibian August illustrations.

Living during the Late Triassic of Colorado, USA, (~220 mya), this 30cm long (1′) amphibian had a skull showing a mixture of features shared with both temnospondyls and modern caecilians – providing a vital “missing link” in their evolutionary history. Previously the oldest known caecilian-relative was the Jurassic-aged Eocaecilia, which already had much more modified anatomy making it harder to definitively link to other known groups.

Chinlestegophis seems to have been part of the stereospondyl branch of the temnospondyls – and an unexpected side effect of adding caecilians into this group is that many temnospondyls could now potentially also be classified as true members of Lissamphibia.

An example family tree showing this new version of amphibian relationships. If we define Lissamphibia as including all living amphibians and their extinct relatives back to their last shared common ancestor, then everything within the grey box is a lissamphibian!

Of course, this is still just one hypothesis of amphibian evolution among several other competing ideas. Maybe it’s right, maybe it isn’t – as always, we need more fossil evidence! – but it’s certainly an interesting and surprising new development in the ongoing saga of “what are lissamphibians? we just don’t know”.

2023 Update: …But the discovery of Funcusvermis suggests Chinlestegophis isn’t a caecilian at all, but instead an unrelated case of convergent evolution!

Ambulocetus

Ambulocetus natans, the Eocene “walking whale” – who might not actually have been able to walk at all!

A study published in 2016 suggests this early cetacean was actually fully aquatic and unable to support its own weight on land. So here’s an updated version compared to the Ambulocetus I did a couple of years ago.

Pakasuchus

Pakasuchus kapilimai, a notosuchian crocodyliform from the mid-Cretaceous of Tanzania (~105 mya). This 50cm long animal (1′8″) had an elongated body and relatively long limbs, and would have been an active terrestrial predator chasing after fast-moving small prey like insects.

The bony osteoderms on its body were much smaller and sparser than those found on most of its relatives – except for its tail, which was still heavily armored.

It also had some of the most complex teeth of all known crocodilians, with surprisingly mammal-like ‘canines’ and ‘molars’ that gave it the ability to chew its food.

Geikia

Geikia elginensis, a dicynodont synapsid from the Late Permian of Scotland (~254-252 mya). Known only from a single skull discovered in the 1890s, it would have measured around 50cm long and was closely related to South African forms like Bulbasaurus.

It had an unusually shortened snout and forward-facing eyes – sort of like a pug with a beak – and a pair of protruding nasal bosses on its snout. It was probably a selective browser, biting off small pieces of vegetation at a time, and its large eyes and stereoscopic vision suggest it may have been nocturnal.