paleoart – Page 55 – Nix Illustration

Mirischia

Mirischia asymmetrica, a theropod dinosaur from the Early Cretaceous of Brazil (~112-99 mya). Although known only from its hips and a few other partial bones, these pieces were so well-preserved that it was given a genus name that translates to “wonderful pelvis”.

In life it would have been about 2m long (6′6″), but since the known fossil represents a subadult its full-grown size may have been a little bit larger. It was probably a member of the compsognathids, closely related to Compsognathus and Aristosuchus – which would make it the only representative of that family currently known from the Americas.

The ischium bones of Mirischia’s pelvis were oddly asymmetrical, hence the species name ‘asymmetrica’, with one side featuring a hole and the other side only having a notch in the same position. The fossil specimen also had thin-walled bird-like bones, and soft-tissue impressions of intestines and a posterior air sac.

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.

Synophalos

Synophalos xynos, a shrimp-like arthropod from the Early Cambrian of China (~515 mya). Thought to be closely related to stem-crustaceans like Waptia, it was about 2cm long (0.75″) and had a bivalved carapace with a segmented body ending in a forked tail.

Unlike any other known arthropods, however, it formed long “conga line” chains of up to twenty individuals, with the tail of each animal locking securely into the shell of the next. The function of the these chains is unknown, although suggestions include some sort of mating behavior, migration, or defense against predators.

Only one specimen was found completely on its own, and its slightly longer carapace suggests it may represent a different solitary life stage of these strange little creatures.

Turtle-jawed moa-nalo

The turtle-jawed moa-nalo (Chelychelynechen quassus) was a large flightless goose-like duck from the Hawaiian island of Kaua‘i. About 90cm tall (3′) and weighing around 7kg (15lbs), these birds and their relatives were descended from dabbling ducks and existed on most of the larger Hawaiian islands for the last 3 million years or so – before going extinct around 1000 years ago following the arrival of Polynesian settlers.

Chelychelynechen had an unusually-shaped bill, tall and broad with vertically-oriented nostrils, convergently similar to the beak of a turtle. It would have occupied the same sort of ecological niche as giant tortoises on other islands, filling the role of large herbivore in the absence of mammals.

Mauriciosaurus

Mauriciosaurus fernandezi, a polycotylid plesiosaur from the Late Cretaceous of Mexico (~94-89 mya). About 1.9m long (6′3″) with a flipper-span of 1.5m (4′11″), it’s known from a near-complete skeleton with preserved soft tissue impressions. The fossil shows evidence of rows of very tiny scales, the skin outlines of the flippers, and also a thick layer of insulating blubbery fat.

Its body shape in life would have been similar to modern leatherback turtles, roughly teardrop-shaped and hydrodynamic – much chubbier than most plesiosaur reconstructions had been previously depicting!

Josephoartigasia

The biggest known rodent of all time, Josephoartigasia monesi from the Pliocene and early Pleistocene of Uruguay, South America (~4-2 mya). Similar in size to a modern bison, it stood about 1.5m tall at the shoulder (4′11″) and weighed around 900kg (~2000lbs).

Despite looking like an extra-large capybara, it was only distantly related to the modern giant rodents. Its closest living relative is actually the much smaller pacarana.

Its 30cm long (12″) incisors could produce a large amount of bite force, and it may have used them in a similar manner to elephant tusks – rooting in the ground for food, stripping trees and branches, or defending itself from predators.

Herrerasaurus

One of the earliest known dinosaurs, Herrerasaurus lived during the Late Triassic (~231 mya) in what is now Argentina, South America. It was a fairly lightly-built bipedal carnivore, with the largest specimens reaching sizes of just over 5m long (16′4″).

The exact classification of herrerasaurids is still somewhat unclear, with different analyses putting them in different positions on the early dinosaurian family tree. They’re generally considered to at least be closely related to basal theropods – but a recent analysis that reshuffles dinosaur relationships suggests their resemblance to the theropods might be a result of convergent evolution, with them being the sister group to sauropods instead.