parareptilia – Nix Illustration

Hwiccewyrm

Hwiccewyrm trispiculum lived during the late Triassic, around 208-202 million years ago, in what is now England. It was one of the last known members of the procolophonid family, a lineage of small stocky lizard-like animals that had been widespread and abundant earlier in the Triassic.

(Traditionally procolophonids are classified as parareptiles, but some recent studies suggest this group is paraphyletic or polyphyletic, with some “parareptiles” potentially nesting within the diapsids instead.)

Measuring around 30cm long (~1′), Hwiccewyrm had wide flaring cheek bones ornamented with large spines, and like some other procolophonids it may also have had bony scute armor on its body. Its large blunt teeth suggest it was feeding on particularly tough foods such as fibrous vegetation or hard-shelled invertebrates.

Eudibamus

Eudibamus cursoris, a bolosaurid from the Early Permian of Germany (~284-279 mya).

Although very lizard-like in appearance, this animal was actually part of a completely extinct group known as parareptiles – a diverse group of early sauropsids who were once thought to be the ancestors of turtles, but are now considered to instead be the evolutionary cousins to the true reptiles.

With a total length of about 25cm long (8-10″), the structure and proportions of its limbs suggest it could run fast on its hind legs, making it one of the earliest known examples of bipedal locomotion. Since its teeth were adapted for a herbivorous diet, it wasn’t using its speed to chase down prey but was instead probably sprinting away from predators.

But unlike the sprawling running of some modern lizards, Eudibamus may have been capable of holding its legs in a more upright position directly under its body, convergently evolving a more energy-efficient posture similar to that of later bipedal animals like dinosaurs.

Colobomycter

Colobomycter pholeter, a parareptile from the Early Permian of Oklahoma, USA (~289 mya). Although known only from partial skull fossils, its full size was probably around 30cm long (1′).

It had huge fangs at the front of its jaws, along with a few other enlarged teeth further back, all with serrated edges that show it was clearly a predator. What exactly it was feeding on with this unusual tooth arrangement is unknown – but proposed ideas include piercing through hard-shelled arthropods, or stabbing into smaller vertebrate prey.

Bunostegos

Bunostegos akokanensis, from the Late Permian of Niger (~260 mya). About 2.5m long (8′2″), similar in size to a modern cow, it was a member of a group known as the pareiasaurs – stocky herbivorous reptile-relatives with osteoderm armor in their skin and knobbly bony nodules on their skulls.

The anatomy of its limb bones suggest it walked fully upright, with its legs held vertically under its body. This sort of posture has independently evolved multiple times in different tetrapod lineages, but Bunostegos is one of the earliest known examples.