Thliptosaurus (meaning "compressed lizard") is an extinct genus of small kingoriid dicynodont from the latest Permian period of the Karoo Basin in KwaZulu-Natal, South Africa. It contains the type and only known species T. imperforatus. Thliptosaurus is from the upper Daptocephalus Assemblage Zone, making it one of the youngest Permian dicynodonts known, living just prior to the Permian mass extinction. It also represents one of the few small bodied dicynodonts to exist at this time, when most other dicynodonts had large body sizes and many small dicynodonts (such as Diictodon) had gone extinct. The unexpected discovery of Thliptosaurus in a region of the Karoo outside of the historically sampled localities suggests that it may have been part of an endemic local fauna not found in these historic sites. Such under-sampled localities may contain 'hidden diversities' of Permian faunas that are unknown from traditional samples. Thliptosaurus is also unusual for dicynodonts as it lacks a pineal foramen, suggesting that it played a much less important role in thermoregulation than it did for other dicynodonts. While the name literally translates to "compressed lizard", referring to the severely crushed and flattened skull of the only known specimen, it also alludes to the Biblical thlipsis, a time of tribulation and hardship preceding the End Times, alluding to the existence of Thliptosaurus just before the mass extinction at the end of the Permian, also known as the Great Dying.
Description Thliptosaurus was a small dicynodont (skull length of only 8.6 centimetres (3.4 in) long), but it displays several characteristics indicative of maturity in dicynodonts. Only the skull is known, but like other related dicynodonts it would have been a squat, sprawling quadruped with a short tail and a large head with a tortoise-like beak. Thliptosaurus appears completely toothless, lacking even in the distinctive tusks found in some other dicynodonts (including the closely related Dicynodontoides), although teeth may be obscured by the lower jaw if they are present. The post cranial skeleton is unknown, but probably resembled that of other kingoriids, such as Kombuisia.
Skull The skull of Thliptosaurus is fairly typical for dicynodonts, being broad at the back with very large temporal fenestrae, with a much shorter snout that gently tapers to a blunt point. The nostrils aren't visible on the specimen, meaning they must have been placed on the very front of the snout facing forwards, and not on the sides. The tuskless caniniform process of the maxilla is prominent and sits well forward of the eyes. The front margin of the caniniform process is long and slopes gently downwards from the front, while the back margin rises steeply up to meet with the zygomatic arch below the eyes. The caniniform process is similar to that of Dicynodontoides, but is lacking the tusks found in that genus. No other teeth are visible on the specimen, but as much of the maxilla is covered by the lower jaw it is impossible to be sure. The nasal bones sport three prominent well-pitted bosses with a rough, rugose texture. These bosses resemble those of Dicynodontoides, with two flaring laterally over the front of the snout, split by the single fused premaxilla, and meeting with a third medial boss behind them. The intertemporal region, or bar, is unusually wide for a kingoriid, composed of the broad frontal bones in the front and the flat exposed parietal bones behind them, each contacting with the single preparietal (a unique bone found in dicynodonts and some other therapsids) just behind the eyes. Very unusually for a dicynodont, Thliptosaurus has no visible pineal foramen, and the suture between the parietals appears uninterrupted for their whole length. Even if the parietal foramen existed and was obscured by deformation during fossilisation, it would have to have existed as a very thin slit between the parietals that did not contact the preparietal, which itself would be a highly unusual condition for a dicynodont. However, comparisons with other kingoriids indicate that the absence of the pineal foramen is likely a genuine feature. Unfortunately, the palate is mostly obscured by the tightly occluded lower jaw, leaving only the pterygoids and the basicranium (the part of the skull underneath the braincase) readily visible. The pterygoids are relatively long and narrow, and straight for much of their length like those of Compsodon and Dicynodontoides. The two pterygoids meet at a median pterygoid plate positioned relatively far back on the skull, which also results in the rami that contact the quadrate being angled at approximately 60 degrees to the skull's long axis. The occiput is poorly preserved and few details can be discerned, but the overall structure appears typical for dicynodonts, as is the basicranium.
Mandible
The mandibular symphysis of the dentaries is long, creating a long, flattened shovel-like beak tip. The rest of the jaws is otherwise roughly v-shaped, as is typical for dicynodonts. The dentary has a tall plate on its sides that obscures the external mandibular fenestra, an unusual condition amongst dicynodonts. The coronoid process (a site for jaw muscle attachment) is unusually short compared to that of other kingoriids. The dentary also has a short horizontal shelf about halfway up its side, representing a greatly reduced lateral dentary shelf (a site of attachment for the external lateral adductor, an important jaw muscle in dicynodont feeding). The reflected lamina of the angular is relatively short, surrounded by a concave lateral exposure on each side. The articular has a curved, convex upper surface that contacts the condyles of the quadrate and extends beyond them, facilitating palinal (backwards) motion of the lower jaw, typical of dicynodonts.
… excerpt ends here. Continue reading the full article.
