The origin of one of the first groups of marine reptiles, the Placodonts, is now becoming clear, thanks to the new discovery of a fossil skull in the Netherlands. The 246-million-year-old skull, discovered in the region that was once the Tethys Ocean, shows that these highly specialized marine reptiles, one of the earliest saurians, very likely originated in Europe.
The placodonts lived for about 40 million years or so in the flat coastal regions of the Tethys Ocean, from around 250 million years ago to 210 million years ago. Possessing their “trademark” crushing teeth, they fed primarily on shellfish and crustaceans, but were likely opportunistic predators as well. The distinctive features of these teeth really make them stand out in the fossil record; “the upper jaw had two rows of flattened teeth – one on the palate and one on the jawbone – while the lower jaw only had one set of teeth ideal for crushing shellfish and crustaceans.”
Despite what we know about them, their origins have been somewhat unclear. But with this discovery of a juvenile’s skull in a 246-million-year-old sediment layer those origins are now becoming more clear. The new fossil skull found in Winterswijk (Netherlands) is very clearly the earliest form of all known placodonts, the ancestor of all of the later forms. And the fossil’s exceptional state of preservation really makes it stand out from previous finds, all of the characteristics of the 2-centimeter-long skull are apparent in fine detail
“Unlike all the other placodonts discovered to date, the Winterswijk specimen has conical, pointed teeth instead of flattened or ball-shaped crushing ones,” explains Torsten Scheyer, a paleontologist at the University of Zurich. “Which means the pointed teeth on the lower jaw slotted precisely into the gap between the palate and upper-jawbone teeth when biting.”
“The group’s trademark double row of teeth in the upper jaw is proof that the new find is actually a placodont. According to the researchers, the teeth of Palatodonta bleekeri, the scientific name given to the Winterswijk specimen, were specialized in gripping and piercing soft prey.”
“The double row of teeth in the new find combined with its considerable age lead us to conclude that it is a very early placodont, from which the later forms developed,” says Scheyer. The formation of crushing teeth and the specialization of a diet of shellfish and crustaceans thus developed later within placodont evolution.
This Palatodonta bleekeri skull is also helping to clarify the origins of the placodonts. Earlier finds had already narrowed down their likely-place-of-origin to the shelf sea areas off of either present-day Europe or China. With the very old age and basal form of this fossil found in the Netherlands, it is looking very likely that they originated in Europe.
It’s interesting to imagine the climate and time period that these animals lived in. 248 million years ago the world was beginning to emerge from the dead zone that followed the End-Permian mass extinction event. But the climate then was still pretty extreme, being “generally hot, arid, rainless and dry, and deserts were widespread.” The poles remained somewhat temperate though, offering a refuge for many life forms. There was an enormous loss of biodiversity during the End-Permian extinction event though, that took upwards of 30 million years to recover from, so the fauna that was present at the time was relatively homogenous. The tropical regions at the time were largely devoid of “complex” life, being inhabited mostly by animals such as mollusks.
In some ways, the early-Triassic may serve as a useful proxy to imagine the future effects of modern anthropogenic climate change. A shift towards the poles, mass extinctions, desertification, boom-and-bust cycles caused by population-booms and resource exploitation, and mass migrations/increased competition.
Source: University of Zurich
Image Credits: Rekonstruktionszeichnung: Jaime Chirinos; UZH; Triassic via Wikimedia Commons