March 28, 2013
Ancient Ocean Dinosaur’s Unusual Teeth Betray European Origin
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April Flowers for redOrbit.com - Your Universe Online
Placodonts inhabited the flat coastal regions of the Tethys Ocean, in what is modern day Europe and China, for about 50 million years. These ocean-dwelling reptiles of the Triassic period had one truly distinctive feature — their unusual teeth. They had two rows of flattened teeth on the upper jaw — one on the palate and one on the jawbone — and just one set on the lower jaw that were ideal for crushing shellfish and crustaceans.
Scientists have been unclear about the evolutionary origins of the placodonts, but a new find in a 246-million-year-old sediment layer has shed light on not only the origin of the extinct marine dinosaur but also on its place in the tree of life.
Torsten Scheyer, a paleontologist at the University of Zurich, led the Swiss-German team of scientists that describes the skull found in Winterswijk, the Netherlands, as the earliest known form of placodonts. This specimen, a juvenile, lived about 246 million years ago and is exceptionally well persevered. The skull is around two centimeters in size with characteristics that set it apart from other placodont fossil specimens.
To date, the earliest placoconts have the group's trademark double row of crushing teeth lining the upper jaw. The flattened teeth, from which these animals receive their name, only appear in more derived placadonts.
"Unlike all the other placodonts discovered to date, the Winterswijk specimen has conical, pointed teeth instead of flattened or ball-shaped crushing ones," explains Scheyer, "which means the pointed teeth on the lower jaw slotted precisely into the gap between the palate and upper-jawbone teeth when biting."
The double row of teeth in the fossil skull is proof that this new find is, indeed, a placodont. Palatodonta bleekeri, the name given to the new specimen, specialized in gripping and piercing soft prey with their teeth.
"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.“¯According to the team, the formation of crushing teeth for a specialized diet of shellfish and crustaceans appear to have been later evolutionary developments for the placodonts.
The small skull of the Palatodonta bleekeri offers new information for the ongoing debate on where the placodonts originated. Previous specimens suggested an origin in the shelf sea areas of either China or Europe. However, the considerable age of the new specimen seem to confirm the European origin of placodonts. Scheyer and his team are hoping to find more exciting fossils in Winterswijk that will reveal more about the evolution of this species.
The findings of this study were published in a recent issue of Nature Communications.