A research team led by Dr. Torsten Scheyer of the University of Zurich has discovered the skull of an early ancestor to the placodonts, a group of marine reptiles that thrived throughout the Triassic period over 245 million years ago. The newly discovered species,Palatodonta bleekeri, found in Winterswijk, the Netherlands has been identified as a juvenile of the superorder Sauropterygia.
Placodonts, also classified as Sauroptergyia, are commonly distinguished by their two rows of upper teeth on the palate and the jawbone, with a single row of teeth on the lower jaw. Typical placodonts have large, flattened teeth, while the earliest placodonts’ teeth are more rounded.
Palatodonta bleekeri, whose skull was a mere two cm in diameter, has a similar dental arrangement, confirming its relation to the placodonts, but with rows of pointed, interlocking teeth. The dental structure likely provides a link between the common flat-toothed placodonts and diapsids, which display the ancestral pointed teeth. The discovery offers important evidence to support the consensus that Sauroptygeria are grouped within Diapsida.
Palatodonta is not a juvenile of any known placodont, as placodonts do not show development of tooth shape throughout their lifetime. Instead, it is likely a stem representative with a very different diet and lifestyle from other placodonts.
Pointed teeth are better suited for sifting through sediment, and for gripping and piercing soft prey. Flattened teeth, on the other hand, are ideal for crushing hard-shelled prey such as shellfish and crustaceans. With this new link, it can be inferred that the dentition in Palatodonta represents an intermediate condition in the developmental transition from interlocking, piercing teeth to extreme crushing dentition.
The evolutionary origins of the placodonts has been, until now, unclear. Previously speculated to have originated in the shelf sea regions of present-day China, the discovery now provides solid evidence that the placodonts originated in Europe and the western Middle East, and then spread eastward. This area was also home to over 60 known species of marine reptiles in the Middle Triassic period, marking the region as a “biodiversity hotspot,” according to Scheyer’s team.
Read the entire placodont study in the journal Nature Communications.
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