Platecarpus

Platecarpus ("flat wrist") is an extinct genus of aquatic lizards belonging to the mosasaur family, living around 84–81 million years ago during the middle Santonian to early Campanian, of the Late Cretaceous period. Fossils have been found in the United States and possible specimens in Belgium and Africa. A well-preserved specimen of Platecarpus shows that it fed on moderate-sized fish, and it has been hypothesized to have fed on squid, and ammonites as well. Like other mosasaurs, it was initially thought to have swum in an eel-like fashion, although another study suggests that it swam more like modern sharks. An exceptionally well-preserved specimen of P. tympaniticus known as LACM 128319 shows skin impressions, pigments around the nostrils, bronchial tubes, and the presence of a high-profile tail fluke, showing that it and other mosasaurs did not necessarily have an eel-like swimming method, but were more powerful, fast swimmers. It is held in the Natural History Museum of Los Angeles County. Isotopic analysis on teeth specimens has suggested that this genus and Clidastes may have entered freshwater occasionally, just like modern sea snakes. Platecarpus had a long, down-turned tail with a large dorsal lobe on it, steering flippers, and jaws lined with conical teeth. A complete specimen LACM 128319 shows that it grew up to long. The platecarpine mosasaurs had evolved into the very specialized plioplatecarpine group by the end of the Cretaceous. The skull structure of Platecarpus is unique among mosasaurs. This genus is characterized by a short skull, and has fewer teeth than any other mosasaur (around 10 teeth in each dentary). LACM 128319 preserves matter within the sclerotic ring that may possibly be the retina of the eye. Small structures in the retina, each around 2 μm long and observed by scanning electron microspectroscopy, may represent retinal melanosomes preserved in their original positions. The respiratory tube is also known in LACM 128319, preserved as cartilaginous tracheal rings.