Name Meaning: Flat Wrist
Geologic Era: Cretaceous
Location Found: Texas
Estimated Range: Most fossils found in USA, but also found worldwide
Size: 4.3 meters long
Extinction: 80 million years ago
Platecarpus is represented here with a limb bone, most likely a humerus. This bone is particularly well preserved, with the articulating surfaces mostly intact, if a little bit worn. While it may not look much like a human humerus, mosasaur limbs were primarily made of phallanges (finger bones), while the other bones such as the radius, ulna, and humerus tended to be more compacted and reduced.
For a mosasaur, Platecarpus was on the smaller side at only a little over 4 meters in length. This small size meant that Platecarpus stood a better chance of preservation than larger animals, which is why it is rather well represented in the fossil record. Most of the Platecarpus fossils documented come from the Midwestern to Southern United States, in what was once the Western Interior Seaway. Platecarpus would have shared this environment with other, much larger mosasaurs, large sharks, and elasmosaurs. Platecarpus itself probably fed on anything smaller than it was, putting fish and smaller sharks on the menu, and possibly juvenile mosasaurs and elasmosaurs as well.
Platecarpus helped paleontologists gain insight into the true appearance of mosasaurs. Until discoveries on Platecarpus and other related species, it was assumed that mosasaurs had an eel-like tail. A Platecarpus specimen was found, however, that had an impression of a tail fluke preserved. This showed a tail structure closer to icthyosaurs than to terrestrial reptiles, from which Platecarpus and its relatives were likely descended.
What this meant for an animal like Platecarpus was that it would have been exceptionally fast in the water, easily able to outswim larger mosasaurs. This meant that Platecarpus would have been difficult prey for large mosasaurs, as they would not be able to keep up with Platecarpus over a long chase. Sharks would have better odds of catching Platecarpus, being even better adapted to the water than it was.
While somewhat snakelike in appearance, mosasaurs such as Platecarpus’ closest living relatives are monitor lizards, such as the Komodo dragon. Soft tissue preservation indicates that Platecarpus had two functioning lungs, where a snake only has one. This was deduced from remains of a trachea (or more specifically, the cartilage rings of a trachea) that showed evidence of branching into two halves in the anterior thorax.
This condition is seen in animals with two lungs, as each trachea half, or primary bronchus, leads to a lung. As a marine reptile, Platecarpus probably had a metabolism similar to cold blooded animals, and would probably regurgitate or pass harder parts like shells. Platecarpus might have confined itself to softer foods when possible, but was probably also an opportunistic predator.
Western Interior Seaway Diagram: Public Domain, https://commons.wikimedia.org/w/index.php?curid=69467
Skeleton: By MCDinosaurhunter – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=41268827
Life Restoration: Life Restoration: By Creator: Dmitry Bogdanov – firstname.lastname@example.org, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=11151274