2/8/2015
Many sea-monster-like fossils have been discovered near Los Angeles.
Great Sea-Dragons by Thomas Hawkins
They are called mosasaurs. Plesiosaurs and tylosaurs are types of mosasaurs. The famous paleo-artist Charles R. Knight drew and painted reconstructions of the animals for the Los Angeles County Natural History Museum.
Mosasaurus painting by Charles R. Knight
Years later, I was asked to draw bone maps of the fossilized Mosasaur skeletons for the Museum. New discoveries have led to new knowledge about the beasts. Their remains are on display in the Museum's new Mesozoic Dinosaur Hall.
Plesiotylosaurus bone map by Michelle Leveille of Artifact Graphics, for the Natural History Museum of Los Angeles County.
Mosasaurs may be in the dino hall, but technically they were not dinosaurs. (Neither were pteranodons.) They were reptiles. Dinosaurs are reptiles that walked with their feet below their hips, among other things. Neither marine reptiles nor flying reptiles walked with their feet below their hips, so they were not dinosaurs.
A tylosaurus, which is a type of mosasaur,
described by Henry Fairfield Osborn in 1899.
Plotosaurus bone map by Michelle Leveille of Artifact Graphics, for the Natural History Museum of Los Angeles County.
Scientists who discovered the fossils in the late 1800s interpreted bits of cartilage impressions along the back as evidence of an undulating dorsal fin.
Tylodon by Charles R. Knight
Later discoveries caused paleontologists to realize that the cartilage was part of a solid dorsal ridge, somewhat like the dorsal fin on a shark.
Platecarpus bone map by Michelle Leveille of Artifact Graphics for the Los Angeles County Natural History Museum.
The longer-necked mosasaurs were the plesiosaurs. When I think of these, I always think of the Loch Ness Monster.
Nessie
The morenosaurus was a type of plesiosaur. Here is a morenosaurus bone map. The Los Angeles County Natural History Museum has the fossilized remains of two morenosaurs: an adult and a juvenile. One was found in Fresno County, in Central California.
Morenosaurus with gastroliths, bone map by Michelle Leveille of Artifact Graphics, for the Los Angeles County Natural History Museum.
The adult had fossilized gastroliths in its gizzard. These are like stones in the stomach for grinding food. They are shown in orange above.
Polycotylus was another type of plesiosaur. Unlike many reptiles which lay eggs, there is fossil evidence that this marine reptile gave live birth.
Polycotylus bone map by Michelle Annette Leveille for the Los Angeles County Museum of Natural History
and in our other blog posts.
Frilled To Meet You is about Ceratopsians such as triceratops,
Avian Dinosaur Bone Maps (archaeopteryx) and
You Need To Get Into Theropod is about Theropods such as T. rex,
and Pterodactyls! is about Pterosaurs such as quetzalcoatlus.
More are coming soon.
I welcome your comments!
- Michelle Annette Leveille
