It is pretty unusual to see fish in the UCMP. It’s not that we don’t have any fish specimens — we have over a million fossilized fish fragments. It’s just that none of our museum scientists focus on fish, and so the museum’s fish parts tend to stay in the cabinets. But this past summer, Ralph Stearley of Calvin College visited the UCMP, and he did a little fishing.

Ralph pulled some spectacular specimens from the murky depths of the cabinets. The two specimens shown here are exceptional — nearly all the bones are in place, and one of the specimens even has imprints of scales! It is really rare for fish to fossilize like this — most of the time, fish break apart into individual bones and tiny scales.

These two specimens are salmonids. They are related to salmon, char, and trout — their closest living relative is probably the Dolly Varden. They lived 15-10 million years ago, in the ancient lakes that back then dotted Western Nevada. They were collected by UCMP curator Howard Hutchison in 1975, in an area called Stewart Valley. This site contains fossilized vertebrate, insect, fish, and plant material — it is rare to find so much taxonomic diversity in one place. Hutchison and his colleagues really got a sense of the entire fauna that once inhabited the area.

Ralph was excited to find these salmonid specimens in our collection — he and his collaborator, Gerald Smith of the University of Michigan, study the biogeographic history of salmonid fish. These specimens provide evidence that salmonids once lived in Western Nevada. For Ralph and Gerald, these fish are definitely keepers.

Not to be rude, but what in the world is a rudist? Well, rudists are invertebrates, and they lived in the world’s oceans during the late Jurassic and the Cretaceous, about 150-65 million years ago; they are now extinct. They are bivalves — the name means “two shells.” Today’s familiar bivalves, clams and mussels, have two shells that are more or less symmetrical. But rudists were a bit unusual: their two shells were very different from each other. One shell was either conical or coiled, and it was attached to the ocean floor (or neighboring rudists). The other shell sat on top, like a little hat. The organism lived inside. They were probably filter feeders, feeding on plankton in the water, like many other bivalves today.

Rudists would grow on top of one another and form rudist reefs. They were the major reef-building organisms of their time — corals weren’t so abundant back then. Reefs are really important habitats for other marine organisms, like fish and crustaceans. So rudists played an important role in the ancient ocean.

So if rudists were so ecologically important, how did they get stuck with such an odd name? Lamarck dubbed them rudists in 1819, but it’s a little unclear what he meant. The Latin word rudis means rude, raw, or uncultivated. The Latin word rudus means rubble, or broken stone — specifically, the stones that made up Roman roads. Rudists do seem sort of coarse and unrefined, and they do look an awful lot like stones. But who knows what Lamarck was thinking.

This fossil rudist was found in Chiapas, Mexico. Learn more about rudists on the UCMP’s rudist page.

Imagine you are driving down I-5, just north of Bakersfield, in California’s hot and dusty central valley. Except that it’s the Cretaceous Period, 80-65 million years ago, and the central valley is actually an inland sea. And instead of seeing cows standing by the side of the highway, you see mosasaurs swimming through the salty water.

Mosasaurs were marine reptiles that lived during the late Cretaceous, in oceans all over the world. They had fins on their long bodies, and sharp teeth in their long jaws. They ate fish, ammonites, and possibly even other mosasaurs. Lucky for us, mosasaurs are now exctinct — they died out with the dinosaurs at the end of the Cretaceous.

This particular fossil was found in 1937 by a high school student named Allan Bennison. Just the previous year, Bennison found the first dinosaur fossil in California. He used to ride his bicycle from his home in the San Joaquin Valley to the Moreno formation, where this fossil was found, a distance of 35 miles. Bennison went on to study at Berkeley, where he earned a degree in paleontology in 1940. This species was named after him: Plotosaurus bennisoni.