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Rhinconichthys as restored by Robert Nicholls.

Paleo Profile: The Purgatoire River’s Whale Fish

If you could take a dip in the Cretaceous sea that covered Colorado around 92 million years ago, you might spot what would initially look like a pretty plain fish. Around six feet long, or a comparable to a mid-sized tuna, the streamlined swimmer would have a bullet-like profile. Until it opened its mouth. In one swift motion the long lower jaw would snap open, creating a planktivorous parachute to catch some of the ocean’s smallest morsels.

We know such a fish existed thanks to fossils discovered by paleontologist Bruce Schumacher and described with his colleagues earlier this year. They named the filter-feeder Rhinconichthys purgatoirensis, a new species of a genus that had previously been found in England and Japan. The Colorado species is significantly older than its evolutionary siblings, however, punting Rhinconichthys back in time as well as establishing that these fish were present in the Western Hemisphere through much of the Cretaceous.

Not that Rhinconichthys was the only filter-feeding fish around. Along with other research that has identified and named the giant Bonnerichthys and planktivorous sharks, Schumacher and coauthors point out that there was a wide array of filter-feeding fish throughout Cretaceous time. This is about more than species counts. Where there are big planktivores, there has to be enough plankton for them to eat. Before mantas, before whales, fish such as these were the largest creatures to strain the seas.

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The skull of Rhinconichthys purgatoirensis. From Schumacher et al., 2016.

Fossil Facts

Name: Rhinconichthys purgatoirensis

Meaning: Rhinconichthys is a tribute to an unpublished name coined by 19th century paleontologist Gideon Mantell for specimens of this genus found in England, while purgatoirensis for Colorado’s Purgatoire River drainage where the new species was found.

Age: About 92 million years old.

Where in the world?: Rhinconichthys purgatoirensis was found in eastern Colorado, with other species turning up in England and Japan.

What sort of critter?: A filter-feeder belonging to an extinct group of ray-finned fish called pachycormiformes.

Size: Estimated at over six and a half feet in length.

How much of the creature’s body is known?: Rhinconichthys purgatoirensis is represented by a skull, pectoral girdles, and pectoral fins


Friedman, M., Shimada, K., Martin, L., Everhart, M., Liston, J., Maltese, A., Triebold, M. 2010. 100-million-year dynasty of giant planktivorous bony fishes in the Mesozoic seas. Science. doi: 10.1126/science.1184743

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