Paleo Profile: The Purgatoire River’s Whale Fish

Rhinconichthys as restored by Robert Nicholls.
Rhinconichthys as restored by Robert Nicholls.

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.

The skull of Rhinconichthys purgatoirensis. From Schumacher et al., 2016.
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Meaning: Rhinconichthys is a tribute to an unpublished name coined by 19th century paleontologist Gideon Mantell for specimens of this genus found in England, while purgatoirensis for Colorado’s Purgatoire River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

References:

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

Schumacher, B., Shimada, K., Liston, J., Maltese, A. 2016. Highly specialized suspension-feeding bony fish Rhinconichthys (Actinopterygii: Pachycormiformes) from the mid-Cretaceous of the United States, England, and Japan. Cretaceous Research. doi: 10.1016/j.cretres.2015.12.017

Previous Paleo Profiles:

The Unfortunate Dragon
The Cross Lizard
The South China Lizard
Zhenyuan Sun’s dragon
The Fascinating Scrap
The Sloth Claw
The Hefty Kangaroo
Mathison’s Fox
Scar Face
The Rain-Maker Lizard
“Lightning Claw”
The Ancient Agama
The Hell-Hound
The Cutting Shears of Kimbeto Wash
The False Moose
“Miss Piggy” the Prehistoric Turtle
Mexico’s “Bird Mimic”
The Greatest Auk
Catalonia’s Little Ape
Pakistan’s Butterfly-Faced Beast
The Head of the Devil
Spain’s Megatoothed Croc
The Smoke Hill Bird
The Vereda Hilarco Beast
The North’s Sailback
Amidala’s Strange Horn
The Northern Mantis Shrimp
Spain’s High-Spined Herbviore
Wucaiwan’s Ornamented Horned Face
Alcide d’Orbigny’s Dawn Beast
The Shield Fortress
The Dragon Thief

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