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Temporal range: Late Oligocene
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Eutheria
Order: Desmostylia
Family: Desmostylidae
Genus: Cornwallius
Hay 1923
Species: C. sookensis
Binomial name
Cornwallius sookensis
Cornwall 1922

Cornwallius is an extinct herbivorous marine mammal of the family Desmostylidae. Cornwallius lived along the North American Pacific Coast from the Early Oligocene (Chattian) through the Oligocene (28.4 mya—20.6 Mya) and existing for approximately 7.8 million years.[1][2]

The type locality is the Chattian Sooke Formation, Vancouver Island, British Columbia, Canada (48°24′N 123°54′W / 48.4°N 123.9°W / 48.4; -123.9, paleocoordinates 48°00′N 115°00′W / 48.0°N 115.0°W / 48.0; -115.0).[2]

Cornwallius was named by Hay 1923. Its type is Desmostylus sookensis, named by Cornwall 1922 and recombined to Cornwallius sookensis by Hay 1923.[3]

Fossils have been discovered from Baja California Peninsula, Oregon and Washington coasts, and Unalaska Island.[4]


  1. ^ Cornwallius in the Paleobiology Database. Retrieved June 2013.
  2. ^ a b Muir Creek (Oligocene of Canada) in the Paleobiology Database. Retrieved June 2013.
  3. ^ Cornwallius sookensis in the Paleobiology Database. Retrieved June 2013.
  4. ^ Beatty 2006b