Class: Mammalia

Order: Condylarthra

Family: Hyopsodontidae

Genus: Hyopsodus

Species: Hyopsodus fastigatus, H. lepidus, H. loomisi, H. lysitensis, H. markmani, H. mentalis, H. minor, H. minusculus, H. paulus, H. pauxillus, H. sholemi, H. simplex, H. tonksi, H. uintensis, H. walcottianus, H. wardi, H. wortmani, H. wardii

When and where Hyopsodus lived: Age: Early to late Eocene – 55.8 million years to about 45 million years Distribution: North America, Europe and Asia

General Description

Hyopsodus thrived during most of the early and middle Eocene specifically in the North American western Rocky Mountain region from present-day Saskatchewan to New Mexico (Gazin, 1968).  This small mammal, ranging from rat-size species to larger raccoon-size species, achieved its highest population levels during the warm, subtropical environments of the early and middle Eocene.  By the late Eocene, Hyopsodus populations waned during cooler, arid, savannah-like conditions, and it was extinct prior to the end of the Eocene (Ui3).  During the early and middle Eocene, however, Hyopsodus was the most characteristic mammal well surpassing all other genera in numbers.  In the Bridger Formation of Wyoming, Hyopsodus represents over 60% of the fossil animals found.  As many as three species can be found in the same fossil beds.

Hyopsodus had an odd body shape very much like that of a weasel or dachshund.  It had a long, slender body and relatively short legs with five-toed claws and a long tail, sometimes jokingly called a tube-sheep or hot dog on legs.  It’s somewhat muscular chest tells of a propensity for digging or rooting and it was likely an herbivorous ground and tree dweller.  It may also have been a swimmer as it is often found in near shore lake deposits of the Bridger Formation in Wyoming.  Complete articulated skeletons are known from the Green River Formation, which is a lacustrine geologic formation (lake deposits).

First identified by Leidy in 1870, Hyopsodus was a Condylarth, a generalized group of  now extinct, ungulate mammals that lived in the Paleocene and Eocene.  However it is still debated among paleontologists on whether the condylarths are a related group .  It likely would have competed ecologically with the earliest modern even-toed ungulates, the artiodactyls (hippos, deer, antelope, pigs, giraffes and peccaries) and odd toed ungulates the perissodactyls (horses, tapirs and rhinos).  The early ungulates were rather small and similar in size or a little larger than Hyopsodus.



Hyopsodus had a full compliment of 44 teeth with simple incisors, canine and first premolars (which was single rooted) (Gazin 1968)









Gazin, C. Lewis 1968. A Study of the Eocene Condylarthran Mammal Hyopsodus, Smithsonian Miscellaneous Collections, Volume 153, Number 4.

Prothers, Donald R. After the Dinosaurs –Tthe Age of Mammals, Indiana University Press

Rose, Kenneth The Beginning of the Age of Mammals, The John Hopkins University
 Press, 2006

Authored by Carmen Nue

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