Mesohippus sp & Equus sp

Class Mammalia, Order Artiodactyla, Family Equidae

Geologic Times: Late Eocene (~35 mya) and Equus: Early Pleistocene (~1.5 mya)

Size (25.4 mm = 1 inch): Mesohippuis:130 mm overall without astragalus (25 mm)
Equus: 290 mm overall without astragalus (65 mm)

Fossil Site: Mesohippus: Arner Ranch, White River Badlands, Sioux County, Nebraska
Equus: (limb bone) Venice Beach, Sarasota County, Florida; (astragalus) Leisey Shell Pit, Hillsborough County, Florida

Code: FGF02

Price: Sold

Description: These examples of members of the Equidae are separated by some 2500 miles in space and 33+ million years in time. They very well demonstrate Cope’s Rule which says over time a lineage tends to increase in size. While Cope himself never made the statement, it has been attributed to him, often extended as the Cope-Deperet Rule, including the person who was a devotee of Cope. The complete central portion of the foot from the toe upward is preserved for the Mesohippus, a species that also still had two other smaller toes flanking the central one. The lower bones have been articulated and glued together. Also included is the astragalus or “ankle bone”. The Equus specimen includes the corresponding two upper bones which can be seen to be far larger in conformance with Cope’s Rule. While the rule does not hold true in all cases, it is useful in demonstrating here how the lineage of horses changed over time.