Hemicyonidae

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Hemicyonidae
Fossil range: Early Miocene to Pliocene

Hemicyon sansaniensis

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	†Hemicyonidae

Genera

†Agriotherium
†Dinocyon
†Hemicyon
†Phoberocyon
†Plithocyon
†Zaragocyon

Hemicyonidae the so-called "dog-bear", literally "Half Dog" (Greek:`Hmikuwn/"hemi-kuôn"), is an extinct family of bear-like Carnivora. They were about 1.50 m (5 ft) long, 70 centimetres (28 inches) tall, with somewhat tiger-like proportions and dog-like teeth. They lived during the Miocene (ca. 22 million years ago) in Europe, Asia and North America to possibly the Late Pliocene (ca. 2 million years ago) in Eurasia and Africa. Hemicyonidae are widely accepted to have been hypercarnivorous and highly predaceous. Unlike modern bears, Hemicyonidae walked on its toes, ie., it was not plantigrade but digitigrade with long metapodials. This suggests that Hemicyonidae must have been an active hunter and a good runner, and presumably hunted on the plains, possibly in packs. This also distinguishes it from the plantigrade short metapodials that bears have and gives it a greater affinity to the digitigrade long metapodials like dogs.

Classification of the hemicyonids has become complicated. Some classifications subdivide the Hemicyonidae into two subfamilies: Phoberocyoninae (including Phoberocyon and Plithocyon) and Hemicyoninae (including Zaragocyon, Hemicyon, and Dinocyon). The earliest known occurrence of the hemicyonids is in Europe from 22.8–20 Ma of Spain: Phoberocyon hispanicus from Loranca and Zaragocyon daamsi from Cetina de Aragon. Hemicyonids lived continuously in Europe. The earliest hemicyonine so far found from North America is Phoberocyon johnhenryi from the Thomas Farm local fauna, Florida, 19–18 Ma. This species of the genus Phoberocyon is confirmed by diagnostic features of the lower dentition: posterior accessory cusps in lower premolars and paraconid in m2, and it is a more derived species than Phoberocyon hispanicus in that it is larger and has diastemata between the premolars. All the American hemicyonids are more advanced in character, and are assigned to genus Plithocyon. They are known from the Barstovian of California, New Mexico, Nebraska, Wyoming and the Love Bone Bed Local Fauna in Florida. In Asia, the earliest hemicyonid is Phoberocyon youngi from Shanwang, Shandong (16 Ma) and is very close to the North American Phoberocyon johnhenry. The latest occurrence in China is from the Tung-Gur Formation, Nei-Mongol (13 Ma). Dispersal probably occurred from Europe to North America prior to 19 Ma and the American Plithocyon is probably a descendant of the Phoberocyon.

The genus Agriotherium is sometimes considered a member of the family Hemicyonidae due to the presence of many similar hemicyonine characters (unelongated molars, premasseteric fossa, etc.) and this strongly substantiates its closer affinity with hemicyonines rather than with ursines. Agriotherium has its longest history in Asia. The most primitive and earliest form is from a Hipparion fauna in Hezheng, Gansu, 9 Ma. All other forms of Agriotherium occurred in the Pliocene (5.3 to 2 Ma) in Eurasia and Africa, leaving a hiatus in the record between 9 and 5.3 Ma. In North America, Agriotherium appeared suddenly around 7 Ma and probably emigrated from Eurasia. Agriotherium fossils have been found at Coffee Ranch, Texas (6.6 Ma); Guymon Local Fauna, Oklahoma; Mount Eden Local Fauna, California; and Old Cabin Quarry, Quiburis Formation (late Hemphillian), Arizona. The occurrence of Agriotherium in North and Central America is thus limited to the later half of the Hemphillian (7–5 Ma).^[1]

Hemicyonidae fossil evidence may also have been found in the Gaillard Cut Local Fauna, former Canal Zone, Republic of Panama, but it is indeterminant with Amphicyonidae. Despite its close proximity to South America, given the geolgical context, the Gaillard Cut Local Fauna are distinctly North American fauna and the age of this assemblage is dated between 19.5 and 14 Ma. ^[2]