Equus simplicidens
a.k.a.‭ ‬American zebra,‭ ‬Hagerman horse

Name: Equus simplicidens.
Phonetic: Ek-wiss Sim-pliss-e-dens.
Named By: Edward Drinker Cope‭ ‬-‭ ‬1892.
Synonyms: Asinus pons,‭ ‬Equus pons,‭ ‬Equus shoshonensis,‭ ‬Hippotigris simplicidens,‭ ‬Plesippus shoshonensis.
Classification: Chordata,‭ ‬Mammalia,‭ ‬Perissodactyla,‭ ‬Equidae.
Species: E.‭ ‬simplicidens.
Diet: Herbivore.
Size: Between‭ ‬110‭ ‬-‭ ‬145‭ ‬centimetres tall at the shoulder.‭
Known locations: Mexico and across the USA.
Time period: Pliocene to the Pleistocene.
Fossil representation: Remains of well over‭ ‬100‭ ‬individuals,‭ ‬some of which are almost complete.

       Equus simplicidens was first identified by the famous American palaeontologist Edward Drinker Cope in‭ ‬1892,‭ ‬and many other species and genera named since this time have been identified as actually being further specimens of Equus simplicidens,‭ ‬hence the growing list of synonyms.‭ ‬Equus simplicidens stands out as one of the earliest known species of the Equus genus,‭ ‬the genus that essentially includes all modern horses,‭ ‬from thoroughbred race horses to custom bred working breeds like shire horses,‭ ‬to ancient modern breeds like Dartmoor Ponies.‭
       In appearance,‭ ‬Equus simplicidens is thought to have resembled Equus grevyi,‭ ‬which is better known as either Grevy’s zebra or as the imperial zebra,‭ ‬and currently lives in Kenya and Ethiopia.‭ ‬For this reason Equus simplicidens is also known by the more common name of the‭ ‘‬American zebra‭’‬,‭ ‬but a bone bed of Equus simplicidens remains discovered in Hagerman,‭ ‬Idaho has also resulted in a second common name of‭ ‘‬Hagerman horse‭’‬.‭
       Most remains of Equus simplicidens are dated to the Pliocene period,‭ ‬though some remains from Mexico and the US states of California and Texas have been interpreted as coming from Pleistocene age deposits.‭ ‬Equus simplicidens likely inhabited open grasslands since not only was it physically suited to such ecosystems,‭ ‬but by the time of the Pliocene,‭ ‬grasslands had become the dominant type of ecosystem across North America.‭
       Equus simplicidens probably lived in herds that would move around the countryside as they grazed.‭ ‬Evidence for this come from the Hagerman bone bed‭ (‬more commonly known as the‭ ‘‬Gidley Horse Quarry‭’) ‬briefly mentioned above which was discovered in‭ ‬1930‭ ‬by James W.‭ ‬Gidley.‭ ‬Initial interpretation of this fossil site was that it used to be a watering hole where old and infirm individuals of Equus simplicidens went to drink,‭ ‬but died as they did so.‭ ‬However this does not explain the overwhelming abundance of just one species of horse,‭ ‬and current thinking is that the remains are of a herd of horses that drowned while crossing a river,‭ ‬perhaps one that was swollen from beyond its normal levels by flood water.‭ ‬This does not mean that the entire herd was drowned,‭ ‬but the older,‭ ‬injured and generally weaker individuals were simply incapable of swimming all the way across,‭ ‬and therefore drowned in the attempt.‭

Further reading
- A contribution to the vertebrate paleontology of Texas. - Proceedings of the American Philosophical Society 30(137):123-131 - E. D. Cope - 1892.892.
-‭ ‬A new Pliocene horse from Idaho,‭ ‬James W.‭ ‬Gidley‭ ‬-‭ ‬1930


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