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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