''Equus stenonis'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

equine Equinae is a subfamily of the family Equidae, known from the Hemingfordian stage of the Early Miocene (16 million years ago) onwards. They originated in North America, before dispersing to every continent except Australia and Antarctica. They are ...

that lived in Western Eurasia including Europe during the

Early Pleistocene The Early Pleistocene is an unofficial epoch (geology), sub-epoch in the international geologic timescale in chronostratigraphy, representing the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently esti ...

Taxonomy and evolution

The species was first named in 1867, with the type specimen being IGF 560, a skull with a now lost (but preserved as a cast) associated mandible collected from Terranuova Bracciolini in Italy. Several subspecies have been named, including ''E. stenonis vireti'', ''E. stenonis guthi'', ''E. stenonis pueblensis'', ''E. stenonis olivolanus'' and ''E. stenonis stenonis,'' which likely represent different ecomorphotypes adapted to varying local conditions. ''Equus stenonis'' and other Early Pleistocene Old World ''Equus'' species are suggested to be closely related and perhaps descended from the North American species ''

Equus simplicidens ''Equus simplicidens'', also known as the Hagerman horse and American zebra, is an extinct species of Equinae, equine native to North America during the Pliocene and Early Pleistocene. It is one of the oldest and most primitive members of the genu ...

'' (also known as the "Hagerman horse"). The ancestor of ''Equus stenonis'' as well as other Early Pleistocene Old World ''Equus'' species are thought to have arrived from North America across the

Bering Land Bridge Beringia is defined today as the land and maritime area bounded on the west by the Lena River in Russia; on the east by the Mackenzie River in Canada; on the north by 72° north latitude in the Chukchi Sea; and on the south by the tip of the ...

as part of the ''Equus'' Datum event at the beginning of the Pleistocene, approximately 2.6 million years ago. ''Equus stenonis'' is typically considered to be closely related to other Early Pleistocene Eurasian ''Equus'' species which are collectively referred to as "stenonines" or "stenonoids". The African species ''Equus koobiforensis'' and ''E. oldowayensis'' are closely related to ''E. stenonis''. ''E. stenonis'' has been proposed to be closely related and possibly the ancestor of both

zebras Zebras (, ) (subgenus ''Hippotigris'') are African equines with distinctive black-and-white striped Animal coat, coats. There are three Extant taxon, living species: Grévy's zebra (''Equus grevyi''), the plains zebra (''E. quagga''), and t ...

and asses. Barron-Ortiz et al. (2019) resurrect the genus ''Allohippus'' for ''Equus stenonis'' based on the results of their cladistic analysis regarding the interrelationships of the genus ''Equus,'' though this was subsequently rejected by other authors.

Description

Populations of ''Equus stenonis'' varied considerably in body mass across time and space, varying from as low as , to over , making it medium-large sized among equines. The feet are monodactyl, the head is large and elongated and has an undulated top profile in side-view, the nasal notch is deeply incised. The braincase is flexed downward and is relatively small. The teeth have a v-shaped linguaflexid separating the

metaconid Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...

and metastylid, similar to other "stenonines". The limb bones are relatively large and robust. The metapodial bones of the foot are proportionally elongate and robust, with the central digit having a massive morphology, with a large v-shaped muscle scar.

Distribution and chronology

''Equus stenonis'' is known from remains found across

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, from the

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Greece Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...

, as well as the Dmanisi site in

Georgia Georgia most commonly refers to: * Georgia (country), a country in the South Caucasus * Georgia (U.S. state), a state in the southeastern United States Georgia may also refer to: People and fictional characters * Georgia (name), a list of pe ...

, spanning part of the Early Pleistocene, the oldest remains dating to approximately 2.5 million years ago, while the youngest dates are uncertain, ranging from 1.8-1.3 million years ago.

Palaeoecology

Dental wear patterns of the species' teeth from the Coste San Giacomo locality in Italy suggest that ''E. stenonis'' was a grazer. It sometimes co-occurred with the larger, mainly

browsing Browsing is a kind of orienting strategy. It is supposed to identify something of relevance for the browsing organism. In context of humans, it is a metaphor taken from the animal kingdom. It is used, for example, about people browsing open sh ...

stenonine '' Equus major''.

References

{{Taxonbar, from=Q15411518 Prehistoric mammals of Europe Prehistoric mammals of Asia Equus (genus) Fossil taxa described in 1867

Taxonomy and evolution

Description

Distribution and chronology

Palaeoecology

See also

References