Equus altidens

*Equus altidens* is an extinct species of horse that lived in Spain, France, the United Kingdom, Italy, Germany, the Czech Republic, Romania and Georgia from the Early to Middle Pleistocene.

## History

In 1982, a fossil from Orce, Spain was discovered and concluded to been of a juvenile *Homo* sp. by discoverers, Josep Gibert, Jordi Agustí and Salvador Moyá-Solá, as only the external morphology was visible at this time and the internal surface was obscured by a clump of matrix that could not yet be prepared due to a lack of proper tools. It was made very popular in the press as the (then) earliest European in 1983, and presented in a conference. However, review suggested that it was of a donkey, which was reinforced when the matrix was prepared and revealed a small crest typical of an equine. The three were demonized by press, with only Gibert keeping his opinion unchanged. Countless sources continued debate over the origin of the Orce Man cranial fragment It seems consensus that the morphology of the specimen (including the coronal suture and a small crest in the endocast), as well as a vault shape that seems to have been altered by crushing sediment falls well within the range of a young *E. altidens*. Some have suggested that a crest in the endocast can be observed in *Homo ergaster* and one Roman girl. Yet, many agree that the range of morphological diversity in *Homo* does not prove that the specimen is human when the other anatomy suggests otherwise. Although informally, this cranial fragment was once called "Homo orcensis", and there has been solid evidence for hominin occupation of Venta Micena around this time.

## Description

*E. altidens* is considered a species of medium size and slender proportions and adaptation to running. The lower teeth in *E. marxi* often contain a pli protostylid fold, even in the P2, an asymmetric double knot, deep ectoflexid on the molars, a gracile skeleton and metapodials (like *Equus granatensis*), less developed distal keel and distal tuberosities. Specimens at Dmanisi have morphology similar to zebras and hemiones. In 2021, its species diagnosis was emended: it is larger than *Equus stehlini* and smaller than *E. livenzovensis*, *E. major*, *E. sussenbornensis* and *E. stenonis*; moderate cranial size; retracted nasal notch to P2 mesostyle; shallow preorbital fossa with no peripheral rim; high preorbital fossa;prominent facial-maxillary crest; elongate and caudally projecting occipital; typical stenonian cheek teeth; triangular and lingually flattened maxillary protocone; somewhat deep postprotoconal groove; moderately incised hypoglyph; sometimes obliteratedpli-caballin in worn maxillary cheek teeth; consistent V-shaped linguaflexid mandibular cheek teeth separating a rounding metaconid and a metastylid that is often lingually oriented; very deep incision in the molar ectoflexids; and mc3s, mt3s and 1ph3s that are slenderer than all other stenonians.

## Paleobiology

*E. altidens* is unreliably to biochronologically trace. Concurrent arrival has been suggested to have occurred at Dmanisi 1.8 million years ago in Western Asia, as suggested by *E.* aff. *altidens* remains found at Dmanisi and Southeastern Europe. It has also been suggested that they dispersed into Europe (from China) 1.2 million years ago. Alberdi and Palombo (2013) suggest (using the combination *E. altidens altidens*) that the first of this taxon appear in Italy 1.5 million years ago, although such teeth have affinities suggesting a true age of ~1 million years or younger. Venosa-Loreto, slightly younger than Notarchirico, has an estimated age of 600,000 years, which was suggested by Boulbes and Asperen (2019) to be one of the last appearances of *E. altidens* before going extinct. However, some remains from Mosbach, about 500,000 years old, show affinities with Süssenborn and require more work. In 2021, the remains at Dmanisi were confirmed to be of *E. altidens*, with Bernor et al. suggesting that they comprise one of the oldest and well-calibrated occurrences of this species. Dmanisi populations were well adapted to the recent aridity. Its adaptations allowed it to become one of the most widespread taxa in its temporal range.

## Classification

*E. altidens* is sometimes grouped into the subgenus *Sussemionus*, which is controversial as the evolutionary history of these horses is in flux. *E. altidens* and *E. granatensis* are also regarded as part of a group of species, with the latter being contested. The former is sometimes called a stenoid who evolved as the last form of said group in Europe, with others suggesting a part of the North American *Sussemionus* or of African origin. It was suggested to have lived from 1.8 to 600,000 years ago. Another species at Süssenborn, *E. marxi*, was considered by Museil (1969) and defined by a small and narrow crown; variable upper protocones (often with an elongate lingual distal part); mesostyle often divided in two; deep post-protoconal valley and a moderately developed or absent pli caballin on worn molars. This taxon is not often accepted, and is subsumed into *E. altidens*. Fossils at Venta Micena are sometimes allocated to *E. a. granatensis*. Some also suggest that this taxon is poorly defined and should be cautiously used. Bernor et al. (2021) consider *E. altidens* a fully distinct taxon that should not be split into several subspecies. It has also been suggested that it and *Equus granatensis* are the same taxon, representing ecomorphotypes, which is not supported. Von Reichenau (1915) named the species and assigned a right p2 as the lectotype. It is considered closest related to *Equus hemionus* and *Equus grevyi*.

## Notable Specimens

* "Orce Man"/"Man of Orce"/"Orce Donkey"/"Venta Micena fossil" VM-0: Discovered in 1982, published in 1983 and prepared in 1984, partial parietals, part of the sagittal and coronal suture and part of the occipital was found from the Venta Micena site. It was then intensely studied. It was then considered to be of a young *E. altidens*, since the crest present in the specimen are common in equines.

## Synonyms

* *E. marxi*
* *E. a. granatensis*
* *E. a. altidens*
* *E. stenonis mygdoniensis*
* *E. mygdoniensis*
* *E. granatensis*?
* "Homo orcensis"
* *E. alfidens* (lapsus)
* *E. (Sussemionus) altidens*

## Paleoecology

At Süssenborn, *E. altidens*, a medium or small-sized species was contemporaneous with the larger species, *Equus suessenbornensis*. Occurrences of the species have been reported from Venta Micena, Dmanisi, Akhalkalaki, Süssenborn, Bois de Riquet, Pirro Nord, Slivia, Ponte Galeria, Soleihlac, Pakefield, Voigstedt, Huescar-1, Cullar de Baza-1, Venosa-Loreto, Mosbach?, Farneta, Cueva Negra, Polylakkos, Libakos, Gerakarou 1, Happisburgh, Vallparadís Estació, ?Quibas-Sima, Barranc de la Boella, Barranco León and Gran Dolina (Atapuerca), to name several. Throughout these localities, it is contemporaneous other *Equus* including *E. hipparionoides* (Akhalkalaki), *E. stenonis* (Dmanisi), *E. mosbachensis* (Happisburgh) and *E. granatensis* (Venta Micena and other sites). It frequented less open and dry environments, such as steppes, specializing in herbaceous plants and supplementing with woody plants when grasses were made less available. In some of these sites, it was contemporaneous with human species such as *Homo georgicus* (Dmanisi, Venta Micena?) and *Homo antecessor* (Gran Dolina). At Dmanisi, it is 4x more common than *E. stenonis*, which may be tied to its predominant grazing behaviour. At Venta Micena, it is by far the most abundant element of the fauna.

## References

1. ↑ https://www.sciencedirect.com/science/article/abs/pii/S0047248497901214?via%3Dihub
2. ↑ https://brill.com/view/title/54320
3. ↑ https://www.studocu.com/es/document/universidad-de-alicante/prehistoria-en-la-peninsula-iberica/temario-prehistoria-de-la-peninsula-iberica/9530096
4. ↑ https://fr.wikipedia.org/wiki/Enfant\_d%27Orce
5. ↑ https://www.frontiersin.org/articles/10.3389/fevo.2021.622412/full?&utm\_source=Email\_to\_authors\_&utm\_medium=Email&utm\_content=T1\_11.5e1\_author&utm\_campaign=Email\_publication&field=&journalName=Frontiers\_in\_Ecology\_and\_Evolution&id=622412
6. ↑ 6.0 6.1 6.2 6.3 https://www.researchgate.net/publication/335723352\_Biostratigraphy\_and\_Palaeoecology\_of\_European\_Equus
7. ↑ 7.0 7.1 7.2 7.3 7.4 https://www.sciencedirect.com/science/article/abs/pii/S0047248421001032
8. ↑ 8.0 8.1 https://www.sciencedirect.com/science/article/abs/pii/S0277379121003620
9. ↑ 9.0 9.1 https://www.sciencedirect.com/science/article/abs/pii/S1040618211006793
10. ↑ https://www.researchgate.net/profile/Omar-Cirilli/publication/358751878\_EQUUS\_STEHLINI\_AZZAROLI\_1964\_PERISSODACTYLA\_EQUIDAE\_A\_REVISION\_OF\_THE\_MOST\_ENIGMATIC\_HORSE\_FROM\_THE\_EARLY\_PLEISTOCENE\_OF\_EUROPE\_WITH\_NEW\_INSIGHTS\_ON\_THE\_EVOLUTIONARY\_HISTORY\_OF\_EUROPEAN\_MEDIUM-\_AND\_SM/links/6213d8fd08bee946f3943cb4/EQUUS-STEHLINI-AZZAROLI-1964-PERISSODACTYLA-EQUIDAE-A-REVISION-OF-THE-MOST-ENIGMATIC-HORSE-FROM-THE-EARLY-PLEISTOCENE-OF-EUROPE-WITH-NEW-INSIGHTS-ON-THE-EVOLUTIONARY-HISTORY-OF-EUROPEAN-MEDIUM-AND.pdf
11. ↑ https://www.mdpi.com/2079-7737/11/9/1258
12. ↑ https://fr.wikipedia.org/wiki/Homme\_d%27Orce
13. ↑ https://www.researchgate.net/profile/Pg-Silva/publication/357380962\_Tabla\_cronoestratigrafica\_del\_Cuaternario\_de\_la\_peninsula\_iberica\_Extended\_Version\_30\_Nuevos\_datos\_estratigraficos\_paleontologicos\_y\_arqueologicos/links/61cb6dbee669ee0f5c6fb537/Tabla-cronoestratigrafica-del-Cuaternario-de-la-peninsula-iberica-Extended-Version-30-Nuevos-datos-estratigraficos-paleontologicos-y-arqueologicos.pdf
14. ↑ https://www.sciencedirect.com/science/article/abs/pii/S0003552121001990
15. ↑ https://www.tandfonline.com/doi/abs/10.1080/08912963.2021.2024179
16. ↑ https://link.springer.com/chapter/10.1007/978-3-030-68442-6\_12
17. ↑ https://www.tandfonline.com/doi/abs/10.1080/08912963.2021.1935920
18. ↑ https://www.sciencedirect.com/science/article/pii/S0277379122001007
19. ↑ https://link.springer.com/article/10.1007/s10816-022-09550-0
20. ↑ https://institucional.us.es/revistas/spal/9/art\_9.pdf
21. ↑ https://onlinelibrary.wiley.com/doi/full/10.1002/jqs.3270
22. ↑ https://www.sciencedirect.com/science/article/pii/S1631068302000325
23. ↑ https://sciencepress.mnhn.fr/fr/periodiques/comptes-rendus-palevol/20/17
24. ↑ https://www.semanticscholar.org/paper/A-hominid-from-the-lower-Pleistocene-of-Atapuerca%2C-Castro-Arsuaga/00fabc8917f38157eb7d2975e011468ca454ea24?p2df
25. ↑ https://www.nature.com/articles/s41598-021-93261-1