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Extinct genus of mammals

Deinotherium is an extinct genus of large, elephant like proboscideans that lived from about the middle Miocene until the early Pleistocene. Although its appearance is reminiscent of modern elephants, Deinotherium possessed a notably more flexible neck, with limbs adapted to a more cursorial lifestyle, as well as tusks which grew down and curved back from the lower jaw, as opposed to the upper mandible tusks seen in extant elephants. Deinotherium was a widespread genus, ranging from East Africa, north to southern Europe, and east to the Indian subcontinent. They were primarily browsing animals, with a diet largely consisting of leaves. The genus most likely went extinct due to environmental changes, such as forested areas gradually being replaced by open grasslands, during the latter half of the Neogene. Deinotherium thrived the longest in Africa, where they were found into the early Pleistocene.

Deinotherium has a long history, possibly dating back as early as the 17th century when a French surgeon named Matsorier found the bones of large animals in an area known as the "field of giants" near Lyon. Matsorier is said to have exhibited these bones across France and Germany as the supposed bones of a French monarch, until he was exposed and the bones were handed over to the French National Museum of Natural History. Another early hypothesis suggested that Deinotherium was a sirenian that used its tusks to anchor itself to the sea floor while sleeping. The general anatomy of Deinotherium is similar to that of modern elephants with pillar like limbs, although proportionally longer and more slender than those of other proboscideans. The bones of the toes are longer and less robust than in elephants and the neck likewise differs notably in that it is relatively longer, however still quite short compared to other modern browsers like giraffes. The permanent tooth formula of D. giganteum was (deciduous ), with vertical cheek tooth replacement. Two sets of bilophodont and trilophodont teeth were present. The molars and rear premolars were vertical shearing teeth, and suggest that deinotheres became an independent evolutionary branch very early on; the other premolars were used for crushing. The cranium was short, low, and flattened on the top, in contrast to more advanced proboscideans, which have a higher and more domed forehead, with very large, elevated occipital condyles. The largest skulls of Deinotherium reached a length of The nasal opening was retracted and large, indicating a large trunk. The rostrum was long and the rostral fossa broad. The mandibular symphyses (the lower jaw bone) were very long and curved downward, which, with the backward curved tusks, is a distinguishing feature of the group. Although the presence of an elephant like proboscis or trunk in Deinotherium is evident thanks to the size and shape of the external nares, the exact shape and size of this trunk is a matter that has long been debated. Historic depictions commonly portray it as very elephantine with a long trunk and tusks breaking through the skin below an elephantine lower lip. In the early 2000s Markov and colleagues published papers on the facial soft tissue of Deinotherium contesting these ideas, instead suggesting an alternative soft tissue reconstruction. In the first of these publications the authors argue that, due to the origin of these animal's tusks, the lower lip should be situated beneath them as they evolved their classic downturned appearance. They further suggest that, while a trunk would be present, it would likely not resemble that of modern elephants and instead be more robust and muscular, which they reason is evidenced by the lack of a proper insertion surface. Although later research concurs that the trunk or proboscis of Deinotherium was likely notably different from those of modern proboscideans, the idea of a short tapir like trunk is questioned. In particular, it is pointed out that the tall stature and still relatively short neck of Deinotherium would render it very difficult for the animal to drink without assuming a more complex posture. Thus it is suggested that the trunk must have been at least long enough for the animal to effectively drink.

The origin of Deinotheres can be found in the Oligocene of Africa with the relatively small bodied Chilgatherium. Initially restricted to Africa, the continued northward movement of the African Plate eventually caused the Proboscidean Datum Event, during which proboscideans diversified and spread into Eurasia, among them the ancestral Prodeinotherium, thought to be the direct predecessor of the larger Deinotherium. Generally, Deinotherium displays relatively little change in morphology throughout its evolution, but a steady increase in body size from 2 meters shoulder height in Prodeinotherium to up to 4 meters in later Deinotherium species and a mass far exceeding even large African elephants. The reasons for this rapid increase in body size is interpreted to have had multiple factors influencing it. On the one hand, increased size is an effective predator deterrent, especially during the Miocene when carnivorans had reached a great diversity including hyaenodonts, amphicyonids and large cats. Secondly, continued aridification during the Miocene increasingly split up woodlands, with greater distances of open landscape stretching between the food sources of browsers such as Deinotherium. This also accounts for the morphological adaptations seen in the limbs of Deinotherium, better suited for long distance travel. Furthermore, the appearance of Deinotherium coincided with falling temperatures during the middle Miocene. According to Bergmann's rule, these circumstances favor increased body mass for maintaining heat in cold temperatures. Despite the many key adaptations deinotheres developed for effective foraging, the continued aridification that progressed throughout the Miocene eventually led to the extinction of the group, which failed to survive without readily available food sources matching their diet. Populations in Western Europe were the first to disappear, followed later by those in Eastern Europe. While European lineages of Deinotherium had gone extinct with the onset of the Pliocene, the genus managed to survive notably longer in its southern range in Africa. The last known Deinotherium remains, assigned to D. bozasi, were found in sediments dating to the Pleistocene, approximately 1 million years ago.

Several key adaptations suggest that Deinotherium was a folivorous, browsing proboscidean that preferred open woodland habitats and fed on the leaves of the tree canopy. In Asia D. indicum has been associated with wet and warm, low energy woodland and in Portugal deinotheriid remains were found in regions corresponding with moist, tropical to subtropical woodland conditions likened to modern Senegal. and the Mainz Basin in Germany indicate that Deinotherium was not a permanent resident in some areas it inhabited. In Austria it has been suggested that they traversed areas on a regular basis, while in Germany there is evidence for the animals range shifting with changing climatic conditions, present during subtropical climate conditions and absent in subboreal conditions.