Deinotherium

Deinotherium is an extinct genus of large, elephant-like proboscideans that lived from the Middle Miocene until the end of the Early Pleistocene. Although its appearance is reminiscent of modern elephants, Deinotherium differered considerably from modern elephants in several anatomical details: it possessed a notably more flexible neck, proportionally more slender limbs, tapir-like teeth, as well as tusks which grew down and curved back from the lower jaw (mandible), and lacked tusks growing from the upper jaw. Several species of Deinotherium grew larger than modern elephants, not uncommonly reaching shoulder heights of and body masses of , making them among the largest land mammals ever. Deinotherium was a widespread genus, during the Miocene they ranged across East Africa, and Eurasia from Western Europe to the Indian subcontinent. They were 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 survived until the end of the Early Pleistocene, around 1 million years ago.

History and naming

In 1613, a gravestone engraved with the name "Theutobochus Rex" was reputedly excavated from a sand pit in the vicinity of Langon, near Montrigaud in southeast France, also reputedly alongside enormous bones, and silver coins depicting the Roman Republic leader Gaius Marius, who had defeated the Germanic king Teutobod (who by the 17th century was often mythologised as a giant) and his army in southern France around 100 BC. A French surgeon named Mazurier exhibited these relics across France, and for some time they were located in apartments owned by Queen of France Marie de' Medici. However, the veracity of the story was quickly questioned and subject to much controversy, with a long-running dispute via an exchange of pamphlets between the University of Paris surgeon Nicholas Habicot, who argued for a giant identity, and botany student and anatomist Jean Riolan who argued based on comparative anatomy that the bones represented some kind of large animal (in Riolan's opinion likely an elephant), and that the supposed discovery was either mistaken or a fraud.

21 years later in 1634, French polymath Nicolas-Claude Fabri de Peiresc asked the physician Nivolet to investigate the site and the relics (except the tombstone, which was now missing). Following the details of a report that Nivolet sent to him Peiresc concluded that the story was a hoax (based on the fact that the coins were actually from Massalia and did not depict Marius, and that it was unlikely a Germanic leader would have a gravestone written in Latin which he and his people did not speak) and later after another discovery of another supposed giant within the vicinity of Montrigaud, like Riolan concluded the remains represented those of an elephant.

The genus Deinotherium and the species D. giganteum was coined in 1829 by German paleontologist Johann Jakob von Kaup based on a complete but broken mandible (lower jaw) discovered in sands near Eppelsheim, southwest Germany. Kaup originally incorrectly reconstructed the jaw's tusks as being upward facing, but corrected this several years later. A second species D. bavaricum was named in 1831 by German paleontologist Christian Erich Hermann von Meyer based on remains found in Bavaria, which von Meyer regarded as comparable to rhinoceroses, but is now recognised to belong to the separate deinotheriid genus Prodeinotherium. In 1834 French paleontologist Édouard Lartet studied additional remains of Deinotherium that had been recovered in France. In 1836, Kaup's friend August von Klipstein found a skull of Deinotherium also within the Eppelsheim area, which was later in 1837 exhibited in France.) found near the Epplesheim jaw as belonging to Deinotherium, by 1837 he came to regard Deinotherium as a "pachyderm" (an obsolete zoological term to describe large terrestrial mammals with thick skin, such as elephants, hippos and rhinoceroses). French zoologist Hercule Eugène Straus-Dürckheim in an 1837 publication assumed that the head was too heavy to have belonged to a terrestrial animal and argued that Deinotherium was a marine mammal intermediate between cetaceans (whales, dolphins, etc) and pachyderms. An aquatic ecology was also supported by British paleontologist William Buckland in an 1838 publication, who also suggested that it used its tusks to cling to river banks and was a burrowing animal. 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, though still quite short compared to other modern browsers like giraffes.

The permanent tooth formula of D. giganteum was <math>\frac{0.0.2.3.}{1.0.2.3.}</math> (deciduous <math>\frac{0.0.3.}{1.0.3.}</math>), with vertical cheek tooth replacement as is typical for mammals, as opposed to the horizontal tooth cheek tooth replacement exhibited by elephantimorph proboscideans. Two sets of bilophodont (two-ridged) and trilophodont (three-ridged) 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 symphysis (the fused frontmost-part of the lower jaw) were very long and curved downward, which along with the backward-curved tusks, are 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.

Species

thumb|Deinotherium giganteum model at the

Throughout the long history of deinotheriid research, 31 species have been described and assigned to the family, many on the basis of poorly sampled material, especially teeth of varying size. The amount of species recognized by authors differs depending on researchers, but the three species most commonly considered valid are listed below.

;D. bozasi

:Known from East Africa, Deinotherium bozasi was the last known species of Deinotherium, surviving in the Kanjera Formation, Kenya, until the early Pleistocene roughly 1 million years ago. It is characterized by a narrower rostral trough, a smaller but higher nasal aperture, a higher and narrower cranium, and a shorter mandibular symphysis than the other two species. In a 2013 publication Martin Pickford notes that D. bozasi has mandibles anatomically similar to those of D. proavum, however most specimens are smaller than those of the European species. To explain this, two hypotheses are suggested, one that they share a common ancestor and the other that D. bozasi may be an example of Allen's rule, which states that animals at lower latitudes are typically smaller than relatives at higher latitudes.

;D. indicum

:The Asian species, D. indicum is distinguished by a more robust dentition as well as p4-m3 intravalley tubercles and found across the Indian subcontinent (India and Pakistan) during the Middle and Late Miocene. It disappeared from the fossil record about 7 million years ago (Late Miocene). Although it is generally regarded as valid, some researchers argue that it is synonymous with D. proavum and that the later name would take precedence. Pickford, for instance, argues that fossils from Iran create a geographic link between European populations and the Indian specimens, concluding that they may be one single wide ranging species.

One hypothesis opposing this three-species model suggests that, rather than being a single consistent species lasting throughout the Miocene, D. giganteum actually represents multiple chronospecies, with the type species only applying to the intermediate form.

Other species that have been described include:

;D. levius (Jourdan, 1861)

:D. levius is a European species of Deinotherium recovered from sediments dating to the late Astaracian to Aragonian. While it is considered a synonym of D. giganteum by some researchers, others propose that it is a stratigraphically distinct chronospecies and the earliest of European Deinotherium. In accordance to this hypothesis, D. levius would eventually give rise to D. giganteum by the Vallesian stage of the Miocene,

:D. proavum is a large bodied species of Deinotherium that may be a junior synonym of Deinotherium giganteum. Other research meanwhile proposes that it, alongside D. giganteum and D. levius, is part of a single anagenetic lineage of Deinotherium species. For this hypothesis it has been suggested that it evolved from D. giganteum during the late Vallesion to Turolian, with early members of the species still being similar in size to its ancestor before surpassing it later during its range. However, the assignment of specimens to D. proavum is largely based on stratigraphy and size, making the differentiation between species difficult, especially with some research suggesting that the two species continued to coexist.right|thumb|Skull of D. giganteum

;D. gigantissimus

:D. gigantissimus from Romania is typically considered to be a larger specimen belonging either to D. giganteum from Bulgaria, another notably large deinothere, described in 2006 but usually lumped into other European species by subsequent publications.

Distribution

Deinotherium was a widespread genus, found across vast areas of East Africa, Europe, the Arabian Peninsula and South to East Asia. In Europe fossils are especially common in the southeast, with up to half of known specimens in the region originating in Bulgaria. Especially significant specimens include those found in Ezerovo, Plovdiv Province (type specimen of D. thraceiensis) and near Varna.

Deinotherium may have ranged as far north as southern Finland, based on a fragmentary humerus provisionally identified as belonging to Deinotherium found in glacial erratic deposits in the region. The western range of Deinotherium spans most of West and Central Europe including Hungary, the Czech Republic (Františkovy Lázně), Austria

Phylogeny of Proboscidea showing the position of Deinotherium, following Hautier et al. 2021: though the deinotheriid affinities of Chilgatherium have been doubted by some authors. The oldest undoubted deinothere remains are known from the late Oligocene of Kenya, around 27-24 million years ago. allowing proboscideans spread into Eurasia, among them Prodeinotherium, thought to be the direct ancestor 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.

In the Indian subcontinent, remains of Deinotherium span from around 13.5 million years ago to 8 million years ago. Deinotherium first appeared in Europe around 13-11 million years ago (MN 7-8), The extinction of Deinotherium in Africa in the Early Pleistocene likely related to the spread of C<sub>4</sub> grasslands.

Paleoecology

thumb|left|Historic illustration of Deinotherium by [[Heinrich Harder]]

Several key adaptations and isotopic evidence suggest that Deinotherium was a folivorous, browsing proboscidean that preferred open woodland habitats and fed on the leaves of the tree canopy. 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 individuals inhabited relatively broad areas and were not confined to small home ranges. 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.

One of the most enigmatic features of Deinotherium are their downturned tusks and their function. Research conducted on Deinotherium suggests that these tusks were likely not used for digging, nor are they sexually dimorphic, leaving use in feeding as their most likely function. These tusks exhibit patterns of wear, in particular on their medial and caudal sides. In a 2001 paper Markov and colleagues argue that Deinotherium could have used its tusks to remove branches that would have gotten in the way of feeding, while using the proboscis to transport leaf material into its mouth. From there Deinotherium would have used a powerful tongue (inferred based on a notable trough at the front of the symphysis) to further manipulate its food. Different tusk anatomy in young individuals would suggest altered feeding strategies in juveniles.

History and naming

Species

Distribution

Paleoecology

Notes

References

Further reading