The deinotheriids - giant tapir-elephants

Consider the loss and otherwise total destruction of Shakespeare's works. All of them except two or three - say, The Winter's Tale and The Two Gentlemen of Verona, certainly not the greatest or most culturally significant. Quite a blow for the world of literature, I'm sure you'll agree.

The proboscideans have suffered a similar fate. The African bush elephant, the African forest elephant, and the Asian elephant are the last remnants of a large and diverse group that once spanned several continents. Order Proboscidea has produced many spectacular creatures - moeritheres, shovel-tuskers, mammoths, mastodonts... and deinotheres, which will be the subject of this post.


Family Deinotheriidae diverged relatively early from the rest of the Proboscidea. They belong to the Deinotheroidea, a suborder separate from the more familiar Elephantoidea and outside the Elephantiformes. Shoshani and Tassy (2004) place the Deinotheroidea, Barytheriidae, and Numidotheriidae within the Plesielephantiformes, a sister-taxon to the Elephantiformes. Some radical classification schemes place them outside the Proboscidea, but this is unlikely.

Deinotheres first appeared in the late Oligocene of Africa, specifically Chilga, Ethiopia (Sanders et al., 2004). From there, they spread into Europe and Asia where they thrived until the mid-Pliocene. The last deinotheres were found in Africa, their land of origin, where they made it to the early Pleistocene and were contemporaries of early hominids.

The deinotheriidae was not a particularly speciose group, but it was reasonably successful during its lifespan. Three deinotheriid genera are known, divided into the Chilgatheriinae (Chilgatherium) and the Deinotheriinae (Prodeinotherium and Deinotherium). The species follow each other temporally and replace the previous species. The late Oligocene Chilgatherium is the earliest known deinothere, described in 2004 on the basis of a few distinctive molars (Sanders et al., 2004); it was around pig to hippo-size. Prodeinotherium appeared later, during the mid-Miocene, and remains have been found in Africa, Europe, and Asia; the animal was about the size of a small elephant. Deinotherium was the last deinotheriid, and the best-known (and certainly the only one that appears in popular-paleontology books). It lived from the mid-Miocene to the Pleistocene in Europe, Asia, and Africa. It was also huge, standing 5m tall and weighing 14 tons, at an estimated maximum, making it one of the largest land mammals ever to exist. Only Indricotherium and the controversial Mammuthus sungari were larger.


The most instantly recognizable feature of deinotheriids are their tusks. The upper tusks are entirely absent, while the lower tusks curve downward in a hooked shape and point to the ground. It is unknown whether or not the earliest deinotheriid had those tusks, but both of the later species had them. Apart from that, deinotheriids had diagnostic molars and relatively low, flattened skulls.

The exact function of the tusks remain unknown. At one point, when Deinotherium was assumed to be amphibious, it was suggested that they were used by the animal to haul itself out of water, like a walrus (Osborn, 1936)! Deinotheriids may have used their tusks to root out tubers, pull down branches, strip bark from trees, or fight other deinotheres, but this remains speculative.

Image of Deinotherium skull and teeth from Wikipedia.


The teeth of deinotheres were best suited to browsing from trees. Harris (1975) compared their feeding to that of tapirs, with similar shearing actions. With their great height, deinotheres could easily have browsed in the branches of trees. They were probably very good at it, too, since the basic deinothere plan did not change throughout their evolution.

The trunk of deinotheres is a different matter entirely. Most artists depict Deinotherium and its relatives as nothing other than overgrown elephants with downward tusks, as evident in the adjacent picture. However, more recent research indicates that something far more bizarre was going on in the deinotheriids...

When Osborn first reconstructed Deinotherium back in 1910, he drew it with a short, flap-like trunk much like a tapir's, but later dropped that reconstruction for no known reason (Markov et al., 2001).

This reconstruction was revived by Markov et al. (2001). From a study of the skull's shape, they deduced that Deinotherium must have had a short, tapir-like snout hanging over its descending lower jaw. A long trunk was not necessary, as a browser standing 5 m high at the shoulder had little need to reach the ground. The tusks remained free for whatever purpose they served, and the nostrils, at the end of the proboscis, could smell and inspect food.

To be sure, it's quite a dramatic suggestion, and, if correct, further demonstrates just how diversified proboscideans were during their long history.

Image by Velizar Simeonovski, from Markov et al. (2001).

While the other two species of deinothere invariably get shortchanged, Deinotherium is fairly common in popular-paleontology books, usually in group pics of elephant evolution. For some reason, three-quarters of Deinotherium pictures show it with its mouth open. Deinotherium also got a role in Walking With Beasts, in which a bull Deinotherium in musth almost steamrollers a young Australopithecus. That's awesome.

All pictures, unless otherwise noted, are from earlyimage.


References

Harris, J.M. (1975) Evolution of feeding mechanisms in the family Deinotheriidae (Mammalia: Proboscidea). Zool. J. Linn. Soc. 56: 331-362

Markov, G. N.; Spassov, N.; and Simeonovski, V. A reconstruction of the facial morphology and feeding behavior of the deinotheres. The World of Elephants, International Congress, Rome 2001

Osborn, H. F. (1936) The Proboscidea.

Sanders, W.J.; Kappelman, J.; and Rasmussen, D. T. (2004) New large-bodied mammals from the late Oligocene site of Chilga, Ethiopia. Acta Palaeontologica Polonica Vol. 49, no.3, pp. 365-392

Shoshani, J. and Tassy, P. (2004) Advances in proboscidean taxonomy & classification, anatomy & physiology, and ecology & behavior. Quaternary International, Volumes 126-128, 2005, Pages 5-20