Elephantidae—Mammoths // Gomphotheriidae—Gomphotheres // Mammutidae—American Mastodon
Pleistocene proboscideans in general have many of the traits we associate with elephants, such as a trunk (an elongated hose-like extension containing the nasal passages), tusks (the enlarged second upper incisors; in some extinct forms, the second lower incisors also formed tusks), and a relatively large size. The head is large relative to the body in most; this is accomplished by having a large number of sinuses allowing large size without concomitant weight. Presumably the increased size forms surfaces for muscle attachments necessary to support the heavy tusks.
The skeleton is adapted to support the great weight. The limbs are columnar, with the upper limb bones (humerus and femur) elongated and the lower (radius and ulna in the forelimb, tibia and fibular in the hind limb) shortened. The ankle and wrist, along with the feet, are massive, with five wide-spread toes and a mass of connective tissue cushioning the heel. In many ways, the skeletal proportions are the opposite to those seen in mammals adapted for fast locomotion (cursorial). Although, judging from modern elephants, respectable speed may be attained, sloping ground presents a danger and jumping is out of the question. The Mammoth Site in the Black Hills of South Dakota is instructive; the site apparently was a sink with water at the bottom; a number of mammoths made their way down the sloping sides, presumably for water, and then found themselves trapped, unable to navigate up the slopes.
Fig. 1. Mounted skeleton of Mammuthus columbi, Nebraska State Museum. Note the columnar nature of the limbs and the enlarged cranial vault. Photograph © N. Lindsley-Griffin.
There may be some question on the part of readers as to how we know extinct proboscideans had trunks. Luckily, the similarity between extinct and living species and subsidiary evidence from other taxa are compelling. The configuration of the nasal opening is very different among animals with trunks (the proboscis, or "nose" that gives the order its name) compared to those without. The opening is high on the skull, between the orbits for the eyes. The tendency can be seen to lesser extent even in the tapirs, whose "trunk" is short.
In a few cases, soft anatomy has been preserved by freezing in Arctic permafrost, enabling us to know that the ears of the Woolly Mammoth, for example, were relatively small. We also could have guessed this was the case from biological knowledge, since mammals in cold climates tend to have smaller ears than close relatives in warmer areas; large exposed surfaces are wide open for frost bite. The Proboscidea apparently originated in Africa, later spreading to other continents with the exception of Australia and Antarctica (Kurtén and Anderson 1980).
Three families of proboscideans are known from the Pleistocene of the region: Mammutidae (mastodon), Gomphotheriidae (gomphotheres), and Elephantidae (mammoths). The mammoths are relatively late comers to the New World, showing up around 1.6 mya (Morgan and Lucas 2005). They and the mastodons survived until the end of the Pleistocene (with one island population surviving well into the Holocene), but gomphotheres appear to have disappeared from our region by the end of the Early Irvingtonian (Morgan and Lucas 2005).
Literature. Kurtén and Anderson 1980; Morgan and Lucas 2005.
Last Update: 19 Nov 2008