fossils

Stegodon, the “elephant” with sideways trunk

34f1d64c52c45a6bdce31bc5e48b86cc

Julio
Lacerda

Staff Artist and Writer
Even though only two kinds of elephant are alive today the history of their family, scientifically known as Proboscideans, is one of success. They managed to live on most continents around the globe, from Southeast Asia to South America, and adapted to different climates and habitats. And few species were so successful as Stegodon.

Stegodon may have looked superficially very familiar to us, but its direct ancestors lived even before Asian elephants, African elephants, and mammoths began their separate evolutionary journeys. They existed from 11 million years ago to as recently as 6,000 years ago in Asia, Africa and even North America.


But despite possibly looking a lot like the elephants of today, Stegodon had a very remarkable feature: its tusks could grow to be 10 feet long, about a third of a bus’ length and almost as long as its entire body. Unlike its more famous long-tusked cousins, the mammoths, Stegodon’s tusks sometimes grew so close together that there wasn’t enough space for its trunk to lie in between. Older individuals may have needed to carry their trunks sideways over one of the tusks.


There are several different species within the genus Stegodon, which is a testament to their prosperity. Some were among the biggest proboscideans ever to live, like Stegodon zdansky from China that could reach a height of almost 13 feet and 12.5 tons. Others, very interestingly, went in the opposite direction.


Like modern elephants, Stegodon was probably a capable swimmer, and that may be how it colonized a number of islands throughout Asia from the Philippines to Japan. Some of those isolated populations then suffered from a phenomenon called insular dwarfism, in which big animals progressively get smaller after several generations living in small islands due to the limited space and available food. As a result, the Stegodon sondaari that lived on Flores Island, Indonesia, may have weighed as little as 660 pounds and was smaller than a water buffalo. It coexisted with another dwarf creature, this time our own relative: Homo floresiensis, also informally known as “Hobbits”.


Similar as it was to the charismatic elephants of our time, Stegodon was something unique. Even though the word “elephant” may conjure a very uniform concept – a big gray animal with pillar-like legs, floppy ears and a big trunk – the two groups of elephants alive today are very distinct and separated by at least 5 million years of evolution. Asian elephants and African elephants may look like close relatives, but they took very different paths throughout their history which are reflected in their different anatomies and geographical distribution. An even larger gap separates those two from Stegodon.


And the more you go back in time, the stranger the proboscideans become. Numerous species have lived and gone extinct since the earliest known member of the group, the tapir-like Eritherium from Morocco, appeared 60 million years ago – only 6 million years after the great dinosaur extinction. Many had four tusks instead of the familiar two, like Gomphotherium. Others, such as the enormous Deinotherium, had tusks coming out from its chin. And a few, like the bizarre Platybelodon, were doing something completely different than any elephant. 


All of those unusual animals eventually disappeared. Despite being seemingly very numerous and certainly quite widespread until recent times, even Stegodon eventually went extinct. While the ones that lived on islands were surely more vulnerable due to the more fragile and limited environments in which they lived, scientists don’t know for sure what caused the disappearance of those on the mainland. As is the case for many animals that haven’t survived to the present day, it’s possible that changing climates, competition with other species and even human interaction may have been a factor in their demise.

Image Credit: Lucas Lima

34f1d64c52c45a6bdce31bc5e48b86cc

Julio
Lacerda

Staff Artist and Writer


http://sulc.us/ge5n1
http://www.eartharchives.org/articles/stegodon-the-elephant-with-sideways-trunk/