Episode 66 – Elephants

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In this episode, we take a deep dive into the largest land mammals that have ever lived. We’ll explore the handful of modern species and their extraordinarily diverse evolutionary history. From mammoths to mastodons, shovel-tuskers to miniature island-dwellers, the fossil record is full of bizarre elephants.

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Proboscideans

Proboscidea is the order that includes all modern elephants and their closest relatives. Today, only three species represent this group: the Asian elephant, African bush elephant, and African forest elephant. But in the past this group included an amazing diversity that spanned across Africa, Asia, Europe, and the Americas.

Palaeoloxodon namadicus, the Asian straight-tusked elephant, was a particularly large proboscidean. According to certain estimates, it may represent the largest land mammal of all time, potentially reaching 17 feet tall and 22 tons. Image by Royroydeb from Wikimedia Commons.

This group got their start in Africa just under 60 million years ago. The earliest proboscideans didn’t look much like elephants. Many, like Eritherium, probably lacked tusks and only a few may have had the beginnings of a trunk. These were also quite small, often no taller than about a meter (3 or 4 feet).

Phosphatherium is one of the earliest recognized proboscideans, dating back to 58 million years ago in Morocco. Image by DagdaMor from Wikimedia Commons.

Moeritherium is a bit younger, 37-35 million years old, and very small at around 2 feet tall. It’s a little more elephantine in that it had small tusks and likely had a simple trunk. Image by Momotarou2012 from Wikimedia Commons.

During the Miocene, as Africa and Eurasia grew closer, proboscideans began to spread across the Old World. Here, we start to see larger and more diverse groups. They start to look like elephants!

Deinotheres had no upper tusks, but had unique lower tusks that pointed down and curved backwards. They likely used these for shearing plants down to make feeding on them easier. Pictured here is a skeleton of Deinotherium gigantissimum. Image by Flavius70 from Wikimedia Commons.

Mammutids, more commonly known as mastodons, are similar in appearance to modern elephants, though not closely related. This is a skeleton of the American Mastodon, Mammut americanum. Image by Ryan Somma from Wikimedia Commons.

Mastodons were a diverse group. This jaw belong to a mastodon found at the Gray Fossil Site. It still has cusped mastodon molars but also prominent chin tusks. Image by David Moscato.

Among the most bizzare proboscideans were the aptly named “shovel-tusked elephants.” This included gompotheres and amebelodontids. Thanks to analysis of the wear patterns on those tusks, scientists suspect the tusks weren’t really being used for digging (as was once thought!) but that they used their specialized lower tusks for stripping vegetation off trees.

Gomphotheres had a huge distribution, ranging through Eurasia, Africa, North America, and some even made it to South America. This is Gomphotherium productum. Image by Ryan Somma from Wikimedia Commons.

Platybelodon, which means “flat-spear tusk,” was an amebelodontid from Africa and Asia during the Miocene. Growth series show that they were born with much smaller “shovels” which widened with age. This is a skull of Platybelodon grangeri. Image by Momotarou2012 from Wikimedia Commons.

As the Miocene continues into the Pliocene we see the first proboscideans make it into North America, as well as the rise of the Elephantids, which include modern elephants and mammoths.

Stegodontids were known in Asia and Africa from the Miocene to the Late Pleistocene. Some members had extraordinarily long tusks up to 10 feet long. Certain individuals’ tusks were so close together researchers have questioned whether they could fit a trunk between them. This is a skull of Stegodon ganesa. Image by Ghedoghedo from Wikimedia Commons.

The Colombian mammoth, Mammuthus columbi, lived in the southern areas of North America as far south as Costa Rica. They were particular large mammoths at up to 13 feet tall, and likely less woolly than their more northern cousins. Image by WolfmanSF from Wikimedia Commons.

Woolly mammoths, Mammuthus primigenius, are among the best understood of all the fossil elephants. This is not only because they were the most recent to disappear but also because we have found frozen individuals with soft tissue intact. This has revealed the many adaptations they had for surviving in the cold Arctic. Pictured here is Lyuba the Siberian mammoth calf. Image by Ruth Hartnup from Wikimedia Commons.

Believe it or not, several extinct proboscidean groups made it to islands, where they experienced insular dwarfism. These dwarf elephants ranged from 7 feet tall all the was down to under 3 feet tall.  On Wrangel Island, a dwarf population of woolly mammoths survived up until a mere 4,300 years ago.

Mammuthus exilis experienced dwafism on the Channel Islands off the coast of California. They stood about 5.6 feet tall and likely weighed between 1000-2000 pounds. Image by Franko Fonseca from Wikimedia Commons.

The vast majority of proboscideans die out at the end of the last inter-glacial period during the Late Pleistocene Megafaunal Extinction.

Other links
Ancient DNA changes everything we know about the evolution of elephants
Mastodons to the Max – the Pacific mastodon
Elephants Have a Sixth ‘Toe”

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If you enjoyed this topic and want more like it, check out these related episodes:

• Episode 107 – Tusks
• Episode 144 – Evolutionary Gigantism and Dwarfism
• Episode 4 – Island Evolution
• Episode 35 – De-extinction

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