EPOW - Ecology Picture of the Week

Hippo Old, Hippo New

Left:  Gorgon-eyed River Horse (Hippopotamus gorgops), Oldupai Gorge, Tanzania
Right:  Hippopotamus (Hippopotamus amphibius), Masai Mara, Kenya

Explanation:  What could be bulkier than a hippo?  An extinct hippo!

In the photos above, on the left is a remnant of the skull of an extinct hippopotamus that roamed Africa in the Miocene and even entered Europe in the early Pliocene.  It eventually fell extinct before the great Ice Age.  This skull was displayed in a small museum at Oldupai (a.k.a. Olduvai) Gorge -- where the Leakeys discovered evidence of ancient proto-humans -- in northern Tanzania.

On the right is its modern-day cousin, here stretching its jaws in a show of territoriality at other hippos in this vegetation-choked and summer-shrinking pool in the Masai Mara of southern Kenya.

So why did the ancient form of hippo vanish?  The traditional hypothesis is that ancient humans hunted them to extinction, but recent studies suggest that it was environmental changes, probably caused by climate shifts, that did the trick.  The study suggests that it was falling levels of carbon dioxide in the atmosphere (not increases, as in today's world), causing shrubs and trees to be replaced by expanding grasslands.  Also, its demise seems to predate the appearance and spread of early humans. 

Back to the question of bulk.  "New" (modern) hippos weigh approximately 2,900 to 4,000 pounds (1,300 to 1,800 kilograms).  But that's nothing.  The "old" hippo apparently weighed something like 8,600 to 9,900 pounds (3,900 to 4,500 kilograms); that's like two and half modern sedan cars!