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Short Sharp Science: A New Scientist blog

Giant crocs preyed on our ancestors

croc skull.JPGOur ancestors had good reason to be wary of going near the water, at least at two key African sites known for their hominid fossils. At both the Olduvai Gorge site in Kenya and the Koobi Fora site in Kenya, early humans shared the land with large crocodiles, and hominid bones from Olduvai show the marks of crocodile teeth.

Crocodile specialist Christopher Brochu of the University of Iowa reported the findings on Thursday at the Society for Vertebrate Paleontology meeting in Cleveland.

He discovered our ancestral encounters with crocodiles while studying how the powerful predators evolved on southern continents over the past 20 million years.
Anthropologists had previously found crocodile bite marks on hominid bones from Olduvai dating back about two million years. Brochu found the likely culprit - an extinct species that could grow to about six metres long, the size of its modern relative, the Nile crocodile.

croc.jpgThe older Koobi Fora crocodiles reached up to 7.5 metres long, bigger than any living crocodile. The australopithecines who lived in the area were smaller than the Olduvai hominids (see image, left), so they would have had less chance against the predators.

"Those hominids would not have lasted long in the water," Brochu told me.

So the discovery of big hungry crocodiles is not helpful to supporters of the theory of the aquatic ape, which holds that our ancestors lost the hairy hides of their chimpanzee and gorilla cousins when they moved into the water. Without rifles, any apes trying to go aquatic would have wound up as crocodile meals rather than our ancestors.

The crocodiles, on the other hand, had no such problems. In fact, when he compared the African crocodiles with their South American counterparts, he found they were so closely related that some must have swam across the South Atlantic between 5 and 10 million years ago.

Jeff Hecht, New Scientist correspondent

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Wasn't the hypothesis of aquatic hominids centered around a marine environment, and not African rivers?


That is my recollection of the theory - which has some very interesting points, like explaining the shape of our noses (streamlined for swimming), and the thumb web, both of which are unique among apes.

The crocs were also aquatic, yet because they preyed on hominids does not preclude anything. We don't know how high the risk was compared to land predators, which pretty dangerous at the time. And we don't know how difficult it was to avoid the crocs. Personally, I would rather be stalked by a croc than a leopard. (Yes, I know they don't stalk, just making a point.)


The "aquatic ape" idea originally was centered on marine living, and some forms of it still are. Others have dropped that idea because of some uncomfortable facts. If you want details, BTW, my web site, which you can get to by clicking on my name, has them.

At any rate, crocs are present in both fresh and salt water, so either environment presents the problem. There are a number of reasons why aquatic predators are a much bigger problem than terrestrial, and my site has a lot of info on them (Chris Brochu and I used to post in newsgroups on this subject). In brief, crocs are generally not seen at all before they attack, and they don't respond to bluff or counterattack at all well. The opposite is true for terrestrial predators, and we can see that in how chimps respond to predators (generally by confrontation and harrassment rather than simply by running away).

The other bits there suggested as things due to aquatic living -- noses and a small amount of finger webbing -- as well as a host of others, simply aren't true. Again, there's a lot on my site about all of this, but in brief, for noses, they're a side effect of the change in our faces at the time of the relatively large amount of brain expansion about 1.7-2 million years ago and this can be seen in fossil studies. As for the small amount of webbing we see in people's hands, this is common enough in both gorillas and siamangs; there is no reason to invoke aquaticness for this feature.

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