Animal Sea Crossings, Hippo Bleg

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Via Razib, I checked out Clive Finlayson’s The Humans Who Went Extinct. On the human migration to Australia, Finlayson writes:

The long-tailed macaque, primate beachcomber par excellence, can teach us another lesson. These monkeys have managed to establish viable populations on a number of remote islands over a wide area of south-east Asia. They even reached the Nicobar (south of the Andamans) and Philippine Islands, which were never connected to the mainland…

Nobody, to my knowledge, has suggested that these macaques had found ways of making canoes or other watercraft and they do not seem to have developed maritime navigation sk ills either. The simple combination of their habits, which often brought them close to drifting rafts, and chance allowed them to populate many distant islands. Yet when it comes to the dispersal of humans across these same islands and onto Australia the prerequisites in all accounts of the epic journeys are watercraft and navigation skills.

That is, rather than humans settling Australia via rafting across the long channel across from East Timor, Finlayson suggests that instead humans were washed out to sea onto New Guinea, more in the manner of other species which have managed the same trick. Presumably his argument would also apply to other early human island hopping events, such as on Crete. The tenor of the book is based on arguments such as this, which reject human triumphalism in favor of naturalistic primate comparisons.

To me, however, this adds to the puzzle of how there were Hippos in Madagascar. Contrary to popular impression, adult Hippos can neither swim nor float; they navigate in the water by pushing up from the bottom. Their daily dietary needs are quite large, involving the consumption of up to 150 lbs of grass a day.

So how on earth did they manage their way across the ~275 mi channel between Africa and Madagascar? This strait — at times miles deep — was sufficient to keep out the vast majority of African wildlife, preserving a largely endemic plant and wildlife. Humans never made it across before inventing watercraft. There are a few islands in between, which at the present day largely lack the fresh water needed to sustain viable hippo populations. Only a handful of mammals have made the transit in the last 50 million years, most of which were fairly small in size.

And it’s not like this was a freak event. Hippos made it to several Mediterranean islands, establishing dwarf island populations. If anyone has insight on this pressing question, do let me know in the comments.

7 Comments

  1. What distances are these macaques claimed to travel across?

  2. ~90 mi from Sumatra to the Nicobar islands.

  3. Maybe some Hippos eat seaweed, and young hippos get washed out to sea on debris, during hurricanes?!

  4. I have got to read Clive Finlayson’s book. If this bit about people drifting to Australia is typical, it should be funny as hell.

  5. What is the time period for the dward mediterranean hippos, and what islands? The mediterranean filled with water relatively recently.

  6. Wouldn’t the Japanese macaques (snow monkeys) be the most distant?

  7. Adding this after nearly a year (didn’t notice the “hippos can’t
    swim” passage originally.

    Memory is tricky but I’m almost certain I’ve seen hippos swim.
    I seem to remember a mother hippo swimming circles in a pool, its baby following close behind. I was acquainted with the curator of that zoo (Johnny Werler at Houston) and he’s now deceased. I know another guy with somewhat more extensive knowledge of hippos and, though i haven’t spoken with him in some time, will try to reach him by phone to clear this point.

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