Dwarf Elephants - Planet Earth Online

03 April 2012

Interview with

Victoria Herridge, Natural History Museum

There's an awful lot that scientists can learn about the past from fossils but one particular extinct species is proving a tough nut to crack.  Dwarf elephants last roamed the Earth more than 10,000 years ago.  About a metre tall fully grown, they are even considered by some to be responsible for the legend of the one eyed cyclops.  But although they have been studied for 150 years, fundamental information about dwarf elephants is still missing and no one is exactly sure how the different species evolved.  Palaeontologist Victoria Herridge from London's Natural History Museum is part of an international project trying to solve the mystery.  Victoria studies dwarf elephant fossils found on a number of Mediterranean islands.  Sue Nelson went to meet her in one of the museum's basement stores...

Victoria -   In here, we have a whole draw full of dwarf elephant teeth fromPhotograph of a fossil cast of a pygmy species of Elephas skeleton taken at the North American Museum of Ancient Life. Cyprus.  They're all different sizes but most of them are smaller than the size of my hand which sounds quite big for a tooth, but for an elephant tooth, that's absolutely tiny.  They have six teeth through their life and as the elephant grows bigger, their teeth grow bigger.  So the smaller teeth are actually the teeth of younger elephants.  It seems that on islands when big animals become isolated, they tend to evolve to become smaller and conversely, the small animals, like mice and rats, tend to evolve to become larger, which is an interesting phenomena we call the 'Island Rule.'

Sue -   As this project wants to look at the different environmental changes and the effect that had on the species, I assume then that that means that you suspect that the changing climate had something to do with their evolution, why they became the size they did and perhaps why they became extinct as well?

Victoria -   Yes, it's certainly a possibility.  If you look at modern day islands, we know that the number of species that live on an island is related to how big the island is and also, how difficult it is to get to that island from the mainland.  So because there's this relationship, it seems sensible to assume that that islands and the animals that live on them might be affected by sea level change.  So, if the sea level were to rise as we fear it might do in the next few years, you would effectively see a greater impact of that on islands.  So using that as a starting point, we then thought - the period we're interested in, which is called the Quaternary - the last 2 ½ - 3 million years - a lot of that was characterised by these shifts between ice ages and warm stages, and that will then be followed by a rise in sea level.  So we think for instance at the peak of the last ice age, the sea level was 120 meters or so lower than it is now.  Yeah, so quite an extreme difference.  

But because it has happened several times, about every 100,000 years, what you've got there is a repeated example of this situation changing.  So we aren't looking at the effects of the climate per se, it's more of the associated impacts of that climate change, i.e. sea level change that may affect the environment in which animals find themselves.  Now, Sicily is very, very close to mainland Italy, but the sea that separates the two is about 100 metres or so deep.  And so, 120 metres of sea level drop would join Sicily to the mainland.  It would also join Malta to Sicily and so, at low sea level, what you might get is, the mainland reaching out and encompassing Sicily and Malta, and that would become part of the mainland.  Now, when the climate shifted again and you've got a change from say, an ice age back to a warm stage then of course, sea level would rise and you'd find yourself with two islands, Sicily and Malta.  The animals that were there, that had been effectively been mainland animals until that sea level change, now become isolated on these islands and it's following that isolation that we think the evolution towards becoming smaller happened.  So, we are wondering whether or not you can effectively associate some of these species with some of those climatic driven sea level changes of the past.  

If I just lift up this very heavy tooth here...

Sue -   Yeah, you need two hands for that one.

Victoria -   Yeah, two hands.  This is not going to fit in one hand.  You can how heavy it is from the clunk there.

But this is a straight-tusked elephant tooth from Clacton-on-Sea in Essex.  So we had straight-tusked elephants in the UK, but that species actually stretched all the way across Europe, down to the far south, so into Greece, into Italy.  This makes sense because we think this was probably the ancestral species of these dwarf elephants that somehow reached these islands, perhaps at low sea level, and then became isolated on those islands when the sea level rose again.  When it was isolated there, it evolved from being very, very large - a straight-tusked elephant would've been about 4 metres tall, much taller than the African elephant which comes in at about just over 3 metres, and would've weighed about 10 tonnes.  Contrast that again with the African elephant, the largest living land mammal that's about 7 tonnes, and it would've evolved on those islands to something as tiny as this 1 metre tall species, and that's a very extreme example of evolutionary change.  It's a wonderful example because it obviously happens again and again on different islands.  

Because this happens so many times, it starts to give us a natural experiment, these islands are kind of like a natural laboratory for evolution in real space and time.  It's a really neat potential way of getting our hands on, how quickly evolution happens, and potentially, how and why it happens.  That's why studying these elephant species potentially will give us greater insight into a much broader evolutionary and biological trend.

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