Continental mashup

Today's topic comes to us not because it's some earthshattering discovery that overturns what we've understood, but solely because it's really cool.

You probably know the general rule that isolated ecosystems -- islands, especially -- tend to evolve in their own direction, resulting in a flora and fauna that is completely unique.  Two of the most common places cited as illustrations of this general rule are Australia and Madagascar, home to two of the oddest collections of species on Earth.  Australia's species are so different from the (relatively) nearby biomes in southeast Asia that it was noticed over 150 years ago by British naturalist Alfred Russel Wallace, and the boundary was named "Wallace's Line" in his honor.  It's an amazingly sharp edge.  Wallace's Line runs between Borneo (to the west) and Sulawesi (to the east), and between Bali (to the west) and Lombok (to the east); the distance between Bali and Lombok is only 35 kilometers, but their flora and fauna are so different it was apparent to Wallace immediately.  North and west of Wallace's Line, the animals and plants are the typical assemblage you see in all of southeast Asia.  South and east of it, you get the families you find in Australia.

Another case of this was the linkup of North and South America, forming the Isthmus of Panama three million years ago.  Prior to this, South America had been isolated for 150 million years, resulting in the evolution of a completely unique group of living things, including the giant ground sloth (Megatherium) and the armored-tank glyptodons.  When the connection formed, this allowed the North American carnivores (especially dogs, cats, and weasels) to migrate south.  Humans eventually followed.  The result -- extinction of most of the South American megafauna.  (One of the only species to make the return trip successfully is the armadillo.)

The research that brings this topic up is a study showing that this kind of thing has been going on throughout the Earth's history.  In this case, a team of paleontologists and geologists has shown that a similar scenario unfolded forty million years ago, during the Eocene Epoch, when three land masses collided -- what are now Europe and western Asia, and a low-lying island in between that has been named Balkanatolia (because what's left of it now forms the Balkans and Anatolia).  Here is the layout prior to the collision, and where those land masses are today:

So here, we have not two but three assemblages of species suddenly finding themselves being stirred together.  The result has been named the Grande Coupure (the "great break"), when most of the endemic European fauna -- groups like the paleotheres, distantly related to horses, and the European primate family Omomyidae -- vanished completely.  The winners were the ancestors of who you see now, pretty much across the entire region; canids, true perissodactyls and artiodactyls (for example, horses and pigs respectively), squirrels, hamsters, beavers, and hedgehogs.

Sometimes, who wins and who loses is due as much to luck as it is to fitness.  The species that became extinct in these continental fusion events were doing just fine before the land masses linked together; had North and South America not joined, we might well have giant ground sloths and glyptodons today.  (Of course, those kinds of counterfactual speculation are probably pointless.  Any number of things besides predation by North American mammals could have led to the extinctions.  After all, there have been a lot of changes, climatic and otherwise, since then, and megafauna always seem to get hit hardest by rapidly-shifting conditions.)

But it's cool to find another example of this effect.  And it also gives us a hint of what's to come.  The Australian Plate is moving generally northward at about seven centimeters per year, and will inevitably collide with Asia in a hundred million years or so.  This fusion will erase Wallace's Line and allow for mixing of the two faunal and floral assemblages.

Who will win?  No way to tell, but considering how badass some of the Australian animals are (saltwater crocodiles, cassowaries, brown snakes and taipans, and funnel-web spiders, to name just a few), I'm putting my money on the Land Down Under.

**************************************

Analysis of a triple-whammy

I always find it wryly amusing when I hear someone talk about the Strong Anthropic Principle -- the idea that the universe was fine-tuned by a creator to be hospitable to life, particularly human life -- because it doesn't take much of a close look to become aware of exactly how inhospitable the universe actually is.

Even here on Earth, the situation is kind of dicey.  Our planet's history is really one cataclysm after another; that our own particular lineage survived is probably more a matter of luck than anything else.  In fact, only 74,000 years ago, climate havoc caused by the eruption of the Indonesian volcano Toba is thought by some scientists to have nearly wiped out our species -- they estimate the "Toba bottleneck event" to have reduced the entire population of Homo sapiens to under ten thousand individuals.  (For reference, that means that the human population of the whole planet was about as many people as currently live in Sitka, Alaska.)  Besides major volcanic eruptions, add in earthquakes and tsunamis, global marine anoxia events, and meteor strikes, and you can see that where we live isn't nearly as hospitable as it might look at first.

So the truth lies closer to the Weak Anthropic Principle -- of course the universe, and the Earth in particular, have the conditions necessary for life to exist, because if they didn't, we wouldn't be here to consider the question.

The reason all this catastrophic stuff comes up is a paper that came out a couple of weeks ago in Nature Communications Biology.  Entitled, "Widespread Loss of Mammalian Lineage and Dietary Diversity in the Early Oligocene of Afro-Arabia," by Dorien de Vries (of the University of Salford), Steven Heritage (of Stony Brook University), and Matthew Borths, Hesham Sallam, and Erik Seiffert (of the Duke University Museum of Natural History), it looks at a little-known extinction event that was apparently the result of a one-two-three punch that nearly halted the mammalian species in Africa in their tracks.

Which, of course, also includes our own ancestors.

Some of the Eocene animal groups affected by the extinction -- the left two are primates, the upper right a hyaenodont, and the lower right a prehistoric rodent.  [Photo by Matthew Borths]

The researchers had their first clues about the magnitude of the event, which occurred on the order of thirty-three million years ago, from looking at fossilized mammal teeth from East Africa, and found that right on the boundary of the Eocene and Oligocene, the number of mammal species dropped drastically.

"In our anthropoid ancestors, diversity bottoms out to almost nothing around thirty million years ago, leaving them with a single tooth type,” said Erik Seiffert, senior co-author of the paper, in an interview with EurekAlert.  "That ancestral tooth shape determined what was possible in terms of later dietary diversification...  There's an interesting story about the role of that bottleneck in our own early evolutionary history.  We came pretty close to never existing, if our monkey-like ancestors had gone extinct thirty million years ago.  Luckily they didn’t."

What seems to have driven the extinction was a triple-whammy -- rapid cooling of the climate after the equally catastrophic Paleocene-Eocene Thermal Maximum (during which the global average temperature was eight degrees warmer than it is now), followed by the huge Chesapeake Bay meteorite collision and a near-simultaneous massive eruption of flood basalts in Ethiopia.

Diversity plummeted.  More interestingly, the extinction preferentially spared generalists -- mammals which, from their tooth morphology, apparently could eat a variety of different kinds of food.  Specialists got hit the hardest, once again reinforcing the general evolutionary concept that if the ecosystem is stable, specialization is a good thing, but during periods of rapid change, it's the generalists who come out on top.

This -- as Seiffert says, luckily for us -- left our own distant ancestors to continue loping about on the African savanna, and also knocked out a lot of the competition.  The shape and structure of our own teeth reflect that event.  "We lost a lot of diversity at the Eocene-Oligocene boundary," said study co-author Matthew Borths.  "But the species that survived apparently had enough of a toolkit to persist through this fluctuating climate."

This should be yet another cautionary note about the fragility of the Earth's suitability for humanity, not to mention our current heedless messing-about with the planetary climate and ecosystems.  It's unlikely to, of course.  We don't have a very good record of listening to scientists, even when our own survival is at stake.  Part of this is that in recent memory we haven't had to deal with planet-wide natural disasters -- it's made us cocky.

"We've always been fine before," is the general attitude.

All it takes is reading the de Vries et al. paper to realize that "always" is singularly inapt.

**********************************

My master's degree is in historical linguistics, with a focus on Scandinavia and Great Britain (and the interactions between them) -- so it was with great interest that I read Cat Jarman's book River Kings: A New History of Vikings from Scandinavia to the Silk Road.

Jarman, who is an archaeologist working for the University of Bristol and the Scandinavian Museum of Cultural History of the University of Oslo, is one of the world's experts on the Viking Age.  She does a great job of de-mythologizing these wide-traveling raiders, explorers, and merchants, taking them out of the caricature depictions of guys with blond braids and horned helmets into the reality of a complex, dynamic culture that impacted lands and people from Labrador to China.

River Kings is a brilliantly-written analysis of an often-misunderstood group -- beginning with the fact that "Viking" isn't an ethnic designation, but an occupation -- and tracing artifacts they left behind traveling between their homeland in Sweden, Norway, and Denmark to Iceland, the Hebrides, Normandy, the Silk Road, and Russia.  (In fact, the Rus -- the people who founded, and gave their name to, Russia -- were Scandinavian explorers who settled in what is now the Ukraine and western Russia, intermarrying with the Slavic population there and eventually forming a unique melded culture.)

If you are interested in the Vikings or in European history in general, you should put Jarman's book in your to-read list.  It goes a long way toward replacing the legendary status of these fierce, sea-going people with a historically-accurate reality that is just as fascinating.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]