Friday, October 18, 2013

Mammoth or mastodon?

Let's suppose you've decided to make a name for yourself in cryptozoology. Everyone and their chupacabra is out looking for sasquatches and lake monsters. Your way to fame will be through finding your own monster and carving out your own turf. So you pack up your extra grainy, black and white camera (the preferred tool of cryptozooligists everywhere) and head off to a lost valley in Montana known only to you and the wizened shaman who told you about it. After a day of fruitless searching, you're heading back to camp. It's that hour between day and night when the light is at its most deceptive. Suddenly, you hearing a crashing the underbrush and there it is. It's the biggest animal you've ever seen! It's covered with long hair! It has a trunk and tusks! You've discovered the last mammoth! Or mastodon. Are they the same thing? If they're not, what is the difference?

First of all, they are not the same thing. They are not even that closely related. They are two different species, in two different genera, in two different families of the order Proboscidea. They are about as closely related as you and a ring-tailed lemur. Today, the order Proboscidea is represented by three species, in two genera of the same family, but, in its evolutionary history, the order has produced at least two suborders, eight families, thirty eight genera, and almost two hundred species. At the end of the last ice age, the number of poboscidean species wandering the earth was in the high teens. They inhabited every continent except Australia and Antarctica. They lived in forests, prairies, jungles, around the edges of deserts, and out on the tundra. They could be found on seacoasts, islands, and high in the mountains.

If mastodons are way over there, where is the mammoth? Mammoths, and there have been about eight species, have their own genus, Mammuthus. They split off from Asian elephants (genus Elphas) about six million years ago. This was after the latter split off from African elephants (genus Loxodonta). At the time, all three genera lived in Africa. As mammoths moved north from Africa into Europe and Asia, they gradually evolved from one species into another to adapt to new climates and in response to the world cooling into the ice ages.

Eventually, two species of mammoth made their way into North America. Yes, two. There is nothing simple about elephant evolution. The steppe mammoth (Mammuthus trogontheri) evolved in northeastern Asia somewhat less than two million years ago. This was early in the ice ages. This species was adapted to a cool dry climate. It spread to the north and west. The northern group crossed the Bering Straits during a period of low sea levels--that is, just before or just after a glacial period when lots of water is still locked up in ice caps, but the climate in Alaska is still somewhat temperate (my own opinion is that it was after a glacial maximum). This group moved into North America and adapted to grasslands and lightly forested areas. In time, it populated most of the contiguous US and Mexico down to the valley surrounding Mexico City. This population, adapted to a temperate and we call the resulting species the Columbian mammoth (Mammuthus columbi).

The steppe mammoths that stayed in Asia eventually spread back across the grasslands of central Eurasia (the steppes) all the way to Ireland and Spain. These mammoths adapted to the coldest climate. They became a keystone species involved in creating an Arctic grassland in areas that are now tundra. We call this lost ecological system, the mammoth steppe. As opposed to the current steppe which runs through central Eurasia south of the forest zone, the mammoth steppe existed in the dry, cold region north of the forests. These mammoths became shorter and stockier that other than the Columbian mammoth. Their hair became longer and the developed a layer of wool next to their skin. AS you may have guessed, this is the woolly mammoth (Mammuthus primigenius). During an interglacial period about 500,000 years ago, a population of these mammoths crossed into North America. During the last few glacial periods, they created mammoth steppes on both sides of the American ice sheets, in the northern US states and Canadian prairie provinces and in Alaska and the Yukon.

Okay. I understand the mammoths. What were the mastodons doing during all of this? Mastodons were going nuts, creating new species left and right. The ancestors of mammoths and mastodons split from each other early in the evolution of Proboscidea, possibly over forty million years ago. The majority of proboscid species are on the mastodon side of the order. The ancestors of mastodons entered the New World long before mammoths, possibly in more than one wave. There were three or four species living in South America when humans arrived and the best known species (Mammut americanum) living in North America. Mastodon remains have been found all over the forty eight contiguous states and as far south as Honduras.

We're finally there. We have mammoths and we have mastodons and we have them living side by side in North America. Doesn't that pose a problem? How can you have two large hungry animals filling the same ecological niche? The answer is: you almost never can. Mammoths and mastodons didn't fill the same niche. Forty million years of separate evolution produced two similar looking animals, but the two animals had different feeding habits. Mammoths were primarily grazers. The ate grasses and herbs. They can eat other plant matter, such as tree bark, but their teeth and digestive systems are best suited for ground plants. Mastodons were primarily browsers. They ate mostly leaves and small branches. Where we have found gut contents for mastodons, it has been mostly made up of conifers such as pine, spruce, and fir. Mammoths were found mostly on prairies and grasslands and mastodons in boggy forests. There would have been some overlap around the edges of their ranges, but no extensive contact.

Mammoth tooth discovered during the Thirty Years War. Source.

The first evidence of this difference was their teeth. Mammoths, like elephants, had big loaf shaped teeth made up of parallel plates that were used to grind their food. They had one in each jaw, for a total of just four. Grinding eventually destroys the teeth, so they grew a new pair every ten years or so. Mastodon teeth look more like a familiar molar. They were enamel covered and had high knobby cusps. They had two in each jaw, for a total of eight. This kind of tooth is good for tearing branched apart.

When large numbers of mastodon bones arrived in Europe in the Eighteenth Century, the teeth presented a problem. The ivory and other bones made it easy to recognize it as similar to elephants and mammoths. Were the remains found in some unique place where mammoths came to die, leaving all their bones, except the teeth, and where some other large animal came to die, leaving none of its bones, except the teeth? Putting the teeth and skeletons together as a single animal created a particularly horrifying image. Molars with pointed cusps, like the mastodon had, were thought to be a sign of meat eating. Some of the published descriptions of the animal imagined it pouncing on entire herds of buffalo and tearing them to shreds.

Mastodon tooth found near the Ohio River in 1739. Source.

By the end of that century, people like Ben Franklin on this side of the Atlantic and Baron Cuvier on the other, had managed to convince the scientific community that mastodons and mammoths were distinct species, separate from elephants, and, almost certainly, extinct. That last part was a disturbing idea that bordered on religious heresy. Extinction implied that God's creation came with extra, unnecessary parts. This flew in the face of how Europeans conceived of creation. The world, to them, was a perfect machine. Every part had its own mysterious purpose. Superfluous parts meant the world was not perfect and, possibly, that God was not perfect. Many flat out refused to believe that extinction was possible. These animals had to still exist in some unexplored corner of the world. When Thomas Jefferson sent Lewis and Clark to explore the headwaters of the Missouri river and continue on to the Pacific coast, his instructions explicitly included orders to look for mammoths and mastodons.

From the above, you've probably guessed that the chief determiner of their uniqueness was the teeth. When Baron Cuvier presented the paper that was seen as the final word in the argument, he coined the name mastodonte. The etymology is from the Greek "masto" meaning breast or nipple and "dont" meaning tooth. Cuvier thought the cusps of the teeth look breast like. He probably needed to get out more often. Jefferson, with his American charm, called the mastodon "bubbie toothed." Cuvier was too late with his name. Just a few years earlier, his peer Joseph Blumenbach had taken the initiative in giving the two extinct animals Linean binomials. The mammoth, he thought, was too close to the Asian elephant to deserve separate genus. He named it Elphas primigenius, meaning the primeval, or first, elephant. This was factually wrong. Woolly mammoths evolved much later than Asian elephants. The mastodon, he confusingly named Mammut americanum, meaning American mammoth. When paleontologists eventually decided to put the woolly mammoth in its own genus, along with later discovered mammoths, they named it Mammuthus primigenius which is still wrong because it was the last mammoth.

Let's get back to your budding cryptozoology career. The beast in the brush did not stop long enough to give you a big toothy grin so you could figure out its dietary preferences. Don't worry, despite two centuries of bad illustrations making them look the same, there are significant enough differences in appearance to make an identification. Thanks to finding almost intact frozen mammoths, we know more about them than any other prehistoric, extinct animal. This includes details of their appearance. We know what their ears looked like and what the very tips of their trunks looked like. We don't know as much about fine details of mastodon appearance, but we know enough.

A very nice person made this and donated it to Wikipedia. Source.

Woolly mammoths have a distinct and well known profile. Their back slopes down from their shoulders to their hips. This is not formed by and great difference in the length of their legs. Instead, it is caused by long dorsal spines on their thoracic vertebrae. This humped area is used to store fat for the winter. The woolly has a high domed head tight against its shoulders and tusks that begin pointing almost straight down before making a tight corkscrew curl back up almost to eye level. Columbian mammoths differ from woollies by being taller. Their legs are longer and the hump is less pronounced. Their hair probably wasn't as dense as on the woolly.

Mastodons had shorter legs and longer bodies than either mammoth. The line of their back was fairly straight. Their heads projected further forward as did their tusks. The curve of the tusks was more like those of modern elephants. Baby mastodons had short tusks in their lower jaws, though they shed these when their adult teeth came in and reshaped their jaws. Mastodons probably had longer tails than woolly mammoths, though you would only notice that if you saw them together. Like the Columbian mammoth, mastodons didn't have fur as thick as the woolly's wool.

There you have it, the key to a good photographic identification of a mammoth or mastodon is to catch them in profile, maybe in the crest of a hill, silhouetted by the setting sun. Good luck with that.

1 comment:

joel hanes said...

Thanks. Fascinating as always; on this topic you're the best.