Was There Something in the Water?

Hey there every peoples!

I have always had an interest in ancient elephants. Ever since I first laid eyes on the woolly mammoth at the Royal British Columbia Museum, they have always held a spell on me. It has only been in recent years that they have drawn me in as a research interest. Despite being a diverse and very successful group with a broad array of adaptations, not a lot of work has been done on them outside of naming new species and studying their Ice Age members. However, the first serious research question I ever came up* with involves our old friend the American mastodon.

*I say I came up with it, but I doubt I was the first to consider it.

Mastodons are big animals. Being relatives of elephants, that should be a given. They are invariably described as reaching 10 feet tall and weighing in excess of 5 tons. Like all prehistoric animals, these figures are based on the largest known specimens and fail to take variation into account (especially in museums, where mounted skeletons are rarely as big as the diagrams seen in books). Variation in size can be due to things like geography, diet, habitat, and even genetics. When I was growing up, my books said that mastodons were from the Midwest (places like Ohio, Michigan, Indiana, and Illinois). This fact didn’t mean much to me until my college years.

In 2007 I attended my first field trip  with the once great San Bernardino County Museum. We went to the newly opened Western Center for Archaeology and Paleontology (now the Western Science Center), home to the fossils treasures uncovered during the construction of the Diamond Valley Lake reservoir. As the erudite Eric Scott explained the fossils to us, he explained that the museum’s unofficial mascot, Max, was a bit of a surprise. The first bone of Max found was his pelvis. According to Eric, it was so large they first thought it was a mammoth. It wasn’t until they uncovered his skull that they realized they had a mastodon. Say what?

The enormous skull of the mastodon Max, on display at the Western Science Center, Hemet, California.

You see, this confusion stem from the La Brea Tar Pits. At the time the best comparative material in the region (neigh California) was from Rancho La Brea. And, the mastodons there are runts by elephant standards. Just look at the female and her calf on display in the Page Museum:

The positively shrimpish mastodons of Rancho La Brea.

She is barely 6 feet at the shoulder, and the calf is the size of a pony. Sure, females are smaller than males, but that would mean the males probably didn’t exceed 7 feet at the shoulder (far below the 9 to 10 feet of the Midwestern specimens). So, it is no wonder that Max created such a stir. In fact, studies would later conclude that he is the largest mastodon in western North America, as large as the biggest individuals from the Midwest. And Max wasn’t alone. All the mastodons found in Diamond Valley were large. And the La Brea mastodons weren’t alone either. All mastodons in California outside of Diamond Valley were unusually small. What was going on? Why were the mastodons of Diamond Valley so much larger than in the rest of California? I had no idea. I’m not sure anyone else did. This information sat around in my mind for years until one day something just clicked.

The forelimb of a diminutive mastodon from San Diego County (formerly on display at the San Diego Natural History Museum). If it was flat on the floor and had it’s scapula, it wouldn’t reach 6 feet.

Skull from Santa Cruz county. Only half the size of the ones from Diamond Valley.

A smallish mastodon radius from Jerupa, Riverside County.

A mastodon found during construction of a community center, Laguna Hills, Orange County. A bit on the large side, which in this context means he was around 7 feet at the shoulder. Not bad, but still not as big as the mastodons in Diamond Valley or the Midwest.

Mastodon fossils found during construction of toll roads, Orange County. The femur is less than three feet long.

Bones of a mastodon found in Arroyo Grande, San Luis Obispo County. The size of the bones suggests an animal between 6 and 7 feet tall.

I have given up trying to figure out how my mind works. Something I see or hear could cause it to make the most strained and far reaching connections that seemingly come out of nowhere. My mind made one of these connections one day when I was randomly thinking about the size disparity between American mastodons. I remembered a small blurb from the intro section of a National Geographic issue. It was on the Burning Tree Mastodon (BTM), named after the golf course in Ohio where it was found. The Burning Tree Mastodon is touted as being one of, if not the, largest mastodon ever found in North America. BTM was not just notable for his size but also what was found with him. Amongst the bones was a wad of plant matter that scientists determined was preserved gut contents. The cold muck of the bog had preserved the BTM’s last meal. According to the article the gut contents consisted of water lilies, pond weed, and swamp grass. Why is this important to the mystery of size in American mastodons?

Cast of the Burning Tree Mastodon on display at the Cincinnati Museum Center, Ohio. By flickr user Chris.

The scientist quoted in the article said: “That is a very rich and nutritious diet. This guy was focusing on yummy stuff.” That’s when it hit me. Could diet be the key to why mastodons were so large in the Midwest and so small in California? It’s not unheard of. Coastal brown bears are bigger than grizzlies because the former eats more meat (thanks to huge salmon runs). The aquatic vegetation being described as “rich and nutritious” got me thinking. The Midwest, even today, is full of marshes, swamps, ponds, and rivers brimming with plants. California during the Ice Age had more water than today. Even the Mojave Desert was dotted with lakes and streams. But, it lacked the extensive wetlands seen in the Midwest. That is, except for one place: Diamond Valley. One mastodon, Little Stevie, was found in wetland deposits. Was this the key to the puzzle of mastodon size? It was starting to look that way.

Of course this is all just speculation on my part. Conducting actual research is another matter. How would one go about investigating this? For starters, we would need to examine the diet of the animals. One way to do this is with stable isotopes. This technique has been used to tell if an animal is a browser or a grazer. At the 2013 SVP, I spoke with a scientist who does isotope studies. She said she didn’t know if this technique could differentiate between terrestrial and aquatic vegetation (but she then said that is research to be done). What else could we do?

There is microwear analysis. In this process, casts are made of the surfaces of an animal’s teeth. The casts are then put under a scanning electron microscope. This allows us to see microscopic scratches on the surface of the surface of the tooth. Different diets leave different scratch patterns. By comparing these patterns to those of modern animals with known diets, we can infer the diet of the extinct animal. How would we tell terrestrial brush from aquatic plants? Same thing as before. Compare the patterns to those of modern animals with various diets—for instance, giraffes and deer for browsing, manatees for water plants, and moose and capybaras for a mix of the two. At least that’s the idea and I’m sticking with it (until I find out I shouldn’t).

Nothing in paleontology comes easy. The snippets of facts you see in exhibits and the long winded treatises you read in books are the end result of a lot of work. Gathering data and conducting studies can take years. Care must be taken to keep the process as pure as possible so as not to get misleading results. Because then you’d have to do it all over again, if you can (especially with destructive methods like isotope analysis). And it may lead to a totally different conclusion then what you were hypothesizing. Mastodon size differences are no different. This is a riddle that will require lots of hard work from numerous people to crack. I may or may not be one of them. My only hope is that will one day be solved.

Till next time!

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