It may seem unlikely to uncover details about what an animal ate thousands of years after its extinction, absent of so much of the flora and fauna that co-existed with that animal.
It might seem even more improbable to illicit that information from fossilized teeth alone.
And yet, this is exactly what Dr. Brooke Crowley and Eric Baumann of the University of Cincinnati have done.
[image of Eric Baumann and Dr. Brooke Crowley on Khardung La, India; courtesy of Dr. Crowley)
They sampled molars from eight different mammoths and four mastodons, each with a known provenance in the Cincinnati region. Analyzing stable isotopes within each tooth provided information not only about each animal’s diet, but also its habitat.
“Isotopes in our tissues,” Dr. Crowley, Assistant Professor of Quaternary Paleoecology, explained in a phone interview, “are environmental integrators.”
“What we like to say is that isotope values in an animal’s tissues can tell you something about its life. That could be the diet, it could be the environment the animal inhabits, or, in the case of strontium, it could be the actual locality where it lives.”
Over the past 30 years, studying stable isotopes has become an increasingly popular method of understanding both paleontological and archaeological finds in more depth.
These chemical signatures reveal details incorporated within the body over its lifetime and remain in its bones past its death. In other words, what one eats and drinks leave traces of elements that point back to that very same diet and to the region from which one drank water. That organic material has footprints, and scientists—using mass spectrometers and other types of analysis—can read and interpret them.
Remarkably, these chemical footprints remain, even after thousands upon thousands of years. And teeth, with their sturdy crystalline structure, seem to offer reliable stable isotope data.
Dr. Crowley and recent graduate Eric Baumann described their research in a paper to be published in Boreas. Carbon isotopes revealed broad information about what these twelve proboscideans ate; strontium and oxygen isotopes uncovered the region and climate in which these animals lived.
They began their research expecting to uncover that the two species were nomadic, that their teeth were discovered in areas geographically distant from their place of origin. They also expected that mammoths and mastodons ate different types of vegetation.
While their research confirmed the different diet, it provided surprising results for habitat: with the exception of one mastodon, all of these animals actually lived and remained within the Cincinnati region.
In response to why they originally thought these animals might be nomadic, Dr. Crowley pointed to the behavior of existing species.
“Most large animals aren’t sedentary.”
“In general,” she explained, “big creatures move a fair amount; they have large stomachs and they eat a lot of food. And there may be different reasons for moving. It could be a dietary need, it could be there’s some particular nutrient in the soil that they want from time-to-time, or there may be a particular region they like for birthing or mating.”
We see this today in humpback, gray and blue whale populations on either side of the North American continent, migrating from warmer regions in the ocean to colder regions thousands of miles north.
“African elephants, in particular, are typically very destructive by nature. They are what we call ‘environmental engineers.’ Their behavior changes the environment around them.”
Perhaps the most notable affect elephants leave in their wake are the trees they knock down. Consider, too, that elephants eat 160 – 300+ pounds of vegetation a day per elephant.
“[T]hey heavily modify an area. Then they move and modify another area. And they typically have pretty large home ranges. Some populations seasonally migrate from one place to another; others are just more continuously on the move.”
But, she cautions, “we can’t necessarily use that information to interpret the behavior of extinct species. They’re not necessarily that closely related. But it is something we have to go on.”
In their research, the authors include data from water samples taken from rivers and creeks in Ohio and Kentucky.
What, one might wonder, do modern-day water samples have to do with ancient teeth and their composition?
Strontium within water reflects the geology from which it came. This information is stored within teeth, thereby leaving yet more footprints the scientists can interpret.
Of the types of isotopes analyzed, Dr. Crowley explained that “[a] lot more work has been conducted on carbon and oxygen. So we didn’t really need to establish a local baseline for either of those two isotopes. But strontium’s a little less studied, and we didn’t know what sort of regional variability to expect.
“Without any comparative baseline, it’s hard to interpret what strontium in the animals might mean. We could say, ‘well, they’re all really similar’, but if we didn’t really know what to expect for this region, we wouldn’t know if they’re similar to the region or if all of those animals may have come from somewhere else. So we needed to establish a local baseline.”
In other words, they needed to understand the chemical signatures within local water in order to see if they matched the chemical signatures within these teeth.
“[This is] the first step,” she continued, “in what will hopefully be a long-term research direction: thinking about North American fauna and ecological change over time here on our own continent.”
When asked if this meant she would study other extinct animals or continue researching mammoths and mastodons, her response was “potentially both.”
“Currently I’m [working on a] project using strontium isotopes to look in a little more depth at particular individuals.”
[image of Dr. Brooke Crowley with a bison scapula; courtesy of Dr. Crowley]
She referenced a mastodon from Michigan as an example.
“[W]e’ve sampled little increments of his tusk to see how he moved during his lifetime.”
“One drawback of teeth,” she mentioned, “is that they just give you a relatively brief snapshot in time, whereas a tusk gives you a continuous record of an individual’s life.”
But she is equally interested in what she described as “big-scale patterns” of behavior across various species. And in this research, ‘behavior’ refers to details about their diet, and whether specific species roamed or remained in a specific region.
“If there is any living taxa that we could sample,” she added, “it would be interesting to see how they may have changed, even if they didn’t go extinct.”
“There’s interesting work that’s been done,” she said, referring to research of one of her colleagues, “[regarding the origins of] fossil deposits that indicates mastodons may have retreated to a particular part of the United States just before the Terminal Pleistocene.”
The Pleistocene is a period of time on earth that dates from about 2 million years ago through about 11-10, 000 years ago. The ‘Terminal Pleistocene’ refers to an extinction event within this period.
“Prior to the Terminal Pleistocene, they were found all over the United States. At the Terminal Pleistocene, they’re only found in a little tiny patch of the United States. Something affected their distribution. And I call it ‘retreat’ because it’s a much smaller distribution than they had before.
“By analyzing isotopes in bones and teeth, we would potentially be able to build off of these fossil distributions to paint a more interesting ecological picture of the Terminal Pleistocene.”
Painting more interesting ecological pictures is a strong focus of Dr. Crowley’s work. A scientist who has travelled extensively throughout the world, her research has taken her to the Canary Islands, the Dominican Republic, Trinidad and Madagascar. Reading her blog and her website, one recognizes a distinct fondness for the aforementioned African country.
When asked if Madagascar was where her heart was, she responded, “In many ways, yes. Part of that is that I’ve devoted a lot of time and energy into learning a lot about it. So, now I’m invested.”
“There are certainly conservation issues in our own country,” she continued, “but there are other places–and Madagascar is one of them–where there’s a real need to try to make some changes happen now for future conservation and biodiversity management.”
“Up until recently, the recent past of Madagascar was rather understudied. It turns out that there are a lot of interesting questions that are still unanswered.”
Her website, Agoraphotia.com, describes her specific interests:
I investigate ecological interactions among living and recently extinct animals using stable isotope biogeochemistry. My interests include niche partitioning, conservation biology, and paleoecology. I am particularly interested in the causes and consequences of recent extinctions, and the ecological repercussions of habitat fragmentation and degradation.
She has studied fossilized rodents, lemurs and orangutans; she has researched climate change; she has studied plants and soil.
•Assessing the utility of stable oxygen isotopes in distinguishing dietary niches.
•Distinguishing isotopic niches of fossil rodents in the Dominican Republic.
•Establishing the stable isotope ecology of modern and Prehistoric Trinidad.
•Exploring ecological change following human settlement on the Canary Islands.
•Identifying responses of the animal community to climate change and human impacts in Madagascar.
•Quantifying spatial variability in bioavailable strontium and assessing changes in mobility patterns of extinct and extant North American megafauna.
Prior to the University of Cincinnati, she lectured at the University of Toronto and volunteered at the Royal Ontario Museum in the OWLS (Open the World of Learning to Students) program.
She describes herself as “a relatively new professor in Cincinnati”, one who actively works to try and include students into her research projects. In this, she feels she has been successful, as she has had a number of students involved in her postdoctoral and graduate research and currently has students working with her in the lab.
The study of proboscidean teeth that lead to the paper to be published in Boreas was, she said, “originally designed to be a student project.”
Given her vast and varied experience, one might wonder why the focus was extinct North American fauna.
Explaining that most of her students are either from Ohio or the surrounding region, she said, “It’s a little more relevant for them to think about animals that lived in their backyard than animals that lived on the other side of the planet.”
This, too, is why they used teeth from the Cincinnati Museum of Natural History, rather than the collections of other neighboring state museums.
[image of Dr. Crowley in Madagascar next to a sign that warns visitors that “Lake Ravelobe is forbidden” and that “Crocodiles attack”; courtesy of Dr. Crowley]
“Many of the reasons that I do what I do and that I am where I am is because of other people who have helped me along the way or inspired me. And really one of the biggest reasons that I wanted to go into academia in the first place was because I feel like I have been empowered in many ways to try to make a difference.
“And I feel like that’s something that I can share with others and then try to make a difference by empowering others and helping them find their way and be compassionate as well.
“So that’s sort of my goal.”
She chuckled. “I don’t know how much I have really met that goal, but I do try, and I’m still pretty new to being a professor. So, I’m finding my way. It’s a challenge, but it’s a good learning experience, and I find it to be pretty rewarding.”
[image of Dr. Crowley on a promontory in Tenerife, Canary Islands; courtesy of Dr. Crowley]
A Mammuthus primigenius-sized THANK YOU to Dr. Brooke Crowley for her generous time, help and fascinating responses to my questions! What a great honor to connect with her!
You can read the paper in Boreas, Stable isotopes reveal ecological differences amongst now-extinct proboscideans from the Cincinnati region, USA: http://onlinelibrary.wiley.com/doi/10.1111/bor.12091/abstract
I had a very difficult time grasping the concept of isotopes. This is due to my struggle with chemistry in general and not a reflection of the gracious people below who took the time to try to help me understand it. I extend sincere thank you’s to:
- Dr. Brooke Crowley
- my dad
- my sister-in-law who studies science
- Dr. Suzanne Pilaar Birch (@suzie_birch)
- Ariel Zych (@Arieloquent) and Science Friday (@scifri)
If you are interested in understanding more, here is further reading:
- Dr. Brooke Crowley, Stable Isotope Ecology: http://crowleyteaching.wordpress.com/courses/stable-isotope-ecology/
- Stable Isotopes in Zooarchaeology: http://sizwg.wordpress.com/bibliography/
- New insight from old bones: stable isotope analysis of fossil mammals, by Mark Clementz: http://www.mammalogy.org/articles/new-insight-old-bones-stable-isotope-analysis-fossil-mammals
- Applications of Stable Isotope Analysis, K. Kris Hirst: http://archaeology.about.com/od/stableisotopes/a/si_intro.htm