“Good morning!”
It’s not just a greeting; it sounds like a proclamation.
The voice on the other end of the phone is deep, melodic, and—as our conversation progresses—punctuated with moments of laughter. We have been discussing paleontology in the Yukon, and with each new detail, I begin to wonder why this territory is not making regular international headlines.
Dr. Grant Zazula’s work is fascinating, and it is neither a short phone call nor the only communication we’ve exchanged. And yet, it is all that I can do not to encourage him to keep going, long after social decorum dictates that he has been more than generous with his time.
[image of Dr. Grant Zazula with a mastodon ulna, part of the Earl Bennett mastodon, courtesy of the Government of Yukon]
Dr. Zazula is the Yukon paleontologist, a job that has only existed since 1996. His own tenure began in 2006. With an office in Whitehorse, the capital of the territory, his work oversees an expanse of Canada that abuts Alaska. It is a land of dramatic beauty, where colors dance in the sky and mountains tower in silent grandeur.
Embed from Getty ImagesHis most recent paper, co-written with 14 other people, made news throughout the world and continues to attract media attention. In it, the scientists present data that completely overturns previously believed information about extinct animals and the impact that humans may or may not have had upon their survival.
“[T]here were two radiocarbon dates in the literature from Yukon mastodons,” he explained in an email. “One that was ~18,000 and the other 24,000 years old.”
“Based on analysis of the paleoecology, that was a time when steppe-tundra grasslands covered Alaska, Yukon and Beringia. There were probably no trees, few shrubs and almost no standing water. It was very cold and, especially, dry. This seemingly is not good mastodon habitat. So either the dates were incorrect, or our understanding of mastodon ecology, behavior and adaptations need[s] to be revised.”
Various species of mastodon once existed throughout the world. Although their fossils look elephantine, they are not believed to be direct ancestors of today’s elephants. They are, however, part of the same umbrella mammalian group: the Proboscidea (so-named for the trunks possessed by many—but not all–of their members). In North America, that group contained the American mastodon (Mammut americanum), the woolly mammoth (Mammuthus primigenius), and the Columbian mammoth (Mammuthus columbi).
[image of the Cohoes mastodon, NY State Museum, Albany; taken by the author]
Mastodons tended to have straighter tusks and were shorter than their mammoth cousins. They also ate hardier vegetation, food that required a much different tooth structure than mammoths.
[image of mastodon tooth, courtesy of the Indiana State Museum]
[image of mammoth tooth, courtesy of the Indiana State Museum; for more info about the differences between mammoths and mastodons, see this post.]
Parts of Siberia, Alaska and the Yukon were once connected in an area known as “Beringia.” The Bering Strait did not yet exist, enabling animals and eventually the first humans to cross into our continent. It is believed that humans arrived in what is now North America about 14,000 years ago.
And this is where the research of Dr. Zazula and his colleagues becomes particularly important.
Prior to their paper, one theory to mastodon extinction laid the blame upon first humans: it was proposed that they overhunted these animals.
Sampling 36 fossils and presenting 53 new radiocarbon dates, Dr. Zazula and his colleagues found that mastodons within Alaska and the Yukon were much, much older than the originally published dates. In other words, their research suggests that mastodons from what was once Eastern Beringia were no longer present when the first humans appeared.
The path to this remarkable research did not happen overnight.
The foundation appears to have been laid by two different events: by the chance meeting of Dr. Zazula and a gold miner, and later, by the PhD work of a graduate student.
If one reads the acknowledgements on the aforementioned paper, Dr. Zazula references Earl Bennett as both the donor of a partial mastodon skeleton and his inspiration to learn more about mastodons within the Yukon.
“Earl is a great Yukoner,” Dr. Zazula wrote when asked about this. “He mined for gold underground in the winters with a pick and shovel, decades ago. He worked on big gold dredge machines. And, he loves paleontology.
“While mining, he made collections of Ice Age bones that were just left around the mining camp or were encountered while mining. He eventually amassed an amazing collection.
“In the early 1970’s a gold dredge on Bonanza Creek hit a skeleton of a mastodon. An incredibly rare find! Someone collected it and was looking to sell it. So, Earl bought the skeleton just to make sure that it never left the Yukon. He had it in his garage for decades.
“One day a mutual friend introduced me to him in a coffee shop, about a year after starting my job [as the Yukon paleontologist]. He said that he had a mastodon skeleton and wanted me to see it. I ‘corrected’ him, saying that it was more likely a mammoth, because we almost never find mastodons in the Yukon. He assured me he know the difference and said he would see me tomorrow at my office.
“The next day he backed his truck up and in it was a partial mastodon skeleton. I couldn’t believe it. There were several postcranial bones, some vertebra, scapula, parts of the skull and parts of the mandible with teeth. It was amazing. I wanted to find out how old it was, and that was one of the inspirations for this project. Earl is a good friend now and big supporter of our research.”
[Paleontologist Grant Zazula with a partial American mastodon (Mammut Americanum) skeleton found on Bonanza Creek and donated to the Yukon fossil collection by Earl Bennett, from Ice Age Klondike, courtesy of the Government of Yukon]
That partial skeleton was indeed one of the many fossils sampled for the paper.
Dr. Jessica Metcalfe, one of the co-authors, also prompted this research when conducting work for her PhD.
“[S]he was doing a project looking at stable isotope ecology of mammoths and mastodons in various places in North America,” said Dr. Zazula.
[image of Dr. Jessica Metcalfe with mammoth bone, courtesy of the Government of Yukon]
Her work included Yukon fossils that were sent to the lab at the University of Arizona to be radiocarbon dated. Those dates turned out to be older then 50,000 years old.
“So that’s what got me thinking,” he continued, “‘well, maybe those original published dates are wrong.’”
“The first step was to re-date [the specimens that had produced the original published dates]. The new dates turned out to be >50,000 years. So we knew there was a problem with the previous dates. We figured then we should date as many as we could get our hands on.”
This lead Dr. Zazula to connect with Dr. Ross McPhee, another co-author.
“I got in touch with him early because he oversees collections at the American Museum of Natural History, [and] he has a big interest and lots of experience working on Ice Age extinctions. [H]e’s an excellent writer and really kind of kept us going with some of the writings. He was really integral to keeping things together.”
The paper eventually involved a total of 15 people.
“I feel pretty strongly that if you worked on it and contributed to it, then you should be considered an author,” Dr. Zazula stated. “So it ended up being a long list.”
One of the first aspects their paper addresses is the reason behind why the original published dates are incorrect: the dating analyses were contaminated by fossil conservation methods.
“Humic acids in soils can be absorbed by the bones and teeth and chemically bind themselves to the collagen,” he wrote, explaining further. “So, modern ‘young’ carbon in those acids basically contaminates the ‘old’ collagen in the ancient fossil. And, it can be tricky to remove.
“The same with consolidants in museums. Varnish, glue, and other substances to preserve fossils can be absorbed into the bone and chemically bind with the collagen in the bone. These substances probably contain young, modern carbon which messes up the radiocarbon dating measurements.”
When asked whether museums continue to use the same preservation products that contaminated the dates, he wrote, “Yes, for sure. The thing is now museums keep better records of what they use. Many of the fossils we dated were collected in the 1940’s or at least several decades ago. Museums were not that vigilant about keeping detailed records on those things then. Also, they seemed to put preservatives on everything. Now, at least if we know what was put on it, the chemistry can by developed to remove it. Most of the common preservatives now are soluble in alcohol or acetone and can be dealt with. The problem is when they are unknown.”
We discussed this further by phone.
“One thing about Alaska and the Yukon,” he said, “is that the Ice Age bones that come out of the ground are so well preserved because of the permafrost. In other localities, say, the deserts of the American Southwest or the Great Basin or the Plains, where bones have been out in the sun and [are] dry and hot, they [sometimes] fall apart really easily when they come out of the ground. They need to be glued and consolidated with these various types of museum products.
“So you kind of have to weigh the different values.
“Say if it’s a specimen that’s already been radiocarbon dated, and it starts to slowly disintegrate, well, then you kind of have to intervene or else you’re just going to end up with a box of dust and broken bone. You have to decide whether the importance is more with display or preservation of the morphology versus needing to radiocarbon date or other types of analysis.
“[Y]ou have to look at the pro’s and con’s of whether the sampling [for radiocarbon dating] will ruin the specimen or not, and what is the potential information that can be gained by doing it. To me, I feel that having a research collection [in the Yukon], it’s all about research and learning new things from these specimens.”
Ultimately, I wondered whether Dr. Zazula expected the results he and his colleagues uncovered.
“I wasn’t quite sure,” he answered. “I had the gut feeling that these previously published radiocarbon dates were probably wrong. It didn’t make a lot of sense ecologically to have mastodons living in the far North when it was seemingly habitat they couldn’t live in: habitat with grassland and cold, dry steppe tundra conditions, no trees and very few shrubs.
“But there [was] also a part in the back of my mind that thought, ‘well, if those [previously published dates] were right, that’s maybe even more interesting because they are telling us something about mastodons and their behavior and their adaptations that we didn’t know before.’”
————
It was a great honor and pleasure to connect with Dr. Grant Zazula! Not only patient with my myriad questions, he is an adept and fascinating ambassador for the Yukon. A Mammuthus columbi-sized thank you to him!
A Mammuthus columbi-sized thank you to Dick Mol, as well, who is the reason behind this post!
[image of Dick Mol with fossil horse skull, found near Dawson City, Yukon; courtesy of the Government of Yukon]
Yukon Paleontology Program: http://www.tc.gov.yk.ca/palaeontology.html
Articles and publication referenced:
- American mastodon extirpation in the Arctic and Subarctic predates human colonization and terminal Pleistocene climate change, Grant D. Zazula et al, Proceedings of the National Academy of Sciences of the United States of America (PNAS), vol. 111, no. 52, December 30, 2014
- Ice Age Klondike, by Grant Zazula and Duane Froese, Government of Yukon, 2011
- Nursing, weaning, and tooth development in woolly mammoths from Old Crow, Yukon, Canada: Implications for Pleistocene extinctions, Jessica Z. Metcalfe et al, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 298, Issues 3–4, 15 December 2010, Pages 257–270
Listen to Dr. Zazula discuss his paper on the CBC’s Quirks & Quarks: http://www.cbc.ca/radio/quirks/quirks-quarks-for-dec-6-2014-1.2864605/mastodons-made-an-early-exit-from-the-north-1.2864634
