Something has been discovered in Tennessee—something that only exists in one museum. It’s something enormous, slightly puzzling, and possibly the first of its kind discovered. Five years after its excavation, it remains incomplete.
The mastodon skeleton slowly taking shape in Tennessee is no secret. Pictures and descriptions of its progress have been posted on social media from the beginning, and while those who are aware of it are intrigued, it hasn’t made many headlines. Yet.
Out of the gray
The Gray Fossil Site near Gray, Tennessee, was found by accident during road construction in 2000. Thanks to the efforts of local people and the state government who recognized the importance of the site, construction halted. A museum was erected several years later. Bits of bones and one shattered tusk were all that had been found when the site was preserved, but the area is proving to be voluminous in its fossil content.
“We used to catalog 1,000 specimens a year—[Individual specimens] could be a tapir, frog, snake, whatever,” Gray Fossil Site Lab and Field Manager Shawn Haugrud explained by phone. But additional volunteers have helped boost the pace: “A couple of years ago before the pandemic, we catalogued 10,000 specimens—so 10 times as many fossils.”
This area is an approximately 5 million-year-old sinkhole. It has preserved a wealth of fossil vertebrates and plants, over 100 species of each to date, from what was once a distinctive ecosystem. And the largest, perhaps most mysterious discovery of them all? The Gray Fossil mastodon.
That’s what it’s called at the moment. Found lying on its side among and underneath boulders, this ancient mammoth relative has the requisite tusks, four limbs, and overall body shape of a mastodon. But it’s different enough to give scientists pause. When compared to other known North American mastodons—a genus that is, with increasing research and discoveries, beginning to expand—it doesn’t match.
This fossil was the subject of a presentation by Dr. Chris Widga, head curator at the Gray Fossil Site, at the Eighth International Conference on Mammoths and Their Relatives (ICMR) this past October. Unlike massive paleontological conferences, the ICMR is both remarkably small and comparatively new. According to Dick Mol and Dr. Adrian Lister, both renowned mammoth scientists who have been heavily involved in these conferences, the first ICMR was in 1995 and originated as a mammoth-centered conference hosted in Russia. Since then, it has grown into one that includes research about both extinct and extant proboscideans, a family of vertebrates whose prominent feature usually includes a proboscis (a trunk) and encompasses today’s elephants.
The conference is held in a different part of the world every three to four years. At the previous 2017 conference, “India put up a proposal for hosting the 8th conference at Bangalore,” wrote Dr. Raman Sukumar, organizer of this year’s ICMR and honorary professor at the Centre for Ecological Sciences, in an email. “The scientific steering committee of the conference voted overwhelmingly in support of the Indian proposal to host the 8th conference at Bangalore in 2020.” But due to the pandemic, the Indian Institute of Science hosted this online. One hundred thirty-seven people from 27 countries participated.
Not like the others
Showing the Gray Fossil mastodon’s skull in comparison to both earlier and later mastodon species, Widga explained just why they aren’t ready to say exactly what it is they’ve found. Even visually, the differences are immediate.
“The record of early North American mastodons is extremely fragmentary, and the character[istics] that we've used to tell them apart, historically, don't often hold up to modern scrutiny,” he wrote. “This is why it is difficult to fit the Gray mastodon into any existing evolutionary framework. BUT what we do have points to a novel suite of morphological features, suggestive of a new species.”
North America was home to more than one ancient tusked beast. The iconic mammoth—woolly or Columbian—has received considerably more attention and research until recently. It has long been assumed that at the middle to end of the Pleistocene, this continent was home to just one species of mastodon—the American mastodon (Mammut americanum)—an assumption that was shattered in 2019 with the discovery of the Pacific mastodon (Mammut pacificus). Earlier types of mastodons, particularly those that would have been contemporaneous with the Gray Fossil, exist in the form of fragmentary pieces found throughout the country—an isolated molar here; a bit of tusk or mandible there. No one, other than the Gray Fossil Site, has an entire North American mastodon skeleton this old.
“[The Gray Fossil mastodon] has the potential to fit into this very fragmentary record,” Widga said in a video interview, “and be somewhat of a Rosetta Stone.”
Modern preservation
How those at the Gray Fossil Site have excavated, documented, and prepared it is another wonder unto itself. This team uses technology at every turn—sometimes, chuckled Widga, to a bit of an extreme. But doing so has added insight into what happened to this animal in a number of ways.
Basic excavation—paleontological or archaeological—means recording where bones are found in any site. Using survey-grade technical equipment is a step beyond the basics. The Gray site team used this equipment to take hundreds of shots, mapping each bone in its location such that they compiled over 30,000 recorded survey points in a database, per Dave Carney, an East Tennessee State University student.
Spatial analysis becomes particularly powerful when it allows the data to be presented and reviewed in various ways. His research may help us understand how this animal might have died and how it became preserved. Understanding the relation of boulders to the fossil coupled with sediment analysis suggests that this animal may have been swept away in a catastrophic landslide—one that either carried its already dead body into the bottom of the pond or killed it, pinning it under water with massive rocks. The team is still working on this hypothesis.
Reconstructing the fossil has been the most time-consuming aspect of the whole process, one that is remarkably detailed. Although located in a roughly anatomical position within the sediment, the mastodon bones were often fragmented into tiny pieces. The team jacketed larger elements of the skeleton, such as the jaw and the skull, but other bones were taken the few hundred feet from the site to the museum directly on a tray. Once inside, Haugrud and his volunteers would each take 10 pieces, clean them, glue them together, and repeat the process until the fragment supply was exhausted.
“The world’s slowest teleporter”
Most fossil preparators, Haugrud said, will prepare a fossil within its jacket, even if that particular fossil is crushed, as it can offer important information regarding how it came to appear in such a state. But, he explained, “That’s why Chris [Widga] and I scan things. You can have your cake and eat it, too.”
In other words, they scan the fossils as taken from the field, saving that information digitally. “But then I can take it,” Haugrud said, “and put all the pieces back together, break-to-break, so that it’s actually the shape and size it was in real life.” It’s a process Haugrud describes as "the world’s slowest teleporter": rebuilding the fossils of a beast that once stood approximately 3.3 meters high and weighed an estimated 12-13 tons, piece by unbelievably small piece, to form a complete and massive whole.
The technique they use to bring these pieces back together is one that Haugrud himself developed. Polyvinylbuterol, or ‘Butvar,’ is used in other prep labs, but not necessarily in the thread-like webbing that Haugrud has created. “I had observed that Butvar could create small strings unintentionally when the applicator pulled away,” he emailed, “so I decided to conduct experiments to see if I could make threads and fills out of it, and it worked beautifully.”
“The threads are tight, like the metal tensioners used on suspension bridges and other structures,” he continued. “The threads support from all angles, so although they technically have some flex they create a rigid structure that can hold shape.”
In another nod to innovation, the team used the 3D scans of the more complete side of the skull, mirrored it so that they have an entire digital skull, and then 3D-printed it using Butvar plastic. They’re now using this 3D-printed structure to reconstruct the fossil fragments of the mastodon skull.
Each complete skeletal element—the skull or femur, for example—is then 3D-scanned. This will eventually enable them to share the entire fossil online, offering access to researchers globally.
“Mastodons are a challenge to work with because they are so big,” Widga stated, “and very few museums have collections that are diverse enough to figure out some of the big taxonomic and morphological questions. 3D-scanning is a game-changer for that very reason.”
Beyond the bones
At the same time that one part of the team is finishing up on reconstruction, others on the team are investigating other aspects of this animal. “In some ways,” Widga offered, “we are asking questions that don't normally get asked of the fossil record.”
For example, he and Sarah Keenan, now an assistant professor at the South Dakota School of Mines & Technology, have previously collaborated on research at the Gray Fossil Site. They’ve bounced around ideas to explain how “this giant rotting carcass in this tiny little sinkhole pond” might have impacted the environment around it.
There is still a lot yet to be learned about this mastodon and so much more yet to be excavated. In his talk at the ICMR, Widga noted that there is exciting evidence of at least four, possibly more than nine, other mastodons yet to be pulled from the ground at the Gray Fossil Site.
“In northeastern Tennessee we are a household name,” Widga admitted. “But often, if you ask a person more closely, it becomes ‘I’ve always meant to visit the Gray Fossil Site, but have never made it!’ To most locals, the Gray Fossil Site is their neighborhood natural history museum, nothing too special besides having some strange animals.”
Perhaps this is about to change.
Jeanne Timmons (@mostlymammoths) is a freelance writer with a strong passion for paleontology. Based in New Hampshire, she writes about paleontology (and some archaeology) on her blog mostlymammoths.wordpress.com.
