Eliann Stoffel – Unlocking the Secrets of a Forgotten Mammoth

A rather large bone, revealed by his bulldozer, prompted William McEvoy and his crew to cease work on the road and call the police. The police then called the local archaeological society, who, in turn, called an archaeologist at the local Natural History Museum.

When word got out that a mammoth had been discovered, visitors began pouring in to see the site.  Just a few miles outside of the town of Kyle in Saskatchewan, Canada, the excavation of these fragile bones from the hard clay was witnessed by an ever-growing number of people.  It is estimated that 20,000 visitors came to see the site that autumn in 1964.

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Eventually, the plaster casts protecting the bones were taken to the Natural History Museum (now known as the Royal Saskatchewan Museum); radiocarbon dating was conducted.  Possible museum displays and skeletal reconstructions were discussed.

And then?

Nothing.

Once the cause of great local excitement, the bones of the Kyle Mammoth faded from view.

The references above to archaeology are not errors.  Although the bones found were paleontological in nature, the focus on the find—and, indeed, the very reason they were recently resurrected—was to determine whether there was any evidence of human-proboscidean interaction.  When no stone tools were recovered in the surrounding sediment and with no obvious signs of butchering on the bones, interest in the fossil seems to have collectively disappeared.  For over 50 years, the various bones found on that stretch of road have been shelved in the Museum’s collections.

“I had always planned on doing my thesis at the University of Saskatchewan and I knew I wanted to do my thesis on hunting and butchering strategies utilized by Paleoindian people,” explained Eliann Stoffel, a recent graduate, in an email.

Her interest was not specific to any one species of megafauna. She hoped to study any and all large animals ancient people may have hunted: camels, bison, horse, proboscidea.

“I had approached my supervisor, Dr. Ernie Walker, with this topic and he had spoken with a member of the Saskatchewan Archaeological Society, Frank McDougal, who had suggested taking a look at the Kyle Mammoth.”

Which is how the long-forgotten fossil came back into view in 2015.

“We knew that the mammoth belonged to a time when people were in North America and actively hunting mammoths so we had the possibility of finding some sort of evidence of humans on the Kyle mammoth.”

This evidence is rare in the area known as the Northern Great Plains, an area that encompasses Saskatchewan (as well as another Canadian province and five U.S. states).

“It was one of those projects,” she said later by phone, “that, as soon as it came up, I couldn’t turn it down.  It needed to be done.”

Travelling between Saskatoon and Regina (where the Royal Saskatchewan Museum and the fossil are located), Eliann spent many hours studying and analyzing the bones from the 1964 excavation.  This included five boxes of bone fragments as well as 56 complete or near-complete bones, such as vertebrae, mandible, a partial tusk, and ribs.  Also included were ungulate bones, which—like the mammoth—did not comprise a full skeleton and did not present any clear association with its proboscidean fossil companion.

 

figure-4-1-kyle-mammoth-bones-eliann-stoffel-thesis

About 20% of the mammoth skeleton survived; image courtesy of Eliann Stoffel, University of Saskatchewan

 

Eliann’s thesis presents a comprehensive taphonomic analysis of the mammoth bones, and this was done because she and her advisors “knew that we needed to keep in mind that we might not find any evidence of human involvement.”

The idea of determining who or what made any kind of marks on a fossil seems like an overwhelming challenge.  This was not an animal that died the other day.  In this case, it died roughly 12,000 years ago. That is a considerable amount of time in which—after an animal is butchered, killed or otherwise dies of natural causes–it can be scavenged after death, it can be moved and scraped by natural elements, it can be affected by its fossilization, and then possibly affected by the process of discovery (in this case, by a bulldozer). How is anyone able to read the marks on fossil bones and know what they represent?

“[T]he first giveaway is the colour,” she wrote. “Bone, when it has been buried for a long time, tends to become stained from the surrounding sediment but only the outer surface. So when someone (an excavator) knicks the bone, the unstained inner portion of the bone is exposed and tends to be a lighter colour.

“The other indicator can be the clustering of marks. [With] butchering, there tends to be more than one cut mark on the bone in the same general area, usually at muscle attachment sites, and they tend to be orientated in the same direction. Rarely do you find cut marks that intersect each other. They are usually parallel. In accidental knick marks there is usually just the single mark and it tends to be located in a spot that you wouldn’t generally find cut marks (i.e. on joint surfaces or midshaft of a long bone).”

 

figure-b-15-kyle-mammoth-eliann-stoffel-thesis

 

Photo of the Kyle Mammoth right mandible from her thesis; courtesy of Eliann Stoffel, University of Saskatchewan

 

Contrary to initial review in the 1960s, Eliann discovered a few tantalizing signs that this mammoth may have, indeed, suffered from trauma induced by ancient humans.  From a suspicious-looking lesion to a possible puncture wound on vertebrae to a puzzling set of lines in a bone fragment, there was reason to wonder whether humans had been responsible for these scars.

Ultimately, however, the first two were determined to be pathological. The lesions conform to known understanding of malnutrition in the form of osteolytic lesions.

Knowing her hope to find evidence of human interaction, I asked if this was a bit of a disappointment.

“[I]t was a bit of a kick in the knees,” she admitted, “but still a super interesting avenue of study in terms of pathology. I am more than thrilled with my findings though!”

 

figure-5-5-kyle-mammoth-eliann-stoffel-thesis

figure-5-1-kyle-mammoth-eliann-stoffel-thesisImages courtesy of Eliann Stoffel, University of Saskatchewan

 

Another startling discovery appeared in what she describes as a “spongy” bone fragment, shown above, which contain traces of blood vessels.

“I remember bringing it to my supervisor and we both scratched our heads over it…So we called on our resident bioarchaeologist Dr. [Angela] Lieverse to take a look and she wasn’t sure but suggested possibly something vascular. Sure enough, when I searched for studies fitting that criteria, a couple articles turned up. So it seems that it is an occurring phenomena but possibly not that common,” Eliann wrote.

Ultimately, Eliann determined that this was a young male woolly mammoth (between 28 – 35 years old) that was still growing at the time of its death.  She estimates it was 328.66 cm (approximately 10.8 feet) tall.  While the large open wound on one of the vertebra points to a possible puncture wound from Clovis weaponry, other pathological features point to a mammoth suffering from malnutrition.

Eliann’s enthusiasm for those who helped her in her research was apparent.

“[T]he folks at the [Royal Saskatchewan M]useum were more than happy to help in any way possible,” she expressed, “and it is something that I have always appreciated! Also my major funders [were] the Saskatchewan Heritage Foundation, the Saskatchewan Archaeological Society, and, of course, the Department of Archaeology and Anthropology at the [University of Saskatchewan].”

More than just a strenuous academic endeavor, Eliann’s research has painted a picture that has been missing for decades on a significant local paleontological find.

“The [people in the] town of Kyle identify with this mammoth.  As you come into Kyle, there’s this statue of a mammoth.  Their sign that says ‘Welcome to Kyle’ has a picture of a mammoth on it.  It’s clear that they identify with it.”

 

 

A Mammuthus primigenius-sized THANK YOU to Eliann Stoffel—not only for her time in emails and by phone–but also for her gracious permission to use a number of pictures from her work!  Her thesis is fascinating and well written.  I recommend it to all!  Eliann, may you find many mammoths with evidence of human association in the future!

Another enormous thank you to Dr. Angela Lieverse, head of the Department of Archaeology and Anthropology at the University of Saskatchewan, who was also responsible for the generous use of images from Eliann’s thesis!

And I am very grateful to Dr. Emily Bamforth at the Royal Saskatchewan Museum for connecting me to Eliann! I could not have written this otherwise. THANK YOU!!

*****

References:

  1. The Kyle Mammoth: An Archaeological, Palaeoecological and Taphonomic Analysis, Eliann W. Stoffel, July 2016, University of Saskatchewan
  2. Shedding Some Light on the Kyle Mammoth, David Zammit, Swift Current Online, Nov. 13, 2016; the article that brought Eliann Stoffel and the Kyle Mammoth to my attention!
  3. PDF about the Kyle Mammoth from the Royal Saskatchewan Museum

Screenshot Kyle Mammoth RSM

Screenshot from the aforementioned PDF of the Kyle Mammoth, Royal Saskatchewan Museum

Maiasaura Life History Project: The Art of Scientific Research (Part 2)

It’s one thing to be a detective. It’s another to be an artist: shifting expectations, making unlikely comparisons, causing one to consider entirely new perspectives.

Comparing elements of extant alligators and red deer to an extinct hadrosaur certainly changes how one views paleontology.  There is something unifying about it, connecting traits of living species—creatures that share the world with us today—to species that died out millions of years ago.  Instead of a scientific field one might put into a box labeled “the study of the past,” it becomes an increasingly complex vine weaving the past with the present.  And if animals as seemingly disparate as alligators, red deer and hadrosaurs share similarities, what else among us does?

Maiasaura HWB - Maiasaura replica

Maiasaura peeblesorum model; courtesy Dr. Holly Woodward Ballard

This connection was made all the more apparent in speaking with Dr. Holly Woodward Ballard about her background and her recent paper.  Her love of dinosaurs and microscopes were a perfect match for osteohistology, a field she pursued during her Masters.

Dr. Jim Farlow and Dr. Jack Horner—both members of her PhD committee and who have experience studying the bone microstructure of alligators and Maiasaura respectively—contributed to her Maiasaura peeblesorum research. They acknowledge that comparing alligator bone growth to dinosaurs has been done before; alligator bone growth has been studied extensively.

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Red deer on the Isle of Rum, however, have been studied even longer. Dr. Woodward Ballard and her colleagues found similarities to Maiasaura in their survivorship rates, as well as within their bone microstructure.

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Just as the red deer in Scotland, Maiasaura seem to have experienced a high mortality rate in the first year.  If, however, they survived that first year, they seemed more likely to live through sexual maturity, which may have been between 2-3 years of age. Eight or nine years marks another difficult year for both species. This is when their bodies appear to decline, or senesce, and they are at greater risk for mortality at this age.  Dr. Woodward Ballard and her colleagues note that one Maiasaura tibia with 10 lines of arrested growth (“LAGs”, indicating 10 years of life) appeared to still be growing.

“We have to understand the biology of modern animals and how it works before we can make any kind of hypotheses or inferences into extinct animals,” she explained. “The most important thing I learned from this experience was that we really don’t know as much as we should know about how modern animals grow and the life history details that are stored their bone tissue.”

“It’s sort of circular in that the more we learn about modern animals to apply it to the extinct ones, the more we learn about how bone biology works, how bone grows, and that has direct applications to the medical field, to veterinary biology, and to all kinds of modern fields where bone biomechanics and that sort of thing play a big role.”

Studying bones was only part of the research.  The other involved applying statistical models to the data compiled.  There are advantages to so many fossils from what the authors of the paper described as a  “monodominant” bonebed.  As mentioned in the previous post, the Maiasaura bones originate from three bonebeds in Montana, but these bonebeds are from the same stratigraphy across 2 km.  This means that the scientists can be relatively sure these animals experienced the same environmental stresses.  Differences in the bones, therefore, would indicate differences within each animal instead of being caused by external factors.

And the number of tibia studied in this paper was highly significant.

“There was one paper that came out about the mortality rates–survivorship curve distribution,” said Dr. Liz Freedman Fowler of Montana State University, co-author of Dr. Holly Woodward Ballard’s paper, “and the math in that was fairly complicated. Holly wanted to make sure that she did it right, and so that’s where I came in. It is quite complicated math making sure that you get all the different steps right.  Because the paper was critiquing and criticizing a previous paper that had done it wrong slightly, we wanted to use the methods of this kind of revision paper to make sure that we analyzed things appropriately.”

Dr. Liz Freedman Fowler new dinosaur

Dr. Liz Freedman Fowler with a painting of an entirely separate (and new!) species of hadrosaur she helped discoverProbrachylophosaurus bergei; photo by Sepp Janotta of the Montana State University News Service

 

“[A sample size of 50] was their suggestion,” she explained further, “because the previous histology papers that have been looking at mortality rates, they’ve been using a much smaller sample size: 10-15 individuals, [for example], which is still big for paleontology. But, you know, the smaller your sample size, the greater the chance that what you’re seeing is just random variation in your sample.  Whereas when you get a larger sample size, you can be more confident that you’re more accurately representing the population.

“Normally with dinosaurs you only have maybe two or three examples of a single species. So there’s really not much you can do mathematically because there’s just not enough data to run statistics on.”

Referenced throughout their paper was one published in Paleobiology in 2011 by David Steinsaltz and Steven Hecht Orzack.  The Steinsaltz/Orzack paper was a response to one published in Science in 2006.

“Based on [Steinsaltz and Orzack’s] modeling,” Dr. Woodward Ballard explained, “they recommended that the minimum sample size of 50 is what you would need for an extinct population in order to figure out what the shape of the survivorship curve is.  It’s not really a hard-and-fast rule.  But this is the only time that mathematicians have actually suggested a minimum number for producing statistically robust survivorship curves for dinosaurs. The fact that we were able to then meet their suggested requirements was pretty important.”

Upon first reading the paper by Dr. Woodward Ballard et al, I believed that one needed a sample of at least 50 fossils of a species in order to estimate a statistically-significant survivorship curve.  But—of all numbers—why 50? And why so many when most bones of extinct species are not as abundant as those found so far for Maiasaura?

Over the course of a conversation with Dr. Steven Orzack, I learned that what he and his co-author offered was a way to decrease potential misclassification errors in statistical calculations.

In simplest terms, they were raising the bar.

The 2006 paper by Erickson et al had used a sample size of 22 different Albertosaurus skeletons to calculate a convex survivorship curve. Convex, in other words, means that the survival rates decrease with age.

Yale - Albertosaurus side great

Cast of Albertosaurus libratus from (appropriately for this post) Red Deer River Valley, Alberta, Canada at the Yale Peabody Museum; image taken by the author of this blog

 

By using computer simulation to repeatedly “resample” that estimated curve, as well as a survivorship curve that was not convex (one in which some survival rates increased with age), Steinsaltz and Orzack found that about 10% of the simulated samples of size 22 taken from the non-convex sample would look convex. Such a result would mislead a scientist to misclassify the underlying survivorship curve as being convex when, in fact, it was non-convex.  When they repeated this process by more than doubling it to a sample size of 50, they discovered the misclassification error rate fell to less than 1%.

Paleontologists don’t always have access to a wealth of fossils from the same species.  This is something Dr. Orzack—trained as both a paleontologist and a neontologist—knows all too well.

HMNH - Deionychus

HMNH - Deionychus skull

Images of a partial Deinonychus skeleton, discovered in Montana in 1974 by Dr. Steven Orzack and a team of Harvard researchers, now at the Harvard Museum of Natural History; images taken by the author

 

“I don’t have any problem with sample sizes of 22 in the sense that if that’s the best you have, that’s fine,” he said. “What would have been better is [if Erickson et al had done] the statistics better.”

“Convexity,” he stated, “is a very specific claim.”

“[There are] weaker conclusions you can make about how survival rates change with age than [those published in the paper by Erickson et al.] If you boost your sample size to 50, you have a much lower probability of saying incorrectly that there is convexity when there isn’t,” he concluded.

“Paleontology is moving in a much more mathematical and analytical direction,” Dr. Freedman Fowler explained. “ We’re trying to be more rigorous and treat it more like a modern science.  That’s why we often use the term ‘paleobiology,’ instead of just ‘paleontology’ now. We’re trying to use the science and the tools of modern biology to look at how fossil organisms lived and kind of reconstruct their lives.”

And certainly, the math contained within the paper by Dr. Woodward Ballard, Dr. Liz Freedman Fowler and their colleagues is—to someone like myself—a bit overwhelming.

When speaking with Dr. Freedman Fowler, I asked her if her mathematical skills were rare within the field.

“I wouldn’t say ‘rare’,” she replied, “but it’s certainly not all of us. There are quite a lot of other paleontologists that use R and use math and things. But it’s a minority that goes in that direction.”

Maiasaura HWB - Maiasaura life history

FIGURE 6. Survivorship curve for Maiasaura. Sample size of 50 tibiae was standardized to an initial cohort of 1000 individuals (assumes 0% neonate mortality). Survivorship is based on the number of individuals surviving to reach age x (the end of the growth hiatus marked by LAG x). Age at death for individuals over 1 year old was determined by the number of LAGs plus growth marks within the EFS, when present. Error bars represent 95% confidence interval. Mean annual mortality rates (μ^) given for age ranges 0–1 years, 2–8 years, and 9–15 years. Vertical gray bars visually separate the three mortality rate age ranges; courtesy Dr. Woodward Ballard.

 

“Paleontology is very collaborative because it’s such a broad and interdisciplinary field. Nobody can be an expert in everything.”

When I asked her whether the sub-fields within paleontology have always been so diverse, she responded, “It is certainly a more recent development, and that’s true for many sciences.”

“[Looking back at] papers written 50 years ago, they’re almost all single authors. They’re also much more simple. These papers were just ‘I found this new species. Here’s what it looks like.’  There wasn’t much analysis.

“But now, as all these different branches of science have grown–all the different subfields within biology and geology and chemistry–we’re getting so many more tools that we can use to analyze fossils and look at them in all these different ways.  We’re also having a much larger sample size of fossils. We’re constantly out in the field collecting new specimens and that’s filling in gaps.  Between two species, [for example], we now find the intermediate species.  And we’re getting more complete growth series—the ontogenetic series—of animals. We’re out there finding juvenile dinosaurs and sub-adult dinosaurs and comparing them to the adult dinosaurs.

“Because we’re always adding this data, we always have more and more to work with. So we’re able to do types of analyses that we couldn’t 50 years ago. It was just impossible.”

And this paper is only the beginning. Dr. Woodward Ballard explained that she wants to “really make Maiasaura the dinosaur that we know the most about and really use it as a model to compare to other dinosaurs.”

In a moment of reflection, she said, “I get this question a lot:  ‘Well, great, you’re studying dinosaurs, but what’s that going to do for me?’”

She hopes that the interest in dinosaurs will pull people into science in general, describing a scenario in which the kids—wanting to see dinosaurs—visit a museum with their parents.  While there, the family may learn of other scientific discoveries, prompting even more interest in various scientific fields.

“The more we can make dinosaurs these realistic animals, [not just animals that are no longer around], I think it’s really going to get [kids] interested in science and the world around them.  Being able to continue to add more information to Maiasaura, I think, is going to be the way to really draw people in.”

“The big thing for me,” she said, “is not only collecting fossils, but [also] bringing college-aged kids to Montana to see a different part of the United States, [especially those] kids who might not [otherwise] have the opportunity to be exposed to science.”

“There’s still so much that can be done with the Maiasaura bonebed,” she continued, “with Maiasaura as an animal, so [many] opportunities for outreach and scientific investigation. I spoke with Jack Horner about this during my dissertation work and afterwards; I told him that I would really like to be able to work on Maiasaura potentially for the rest of my career. He thought it was a great idea.  I’ll do other research, too, but I plan to get out to Montana every summer.

“There’s just so much work that I decided to call it the ‘Maiasaura Life History Project’ and every paper that comes out will just be adding to what we already know about Maiasaura.”

At this time, there is no overall funding for the project. Dr. Woodward Ballard is currently writing grant proposals for future expeditions.

 

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Dr. Holly Woodward Ballard; photo by Dr. Karen Chin, courtesy of Dr. Woodward Ballard

 

 

References:

  1. Maiasaura, a model organism for extinct population biology: a large sample statistical assessment of growth dynamics and survivorship; Holly N. Woodward, Elizabeth A. Freedman Fowler, James O. Farlow, John R. Horner, Paleobiology, October 2015
  2. Statistical methods for paleodemography on fossil assemblages having small numbers of specimens: an investigation of dinosaur survivorship rates; David Steinsaltz, Steven Hecht Orzack, Paleobiology, Winter 2011
  3. Largest dinosaur population growth study ever shows how Maiasaura lived and died, Montana State University, MSU News Service
  4. MSU team finds new dinosaur species, reveals evolutionary link, Montana State University, MSU News Service
  5. Tyrannosaur Life Tables: An Example of Nonavian Dinosaur Population Biology; Gregory M. Erickson, Philip J. Currie, Brian D. Inouye, Alice A. Winn

 

**I need to stress that the methods used in this paper and the overall research by Dr. Woodward Ballard and Dr. Liz Freedman Fowler were extremely complex. Dr. Woodard Ballard, Dr. Freedman Fowler and Dr. Orzack graciously walked me through scientific and statistical elements that I had trouble understanding. If there are any errors in this post, they are my own.

Also, while comparisons between extant and extinct species may be normal to those in the field, it was not as dramatically apparent to me until this paper. 

I would like to extend, again, an enormous THANK YOU to Dr. Holly Woodward Ballard. I would also like to extend that same thank you to Dr. Liz Freedman Fowler and Dr. Steven Orzack.  It was a great pleasure and honor speaking with each of them–not to mention fun!–and I am profoundly grateful for their generosity!  

I am very eager to learn more as the Maiasaura Life History Project continues!! 

Maiasaura Life History Project: Paleontology at an Entirely New Depth (Part 1)

I envy the future.

I really do.

Every time I read a dinosaur book—whether a kids’ book with my nieces and nephews or otherwise—I am reminded just how much we’ve learned since I was young. It is staggering, the amount of information available to dinosaur enthusiasts. Whether it is in the number of new species discovered each year, the unbelievable details paleontologists glean (from teeth alone!), or the new technology that helps scientists unravel the once unknowable.

If this is what we know now, and in the relatively brief time since paleontology was first established, what are we going to know fifty years from now? A century? A millennium?

I think about the future almost as much as I marvel at the past. Assuming our knowledge base only increases, the future of paleontology promises to reveal what can only be—at this point in time—imagined.

Which is why when I learned of the Maiasaura Life History Project, I had to know more.

Dr. Holly Woodward Ballard wants to flesh out one particular species of dinosaur such that we know it almost as intimately as living animals today.  That species is a type of hadrosaur, an extinct herbivore from the late Cretaceous. Thanks to almost 40 years of excavation in Montana, we have thousands of its fossils from which to extract information and this, according to Dr. Woodward Ballard, is to be her life’s work.

Holly Woodward-WCA-Branvold Quarry-Aug5-2015

Dr. Holly Woodward Ballard at Branvold Quarry, August 2015; Photo taken by Dr. Karen Chin, courtesy of Dr. Woodward Ballard

Maiasaura peeblesorum was inadvertently discovered in the late 1970s, both by the people who initially found the bones and by the paleontologists who eventually described them.  “Inadvertently” because Marion and John Brandvold, the people who found the bones, didn’t know what they’d found, and because Dr. Jack Horner and Bob Makela—who had done extensive research prior to their expedition—did not expect to find the object of their search in a local fossil shop they visited on a whim.

The 1988 book “Digging Dinosaurs” by Jack Horner and James Gorman describes this discovery. In it, there is a fascinating anecdote: Prior to 1978—the year Maiasaura peeblesorum was found—they say that the number of adult fossils found globally could be listed in a volume the size of a book. The number of juvenile fossils could be listed in something the size of a pamphlet.  But the number of known baby fossils could fit on an index card.

All of that changed thanks to Dr. Horner and Bob Makela. The Brandvold bones gave them specific clues about where to look and what to look for.  Their subsequent excavations revealed not only numerous baby dinosaurs, but actual nests. These significant discoveries prompted the following revolutionary ideas: that some dinosaurs may have cared for their young and that they may have been warm-blooded. The latter hypothesis continues to be debated today.

Paleontologists have been digging in the area ever since.  Their efforts have produced one of the few species of dinosaur to be so well represented in the fossil record, a fact that inspired Dr. Woodward Ballard in her research at Montana State University.

Maiasaura field site Montana

Maiasaura field site in Montana, photo courtesy of Dr. Woodward Ballard

Jack Horner, her PhD advisor, proposed the idea that she focus on population histology—revealing the growth history of a specific dinosaur species.  Given her interest in osteohistology and the wealth of Maiasaura fossils, this seemed a perfect fit.  Her dissertation was but a prelude to the work that followed.

This past October, Dr. Woodward Ballard, now of Oklahoma State University, Dr. Liz Freedman Fowler and Dr. Jack Horner of Montana State University and Dr. Jim Farlow of Indiana Purdue University published a paper in Paleobiology on the growth and survivorship rates of Maiasaura peeblesorumThe paper was unique in that, unlike most dinosaur species, they had 50 bones with which to analyze and sample.

Bone microstructure, much like trees or proboscidean tusks, records the growth of an animal in rings. In this case, Dr. Woodward Ballard was able to identify the “lines of arrested growth” (or “LAGs” for short).

“A LAG,”she explained by phone, “represents a period of missing time.”

Growth rings in Maiasaura bone

Growth rings in Maiasaura bone, courtesy of Dr. Woodward Ballard

The paper is a fascinating glimpse into the depth of detective work paleontologists must do in order to understand long extinct species. Comparing bone growth in extant reptiles and mammals to these fossil bones, using complicated statistical models, and analyzing bone structure under the microscope, the authors offer an extraordinary view into the life of Maiasaura.  It is, to date, the largest sample set of a single dinosaur species analyzed to such a degree.

Fifty Maiasaura tibiae from three Montana bonebeds provided the details. This specific leg bone was chosen for analysis because it displays histology so clearly.  The same is not true, for example, of a hadrosaur femur.

“The femur,” Dr. Woodward Ballard said, “is special in all hadrosaurs, [not just] Maiasaura. It has this big flange coming off of it, and it’s this spur bone that a fairly large tail muscle was attached to.”

“Because bone responds to stress and remodels based on the stress that’s applied to it, this flange of bone is always changing and getting larger as the [animal grows.] The remodeling that occurs within [this] bone overprints–or erases–the original signal that was there. So it’s very hard to get at that same record of growth in the femur because it’s constantly being erased in that particular area.”

One of the things they discovered through lines of arrested growth (LAGs) was that most of the tibiae in this study belonged to Maiasaura younger than a year old.

But deciphering this required understanding bone growth in living species.

“We have to use modern animals and use what we see in their bones as a basis for what we say in the fossil record,” she replied when asked about this. “We have to assume that the same processes today were working back in the Cretaceous (in this case).”

So they looked to previously published alligator studies and those of the red deer on the Isle of Rum, Scotland—one of the most extensively studied mammals anywhere in the world.

Acknowledging that these inferences should be treated with some caution, they note similarities in tibia bone growth between alligators and Maiasaura. Growth marks within the bone and lines of arrested growth (LAGs) are similar in red deer and this species of dinosaur.

“When the growth is being kept track of from year-to-year, we find that one LAG appears every year for every year of growth,” she explained.

Hence, if there are no LAGs in the bone, it indicates that the animal was less than a year. And the high mortality rate among such young animals—considerably smaller than their enormous parents and therefore not as able, perhaps, to aptly defend themselves—is not necessarily surprising.  The paper also calculates survivorship rates among Maiasaura, enabling us to know how old the dinosaur was at sexual maturity, how long it tended to live, the age at which it was at higher risk for mortality among its species.

“Once I compiled the data from Maiasaura,” she said, “got all the bone measurements, got all the LAG circumference measurements within the bones—I realized that I wanted this paper to be more than just quantitative and simple growth curve graphs. I mean, I could do that much, but I really wanted it to be statistically strong, very robust, something that followed the rules put forth by other papers, such as the Steinsaltz and Orzack paper. [Dr. Liz Freedman Fowler] was just a natural choice to have to help me figure out what to do with all this data.”

————–

In Part 2: more detail about the Maiasaura peeblesorum survivorship curves, as well as applying complicated statistical methods to paleontological data.

An enormous and sincere thank you to Dr. Holly Woodward Ballard for her generosity: her time, her patience, her willingness to go over points I had difficulty understanding and for the beautiful pictures accompanying this post!

References:

  1. Maiasaura, a model organism for extinct population biology: a large sample statistical assessment of growth dynamics and survivorship; Holly N. Woodward, Elizabeth A. Freedman Fowler, James O. Farlow, John R. Horner, Paleobiology, October 2015
  2. Digging Dinosaurs, John R. Horner and James Gorman, 1988, Workman Publishing Ltd
  3. Largest dinosaur population growth study ever shows how Maiasaura lived and died, Montana State University, MSU News Service

Digging Dinosaurs book cover

Jack Horner - inscription for post

Treasured copy of “Digging Dinosaurs”, the book that details the discovery of Maiasaura peeblesorum and its nests, signed by Jack Horner at the Boston Museum of Science when the author of this blog met him in 2013

Meet Dr. Katy Smith – Mastodon Detective

If you imagine the Great Lakes region over 10,000 years ago, you might see large, hairy beasts with relatively straight tusks grazing around boggy areas or moving within dense forests.  Their fur and overall appearance might cause you to confuse them with woolly mammoths, but these are the mammoths’ shorter, stockier cousins.  And if any of them would let you get close enough to inspect their mouths, you’d see in an instant that their teeth are completely different than those of mammoths.

 

[image of contemporary boggy area in Alaska, courtesy Getty Images]

 

Whereas mammoths are believed to have eaten grasses and even flowers, mastodons needed teeth suited to the mastication of hardier stuff: shrubs, parts of trees, perhaps pinecones?   Mastodon teeth, with the bumps and ridges one might associate with carnivores, are easily recognizable as ‘teeth.’  Mammoths, in contrast, needed to grind food, producing teeth with spherical lengths of ridges across each tooth.

ISM - Mastodon tooth

 

[image courtesy of Ron Richards, Indiana State Museum, for this post: Mammoths and Mastodons in Indiana – Part 1.  Can you tell which tooth belongs to which species?]

 

ISM - Mammoth tooth

 

[image courtesy of Ron Richards, Indiana State Museum, for this post: Mammoths and Mastodons in Indiana – Part 1.]

And while woolly mammoths pervade popular culture and interest, there are some, like Dr. Katy Smith, Associate Professor of Geology at Georgia Southern University and Curator of the Georgia Southern Museum, who prefer their lesser-known cousins and have made fascinating contributions to our understanding of them.

Mastodon discoveries usually produce the fossils of a single animal, and rarely a complete skeleton. Rarer still, finding skeletal remains of multiple mastodons at the same site.

Such a unique discovery occurred in 2005, when more than 300 fossils were found in Hebron, Indiana.  Now known as the “Bothwell site,” it was originally going to be the location of the landowner’s pond.  Instead, Indiana State Museum paleobiologist Ron Richards and his crew uncovered bones that included numerous mastodons (Mammut americanum), giant beaver (Castoroides) and hoofed animals with even-toes (artiodactyls).

ISM - 2005 Bothwell Mastodon 2

 

ISM - 2005 Bothwell Mastodon 1

[images of the Bothwell site dig, courtesy of Ron Richards, Indiana State Museum, for this post: Mammoths and Mastodons in Indiana – Part 2.]

 

Four years later, the Bothwell site became the focus of Katy Smith, her dissertation, and two subsequent papers she co-wrote with Dr. Daniel Fisher at the University of Michigan.

But let’s take a moment to consider what paleontologists uncover. However rudimentary this may seem, it is important to note that bones are generally not discovered in neat order, intact and with each skeletal component attached where it would have been in the life of the animal.

Consider, too, that not all bones survive.  And those that do are often broken or in terrible condition.

So even at a site such as Bothwell, which produced lots of fossils, a paleontologist’s job is no less challenging.  The pieces of information are incomplete, mere clues to the animals that died there.

The questions, however, are profuse.

Why were so many animals found in that one spot?

If, as it is currently debated, mastodons shared behavioral traits with modern-day elephants, was this a family unit?

If so, was this group—like elephants–comprised largely of female and juvenile mastodons?

And why were other unrelated animals discovered among them?

Did a sudden disaster kill them all?  Were humans involved?

 

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Sexual dimorphism is another way of referring to the traits that make an animal either female or male.  Some of us would assume, since mastodon pelvic bones were not among the Bothwell fossil assemblage, that the sex of these animals would remain unknown.

There were 13 mastodon tusks, only four of which were complete. And this, remarkably, is what prompted Katy Smith’s research.

“I wanted to know if I just had tusks, what can I do to figure out if I’m looking at a male or a female,” she explained by phone.

Katy Smith - measuring an African elephant tusk

 

[image of Dr. Katy Smith measuring an African elephant tusk in (what this author believes must be one of the greatest places on earth) the basement and fossil collection of the University of Michigan; courtesy of Dr. Katy Smith]

 

“Other people have looked at [sexual dimorphism], but I wanted to look at it specifically with the Bothwell mastodons, because they were inferred to be female, and female mastodons are less common in the fossil record than males.

“When I presented preliminary results from my research in a paleontology class, the professor said, ‘Why don’t you try multivariate analysis?’ And it just kind of spiraled from there.”

Multivariate analysis,’ as the name implies, means using more than one type of measurement or observation towards a hypothesis.  In other words, rather than simply using size as a determination of sexual dimorphism, applying numerous methods and statistics that support or disprove it.

Already, the amount of information scientists have pulled from tusks alone is fascinating.

Tusks are teeth.  They are described, in Dr. Smith’s dissertation as “hypertrophic incisors.” And, unlike human teeth, they continue to grow the entire life of the animal. So where we can simply look at a human tooth and know immediately whether it is from an adult or a child, the same cannot be done with tusks.

What their hardy structure records includes the age of the animal, growth in winter or summer months each year, their overall diet, and periods of nutritional stress.  (As described in an earlier post, Proboscidean molars can even provide details regarding where they roamed during life.)

But much of this information can only be gleaned from well-preserved, intact tusks, as well as from cutting into and examining their chemical composition.

“If you don’t know what the sex of the animal is before you look at tusk microstructure,” she said, “it can be hard to interpret what you’re looking at.”

Part of what Dr. Smith hoped to discover were similarities in the tusks where sex and age had already been determined.  If certain structural elements were the same across female mastodon tusks, such that they tended to differ from male mastodon tusks, this might help determine sexual dimorphism in future tusk discoveries.

She also hoped to discover any similarities between the tusks of extant elephants and mastodons.

Katy Smith -longitudinally bisected tusk

 

[image of longitudinally bisected tusk, courtesy of Dr. Katy Smith] 

 

Thus, she studied and measured tusks of both species from numerous museum collections. (Asian elephant tusks were not used, as female elephants of this species tend to have either tiny tusks or no tusks at all.)  She rather amusingly refers to the approximate amount of tusks involved as “5,000 pounds of tusk.”

Her dissertation and the two papers describe the type of analysis performed in detail.  Among them were canonical variates analysis (CVA) and discriminant function analysis (DFA).

“Fortunately, we didn’t have to cut into the tusks to do those measurements. You just insert a stiff wire into the pulp cavity.”

“We think about tusks sometimes as stacks of sugar cones, because they actually grow in a kind of [layered] cone structure. So you think about one sugar cone, and then you put another one inside that one and then another one inside that one and so on and so forth. And the last sugar cone is empty. There’s nothing in it. That represents the pulp cavity.”

“[Analyzing the] pulp cavity is probably one of the best single measurements that you can use to distinguish between male and females. [I]n females, that pulp cavity will terminate before the gum line, and in males, it will terminate after the gum line, closer to the tip.

“This is something that we saw in almost every mastodon. So it was kind of cool.”

 

Katy Smith - female mastodon

 

[image of female mastodon skull and tusks, courtesy of Dr. Katy Smith]

 

“If we could have cut every tusk, I would have,” she admitted, and laughed. “But it was a matter of collecting these measurements at different museums. And so I would just go there and collect all of them, and that was how we’d get the pulp cavity depth.”

“I’ve always been interested in paleontology,” she said when I asked her how she got started.

“I’m one of those kids who just never grew out of it. My parents used to take me to the museum all the time, and I used to spend hours and hours staring at the dinosaur dioramas there, just loving it.  I told my kindergarten teacher I wanted to be a paleontologist. I never changed! My 5-year-old self grew up and became a paleontologist.”

But her interests moved away from dinosaurs when she realized that their fossil record in Wisconsin, her home state, was rare to nonexistent.

After all, she said, “I started just wanting to explore what was underneath my feet.”

It wasn’t until grad school at Michigan State, where she met the late Dr. Alan Holman, that she realized her passion for mastodons.  His own interest in the species was infectious, and it was through him that she learned of the numerous mastodon (Mammut americanum) fossil discoveries in the area.

“Wow!” she said, recalling her initial reaction. “There are over 300 mastodons in Michigan. This is exciting!”

Katy Smith - male mastodon

[image of male mastodon skull and tusks, courtesy of Dr. Katy Smith]

Not surprisingly, she did her PhD work at the University of Michigan, home to Proboscidean expert Dr. Daniel Fisher, who was her advisor.

“I wanted to work with him,” she explained, “because I wanted to continue working on mastodons, and he had a couple of ideas for projects. One of them included this assemblage of mastodons from Indiana, which were—supposedly—all female.”

What she discovered regarding the Bothwell site is both thought-provoking and fascinating:

  • 8 tusks were determined to be female; the other 5 are unknown
  • the ages of the mastodons range between 19 and 31 years old
  • there is evidence that at least one juvenile might have been among them (a “juvenile tooth crown” was found)
  • given that two mastodons died in winter, and another two died either in late summer or early autumn, this indicates that the collective deaths of these animals didn’t happen at the same time (hence, not a single event)
  • none of the mastodons appeared to be under nutritional stress when they died
  • members of a family unit would be expected to have the same “isotope profiles”–chemical signatures in their teeth–but these do not

Based on the evidence provided, Dr. Smith wonders whether these animals were part of a meat cache for humans (members of the Clovis culture) that co-existed at that time.

But perhaps the single most remarkable result of her research is helping other paleontologists–who often have nothing more than a single tusk–determine the sex of that animal using her different types of analysis.

Prior to her dissertation, only one female mastodon tusk had been analyzed for growth rate.  To date, I am unaware of any other publication (paper or book) that helps detail the sexual dimorphism in mastodons by tusks alone.

When I remarked upon this, I asked her if others had cited her work.  Her response, after stating that others had, was equally fascinating to me.

“It’s always the hope as a scientist that you’re contributing in some way,” she said, “and you know that you’re contributing if somebody else is using what you’ve done.”

 

An enormous and sincere THANK YOU to Dr. Katy Smith for her generous and fascinating answers to my many questions, her gracious help when I had trouble understanding certain points, and for being so much fun with whom to connect! I cannot express how much I wish I could attend her classes, nor how fascinating I found her dissertation. I am profoundly grateful that she shared it with me!

A sincere thank you to my Dad, as well, for helping me understand tooth components (i.e.: dentin, cementum)!

**A quick reminder that I am neither a scientist nor a paleontologist, so any errors in this post are my own.

Bothwell Mastodont Dig, courtesy of Indiana State Museum; many thanks to Bruce Williams and Leslie Lorance!

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References:

 

Other references:

 

Cohoes mastodon size comparison

[image of sign in the NY State Museum illustrating the size difference between an extant elephant, a woolly mammoth and the Cohoes mastodon; picture taken by the author]

From the Depths of an Indiana Cave: A Fossil Treasure Trove

Around perhaps 25,000 years ago in Southern Indiana, an injured Dire Wolf made its way into a cave and never came back out. With three good legs and one that had been out of socket for a year or so, the wolf crawled through the smaller spaces and eventually—whether through an accidental fall or otherwise—landed at the bottom of a deep pit. It was trapped.

Ron Richards, Senior Research Curator of Paleobiology at the Indiana State Museum, and his crew discovered its skeleton after digging in that particular room for 3 or 4 seasons.

Ron took that set of bones to pathologists for more information. However long that injury was sustained, and it was not a short amount of time, that wolf was a survivor. They determined the one leg probably didn’t touch the ground, but that it could probably still run using the other three.

“What normally is a circular ball-joint on his thighbone was flattened on one whole side,” Ron explained in a phone interview.

“I think that probably affected his ability to back out. Maybe he smelled some rotting carcass smell or something, got too near and couldn’t back out, and probably went over the top [of the pit.]”

A reconstruction of that event, complete with an actual cast of that specific room in the cave, can be seen at the Indiana State Museum today.

What may not be apparent was the work involved in creating that cast.

The word “cave” might invoke images of enormous open spaces underground. This is not at all that kind of cave. Not at the initial opening, nor at any space within as one moves deeper inside.

“Years ago, you had to go into a belly-crawl,” Ron said of the entrance, “but now we’ve moved through it so much, we can do a hands-and-knees crawl.”

They built a platform to work above water pooling at the bottom of the pit, and—in order to keep the walls dry for rubber molds—they used blowtorches. Ron, cave dig crewmembers and people from RCI (Research Casting International) worked together on the beginning stages of the room’s cast. The finished product was done at RCI headquarters in Ontario.

RCI - Dire wolf replica

[Image of the cave cast and wolf replica, http://www.rescast.com, by Research Casting International for the Indiana State Museum]

Nothing done in that cave is an easy process.

When Ron first began digging in that cave, he said, “I thought it would take 9 people 9 days, and we could finish the project.”

That was in 1987. The dig was prompted by the discovery of a single peccary bone.

Ever since, for approximately two weeks each year, Ron and his crew have returned to dig.

“[It was] the first big cave dig we had done,” he continued, describing that first year. “We’d done a couple of mastodon digs at the time, but we really had no money for the budget. There was nothing there. We had no trained staff. We had almost no equipment.”

“I remember pulling this together, pulling different people from different sections of the museum.”

And when it came to potential funding for this excavation, Ron recalled that he was asked, ‘Can’t you do this another time?’

“I didn’t know what to say,” he admitted, “so I didn’t say anything. The next day, we got the gear loaded, and we headed down for the cave. We just did not look back!”

“As it worked out, we dug, we found more bone: parts of little peccaries, parts of big peccaries, and other animals that no longer occur in the region.”

Peccaries are relatives of modern pigs, but instead of upper canine teeth that curve up—as in modern hogs—their teeth “drive straight down like daggers,” as Ron explained. Today, modern peccaries live within the Southwest United States, as well as in Central and South America. But during the Ice Age, peccaries were common in Indiana and Eastern U.S.

Peccary Fig 02  iceage13a upgraded

[Pleistocene peccary by Karen Yoler, image courtesy of Ron Richards, the Indiana State Museum.  Per Ron Richards: “This image is artist Karen Yoler’s  concept of what the peccary looked like.  We did drop off the larger dew claws on the front legs and added a little more canine tooth size and gave it a more perpendicular orientation.”]

 

Embed from Getty Images

[Angry javelina–or collared peccary–close up. Javelina go by many names such as wild pig,boar,etc.; image and caption from Getty Images.]

Working deep in the cave initially, the crew created a system that they continue to use, with some improvements, to this day: some people dig in the cave and place the soil into buckets; other people haul the buckets out of the cave and bring them down to a stream; still others screen the soil for fossils.

All of the data is recorded; all of the soil is screened.

“Above you are big spiders—lots of cave spiders and cave crickets. They don’t bother you, but some people get the heebie-jeebies, you know? I mean, you look up, and there [are these] massive things moving around,” he said and chuckled.

In recent years, they’ve developed what Ron refers to as “tramways,” 60-70 feet of ramps created by parallel boards with cross slats. Tramways—some with rollers—help bring the buckets out of the entrance to the cave and down the hillside.

ISM - Cave with tramway

 

[Digging…with the tramway in position for hauling buckets of sediment out, image courtesy of Ron Richards, the Indiana State Museum.]

To help carry 15-20 buckets at a time down to the spring to be screened, they employ an ATV with a tractor.

“[From all of the] tons of soil that gets screened,” Ron stated, “[there remains some] soil that’s left with small bones. We bag that out, bring it back to the museum, and then they rescreen it and clean it. And then–spoonful by spoonful–they go under the binocular microscope, and they pick out all the small bones and teeth.”

His crew is a dedicated group: leaving their hotel rooms at 8am and working throughout the day—with a short break for lunch–until 5pm (or later if the weather holds). Ideally, there are nine crewmembers per season, but they have done it with less people. Digging has sometimes required breaking rock, so among the many tools used are sledgehammers and chisels.

ISM - Cave digging

 

[Digging for peccary bones, image courtesy of Ron Richards, the Indiana State Museum.]

 

Over the years, the cave rooms have gained descriptive names: the Peccary Room, for example, the X Room, and the Bat Room.

The “Microfauna Room” was named after the large amount of small bones they found when they began digging through the top layers of soil and rock. This is where the aforementioned Dire Wolf was discovered.

“Near the bottom of that room, down at the 25,000-yr level,” Ron explained, “we began to get fairly complete skeletons of things like Dire Wolf, Black Bear, an otter, a snowshoe hare, a lot of small shrews and mice.”

“We really believe that those animals fell in this pit. They dropped, and they went down about 15-20 feet. I think most of the time it was probably full of water.

“It’s just a lonely place to be. Whether they could stand at the bottom, I don’t know. But there’s no way out.

“There [was] enough mud washing in from the ceiling of that room that they were buried under real fine sediments. And that preserved them very well.”

Some of the fossils discovered have been both remarkable and rare. A tapir tooth—only the second to be found in the entire state of Indiana—was found in the cave. Several beautiful armadillo (Dasypus bellus) plates [osteoderms] have been discovered have been discovered (that is the actual name; ‘beautiful’ is not necessarily a description). Ron painted a picture of this by saying, “When one animal dies, there’s about 3,000 plates that disintegrate and go everywhere, like little dominoes.”

“Two years ago,” he said, describing the ‘Twilight Room’, “we started finding some articulated peccary skeletons.”

“Deep in the cave we didn’t find a lot of that. The bones would be disturbed, and you could just see sort of a jumbled mass that had been moved by water, by gravity, [or] by other animals.”

“In this room, we found things that were articulated, feet in place, all of the little toes in place. Really unusual.”

The earliest fossils found were parts of a giant land tortoise, a species that cannot live in cold climates. Finding this indicated that the area, at that time, did not freeze.

Also found were fossils of a pine marten, a species that, conversely, lives in Northern climates today.

And as for peccaries, Ron estimates that they have found the bones of approximately 650 individuals. They determined this number by by counting the total number of large, pointed canine teeth and dividing by four.

ISM - flat-headed peccary

[Bones & skull of the flat-headed peccary, image courtesy of Ron Richards, the Indiana State Museum.]

“So the question is then: did they live here? Or did they all have a misfortune and die here? It’s a little of both, but it’s mainly that they probably inhabited this cave and rock shelter for most of that time period.”

Ron mentioned that a number of the fossil discoveries in the cave are new to him.

So how does one identify unfamiliar fossils?

“We have a general reference collection of modern bones,” he replied, “and there is a big collection at Indiana University, Bloomington that I had become very familiar with in the 1970’s and 1980’s.”

He went on to explain that he referenced available literature and visited other museum collections.

“I had written correspondence,” he continued, “and the mailing of specimens with several experts in the eastern United States. My foremost ‘mentors’ were Dr. Russell Graham (then The Illinois State Museum), and the late Dr. J. Alan Holman (The Museum, Michigan State University), but I also had open correspondence with the late John E. Guilday (Carnegie Museum of Natural History), the late Dr. Paul W. Parmalee (The McClung Museum, University of Tennessee), Dr. Holmes Semken (University of Iowa) and the late Wm. R. Adams (Zooarchaeology Laboratory, Indiana University).”

“Everything [is] dug in square units,” he said. “We have thousands of these units. We can show the distribution and abundance of anything that pretty much died in that cave for thousands of years.”

And the work is hardly done. Ron estimates that the digging portion may be completed within the next 5 seasons (5 years), but the analysis of the immense amount of fossils has yet to begin.

“We’ve got probably 30 radiocarbon dates from the cave. Every year, we get one or two more.”

Ron explained that the cave has, so far, produced “probably 7,000 small plastic boxes of small bones, and 2,000-3000 larger containers of larger bones.”

“It’s my job to identify those. But, you understand,” he said, laughing, “life is short. I could spend all my time, day and night, just working with that alone. It’s an immense project.”

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Many, many thanks to Ron Richards, whose generosity astounds me.  I am profoundly grateful for his time, his patience with my “volley of questions” and his fascinating descriptions.  It is always a pleasure and an honor connecting with him!

A sincere thank you to Bruce Williams for prompting this post!

**The name and location of this cave were intentionally left out for security reasons.

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[Image of the Indiana State Museum, Getty Images]