Rewriting the Story of How They Died – Columbian Mammoths in Waco

[[The following text has been edited from the original post.  Email me for the original post: mostlymammoths (at) gmail.com or read the full scientific paper by the authors here.]]

*****

Sometimes, it just takes a different point of view.

The largest known potential nursery herd of Columbian mammoth fossils in the world exists in Waco, Texas.  Of the 25 mammoth skeletons found to-date, 16-22 of them died at the same time. Something catastrophic occurred to these animals in the Pleistocene, but just what remains inconclusive.

While some speculate death by lightning, disease or miring, the predominant theory maintains that this is a herd of mammoths that died and were buried in the same flash flood.  It’s an idea that has stuck for many years given the existence of aquatic fauna and the evidence of an ancient river upon which many of the fossils have been found.

Female W - Waco Mammoth NM - Larry D. Moore

Image of Female Mammoth “W” at the Waco Mammoth National Monument, photo by Larry D. Moore CC BY-SA 3.0, 2013

 

But Logan Wiest, Don Esker and Steven Driese of Baylor University have a different hypothesis, one published this past December in Palaios.  By studying traces on the bones available in situ, as well as those available in the nearby Mayborn Museum, they offer an entirely new idea: water didn’t kill them; its absence did.  Struggling to find water in a drought, these animals may have collapsed and died at a watering hole that could no longer sustain them or anything else.

Columbian mammoths were enormous animals.  In general, they are known to be much larger than woolly mammoths and considerably larger than mastodons, both of which were behemoths in their own right.

The mammoth skeletons at Waco are thought to be a matriarchal herd, consisting mainly of females and youth (no calves).  The evidence suggests a herd, and there is more research to be done to prove it using stable isotopes.  A single bull has been discovered in a different geologic layer.  Separate fossils of other species—none of them complete except for a western camel—have also been found throughout the site.

Don admitted he didn’t have an alternative explanation for the death of so many animals. He invited his colleague, Logan Wiest, to take a closer look at the fossil evidence.

“I’d brought [Logan] in hoping he’d look at the [site’s paleosols],” Don said. “I knew he was a trace fossil expert, so I’d hoped he [might] tell me a little bit about the conditions based on worm burrows, [for example].

“What he found instead was much more interesting! He found that there were all kinds of bite marks on the bones.  We didn’t find those all at once.  It actually took quite a while [before] we recognized what we were seeing as bite marks.  A lot of literature research and a lot of staring at bones.  Those bite marks shouldn’t have been there if the mammoths were immediately buried.

“One of the first things he noticed and was able to identify quickly were dermestid beetle bite marks: pits that the beetles dig in the bones when they’re going to lay eggs.

“I thought that perhaps [evidence of dermestid beetles] might be there, but I didn’t realize the significance of [that evidence].  He’s more of an expert on this than I am.

“And he knew that dermestid beetles don’t eat wet meat.  It actually has to be almost completely dessicated–no moisture left at all, just the fats and proteins–before the dermestid beetles will touch it. And that didn’t fit well with animals that were killed in a flood and rapidly buried.

“Dermestid beetles also don’t burrow. Even a single inch of soil is enough to keep dermestid beetles from digging down to perfectly good meat.  They can’t dig.”

Figure 7 - Palaios

FIG. 7.—Cubiculum isp. on various skeletal elements. A) Slightly elliptical, hemispherical bore on in situ rib of mammoth W. B) Hemispherical boring on mammoth U phalanx (545-BU-MMC). C) Shallow bore on femoral articulation surface 761a-BU-MMC. D) Shallow bore on eroded long bone of mammoth D limb fragment (203-BU-MMC). E) Hemispherical bore in cancellous bone on the surface of a spiral fracture (20-BU-MMC). F) Comparative trace generated by captive hide beetles on a wild-hog skull (Sus scrofa). Note the similarities in size and morphology to Figs. 7A-E.

 

Used with permission, PALAIOS, v. 31, 2016, © SEPM Society for Sedimentary Geology 2016.

 

“So, it was Logan looking at this and trying to think about what might be causing this instead of a flood, and he said, ‘Well, how about a drought?’

“I knew about some other evidence that really fit with that. So that clicked with me very quickly, particularly the fact that we’ve got both aquatic and terrestrial animals—a great diversity of them all in the same place.  What that suggested to me was a diminishing watering hole. And I wouldn’t have realized that if Logan hadn’t noticed the dermestids and figured out the drought angle.”

Beyond studying the available literature for trace fossil search images, they tested their ideas on the heads of deceased wild hogs using extant dermestid beetles. In effect: they put the fleshy heads into a contained area and let loose the beetles, who proceeded to consume all of the flesh, leaving clean skulls. It’s an efficient and chemical-free method used by scientists and museums the world over.  But for Logan, Dan and Steven, this provided more data for comparison. Traces left by the beetles on the wild hog skulls are similar to traces on the fossils in Waco.

 

dermestid-beetles-lisa-buckley1

Screenshot of a tweet regarding the use of dermestid beetles from Dr. Lisa Buckley, paleontologist and ichnologist at the Peace Region Palaeontology Research Centre

 

“Previous studies have attributed trace fossils of this size and morphology to dermestid beetles,” Logan wrote in response to what prompted them–of all insects that might have left traces on fossils–to think of dermestid beetles.  “We simply wanted to test this notion by providing bone to dermestid beetles and seeing if these traces could be duplicated under controlled conditions. The beetles came from a nearby museum, but they are also native to Texas. We used the head from a hog simply because wild hogs are easily accessible in central Texas.”

A true ichnologist, Logan added, “I’ve also spent a great deal of time observing bones of modern cattle that were scavenged upon in pastures near my home.”

They didn’t just find evidence of ancient dermestid beetle traces; they found traces of animals who gnawed at the bones: rodents and carnivores, including a possible saber-toothed cat.  It is important to consider that animals drowned and then rapidly buried in a flash flood would not be accessible to these terrestrial scavengers.  This indicates that these Columbian mammoth carcasses were exposed on land long enough to be at least partially devoured.

That, too, is key. Remember that most of these mammoth fossils are articulated skeletons, complete except for missing tails and parts of their feet.  In an area devastated by drought, even scavengers would lack the energy to completely devour and tear apart a carcass.  All of these clues add more weight to the scenario proposed by these authors.

Figure 5 - Palaios

FIG. 5.—Brutalichnus brutalis on M. columbi skeletal elements. A) Arcuate grooves on femoral head 761a-BU-MMC. B) Relatively deep, arcuate grooves on mammoth Q in situ patella. C) Isolated arcuate groove on proximal radius (40-BU-MMC) of mammoth B. Note the similarity in curvature between the arcuate groove and the saber-toothed cat canine recovered from WMNM. The tooth is 6.4 cm for scale. Also note the faintly colored lines that are parallel to the arc of the groove. Dashed white box highlights the area depicted in D. D) Close-up image of groove depicting the microfractures within the trace on 40-BU-MMC. Notice how the fractures are all open towards the upper-right corner of the image, indicating the trace was generated from a force moving from the upper right towards the lower left. E) In situ femur of bull mammoth at WMNM. F) Arcuate grooves on mammoth Q phalanx 522-BU-MMC.

 

Used with permission, PALAIOS, v. 31, 2016, © SEPM Society for Sedimentary Geology 2016.

 

Describing the tools they used to study the fossils in situ, Logan wrote, “The low-angle light creates a shadow which makes the small structures on the bone surface to be easier to see and photograph. We used a Dino-Lite portable microscope to study the fossils mainly because we are unable to transport the mammoth remains from the site to the laboratory. Studying the fossils in place is the best way to ensure preservation of the original positions.”

In other words, because the fossils remain where they were found, they studied those available directly at the site.  Their paper states that the in situ fossils comprise 30% of the available Waco fossils.  The rest reside at the Mayborn Museum, some of which are available in their collections, but most of which remain unopened in their plaster jackets.

“It’s an amazing site,” Don enthused, “and there’s decades and decades of research there, on top of potentially a lot more excavation, too, because they are in NO WAY finished excavating. What they’ve got probably represents a fairly small fraction of the whole deposit.

“One of the things that Logan and I were speculating about [is] if you’ve got a really big regional drought, that should show up in multiple places in the geologic record, especially right in that area.  The bed that we’ve got marking the drought as this depositional hiatus could be covered with bones for acres and acres in every direction.

“And we know that it’s covered in bones at least 80 or 90 feet away from where the known deposits are because we’ve done core sampling that have pulled out large bone fragments.  We only did a couple of them—a couple at random!—and they hit bones both times.”

 

Figure 4 - Palaios

FIG. 4.—Machichnus regularis on various skeletal remains of M. columbi (unless otherwise noted). A) Rodent gnaw marks on rib 764b-BU-MMC. B) Rodent traces on mammoth E limb fragment 203a-BU-MMC. C) Rasps on vertebra of in situ camel. D) Rodent gnaw marks on in situ neural spine of juvenile mammoth T in L1. E) Rodent traces on in situ left scapula of bull mammoth (Q) in L2. F) Close-up image of the same trace depicted in view E.

 

Used with permission, PALAIOS, v. 31, 2016, © SEPM Society for Sedimentary Geology 2016.

 

 

The Waco Mammoth site itself has been around for 39 years, but it has only been part of the National Park Service since July 2015, thanks to President Barack Obama and the work of many people years beforehand who helped bring that to fruition.  Don and I discussed this by phone, given the current political climate and the fears that some National Monuments might lose their status.

“That’s really worrisome,” he remarked. “And what really sticks in my craw about the Waco Monument in particular is that it’s costing the Federal Government almost nothing.  The city of Waco is paying for almost all of the upkeep.  The original buildings? That wasn’t tax money. That was done by good old fashioned fund-raising. And the day-to-day operations are almost all city.  There are a couple of rangers there alongside city employees and some signage and brochures. And that’s really all the Federal Government’s paying into it.”

“It’s a really incredible place.  There are not a lot of sites like this anywhere, as far as in situ fossils sites go.”

*****

A Mammuthus columbi-sized THANK YOU to Don Esker and Logan Wiest for their remarkable generosity in answering my questions and for sharing their research with me.  It was an enormous pleasure speaking with and communicating through email with them.  I loved reading their research and hearing more of the history behind it!!

You can read the paper here.

A sincere and enthusiastic thank you to Kathleen Huber, Managing Editor at Palaios, for her gracious permission to use the figures contained in this post!

References:

  1. The Waco National Monument may represent a diminished watering-hole scenario based on preliminary evidence of post-mortem scavenging, Wiest, Logan A.; Esker, Don; Driese, Steven G., Palaios, December 2016, DOI: 10.2110/palo.2016.053
  2. Waco National Monument, Waco, TX
  3. City of Waco, TX – Waco Mammoth National Monument, Waco, TX
  4. Mammoth Opportunity, Jeff Hampton, Baylor Arts & Sciences Magazine, Fall 2016
  5. What is Ichnology? from Introduction to Ichnology, Anthony J. Martin, Emory University (This page offers a great explanation of some of the more technical ichnological terms included in the scientific paper referenced for this post. I also recommend Dr. Martin’s book, “Dinosaurs Without Bones” for a more comprehensive look into ichnology.)
  6. Flesh-Eating Beetles Explained, Mollie Bloudoff-Indelicato, National Geographic, January 17, 2013

 

waco-mammoths-3-from-city-of-waco-video

Screenshot of the entrance to Waco Mammoth National Monument from a video done by the City of Waco

Persistence Cave: A rich resource for paleontological research

Caves whisper exploration and discovery.

Anyone who has ever set foot in a cave of any size cannot help but wonder what lies beyond, what lurks in the crevices, the darkness.  Stepping into a cave is stepping into the entrance of mystery just waiting to be revealed.  In a world that has been largely tamed to fit the human species, there are few spaces that still hold an element of danger.  These unknown spaces beckon to the adventurous: “Explore me!” And who wouldn’t answer that call?

Me, that’s who. I am perfectly happy learning about the discoveries in caves from other people, thank you very much.

For people like me, Twitter and blogs have provided tantalizing glimpses of such explorations the world over.  And one of the more fascinating adventures has taken place at Persistence Cave, just one cave of many at Wind Cave National Park, South Dakota.

“Wind Cave National Park is full of fossils. Almost everywhere you go there’s going to be fossils: in the cave and at the surface. So Wind Cave National Park actually has [perhaps] 30-40 fossil sites.”

PhD student Jeff Martin explained more about the work he and his colleagues conducted there last season as he and his wife were literally driving to Texas to begin a new chapter in their lives. He was in the moving truck; his wife was in the jeep ahead.  Jeff and I had been in touch by email from time-to-time over the past year. As luck would have it, and thanks to his seemingly unending generosity, the time to discuss Persistence Cave by phone was while he was on the open road.

Wind Cave—as we know it now—was named because of the air that blows through an opening within.  It was considered a sacred place to the Native Americans long before settlers knew of its existence.  The Lakota people refer to the Black Hills (where Wind Cave is located) as ‘He Sapa’, (although it is listed as ‘Paha Sapa‘ on the Wind Cave National Park site).  Eventually, in 1903, it became the 8th National Park, but the first one to center around a cave.

Persistence Cave, a much smaller and less-explored cave in the park, was discovered by accident by Marc Ohms, spelunker and physical science technician for the park, in 2004.  His initial foray into the cave was brief: moving a cap rock, peering inside, seeing a rattlesnake, and deftly removing himself from the opening.

But its value as a fossil site was discovered thanks to another member of the park.

“Rod Horrocks, Wind Cave National Park Physical Scientist, in 2013, collected some sediment for preliminary analysis to see whether the site is paleontologically productive,” Jeff explained by email earlier.

It was, and this analysis is what eventually brought several scientists from diverse locations together.

Rod Horrocks sent the material to Dr. Jim Mead, Persistence Cave Project Leader, then at East Tennessee State University, where Jeff was a Master’s student at the time.  Jeff eventually moved to the University of Maine for his PhD, where Dr. Jacquelyn Gill was his advisor.

Sharon Holte, PhD Candidate at the University of Florida, was also a previous Master’s student of Jim’s, as well as Dr. Chris Jass at the Royal Alberta Museum,” wrote Jeff, explaining the connections between the Persistence Cave teammates. “He knows that we each excel in different aspects of vertebrate paleontology, and he invited each of us to collaborate on [and] bring our expertise into the research project. I brought Dr. Gill with me to the Black Hills to see the cave and to learn how a paleontological excavation is usually conducted. She brings a different set of skills related to paleoecology and palynology.”

Also on the team are undergraduate Chason Frost from the University of Maine who studies horticulture.  His skills and those of Dr. Gill help the group understand that fossil plants and pollen found in the cave.

Sharon Holte, aside from being one of the three principal spelunkers in this dig, is in charge of educational components.  Chris Bell at the University of Texas Austin studies the fossil rodents; Dr. Chris Jass and Dr. Jim Mead study fossil rodents as well, but include fossil snakes.

“Each person has their role,” he said, “their own ecological-niche, if you will.”

And Jeff?  He is the “bison guy.”

“My PhD research and dissertation focuses on bison body size adaptation to climate change over the past 40,000 years and how does that evolutionary legacy influence the bison we ranch today,” he wrote before he graduated this past Spring. “To answer this, I am using Persistence Cave and other fossil sites in Wind Cave National Park boundaries to geographically isolate my variation to only local animals.”

Wind Cave National Park, currently home to 400+ extant bison, offers information on both fossil bison and their living descendants.

 

EPSON DSC picture
EPSON DSC picture; bison at Wind Cave National Park, public domain from the National Park Service

 

“Collectively, we (Jacquelyn, Chason, and I) will then also look at the pollen grains and macro-botanicals preserved in the sediment to reconstruct the paleoecology and paleoclimate of the Black Hills through the last 11,000+ years to today. This is [to understand] the climate and ecology the bison were living in at these times.”

But let’s get back to the cave itself.

Below is an image of Natural Trap Cave (another exciting fossil cave dig in Wyoming; photo from myfossil.org):

 

Natural Trap Cave from myfossil.org

 

Compare that to an image of Persistence Cave from the top looking in (photo: Chason Frost as posted on Jeff Martin’s blog here):

 

Photo by Chason Frost - Persistence Cave entrance from Jeff's blog

 

 

 

And one of Sharon Holte peering out:

 

CB - SHolte peering out of cave

 

 

Finally, below is an image from the Rapid City Journal of “a tight spot in Wind Cave” (photo: National Park Service):

Marc Ohms WCNP National Park Service

 

When I asked about how this image compares to the space within Persistence Cave, I was surprised by Jeff’s email response.

“The picture above is much larger than the cave we are working in,” he described of the 2015 dig.  “The cave is very narrow and only fits one person’s shoulder width and up to 1.5 shoulder widths in places. The vertical height is similar to the above photo though.”

“I’m a broad shouldered fella’ and very, very tall,” he continued by phone recently. “The space in there to turn around is not quite enough for me, so I’d have to climb in and then climb backwards out.”

“Chris Jass and I are both the exact same height. Chris is a far more experienced spelunker, and even Chris wasn’t going in there.”

Sharon Holte, Chason Frost and Jim Mead were the principal spelunkers for the site.  Only one person could be in the cave at a time, and their only source of light came from a headlamp.  Trowels, buckets and ropes: their only tools.

 

CB - Sharon Holte important gear


“I thanked them endlessly, and I still thank them for all the work they were doing down in there,” Jeff said of his three colleagues. (A video of Sharon’s work in the cave can be found here.)

Work involved taking chunks of sediment in buckets out of the cave, tagging it, labeling the information (where that sediment appeared on the appropriate grid, at what depth, etc.), bagging that sediment, and then sending it down—by zipline, of all things!—to the truck below, where it could be taken to be screenwashed by other team members. (You can see a video of that process here, on Jeff’s blog.)

 

CB - screenwashing for microfossils

Screenshot of tweet during the 2015 Persistence Cave (#cavebison) dig

 

Their fossil discoveries have been diverse. Jeff wrote that “[a] camelid, (the species is unknown at this time), has been an extraordinary find. We have 5 different kinds of snakes and at least 5 different species of bats. [A] pika is also an intriguing find.”

 

 

CB - Jim Mead and snakes

CB - fossils found

 

CB - snake fossil

 

CB - toe bone and Jeff Martin

 

CB - Jeff Martins favorite bone found at that point

Screenshots of some of the many tweets during the 2015 Persistence Cave (#cavebison) dig

 

“One of the fun things that we ran across was a ton of Ponderosa pine needles,” he mused later by phone. “That’s the primary tree out there now.  Today, they’re mostly a two-needle bundle. In the past, it seems as though they were a three-needle bundle. And we don’t know exactly what that means yet.  So we’re trying to figure out if that means anything at all; if it’s a genetic difference; or if it truly is an environmental difference that it’s responding to.”

 

CB - Twitter conversation about plants

Screenshots of some of the many tweets during the 2015 Persistence Cave (#cavebison) dig; the scientists involved in this dig didn’t just conduct research, they also conducted outreach to the larger public through social media.

 

 

Work did not continue as expected on the site this year for a number of reasons, but it’s not over yet.  Studies on the fossils continue at the University of Maine (pollen and plants); the bison fossils have travelled with Jeff to Texas A&M University where he is now in wildlife sciences; and the rest of the fossils are housed at The Mammoth Site, where Dr. Jim Mead is currently Chief Scientist and Director.

The Mammoth Site is another major connection between many of the team members, as they have each “worked [there] at some point…over the last 40 years.”

As many know, that site is a paleontological (and proboscidean!) goldmine turned museum, thanks to the work of many, including the late Dr. Larry Agenbroad.  Over 60 mammoth fossils have been discovered there to-date, among other fossil species.

Bonebed at The Mammoth Site

Image of the bonebed at The Mammoth Site where excavations continue to this day

 

“He was probably THE reason that I got into the School of Mines [as an undergrad] and was also the reason I got into paleontology,” Jeff said of Dr. Agenbroad.

“I’m not alone,” he continued. “There are several of us that are like that.  We all stem from Larry.”

The reverence in his voice was not difficult for me to understand.

Jeff’s introduction to this paleontologist began when he was much younger, through the 2000 documentary “Raising the Mammoth.” The film focuses on the Jarkov mammoth, and Bernard Buigues’ attempts to excavate it.  The team Buigues calls upon to help include some giants of proboscidean research: Dick Mol and Larry Agenbroad.

A year or so after seeing that film, Jeff’s family traveled to The Mammoth Site.  It was winter in South Dakota, and, he said, his family basically had “the run of the whole place.”  With a graciousness I am sure permeates everyone who works at that site, one of the interpreters (‘docents’) offered to bring Dr. Agenbroad out to meet them.

“There’s 8-year-old me that’s just giddy with joy to be able to meet one of my idols,” Jeff shared with no small amount of enthusiasm. “And then he said, ‘You’re a little bit too young to work for me. Come back when you’re older.’”

“So that’s exactly what I did. I worked for him in [the summers of] 2007 at the Hudson-Meng Bison Kill Site and  2008 and 2009 at the Mammoth Site as an intern while I was at the School of Mines.”

Dr. Agenbroad passed away two years ago, followed by his wife, Wanda, a month later.  This saddened me as someone who did not know him closely; I could only imagine how this affected Jeff, who had.

“I’ve made my peace with it,” he acknowledged, and then said something that truly moved me: “I have several things that Jim [Mead] gave me…and one of them is a pocketknife that I carry on me every single day. One of the same pocketknives that Larry carried on him every single day. So I’ve got Larry with me, right now, as a matter of fact.”

Jeff and his colleagues hope to resume work at Persistence Cave next year.

As we discussed some of the findings from last year’s dig, he said, “The oldest date right now at Persistence Cave is at 39,000 and the youngest date is at 3,200.  We have some 37,000 years of deposits with bison throughout. And we also have [modern-day] bison living at the surface!”

Jeff’s research, both of Persistence Cave and of Project Bison, underscore his passion for this animal, as well as the desire to understand its ecological significance.

“I’m looking at both the fossil record and looking at their body size, using the calcaneum [heel bone] as the proxy for body mass. And then also comparing that to modern bison that have just recently passed away within the past 1-3 years.  That’s what I was doing this past summer: going to carcass sites and measuring their calcanea. The unique thing about Wind Cave is that they have almost every single animal microchipped. So they can track this animal throughout its life. On top of that, they bring them in once a year and weigh them. So now we have a known mass of these animals and now a known measurement, because I measured some of their calcanea.

“I’ve got some [fossil bison calcaneal] measurements that go up to 180 millimeters, and I also have Bison bison today that the longest that I’ll find are 130 millimeters.  So quite a body size change in between the fossil and modern.”

Jeff presented some of his research at last year’s Society of Vertebrate Paleontology (SVP) meeting in Dallas.

Describing the results, he explained, “As it gets colder, bison get bigger.  As temperatures are increasing, bison get smaller. That has modern day application to the bison industry today. If we’ll have smaller bison with future global warming, we’re going to have to change our management options.”

As I pondered all of the information Jeff had shared with me about the work he and his colleagues had done, I couldn’t help but go back to the images of how small the cave actually is. If Wind Cave National Park has an abundance of fossil sites, why go through the trouble of trying to access this one?

“Surface localities often represent a one-time event,” he explained. “Persistence Cave represents many events over a long period of time. That’s the unique part of this locality.”

I will continue to enjoy their adventures from the safety of my computer!

 

**************

Jeff Martin: you were extraordinarily generous with your time and responses to my myriad questions.  Likewise, I am in awe of how open you were with your experiences.  For being willing to share all of this, I am truly grateful.  It was an honor and a pleasure connecting with you!

When #CaveBison starts up again, you can be sure it will be on Twitter!  Follow these scientists:

@BisonJeff

@JacquelynGill

@SharonHolte

@Pocket_Botanist

@MammothSite

 

You can follow Jeff’s research here and here

Jacquelyn Gill is one of three hosts of the podcast, Warm Regards, which discusses climate change.