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


Natural Trap Cave from


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:







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.



Dr. Ben Thomas: (Part 2) Searching the Jungle for Maya Artifacts

“I talk to students and the last time they probably discussed the Maya was in the 4th grade. So they have a 4th-grade understanding of it. Which is kind of interesting to me.  I’m always like: when are the American kids going to learn about American history?”

Along with his work at the Archaeological Institute of America (AIA) as Director of Programs, Dr. Ben Thomas teaches Mesoamerican art at Berklee College of Music.  His undergrad and PhD work focused on archaeological sites in Central American countries.

The ‘American history’ of the Maya goes back to about 12,000 BCE, and it is a culture that continues to exist today in Mexico and the Yucatán peninsula.

The ancient Maya were the first known to create the zero—an extraordinarily complex mathematical concept. They were astronomers. They were, among many other things, writers, artists, scientists, farmers, builders, engineers.  Remnants of their great cities exist in the pyramids and stone structures that survive amidst the jungles.

Embed from Getty Images

Group A plaza at Caracol, the largest Maya site in Belize; photo courtesy of Tom Schwabel, Getty Images.

Embed from Getty Images

Mayan Temple at Caracol, Belize; photo courtesy of Steve Geer, Getty Images.

It is the writers and artists that pull at my imagination the most.  Prior to the Spanish conquest, the Maya people were prolific writers.  They created thousands of books, known today as codices, filled with pages of beautiful Mayan characters inked on pounded bark.


Image of the Madrid Codex (also known as the Tro-Cortesianus Codex or the Troano Codex) at the Museo de America, Spain; in the Public Domain, courtesy of Michel Wal, Wikipedia.

Dresden Codex Page 2

Page 49 of the Dresden Codex; photo in the Public Domain, courtesy of Wikipedia.


With the exception of four, all of them–these doorways into the minds and thoughts of ancient people–have disappeared from history. Religious zeal (a belief that these books were ‘the work of the devil’), colonial arrogance, and the desire to Christianize Mayas prompted the Spanish to have these books destroyed.  It is a loss that I cannot fathom, but one that I felt profoundly, physically in the pit of my stomach, gazing upon one of the four remaining Mayan codices at an exhibit last year.

Codex from exhibit

A rather poor image of the codex on exhibit in Maya: Hidden Worlds Revealed; taken by the author last year at the Boston Museum of Science


Linda Schele and David Freidel, in the book “A Forest of Kings”, state that the Mayan word its’at means “one who is clever, ingenious, artistic, scientific, and knowledgeable” (page 379).  It is also, according to these authors, another word for a scribe or an artist.


Peabody - Mayan scribes paint pot

Maya scribe ink pot (a conch shell), in which different ink colors would be placed in each section; taken by the author at the Harvard Peabody Museum.


Although the majority of Mayan codices have been lost, some of their writing survives in stone. Mayan glyphs—carved upon stone altars, giant stelae, and other stone facades—were finally understood in the 20th century.  This remarkable achievement was thanks to years of work by a number of individuals, culminating in final decipherment in 1986 by a teenage epigrapher.

Peabody - Mayan stelae and altar Q

Casts of Maya stelae from Guatemala and Altar Q in the foreground from Copán, Honduras at the Harvard Peabody Museum; photo taken by the author.

Peabody - Mayan stela

Detail of a cast of a Maya stela from Guatemala at the Harvard Peabody Museum; photo taken by the author.  An important contributor to our understanding of Mayan glyphs and writing used to work at this museum: Tatiana Proskouriakoff.


Did this relatively recent discovery correlate to our understanding of the Maya?  Are we only now beginning to unravel the depths of ancient Maya culture?

“Maya archaeology, Mesoamerican archaeology, I wouldn’t say it’s in its infancy,” Dr. Thomas replied. “We’ve been doing this now since the late 1800s, but really systematically with scientific methodology since probably the early 1900s.

“I think we know a huge amount about the ancient people of the Mesoamerican region.

“Some things we [once] had no idea about we know a lot about now: about settlement patterns, about construction techniques, about trade networks, linguistics. So I wouldn’t say that the discipline of Mesoamerican archaeology is in its infancy, but certainly there’s a ton more to find.”

But, he added, “[s]ome of it will never be discovered because it’s under modern construction.”

Dr. Thomas spent time in Guatemala during his grad school years, but his dissertation fieldwork took place in Belize.  He was part of a group at Boston University called XARP, the Xibun Archaeological Research Project.  The Mayan ‘x’ is pronounced ‘sh’; hence, XARP is pronounced: sharp.  Xibun is another way of spelling ‘Sibun,’ the name of both a river and an area in central Belize.


Embed from Getty Images

Map of Belize by Poligrafistka, Getty Images.


“When we were looking to do our research–to pick a new area,” he explained, “[the Sibun region] was very attractive to us because so much of it was not really understood.”

Part of the reason may have been due to the Sibun River’s frequent flooding; part of it may have been how inaccessible the area was—miles upon miles of dense jungle.

Looking at the sheer scale of the area, the massive distance on either side of this river, and seeing pictures of the dense brush and tree cover of the jungle, the task of finding anything remotely recognizable as an artifact from the Maya seemed insurmountable.

As Dr. Thomas had mentioned, “The organic material is gone, especially in Belize and the tropics in general in that area because it’s so hot and humid. And the soil is acidic. Organic materials do not preserve well.”

Absent enormous stone structures, how would anyone know where to even begin to look for ancient remnants?  Surely, they could be anywhere, and this was not an enormous team of archaeologists, equipped with technology like LiDAR to help them locate buried ruins.

The answer?

“We did a lot of research: looking at everything that was published about the area, we interviewed landowners, we talked to local people to get an idea of what they had seen on their property, we looked at all the maps and the geological surveys that had been done for Belize.

“Because of all the research we’d done, we [had a better understanding of] Maya settlement patterns. All of the studies would say, [for example], 70% of the Maya settlements are within a kilometer of a river.  There are things that you can look at to sort of try to set up a predictive model of where Maya sites would be.”

Xibun Archaeological Research Project - surveyor setting up the Total Station

Setting up a survey in the jungles of Belize. Photo courtesy of Patricia McAnany and the Xibun Archaeological Research Project.

“The big thing I always tell people is that if it’s good for us to live there today, then it was good for [ancient people], unless something bad and really drastic has happened. [Generally speaking,] if there’s a good water source, plenty of good land for agriculture, food sources—whether it’s animal or plant—and some raw materials, that’s where people lived.”

“We had people walking through the jungle looking for things. And what you’re looking for is clusters of artifacts and features, but sometimes they’re so overgrown that you may not see them.”

“We had machetes, and we used them to clear as we were walking along.”

Despite this, I still couldn’t understand how Maya ruins—the soft limestone of their structures eroded over the centuries—could be found in such conditions.

“[When it comes to finding the archaeologically important mounds,],” he said, “you realize you’re walking uphill. Or, you know, you might be able to see [them directly.] After a while you get kind of used to it, how the land should look and what you’re seeing.”

Xibun Archaeological Research Project - walking over a pyramid that has been completely obscured by vegetation

Walking over a pyramid that has been completely obscured by vegetation in Belize. Photo courtesy of Patricia McAnany and the Xibun Archaeological Research Project.

XARP - same pyramid that we were walking over after we cleared off the vegetation

The very same area as in the photograph above, but cleared of all vegetation, revealing the remnants of an ancient Maya pyramid. Photo courtesy of Patricia McAnany and the Xibun Archaeological Research Project.

Images of dense jungle immediately brought another concern to mind: snakes.

Dr. Thomas smiled. “Snakes [were] an issue. Scorpions. But the things that [were] really, really annoying [were] the bugs: mosquitoes, ticks.”

Eventually, the XARP team sought answers to four questions about the Maya in the Sibun:

  1. What was the nature of Maya settlement along the river?
  2. What was the role of cacao in the Sibun and could we find evidence of ancient Maya cacao production?
  3. What was the effect of Christianity on the Sibun and could we find the visita mentioned in the Spanish records?
  4. How were the caves used?

Unfortunately, they were unable to find evidence of ancient cacao production.  Part of the issue was not knowing what, exactly, to look for.  How does one find remnants of ancient orchards?  And after years of modern cacao growth in Belize, in which hybrid cacao has been introduced, what does ancient cacao even look like?  Other clues to cacao production—the ceramics involved in drinking cacao, for example—would have provided evidence, but these could not be found.


 Cacao pods; image courtesy of nullplus, Getty Images.

Caption from Getty Images: Cacao Plant with Fruit (Theobroma cacao). Maya are generally given credit for creating the first modern chocolate beverage. They ground cocoa seeds into a paste, and mixed it with water, cornmeal, chile peppers, and other ingredients. Photo courtesy of SPrada, Getty Images.


Their quest to find a visita, a Christian church built by Spanish conquerors, was also unsuccessful.  In the 1500s, Spanish overseers known as encomanderos were each given pieces of land (encomiendas) to use as they saw fit.  Visitas were built on this land to further Christianize the local people.

Because the Maya did not employ metal, anything made out of this substance would indicate a colonial presence. They may not have found a visita, but the team did find remnants of colonialists in the form of clay pipes, lead shot, a rusted knife, and gun flint.

“Before we started all this, we knew of 3 sites,” he explained, referring to the only known Maya sites in the Sibun region by the 1990s, one of which is on land owned by the Hershey Corporation.

Ben Thomas - Excavation in progress at another site along the Sibun

Excavating along the Sibun River. Photo courtesy of Patricia McAnany and the Xibun Archaeological Research Project.

Ben Thomas - excavation 1

Ben Thomas - excavation 2

Ben Thomas - excavation 3

Ben Thomas - excavation 4

Ben Thomas - excavation 5

Stages of excavation. Photos courtesy of Patricia McAnany and the Xibun Archaeological Research Project. Samuel Oshon–upon whose property these excavations were conducted–remembers seeing Charles Lindberg fly over his land!


“By the end of it, we had 22 sites, [19 of which we had discovered.] And we had mapped and explored about 18 caves in quite a bit of detail.”

Caves were, and continue to be, a particularly sacred place to the Maya.  They are, among other things, believed to be connected to Xibalba, the Maya Underworld, which was both feared and revered in equal measures.

Ben Thomas - cave

Photo of XARP exploring a cave, courtesy of Patricia McAnany and the Xibun Archaeological Research Project.

“They were bringing things in [to the caves],” Dr. Thomas said of their discoveries in local caves. “So you find pots with the remains of food. But then some of [the pots], they’re upside down, and they had holes in them. They were doing something else with them.”


Ben Thomas - cave ceramics

Ancient Maya ceramics in a cave. Photo courtesy of Patricia McAnany and the Xibun Archaeological Research Project.


A particularly significant artifact located in the caves were metates—the stone tools used to grind maize, perhaps the most important crop throughout the Maya universe.

“But those things are heavy!” he emphasized of the metates. “These things can weigh 40 – 60 pounds. It’s solid stone. And there [are] several of them.”

Ben Thomas - cave ceramics and metate

Photo inside a cave with ceramics and metate (grindstone) on the right courtesy of Patricia McAnany and the Xibun Archaeological Research Project.


He described not only how difficult it was to get to, but then enter one particular cave.

“The fact that they’re bringing [metates] in there, [when] it’s not easy to do, I think it does speak to the importance of the rituals.  They’re willing to invest the time and the energy for these rituals.”

“But they’re also taking things out! We noticed on the sites [outside of these caves that] they would have stalactites or stalagmites, [sometimes] on the house floors, sometimes they’d be in burials.

“We think of a cave as a sacred space with spiritual energy [so], I think, taking something from there would have that spiritual energy connected to [it].”

“People still do it,” he said, referencing relics in many of today’s Christian churches, in which the bones of saints are enshrined.

Dr. Thomas and I had been conversing for well over an hour at this point.

“[Archaeology],” he concluded, “[is really] a database of human behavior, starting from thousands of years ago to now. We’re chronicling it: how people behaved, how they reacted to things.  A lot of times the collapse of societies is brought on [by events such as] climate change,  [for example; or] it’s brought on by overexploitation of natural resources; [or by] people not adjusting or adapting to their circumstances.  [Those are] all data-points that we have that people should be looking at. What are we doing to our environment now? How are we reacting to things now?”

“Because in some ways, none of this is new. I think what has changed now is the scale of things.”


I extend an enormous THANK YOU to Dr. Ben Thomas.  Not only was it a great honor and pleasure speaking with him for such an extended period of time, but it was no small task to find time in his extraordinarily busy schedule.  He helped pave the way for my increased interest and enthusiasm for the Maya culture. I am very grateful!
A huge THANK YOU to Caitlin Davis for connecting me to Dr. Thomas!


  1. “A Forest of Kings”, by Linda Schele and David Freidel, William Morrow and Co., 1990
  2. “Breaking the Maya Code”, by Michael D. Coe, Thames and Hudson, 1992
  3. “Handbook to Life in the Ancient Maya World”, by Lynn V. Foster, Facts on File, Inc., 2002


Image of Palenque, a Maya city-state in Chiapas, Mexico; courtesy Getty Images.