Of Sacred Mules and Sauropod Tracks

Legends and storytelling are an intrinsic part of being human. Given this statement, you might then also think of myths and other stories you’ve heard throughout your life. Which were the most memorable, and why? With such remembrances, your next step may be to do something else that is very much a part of being human, which is to wonder whether that myth or story holds some lesson applicable to real life. Whether a story is an accurate account of reality is beside the point, as its imparted teachings are sometimes more important than factual accuracy.

Avelino-Sauropod-TracksModern scientists say these depressions in a tilted rock surface near Sesimbra, Portugal were made by sauropod dinosaurs in soft sediments during the Jurassic Period more than 150 million years ago. But what if you lived in this area during the 14th century? How would you explain these depressions? While you’re thinking about that, here’s another question: If I hadn’t told you these were dinosaur tracks, would you even know they were tracks? (Photograph by Anthony Martin.)

Yet, what if reality and scientific reasoning – with the latter thriving on a spirit of disproof – rudely intrudes on a good story, disrupting its original intent? In such instances, a legend previously regarded as literal truth may lose its narrative power, as we begin to doubt not just its details, but also its intent. Can anything useful be salvaged from a myth when skepticism assaults faith? Should we completely reject parables once we know foxes do not talk about grapes, sour or otherwise?

Less than two weeks ago I visited a place where the basic facts of a long-held legend had been disproved, yet a lesson from it remains. The place is Cabo Espichel, marked by a lighthouse, church, and small chapel on a plateau high above rocky cliffs along the southwest coast of Portugal. Cabo Espichel is about a 90-minute drive from the modern metropolis of Lisbon, yet it felt far more remote, and very much connected to a medieval past.

Cabo-Espichel-OutcropsA view of Lagosteiros Bay from the top of Cabo Espichel. Also check out those gorgeous outcrops of tilted Jurassic and Cretaceous rocks! Gee, I wonder what trace fossils might be in them? (Photograph by Anthony Martin.)

The legend associated with that place concerns a 14th century visitation there by someone named Mary, who is also known by many other names: Saint Mary, Mary of Nazareth, Blessed Virgin Mary, Our Lady, The Madonna, or very simply the Mother of Jesus. Given the Catholic culture that is very much still a part of the Iberian Peninsula, her purported arrival to Portugal there was (and still is) considered a blessing and a ringing endorsement of Christianity there. Accordingly, the church complex is called the Santuário de Nossa Senhora do Cabo Espichel (“Sanctuary of Our Lady of Cape Espichel”).

Cabo-Espichel-ChurchIchnologists approaching the Santuário de Nossa Senhora do Cabo Espichel, Portugal, not on the way to confess their sins (that would have taken way too long), but to see the small chapel behind it, as well as some great coastal outcrops of Mesozoic rocks. So you might say they were there for a different type of worship. (Photograph by Anthony Martin.)

How did Mary get to Portugal from the Middle East? Given the absence of airlines then, she and the Baby Jesus traveled by boat. Once the Mother and Child reached the shore of Lagosteiros Bay below Capo Espichel, a giant mule carried them up the steep rock faces of Cabo Espichel. This scene came in a vision to two men in the area, who shared the same dream of her arrival on the same night. In a splendid example of confirmation bias, their testimony was taken quite seriously by the local populace and beyond, and has endured since.

Sauropod-Tracks-Cabo-Epsichel-3Cliff face below the present-day chapel and church at Cabo Espichel, with well-exposed and tilted bedding planes of sedimentary rock. This would have been the most likely route for a mule (giant or otherwise) to have accessed the top from Lagosteiros Bay. Photo is a still taken from an online edited drone video titled “Cabo Espichel – Dinosaur Trackway Adventure.” Related to the question asked in the previous caption: Huh, I wonder what those depressions on the rock face might be, how they relate to the legend, and the title of that video?

In commemoration of this momentous event, the church and chapel – the latter called Ermida da Memória (Chapel of Memory) – were built near the precipice. Portuguese royalty hosted annual feasts there, and many pilgrims put it on their spiritual “bucket list” as a must-visit place. Today, it is still visited by devout Catholics, who may be imagining themselves walking on the same holy ground trodden by Mary and her miraculous mule.

Ermida-da-MemoriaThe Ermida do Memória seen from afar on Capo Espichel. Imagine it in the darkness of night, when suddenly a glow comes from the bay below. Inside this light, the head of a giant mule appears, and as more of its body emerges from the cliff edge, you see Mother Mary astride it carrying the Baby Jesus, accompanied by an aerial escort of angels and the most beautiful music you’re ever heard in your life. OK, Guillermo de Toro, I just wrote the scene for your next movie: the rest is up to you. (Photograph by Anthony Martin.)

So where did this legend come from: crazed fishermen who had spent one day too many at sea, villagers imbibing enthusiastically on local vinho verde, or clergymen overcome by ecclesiastic visions? No, this story actually had evidence backing it up. All one had to do is get in a boat just offshore, and you could see for yourself enormous footprints in the rocks leading from the sea to the top of the cliff at Cabo Espichel.

Sauropod-Tracks-Cabo-Espichel-1They’re a little tough to see from this far out, but the big white arrows help. The “mule tracks” are on tilted strata just above the bay, and compose diagonal-walking patterns. (Photo taken as still from video Cabo Espichel – Dinosaur Track Adventure. I would have prefaced that information with “Spoiler Alert,” but you did read the title of this post, right?)

Sauropod-Tracks-Cabo-Espichel-2A closer view of a rock surface with the diagonal-walking pattern clearly defined, accentuated by vegetation growing in the depressions. Don’t believe me that these are from the same site? Look up “Cabo Espichel, Portugal” on Google Earth™, scan the rock surfaces just north of the chapel, and see them for yourself. (Photo again is still taken from video Cabo Espichel – Dinosaur Trackway Adventure.)

These tracks, people said, marked where the weight of the mule pressed into the rocks. Even better, some of these tracks formed patterns clearly made by four-legged animals, and individual tracks were crescent-shaped, resembling the feet of mules or other horse-like animals. As a result, one name applied to this place is Pedras de Mula, which translates as “Rocks of the Mule,” although Pegadas de Mula (“Tracks of the Mule”) is also applied.

Every good story also needs images, and this one has a particularly noteworthy visual aid. The building of a chapel on the site in the 16th century contains tile artwork commemorating this divine calling; however, the tile was probably made later, in the 18th century. Although the chapel interior is closed to the public, a open slot in its door afforded a glimpse of this depiction, aided by the zoom lens on my camera. Like any good illustration, the story is neatly encapsulated in the tiles: Mother Mary and The Baby Jesus riding on a mule, with angels in tow and stunned onlookers properly prostrating.

Pedras-de-Mula-118th century tiled artwork inside the Ermida do Memória depicting the legend of Mary’s visitation of Cabo Espichel. To all artists out there (and I’m one of you), the original creator of this work is unknown, hence image credit cannot be assigned here. (Photograph by Anthony Martin.)

Centuries later, ichnology happened. Beginning in the mid-1970s, geologists and paleontologists realized that the Mesozoic rocks of Portugal, including those at and near Cabo Espichel, held dinosaur tracks. This consciousness has been affirmed many times since, with discoveries of tracks belonging to a wide variety of Jurassic and Cretaceous dinosaurs: theropods, ornithopods, stegosaurs, and sauropods among them. Portugal is now rightly renown as one of the best places in the world to see thousands of well-preserved dinosaur tracks, all within just a few hours drive of one another.

Saruopod-Tracks-Cabo-Espichel-4A close-up of a dinosaur trackway – probably from a sauropod – on one of the rock surfaces at Cabo Espichel. As folks would say in my part of the U.S., “Those ain’t from no mule.” (Photo is still from video Cabo Espichel – Dinosaur Trackway Adventure.)

Vanda-Santos-Avelino-Sauropod-TracksDr. Vanda Faria dos Santos, Portugal’s premier dinosaur tracker, telling us about the sauropod tracks at the Avelino tracksite, just south of Cabo Espichel. Notice the abundant depressions on a tilted rock face, very similar to those at Cabo Espichel. (Photograph by Anthony Martin.)

Of these tracks, those of sauropods were the most relevant to the tale of Cabo Espichel. The majority of sauropod tracks in Portugal are very large, especially those of the rear-foot (pes), which can be about a meter long and nearly as wide. The front-foot (manus) impressions are smaller, but still approach a half-meter wide, and are crescent-shaped. You know, like those of a horse, or mule.

Sauropod-Manus-AvelinoFront-foot (manus) track made by a Late Jurassic sauropod preserved as a cresent-shaped depression at the Avelino tracksite near Sesimbra, Portugal. (Photograph by Anthony Martin.)

A detailed field study of the tracks at Cabo Epischel, done by Martin Lockley, Christian Meyer, and Vanda Santos in 1993 and published in 1994, confirmed that the “mule tracks” at Cabo Epsichel were indeed those of sauropods. The original surfaces were of soft sediment and horizontal; only later did a combination of cementation and plate tectonics harden and tilt these rocks, with coastal erosion finally rendering their current appearance. Moreover, ten sauropod trackways on one of the bedding-plane surfaces there recorded the herding movements of seven smaller sauropods (juveniles) and three larger ones (adults), all of them walking in more-or-less the same direction. These results thus made the site scientifically famous, as it was one of the first convincing examples of family herding behavior in sauropods demonstrated from their footprints.

Lockley-et-al-Sauropod-Track-Map-Cabo-EspichelTrackway map of bedding plane at Cabo Espichel in article by Lockley, Meyer, and Santos (1994). The map shows parallel smaller (juvenile) sauropod trackways (numbers 1-7), followed by two larger (adult) sauropod trackways (numbers 8-9); another adult trackway is not on this figure, but was below the other two.

Here’s the full edited aerial-drone video linked previously, Cabo Espichel – Dinosaur Trackway Adventure. The video credit only says “rlage3,” so if the person/people who produced this would just let me know who you are, I’m more than glad to give full attribution. In the meantime, thanks much for providing such a nice overview of this beautiful and ichnologically rich area!

This situation with competing stories is where ichnology excels, as it is also a science based on storytelling. Granted, the story told by ichnologists is radically different from the one first accepted by the 14th century people of Portugal, or those since who have accepted the faith-based explanation for the tracks. On a personal note, I’m ex-Catholic; hell, I was an altar boy, went to a Catholic college for my undergraduate studies, and my mother was a more devout Catholic than most pontiffs. Thus I have much empathy for how people of faith (especially Catholics) feel about such things. So if pilgrims still chose to believe the tracks of Cabo Espichel were made by a giant mule bearing Mary and Jesus, and this fills them with joy, I’m cool with that. Just don’t tell me our science is wrong.

So now I will leave you with two provocative thoughts. The first is that the tile artwork in the chapel is the first known illustration of dinosaur tracks. Is it a scientifically accurate, to-scale, 3-D rotating digital model of a dinosaur trackway? No, but it’s still an illustration, and even though its interpretation does not qualify as science, it clearly shows a large, diagonal-walking trackway pattern on an inclined cliffside at Cabo Espichel. Let that sink in for a second: an 18th century artist must have seen dinosaur tracks on a bedding plane somewhere in that area, and faithfully reproduced them in a recognizable pattern.

Pedras-de-Mula-2Close-up of tile artwork in the Ermida da Memória, connecting the trackway pattern to a mule, but which we now can be sure was inspired by the trackway of a Late Jurassic sauropod dinosaur. (Photograph by Anthony Martin.)

The second thought is that although the interpretations of this trackway might differ radically, what they share is true: These impressions in the rock were made by enormous, walking, four-legged animals. How many modern people today, their eyes no-doubt glued to their 21st-century devices, would stumble in such tracks, possibly never recognizing their connection to animal life? So rather than make fun of the people of Portuguese past, or whoever else must have observed the tracks preserved in the rocks of Cabo Espichel, we should celebrate those who recognized these depressions as traces of life. In this sense, then, the faith-filled people of the past were doing their own form of ichnology in Portugal, centuries before we modern ichnologists walked in the same place.

Afterword: Many other paleontologists and science historians have written about the discovery of the first known sauropod tracks in Portugal, so I will not repeat nor summarize their contributions here. Instead, I’ve included the following bibliography. Many thanks to Drs. Vanda Santos, Paulo Caetano, Carlos Neto de Carvahlo, and Joana Rodrigues for teaching other ichnologists and me about the long ichnological history of Cabo Espichel.

Further Reading

Atunes, M.T. 1976. Dinossáurios Eocretácios de Lagosteiros. Ciéncias da Terra (UNL), 1: 1-35.

Atunes, M.T. 1990. Dinossáurios em Sesimbra e Zambujal – Episódios de há cerca de 140 milhões de anos. Sesimbra Cultural: 12-14.

Chure, D. 2012. Sacred birds, lucky rhinos, and The Virgin and the sauropod. Land of the Dead (blog), January 7, 2012.

Lockley, M.G., Meyer, C.A., and Santos, V.F. 1994. Trackway evidence for a herd of juvenile sauropods from the Late Jurassic of Portugal. Gaia, 10: 29-40.

Lockley, M.G., Novikov, V., Santos, V.F., Nessov, L.A., and Forney, G. 1994. “Pegadas de mula”: an explanation for the occurrence of Mesozoic traces that resemble mule tracks. Ichnos, 3: 125-133.

Santos, V.F. 2008. Pegadas de dinossáurios de Portugal. Museo Nacional de História Natural da Universidade de Lisbõa, Lisbõa, 123.


Deep in the Dinosaur Tracks of Texas

Given the continuing public mania over dinosaurs, and recent important discoveries of yet more exquisite specimens of feathered theropod dinosaurs discovered in countries far away from the U.S. (here and here), it is sometimes easy to forget what has long been known about these animals, and right here in my own “backyard” (globally speaking).

Need to see some of the best dinosaur tracks in the world, and you live in the southeastern U.S.? Guess what: you can seen them in Glen Rose, Texas. Not China, Mongolia, Canada, Utah, or some other far-off land inhabited by strange people with unusual customs, but Texas. Saddle up! (Photograph by Michael Blair, taken in Dinosaur Valley State Park, Texas.)

So on July 22, just to jog my memory a bit, I flew from Atlanta, Georgia to the Dallas-Ft. Worth (Texas) airport, and only a few hours later was gazing upon dinosaur tracks accompanied by the burrows of invertebrate animals, both trace fossils having been made more than 100 million years ago. It was a fitting welcome to Glen Rose, Texas, a place famous for its dinosaur trace fossils since the 1930s, and where dinosaurs were an integral part of its culture long before it was cool, hip, and contemporary elsewhere.

In Glen Rose, Texas, the dinosaur tracks are so abundant, you can choose whether to see these just outside of your hotel room, or go to the hotel jacuzzi and pool. Naturally, I chose both. (Photograph by Anthony Martin, taken in Glen Rose, Texas.)

So just how did I end up in Glen Rose, Texas, looking at Cretaceous dinosaur tracks and invertebrate burrows? I was lucky enough to be there as an invited participant in an expedition sponsored by the National Geographic Society. I say “lucky” because luck was certainly a part of it, a fortuitous connection made through my writing a book about the modern traces of the Georgia coast. James (Jim) Farlow, a paleontologist at Indiana-Purdue University Fort Wayne (IPFW) and an associate editor with Indiana University Press, reviewed the first draft of my book, but he was also in charge of this dinosaur-track expedition to Glen Rose. Evidently he was impressed enough about what I knew about invertebrate burrows (or at least what I wrote about them) that he considered me as a possible member for his team of scientists, field assistants, and teachers on this expedition.

Dr. Jim Farlow, the world expert on the Glen Rose dinosaur tracks, having a reflective moment at Dinosaur Valley State Park near Glen Rose, Texas. What’s with the broom? He and other people in the expedition used these to sweep river sediment out of dinosaur tracks submerged in the river. In 100° F (38° C) temperatures. On the other hand, I just described invertebrate trace fossils, which was more of a job, not work. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

Thus when Jim asked me last fall if I would be interested in joining them to describe and interpret the Cretaceous invertebrate burrows that occur with the dinosaur tracks there, I jumped at the opportunity. The Glen Rose dinosaur tracksites, most of which crop out in the Paluxy River bed in Dinosaur Valley State Park, are world famous for their quantity and quality, and they connect with an important part of the history of dinosaur studies. Going there, experiencing these tracks for myself, and better understanding their paleoecological and geological context would be of great benefit to me, my students, and of course, you, gentle readers.

Just to back up a bit, and clarify for anyone who doesn’t know why these tracks are so darned important, here’s a brief background. In November 1938, Roland T. Bird, an employee of the American Museum of Natural History and a field assistant to flamboyant paleontologist Barnum Brown (the guy who named Tyrannosaurus rex), saw large, isolated limestone slabs with theropod dinosaur tracks in a Native American trading post in Gallup, New Mexico. Upon inquiring about the origin of these tracks, Bird was told they came from Glen Rose, Texas. So he set out in his Buick for Glen Rose to see for himself whether these tracks were real or not, and whether there were any more to see in the rocks around Glen Rose. The theropod track set in the town bandstand – pictured below – was one of the first sites that greeted him, and Glen Rose locals told him about the tracks in the Paluxy River.

Glen Rose, Texas, the only place in the world where the town bandstand has an Early Cretaceous theropod dinosaur track on display. Wish I could also tell you about all of those little holes in the rock with that track, but I can’t right now. Nonetheless, rumor has it they are burrows made by small, marine invertebrates that lived at the same time as the dinosaurs. (Photograph by Anthony Martin, taken in Glen Rose, Texas.)

Bird had hit the jackpot, the motherlode, the bonanza, the surfeit, the, well, you get the point. Not only did the Paluxy River outcrops contain hundreds of theropod dinosaur tracks – many as continuous trackways – but also the first known evidence of sauropod dinosaur tracks.

A couple of beautifully preserved theropod tracks under shallow water in the Paluxy River. Note that the track at the bottom also has a partial metatarsal (“heel”) impression, and look closely for the digit I (“thumb”) imprint on the right. Scale is about 20 cm (8 in) long. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

Funny how those “potholes” in the limestone bedrock of the Paluxy River have oblong outlines and form regular alternating patterns, isn’t it? Well, them ain’t no potholes, y’all. They’re sauropod tracks, and were among the hundreds recognized as the first know =n such tracks from the geologic record. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

The discovery of sauropod tracks was as huge as the tracks. Up until then, sauropods were assumed to have been so large that they could not support their weights on land and spent most of their time in water bodies. These tracks said otherwise, that these sauropods were walking along mudflats along with the theropods. In short, the trace fossil evidence contradicted the assumed story about how these massive animals moved. After all, trace fossils are direct records of animal behavior, and if interpreted correctly, can tell paleontologists more about what an animal was doing on a given day than any amount of shells, bones, and yes, even feathers.

Sauropod tracks from the main tracksite in Dinosaur Valley State Park, Texas. The sauropod was moving away in this view, and the trackway pattern is a typical diagonal-walking one, right-left-right. In parts of this trackway, both the manus (front foot) and pes) rear foot registered, something Bird noticed in 1938, his observation accompanied by more than a little bit of excitement. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

The details preserved in these sauropod tracks are also astounding. Most sauropod tracks I have seen elsewhere, in Jurassic and Cretaceous rocks of the American West, Europe, and Western Australia, are only evident as large, rounded depressions that you would only know are tracks because they form diagonal-walking patterns. In contrast, the Glen Rose tracks include all five toe and claw impressions on the rear feet (pes) and full outlines of the front feet (manus). The original calcium-carbonate mud in the shoreline environments where the sauropods walked, similar to mudflats I’ve seen in the modern-day Bahamas, is what made this exquisite preservation possible. The mud had to be firm enough to preserve these specific details of the sauropods’ feet, but not so soft that the mud would collapse into the tracks after the sauropods extracted their feet.

Beautifully preserved tracks, manus (top) and pes (bottom). Note the five toe impressions in the pes, which along with its size confirms that these were made by a large sauropod. Meter stick for scale. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

One sauropod trackway, preserved with a theropod trackway paralleling and intersecting it, was actually quarried out of the river and taken to the American Museum. Once there, its pieces stay disassembled for years, before Bird helped with putting the puzzle pieces back together so that it could be used as part of a display there.

Archival video footage of Roland Bird and his field crew working on the dinosaur tracks in the Paluxy River near Glen Rose, Texas. More about this tracksite and its role in the history of dinosaur paleontology is ably conveyed by Brian Switek here.

Photos at the visitor’s center at Dinosaur Valley State Park, showing the sequence of clearing (left) and extraction (right) of the limestone bed containing the theropod and sauropod dinosaur tracks. (Photographs taken of the photographs, then enhanced, cropped, and placed side-by-side by Anthony Martin.)

A lasting trace today of Roland Bird and his field helpers from the 1940s, in which they took out a sauropod and theropod trackway from this place and transported it to New York City. (Photograph by Anthony Martin, taken in Dinosaur Valley State Park, Texas.)

Other than some of the best-preserved Early Cretaceous dinosaur tracks in the world, one other claim to fame for the Glen Rose area, and not such a proud one, is its attraction to evolution deniers, a few charlatans who used the tracks to promote what might be mildly termed as cockamamie ideas. You see, Glen Rose is also the site of the infamous “man tracks.” These tracks are preservational variants of theropod tracks that – through a combination of the theropods sinking into mud more than 100 million years ago and present-day erosion of the tracks in the Paluxy River – prompted some people to claim these were the tracks of biblical giants who were also contemporaries of the dinosaurs. (Perhaps this is as good of a time as any to start humming the theme music for The Flintstones.)

Rare documentary footage of humans and dinosaurs interacting with one another during the Early Cretaceous Period, or the Late Jurassic Period. Whatever. Note the inclusion of other seemingly anachronistic mammals, too, such as the saber-toothed felid Smilodon. Perhaps this footage could be included in the curriculum of some U.S. public schools, providing a formidable counter to the views of 75 Nobel laureate scientists. Then we’ll let the kids decide which is right.

I will not waste any further electrons or other forms of energy by continuing to flog this already thoroughly discredited notion, but instead will direct anyone interested to a thorough accounting of this debacle to some actual scholarship here, summarizing original research by Glen Kuban and others in the 1980s through now that have laid to rest such spurious notions. Speaking of Mr. Kuban, I was delighted to meet him for the first time during while in Glen Rose (we had corresponded a few times years ago). I was even more gratified to spend a few hours in the field with him, discussing the genuinely spectacular trace fossils there in Dinosaur Valley State Park with these directly in front of us. Again, I’m a lucky guy.

The expedition was scheduled in Glen Rose for three weeks during late July through early August, but with so many commitments for this summer, I could only carve out a week for myself there, from July 22-29. Fortunately, this was enough time for me to accomplish what was needed to do, while also having fun getting to know the rest of the expedition crew – teachers, artists, videographers, laborers – and enjoying wonderful discussions (and debates) with colleagues in the field. The people of Glen Rose were also exceedingly welcoming and accommodating to us: we felt like rock stars (get it – “rock”?), and were feted by local folks three nights in a row during the week I was there. Many thanks to these Glen Rose for the the exceptional hospitality they extended to our merry band of paleontologists, geologists, river sweepers, or what have you.

You can’t see it, but I’m standing in a sauropod dinosaur track, which is a little deeper than the rest of the river bed. You also can’t see the invertebrate burrows that are in the limestone bedrock, which is fine, because I can’t show them to you yet anyway. But be patient: you’ll learn about them some day. (Photograph by Martha Goings, taken in Dinosaur Valley State Park, Texas.)

I can’t yet say much more about what I did during that week, as all participants signed an agreement that National Geographic has exclusive rights to research-related information, photos, and video unless approved by them. But if you’re a little curious about the daily happenings of the expedition (which just ended last week), Ray Gildner maintained a blog that succinctly touched on all of the highlights, Glen Rose Dinosaur Track Expedition 2012.

Still, I can say, with great satisfaction, that I did successfully describe and interpret invertebrate trace fossils that were in the same rocks as the dinosaur tracks. Hopefully my colleagues and I will have figured out how these burrows related to environments inhabited by the dinosaurs that walked through what we now call Texas.

All in all, my lone week in the Lone Star State was a marvelously edifying and educational experience, one I’ll be happy to share with many future generations of students and all those interested in learning about the not-so-distant geologic past of the southeastern U.S.

Group photo from the Glen Rose Dinosaur Track Expedition 2012. Names of all participants can be found here, but in the meantime, just sit back and admire those Dinosaur World t-shirts everyone is wearing. (Photograph by James Whitcraft or Ray Gildner: they can fight over who actually took it. Although, the automatic timer on his camera took the photo, so maybe it should get credit instead.)

Further Reading

Bird, R.T. 1985. Bones for Barnum Brown: Adventures of a Dinosaur Hunter. Texas Christian University Ft. Worth, Texas: 225 p.

Farlow, J.O. 1993. The Dinosaurs of Dinosaur Valley State Park. Texas Parks and Wildlife Department, Austin, Texas: 30 p.

Jasinski, L.E. 2008. Dinosaur Highway: A History of Dinosaur Valley State Park. Texas Christian University, Ft. Worth, Texas: 212 p.

Kuban, G.J. 1989. Elongate Dinosaur Tracks. In Gillette, David D., and Martin G. Lockley (editors), Dinosaur Tracks and Traces, Cambridge University Press, Cambridge, U.K.: 57-72.

Pemberton, S.G., Gingras, M.K., and MacEachern, J.A. 2007. Edward Hitchcock and Roland Bird: Titans of Vertebrate Ichnology in North America. In Miller, William, III (editor), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam: 32-51.