Harvester Ants - July

 Harvester Ants - July

Several months ago we decided to build a section of the backyard into a raised bed for native flowers. In the process we redirected a small footpath and moved a few wheelbarrows of soil. Unfortunately, a young mound of harvester ants (Pogonomyrmex occidentalis) happened to be in the way. I tried placing stones around the mound so that it wouldn’t be buried, but in the end we had to sacrifice the ants. When we were finished with the project, the ants were buried under four to five inches of sandy soil. 

Then several days later, to my surprise, I discovered that the ants were still alive and had a new entrance connecting to their underground chambers. It wasn’t on top of the new flower bed but at the base of the new rock retaining wall. Now, these several months later, I think of their remarkable persistence every time I walk by their new mound. 

And then this last week, I learned a little bit more about the ability of harvester ants to move small stones and piles of dirt. I was studying insects on the east slope of the Pine Valley Mountains northwest of Leeds (Utah) when I discovered what first looked like an abandoned mound. You can tell that a mound is a harvester ant mound quite easily by the many small pebbles that form an asymmetrical cone and by the disk surrounding the cone that is bare of vegetation. Sometimes the ants will add bits of dried plants or dead insects on the mound as well. I have a hunch that they are drying them out to preserve underground for a future time of need. 

In this case, the small pebbles and thin blades of grass were present but were no longer covering a mound. They were lying flat and there were divots where there should have been an even convexity covered with red ants. This is not an unusual finding in the deserts of the Southwest where ant mounds are born and die as if they were individuals themselves. In fact ants (and sometimes their mounds) are often called superorganisms because of this. Workers are genetically the same and do not reproduce, and yet they are essential for the survival of the queen and the production of new ants. The individual ants really do act only for the benefit of the colony. A worker that will never have offspring of its own will recklessly defend the colony against any and all threats without giving a second thought about sacrificing her own life. The survival of the colony is all that counts. 

And yet the mound “dies” when the queen expires and no new ants are born. Eventually there is a gradual attrition of the existing workers. So when I saw the flattened mound, I didn’t think much of it. But, as it turned out, the mound wasn’t really dead. Out of the corner of my eye, I noticed a bit of movement. There were a few of my little red friends still occupying the nest. How sad, I thought, their efforts are doomed to failure. It seemed that the queen had died and these were the last survivors.

Then I noticed something else. A small black ant - maybe a third the size of the harvester ants - jumped on the back of a larger ant and began biting its neck. The harvester ant did not tolerate this at all, and in less than a second managed to fling it to the ground. I was quite surprised by the affrontary of such an undersized ant. What chance did it have against the much larger harvester ants? But I soon learned that I had misjudged the situation. The little dark ants (Conomyrma insana) were launching a full attack. 

They were harder to see than the harvester ants. But once I adjusted my vision to the smaller insects I could see that there were over a thousand milling around the erstwhile mound. The few harvester ants that remained were all concentrated around the two openings defending themselves, and what remained of their home, from the attackers. 

I watched this battle play out for several minutes, adjusting my position every few seconds so the black ants wouldn’t start climbing up my pants. When the opportunity presented itself I managed to get close enough to the colony entrance to take a few pictures. That is when I noticed the seriousness of the situation. 

There were harvester ant heads circling one of the openings. The bodies were in the shadows within and were harder to see. But the heads, with their imposing mandibles front and center, were packed as close together as possible - kind of like musk oxen of the far north protecting their young in a ring. Any black Conomyrma would have had quite a challenge getting inside that entrance. 

Then as the sun dipped lower in the west, the ring of heads began to break. The warriors became porters. Pebbles the size of the ants themselves were picked up in their heavily sclerotized mandibles and placed in front of the opening. The ants were closing up the mound for the night and I was left wondering how this would all play out. How, in fact, had this habit even evolved. 

The immediate scene suggested that the closure was an act of defense. But the scientific literature includes several examples of harvester ants closing up for the night when there is no apparent threat nearby. I know this is the case with the ants in my own yard. Mounds can be closed up in the middle of the day if it is too hot or too cold. And sometimes they are active in the middle of the night, while at other times they are closed. I decided to go looking for other nocturnal insects and leave the ants to their nests.

The sun was low in the horizon and because there had been a short rainstorm earlier in the day, the desert air was pungent with the aromatic scents of manzanitas and live oaks. The western sky was orange tinged with scarlet, reminding me of how lucky I was to be looking for small creatures in such a beautiful place. 

A young mantis - one of our native brown species (in the genus Litaneutria) - was mincing its way between bunchgrasses looking for whatever might be suddenly moving at this cooler time of the day. So much comes alive in the desert at night. Insects, scorpions, and a multitude of other creatures bury themselves in the loose terra cotta sands during the day when the ground surface temperature is often in excess of 120 degrees fahrenheit. Then, when the sun sets and stars begin to shine through the dimming cyan sky, they crawl out of their hiding places and become active. Predatory insects like mantises need to get a head-start and are likely to emerge first. It could be a good night for this one, with many species ready to emerge from a much longer sleep because of the rain. 

A large longhorn beetle (Prionus californicus) showed up on the sheet I placed near the truck below an ultraviolet light. It was two inches long with a thick dark brown body and strong antennae. I can only wonder at the scents it might be picking up. After admiring it, I encouraged it to fly back into the deepening shadows of the night.

Twilight was over and the milky way was fully visible as a band of luminescence across the sky. I ambled over to the harvester ant mound and found that it was now deserted. Both the black ants and the red harvester ants had gone to bed. Moreover, the tunnel openings had been completely sealed. My thoughts turn to the mound I buried all those months ago and how I had under-estimated the earth-moving abilities of this insect. I learned that a developed mound has enough tunnel space to sequester very large amounts of soil if needed. If the entrance tunnels get covered, the ants inside the mound can move the soil into one (or several) of their excavated chambers until they have made another opening. Then, if needed, they can move the soil out of the mound once the entrance is cleared.

This is an impressive ability all by itself. But it is also impressive to me how these ants get by with the change in atmosphere inside the closed system of tunnels. Scientists have shown that oxygen levels go down and carbon dioxide goes up. In the case of the ants in my yard (with several inches of sandy soil dumped over their mound) they were completely covered for at least two days before I saw them emerge from a new entrance. How did they manage to survive in this harsh environment for so long?

This is a question that has not been adequately worked out for harvester ants (or for many other ants for that matter). An extreme example of a low oxygen environment occurs in the mangrove swamps of Australia where a large ant (Camponotus anderseni) makes its tunnels. Twice each day, the tunnels get submerged with the high tides and the larger ants plug up the entrances to the tunnels with their heads (Nielsen et al., 2006). This happens day-in and day-out all year long. 

Many other kinds of insects also have to deal with low oxygen (hypoxia) or no oxygen (anoxia) conditions. Some tiger beetle larvae living in riparian areas get inundated periodically during flood season. Insects living in dung heaps, in carrion, in decaying wood, or even as parasites within a digestive tract of other animals all have to deal with extensive periods of oxygen deprivation (Hoback and Stanley, 2001). These adaptations seem to have evolved several different times among insects. And it probably occurs in a lot of situations that we are not aware of. Harvester ants are very likely one of these groups. 

Such an explanation would be extremely improbable for a mammal or other warm-blooded animal. Our energy demands are just too high. But insects are not warm-blooded and perhaps they can use a process similar to fermentation to get them through longer periods when they are sealed off from the outside world. One interesting by-product of the fermentation process is alcohol - which would be somewhat toxic to certain dangerous organisms that might flourish in a damp and oxygen-deprived cave. Do harvester ants occasionally seal themselves off in order to fumigate their nests from molds? Who knows? There is an interesting story here that needs to be worked out. 

We have been studying harvester ants for a few generations now. We have learned quite a bit about its troglodytic ways. It is clear the ants do very well in desert soils. They specialize in gathering seeds and a few small arthropod corpses now and then. The main harvester ant in our garden is the Western harvester ant. We have six or seven harvester ant species in the state of Utah. Most of them are only known from a couple of counties in the southern part of the state. But the Western harvester ant occurs in every county and from elevations between 3,500 and 9,000 feet (Allred, 1982). 

Earlier in the week I decided to go out and look at the ants in the yard. It was early afternoon and hot. My thermometer read 96 degrees in the shade. I shouldn’t have been worried about the ants in this heat. But their pebbly mounds are taking the full brunt of the sun and I know that some of the ants will be out foraging or guarding the nest in uncomfortable conditions. 

I sit on the dirt path next to one of the mounds. Normally this is not a good idea because it is covered by ants - ants that soon begin climbing onto my legs. In this heat, however, I don’t need to worry. Almost all the ants are underground. The few that are out are behaving frenetically. They seem to be running in random directions and incredibly fast, as if they were frantically delusional. 

A few of their sister ants are running in and out of the mound entrance, seemingly uncertain as to what they should do. One of the outside ants hurries inside. As soon as she is in the shade of the mound one of the other ants runs outside as if to take her place. Scientists have not been able to confirm that ants are intentionally coordinated this way. Their actions generally seem completely random. And yet out of this apparent confusion there is an order that emerges as if by magic. I would not be surprised if there is some sort of tag-team communication that takes place between these few hardy ants that are out on patrol on such a hot day. Why would any of them be outside under such conditions if these insects weren’t adapted to defend their mound? There seems to be some way of taking turns.

Western harvester ants make their mounds in such a way that captures the morning sun (Romney, 2002). The southeastern side is longer and slopes more slowly than the other sides - at least in the majority of mounds. In the morning it is noticeably warmer than the other sides even though, by midday, all sides are about the same temperature. Inside the mounds, adult ants stay busy moving the grub-shaped larvae into different chambers depending on temperature. By evening, almost all of the immature ants have been moved to the brood chambers on the southeast side - anticipating the first warming rays of the morning sun. 

What occupies the ants inside the mound on such a hot day? Were they moving the brood to lower chambers where it was cooler? When I buried the colony several months ago, did I limit their underground options? How many of the young ants died because there was no place to move them?

I began thinking of a motivational aphorism I learned in Sunday School many years ago. It was written by George A. Smith about a conversation he had with his cousin Joseph Smith, Jr. (the 19th Century founder of the Church of Jesus Christ of Latter-day Saints). It was about not giving up. Joseph knew quite a bit of discouragement in his short life and he told George to, “never get discouraged, whatever difficulties might surround [you]. If I were sunk into the lowest pit of Nova Scotia [Joseph said] and all the Rocky Mountains piled on top of me, I ought not to be discouraged, but hang on, exercise faith, and keep up good courage, and I should come out on the top of the heap.”

It’s funny how memories from long ago can present themselves at unexpected times. But having a giant wheelbarrow worth of dirt dumped over a human-occupied system of tunnels would seem fatal for sure. There is little chance that humans could dig themselves out of such a predicament. But then again, maybe some of us could. Perhaps the truly remarkable nature of the ant-hill exhumation is that it could be repeated any number of times by harvester ants all over the American Southwest.

Now, in July, with temperatures in the upper 90’s every afternoon, I am watching a different kind of perseverance. The ants know how to hunker down in the heat. They bury themselves on purpose. Perhaps their metabolism has to adjust. Maybe they have to sequester themselves from predators and other invading ants for a while. But they are survivors. Sometimes, it seems, it is wise to just close the doors and wait for better times.  

References

Allred, Dorald M. (1982). Ants of Utah. The Great Basin Naturalist 42(4), 415-511. 

Hoback, W. W., & Stanley, D. W. (2001). Insects in hypoxia. Journal of insect physiology, 47(6), 533-542.

MacMahon, J. A., Mull, J. F., & Crist, T. O. (2000). Harvester ants (Pogonomyrmex spp.): their community and ecosystem influences. Annual Review of Ecology and Systematics, 31(1), 265-291.

Nielsen, M. G., Christian, K., Henriksen, P. G., & Birkmose, D. (2006). Respiration by mangrove ants Camponotus anderseni during nest submersion associated with tidal inundation in Northern Australia. Physiological Entomology, 31(2), 120-126.

Romey, W. L. (2002). Does the harvester ant, Pogonomyrmex occidentalis, shape its mound to catch the morning sun?. The Southwestern Naturalist, 47(2), 175-181.

Smith, George A. (1997) The Teachings of Joseph Smith, ed. Larry E. Dahl and Donald Q. Cannon (Salt Lake City: Bookcraft), 195.

 Early Utah Dinosaur Footprints

There are dinosaur footprints scattered all over Southern Utah. Just north of where I live they are embossed like molds on boulders that have fallen from a higher cliff. Some footprints are underground and have been discovered by digging. Others are in plain sight along ridges or near washes. Many beautiful examples can now only be seen by diving into the waters of Lake Powel. 

Utah has so many of these tracks because we have the right kinds of rocks. The layers of Earth that were laid down during the Mesozoic Era (when the dinosaurs lived) are exposed over hundreds of miles in our state. It also helps that, on the Colorado Plateau where many of the tracks have been found, these layers are often blanketed in predictable ways so that the educated purveyor of geologic formations can guess where to look most profitably. These petrified footprints haven’t been covered up by millions of years of falling leaves and accumulating topsoil. Many are fully exposed under the vast Western sky. This means that dinosaur tracks can be found by just about anyone going for a hike and keeping their eyes open.  

OK, It isn’t quite as easy as that - at least not typically. When dinosaur footprints are found it can be a big deal. The prints near Cedar City where I live are announced by a sign on the road where there is a dirt road and a place to park. And this is just for a couple of prints. My neighbors will plan a weekend to have a picnic by the dinosaur footprints. People all over the state care about these relics of the past. The ancient Mesozoic sands aren’t the only things that have been impressed. 

A natural question to ask is: who discovered the first track, or set of tracks, in the state. And the answer would have to be: it is unlikely that we will ever know. During the 19th Century, when tracks were found, they weren’t recognized for what they were. In fact, the first footprint discoveries that we know of were made when the very idea of extinction was poorly understood. Upon seeing dinosaur prints, people thought they were made by extinct birds - which, of course, was a pretty good guess. Some were claimed to have been made by the raven in the biblical account of Noah and the ark - an unexpectedly large raven to be sure. One can only imagine the surprise in Sunday School when this raven was suddenly understood to be the size of an ostrich.

A good place to start our story of dinosaur tracks in Utah is just over the border in Arizona in the year 1933. A young man named Roland T. Bird (RT for short) had just discovered that he might be able to turn his passion for natural history and fossil hunting into a career. This was a game-changing discovery for him. He had become a “lonesome cowboy,” as he described himself, and a bit of a drifter. Set back by a bout with rheumatic fever and having dropped out of junior high school, he never imagined that he would amount to anything.

But RT was interested in the world, and in the vast expanses of the Western US. He also had an old Harley motorcycle with an awkward fold-away trailer attached to the side. Thus provisioned, he was able to spend days (even weeks) in the field. 

His interest in fossil footprints started one day in a lumber yard in Flagstaff. He had recently found the ancient bones of an amphibian-like creature (with the awkward generic name of Stanocephalosaurus) and was nailing together a shipping crate so he could mail the fossils east to the paleontologist Barnum Brown at the American Museum of Natural History, in New York City. 

While building his shipping box, the employees of the lumber yard would stop to see the strange fossil he had attached to his motorcycle. “You know who ought to see this?” one of the men announced. “Rad Linderman, across the street. Why don’t one of us call Rad?”  

It turned out that Mr. Linderman was a collector of relics. He knew of old ruins and Indian artifacts. He was also interested in fossils and struck up a conversation with RT immediately. “There’s a place in the Painted Desert,” he said, “the other side of Cameron…not far from Tuba City…[where] there are dinosaur tracks.”

That little bit of information, offered as just casual conversational grist, piqued RT’s imagination enough to change his travel plans. He shipped his box to New York and drove north to Cameron, Arizona on the Little Colorado River. 

Today, Cameron is the main turn-off for visiting the South Rim of the Grand Canyon. Otherwise, the town is small and most of its economy is based on travelers driving along Highway 89 heading either south to Flagstaff, north to Lake Powel, or west to the park. 

Fifteen miles to the north along the road heading to Tuba City, however, there is a pull-off with a parking area and a home-made dinosaur sign indicating the location of the tracks. This is supposedly the same place RT found the tracks in 1933. It is significant to our story because this young man would do more than anyone - within the state of Utah or elsewhere - to make ichnology (the science of fossil tracks, burrows, etc.) visible to the public. Utah, in particular, has a deep fascination with dinosaur tracks. There are thousands of them throughout the state and they occupy entire rooms of some museums - and extensive outdoor displays in others. 

In the 1930’s however, things were very different. Only a few paleontologists paid any attention to these fossilized prints. In fact, even within the paleontological community, scientists studying tracks were not as well received nor given important university positions as is sometimes the case today. In 1948, Frank Peabody from UCLA published a paper on several Utah track sites. But this was a technical paper published in a scientific journal of limited academic distribution. It did not capture much of the public mind. 

Roland Bird’s fascination with the prints, however, ended up making waves. Not so much from the Arizona prints themselves, but because they would lead him to other print sights, including the famous tracks that he discovered along the Paluxy River in Texas. This particular find would capture the national stage and become a major battle ground between evolutionary biologists and creation scientists. 

This was still in the future, though. Before this history would play out, Bird would visit Utah with his employer Barnum Brown, in search of one very impressive dinosaur footprint that was found in the Chesterfield coal mine, located in a forgotten little place called Sego - now a ghost town north of Moab. 

It was 1937, and news of the print had made its way into several newspapers around the country. In Provo, Utah, The Daily Herald ran a short column of the find in the Sunday paper (for June 13). It read in part: “The ability of Barnum Brown, curator of fossil reptiles at the American Museum of Natural History, would make a bloodhound hang his head in shame.” As for the footprint itself: “It is one of the largest tracks ever discovered.” 

There are a few coal mine footprint casts in Utah museums. Sometimes they are tucked away and unlabelled in odd corners or beneath displays. Many more are in backrooms in the main collection area. The Prehistoric Museum in Price has a particularly nice display of several of these prints - some of which have been found in local mines. 

The early Chesterfield Mine print probably needs a little bit of context. Measuring in at 44 inches long and 32 inches wide, it is indeed a very large print. What made the find truly remarkable, however, is that it was not made by a sauropod. It had a “heel” and three large digits in front. Sauropod prints look more like those of a giant elephant. They are more round or square shaped. They are made by the likes of Brontosaurus and Apatosaurus. The biggest sauropod known is Argentinosaurus. 

Actual dimensions for these giant animals are hard to calculate with certainty. Complete skeletons are rare and estimates are often based on computer models and extrapolations - often from a single recovered bone. A recent estimate of the weight of Argentinosaurus is 65 tonnes. Claims have been made that some of these giants left footprints that were longer than five feet. 

The Chesterfield coal mine print discovered in 1937 is not nearly this size. But for a non-sauropod it was (and still is) one of the largest ever recovered. But what makes it so interesting is the way it was preserved.

Coal is the fossilized and compressed remains of ancient plants. But it doesn’t form automatically just because plants happen to be present. If an ancient tree died and was buried in a relatively arid environment, it might petrify in different ways - perhaps like the beautifully colored log forms at Petrified Forest National Park (in northeastern Arizona). 

To form a residuum as big as a coal bed required an extensive ancient swamp where plants, like mosses, ferns, etc. would die on top of each other and only partially decompose. This cycle of growth and decay would also need to extend over thousands and millions of years while the plants were continually being covered and pressed by other plants and soil accumulating above.  

We now know, thanks to these unusual coal mine footprints, that large ancient animals contributed their own weight to the compressional process of coal formation. Paleontologists recognize at least three different ways that this is likely to have happened. 

First of all, there are the footprints of dinosaurs that walked over moist ground when the swamp was new. Perhaps they also waded in shallow water. These prints are occasionally found in the floor deposits of western coal mines. The area around Price, Utah was a particularly rich source of these rarely seen prints. But whatever species made them, it seems likely that it (or they) made a habit of walking in the decaying swamp muck that had enough of a sandy base to support their weight. We assume this because the floor fossils occur at the interface between the coal deposits and the sandstone beneath. 

A few fossils have also been found from mine cave-ins. This can happen when a goaf (or a hollowed out area of a mine) has been made and abandoned and the supporting timbers have rotted out or been removed. These upper fossils also occur at the coal and sand interface, only these fossils were made after the swampy lands were being covered with sand from above. This seems to have happened at times by ancient windstorms, or more typically by heavy floods bringing eroded sand over the erstwhile swamp. These prints were likely made during a period of ecological change, when the swamps were being replaced. 

The majority of the coal mine fossils were found by miners extending down from the roof of tunnels in the normal course of digging out the coal. My guess is that the millions of years that experienced swampy conditions in the Western US evolved unique dinosaurs with a particular ability to walk in these kinds of habitats. Perhaps there still existed a combination of sand and swamp mud where the prints were preserved. But it is likely that at least some dinosaurs were able to navigate the swamp muck just fine; and in fact, were adapted to do so. 

Several large bird species do this regularly. They also have three forward digits on their feet with one behind like many dinosaurs. The long toes extend over wet soil and submerged branches with ease, only to be removed after bringing the toes together into a narrow extension of the leg. Herons, egrets and storks are classic examples of this pattern. 

Roland Bird was so fascinated by these coal mine fossils that he occasionally got carried away with the finds. One year found RT, Barnum Brown, and their crew chiseling out a set of prints from the States Mine in western Colorado. At one point, RT took a break from the work and began exploring other tunnels of the extensive mine. In the process he came upon a few plant fossils. 

When he showed a couple of the fossils to one of the workers he was surprised to hear that there had once been a goaf filled with much more interesting plant fossils than the ones in the States Mine. The worker told RT, “There was a time I could have showed you some plants that’d make those look like two cents.”

That place turned out to contain all kinds of fossils of ferns and palm leaves, among other things. In fact the place happened to be nearby in the old Red Mountain Mine. Sadly, for RT, there seemed to be no chance of visiting this magical place. The mine had been closed down many years before because it was no longer safe. But RT was persistent, and on several occasions he let the foreman know of his lingering interests. Was there not some way that he could see the room anyway - of getting a few miners together to show him the fossils? But the supervisor repeatedly ignored his comments or indicated that the mine was just too dangerous to visit. In some of the rooms, even the support beams had been compressed by the weight of the mine ceiling or had been completely crushed from the weight of the overburden. 

But in the end RT got his way - partly because he got the support of Barnum Brown. It was a difficult descent. There were several piles of collapsed rubble that they had to work around. And they were not allowed to touch any of the support beams or even the walls or ceiling of the mine. In fact they had to walk in complete silence.

When underground chambers collapse, they often provide subtle hints just moments before doing so. Maybe a pebble will break free and drop to the ground. Or maybe there will be a bit of dust created from no place in particular. Often these hints are missed because of conversation or just the ordinary sound of footsteps. The foreman of the mine that was taking RT and his team to the plant fossils would not allow the group to make any sound at all. He explained that if he heard even a suggestion of moving rocks that he would give the warning and the group would have to move quickly out of harm's way. 

Biologists are sometimes accused of letting their eccentric interests override sound judgment. Or sometimes they become so focused on the project at hand that they forget to pay attention to immediate circumstances. Many years ago, an acquaintance of mine died this way. He had stopped for a drink of water while out looking for an unusual insect in a remote wilderness area. With his insect net, his killing jar, and other equipment on the ground, the very insect he was hoping to find flew right in front of him, or so we think.

He must have quickly grabbed his things and gone after the insect. But in his haste, he made the mistake of placing his glass kill jar in the back pocket of his pants. We don’t know if he actually caught the specimen. He died too quickly to find out. What we do know is that his kill jar was made of glass and was primed with potassium cyanide. When he sat down, the weight of his body broke the glass that cut through his pants and into the skin. The cyanide would have killed him within minutes. 

Roland Bird was luckier. He wasn’t playing around with deadly chemicals. But the possibility of death was certainly real. The history of paleontology in the American West is full of these kinds of circumstances - usually encountered in the name of science. Sometimes risks are made by tempting the weather, at other times by climbing on unsafe rock formations, sometimes by digging fossils out of abandoned mines. 

As the party made their way through the labyrinth of the Red Mountain Mine and finally came upon the room with so many fossilized plants, the mine foreman proceeded to reinforce the ceiling with timbers that had been procured for that purpose. Then RT and his colleagues began to chip away at the rocks. 

This continued for hours until suddenly and without warning, the foreman shouted for the group to run. As they did so a section of the wall and ceiling near an adjacent tunnel collapsed. Some of the equipment was crushed. RT was knocked to the ground and injured his shoulder. Dust covered everything. Minutes later, after the rocks and dust had settled, the group pulled themselves together to evaluate the damage. Fortunately no-one was missing, although a few were hurt. Little was said as the men gathered what they could and walked out of the mine. 

Phased and discouraged, but with a handful of fascinating fossils to show for his efforts, RT continued work in the mines for a while longer before heading back to New York and his work at the museum. But he had become fascinated with footprints. In 1939 he was able to work his way to Texas where he would make the discovery of a lifetime - the discovery that would bring him recognition (for good and ill) beyond the paleontology community. 

References

Barnes, F. A. 1997. Canyon Country Dinosaur Tracks and Trackers. Canyon Country Publications. 

Bird, Roland T. 1985. Bones for Barnum Brown, Adventures of a Dinosaur Hunter. Texas Christian University Press.

The Daily Herald. Expert ready to seek trail of dinosaurs. Sunday, June 13, 1937. 

Parker, L. R., & Balsley, J. K. (1989). Coal mines as localities for studying dinosaur trace fossils. Dinosaur Tracks and Traces. Cambridge University Press, Cambridge, UK, 353-360. 

Parker, L. R., & Rowley, R. L. (1989). Dinosaur footprints from a coal mine in east-central Utah. In Dinosaur tracks and traces. Cambridge University Press, Cambridge, UK,

Paul, G. (2019). Determining the largest known land animal: A critical comparison of differing methods for restoring the volume and mass of extinct animals. Annals of Carnegie Museum, 85(4), 335-358.

Peabody, Frank E. 1948. Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah: University of California Publications, Dept. Geol. Sci. Bull., vol. 27, 295-468.

Peterson, William (1924). Dinosaur tracks in the roofs of coal mines. Natural History, 24, 388-397.

Stokes, Lee. 1982. Essentials in earth history. Prentice-Hall, Englewood Cliffs, N.J.