Dinosaur Gastroliths - The Shining

 

The Secret of the Shining

By John Bradford Branney

 

Figure 1 – Prehistoric flintknapping station lying on the 150-million-year-old Morrison Formation in Central Wyoming. The author took this photograph on 8/11/2020.

You are going to find that my article’s topic is a little bit off the trail of typical prehistoric artifact musings but sometimes new trails are fun to follow. My story is about some super old pre-Clovis artifacts (or technically fossils) that I surface found in 2020 on a private ranch in central Wyoming.

In 2020, I artifact hunted fifty-plus days. I tend to hunt my proven sites too often. My hunting pressure on those sites outpaces Mother Nature’s ability to bring more artifacts to the surface through erosion. To relieve the pressure on my proven sites, I decided to spend more time on two large private ranches in central Wyoming where I had permission to hunt. These are “Wyoming-sized” ranches, so there was a lot of real estate to investigate. The first ranch I visited lies in a geologically active area. The ranch is a gorgeous hunk of land with colorful hogback ridges folded and twisted by geologic faults. Sage and shortgrass valleys separate the ridges from each other. For a geologist like me, it is a dream come true. I can walk through geologic time while finding prehistoric artifacts. Life cannot get any better than that!   

Figure 2 – Polished stone, surface found on

5/18/2020 at newly discovered prehistoric campsite.

On my first day of exploring the virgin territory along the ridges and swales of the ranch, I found a pocketful of chipping debris, crude flake tools, and a few broken projectile point pieces. It took a couple more uneventful trips like that before I discovered my first prehistoric campsite lying on clay soil along the slope of a shaly hogback ridge. I browsed the edges of the chipping debris and determined it was a relatively small campsite. So much for hoping for the next Lindenmeier site! I surface recovered a pocketful of chipping debris, scrapers, crude flake knives, and two nearly complete projectile points from the Late Archaic / Late Prehistoric timeframe. The most intriguing artifact I found was a highly polished stone made from chert that had no business being on that shaly slope or in that prehistoric campsite (figure 2). The stone was too smooth for river polish. Besides, there were no rivers, past or present, anywhere close to that ridge. My first thought was that a prehistoric inhabitant either polished the stone to a high sheen or he or she found it elsewhere and carried it back to the campsite. I believe that prehistoric people were a lot like us and that there had to be a rockhound or two in the crowd.  

When I arrived back home in Colorado and had a chance to study the chipping debris, I noticed that several flakes had highly polished surfaces on the cortex. I started asking myself questions about these odd, polished stones. The mystery was on, and I could not wait to return to that ridge in the next week or so.  

Figure 3 – It was not all polished stones. Perfect 3.3-inch-long Pelican Lake 

knife form surface found on 6/2/2020.  

I studied and rubbed that polished stone for several days. It had become my lucky charm around the house. I could not figure out why the prehistoric human had spent time polishing it to such an extreme finish. Polishing it to a high gloss served no functional purpose and it was too small to use as a mano or a burnishing stone. Grasping at straws, I concluded that just like I had adopted it as a lucky charm, so did some ancient camper on that prehistoric site.  

What about the chipping debris made from jasper and petrified wood and chert with remnants of the same highly polished surfaces? Where did the highly polished stones come from? The ridge was composed of shale, claystone, and mudstone with some interbedded limestone. I never once spotted an ancient river or glacial till deposit along any of the ridges or swales. Besides, I had never seen a river or glacier put a sparkle on a rock like that. It looked like it just came out of a rock tumbler at the local rock shop. Active rivers polish rocks, but they also bang them up. Eventually, I would learn the secret of the shining, but for now, I continue my story…  

Figure 4 – Perfect 1.0-inch-long Mummy Cave arrow point

found amongst the shaly rock on 5/6/2020.

The next time I visited that prehistoric campsite, I hiked up to the top of the ridge. The views from the ridgetop were fabulous. It was like a piece of heaven. The landscapes in every direction took my breath away! To top it off, I discovered a prehistoric flintknapping station with chipping debris and lightly worked artifacts littering the ground (figure 1). I not only found broken flakes but also several glossy mystery stones. The prehistoric flintknappers had sat on that ridge, taking in the views while breaking open the polished stones like eggs and making stone tools out of the pieces. I found something else that had my heart pitter-pattering; fragments and slivers of fossilized bone weathering out of the bedrock almost everywhere. Something happened along that ridgetop a long time before any prehistoric humans ever showed up and I needed to know what! 

Figure 5 – Polished stone found at flintknapping

station on 8/11/2020.

When I got home, I pulled up a map that showed me the surface exposures of geological formations along the ridges and swales I was investigating. I tied the geological map to the topographical map that I used to explore the area. I correlated the geological formations to each ridge and swale I had walked. From south to north, it went from Cretaceous-aged Niobrara, Mowry, Thermopolis, and Cloverly formations to the older Jurassic-aged Morrison Formation.

The ridgetop, flintknapping station and fossilized bone slivers and fragments lay on the mudstone and claystone of the pastel-colored Morrison Formation, the one-hundred-fifty-million-year-old Jurassic Park of dinosaur fossils. I had another clue in solving the mystery of the lustrous stones!

Figure 6 – Fossilized bone fragments eroding from the 150-million-year-old

Morrison Formation of Jurassic age near the flintknapping station. 

The author took the photo on 8/11/2020. 

Two paleontologists by the names of Edward Drinker Cope and Othniel Charles Marsh brought notoriety to the American West during the Great Dinosaur Rush in the late 1800s. The ‘Bone Wars’, as scientists and book writers called them, highlighted the bitter and hostile rivalry between Cope and Marsh in their ‘anything goes’ competition for finding dinosaur bones and naming new dinosaur species. The two egotistical paleontologists resorted to such chicanery as bribery, slander, theft, and even the destruction of dinosaur bones to win the contest. The Bone Wars were not one of the most inspirational stories in paleontological history. It did make the Morrison Formation famous or perhaps infamous. It placed the dinosaur bone quarries at Como Bluff in Wyoming, Dinosaur National Monument in Colorado and Utah, and Morrison, Colorado on the map.

As I sat in my chair thinking about the shiny stones, a light bulb lit up over my head. It was the automatic timer on my lamp. Sorry, I thought we needed a bit of levity! Okay, back to the story…

The evidence for the origin of the glossy pebbles was falling into place; 1). I found polished stones amongst the tawny clays of the Morrison Formation. 2). Prehistoric humans used the mystery stones as a raw material source for making stone tools. 3). The shiny cobbles were completely out of geologic and archaeologic context, 4). Fossilized bone fragments were eroding to the surface of the one-hundred-fifty-million-year-old Morrison Formation.

I had the answer. I am sure some of you have already figured it out.

Figure 7 - https://commons.wikimedia.org/w/index.php?curid=79140803

The glossy stones were dinosaur gizzard stones or gastroliths or as some people call them, Morrison stones. Some of you might be asking yourself why dinosaurs had gizzard stones? We know the turkey at Thanksgiving had a gizzard, but that gobbler was a far stretch from being a brontosaurus, genetically speaking. Some living species of animals have gizzard stones in their gastrointestinal tract to grind food because they lack suitable grinding teeth. Herbivorous birds, earthworms, alligators, crocodiles, and some fish species have gizzards. They eat rocks to help grind the food entering their gastrointestinal tracts. In some modern species, the gizzard stones stay in the muscular gizzard for a long time and become polished from stomach juices and grinding against other rocks, while in other species the stones pass through the intestines and the animal replaces them with more stones.  

Figure 8 – Curious pronghorns near the ridgetop, wondering what the crazy human is looking for.

The author captured this image on 9/30/2020.

In 1906, George Reber Wieland reported finding polished quartz pebbles or gastroliths within the skeleton of a dinosaur. Since then, many scientists believe that Sauropod dinosaurs, those fun-loving, extinct herbivores with long necks, tiny heads, and four thick, pillar-like legs had gizzards (figure 9). Researchers believe that one genera of sauropod called the brontosaurus weighed anywhere between fifteen and twenty-five tons. I can imagine it took a lot of plant material to satisfy the appetite of that husky twenty-five-ton vegetarian. As an analogy, a moo-cow weighing twelve hundred pounds eats around twenty-seven pounds of hay (plant material) per day according to the University of Nebraska at Lincoln (2013). I converted the twelve-hundred-pound cow’s daily consumption of plant material to an equivalent consumption needed for a twenty-five-ton sauropod. The analysis showed that a brontosaurus had to eat around eleven hundred twenty-five pounds of plant material per day to keep up with the cow’s consumption. That dinosaur was eating the equivalent weight of an entire cow in forage every day! Since sauropods had disproportionately small heads and weak dentition, they probably had trouble processing and digesting a half of a ton of forage every day. Gizzards in the sauropods’ gastrointestinal tracts loaded with abrasive rocks ground and processed their nutritional needs. Remember my reference to rock tumblers? Well, sauropods had rock tumblers in their guts! Who knows, the gastroliths might have stayed in the dinosaur’s gizzard for the life of the beast. No wonder they are so shiny!

Figure 9 – Dinosaur gastroliths from the Morrison Formation.

The pale green gastrolith in the upper left is 3.7 inches long.

The author took this photograph.

My conclusions are not without precedent. During the archaeological investigation at the Hanson site in northwestern Wyoming, George Frison and Bruce Bradley (1980: 99-101), found that the Folsom people used dinosaur gastroliths from the nearby Morrison Formation to make tools for cutting, scraping, and engraving. Some debitage and tools had the original polished surfaces of the gastroliths just like I found.

Wrap up the mystery of the shiny stones and tie it up with a pretty bow. I cannot wait until the snow melts and I can return to the north country for more fun in the Jurassic sun!

 

References cited.

1980    Frison, George C. and Bruce A. Bradley, Folsom Tools and Technology at the Hanson Site, Wyoming. University of New Mexico Press. Albuquerque.

2013    University of Nebraska at Lincoln, Determining How Much Forage a Beef Cow Consumes Each Day: UNL website.

1906    Wieland, G. R., Dinosaurian gastroliths: Science, v. 23, p. 819-821.

 

About the Author.

 

John Bradford Branney is a Wyoming native, an author, a geologist, a prehistorian, and an associate editor of Prehistoric AMERICAN. He has written ten books and many magazine articles on Prehistoric America and life in general. Branney is currently writing the fifth and final book in the prehistoric adventure series the SHADOWS on the TRAIL Pentalogy. He lives on forty acres in the northern Colorado mountains with his wife Theresa, three German Shepherds, and a feral cat.