Fossiling in Wyoming

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Niels Laurids Viby (Denmark)

I am a Danish architect and, occasionally, I get the chance to travel to different countries on study tours to look at buildings and get inspiration for the work we do back in Denmark and England (we have an office in London). In September 2006, I went to America, among other reasons, to visit a new herbarium building in Saint Louis, Missouri. However, as I have been infected by that incurable disease which forces you to stop every time you pass any pile of rocks to look for fossils, I did not spend the available weekend in a big city prone to violence. Instead, I got on a plane and flew via Denver to Casper, Wyoming.

There was a good reason for going to that city: two years ago, I spent a week in Solnhofen, Germany during my summer holiday ‘chopping rocks’. Down there, I meet another fossil enthusiast, an American who worked at the local geological museum in Casper. Therefore, it made sense for me to meet up with him and go fossil collecting in the nearby badlands.

Fossil collecting in the USA

It is important to remember that America is NOT Europe when it comes to fossil collecting. Even worse, every State has unique laws that you have to follow or else you are looking for trouble. In Wyoming, you have two possible situations where you could be on:

  • State Land and, if you are not a member of an official museum at work, don’t even think about picking up a fossil. If confronted by the law, it will take time, be expensive and be thoroughly unpleasant; or
  • Private Land, where every fossil belongs to the owner. And all the Ranchers drive around on small, beach buggy-like things equipped with a rifle in front – to shoot coyotes of course. However, given American laws, amateur fossil collectors may have a similar legal status to vermin. And remember, the word is “Rancher” with a capital “R” and not “farmer” with a small “f” – real men push cows around. They do NOT mess with vegetables down in the dirt. So be warned!

Therefore, to go anywhere to collect fossils, you need an American connection. And my friend had arranged that we – after some barter involving assorted alcoholic fluids – could go and look for fossils on Private Land.


But first a few words on Wyoming. This is one of the younger States and is far from being over populated. The two ‘big’ cities – Cheyenne and Casper – have a population of some 50,000 each; the city of Laramie contains some 30,000 people; and other human habitats range from the small to the very small. When you go into a town, a sign will tell you how small.

Fig. 1. Lost Spring – population one – called a ‘city

However, from the viewpoint of a fossil collector, Wyoming is a cornucopia of possibilities with an area that seems, at first sight, to be manageable. The problem in Wyoming is that you can cross the State with ease going from close to the northwest corner (that is the Yellowstone National Park) past Casper to the southeast corner on Interstate 25 and, in principle, you could carry on through South America all the way down to Patagonia.

However, when you get off this road, things are very different. You can (close to the smaller towns) follow what we, in Europe, would consider a small but decently-paved road for a short time. Then, you can carry on onto a strip of decent gravel roads, then bad gravel roads to the Rancher you want to visit – and, from there on, the going is on wheel tracks. In the end, you will often sit in the 4WD contemplating if you are on a real track or whether the ‘track’ is simply where the cows have a habit of walking.

As for the geology, Wyoming includes the foothills of the Rockies. Therefore, you can find virtually every single geological period from the Cambrian to the Palaeogene (up to and including the Holocene), with only a few exceptions. However, as I only had a weekend, I had to concentrate on formations that might contain the kind of fossils you see in museums and dream about finding yourself. So, after long debates over the internet, my friend and I focused on two formations and left out, for example, the famous Green River Formation as that would have involved far too many hours of driving simply to get to and from one the accessible quarries.

The first day was spent on a ranch with Upper Cretaceous deposits: the Lance Formation of Maastrichtian age. This ranch was an interesting place. A couple of years ago, a partial T-rex was found not far from the house. That fossil ended up at a museum after the outlay of huge amounts of US dollars (much of which seemed to end up in the pockets of lawyers). The problem in America is that dinosaur bones are worth serious amounts of money. Therefore, if you find something big, the Rancher will want it for himself. Often, he will have an arrangement with a fossil dealer who collects the cash from a future buyer.

Anyway, we spent the morning walking around quite close to the ranch looking for fossils and the odd rattler. Fortunately the rattle snakes up in Wyoming are rather small and have a poison more or less similar to a European viper – that is, not very much and not very strong. Generally, things that move close to your foot are only rabbits.

There are not that many rocks out in the prairie. However, the good thing is that, when you find some, they generally contain (or are) bits of fossilized dinosaur bones. For example, the Rancher had recently done some minor fencing – several kilometres long that is. In the process, he stumbled on a large rock in the half-ton range that contained a number of ribs from a big dinosaur of an unknown species (as no diagnostic parts were present). A likely candidate is Triceratops.

Fig. 2. Dino ribs.

In the same vicinity, I found several fresh-water mussels, snails and a few Upper Cretaceous plant fossils. I also found small bits and pieces of bone from that dinosaur. Apart from that, I brought back some pieces of dinosaur bone (including a somewhat worn end of a good-sized limb bone and parts of the frill from Triceratops) that the Rancher decided I could take with me back to Denmark as a part of the barter. However, his wife though that, as I had come that far, I should have a decent piece of a rib they had found the other day as well – a very nice woman.

In the afternoon, we went to an outcrop way out in the wilderness that my friend had found some years ago, after he had spent weeks during a summer vacation walking all over the Ranch. Before going to the USA, I had the idea that an “outcrop” was a small section of rocks sticking up from the ground. No way – an outcrop out there is a hole in the ground where wind and water have eroded the surface away.

Fig. 3. An outcrop.

At one spot in this ‘hole in the ground’ was a sandy slope about 10m x 4m, with an anthill at the top. (Anthills out there are not constructed of conifer needles as they are in Denmark: the ants have to use the material at hand, that is, small 2mm to 4mm rocks or whatever they can find, including micro fossils.)

This slope was a “micro site”, that is, a place where the rain was eroding through what had been a hollow in a palaeo-streambed where all kinds of small object had ended up. (When you travel by air, micro sites are very convenient. You can bring back large quantities of interesting fossils without exceeding the weight you are allowed to carry.)

So, after spending several hours crawling up the slope checking everything visible and turning over all the small stones in the anthill, I had a nice collection of small fossils including:

  • Some teeth from a hadrosaur.
  • Some teeth from a Triceratops.
  • Three teeth from probably two different species of small theropod.
  • Some small dinosaur bones, including a rather big, partial phalanx from a theropod. (Given the location, it could be from a young Nanotyranosaurus as teeth from this species have been found at this site.)
  • Teeth and scutes from two different species of crocodiles.
  • Plates from the shell of at least two different species of turtle.
  • Fish material including garfish scales, vertebras and teeth.
  • Small bones that most likely are from mammals or birds.

And from the anthill:

  • A very small 1.5mm dermal tooth from a shark or ray.
  • A 2.5mm-crunching tooth from a multituberculate.

The last item was extremely nice. I had not expected to find anything from a Cretaceous mammal, and certainly not anything that could be identified with a specific genus, in this case, Meiscoessus. My usual problem is trying to put a name on the fossils when sitting in a hamlet back in Jutland, Denmark. In far too many cases, it is impossible even to assign the correct genus – and you might as well forget a species name right away. The literature needed is somewhere in a library in America.

So far so good. The next day was spent at another ranch with Oligocene outcrops – the famous White River Formation. The lower part of this formation is a kind of hard clay/chalk in which you generally find fossils such as the Stylumus turtle, Oreodonts, rabbits, Hyanodon and so on. At the end of the day, we did indeed find this kind of deposit and I did find some fossils including partial jaws with teeth from two different species of Oreodonts. My friend found a rather complete skull of a Hyanodon – a very good fossil and one that was missing from his collection, even after living and collecting in Wyoming for years.

A tell-tale tooth.

But the first six hours on the site was spent on another project. The upper part of the White River Formation consists mainly of very hard sandstone. We started in the morning looking into a gully full of sandstone plates in the rage of 2m by 2m by 0.5m – similar to the kind of concrete slabs used for pavement and certainly as hard. These are not known to contain much by way of fossils and those that are found are extremely brittle. To prepare them can be compared to trying to get a cookie unharmed out of a concrete flagstone.

But when walking around, I suddenly spotted a small curved crevice with bone material in the bottom. At the time, we thought this was probably the carapace of a Stylumus turtle. So we started chipping away with small chisels and found some good bone that did not look like turtle at all, but rather like a flat bone from a mammal such as a shoulder blade or a bone from a skull. After more work, we got down to an unmistakable tooth. So it was a jaw.

It’s a jaw.

After those six hours of hard work, we had a loose rock of some 30kg covered up in a plaster jacket.

Cover at last.
Block ready to go.

The whole package went back to the home of my friend, where his basement is equipped as a preparation lab. He spent a long time that autumn working with power tools until he had liberated an extremely nice fossil: a 38cm left jaw from a Subhyracodon sp, an early example from the line of true rhinos (not to be confused with Hyracodon, the ‘Running Rhino’).

The final jaw.

And, just before Christmas, the postman brought it to my front door in Denmark. So, from now on, it is a very nice part of my collection and wonderful reminder of fossiling in Wyoming.

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