Research Part 1: Fossil Plants and Paleo-climates

Step 1: Research and Fossils.

So how do you make a diorama? First thing’s first, you have to know what story you want to tell. Here at the UWyo Geological Museum, we focus on Wyoming through time. In the first four displays I’m working on, we’re portraying Wyoming during the early Eocene (about 56-49 million years ago), late Eocene (37-34 mya), early Miocene (23-16 mya), and late Miocene (12-5 mya). Yes, I’m kind of skipping the Oligocene. [The Geological Society of America has a handy dandy timeline of the Cenozoic, which you can use to follow along].

hyracotherium

Dawww, it’s the dawn horse!

Next, Mark, the museum’s director, and Kelli, the museum’s manager, figure out which specimens from the collections would work best for each case. These specimens have to be in good condition and not so fragile they can’t be displayed, and they also have to be representative of the type of wildlife you would have found in the area during that specific time period. For example, in the early Eocene display we have a Hyracotherium, not one but two Hyrachyus, a Stylinodon, and an early primate.

Once we have specimens in mind, it’s time to figure out what the background environment should look like, which is where I come into play. I can’t just draw whatever scene I think looks cool or pretty: just like with the specimens, the background must be representative of the flora and climate of that location and time period. While we have a lot of tools for figuring out what the temperature and precipitation were like, and which plants were around, it doesn’t always give us a clear picture, so there’s still some element of creativity required. However, my creative license still has to be rooted in fact, and that requires research.

Since we’re a University museum, all the research materials I needed were at my fingertips. I visited the geosciences library, turned to Mark and Kelli for reference materials, and asked for their opinions on the various research papers I’d run across. They supplied me not just with useful books and websites, but with images that previous scientific illustrators had made. We also looked at other museums, like the Denver Museum of Nature and Science, to see how they depicted the Early Eocene.

How did these other artists know what Wyoming could have looked like millions of years ago? I’m sure they did what I did and talked to scientists who study paleoecology. And how do the scientists know? Well, there are a variety of different fields that yield all sorts of information. Today, let’s start with the fossil record.

fossil palm frond from Eocene Wyoming

A 52-million-year-old palm frond found near Fossil Butte, Wyoming, shows just how warm and wet the climate was back in the Eocene. (Photo from National Park Service website)

Paleobotany

In the same way that fossil skeletons tell us which animals were around in the past, fossil plants give us a glimpse of ancient forests and swamps. Plants don’t typically have hard parts, but it’s still possible for leaves, flowers, stems, and even pollen to fossilize. Sometimes, if you’re really lucky, you even get whole forests of petrified wood or plants preserved in volcanic ash.

To be fair, there are some limitations when it comes to studying plant fossils. Just like the animal fossils you see in museums, plant fossils also require some pretty specific conditions in order to be preserved, so we don’t have a complete record of all the flora from a given time period. In fact, the sedimentary environments like floodplains that tend to preserve the most plant species record a habitat that may not have been used very much by ancient mammals — which is a bit problematic if you’re trying to build an exhibit around mammal fossils! Also, while lake beds tend to yield fairly complete records of the woody plants that grew nearby, all the fossils accumulate at the bottom of the lake so you don’t get a good sense of the vegetation’s spatial distribution on land. That’s why beds of fossils preserved in volcanic ash are so nice: you get the diversity and the spatial distribution all in one.

Still, from the fossil assemblages we do have, we can get a general idea of ancient climates and ecosystems. For example, Alaskan megafossils* from the middle Eocene include palms, lianas, and evergreen leaves with drip tips, which tells us that the arctic was very warm, almost tropical. At the same time, closer to home in the Green River formation in Southwestern Wyoming, you would have found palms, cattails, and plants that are now only found in Eastern Asia. All these Green River plant fossils indicate that the climate in Eocene Wyoming was moist and sub-tropical (the presence of fossil crocodiles is another hint that things were much warmer back then).

Sometimes the morphology (that is, the physical form) of a specimen can help you identify the family, genus, or even species, so you can tell when certain plants expanded into an area or died out. If you can group together enough species from a time and place, you can get a good idea about the way they may have interacted with each other and their environment. This is great for me, since once I can visualize an assemblage, I can re-create a scene! Sometimes these assemblages resemble modern plant communities, and sometimes they’re totally unique, but either way they’re pretty darn interesting.

*A megafossil literally means “large fossil”, or more specifically, it’s fossil where the preserved parts are large enough to show structure, such as stem cross-sections or branching patterns in plants. A microfossil would be something really small, like a spore or pollen grains.


For more on plant fossils:
Wing, S. (1998). Tertiary vegetation of North America as a context for mammalian evolution. In C. Janis, K. Scott, and L. Jacobs (Eds.), Evolution of tertiary mammals of North America, volume 1: terrestrial carnivores, ungulates, and ungulatelike mammals (pp 37-60). Cambridge: Cambridge University Press.
http://www.amazon.com/Evolution-Tertiary-Mammals-North-America/dp/0521619688

Green River Formation Fossils: http://www.ucmp.berkeley.edu/tertiary/eoc/greenriver.html

Bighorn Basin Fossils: http://www.mnh.si.edu/highlight/paleo_plant_2006/index.html

Fossils and Climate Change: http://www.nature.nps.gov/geology/nationalfossilday/climate_change_past.cfm

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