It makes you cry, it makes you sneeze – pollen is everywhere! But did you know that we can find fossilized pollen? Or that it can help us solve mysteries in paleontology? We spoke to Antoine Bercovici, a Peter Buck postdoctoral fellow in the Department of Paleobiology, to learn more, and discovered a mystery that fossil pollen might help solve.
How and where do you find fossil pollen? I didn’t even realize that was something you could do!
Well, if you think about it, pollen is all around us, especially in the air. Lately, we had the highest pollen record for 50 years here in DC - they measured 3000 pollen grains per cubic meter of air. And a cubic meter is not that much! Pollen is also being trapped in water – you find it in tap water, rivers, and lakes. And if you find it in water, you can find it in rocks, since it will get trapped as all the debris in the water settles into sediment. You will find pollen grains trapped inside most terrestrial rocks.
Pollen is perfectly cut out to be a fossil. To give yourself the best chance of fossilization, you want to be very small, produced in large numbers, and spread out, and pollen does all three things. Another great thing is that pollen grains are very resistant. They make a very resistant organic wall called sporopollenin and this wall can survive through almost anything.
To recover fossil pollen, we take very small samples of clean rocks and we dissolve them in a very strong acid called hydrofluoric acid. This type of acid is used to etch glass, which makes it great for this task because it will etch away anything that’s mineral, but organic stuff, like pollen grains, will be unharmed and we can study them.
How did you get interested in fossil pollen?
Pollen is really super exciting to me because it’s beautiful – you really don’t get tired of it. But one of the reasons I went into fossil pollen in the first place was because of some field work I did in North Dakota. When you get out there for the first time, you’re always excited by dinosaurs, because they’re mind-boggling and big. Then you work on them for weeks and weeks, and you realize they are a huge amount of work, and all you get out of it is basically a single bone. All that’s going to tell you is this type of dinosaur died there – and that’s it. I became interested in studying pollen because it gives us tremendous amounts of information and with just a tiny, tiny sample, all of the long extinct vegetation that was around at that time can be reconstructed. By identifying and counting the different species of pollen and spores, I can start to paint a picture of the landscape and, using sedimentology (how rocks are deposited together), I can reconstruct the composition of an entire extinct forest.
How can you reconstruct an environment by looking at a tiny grain of pollen?
It can tell you about the environment because you can reconstruct the plants it came from. The pollen tells you about the climate because plants are extremely sensitive to climate. For example, in North Dakota, you can find palm pollen. Obviously, there are no palms in North Dakota now, but it tells us that in the Late Cretaceous, when I found this pollen grain, North Dakota wasn’t freezing in the winter. Paleobotany is very helpful for climatology because where you find several types of plants, you can find several types of data on past climate.
Can it tell you anything about the animals? Or is that something you have to infer?
It can directly, on some occasions. Some coprolites (fossilized dung) contain pollen grains, so it can tell you what kind of plants the animal ate. It’s been done on some dinosaur coprolites.
What are you currently working on?
One of the other very useful parts of paleontology is what’s called biostratigraphy – which is dating rocks using fossils. You can use microfossils, because you can find a lot of them in a very small sample and do a very high resolution study. You can take samples centimeter by centimeter, and see the change. The same thing can be applied with pollen and spores. I can see where pollen appears and disappears over a period of time - that’s what I’m working on right now, change across the Cretaceous-Paleogene (or K/Pg) boundary, which corresponds to the extinction of the “non-bird” dinosaurs.
Have you discovered anything particularly interesting? Has it confirmed what we knew?
My work in North Dakota has been stratigraphic work, but what brought me to palynology was a site where we had a conflict and we needed to solve the puzzle. We were digging at this site on the K/Pg boundary, and just above it, we had a lot of typical Paleocene fauna - vertebrates, mammals, late turtles and crocodiles, Paleocene plants, and no dinosaurs – so we thought we crossed the boundary. But this site was so close that it was probably some the first evidence of the recovery of animals after the mass extinction. The last piece of data that was missing was the pollen so we could place our finger on where the boundary was. We did the pollen analysis – I didn’t do it at the time, I was still a student – but our palynologist colleague came back to us and said, “Well the entire hill is Cretaceous. You have not crossed the boundary.” We thought that was interesting, because we had Paleocene mammals and Paleocene plants in the rock, indicating that we really should have crossed the boundary. There was obviously a big problem here. We sent another set of samples to another scientist in a different state and he also said it was all Cretaceous. All we could think was that it couldn’t be right!
By Abree Murch, Museum Technician, National Museum of Natural History