For the Jurassic World, Pollen Shows What Plants Grew When Dinosaurs Roamed

For many of us, the pollen that comes with springtime is a nightmare. Sneezing, coughing, runny noses, and an inability to focus are the norm as plants bloom and send their pesky pollen out into the air. However, for palynologists (scientists who study pollen), pollen is far from annoying or an inconvenience. Not only useful for helping plants reproduce, pollen can be used to solve crimes, identify historic land use and plant communities, and even determine how climate has shifted over time. Pollen can tell us more about the world and how it used to be.

In that case, heavy pollen loads can be a good thing. More pollen means more information for scientists working to understand plants of the past.

Palynology is one of the best methods scientists have for understanding how plant communities and climate have changed over the past millennia. Just as forensics experts can solve crimes by examining pollen on clothes to determine where a person has been, palynologists can look at pollen found in sediment samples to determine what types of plants were present in that area during a certain time period.

What can pollen tell us about the environment dinosaurs lived in?

In North Yorkshire, a region of England known for its stark moors and towering rock outcrops, geologic history is literally at your fingertips. As you walk through dales and up over vast limestone formations, you can see the layers of sediment deposited over millions of years (Figure 1). Within these layers in the Middle Jurassic Ravenscar Group lie dinosaur footprints and preserved plant material. In a recent study, Slater et al (2018) used these preserved footprints and plant material to explore the relationship between Jurassic-period dinosaurs and plants in this region.

Figure 1. Stratified sedimentary rocks. The different color layers are soil that was deposited over time and slowly compacted. Different layers indicate different time periods. Image courtesy of Wikimedia.

How do we know what dinosaurs lived in the area?

Slater and his colleagues took samples of rock from cliff faces in north Yorkshire. These rock samples were from the same sedimentary rock layers (and time period) as the dinosaur footprints (Figure 2). After they were collected, the rocks were dissolved in strong acids and then sifted to remove any pollen, spores, or fossilized plant material. Pollen and plant material were then identified to determine what types of plants were present during the Middle Jurassic era when dinosaurs were present.

Figure 2. The image on the left shows imprints from dinosaur toenails. The image on the right shows the footprint of a two-legged dinsoaur. Source: Slater et al. 2018.

How do we know what plants grew?

Most of the pollen within the dinosaur footprint bed was from prehistoric ferns (Figure 3). Conifer and seed fern pollen were also abundant in the rock samples. Lycophytes and bryophytes (Figure 3) were also present, though in much smaller numbers. While many of these plants are now extinct, plants like the Ginkgo Tree (Gingko biloba) and Horsetail (Equisetum species) still exist as the only remaining plants in Families that dominated the Earth during Jurassic times (Figure 4).

Figure 3. Pollen spores from the same layer of rock (or time period) as the dinosaur footprints. Source: Slater et al. 2018.

Figure 4. From right to left: Gingko leaves, Equisetum plants, and moss (a bryophyte) similar to those that may have existed in the Jurassic Era with dinosaurs. Image courtesy of Moonchild73, Wikimedia, and MAKY_OREL.

In comparison with previous studies of fossilized plant parts, the pollen spore counts performed by Slater et al. showed a much higher diversity of lycophytes and bryophytes. This was perhaps due to plant characteristics that make these types of plants less likely to become fossilized. Combined with previous evidence of fossilized plants in the same sedimentary layers, Slater et al. identified a diverse plant community of ferns, trees, mosses, and other leafy plants like Caytoniales (Figure 5).

Figure 5. Fossilized leaves of a Caytionales plant. Image courtesy of Wikipedia.

What did the environment look like?

Because fossilized pollen and spores from certain plants were found within the same layer of rock as dinosaur footprints, scientists can assume that these plants grew in the same area, and at the same time as these dinosaurs were present. The diverse vegetation and low-elevation of the area likely meant that food and water were easily accessible for dinosaurs in this area. Based on footprint studies in North Yorkshire, the dinosaur community was also fairly diverse, perhaps because of the great range of plants available in the region (Figure 6). Footprints of theropods (three-toed dinosaurs like Tyrannosaurus rex), ornithopods (two-legged, herbivorous dinosaurs with beak-like mouths), and sauropods (four-legged herbivores like the Brachiosaurus) were identified in the rock footprint layer. It is difficult to know what specific dinosaurs were present because few fossilized bones exist in the region. It is also difficult to know what specific plants dinosaurs ate, as methods to evaluate dinosaur poop are generally unreliable. However, the presence of certain plant species and families in the same area as herbivorous dinosaurs provides insight into what plants were available for consumption during the Middle Jurassic time period.

Figure 6. A reconstruction of what the plant community may have been like for dinosaurs in the Jurassic Era. Source: Slater et al. 2018.

Why do we care about pollen in the past?

Learning more about the environment that we live in and how it has changed over time can help us learn how plant communities adapt to new environments and pressures. We can also learn more about what dinosaurs ate, how they interacted with their environment, and perhaps gain a better understanding of why they no longer exist.

Aside from how this information may be useful to humans, dinosaurs are fascinating, often mythic creatures that have long held an interest for both the public and scientific communities. Next time you watch a Jurassic Park movie, just imagine all the scientific research on dinosaur footprints, bones, and ancient pollen that helped shape what we see in the movies!

Featured image showcases a range of ornithopod dinosaurs from the Jurassic Era. Image courtesy of Wikiwand.

You can follow the link to Envirobites to read the original article here!

Reference:

Slater, S.M., C.H. Wellman, M. Romano, and V. Vajda. 2018. Dinosaur-plant interactions within a Middle Jurassic ecosystem – palynology of the Burniston Bay dinosaur footprint locality, Yorkshire, UK. Palaeobiodiversity and Palaeoenvironments. 98:139-151. DOI: https://doi.org/10.1007/s12549-017-0309-9