Palaeobotany for Paleoartists VIII: Paleofloras of the Jurassic

Vertebrates (and particularly tetrapods) are the main focus of many paleoartistic reconstruction. This is perfectly understandable: humans tend to care more about things that are more similar to them, with decreasing interest for more distant living beings (see here).

Unfortunately, given the different preservation potentials of the two groups, vertebrate localities are usually devoid of plants, and plant-bearing localities have very few vertebrate fossils (though exceptions do exist, see Crato or Yixian). This makes it extremely difficult for paleoartists to identify appropriate plant taxa to populate the landscapes of their vertebrate reconstructions.

However, something can be done. Even though the exact local vegetation might be unknown, we can still make a guess of the type of plants that might have inhabited a particular fossil formation based on its geographical location.

Climate is a major driver of plant distribution today, and the same can be inferred in the past. Different kinds of vegetation with similar structure and convergent plant types occurr in different climates: treeless tundra in very cold environments, tropical rainforest in warm and wet environments, open savanna in warm and seasonally dry environments etc. This correlation between climate and vegetation can be found in floras from the past.

Moreover, geographical distances and barriers tend to create local floras, with different sets of plant groups occupying the same roles in different geographical areas. For example, extant temperate forests are dominated in the northern hemisphere by Fagaceae, while the southern hemisphere temperate forests are dominated by Nothofagaceae. Mediterranean-type environments in South Africa are full of Restionaceae and Proteaceae, while these families are completely absent in the Mediterranean basin. Similar patterns can also be found in the fossil record: during the Carboniferous and Permian, unique groups of plants with similar ecological roles make up the floras of Angara, Cathaysia, and Gondwana.

Let’s take the Jurassic as an example.

Modelled Jurassic climates based on two different approaches. Image from Noto and Grossman (2010)

The Jurassic earth was characterized by a ‘hothouse’ condition, with no permanent polar ice caps. High latitude environments in Laurasia and Gondwana were characterized by a temperate climate, with warmer conditions at lower latitudes. This localities hosted groups such as the Czekanowskiales (a group of ginkgoalean relatives with long, thin leaves) in the Northern Hemisphere and Ginkgoales sensu stricto in both hemispheres, as well as cycadophytes such as Nilssonia in the Northern Hemisphere and bennettitales with large leaves such as Anomozamites, Pterophyllum, and Nilssoniopteris at higher latitudes and Pseudocycas, Williamsonia, Williamsoniella at lower latitudes. The warmer temperate zones of Asia hosted the peculiar extinct conifer that produced the leaf genus Podozamites.

Reconstruction of the PodozamitesKrassilovia plant by Pollyanna von Knorring. Similar plants occupied the warm temperate climates of East Asia in the Jurassic.

At subtropical latitudes, the climate was characterized by winterwet to arid conditions. These environments were dominated by the Cheirolepidiaceae, an extinct group of conifers that produced the peculiar pollen type Classopollis. These conifers, as well as other groups of conifers such as the Araucariaceae, had scale-like leaves that are well-adapted to environments with high water stress. Bennettitales and cycadophytes with smaller leaves and leaflets, such as plants producing the leaf genera Otozamites, Ptilophyllum, and Zamites, were also present.

Similar patterns can be identified for other periods. Fortunately for everyone, a nice treatment of such paleobiomes and the plants found in them is available in the book “The Evolution of Plants”, a perfect introduction to Paleobotany by Kathy Willis and Jenny McElwain. This would be an excellent resource for all paleoartists interested in paleobotany.

Thanks to Rebecca Dart for inspiring this post!

References

Noto, C.R. and Grossman, A., 2010. Broad-scale patterns of Late Jurassic dinosaur paleoecology. PLoS One, 5(9), p.e12553.

Rees, P.M., Ziegler, A.M., Valdes, P.J., Huber, B.T., MacLeod, K.G. and Wing, S.L., 2000. Jurassic phytogeography and climates: new data and model comparisons. Warm climates in earth history, pp.297-318.

Vakhrameev, V.A., 1987. Climates and the distribution of some gymsosperms in Asia during the Jurassic and Cretaceous. Review of Palaeobotany and Palynology, 51(1-3), pp.205-212.

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