Field of Science

What did sauropods have for breakfast?

One of the more creative presentations at this year's recent botanical meetings was a study on sauropod herbivory by Dr. Carole Gee. Since sauropods were the most massive animals to ever live on land, they had to eat a lot (hundreds of kilos a day) and they were strict vegetatians (herbivores). Presently the largest land animals either eat grass, e.g., bison, or browse tree leaves, e.g., giraffes, and these are all flowering plants now. But back in the Late Jurassic (152 million years ago) the choices were very different and no body had ever thought about the different energy contents of the plants sauropods had to choose among.

Many of the prominent groups of plants from the Late Jurassic survive today, horsetails, ferns, ginkgoes, diverse conifers, and cycads, so assuming modern members of these groups still retain the basic characteristics of their ancestors, the energy content per unit of plant mass can be compared.

Rather surprisingly horsetails had the highest energy content, even higher than modern grasses. Next came Araucarias (monkey puzzle trees and Norfolk Island pines) and ginkgoes, both actually better food than the leaves of modern forest trees. Another talk provided us with a view of the rather open savanna-like forest structure of araucarias based on large numbers of fossil tree stumps preserved in volcanic ash. A perfect place for large sauropods to graze among the tree tops.

Cycads with their tough, hard foliage had the least energy content, and since they are also slow growing, they simply don't produce much leaf material. Today cycads are minor elements of tropical and subtropical communities, but back in the Jurassic they made up about 20%. A couple of ferns with ancient lineages, like cinnamon fern, were pretty good sauropod food, but other more modern ferns have pretty low nutritional levels.

So what good is this? Well, curious minds want to know how ecology worked in the past.

2 comments:

Anonymous said...

That really is surprising about horsetails as foodstuff. I'd have thought all that silicate would have made them both unpalatable and hard to digest. Did Dr. Gee remark on how sauropods dealt with tummies full of glass?

~Shelley

Dr A said...

Sauropods ate rocks that helped pound the vegetation into a mash. And the rounded digestive stones are relatively common fossils associated with their skeletons. Birds eat sand to help with digestion in much the same manner. And yes, it was a surprise that horsetail rated so high. The result for cycads surprised no one.