Dinosaurs Ate Grass – Scientists Eat Crow⤒🔗

Have you ever tried to imagine what a world without grasses would look like? The scenery might well look pretty bleak, with extensive patches of bare soil. We see good examples of this in illustrations of di­nosaurs in their natural surroundings ­scientists have long declared that there were no grasses present in dinosaur com­munities. The plant-eating dinosaurs had to make do, we have been assured, with cy­cads, ferns, horsetails and trees of flowering plants such as palms and magnolias.

Today however, grasses (which are also flowering plants), actually contribute far more than beauty to the environment. They represent extremely important sources of nutrition. Indeed, our whole ecosystem could well crash if grasses disappeared. This group of plants includes sedges, bamboo, barley, oats, fescue and timothy grasses, rice, millet, sorghum and corn among other others. What large grazing animal does not depend upon one or other of these sources of nutrition?

Nevertheless, scientists have stead­fastly maintained that large grazing di­nosaurs survived without grasses. This view will certainly be re-evaluated in the light of a November 2005 article on dinosaur diets which appeared in the journal Science.

20/20 Retrospect←⤒🔗

In retrospect, scientists may well de­cide that it makes sense that dinosaurs ate grass. Many grasses grow continuously when they are grazed. Thus they provide a reliable source of food.

Ferns and cycads on the other hand, restrict growth to once per year. Cycads, which look like squashed down palms, have hard indigestible leaves much like those of conifers. Cycad seeds could well be eaten, but some contain poisonous compounds, at least to people. The stems might be good, but if it was eaten the plant might not survive to grow next year. Alto­gether, without grasses, the vegetation would be hard pressed to support gigantic grazing dinosaurs.

So, in retrospect, scientists say it makes sense that grass was present in communi­ties with dinosaurs. The amazing teeth of the duckbill dinosaurs suggest that their lifestyles were similar to ungulate grazers (deer, bison, gazelles) that we know today.

There were also mammals (gond­wanatherians) present, now extinct, which had teeth shaped much like today's grazers. Now it makes sense that the teeth of these mammals were used for eating grass; in hindsight it all seems so obvi­ous. So why did it take so long for scien­tists to recognize the presence of grasses in these communities?

Missing from the Fossil Record←⤒🔗

Scientists have long been aware that leaves and stems of the cycads, conifers, and ferns are common in the layers of rock which contain dinosaurs, but no grasses can be found. John Lindley (1799-1865) was one of the early experts who reflected on this situation. He wondered whether the fossil record conveys an accurate impres­sion of plant life in the past. He set out to find some answers.

John Lindley was typical of many learned men of his time. He was inter­ested in all aspects of his chosen discipline and consequently he was involved in many diverse pursuits. He was a botanist, specializing in orchid classification, a palaeob­otanist interested in plant fossils, and he was a horticulturist. In 1829 Lindley was appointed to the chair of botany at Uni­versity College, London, a post he held for thirty-one years. In his role as horticultur­ist, he developed the Royal Horticultural Society's garden at Chiswick and started a school of horticulture there. In 1838 he wrote the report which saved the botanic garden at Kew from being abandoned. At the time, it was a neglected royal property. Lindley persuaded the Treasury branch to spend large sums of money to nationalize the property and of course to upgrade and maintain it. In keeping with his interest in plant fossils, Lindley and William Hutton co-authored a three volume work entitled The Fossil Flora of Great Britain (1831-1837). It was in conjunction with the writing of this work, that John Lindley carried out an interesting experiment.

Just Add Water←⤒🔗

In March of 1833, John Lindley filled a huge tank with water. In it he immersed fungi and lichens, mosses, ferns, club mosses, cycads, conifers and flowering plants of various types. Since he was so closely connected to botanic gardens, he was able to obtain many exotic and tropi­cal specimens for his experiment, as well as more typical English plants. The ques­tion this man was asking was, how does prolonged soaking with water affect plant remains. He allowed the experiment to sit for two years and then he examined the contents to see what was still present. Did all the plants last equally well in the wa­ter? This is what he found:

This experiment appears to me to lead to the most important conclu­sions. These things seem clear: firstly that dicotyledonous plants (dicots), in general, are unable to remain for two years in water without being totally decomposed; and that the principal part of those which do possess the power, are the Coniferaid (conifers) and Cycadae (cycads), which are ex­actly what we find in a Fossil state; secondly, that Monocotyledones (monocots) are more capable of resist­ing the action of water, in particular Palms and Scitamineous (group in­cluding bananas, ginger and arrow­root) plants, which are what we principally find as Fossils, but that Grasses and Sedges perish, so that we have no right to say that the earth was not originally clothed with Grasses because we no longer find their remains.¹

Based on this experiment, John Lindley concluded that the proportions of differ­ent plants that we see preserved as fossils, is a function of their resistance to decay. The absence of grass fossils from a given layer of rock was not to be taken as an in­dication that grasses hadn't existed at that time.

But What about the Spores?←⤒🔗

Lindley's experiment explained why grasses weren't found in the fossil record — they decayed too quickly to be fossilized — however plant spores and pollen are much more resistant to decay. If grasses were around in the past, why was grass pollen not identified in sediments with the dinosaurs?

There are few issues in palaeontology as controversial as the study of fossil pollen grains. At first sight it is hard to understand why this should be. The facts of the matter are that spores and pollen grains are made of an exceedingly tough organic compound called sporopollenin. It so happens that these outer coverings are characteristically shaped and decorated in ways which make it easy to tell the plant that released them.

Because the sporopollenin is so tough, these small artifacts can be concentrated from sediment samples by means of treat­ment that uses strong acids or alkalis to dis­solve away everything else. Obviously this technique provides a wonderful way to es­tablish the presence of plant material in sediments which lack large plant fossils.

Ignoring the Evidence←⤒🔗

None of this, of course, is controver­sial. What is controversial is the sugges­tion that these pollen grains came from plants like our modern ones. Based on evo­lutionary assumptions, most scientists refuse to acknowledge that deep sedi­mentary layers might contain remains of modern appearing plants.

Palynologists (spore/pollen grain ex­perts) routinely recognize pollen grains of modern genera and species, if these are found in recent sediments. When it comes to the sediments which buried the dinosaurs, and also sediments lower still, it is a widely accepted convention that the pollen grains will be identified by appearance only. Any resemblance to mod­ern plants is entirely ignored. Specialists who had previously identified such pollen collections in terms of modern plant names, later saw their conclusions dis­counted by others and names based on form only were substituted.

The problem of identifying the pres­ence of grass plants in dinosaur communi­ties now becomes clearer. The sediments might contain ample grass pollen, but no­body would identify it as such because of the custom of describing appearance only. At the higher levels where pollen grains are compared with living plants, grasses have variously been said to have first ap­peared in Oligocene rocks (about 35 mil­lion years ago by evolutionary estimates) or Paleocene rocks (about 55 million years ago by similar reckoning). According to such evolutionary scenarios, this would place the first appearance of grasses ten to twenty million years after the extinction of the dinosaurs.

Finding Gold in Dinosaur Dung←⤒🔗

It was the identification, in dinosaur dung, of tiny silica crystals produced only by grasses that led to the dramatic an­nouncement concerning grasses in di­nosaur diets. These crystals, called phytoliths, form in the thickened walls of certain plant cells. These artifacts are typi­cally destroyed by the strong acids used to concentrate pollen grains. Thus they would never be found along with collections of pollen grains.

The shapes of these crystals are so spe­cialized, that scientists can identify the gen­eral characteristics of the plants which produced them. Thus five very different types of grass phytolith were found in the dinosaur dung. Some of the phytoliths re­semble those produced by modern rice. Some of the plants may have looked like bamboo, only smaller. All we know to this point is that there was considerable variety in the characteristics of the grasses. Evi­dently these plants were an established part of the ecosystem.

Why Did It Take So Long?←⤒🔗

Thus we return to the question as to why it took the scientists so long to docu­ment the presence of grasses with the di­nosaurs. There were at least four reasons:

• It is evident that the scientists were not looking for grasses at these deep levels in the rocks.
• The pollen grains which could have been assigned to the grasses, were in­stead described merely in terms of ap­pearance.
• Phytoliths did not show up because nobody was looking for them. The preparation of pollen grains, in fact, eliminated phytoliths.
• Finally we learn from a long ago experiment by John Lindley of England, that grasses quickly decay in standing water.

Obviously other methods to search for their presence should have been em­ployed. The fact is this recent discovery complicates theories about plant evolu­tion. Indeed this is a classic example of the way in which evolutionary preconcep­tions can bias discovery.