Why Learn about Dinosaur Taphonomy

This chapter summarizes "the Three Ds," its subject matter being death, decay, and disintegration.

Taphonomy, the study of everything that happens to an organism's body after it dies, is a fascinating science. Taphonomy (from the Greek taphos, burial, and nomos, law) was first recognized as a science for studying the post-death phenomena associated with organisms by Russian paleontologist J. A. Efremov in 1940, although some of its principles were discussed by Leonardo da Vinci in the fifteenth century (Chapter 3). This field has since been broadened to include the study of preservation, which requires the understanding of fossilization processes that affect trace fossils (such as tracks, nests, and feces: Chapter 14).

Taphonomy relates to the following circumstances:

■ The probable cause of death.

■ What other animals (including its relatives) might have scavenged on its carcass.

■ How long it took before a body started to bloat and why it bloated.

■ How long a body was above the ground before any part of it was buried.

■ Whether parts of a body broke off and were carried away from the original death site.

■ How far from the original death site a body part might have been transported.

■ Under what circumstances a body part was finally buried and affected by more biological and chemicals processes while underground.

■ Whether an animal's remains were noticeably changed or not during their time buried.

■ Why some parts of animals become body fossils and why body fossils of some animals are rare.

Because all non-avian dinosaurs have been extinct for the past 65 million years, taphonomy is an important science for understanding how their fossils remained preserved during that amount of time. It also indicates how representative our admittedly biased sample might be of the original dinosaur population at any given time during the Mesozoic. Paleontologists acknowledge that the fossil record is an incomplete history of all species that lived and evolved on the Earth. Body fossils of terrestrial vertebrate animals in particular are quite rare, especially in comparison to marine invertebrates or trace fossils of terrestrial invertebrates.

Dinosaurs provide a good example of such rarity. Despite their fame and 165-million-year existence, approximately 80% of all described dinosaur species are only known from less than five specimens for each species; about 50% are known from only one specimen. The only major group of dinosaurs that is well represented in terms of diversity and number of individuals representing each species are the cer-atopsians (Chapter 13). Knowledge that modern vertebrate animals, in particular, show an abundance of herbivores relative to carnivores also raises questions about the circumstances that might have preserved hundreds of carnivorous dinosaurs in one deposit with no herbivores whatsoever (Chapter 9). Similarly, we might ask why other deposits contain an estimated population of thousands of herbivorous dinosaurs, apparently of the same species, whereas the only other body fossils representing another dinosaur species are errant theropod teeth (Chapter 11).

Within this type of study are the added benefits of:

1 gaining a better understanding of organisms and ecosystems associated with dinosaurs (especially in terms of nutrient cycling);

2 learning about the sedimentary environments where dinosaur bodies were buried; and

3 discerning the biogeochemical conditions of sediments enclosing dinosaur body parts.

Determining the cause of death for individual dinosaurs also provides clues toward understanding natural selection in the context of a dinosaur's ecosystem, which relates to dinosaur evolution (Chapter 6). It also helps illuminate more specific aspects of behavior, such as injuries or deaths that might be attributable to intraspecific or interspecific interactions.

Dinosaur trace fossils also are allied with taphonomy because they were subject to some of the same principles of body fossil preservation. The single largest advantage that dinosaurs' trace fossils have over their body fossils is that most trace fossils represent in situ (in place) fossils. Many dinosaur body fossils were probably moved from the original site of death of the animal, but most dinosaur trace fossils, such as tracks (Chapter 14), record the former presence of dinosaurs exactly where they are found. Furthermore, certain dinosaur trace fossils are more abundant than other dinosaur fossils in some areas, which may be a function of their preferential preservation in rocks that normally do not preserve dinosaur body fossils. This abundance also may be a result of one dinosaur making many trace fossils during its lifetime.

Surprisingly, dinosaur taphonomy receives relatively little mention in most books about dinosaurs. This chapter will simply point out how the study of taphonomy as applied to dinosaurs can provide many educational benefits. Taphonomy provides a way to discern the long history of what happened to a dinosaur between the day it died and the day we see its remains for the first time, many millions of years later. It makes for an interesting story.

0 0

Post a comment