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The rates and processes of decomposition and scavenging of large modern mammals (such as elephants) or other vertebrates with body sizes comparable to some dinosaurs (small ones, too) have been observed, some of which died in environments similar to those interpreted for containing dinosaur remains (Fig. 7.3).

Studies from entomology (the study of insects) have documented and calculated the life cycles of fly species associated with laying eggs in animal bodies; carrion-feeding beetles and other scavenging insects have also been studied for their effects on corpses.

The types and amounts of metabolic by-products from both anaerobic and aerobic bacteria involved in the decomposition of organic material have been

Decomposing Opossum Images

FIGURE 7.3 Taphonomic information derivable from an opossum (Didelphis marsupialis) on Sapelo Island, Georgia. Opossum was observed dead in the road at 8:00 a.m., July 31, 2004, and seemed freshly killed at the time; hypothesized cause of death was from being struck by an automobile. At 4:00 p.m. that same day, seven black vultures (Coragyps atratus) were seen around the body; their tracks and a drag mark ending with the body confirmed that it had been moved about 3 meters from the spot where it was originally sighted. Body had been almost completely eviscerated; internal organs and musculature were more than 90% gone. Tire tracks and crushed bones indicated that several vehicles had run over the body both before and after scavenging. Flies were on the body and a noticeable odor was present, the latter probably as a by-product of aerobic bacteria. Temperature was about 30°C, with nearly 100% humidity.

FIGURE 7.3 Taphonomic information derivable from an opossum (Didelphis marsupialis) on Sapelo Island, Georgia. Opossum was observed dead in the road at 8:00 a.m., July 31, 2004, and seemed freshly killed at the time; hypothesized cause of death was from being struck by an automobile. At 4:00 p.m. that same day, seven black vultures (Coragyps atratus) were seen around the body; their tracks and a drag mark ending with the body confirmed that it had been moved about 3 meters from the spot where it was originally sighted. Body had been almost completely eviscerated; internal organs and musculature were more than 90% gone. Tire tracks and crushed bones indicated that several vehicles had run over the body both before and after scavenging. Flies were on the body and a noticeable odor was present, the latter probably as a by-product of aerobic bacteria. Temperature was about 30°C, with nearly 100% humidity.

measured, as have the rates of this type of decomposition in association with temperature and other climatic factors.

■ Paleontological information from both body fossils and trace fossils in Mesozoic rocks indicate the presence of probable scavengers in continental ecosystems, such as flies, crayfish, beetles, and ants (Fig. 7.4).

■ Toothmarks in bone made by other dinosaurs, that are in certain patterns or areas of the bones, suggest scavenging behavior rather than predation, as do teeth left behind by theropods in monospecific beds of herbivorous dinosaurs (Chapter 9).

■ Crushed bone found in areas of dinosaur bone accumulation suggests trampling by large, heavy animals (that is, other dinosaurs: Chapter 14). The same process has also been documented for damage of modern elephant bones by other elephants.

■ Relatively large olfactory bulbs derived from brain endocasts of some carnivorous dinosaurs suggest an enhanced ability to smell. This adaptation

FIGURE 7.4 Pockmarks in sauropod bone from the Late Jurassic of Utah, interpreted as trace fossils formed through beetles gnawing on exposed bones.

Dinosaur Olfactory Bulbs

FIGURE 7.4 Pockmarks in sauropod bone from the Late Jurassic of Utah, interpreted as trace fossils formed through beetles gnawing on exposed bones.

could have been used to detect a decaying carcass over long distances, and is seen in modern vultures with their scavenging lifestyle (Chapter 9).

Currently, no definitive evidence supports fly, ant, crayfish, mammal, or bird scavenging of dinosaur corpses as in the above scenario, but these animals were contemporaneous with dinosaurs and some of their species are observed scavenging today. Although this is a weakly supported hypothesis, such evidence may be found if paleontologists look for traces of such activity, either in bones or sediment associated with bones. Similarly, no evidence supports the scavenging behavior of pterosaurs on dinosaurs, although some pterosaurs are interpreted as carrion feeders on the basis of functional morphology. In contrast, a documented example of a dinosaur feeding on a pterosaur has been interpreted on the basis of matching teeth with distinctive toothmarks found on pterosaur bones (Chapters 8 and 9).

Modifications to the outlined scenario can be made easily by placing the dinosaur body in different environments and times and varying the behaviors of the scavengers. For example, if the body had been washed into a river channel instead of lying on a floodplain, crocodiles and fresh-water fish might have fed on it. If it had fallen near a marine shoreline, crabs, which are common coastal scavengers today, would have been more likely consumers of the corpse instead of crayfish, which live exclusively in fresh-water fluvial and lacustrine environments.

If waves at a shoreline washed up enough to pull a dinosaur body out to sea, its gas-filled corpse would have rafted on the open sea. Likewise, dinosaurs that dwelled in lowland environments, such as coastal swamps, deltas, or estuarine marshes (a life habit shown by numerous dinosaur tracks in such environments: Chapter 14), could have had their bodies washed into nearby channels that emptied into a seaway. Once at sea, a dinosaur corpse would have provided a rich food source for sharks, smaller fish, and marine reptiles, which would have nibbled on its appendages hanging down into the water. This hypothesis, often termed the "bloat-and-float" hypothesis by vertebrate taphonomists, provides an explanation for the rare occurrences of certain dinosaur bones in shallow marine deposits. Joseph Leidy first proposed it in 1858 to explain Hadrosaurus remains in a Cretaceous marine deposit (Chapter 3). Later analyses of dinosaur bones in Middle Jurassic marine deposits of England indicated that they were displaced a minimum of 80 km from the nearest continental environment, which meant that there was plenty of time for marine scavengers to enjoy some dinosaurian snacks. In the cases of

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