Download PDF Dinosaurs A Concise Natural History by David E. Fastovsky

Sinopsis

That we even know there ever were such creatures as dinosaurs is due to dumb luck: some dinosaurs just happened to be preserved as fossils, the buried remains of organic life, in rock. Dinosaurs last romped on Earth 65 million years ago. This means that their soft tissues – muscles, blood vessels, organs, skin, fatty layers, etc. – are, in most fossils, long gone. If any vestige remains at all, it is usually hard parts: generally, bones and teeth. Hard parts are not as easily degraded as the soft tissues that constitute most of the body. 

Making body fossils

Before burial. Consider what might happen to a dinosaur – or any land-dwelling vertebrate – after it dies (Figure 1.1). Carcasses are commonly disarticulated (dismembered), often by predators and then by scavengers ranging from mammals and birds to beetles. As the nose knows, most of the heavy lifting in the world of decomposition is done by bacteria that feast on rotting fl esh. Some bones might be stripped clean of meat and left to bleach in the sun. Others might get carried off and gnawed. Sometimes the disarticulated remains are trampled by herds of animals, breaking and separating them further. So the sum total of all the earthly remains of the animal will end up lying there: a few disarticulated bleached bones in the grass.

If the animal isn’t disarticulated right away, it is not uncommon for a carcass to bloat, as feasting bacteria produce gases that infl ate it. After a bit, the carcass will likely defl ate (sometimes explosively), and then dry out, leaving bones, tissues, ligaments, tendons, and skin hard and infl exible.

Burial. Sooner or later bones are either destroyed or buried. If they aren’t digested as somebody’s lunch, their destruction can come from weathering, which means that the minerals in the bones break down and the bones disintegrate. But the game gets interesting for paleontologists when weathering is stopped by rapid burial. At this point, they (the bones, not the paleontologists) become fossils. A body fossil is what is produced when a part of an organism is buried. We distinguish these from trace fossils, which are impressions in the substrate left by an organism. Figure 1.2 shows two of the many paths bones might take toward fossilization.

After burial. Bone is made out of calcium-sodium hydroxy apatite, a mineral that weathers easily. This means that, after fossilization, many bones no longer have original calciumsodium hydroxy apatite present. This is especially likely if the bone comes into contact with fluids rich in dissolved minerals, such as commonly occurs after burial. If, however, no fluids are present throughout the history of burial (from the moment that the bone is buried to when it is exhumed by paleontologists, a time interval that could be measured in millions

of years), the bone could remain unaltered, which is to say that original bone mineralogy remains. This situation is not that common, and is progressively rarer in the case of older and older fossils.

Content

1. Reaching back in time
2. To catch a dinosaur
3. Dinosaur days
4. Who’s related to whom – and how do we know?
5. Who are the dinosaurs?
6. Ornithischia: armored, horned, and duck-billed dinosaurs
7. Thyreophorans: the armor-bearers
8. Marginocephalia: bumps, bosses, and beaks
9. Ornithopoda: the tuskers, antelopes, and “mighty ducks” of the Mesozoic
10. Saurischia: meat, might, and magnitude
11. Sauropodomorpha: the big, the bizarre, and the majestic
12. Theropoda I: nature red in tooth and claw
13. Theropoda II: the origin of birds
14. Theropoda III: early birds
15. Endothermy, endemism, and extinction
16. Dinosaur thermoregulation: some like it hot
17. The fl owering of the Mesozoic
18. A history of paleontology through ideas
19. The Cretaceous–Tertiary extinction: the frill is gone

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