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Animations
(Animation Requirements)

• Continental Drift
• Phylogenetic Tree of Chordates
• Evolution of Fish Jaws
• Ray-Finned Fishes
• Transition to Land
• Reptilian Diversity

Dinosaurs
Dinosaurs dominated life on land for 150 million years, an incredibly long time. In this enhancement chapter we first travel back through time and watch how the dinosaurs evolved. We then trace the history of dinosaurs through the Triassic, Jurassic, and Cretaceous, examining in detail each of the major kinds of dinosaurs as they take their turns in this long, very interesting evolutionary story.

Dinosaurs. Dinosaurs were the dominant large terrestrial vertebrates for 150 million years, until their extinction 65 million years ago, apparently the result of an asteroid's impact. Although classified as reptiles, at least some dinosaurs appear to have been endothermic (warm-blooded). Many of the later dinosaurs sported feathers, and although some ornithologists object to the idea, there seems little doubt that today's birds are the direct descendants of feathered dinosaurs.

1. The isotopes in their bones suggest dinosaurs were warm blooded.
2. The bird you ate for Thanksgiving was a dinosaur.
3. Despite the great "birdosaur" fiasco, birds are still dinosaurs.
4. A small dinosaur with a heart of stone answers an old question.

The Challenge of Invading Land
The first vertebrates to invade the land were descendants of bony fishes. To successfully invade land, they had to solve five additional problems: 1. how to get around out of water (legs); 2. how to avoid drying out (watertight skin); 3. how to acquire oxygen from air (lungs); 4. how to get more oxygen to muscles (pulmonary vein, making dual blood circulation possible); and 5 how to reproduce out of water (amniotic egg).

Dinosaurs: An Evolutionary Success Story
Dinosaurs are the most successful of all terrestrial vertebrates. They dominated life on earth for 150 million years, an almost unimaginably long time — for comparison, humans have been on earth only 1 million years. During their long history, dinosaurs changed a great deal, because the world they lived in changed — the world's continents moved, radically altering the earth's climates. Thus we cannot talk about dinosaurs as if they were a particular kind of animal, describing one "type" that is representative of the group. Rather, we have to look at dinosaurs more as a "story," a long parade of change and adaptation.

Amphibian Eggs Hatching in Shallow Ponds Thirst for Oxygen
Amphibians evolved from aquatic vertebrates, completely dependent upon an aquatic environment for their existence, into semi-terrestrial animals less dependent on water. Amphibians, however, must return to water to reproduce. Oxygen availability in the water is an important factor in aquatic ecosystems, because it impacts the development of amphibian embryos. Most amphibians lay their eggs in shallow, temporary ponds or wetlands where the eggs are protected from predatory fish. Such habitats, however, are likely to have low levels of oxygen resulting in hypoxic conditions for the developing amphibian embryos. Few studies have examined the effects of hypoxia on amphibian embryo development, hatching success, and survival. M. Christopher Barnhart of Southwest Missouri State University has undertaken such a study, examining hypoxia in four amphibian species. He removed the eggs of frog and salamander species from their natural environments and placed them into an oxygen-controlled chamber where he could monitor hypoxia-induced changes in the developing embryos under conditions of different oxygen availability.