BAESI

1. April 28, 2012Major Evolutionary Transitions 1: Dinosaurs and Birds (Or, “This Chicken Tastes Like a Dinosaur”) Instructor: Jonathan Hendricks Assistant Professor of Paleontology, SJSU, Dept. Geology Email: jonathan.hendricks@sjsu.edu BAESI

2. Slide shows a drawing of the “London specimen” of Archaeopteryx. Archaeopteryx The recognition that birds are closely related to dinosaurs began with the discovery of Archaeopteryx in 1861. “London Specimen”: Jurassic Solnhofen Limestone, Germany. About the size of a crow. 7 more specimens subsequently found. Transitional features between dinosaurs and birds.

3. Slide shows a photograph of the “Berlin specimen” of Archaeopteryx. Archaeopteryx – Berlin Specimen A second, and much better, specimen was found in 1877. “Berlin Specimen”: Has been called “the most important natural history specimen in existence, comparable perhaps in scientific and even monetary value to the Rosetta stone” (Feduccia, 1996). Most illustrated fossil ever. By: H. Raab (Wikimedia Commons)

4. Dinosaur/reptilian features of Archaeopteryx: Mouth full of teeth. Long, bony tail. “Dinosaurian hand” with long fingers and curved claws, including “velociraptor” type curving second digit. “Dinosaurian foot”. No sternum (breastbone). Similarities in fore-limb structure. Bird-like features of Archaeopteryx: Feathers!! Fused collarbones forming a wishbone. Large brain (similar in relative proportions to modern birds). Hind-limb similarities. Archaeopteryx – Dino & Bird Features

5. Slide shows a painting of Archaeopteryx. Paleobiology of Archaeopteryx Oldest known bird or not? Depends who you ask and what phylogeny you consider. The “line” between what is a dinosaur and what is a bird is has become increasingly complicated by amazing recent fossil discoveries. Definite bird fossils are known from Cretaceous and younger deposits. Available evidence suggests that Archaeopteryx was probably not a very good flier.

6. Slide shows a photograph of a reconstruction of a sauropod and a photograph of a chickadee with an arrow connecting the former to the latter; a “NO” symbol is overprinted on the arrow. When we say that birds are dinosaurs, we DO NOT mean that all dinosaurs evolved into birds!! What we mean is that ONE lineage of dinosaurs very likely gave rise to birds. So, which lineage was it? Which Group of Dinosaurs Did Birds Evolve From? By: “Mdf” (Wikimedia Commons) By: “Minnesota Jones” (Wikimedia Commons)

7. So Which Group Was It? Answer: Birds are thought to have evolved from the “maniraptoran” therapod dinosaurs. The “raptors” of Jurassic Park fame are examples of “maniraptorans”. Examples: Deinonychus, Velociraptor, Microraptor, Sinornithosaurus, etc.

8. Deinonychus Stiff Tail. • Slide shows three photographs of a skeleton of Deinonychus. The photographs detail the stiff tail and terrible claw of this dinosaur. Terrible Claw! By: Jonathan Hendricks

9. Evolution of Feathers Why did feathers evolve? The first function of feathers was probably NOT for flying. Feathers ARE NOT a requirement for flight in vertebrates (consider featherless bats and pterosaurs). First function(s) of feathers: • Thermoregulation (downy feathers very good for that, but are long feathers?). • Camouflage or sexual display?

10. Li et al. (2010 in Science) Jurassic of China. Theropod dinosaur that was the size of a chicken. Scientists studied preserved pigmented structures called melanosomes on fossil dino feathers. Melanosomes are present on modern bird feathers (responsible for feather color). Compared fossil melanosomes to those of modern birds to determine color. Anchiornis