Lab7W10TarPits

Lab7W10TarPits - GE 70B: Evolution of the Cosmos and Life

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GE 70B: Evolution of the Cosmos and Life LABORATORY/DISCUSSION 7 Reconstructing the Mammals of the Rancho La Brea Tar Pits INTRODUCTION In today’s laboratory, you will be studying several aspects of the anatomy of bones in living mammals and then applying what you have learned to infer the diets and identify bone fragments of actual fossils of mammals that were recovered from the Rancho La Brea tar pits. Basic knowledge of the anatomy of living animals provides the evidence that helps paleontologists to construct hypotheses about how extinct animals live (i.e. what they ate, how they moved, etc.). Obviously, the more complete the fossil is, the better is the reconstruction of how an animal lived. However, sometimes even a single fossil fragment is sufficient to not only identify the specific tooth or bone the fragment came from, but also to identify the specific animal it came from as well. Although mammals are highly diverse in their shapes and sizes, many of their bones look the same, especially the limb bones. In other words, a femur (thigh bone) in a human looks very similar to a femur in a dog or a horse. This of course should make sense because these bones are homologous among these animals (i.e. all mammals are descended from a common ancestor). Each of the bones has a distinctive set of characteristics that makes it easy to identify and it is possible to identify some bones by knowing only ONE of those characteristics. As for inferring diet of extinct mammals, teeth are an excellent source of evidence, simply because tooth shape and cusp (bump) pattern correlate very well with diet (i.e herbivores (plant eaters), carnivores (meat eaters), and omnivores (plant and animal eaters)). However, in the absence of teeth, aspects of the shape of the skull provide clues about diet. Thus, in today’s laboratory we will have you learn the names of some bones of the skull and limbs, and then have you apply your newfound knowledge to fossils so as to understand how paleontologists go about reconstructing an extinct animal. BACKGROUND ON THE RANCHO LA BREA FOSSIL DEPOSITS The Rancho La Brea fossil deposits in metropolitan Los Angeles are a valuable source of information about the biotic communities of southern California during the Pleistocene epoch (10,000 to 1.6 million years ago). The majority of the fossils of the Rancho La Brea are located within a 23 acre area at Hancock Park on Wilshire Blvd. The fossils occur in gravels and sands that accumulated on the outwash plain between the Santa Monica Mountains and the Pacific Ocean. The main bone accumulations are restricted to the upper 9m of sediments and are underlain by a bed of sand containing marine fossils and representing the last marine deposits in the region. Many of the larger mammals recovered from Rancho La Brea are similar to species that existed in
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Lab7W10TarPits - GE 70B: Evolution of the Cosmos and Life

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