BIO342H5 Lecture Notes - Lecture 19: Bowhead Whale, Petrified Wood, Passenger Pigeon
Document Summary
Fossils: a fossil is any trace left by an organism that lived in the past, 4 general categories of fossil formation, compression fossils, casts and molds, permineralized fossils, unaltered remains, compression fossils. How: compression and compaction from overlying sediment (i. e. the pressure from the sediment), leaves behind a carbon film. Molds consist of unfilled spaces; casts form when new material infiltrates the spaces and hardens into rock. What: preserves internal and external structures (e. g. petrified wood) Transitional forms: darwin"s concept of descent with modification predicts that species are descended with modification from earlier forms. If fossils represent ancestral populations then it should capture evolutionary transitions: that is, species that retain some ancestral traits as well as new traits. Example archaeopteryx: first specimen of archaeopteryx has head, tail, feather, bones showing the transitional forms from earlier pterapod dinosaurs with big teeth and claws to flying dinosaurs i. e. evolution towards the bird lineage.
