The Missing Loonie Riddle
Sources of Evidence for Evolution
1.Fossil Evidence2.Biogeography Evidence
3.Anatomy Evidence4.Embryology Evidence
5.DNA Evidence
1. Fossil Evidence
• As new rock is formed, the older rock layers become deposited under the new rock layers.
• Creates a geological time scale
• In each of the layers of rock, different fossils can be found according to major extinction events.
• Comparing fossils at various depths, one can compare fossil records
Fossil Records: In Summary• Fossils found in young layers of rock (closer to
the surface) are similar to species alive today than the one’s found in older (deeper) layers of rock.
• Fossils appear in chronological order in rock layers.
Transitional Fossils
• Transitional Fossils – a fossil that shows the intermediary links between two groups of organisms with slight different features.
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Transitional Fossils – Evidence of Evolution
• The modern day whale evolved from an aquatic species Dorudon which contained a hind limb.
• Dorudon evolved from terrestrial species which had a function for the hind limbs.
Transitional Fossils
Fossil evidence suggests that modern toothed whales evolved from a terrestrial ancestor.
Modern toothed whale
Rodhocetus kasrani – had small hindlimbs
Ambulocetus natans – likely walked on land
Pakicetus attocki – lived on land
Dorudon and Basilosaurus – (not shown)
Whale Evolution Summarized
2. Biogeography
The study of the past and present geographical distribution of organisms
Geographical Distribution
• Geographically close environments are more likely to be populated by related species than locations that are geographically separate but environmentally similar.
• Species found on islands often closely resemble species found on the nearest islands and continents.
• Animals that are found in areas close to one another are often closely related.
• They may however have different features due to environmental differences.
• E.g. Darwin’s Finches
Closely Related But Different Features
• If two species live far away from one another but live in similar environments they are likely to have similar features. – Environment puts selective pressure for a species to
adapt to the environment.
– Evolved from different ancestors
Distantly Related But Similar Features
Geographical Distribution - Fossils
• Fossils of the same species can be found on the coastlines of neighbouring continents.– Due to the fact that the world was once
Pangaea.
• Closely related species are almost never found in exactly the same location or habitat.– Due to competition
3. Anatomy Evidence• Homologous structures – structures that have
similar structural elements and origin but may have a different function
• Analogous structures – structures of organisms that do not have a common evolutionary origin but perform similar functions.
Analogous Structures
• The camera type eye in vertebrates (e.g. humans) and mollusks (e.g. octopus) evolved separately but function in a similar way.
• Vestigial structures – are remnants of structures that may have had important functions in ancestral species but have no clear function in some modern descendants.
Vestigial Features in Humans
4. Embryology
• The study of early, pre-birth stages of an organism’s development
Embryology Developed
• Embryos of closely related organisms often have similar stages in development.– All vertebrates at some point of development
possess gill pouches (eventually develops into the chin and other skull bone structures).
– All vertebrate animals have tails during development (some will continue to develop their tails while others do not)
5. DNA Evidence• If two species have similar patterns in their DNA,
these DNA sequences must have been inherited from a common ancestor.
Homework/In-class Questions
• # 1, 3, 5, 8-12 (page 340)
