Evolutionary Biology BIOL 3350 Dr Lisa Rapaport Lecture 2 Notes The Evidence for Evolution I Evidence of change in the earth A Geology 1 Fossils are found in layers of sediment in the earth Different layers different types of fossils Azoic layers are always deeper than zoic layers Azoic layers are layers that do NOT contain evidence of past life do NOT have fossils Zoic layers are layers that do contain evidence of past life do have fossils 2 Stratigraphy Different layers correspond with different time periods At the beginning of the Paleozoic time period there was an explosion of many different types of organisms mass extinction of the end of the Paleozoic time period 90 of marine life disappeared during this mass extinction There is a layer of basement rocks at the bottom these rocks are very hard such as granite and schist and do not contain fossils or evidence of past life 3 Principle of superposition Principle of superposition Layers that are found lower in the rock formation are older than the layers that occur higher up The thin reddish layer that is running through the other 3 layers is likely younger than the other 3 layers because of plate tectonic movements when the plates move diagonal layers form when 2 new plates come into contact with each other We do not have absolute dates as to when these layers were formed so we just base their relative time period formations off of their positions among the other layers this is relative dating estimated not exact 4 Principle of cross cutting relationships Principle of cross cutting relationships states than an igneous intrusion is always younger than the rock it cuts across sometimes magma pushes or intrudes into cracks in existing rocks when the melted rock cools and solidifies the resulting feature is called an igneous intrusion Igneous rock rock formed from volcanic eruptions magma that has cooled to rock 5 Principle of faunal succession Principle of faunal succession The lower fossils are more primitive older than the fossils that are in the higher levels of 1 sediment the lower level fossils represent an earlier stage in evolution for group that shows relation also in higher levels 6 Location of fossils allows reconstruction of phylogeny and time since divergence from common ancestors Look how certain traits may have changed through time from organism in lower level to related organism in higher level Guanlong fossil found by scientists that was dated to 160 million years ago 9 foot long fossil of T rex had number of traits found in T rex but lacked some traits Had 3 fingers on its hand instead of 2 3 fingers was a more primitive feature 2 fingers was a more advanced trait that evolved later Body size increased through evolutionary time because it became more important over time 7 Radiometric dating indicates that the earth is very old 4 5 4 6 billion years old B Phylogenies reconstruct evolutionary history Cladogram shows the relationships among a group of species Cladogram is a hypothesis of the pattern of how traits have changed evolved over time The further down on a cladogram is where the more ancient traits are the more recent traits are listed towards the top of the cladogram The species at the tips of the cladogram the terminal nodes are living species Species listed below the terminal nodes are species that are no longer living Species that share a recent branch are more closely related to each other than they are to the other species on the cladogram they share a recent common ancestor Refer to the corresponding cladogram in Lecture 2 PowerPoint Taxon 2 and Taxon 3 are sister taxa Taxon 4 and Taxon 5 are sister taxa Taxon 5 and Taxon 6 are sister taxa Taxon 4 and Taxon 6 are sister taxa Cladists like to have only 2 braches coming off of each node 2 pronged branches C Phylogenies allow us to understand the origin of key innovations In the 1970s John Astrum a professor at Harvard noticed similarities between a group of dinosaurs theropods and birds In 1996 the Sinosauropteryx was discovered It did not have just scaley skin It had a thin layer of filaments on its back and tail Feathers are hypothesized to have evolved in dinosaurs and now they are prominent on birds 2 Simple kinds of feathers proto feathers are hypothesized to have began with dinosaurs Dinosaurs and birds both have wishbones Early beginnings of feathers were found in many dinosaur lineages Hypothesis of the evolution of feathers starting in the theropods Single unbranched little filaments like A were the beginning Now feathers are asymmetric to allow for more aerodynamic feathers in modern day birds The living group is called the crown group because it is at the top of the cladogram birds are still living so they are referred to as the crown group None of the dinosaurs were able to use their feathers to fly because their arms were too short and their bodies were too large but not all birds use their feathers to fly It is likely that dinosaurs used their feathers to run faster on land and eventually this evolved into birds flying as they ran faster and faster their arms got longer and their bodies got smaller all to make them more aerodynamic and able to get off of the ground and create lift this is a hypothesis NOT a theory because theories are ideas that have been tested again and again and have been continually supported D Early hypotheses to explain changes on the Earth 1 Catastrophism Cuvier 1769 1832 Series of floods and successive sedimentation accounts for different layers strata Each layer shows separate creations by God These kinds of catastrophes are no longer seen on Earth today Fossils were left by events that no longer occur on Earth 2 Uniformitarianism Hutton 1788 Lyell 1830 Geological processes are gradual they occur over long periods of time not quick occurrences It is logical to conclude that the Earth is very very old Uniformitarianism hypothesizes that processes that we can observe today account for these changes that we accumulate on Earth changes in the Earth take place over vast periods of time E How old is the earth 1 Radiometric dating Parent isotopes decay exponentially to daughter isotopes Some elements on Earth are not stable they are radioactive by losing neutrons they can become a different element Look at rate of change over time at proportions of radioactive elements at different times to see how much time has passed 3 Overtime the parent isotope decays into another element daughter element until eventually none of