Types of Fossils Fossils -a fossil is evidence of life life Body fossils - elements of original body of ancient organisms (e.g., bones, shells, teeth) Trace fossils - traces and structures recording activity of ancient organisms (e.g., footprints, burrows, tooth marks, root marks, coprolites, egg shells) Chemical fossils - relics of biogenic organic compounds that may be detected geochemically in rocks (isotopically enriched carbon, sponge compounds)
Modes of Fossilization Unaltered: simple burial, some weathering. Permineralized: Dissolved minerals precipitate in pore space. Seen in many vertebrate fossils. Recrystallization: Calcite crystals reorder and grow into each other. Original mineralogy remains, but structure is lost. Replacement: Partial to complete replacement of crystals of one mineralogy with another. Includes silicification, pyritization, phosphatization. Carbonization:carbon film left in place of tissues - this may preserve outlines of soft parts, seen in some lagerstatten deposits.
Preservational Bias Hard parts preserve more easily than soft parts Marine environments preserve more easily than terrestrial (more prone to early erosion) Other factors: Post-mortem transport and fragmentation/energy level Biological activity (predators/scavengers) Water chemistry (ex. oxygen level) at burial site and impact on biological activity Rate of burial Diagenesis/mineralization Tectonic “reworking” of strata Erosion of strata
Lagerstätten Extremely important windows into past! Concentration-Lagerstätten: anomolously high amounts of fossil material *Condensation deposits (decreased rate of sedimentation) *Placer deposits (hydrodynamic concentration by currents, eddies) *Concentration traps (holes, pits, caves) Conservation-Lagerstätten: unusually well-preserved fossils *Often requires anoxic bottom conditions (so no scavenging), quiet water (so bodies are not disturbed), rapid burial (to reduce possibility of mechanical destruction of material) *Stagnation deposits (autochthonous conditions of anoxia, low currents, etc.) *Obrution deposits (assemblage is transported into such conditions) *Conservation traps (amber, for example) Examples: Burgess Shale, Mazon Creek, Green River, Yixian Formation
Extinction Background Extinction: Extinction is occurring all the time. The averate rate of extinction over an extended time period is referred to as the background rate. Mass Extinction: A mass extinction occurs when a large number of taxa go extinct in a geologically rapid interval The Big Five are the five universally recognized mass extinctions. End Ordivician Late Devonian Permain-Triassic Triassic-Jurassic Cretaceous-Tertiary We are currently in a period of human driven extinctions that some consider the sixth big event.
Biostratigraphy CHARACTERISTICS OF A GOOD INDEX FOSSIL: *Abundant *Geographically widespread *Easily preservable *Diagnosable *Found in multiple environments (when dead) *Short species duration IMPORTANT INDEX FOSSILS IN DIFFERENT TIME PERIODS Cenozoic: planktonic microorganisms, especially forams Mesozoic: Ammonoids predominate Late Paleozoic: Ammonoids and conodonts Ordovician - Devonian: Conodonts and graptolites Cambrian - Ordovician: Trilobites
Paleoenvironment Depth: presence of benthic vs shallow water organisms can indicate water depth. Temperature: presence of different faunas suggest paleotemperature. Freshwater vs Marine: ostracods, molluscs, etc can distinguish lacustrine and marine settings Direction of flow: Orientation of fossils indicates direction. Randomly oriented fossils may indicate autochthonous deposit. Parellel oriented long bones, tree trunks, and similar fossils will give indication of directionality of flow
Evolution by Natural selection 1. There is heredity of most features 2. There is variation which itself is inherited 3. There is the capacity for growth in population that far exceeds the capacity of the environment 4. Variation leads to differential survival and reproduction rates in the struggle for existence. 5. Differential reproduction leads to the increase in the frequency of the traits that are responsible, leading over time to divergence in form.
The Three Assumptions of Cladistics All organisms are related by descent from a common ancestor. There is a bifurcating pattern of cladogenesis. Change in characteristics occurs in lineages over time.
Cladistic Method Choose the taxa whose evolutionary relationships interest you. Choose an outgroup, that is, a taxon closely related to the group you are studying. Determine the characters, or features, of the organisms and examine each taxon to determine the character states. Determine the polarity of characters by comparison to outgroups Group the organisms by synapomorphies - shared derived character states. Resolve conflict using the principle of parsimony - as in Occum’s Razor, we assume the simplest explanation is correct. The cladogram which requires the least evolutionary events is therefor prefereable.
Phylogeny of Life
Simplified Phylogeny of Plants
Simplified Phylogeny of Animals
Simplified Phylogeny of Vertebrates
A brief tour of the Phanerazoic
Ediacaran The first body fossils of metazoas (animals) occur 575mya- these animals were soft bodied jellyfish, worms, and echinoderms. Predation appears to have been very rare or non-existant.
Cambrian The Cambrian Explosion occurs. Mineralized skeletons appear and life rapidly diversifies. The majority of living phyla appear by the end of this period. Agronomic Revolution- burrowing Organisms disrupt algal matt ecosytem Trophic Escalation - Predator/Prey interactions lead to increase in complexity
Ordovician Marine fauna continues diversifying: trilobites and brachiopods radiate. Tabulate and rugose corals dominant reef builders. First land plant fossils - spores. Glaciation lowers sea level and causes a severe mass extinction at the end of the Ordivician.
Silurian First truly large scale reefs form. The first jawed fishes appear. First vascular plants - Cooksonia First land animals - arachnids, myriapods and mites. These feed on decaying plant and animal material.
Devonian This period is known as the Age of Fishes - armored jawless fish and armored jawed placoderms, and lobe-finned sarcopterygians are very diverse. The earliest well-preserved actinopterygians occur. The first tetrapods evolve. First seed plants, including the first tree: Archaeopteris - reached heights of 20m Mass extinction in the Late Devonian- the stromatoporid sponge-algae rugose coral reef system is decimated and replaced by new reef systems that included bryozoas, new sponges, calcareous algae Cause of extinction debatable - may have involved sea level / climate change. Asteroid impact has also been proposed but compelling evidence is lacking
Carboniferous First amniote fossils - Hylonomus Insects radiate Large plants and lack of herbivores to consume them leads to massive coal deposits.
Permian Gymnosperms largely replace ferns and lycopsids. Two main lineages of amniotes - the diapsids (reptile line) and synapsids (mammal line) radiate
The end-Permian Mass Extinction This was the largest mass extinction in Earth’s history 90% of all species wiped out The leading explanation is the extinction is related to the massive negative C13 anomaly at the boundary. The cause of the appears to be linked to flood volcanism associated with the formation of the Siberian trappes (largest Phanerazoic eruption event known), which may have raised temperatures enough to cause gas hydrate destabilization and massive CH4 release This would have caused super greenhouse effects, a reduction in atmospheric oxygen levels, and widespread ocean anoxia. Evidence for an impact has been put forth butis controversial
Triassic The Triassic is a time of very high diversity on land, with many groups that exist only in the Triassic. Most major groups of living groups of tetrapods appear during the Triassic- this includes turtles, lizards, frogs, crocodiles, dinosaurs and mammals. The first social insects evolve. The end of the Triassic is marked by a mass extinction that dramatically changes the ecosytem for the rest of the Mesozoic. Extinction linked to either CAMP flood basalts or Manicougan impact crater.
Jurassic Dinosaurs attain dominance of terrestrial ecosystems and the first truly large dinosaurs appear. Archaeopteryx, the first bird, evolves in the Late Jurassic.
Cretaceous Faunas become increasingly provicial. Angiosperms (flowering plants) appear and become widespread Ornithischian dinosaur herbivores replace sauropods as the dominant herbivores. There are still no permanent polar icecaps, but climate is relatively cooler than the Jurassic. The End Cretaceous extinction wipes out non- avian dinosaurs, plesiosaurs, pterosaurs, and ammonites.
R. H. Tschudy, C. L. Pillmore, C. J. Orth, J. S. Gilmore, J. D. Knight, Science, 1984
K-T Environmental Stress Time scale Air blast near impact site hours Heat from reentering ejecta (melt) hours Tsunamis near impact site hours to weeks Continent-scale wildfires days to months Interruption of photosynthesis months Nitric acid rain months Cooling from dust months to years H 2 O greenhouse months to years Sulfate aerosol years Destruction of ozone layer > decades Methane greenhouse> +decades CO 2 greenhouse > +decades Modified from Pope et al., 1994
K-T Conclusions 1. There was a giant impact of an asteroid or comet, producing an essentially global impact layer enriched in Ir and having shocked quartz, and various other impact related materials. 2. The impact site was Chicxulub. 3. In oceans and on the continents the impact layer is at least coincidental with the mass extinction. 4. On the continents a post-impact assemblage existed, dominated by ferns for hundreds to thousands of years.
K-T Conclusions, cont’ 5. In Oceans, extinctions are directly followed by a large negative carbon isotopic shift suggesting a sudden mixing of the global oceans and a change in carbon cycling. 6. Fullarenes with extraterrestrial He isotopic ratios have been reported. 7. There was massive outpourings of basaltic lava to form the Deccan Traps (~10 6 km 3 ). 8. K-T boundary is within Deccan Traps. 9. Extinction of the dinosaurs opened up ecological space allowing ascent of mammals.
Cenozoic Paleocene - Mammals Radiate, large avian predators Eocene - First Whales. At the end of the Eocene, many “archaic” mammals go extinct. Miocene: Grasslands spread, primate diversity lower. Pliocene: NA-SA connected by land bridge: faunal interchange and some extinction. In Africa Bovids radiate and hominid diversity is high Pleistocene - First Anatomically Modern Humans
The latest news in paleontology The discovery of feathered dinosaurs has ended debate on the theropod ancestry of birds. Nesting dinosaurs discovered, proving dinosaurs exhibited bird-like parental care. Advances in histological methodology show that theropod dinosaurs had S-shaped growth curves, intermediate between marsupial mammals and placental mammals. The largest Mesozoic mammal ate dinosaurs!
Hu et al, 2005 That just ain’t right!
Past Questions Talk about early life. Talk about the history of vertebrates. Draw a cladogram of tetrapods. Talk about defining tetrapod characters. Draw cladogram of land plants. Define the characters. Give the age and locality of the oldest vertebrate, tetrapod, mammal. K/T mass extinction - what died, what survived? The plausible reasons for that.