What is Paleontology?

Applications

• Biostratigraphy• Systematics• Functional Morphology• Paleoenvironment Reconstruction• Paleoecology

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 distinguishlacustrine and marine settings

• Direction of flow: Orientation of fossils indicates direction. Randomlyoriented 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 features2. There is variation which itself is inherited3. There is the capacity for growth in population that far exceeds the capacity of the environment4. 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

http://www.mansfield.ohio-state.edu/~sabedon/campbl26_files/image009.jpg

Simplified Phylogeny of Plants

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/plantrelat.gif

Simplified Phylogeny of Animals

http://www.cnrs-gif.fr/cgm/evodevo/enindex.html

Simplified Phylogeny of Vertebrates

http://www.mun.ca/biology/scarr/Vertebrate_Classifications.htm

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.

CambrianThe 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 incomplexity

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

From: http://www.museum.hu-berlin.de/min/forsch/csdp.html

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 H2O greenhouse months to years Sulfate aerosol years Destruction of ozone layer > decadesMethane greenhouse > +decadesCO2 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 (~106 km3).

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.