Lecture 5  Fossils, preservation and paleoenvironment

Focus Question:  What kinds of information can we get from fossils?

1.        Fossils are the remains of ancient organisms, and include

Hard parts-such as bone, teeth, shells

Sometimes soft tissues under special preservation circumstances

Plant remains-trees, leaf imprints, pollen

Biomarkers-such as ancient DNA (aDNA) and organic molecules

2.       Types of preservation include

Unaltered-soft tissues are still present (although maybe frozen, desiccated, or enclosed in amber or volcanic ash

Recrystallized or Replaced by recrystallization of calcium carbonate, or replacement by another mineral

Carbonized-only the carbon film of the organism is left behind, as all the lighter elements are gone-common in plants (think coal) and in fossil fish

Permineralized-the pores of wood and bone can be filled in with minerals (typically silica).  This happens most commonly when the objects are buried where groundwater can reach them.

Molds, Casts, footprints, tracks, trails—the object is long gone, but traces of it remain. 

Biomarkers-organic molecules can be preserved in sedimentary rocks-such as aDNA, plant cellulose, and plant lipids and pigments

3.        Fossils are routinely used to get several kinds of information

A.       Stratigraphic correlation-biozones-sedimentary units defined by their fossil content

Index or Guide Fossils

B.       Reconstruct past environments-fossil assemblages can indicate past ecosystem structure, past environmental conditions

C.      Development of body plans, inheritance patterns, and evolutionary change

D.      Find energy sources, such as oil, gas, and coal.  All these are produced biologically, and the fossil record is used to locate these supplies.

4.        Fossils are the remains of ancient organisms, and organisms are classified as Eukaryotes (their cells all have a cell nucleus that houses their DNA) or Prokaryotes (their cells do not have a nucleus, and the DNA is free in the cell.

Eukaryotes-cells have a nucleus, organelles, and a simple outer wall.

Prokaryotes-cells  have no nucleus, no organelles, but have a complex  outer wall.

A.       Eurkaryotes-The kingdoms of

Animals,

Plants

Fungi

Protists (these are one-celled organisms, and each cell has a nucleus)

B.       Prokaryotes-The kingdoms of

Archaea-single celled microbes with no nucleus in the cell-they like extreme conditions  “extremophiles”

Bacteria-single celled microbes with no nucleus in the cell

All the organisms we will talk about throughout the fossil record fit into these groups.

Focus Question What factors drive variation in populations?

1.        Variation in living things is observed to exist at many levels.

                Variation among individuals in the same family

                Variation among individuals in the same species

                Variation among different species

What is a species?  A species is a group of individuals that breed successfully in nature, and are reproductively isolated from other groups.

2.        Variation, whether at the individual, subspecies, or species level, is driven by

                Ecological processes

                Developmental processes

Genetic processes

                Evolutionary Processes

3.        Today we will be looking at Ecological processes and Developmental processes.  Take some time to become familiar with a few very common ecological terms – here is a short list  – you may already know many of these terms:

Habitat-a geographic setting inhabited by an organism

Population-a group of individuals belonging to a single species, living in a particular area

Community-populations of several species living together in a habitat

Biomes-major regional communities (think desert community, or grasslands community)

Ecosystem-the organisms of a community and their habitat together

Niche -the ecological role of a species in its habitat (for example, the role of browsing herbivore)

Diversity – the number of species that live together within a community

Limiting Factors-environmental conditions that limit a species occurrence (such as temperature, or salinity, or rainfall…)

Opportunistic  species-species that specialize in invading newly available habitats-you probably have seen weeds do this on a newly seeded lawn-dandelions move in very fast.

Competition-the demand by two or more species (or individuals) for a resource perceived to be in limited supply (for food, for a mate, etc.)

Extinction-the complete disappearance of a species from its habitat.

 Carrying capacity-the maximum number of organisms that can be supported in a given habitat

4.        Organisms have tolerances for physical and biological factors that determine where they can thrive, or simply survive.

                Physical factors include temperature, rainfall, sunlight, oxygen supply, soil type…

                Biological factors include predator-prey interactions, availability of food, a mate, competition for niche space…

5.        Niche space can be narrow or wide.  Organisms can co-occupy a habitat by occupying different niches-highest diversity on land is in rainforests, and in the oceans, in coral reefs

6.       Developmental Processes

1)      Environmental influence on how the organism grows and its final shape

This is termed Ecophenotypic variation.  A Phenotype is the outward appearance of an organism.  Eco-refers to ecological influence.

2)      Timing of developmental growth stages influence how the adult organism appears.

This is termed Heterochrony, meaning, variable timing.

3)       Reproductive strategies-some organisms (mostly all invertebrates) alternate sexual generations (both males and females are present) and asexual generations (just the females are present).

4)      Reproductive strategies-producing different kinds of eggs-(mostly all invertebrates) produce in a single clutch of eggs some with different hatching schedules.

Next Lecture-Fossils and Evolutionary Processes