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BIOLOGY 102 |
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Macroevolution Biological Kingdoms Updated: |
Tracing evolutionary history: macroevolution.
Macroevolution is the study of what has happened over the long span of life on earth.
Important consideration: the duration of life on earth has been very long.
There have been several major extinctions and several major proliferations of various life forms.
Evidence used to reconstruct evolutionary history of life.
The geological record: sedimentary history and fossils.
Embryology: developmental pathways reflect evolutionary changes.
Homologies: A guide to patterns of relationship.
Molecular biology: A new set of evidence.
Fossils: what is a fossil?
Fossils are any material left behind which can be used to infer the biology of a once living organism.
Examples include: preserved remains of organisms, mineralized remains of organisms, impressions left by organisms (footprints, leaf-prints), dung or other waste products, food fragments, eggshells, etc.
Some general considerations.
Geology provides a sedimentary record of life (and geochemistry, etc.).
Sediment accumulates "bottom up": deeper sediments are older.
Old sediments have been uplifted by geological forces, exposing past profiles.
There is no complete sequence anywhere, but the exposed sequences can be overlapped and thus linked
Do all organisms leave behind fossils?
Most individuals do not leave any trace.
Some types of organisms are much more likely to leave behind good fossils: clams that live in muddy sediments, microscopic aquatic organisms that form ocean and lake sediments, etc. (see p250).
Some types of organisms lived where it was less likely that fossils would be formed: e.g. desert animals and plants.
What can we learn from fossils?
We can observe important aspects of the morphology (shape) of once living organisms. We can then see whether or not a particular structure had developed. Examples: vertebrae, feathers, scales, teeth, etc.
We can compare similarities with still living forms.
What other inferences are possible?
Diet: The structure of teeth, mouth parts, dung, intestinal structure, etc. tell much about the diet.
Behavior: Structure of joints and bones indicate what motions were possible. Upright posture? Flight?
Habitat: Structures reveal habitat: Water? Aquatic organisms are "streamlined", etc.
The Geological Time Scale
The geologic time scale has been developed by studying exposed layers of rocks in many different locations.
Rock layers can be identified from one location to another by their mineralogy or the fossils they contain.
When they were originally formed, the layers were laid down from the bottom up.
The geological eras (p269)
The oldest time period: pre-Cambrian ("older than Cambrian") 4600 million years ago until 590 million years ago.
Paleozoic ("ancient life") 590 million years ago until 248 million years ago.
Mesozoic ("middle life") 248 million years ago until 65 million years ago
Cenozoic ("recent life") 65 million years ago to the present.
How were these intervals selected?
The boundaries between the eras were set because there were major changes seen in the fossil assemblages.
The chronological ages were later added based on radiometric dating.
The major changes seen in the fossil assemblages turned out to be the result of mass extinctions. e.g. 65 million years ago, the Dinosaurs disappeared.
Where did the names come from?
The names were coined by the geologists who did the original detective work.
Example: Silurian and Cambrian were based on the names of ancient tribes who lived in Wales where the geological work on those strata was first done.
The eras are divided into further intervals.
Eras are divided into Periods. The periods were assigned and named in the same fashion.
For the most recent era, the Cenozoic, the periods are further subdivided into Epochs
Continental Drift
Continents have moved about on the surface of the planet.
Current evidence of continental movements: volcanoes and earthquakes
The areas of greatest activity are around the Pacific ocean ( "the ring of fire"), the mid-ocean ridges, the East African rift zone, and other areas.
The past positions of the continents were different.
250 million years ago, all the continents were together in one large continent (Pangaea)
65 million years ago, the continents had broken apart into their present configuration. (India was then an island).
The present day distribution of species reflects the influence of continental drift.
Examples of the influence of continental drift
Marsupials are present on 2 continents: South America and Australia. (Fossil marsupials have been found on Antarctica as well.)
Flightless birds are present on the southern continents: Africa (Ostrich), South America (Rhea), and Australia (Emu)
Reconstructing macroevolution: data from embryology.
Embryological development of plants and animals provides clues of evolutionary sequences.
Small changes in the pace of development of particular structures can lead to large differences and change in function in the eventual adult structure.
Embryology example: larkspurs.
A small change in the pace of development of petals results in a large difference in flower morphology:
Delphinium decorum has fully developed petals and an open flower morphology. This ancestral flower shape attracts bees.
Delphinium decorum has "underdeveloped" petals, resulting in a closed flower shape that attracts hummingbirds.
Embryology example: vertebrates.
In the development of vertebrates, the early stages are more closely similar: structures important in the adult stage of fish are repeated even in mammals. (figure 16.5)
The early embryos of vertebrates strongly resemble one another because they have inherited the same ancient plan for development.
Embryology example: Homonoid skull morphology.
The skull morphology of chimp and human infants is similar.
Humans retain a more juvenile skull morphology as adults. The result is a skull with a much larger brain capacity.
A change in just a few regulatory genes can effect large changes in adult morphology by simply delaying part of the developmental sequence.
Homologies: Traits useful in reconstructing phylogeny.
Homologies, such as the bones of the vertebrate forelimb, can be used to infer the pattern of divergence.
Ancestral homologies identify ancient relationships and "distant relatives".
Derived homologies identify more recent divergence and "closer relatives".
Biochemical evidence.
Molecular biology has introduced many new techniques to the study of macroevolution.
Molecules evolve over time. Divergences of molecules reveal divergence of the species in which the molecules function.
Examples: DNA/DNA hybridization (Panda example) or Cytochrome C (p256)
Macroevolution: The major kingdoms.
Modern biological classification recognizes 5 major kingdoms.
The major kingdoms represent the major branches of the history of macroevolution.
The 5 kingdoms are:
(1) Monerans (bacteria)
(2) Protistans (single celled eukaryotes)
(3) Plants - (4) Animals - (5) Fungi
The Kingdom Monera
The monerans , mostly bacteria, came first: more than 3 billion years ago.
Monerans are single-celled, with little internal structural complexity.
In spite of their structural simplicity, they represent great biochemical diversity.
Monerans include: producers (photosynthetic or chemosynthetic) and decomposers.
The Kingdom Protista.
Protistans are single-celled eukaryotes. They have considerable structural complexity.
Protista are very diverse: photosynthetic algae, molds, amoebas, protozoans, etc.
Most are free-living, but some are parasitic. Example: Plasmodium, the organism that causes malaria.
The Kingdom Plantae
Plants are multicellular, photosynthetic eukaryotes.
Plants possess distinctive cell organelles that provide photosynthesis: the chloroplasts.
Plants are responsible for nearly all the primary productivity on land.
The Kingdom Fungi
Fungi are multicellular eukaryotes that are heterotrophic: the obtain energy by decomposing other organisms.
A characteristic feature of fungi is that they use "extra-cellular" digestion and absorption to obtain their food.
Most fungi are decomposers. A few are parasites or pathogens.
The Kingdom Animalia
Animals are multicellular eukaryotes that obtain their energy by consuming other organisms.
Animals are very diverse: more than 1 million species on earth.
Many animals are herbivores, but there are also many species of parasites and predators.
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