MACROEVOLUTION and EXTINCTION: Are they related?

I. MACROEVOLUTION deals with large scale patterns of species, genera, familial, ordinal and phyla patterns of change over geological time.

Much of evolutionary record comes from fossil record. Questions that we can ask of the fossil record:

1. What are evolutionary patterns overtime

2. How long does evolution take?

3. What is the evolutionary tree of relationships?

4. Are there patterns of diversification that occur over and over?

5. How did there come to be so many kinds of things and have there been increases in the number of things over geological time.

How do we reconstruct evolutionary history.

1. Geological history and Evolutionary history are related: volcanism, rise of mountains, continental drifting, change in sea level, change size and importance of polar glaciation.

2. How do we determine relationship between taxa? Ochams Razor--simplest answer or fewest changes between two points is most likely. Now called PARSIMONY. A method applied to all in this list.

3. Genetic relatedness of closest living relatives of primitive groups. DNA sequences (ATTGCCAGT etc.),

DNA hybridization, Immunological comparisons--Antibody binding intensity of related forms.

4. Embryology (prebirth) and Development (post birth)

a. Origin of tissues (homologies) from germ plasm. E.g. Changes in structure of aortic arches and jaw structure.

b. Development regulatory changes of genes that control the expression of other genes or control processes that build structures.

5. Comparison among adult structures--homologous vs. analogous structures

a. Homologous structures (homo = same origin) are the same structure that has changed in form from a common ancestor. Map morphological DIVERGENCE of structures with change in structure from a primitive form. e.g. vertebrate forelimb (p192) in all vertebrates has one proximal bone=humerus; two middle bones=ulna and radius; and 5 digits distally. The modification of the bones in all vertebrates show an evolutionary constraint. This is the limits place on what can evolve by what has already evolved. Origin of bones often seen in the embryological development.

b. ANALOGOUS Structures p192) (analogy= a comparison of something different in origin) are structures that differ in origin but CONVERGE MORPHOLOGICALLY by similar function. e.g. Swimming fins of shark (early fish class Chondricthyes), penguin ( class reptilia-birds), and porpoise (class mammalia).

II. GEOLOGICAL and BIOLOGICAL HISTORY of LIFE ON EARTH are interlinked.

Life on earth is a series of adaptive radiations of species followed by rather rapid mass extinctions. Rather than being a slow and gradual process, both radiation of species, genera and families, and their extinction are rapid in geological time.

A. ADAPTIVE RADIATION: In a new environment, an existing lineage fills the niches in that environment with a bursts of microevolutionary speciation. Adaptive radiations are common in the first few million years after mass extinction.

Radiations have taken place in adaptive zones as in 'reef organisms' or 'burrowing in seafloor'. Either the colonist arrives in an unoccupied niche or outcompetes residents.

Radiations may involve a key innovation, a modification of a structure that permits an individual to exploit the environment in an improved or novel way e.g.

a. Wings in birds and bats allowed freedom from predators for a while

b. Warm-blooded organisms active in the cold.

c. Care of young to improve survival of offspring.

B. MASS EXTINCTIONS: Although speciation and extinction occur continuously, these are refinements on a theme. Major new directions in evolution often follow mass extinctions, when many if not most niches are left unoccupied. A mass extinction is an abrupt rise in extinction rates above the background level. Often this is catastrophic and global in which major groups of species are wiped out almost simultaneously.

Possible--massive undersea volcanism, Asteroid or huge meteor impact (65mya, 205 mya), massive glaciations as landmass Gondwana crosses pole(435mya) and changes in sea level and land surface area.

.

In past 10 years asteroid catastrophes find credibility for the most recent extinction event 65mya.

1. Iridium, a heavy element, found on earth sinks to center because of gravity. Source on surface now comes from asteroids and meteorites. A high level of Iridium has been found around the world at the Cretaceous/Tertiary boundary when Dinosaurs disappeared.

2. Hypothesis asteroid 10 km diameter hit earth.

As meteorite turned to dust on impact a darkened cloud spreads Iridium around the globe.

3. Cycle of biotic extinctions is about every 26 million years.

4. Dating meteoritic craters on earth is roughly the same time scale every 28 million years. Two are related and not random. Causes of regularity are debated:

Hypothesis1: Comets from Oort cloud, a massive number of comets circle the sun outside Pluto's orbit, which may be perturbed to give such a cycle.

Hypothesis 2. Solar companion = another object orbiting the sun in eccentric orbit which approaches oort cloud, sending comets crashing towards the earth. Testable, next event 13 million years.

EXTINCTIONS ARE NOT ENTIRELY RANDOM—Specialists loose, generalists survive.

Mass extinctions are not entirely random in who goes extinct. Upto 96 % of all species go extinct (Permian extinction) in one blow. Species rich groups of highly specialized species are big losers. Species poor groups are more generalized, wider distribution, broader ecological tolerance that allow them to exist through a mass

extinction.

C. History of Mass Extinctions

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Period Background Fish Amphibians Reptiles Extinction

Rate

(# families/10^6 yrs)

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CAMBRIAN 1.56 -- -- --

ORDOVICIAN 0.96 50 -- --

SILURIAN 1.96 30 -- --

DEVONIAN 1.50 70 90 --

PERMIAN 2.00 55 80 80

TRIASSIC 2.11 25 90 85

CRETACEOUS 0.74 35 75 80

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D. MAJOR GEOLOGICAL ERAS in earth history show in their fossils the progressive radiations in life forms from a series of large extinction events.

1.PRECAMBRIAN ERA

a. ARCHEAN ERA

First life 3.7-2.5 bya --origin of life on earth

simple bacteria-like things

single cells

first photosynthetic prokaryotes.

Atmosphere of ammonia, carbon dioxide, methane, water vapor, nitrogen.

b. PROTEROZOIC 2.5 billion to 700 mya.

bacterial mats produce oxygen, precipitation of oxidized iron and CaCO₃

origin of eukaryotes-complex single celled organism

having nucleus and membrane bound organelles.

origin of first metazoans

2. PALEOZOIC 700-550 mya to 240 mya

a. origin of organisms with hard parts e.g. Trilobites

b. origins of most phyla of animals of marine invertebrates-sponges, corrals, bryzoans, flatworms, polychaete worms, tunicates.

c. first fishes, first jawed fishes, first move to land amphibians and origin of reptiles.

Ends with Permian extinction of 96% of all marine species.

3. MEZOZOIC 240-65 mya

Flowering plants radiate, gymnosperms still dominate land

dinosaurs radiate

origin of mammals

Nautoloids radiate in sea.

Asteroid impact eliminates large reptiles.

4. CENOZOIC 65mya to present.

Mountain building worldwide. Separation of continents as tropical forest of Pangea breakup.

Radiation of bony fishes

Radiation of flowering plants in a coevolutionary radiation with pollinating insects. Radiation of mammals and birds. . Origin of primates and man.

Sequence of recent glaciations.

Beginning of human caused mass extinction.