Fossils & Mass Extinction

Speciation Overview

  • Speciation: The process through which new biological species arise.

Global Processes Affecting Speciation

  • Influencing Factors:

    • Climate change.

    • Continental drift.

  • Both processes affect species by altering habitats and climates.

Speciation Rates

  • Speciation rates can increase due to geographical isolation caused by continental drift.

Gradualism vs. Punctuated Equilibrium

  • Gradualism: Slow and steady evolution.

  • Punctuated Equilibrium: Evolution occurs in quick bursts followed by long periods of stability.

Mass Extinction and Speciation

  • Mass Extinction: Significant loss of species (over 50%).

    • Leads to less competition and opens ecological niches.

    • It promotes adaptive radiation, facilitating the emergence of new species.

Adaptive Radiation

  • Definition: Rapid evolution of diversely adapted species from a common ancestor.

  • Often occurs after mass extinction events.

Changes in Gene Expression

  • Changes in how genes are expressed can result in significant evolutionary traits.

  • These changes may lead to adaptations in response to environmental shifts.

Continental Drift and Evolution

  • Plate Tectonics:

    • Continents are on tectonic plates that float on the mantle.

    • Their movement can create or destroy habitats, affecting speciation.

Impacts of Continental Drift

  • Alters ecological and climatic conditions leading to species diversification through:

    • Habitat alteration.

    • Changing climates (poles to equator and vice versa).

    • Promoting allopatric speciation by isolating populations.

Fossil Record and Speciation Patterns

  • Fossils of related species found miles apart indicate past connections due to continental drift.

  • Rapid appearance and disappearance of species in the fossil record suggest episodic changes in environments.

Punctuated Equilibria

  • Characterized by brief periods of rapid change (e.g., emergence and disappearance in fossils).

    • These periods often show symptoms of stasis followed by abrupt changes.

  • Gradualism may not always be recorded due to the incompleteness of the fossil record.

Implications of Mass Extinction on Speciation

  • After mass extinction, survivors face different competitive pressures leading to:

    • Adaptive radiation filling available niches due to environmental changes.

    • Evolution of numerous new species from few survivors.

Historical Mass Extinctions

  • Big Five Extinctions:

    • Major losses of species over Earth’s history; more than 50% extinction.

  • Permian Extinction:

    • 96% loss of marine species; longest recovery times (~5-10 million years).

  • Cretaceous Extinction:

    • Over half marine species and all non-avian dinosaurs extinct.

    • Likely caused by an asteroid impact blocking sunlight, affecting photosynthesis.

Evolutionary Changes Post-Mass Extinction

  • Post-extinction environments are often conducive to adaptive radiation

  • Example: New species emerging quickly to exploit vacant ecological niches.

  • Innovative traits (like flight adaptation in animals) lead to colonization of new areas.

Case Study: Hawaiian Silversword Plants

  • Silversword Plants: A prime example of adaptive radiation and allopatric speciation.

    • Colonized Hawaiian islands circa 50 million years ago, adapting to local conditions.

  • Discussions on:

    • Speciation processes involved (e.g., founder effect).

    • Comparison of gene pools between Hawaiian species and mainland relatives.