Lecture 16

Lecture Notes on The Ordovician and the Rise of Land Plants

The Ordovician and the Rise of Land Plants

  • Key Events in the Ordovician Period

    • Rise of land plants and significant developments in marine life.

    • Important biodiversity events, notably the Great Ordovician Biodiversity Event (GOBE).

  • Cambrian Explosion

    • Characterized by a rapid increase in diversity of life forms, particularly with hard parts noted in the fossil record.

    • Darwin's dilemma: Apparent contradiction between slow evolutionary changes and sudden appearance of diverse life in Cambrian.

  • Biodiversity Dynamics

    • The GOBE represents the initial appearance of many major animal phyla in the fossil record, but it is false to say most appeared then.

    • Expansion of plankton during GOBE increased food resources, boosting marine life diversification.

  • Trace Fossils and Early Life

    • Presence of ichnofossils in pre-Cambrian strata indicates early multicellular organisms capable of movement existed before complex body fossils appeared.

    • Kimberella gut contents suggest diets of microbial algal and cyanobacteria mats.

  • Predation Evolution

    • Emergence of predation linked to the evolution of sensory organs, especially eyes, driving predator-prey dynamics.

  • Adaptation of Early Land Plants

    • Shift from aquatic to terrestrial natures required innovations like:

    • Pigments: Evolution of protective pigments and waxy compounds (e.g., flavonoids) helped mitigate UV radiation.

    • Stomata: Key for gas exchange regulation and reducing water loss via transpiration.

  • Geological and Environmental Preconditions

    • Life's transition required specific sedimentary rock types conducive to fossil preservation and coastal, near-shore environments.

    • Early land flora first emerged approximately 430 million years ago, while major innovations in terrestrial ecosystems began in the late Devonian.

  • Significance of Tiktaalik

    • A transitional fossil between fish and tetrapods, exhibiting both fish and tetrapod characteristics, considered a 'missing link' in evolution.

  • The Permo-Triassic Extinction

    • Marked as a major extinction event where around 70% of terrestrial vertebrates and 90% of marine species perished, leading to the concept of the 'great dying.'

    • It was characterized by large extinction rates among insects, and multiple hypotheses for its causes include:

    • Massive volcanic activity (Siberian traps)

    • Ocean anoxia and global warming

    • Marine regression and environmental shifts.

  • Lazarus Taxa

    • Some extinct species may appear millions of years later, termed "Lazarus taxa," possibly due to their survival in isolated refugia.

  • Geologic Time Scale and Major Eras

    • Division of the Paleozoic Era (e.g., Cambrian, Ordovician) with key evolutionary milestones, extinction events like the P-T extinction, and transitions in fauna and flora with each period.