Devonian

When was the Devonian

~419–359 Ma

What key events happened in the Devonian

-Evolution of lobe-finned fish (e.g., Tiktaalik) and first tetrapods

-Terrestrialisation of vertebrates

-First forests form with early tree-like plants

-Explosion of reef-building organisms in shallow seas (2nd most reef rich time period with the first being current day)

-Late Devonian mass extinction affects marine ecosystems

What was the Devonian Reef Maximum

Where reefs were found across wider geographic area and at higher latitudes than any other time in Earth history thus structure/development known in great detail

What is the Rhynie Chert

Fossil found in Scotland containing an entire ecosystem preserved in a silicified hot spring deposit. The small plants, invertebrate land animals, fungi and cyanobacteria were instantly petrified, and have been preserved in astonishing detail. Active ground predators within the microenvironments of the plants were found inside empty sporangia and rotten stems

What impact did the development of plants have on Earth’s systems

Change in atmospheric composition, the hydrological cycle, sediment transport and the nature of the sedimentary rock record, and albedo and global temperatures

How did lobe finned fish evolve into the first tetrapods

Driven by shallow-water environments rich in vegetation and low in oxygen, as well as less competition and more food sources, these fish adapted their fleshy, bony fins into weight-bearing limbs and modified their swim bladders into lungs.

What adaptations did lobe-finned fish face to become tetrapods

-The skeletal structure (like the humerus bone) had to transform from light, flexible fins into robust, elongated limbs capable of bearing weight against the force of gravity

-Fish were "bimodal breathers" (due to deoxygenated waters), using both gills and primitive lungs (modified swim bladders) to gulp air from the surface

-The skull flattened, moving the eyes to the top of the head for spotting prey above the surface. The neck elongated, allowing the head to move independently of the body.

-Still needed to be close to water because amniotic eggs had not yet evolved. Matrix of environments

When was the Late Devonian extinction

~372-359 Ma

What caused the Late Devonian extinction

Three geologic stages with high extinction rates occurring similar time to the first forest forming trees. Land plants developed deep roots, releasing an abundance of nutrients into the oceans that fed algae. Because of this, algae blooms consumed vast amounts of oxygen (O2) in the oceans, suffocating many species. Increase in nutrient delivery to the ocean leading to oceanic anoxia and regionally low levels of dissolved oxygen.

What are the impacts of the Late Devonian extinction

Big losses of reef builders, early tetrapods and placoderm fishes prolonged crisis, climate and reef collapse. 75% of species lost including brachiopods, bivalves and sarcopterygians. 35% of genera and 19% of families also extinct