GEOLOGY

Detailed explanation-1: -The timing of diversification differs for each group of organisms and on each of the Ordovician continents. For example, graptolites reached their peak diversity in the Early Ordovician Epoch, whereas gastropods continued to diversify steadily through the entire Ordovician Period.

Detailed explanation-2: -After this ‘explosion’ of animal phyla, over 40 myr occurred before the start of the Early and Middle Ordovician diversification (ca 485 to 460 Ma) that can be considered largely as an ‘explosion’ of diversity at lower taxonomic levels.

Detailed explanation-3: -The Ordovician is best known for its diverse marine invertebrates, including graptolites, trilobites, brachiopods, and the conodonts (early vertebrates). A typical marine community consisted of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods.

Detailed explanation-4: -Possible causes include changes in palaeogeography or tectonic activity, a modified nutrient supply, or global cooling. The dispersed positions of the continents, high level of tectonic/volcanic activity, warm climate, and high CO2 levels would have created a large, nutrient-rich ecospace, favoring diversification.

Detailed explanation-5: -First vertebrates appeared on Earth in Ordovician, today we classify them as jawless fish. That’s why Ordovician and Silurian periods are often called ‘Age of fishes’. Moreover, first jaw fish also showed up in Ordovician, about 10 million years later.