GEOLOGY

Detailed explanation-1: -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-2: -Bryozoans (moss animals) and brachiopods (lamp shells) were a dominant component of many assemblages.

Detailed explanation-3: -At the time of the extinction, around 100 marine families became extinct, covering about 49% of genera (a more reliable estimate than species). The brachiopods and bryozoans were strongly impacted, along with many of the trilobite, conodont and graptolite families.

Detailed explanation-4: -While all of the phyla but one were established during the Cambrian explosion, taxonomic increases during the Ordovician were manifest at lower taxonomic levels although ordinal level diversity doubled. Marine family diversity tripled and within clade diversity increases occurred at the genus and species levels.

Detailed explanation-5: -During the Ordovician, many new species replaced their Cambrian predecessors. In addition, primitive plants called lycophytes began to move onto land, which was barren until then. Later, in the Devonian, other types of plants colonized terrestrial habitats.