Britannica
Sources used in this answer
Which organisms were most affected by the end-Ordovician extinction?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
Ordovician Period
The distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the Ordovician Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.
The end-Ordovician extinction, which eliminated an estimated 85 percent of all species, primarily affected marine invertebrates that were endemic to specific regions, such as those living in the broad, shallow epicontinental seas.12
Groups that were particularly impacted include:
- Brachiopods: These were hit especially hard, particularly those confined to the continent of Laurentia. Only 17 percent of late Ordovician brachiopod genera survived into the Silurian Period.132
- Trilobites: These organisms experienced significant losses, with 63 percent of genera successfully making the transition to the Silurian.32
- Corals: Tabulate and heliolitoid corals were also affected, with only 29 percent of genera surviving.3
- Other groups: Conodonts, acritarchs, bryozoans, and graptolites were similarly impacted, particularly those that exhibited regional rather than global distribution patterns.12
The extinction occurred in phases, driven by global cooling and significant sea-level fluctuations associated with glaciation over Gondwana, which drained shallow habitats and disrupted marine ecosystems.12