This would have drastic effects on animals because they were aquatic. The fossil record is not complete because many of the animals were of the soft tissue type and did not leave adequate fossils. There are fossils of animals with some type of skeleton such as brachiopods, trilobites and the conodonts. The extinctions caused massive decreases in the diversity of species suffered considerable losses in diversity. During the Ordovician period there was again an increase in biological diversity.
Geologic evidence suggests that the extinction was the result of a period of glaciation.
The formation of ice sheets affected sea levels and changed marine habitats that had deleterious effects on marine life. Echinoderms, trilobites, nautiloids and many other groups were affected but not as severely as in other extinctions. There also seems to have been two peak periods of extinction - one at the beginning of the glaciation when sea levels dropped, and another at the end of the extinction, between 500 thousand and 1 million years later, when sea levels rose rapidly. Most of the lost species lived in aquatic environments, which suggested that global cooling reduced sea levels leading to disruption of the marine environment. Marine species such as Brachiopods, ammonites and many other invertebrate groups and vertebrates such Agnathan and Placodermfish were affected.