Final paragraph
Metazoan invertebrates dominanted Ordovician life. While far less famous than the
Cambrian Explosion, the Ordovician encompassed a massive adaptive radiation where
marine faunal genera increased four fold. Carbonate shell-secreting organisms are
particularly successful, and begin to replace the trilobites in continental shelf
communities. These included appearances and radiations of corals, articulate
brachiopods, bivalves, cystoids, gastropods, nautiloid cephalopods, bryozoa and crinoids.
Reef building is dominated by corals. Now-extinct graptolites thrived and Green algae
from which plants probably evolved became common. The first terrestrial plants
resembling liverworts appeared in the forms; spores from land plants have been identified
in uppermost Ordovician sediments. The first jawed fish appeared late in the Ordovician.
Late in the Ordovician Period (443.7 ± 1.5 Ma), mass extinctions of marine life occured
during which some 60% of genera disappeared, thereby creating niches for benthic
(bottom-dwelling) and planktonic (floating, swimming) organisms.
Original materials
Though less famous than the Cambrian explosion, the Ordovician featured an adaptive
radiation that was no less remarkable; marine faunal genera increased fourfold, resulting
in 12% of all known Phanerozoic marine fauna.[2] The trilobite, inarticulate brachiopod,
archaeocyathid, and eocrinoid faunas of the Cambrian were succeeded by those which
would dominate for the rest of the Paleozoic, such as articulate brachiopods,
cephalopods, and crinoids; articulate brachiopods, in particular, largely replaced trilobites
in shelf communities.[3] Their success epitomizes the greatly increased diversity of
carbonate shell-secreting organisms in the Ordovician compared to the Cambrian.[4]
In North America and Europe, the Ordovician was a time of shallow continental seas rich
in life. Trilobites and brachiopods in particular were rich and diverse. The first bryozoa
appeared in the Ordovician as did the first coral reefs. Solitary corals date back to at least
the Cambrian. Molluscs, which had also appeared during the Cambrian, became common
and varied, especially bivalves, gastropods, and nautiloid cephalopods. It was long
thought that the first true vertebrates (fish - Ostracoderms) appeared in the Ordovician,
but recent discoveries in China reveal that they probably originated in the Early
Cambrian. The very first jawed fish appeared in the Late Ordovician epoch. Now-extinct
marine animals called graptolites thrived in the oceans. Some cystoids and crinoids
appeared.
Green algae were common in the Ordovician and Late Cambrian (perhaps earlier). Plants
probably evolved from green algae. The first terrestrial plants appeared in the form of
tiny plants resembling liverworts. Fossil spores from land plants have been identified in
uppermost Ordovician sediments.
[edit] Fungal life
The very first land fungi probably appeared in the Latest Ordovician, following the
plants. Marine fungi were abundant in the Ordovician seas to decompose animal
carcasses, and other wastes.
It ended with a major extinction event about 443.7 ± 1.5 Ma (ICS, 2004) that wiped out
60% of marine genera.