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Some cystoids (primitive stalked marine animals related to modern starfish and sand dollars) and crinoids (called sea lilies and feather stars; also related to starfish and sand dollars) appeared.Green algae were common in the Ordovician and Late Cambrian (perhaps earlier). The first terrestrial plants appeared in the form of tiny plants resembling liverworts.The event seemingly was preceded by a fall in atmospheric carbon dioxide (from 7000 ppm to 4400 ppm), which selectively affected the shallow seas where most organisms lived.As the southern supercontinent Gondwana drifted over the South Pole, ice caps formed on it, which have been detected in Upper Ordovician rock strata of North Africa and then-adjacent northeastern South America, which were south-polar locations at the time.The corresponding rocks of the Ordovician System are referred to as coming from the Lower, Middle, or Upper part of the column.The faunal stages (subdivisions based on fossil evidence) from youngest to oldest are: Sea levels were high during the Ordovician period, ranging from 180 meters (590 feet) above modern sea level at the beginning to a peak in the late Ordovician of 220m (722ft) and then falling rapidly near the end of the period to 140m (459ft) (Huq 2008).

The very first jawed fish appeared in the Late Ordovician epoch and now-extinct worm-shaped marine animals called graptolites thrived in the oceans.

Gondwana started the period in equatorial latitudes and, as the period progressed, drifted toward the South Pole.

As with North America and Europe, Gondwana was largely covered with shallow seas during the Ordovician.

Coincident with the drop in sea level was drop in the global mean temperature of nearly 10 degrees Celsius (18 degrees Fahrenheit).

During the Ordovician, the southern continents were collected into a single continent called Gondwana.

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