Life before the first mass extinction

  The Ordovivian Period

The Ordovician period - lasting nearly 45 million years - was characterised by prolific life in the seas and limited life forms on land. From Ordovician-aged rocks, the fossil record shows a huge variety of life forms in the oceans.

At this time, the vast shallow seas had a variety of invertebrates and early vertebrates. The marine life comprised many life forms that no longer exist - so it is very difficult to fully reconstruct the environment at that time. Artists impressions (like the image above) cannot be completely accurate, but they do give us some idea.

Ordovician seas had vertebrates like jawless fishes and even the first fish with jaws, i.e. the jawed fish, called gnathostomes, that were the frontrunners of the vertebrate diversity that would emerge over the next 400 million years.

In the oceans, there were sponge-like animals, as well as, trilobites, and early relatives of vertebrates such as conodonts. There were also predators such as the huge scorpion-like eurypterids, and especially the nautiloids, which are molluscs with tentacles, eyes, and moved through a method of jet propulsion. Increasing complexity during the Ordovician period made them into one of the dominant species. These marine environments were also home to abundant red and green algae. Green algae are believed to have given rise to the earliest land plants (about 480 mya).

Eurypterids

Evidence of land plants (simple structures without roots or stems) comes from the fossilised spores, found in Argentina (dating to about 473 mya). This suggests that the first land plants appeared on the Gondwanan subcontinents, which at that time consisted of South America, Africa, India, Australia, Madagascar and Antarctica.

It is estimated that about 440 mya when most of life was restricted to marine environments, the first radiations of plants onto land began. The abundance and diversity of aquatic organisms would undergo major changes, after the first great extinction event which occurred at the end of the Ordovician around 443 mya.

Life during the Permian

Just before the great End Permian extinction event, the world was dominated by a supercontinent (Pangaea) surrounded by a global ocean called Panthalassa. The Permian period lasted from 299 to 251 million years ago.

Models recreating that time indicate that the interior regions of this vast continent were probably dry, with great seasonal fluctuations due to the lack of a moderating effect provided by nearby bodies of water.

Such climatic fluctuations instigated significant changes in the vegetation, which now included a diverse mix of plant groups including seed-bearing plants - conifers in the northern hemispheres and glossoptosis in the South. In fact, the ancestors of today’s ginkgo trees and cycads also appeared during this period. The Permian period saw the development of a fully terrestrial (amniote) fauna and the appearance of the first large herbivores and carnivores. By far, the majority of animals in the Early Permian were pelycosaurs - the sail-backed reptiles - but, by the Late Permian, the massive maiasaurs, and early synapsids were common (which included the large dinocephalians, and a diverse array of herbivorous dicynodonts, as well as, the carnivorous forms), and a host of generally medium to small diapsids.