Paleozoic Geography 

Paleozoic Life

Life changed so much during the Paleozoic - from seaweed to forests, from proto-chordates to mammal-like synapsids - that it is difficult to summarize.  Although Paleozoic means "ancient life" many of the organisms that lived during the later Paleozoic were much closer to those of today than many of the life-forms of the early Paleozoic.  Basically, at the risk of generalization, we might say that the earlier Paleozoic was dominated by invertebrates, while the land remained barren.  The middle Paleozoic saw the rise of strange armoured fish and the first land plants and insects. While the later Paleozoic was distinguished by great forests of mostly spore-bearing trees, inhabited by a rich assortment of arthropods, tetrapods and reptiles on land; and by diverse invertebrates in the sea.

 Cambrian eco-systems were much simpler and less diversified than anything of today, and hence unstable and prone to easy mass-extinction.  Moreover, it is possible to distinguish an earlier Tommotian type fauna (Terreneuvian) from a Middle Cambrian to Early Ordovician fauna.

The initial flowering of metazoans during the Early Cambrian (the "Cambrian Explosion") spread animal life throughout the seas. The typical Furongian marine community was dominated by trilobites, "inarticulate" brachiopods, and eocrinoids. However, the basic pattern for Ordovician and Middle Paleozoic marine communities was established in the great Early Ordovician radiation of marine metazoans. "The Palaeozoic evolutionary fauna originated and diversified during an early Ordovician radiation event. Many of the adaptations high-lighted in the Palaeozoic marine benthos are associated with soft substrates. Articulate brachiopods, stenolaemate bryozoans, stalked echinoderms (crinoids and blastoids), corals, ostracodes diversified together with graptolites within the water column. Most plankton groups may have been recruited from the benthos while events within the plankton ecosystem were shadowed by changes in benthic systems (Rigby and Milsom. 1996). The vigorous early Ordovician radiation set the agenda for much of the Palaeozoic; the majority of adaptations in the invertebrate groups had already been tried and tested by the end of the Ordovician." Benchley & Harper (1998).  

Following the large end-Cambrian and end-early Ordovician extinctions, a new evolutionary fauna originated and diversified during the Ordovician radiation event. This constituted a Palaeozoic marine benthos associated with soft substrates. Articulate brachiopods, stenolaemate bryozoans, stalked echinoderms (crinoids and blastoids), corals, ostracodes all diversified. Higher up in the water column, the plankton and nekton included graptolites and conodonts, cephalopods, and later fish and medusa (scyphozoa). This vigorous early Ordovician radiation set the agenda for much of the Palaeozoic; and most adaptations by the various invertebrate groups had already been tried and tested by the end of the Ordovician. By the Middle to Late Paleozoic marine ecosystems may not have been too unlike those of today.  Ecosystems and energy and nutrient flow on land was much more inefficient, until the rise of reptilian herbivores at the very end of the era (late Permian).


Perhaps the most intelligent creatures to inhabit the earth over this long span of time were the cephalopods, the most intelligent and sentient of all the invertebrates.  Cephalopods were extraordinarily diverse in Paleozoic seas, and were the dominant life-form until the rise of carnivorous fish during the Devonian (mid-Paleozoic).  At the very end of the Paleozoic the Therapsida evolved larger brains than their contemporaries, and paved the way for mammalian intelligence during the Mesozoic and Cenozoic.

The Paleozoic witnessed a number of crises in the history of life, including an early Cambrian, a terminal Cambrian, an Ordovician one, a late Devonian one.  The era was brought to an end by the terminal Permian extinction, the greatest catastrophe in the history of higher life on Earth (although far milder than the Early Proterozoic Oxygen crisis).  There is still disagreement over whether it was caused simply by terrestrial phenomena like loss of geographic isolation and falling sea-levels, or whether (as I feel likely) these factors were aided by an extraterrestrial impact of some kind (similar to the one that saw off the dinosaurs at the end of the Mesozoic).  

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