Animal Life in the Paleozoic

The Cambrian Revolution

- in the latest Proterozoic hardened worm burrows appear in the fossil record
- hard skeletal parts (the "small shellies") first appeared in the lowermost Cambrian about 543 m.y.; early skeletal materials were chitinophosphatic; calcium carbonate became the predominant skeletal material as the Cambrian progressed into the Ordovician (and atmospheric oxygen increased to near present levels)
- most animal phyla evolved during the Cambrian; all later animal species derive from the basic forms established in the Cambrian
- Cambrian animals were "experimental" including many bizarre forms (eg., Burgess Shale species like halucinogenia)

- Trilobites were the dominant animal species of the Cambrian; most were bottom scavengers
- spongelike Archaeocyathids (probably suspension or filter feeders) built "reefs"
- Mollusk bivalves (pelecypods) and snails (gastropods) evolved; pelecypods were not common during the Paleozoic;
- the Brachiopods remained the dominant "bivalve" until Permo-Triassic extinctions at the end of the Paleozoic
- primitive echinoderms evolved; most were attached forms (e.g., crinoids) with filter feeding tentacles
- Upper Cambrian fossil cartilaginous jawless fish is the oldest known vertebrate
- simple seaweeds (multicellular algae) were common
- the thick cyanobacterial mats of the Proterozoic were decimated by bottom grazers like gastropods (snails)
- no land plants or land animals

(see Fossil Animal Phyla)

Ordovician Life

- life's experimentation in the Cambrian settled into a number of orthodox forms
- brachiopods, crinoids, and bryozoans became established as the characteristic bottom-dwelling marine invertebrate assemblage for the remainder of the Paleozoic

Mid Paleozoic Life

Rise of Fishes
- coiled ammonoid cephalopods (descended from the nautiloids) evolved and became the dominant cephalopod hunter in the Devonian
- The Devonian is known as the Age of Fishes
- jawless fish (agnathans), which had been known only by fossilized scales and bony plates since the Late Cambrian, became common in the middle Paleozoic; they were probably clumsy swimming bottom feeders;
- the jawed acanthodian fishes arose in the Silurian, probably as fast swimming predators
- the placoderms, which had heavy head and body armor, evolved in the Silurian
- the sharks evolved in the Devonian
(agnathans, acanthodians, placoderms, and sharks are cartilaginous fishes)
- the ray-finned and lobe-finned fishes also arose in the Devonian; they represent the bony fishes; (99% of all bony fish today are ray fins; one group of lobe fins gave rise to amphibians and higher vertebrates)

Invasion of the Land (first signs were Late Ord spores and burrows)

- 3 problems for land plants a) waterproof cuticle so it doesn't dry out; b) strong support since it can't rely on water buoyancy; c) need new means of passing sperm to egg or remain dependant upon water in which sperm can swim to egg

Spore Bearing Plants
- the first vascular plants (Sil-Dev) were mostly spore-bearing, ground-creepers, with rootless and leafless stalks, that lived near water; vascular system was inefficient
- lycopsids evolved in Early Devonian; most were small ground plants like the modern "club moss" but some grew as trees to 30m; lycopsids have leaves attached directly to the trunk
- the modern horsetails are descendants of the joint-stemmed plants (sphenopsids)
- true ferns were a third important spore-bearing plant group in the Devonian; ferns were the most advanced of the spore bearing plants

- invertebrates quickly followed the plants onto the land in Late Ordovician
- Lower Devonian arthropods (scorpions, spiders, mites, millipedes and wingless insects)
- Late Devonian, first amphibians (vertebrates) evolved from lobe-finned fishes and moved from sea onto land; these were the first tetrapods (four-limbed vertebrate animals)


Late Paleozoic Life

Marine Life
- archaic Devonian fish (Acanthodians, Placoderms) extinct; ray-fin bony fish were dominant vertebrate predators
- ammonoids were dominant invertebrate predators

Terrestrial Plant life
- spore bearing plants require water fertilization for one part of their reproductive cycle
- lycopsids (scale trees) leaves attached to trunk
- sphenopsids (scouring rushes and horsetails)
- tree ferns were the most advanced and the dominant spore-bearing plants
- gymnosperms have a naked seed attached to a leaf or scale; may be wind fertilized; doesn't require water for fertilization; gymnosperms include:
- first gymnosperms: seed ferns with fern-like leaves evolved in the Late Devonian; one of the most important was glossopteris, the late Paleozoic seed fern of the Gondwana continents
- conifers: cone-bearing plants (eg. cordaites, late Pz conifers of the northern continents)
- [the palm-like cycads: and fan-shaped leaf ginkoes: became the commonest trees in the Mesozoic]
- Pennsylvanian coal swamps
- Permian drying lead to dominance of the gymnosperms

Terrestrial Animal life
- Carboniferous, Age of Amphibians; amphibians were the dominant land animals of the Carboniferous; there were many forms including lizard-like, snakelike, crocodile-like; some were quite large; but Carboniferous amphibians (like today's frogs and salamanders) have to lay their eggs in water so they don't dry out and die
- Age of Cockroaches; huge insects in Pennsylvanian; dragonfly to nearly 1 meter
- mid-Carboniferous, first amniotes, this line of amphibians (tetrapods) evolved the amniotic egg which allows oxygen in but water can't get out; the first amniotes gave rise to two important lineages 1) reptiles and 2) reptile-like synapsids; in the Mesozoic the birds would evolve from reptiles and mammals would evolve from synapsids
- Permian drying allowed the amniotes to take over the leading role among terrestrial animals because of their reproductive advantage (didn't have to lay eggs in the water); the Permian is often called the Age of "Reptiles" though it is now clear that the dominant "reptiles" were the synapsids which later gave rise to the mammals, not to a lineage of modern reptiles

- Late Permian Mass Extinction; 90% to 95% of all marine species and 75% of all vertebrate families became extinct; largest extinction known; the cause is not known