Animal Life in the Paleozoic

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- 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

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.  Also, rugose and tabulate corals.

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 first jawed fishes, the acanthodian, arose in the Silurian, probably as fast swimming predators.  They had scales rather than bony plates.
- the placoderms, which had heavy head and body armor, evolved in the Silurian
- the sharks evolved in the Silurian, or by the Devonian
(agnathans, acanthodians, placoderms, and sharks are all 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)

Plants
- 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 but relied on water for reproduction/fertillization

Animals
- invertebrates quickly followed the plants onto the land in Late Ordovician
- Silurian millipedes were followed by other arthropods by the Lower Devonian (scorpions, spiders, mites, 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 groups 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 led 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) sauropsid reptiles which gave rise to dinosaurs and modern reptiles
        and
2) synapsid reptiles, now extinct
- Permian drying allowed these 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

The Guadalupian mass extinction (7-8 m.y. before the terminal Permian mass extinction) killed off 70% of marine species, but had little effect on the land.

The Terminal Permian mass extinction was much worse.  All rugose and tabulate corals, and the last of the trilobites became extinct.  Most ammonoids, crinoids, and bryozoans became extinct.  On land, therapsids were hard hit.   Forests were decimated - woody plants were replaced by non-woody lycopods.  Large concentrations of fungi are found in shallow marine strata, remnants of huge volumes of decaying wood washed into the sea.

All together, 90-95% of all marine species (80-85% of all marine and terrestrial species)
and 75% of all vertebrate families became extinct by the end of the Permian.

We’re not really sure, but three geologic events give hints at major changes.

1)  The Siberian traps, the largest outpouring of flood basalt in the Phanerozoic coincides with the Terminal Permian mass extinction. A smaller flood basalt province in China erupted several million years earlier, approximately conicident with the Guadalupian mass extinction. Some deposits from explosive, felsic volcanoes are also found.  Perhaps sulfur aerosols and volcanic ash darkened the sky causing a sudden, short-term “nuclear winter.”

2)  Carbon Isotopes: a major excursion to lighter carbon isotopes is recorded in marine sediments near the Permo-Triassic boundary. Remember, carbon dioxide containing the lighter carbon 12 is preferentially taken up by photosynthetic organisms. So this excursion means that a huge amount of organic carbon was returned to the atmosphere at the end of the Permian.

One possible mechanism for this is a sudden release of methane hydrates from storage in the seafloor.

Perhaps the warming was caused by the postulated sudden release of methane hydrates.  Remember, methane is a greenhouse gas.