Summary of Paleozoic Bioevents
Permian: Large mass extinction event affect the invertebrates
Pennsylvanian: Fusulinids (Protista, foraminifera) diversiffy
Mississippian: Crinoids, bryozoans, and blastoids become abundant

Renewed adaptive radiation following the extinction of reefs

Devonian: Extinction of may reef building invertebrates near the end of Devonian

Reef building continues

Eurypterids abundant


Silurian: Major reef building

Diversity of Invertebrates remains high


Ordovician: Extinctions of a number of marine invertebrates near the end of the Ordovician

Major adaptive radiation

Suspension feeders dominant


Cambrian: Many trilobites becomes extinct near the end of the Cambrian 

Trilobites, brachiopods, and archaeocyathids are abundant

Permian: Acanthodians, placoderms, and Pelycosaurs become extinct
Therapsids and Pelycosaurs are the dominant reptiles
Pennsylvanian: Amphibians abundant and diverse 


Mississippian: Reptiles evolve


Devonian: Age of Fish. All major groups of fish are present


Silurian: Ostracoderms common

Acanthodians: first jawed fish evolve


Ordovician: Ostracoderms diversify


Cambrian: Earliest vertebrates: jawless fish called ostracoderms

Permian: Gymnosperms diverse and abundant
Pennsylvanian: Coal swamps with flora of seedless vascular plants and gymnosperms

Mississippian: Gymnosperms appear: many have evolved during the upper Devonian?


Devonian: First seeds evolve


Seedless vascular plants diversify


Silurian: Early plants: seedless vascular plants


Ordovician: Plants move on land


Important Facts to Remember:

Chordates are characterized by a notochord, dorsal hollow nerve cord, and gill slits. The earliest chordates were soft ¬bodied organisms that were rarely fossilized. Vertebrates are a subphylum of the chordates.
Fish are the earliest known vertebrates with their first fos¬sil occurrence in Upper Cambrian rocks. They have had a long and varied history, including jawless and jawed ar¬mored forms (ostracoderms and placoderms), cartilagi¬nous forms, and bony forms. It is from the lobe-finned fish that amphibians evolved.

The link between crossopterygian lobe-finned fish and the earliest amphibians is convincing and includes a close similarity of bone and tooth structures. The transition from fish to amphibians occurred during the Late Devonian. During the Carboniferous, the labyrinthodont amphibians were the dominant terrestrial vertebrate animals.

The earliest fossil record of reptiles is from the Late Missis¬sippian. The evolution of an amniote egg was the critical factor that allowed reptiles to completely colonize the land.

Pelycosaurs were the dominant reptile group during the Early Permian, whereas therapsids dominated the land¬scape for the rest of the Permian Period.

In making the transition from water to land, plants had to overcome the same basic problems as animals-namely, desiccation, reproduction, and gravity.

The earliest fossil record of land plants is from Middle to Upper Ordovician rocks. These plants were probably small and bryophyte-like in their overall organization.

The evolution of vascular tissue was an important event in plant evolution as it allowed food and water to be trans¬ported throughout the plant and provided the plant with additional support.

The ancestor of terrestrial vascular plants was probably some type of green alga based on such similarities as pigmentation, metabolic enzymes, and the same type of reproductive cycle.

The earliest seedless vascular plants were small, leafless stalks with spore-producing structures on their tips. From this simple beginning, plants evolved many of the major structural features characteristic of today's plants.

By the end of the Devonian Period, forests with tree-sized plants up to 10 m had evolved. The Late Devonian also witnessed the evolution of the flowerless seed plants (gym¬nosperms) whose reproductive style freed them from hav¬ing to stay near water.

The Carboniferous Period was a time of vast coal swamps, where conditions were ideal for the seedless vascular plants. With the onset of more arid conditions during the Permian, the gymnosperms became the dominant element of the world's flora.