Chapter 12 Life of the Paleozoic

Paleozoic Invertebrates• Representatives of most major invertebrate

phyla were present during Paleozoic, including sponges, corals, bryozoans, brachiopods, molluscs, arthropods, and echinoderms.

• Almost all of the common invertebrate phyla in existence today had appeared by Ordovician.

Paleozoic Vertebrates• Vertebrates evolved during Paleozoic,

including:– Fishes– Amphibians– Reptiles– Synapsids ("mammal-like reptiles")

• The first vertebrates were jawless fishes, which are found in rocks as old as Cambrian in China.

Paleozoic Vertebrates• An advanced lineage of fishes with primitive

lungs and stout fins gave rise to the four-legged animals or tetrapods.

• The transition from water-dwelling vertebrates to land-dwelling vertebrates depended on the evolution of the amniotic egg.

Paleozoic Plants• The first primitive land plants appeared near

the end of Ordovician. • Vascular plants expanded across the land,

forming great forests during Devonian. • The plants progressed from seedless, spore-

bearing plants to plants with seeds but no flowers (gymnosperms).

Paleozoic Extinctions• Several mass extinctions occurred during

Paleozoic, including the largest extinction of all at the end of Permian.

• Other mass extinctions occurred at the end of Ordovician and Devonian.

Diversity during Paleozoic Red arrows

mark extinction events

Paleozoic Life Summary of

invertebrate phyla

• The first animals with shells are called small shelly fossils.

• Small shelly fossils are found at the base of Cambrian, and during Late Neoproterozoic.

• Most disappeared by at the top of the first stage within Lower Cambrian.

Small Shelly Fossils• Many had phosphatic shells, few mm in size. • Shells and skeletal remains of primitive molluscs,

sponges, and animals of uncertain classification, such as Cloudina, that secreted a calcareous tube.

Cambrian Diversification• The initial Paleozoic diversification is known

as "the Cambrian explosion." Abrupt appearance of many types of animals about 535 million years ago, followed by rapid evolution.

• During that episode of explosive evolution, all major invertebrate phyla appeared in the fossil record (except Bryozoa).

Cambrian Substrate Revolution• Infaunal, burrowing animals evolved rapidly

during Cambrian, as indicated by trace fossils and bioturbation of sediments.

• The dramatic change in the character of the seafloor sediments (from undisturbed to highly burrowed) has been called the "Cambrian substrate revolution."

Soft-Bodied Fossils in the Burgess Shale The extraordinarily well-preserved Middle

Cambrian Burgess Shale fauna of Canada provides a window into the past to view the spectacular diversity of Middle Cambrian.

Many soft-bodied organisms are preserved in black shale, along with the soft parts of animals with shells, such as legs and gills of trilobites.

Animals in the Burgess Shale 1. Several groups of arthropods, including

trilobites and crustaceans 2. Sponges 3. Onycophorans (velvet worms)4. Crinoids 5. Molluscs 6. Corals 7. Three phyla of worms 8. Chordates (Pikaia) 9. Many others

Pikaia - One of the Oldest Chordates

• Pikaia is a fish-like lower chordate from the Burgess Shale.

• Modern representatives are called lancelets, such as the genus Amphioxus.

Chordates• Chordates have a notochord or dorsal stiffening rod

associated with a nerve chord, at some stage in their development.

• In vertebrates, the notochord is surrounded by and usually replaced by a vertebral column during embryonic development.

• Vertebrates are chordates, but Pikaia pre-dates the evolution of vertebrae.

• It is thought that vertebrates evolved from organisms similar to Pikaia.

Predators in the Cambrian Seas• The giant predator of the

Cambrian seas, Anomalocaris, up to 60 cm long.

• Predators would have caused selective pressures on prey. The need to avoid being eaten probably encouraged the evolution of hard protective shells.

• Predation probably also caused an increase in diversity of prey, as they evolved to better survive predation.

The Chengjiang fauna

• In 1984, the Lower Cambrian Chengjiang fossil site was discovered in Yunnan Province, China.

• More than 100 species of invertebrates have been found, with extraordinary preservation, including many soft bodied forms.

The Chengjiang fauna • Jelly fish• Annelid worms• Cnidaria • Porifera (sponges) • Brachiopods • Arthropods• Early chordates similar to Pikaia • The world's oldest known fish (Myllokunmingia) • Other species of unknown phyla

Oldest Known Fish The world's oldest known

fish, Myllokunmingia, from the Maotianshan Shale near Chengjiang, in the Yunnan Province of China.

535 million years old.

Ordovician Diversity • Following a slight dip in diversity at the end of

Cambrian, Ordovician seas experienced renewed diversification.

• Global diversity tripled.• The number of genera increased rapidly, and the

number of families increased from about 160 to 530. • The increase was particularly notable among trilobites,

brachiopods, bivalve molluscs, gastropods, and corals.

Late Ordovician Extinction

• An extinction event at the end of Ordovician led to an abrupt decline in diversity.

• This extinction event was apparently related to the growth of glaciers in Gondwana, coupled with a reduction in shallow water habitat associated with the lowering of sea level.

Diversity and extinction during Paleozoic Red arrows

mark extinction events

Devonian Diversity • During Devonian, there was continued

diversification, but this ended with another fairly large extinction event, which extended over about 20 million years.

• Roughly 70% of marine invertebrates disappeared.

• Because of the long duration, the extinction is unlikely to have been caused by a sudden, catastrophic event.

Carboniferous-Permian Diversity • During Early Carboniferous, diversity once

again increased. • Diversity of marine animals remained fairly

constant throughout Carboniferous and Permian.

• Late Permian is marked by a catastrophic extinction event which resulted in the total disappearance of many animal groups.

Five Kingdom Classification System

Monera: (includes Eubacteria and Archeobacteria) Individuals are single-celled, may or may not move, have a cell wall, have no chloroplasts or other organelles, and have no nucleus. Monera are usually very tiny, although one type, namely the blue-green bacteria, look like algae. They are filamentous and quite long, green, but have no visible structure inside the cells. No visible feeding mechanism. They absorb nutrients through the cell wall or produce their own by photosynthesis.

Protista: Protists are single-celled and usually move by cilia, flagella, or by amoeboid mechanisms. There is usually no cell wall, although some forms may have a cell wall. They have organelles including a nucleus and may have chloroplasts, so some will be green and others won't be. They are small, although many are big enough to be recognized in a dissecting microscope or even with a magnifying glass. Nutrients are acquired by photosynthesis, ingestion of other organisms, or both.Fungi: Fungi are multicellular,with a cell wall, organelles including a nucleus, but no chloroplasts. They have no mechanisms for locomotion. Fungi range in size from microscopic to very large ( such as mushrooms). Nutrients are acquired by absorption. For the most part, fungi acquire nutrients from decaying material.Plantae: Plants are multicellular and most don't move, although gametes of some plants move using cilia or flagella. Organelles including nucleus, chloroplasts are present, and cell walls are present. Nutrients are acquired by photosynthesis (they all require sunlight).Animalia: Animals are multicellular, and move with the aid of cilia, flagella, or muscular organs based on contractile proteins. They have organelles including a nucleus, but no chloroplasts or cell walls. Animals acquire nutrients by ingestion

Unicellular Organisms in the Paleozoic Seas • The principal groups of Paleozoic unicellular

animals with a significant fossils record are the foraminifera and the radiolaria, which belong to Phylum Sarcodina.

• These organisms are unicellular eukaryotic organisms, and belong to Kingdom Protista.

Foraminifera • Name: Foraminifera means "hole bearer." • Chief characteristics:

– Unicellular. – Related to the amoeba, with pseudopods. – Foraminifera build tiny shells (called tests) which

grow by adding chambers. – Some species (called agglutinated foraminifera)

construct tests of tiny particles of sediement. This is the most primitive test.

– Other forams construct tests of calcium carbonate.

Foraminifera • Geologic range: Cambrian to Holocene.• Modes of life:

– Benthic or benthonic (bottom dwellers) – Planktic or planktonic (floaters).

Fusulinid foraminifera (fusulinids) • Fusulinids were abundant during Late Paleozoic

(primarily Pennsylvanian and Permian).• Their tests were similar in size and shape to a grain of

rice. • Their internal structure is complex and used to

distinguish different species.• Important guide fossils during Pennsylvanian and

Permian because they evolved rapidly, were abundant, and widespread geographically.

Radiolaria • Chief characteristics:

– Unicellular. – Test or shell composed of opaline silica– Ornate lattice-like skeleton – Often spherical or radially symmetrical with spines

• Geologic range: Precambrian or Cambrian to Holocene. Rare during Early Paleozoic. More abundant during Mesozoic and Cenozoic.

• Mode of life: Planktonic. Marine only.

Radiolaria and the Rock Record

• Radiolarians are important constituents of chert at certain times in geologic history.

• Their tests accumulate on the seafloor today to form radiolarian ooze, particularly in deep water, where any calcium carbonate shells would be dissolved.

Marine Invertebrates in the Paleozoic Seas • The fossils of shell-bearing invertebrates that

inhabited shallow seas are common in Paleozoic rocks.

• Archaeocyathids, sponges, corals, bryozoans, trilobites, molluscs, and echinoderms.

• Many were benthic (bottom dwellers), but others, such as graptolites, were planktonic. Currents carried them over wide areas.

• As a result, they are useful index fossils for global stratigraphic correlation.

Phylum Archaeocyatha • Name means "ancient

cup" • Chief characteristics:

Conical or vase-shaped skeletons made of calcium carbonate. Double-walled structure with partitions and pores.

• Geologic range: Cambrian only. Extinct.

• Mode of life: Attached to the sea floor. Reef-builders.

Phylum Porifera - The Sponges Name means "pore-bearing" Covered by tiny pores

Phylum Cnidaria• Corals, sea fans,

jellyfish, and sea anemones.

• Name: Cnidaria are named for stinging cells called cnidoblasts or cnidocytes.

• Many are soft-bodied but only those which form hard skeletal structures are readily preservable as fossils.

Phylum Cnidaria• Geologic range: Late Precambrian

(Proterozoic) to Holocene for the phylum.• The first corals were the tabulates. • Mode of life: Corals live attached to the sea

floor, primarily in warm, shallow marine environments.

Phylum Cnidaria – Chief Characteristics1. Radial symmetry2. Mouth at the center of a ring of tentacles.

Phylum Cnidaria – Chief Characteristics3. Body form may be polyp (attached to the bottom, with

tentacles on top) or medusa (free-swimming, jellyfish).

Rugose Corals• Most rugose corals

are solitary and conical (shaped like ice cream cones).

• Septae are visible in the circular opening of the cone.

• Some rugose corals are colonial, having hexagonal corallites with septae (such as Hexagonaria from Devonian of Michigan).

Rugose Corals• Geologic range: Ordovician to Permian - all

extinct. • Rugose corals were abundant during

Devonian and Carboniferous, but became extinct during Late Permian.

Tabulate Corals• Tabulate corals are

colonial and resemble honeycombs or wasp nests.

• They lack septae.• They have

horizontal plates within the theca called tabulae. Tabulae are one of the main features of the tabulate corals.

Tabulate Corals• Geologic range:

Ordovician to Permian - all extinct.

• The principal Silurian reef formers.

• They declined after Silurian and their reef-building role was assumed by the rugose corals.

Modern Corals• Modern corals are scleractinian corals.

Scleractinian corals have septae are arranged in multiples of six, and are sometimes called hexacorals.

• Scleractinian corals did not appear until after Paleozoic

• Geologic range: Triassic to Holocene.

Phylum Bryozoa• Name: Name means "moss" (bryo) +

"animal" (zoa). • Chief characteristics:

– Colonial (many microscopic individuals living physically united adjacent to one another).

– The individuals are called zooids, and they are housed in a hard "capsule" called a zooecium.

– The colony is called a zoarium.

Phylum Bryozoa • Individual zooecia (plural of zooecium) are very tiny

(about the size of a pin-hole, a millimeter or less in diameter). They are just large enough to be seen with the unaided eye.

• Bryozoans may be distinguished from corals because of the apertures in the skeleton are much smaller.

Phylum Bryozoa The bryozoan colony may resemble lace or a tiny net, may be

delicately branching, finger-like, circular or dome-shaped. There are more than 4000 living species of bryozoans, and nearly 16,000 fossil species.

Phylum Bryozoa

• Geologic range: Ordovician to Holocene. • Mode of life: Widespread in marine

environments. A few live in freshwater lakes and streams.

Phylum Bryozoa Archimedes, from Mississippian rocks, has a cork-

screw-like central axis with a fragile net-like colony around the outer edge.