Class Reptilia - The Reptiles Mode of life: Complete colonization of land was achieved by the reptiles, which can lay their eggs on dry land. Geologic range: Pennsylvanian to Holocene. The oldest reptile fossils, genus Hylonomus, (300 m.y. old) are found in Nova Scotia inside fossilized hollow trees filled with sediment. These reptiles were about 24 cm (1 ft) long. They resemble modern insect-eating lizards.
Class Synapsida - The Synapsids The synapsids had diverged from the reptiles by Late Carboniferous. The synapsids were long considered to be a subclass of reptile, but more recent cladistic analysis shows that they diverged from ancestors completely different than Hylonomus and other true reptiles.
The Synapsids The synapsids were the dominant terrestrial vertebrates during Permian. This group was formerly called the "mammal-like reptiles," however the name has been abandoned because they are not really reptiles. Synapsids include the pelycosaurs and the therapsids.
Pelycosaurs Several species of pelycosaurs had fins or "sails" on their backs, supported by rod-like extensions of their vertebrae. These sails may have been used as temperature regulating mechanisms. Pelycosaurs lived during Carboniferous and Permian. Sail-backed forms are Permian. Permian pelycosaur, Dimetrodon.
Pelycosaurs Two well known pelycosaurs, which evolved their sails independently were the carnivorous Dimetrodon, and the planteating Edaphosaurus. Dimetrodon has a larger skull and teeth than does Edaphosaurus, suggesting that Dimetrodon was a meat-eater.
Therapsids Therapsids were small to moderate-sized animals with mammalian skeletal characteristics: 1. Fewer bones in the skull than the other reptiles 2. Mammal-like structure of the jaw 3. Differentiated teeth (incisors, canines, and cheek teeth) 4. Limbs in more direct alignment beneath the body 5. Reduction of ribs in the neck and lumbar regions, allowing greater flexibility
Therapsids 6. Double ball-and-socket joint between the skull and neck 7. Bony palate which permitted breathing while chewing (an important characteristic for animals evolving toward mammalian warm-bloodedness). Efficient breathing provides oxygen needed to derive heat energy from food. 8. Whisker pits on the snout. Geologic range: Permian to Triassic.
Therapsids - Cynognathus Mammal-like features are well developed in the therapsid, Cynognathus. Name: From "kynos" meaning "dog" and "gnathos" meaning "jaw" or "tooth."
Therapsids - Cynognathus Examination of the bone on the snout portion of the skull reveals probable "whisker pits," suggesting that they had hair, which may have functioned to insulate the animal and slow the rate of heat loss.
Plants of Paleozoic
Stromatolites - A Photosynthetic Plant Ancestor The earliest photosynthetic organisms were in the sea. Stromatolites, built by photosynthetic bacteria (cyanobacteria, sometimes called blue-green algae), were ancestral to Paleozoic plants. They were not plants themselves. Kingdom Eubacteria.
Stromatolites - A Photosynthetic Plant Ancestor Stromatolites: Appeared during Archean Expanded during Proterozoic Are present in Phanerozoic limestones. Most Precambrian stromatolites grew in shallow marine and intertidal environments, but some lived in freshwater.
Stromatolites - A Photosynthetic Plant Ancestor Stromatolite reefs were widespread during Cambrian, but declined during Ordovician. They are typically found in areas lacking marine invertebrates, which feed on the cyanobacterial mats. The appearance of abundant marine invertebrates during Cambrian led to the decline of the stromatolites. Why? They ate them.
Marine Algae The next step in the evolutionary path to land plants was probably the green algae or chlorophytes. Kingdom Protista. Marine algae fossils are found in some Paleozoic rocks. Types of marine algae: 1. Chlorophytes 2. Receptaculitids
Chlorophytes 1. Chlorophytes - Green algae. Cambrian to Holocene. A close relationship between chlorophytes and land plants is suggested by the adaptation of some species to freshwater and moist soil.
Receptaculitids 2. Receptaculitids are lower Paleozoic marine fossils resembling sunflowers. Produced by organisms of uncertain affinity. Interpreted as lime-secreting algae. Most are found in Ordovician rocks, but they are also present in some Silurian and Devonian rocks as well.
Land Plants Land plants include: 1. Bryophytes - non-vascular plants Mosses, liverworts, and hornworts. Devonian to Holocene. 2. Tracheophytes - vascular plants Trees, ferns, and flowering plants. Silurian to Holocene
Tracheophytes Tracheophytes have vascular tissues, or an internal system of tubes and vessels, that transport water and nutrients from one part of the plant to another. A water transport system is important, because plants generally withdraw water from below the ground. Below the ground there is water but no light. Above the ground there is sunlight but there may not be water. The vascular system allows the plant to take advantage of both places.
Tracheophytes The oldest unquestioned vascular plant fossils occur in Silurian rocks. Small, leafless plants with thin branching stems. These plants are called psilophytes. Spore bodies are present on the ends of the stems in fossils of Cooksonia. Cooksonia, an early vascular plant of Late Silurian - Early Devonian. Height about 4 cm.
Major Advances in Land Plants Three major advances in land plant history, developing more efficient reproductive systems: 1. Seedless spore-bearing plants, appearing during Ordovician, and flourishing in Carboniferous coal swamps 2. Seed-producing, pollinating, but non-flowering plants appearing during Late Devonian (gymnosperms, such as conifers) 3. Flowering plants, appearing during Late Mesozoic (angiosperms)
Spore-bearing Plants The first plants to invade the land were spore-bearing plants. In fact, the first evidence of land plants is the presence of spores in Ordovician rocks. Spores are plant reproductive structures. Familiar spore-bearing plants include mosses and ferns.
Life Cycle of Spore-bearing Plants The life cycle of spore-bearing plants differs from that of the more familiar seed-bearing plants. Alternation of generations between diploid (double set of chromosomes) and haploid (single set of chromosomes) forms. Water is required for fertilization.
The First Seeds Seeds appeared during Late Devonian, although it is not known which plant produced them. Seed-bearing plants became more abundant during Carboniferous. The seed is significant because it freed plants from their dependence on moist environments and allowed them to inhabit dry land, much as the amniotic egg freed animals from their dependence on wet environments.
Invasion of the Land by Plants The invasion of the land by plants profoundly altered the landscape. Plant roots slowed erosion. Decaying vegetation led to soil formation. Plants also provided a food source for animals, which invaded the land after the appearance of land plants. Animals could not have survived on land without a food source (plants) in place.
Evolution of Wood As plants evolved wood, they were able to withstand the pull of gravity and grow taller. During Middle Devonian, the first wood appeared in plants of the genus Rhynia. Rhynia, a Middle Devonian vascular land plant with woody tissues called xylem.
The First Trees The first trees were present by Late Devonian. By Carboniferous, trees reached 30 m tall or more, with trunks 1 m in diameter.
Carboniferous Coal There are more plant fossils in Carboniferous strata than in any other geologic interval. Plants gave Carboniferous its name, because of the vast coal deposits which formed from plant remains in lowland swamps. Coal is dominated by the element carbon. Coal represents an enormous biomass of plants because it takes several cubic meters of wood to make one cubic meter of coal.
Common plants of Carboniferous 1. Lycopods or Lycopsids - club mosses 2. Sphenopsids - horsetails, scouring rushes 3. Ferns 4. Gymnosperms a. Seed ferns b. Cordaites c. Conifers d. Ginkgoes
Lycopods or Lycopsids Phylum Lycopodophyta or Lycopsida Club mosses, scale trees Spore-bearing plants were confined to swamps because spores require moisture to germinate. Some grew to be 30 m tall and 1 m diameter. Geologic range: Silurian to Holocene. (Only a few species persisted after Permian.) Common genera = Lepidodendron and Sigillaria.
Sphenopsids Phylum Equisetaphyta or Sphenopsida Spore-bearing and similar to living horsetails or scouring rushes. Interpreted as living in moist areas or standing water. Geologic range: Devonian to Holocene. (But only a few persisted after Permian.) Common genus = Calamites
Ferns Phylum Polypodiophyta Ferns are vascular plants that reproduce by means of spores. They live in moist habitats. Geologic range: Devonian to Holocene.
Gymnosperms Phylum Pinophyta or Gymnospermophyta Conifers, cycads, ginkgoes, and various evergreen plants without flowers The word "gymnosperm" means "naked seed." Seed-bearing plants. No flowers. Seed-bearing plants no longer require moist habitats. This led to the expansion of plants into drier areas. Geologic range: Middle Paleozoic to Holocene.
Seed ferns Gymnosperms. Class Pteridospermophyta Fernlike leaves, but reproduced with seeds instead of spores. Geologic range: Devonian to Holocene. Common genera = Neuropteris and Glossopteris. One of the best-known is Glossopteris, which lived in Gondwana during Carboniferous and Permian. They were sometimes associated with glacial deposits, suggesting that they were adapted to cool climates.
Cordaites Gymnosperms. Class Pinopsida, Order Cordaitales Seed-bearing gymnosperms with strap-like leaves that were ancestors to the modern conifers. Tall trees (up to 50 m). Abundant in Carboniferous coal swamps. Extinct by the end Permian.
Conifers Gymnosperms. Class Pinopsida, Order Coniferales The word "conifer" means "cone bearing." Trees with cones which contain seeds. Today conifers are represented by trees such as pines, cedars, hemlocks, spruces, firs, etc. Conifers spread widely during Permian, perhaps as a result of the drier conditions which led to the demise of the coal swamps.
Ginkgoes Gymnosperms. Class Ginkgopsida Deciduous trees (they drop their leaves) Fan-shaped leaves. They produce a fleshy fruit but have no flowers. Geologic range: Early Permian to Holocene. Maximum diversity during Jurassic. Represented by a single species today, Ginkgo biloba. It is extinct in the wild, but is widely grown as an ornamental tree.
Mass Extinctions of Paleozoic Paleozoic was a time of adaptive radiations and extinctions. Many of the geologic periods of Paleozoic began with adaptive radiations, or times of rapid evolution of organisms. Several of the Paleozoic periods ended with extinction events of varying severity.
Mass Extinctions of Paleozoic The three most catastrophic extinctions during Paleozoic Era were at the following times: End of Ordovician (443 m.y. ago) End of Devonian (359 m.y. ago) End of Permian (251 m.y. ago) Permian extinction was the most severe. The extinction at the end Permian is considered to be the most catastrophic mass extinction in the history of life.
Diversity of marine animals, and extinction events over geologic time.
Late Ordovician Extinctions Following a slight dip in diversity at the end Cambrian, Ordovician was a time of renewed diversification. The number of genera increased rapidly, and the number of families increased from about 160 to 530. This increase was particularly dramatic among trilobites, brachiopods, bivalved molluscs, and gastropods. An extinction event at the end of Ordovician led to an abrupt decline in diversity.
Late Ordovician Extinctions The extinction occurred in two phases. First phase - affected planktonic and nektonic (floating and swimming) organisms such as graptolites, acritarchs, many nautiloids and conodonts, as well as benthic (bottom-dwelling) organisms such as trilobites, bryozoa, corals, and brachiopods. Second phase - affected several trilobite groups, corals, conodonts, and bryozoans.
Late Ordovician Extinctions Both phases of the extinction event were related to global cooling and the growth of glaciers in Gondwana. Glaciation was coupled with the lowering of sea level and a reduction in shallow water habitat. As the climate cooled, tropical organisms showed the greatest decline. As warming occurred and the glaciers began to melt, organisms which were adapted to the cooler conditions began to suffer extinction. This was the second phase of extinctions.
Late Devonian Extinctions Late Devonian extinctions occurred over a span of about 20 million years, and appear to have been the result of an ecological crisis in the seas, perhaps induced by changes occurring on the land.
Late Devonian Extinctions Devonian saw the appearance of trees and spread of land plants. This would have accelerated weathering rates, leading to large volumes of nutrients being washed into the seas. Large quantities of nutrients in the water (such as phosphorus) causes algal blooms. Bacteria breaking down large quantities of dead algae uses up all of the oxygen in the water, causing anoxic conditions (= "without oxygen"). This process is called eutrophication, and it occurs today in lakes, and causes massive "fish kills."
Late Devonian Extinctions Extensive Devonian black shale deposits (for example, the Chattanooga Shale) suggest the widespread occurrence of anoxic conditions in the Devonian sea. Glaciation may have been an additional contributing factor. By Late Devonian, South America had drifted over the South Pole, and glaciations occurred. Overall, 70% of marine invertebrate families went extinct during Late Devonian.
Late Devonian Extinctions Organisms most strongly affected (but not totally wiped out) by the Devonian extinction were: Tabulate corals Rugose corals Stromatoporoids Brachiopods Goniatite ammonoids (cephalopod molluscs) Trilobites Conodonts Placoderm fish
Late Permian Extinctions Late Permian is marked by a catastrophic extinction event which resulted in the total disappearance of many animal groups. This was the largest extinction event in the history of life, exceeding even the extinction event at the end of Cretaceous, which killed the dinosaurs.
Late Permian Extinctions More than 90% of all marine species that existed during Permian disappeared or were severely reduced in number. Nearly half of the known families disappeared. Tropical forms experienced the most extensive losses.
Late Permian Extinctions The following marine organisms were extinct by the end Permian: Fusulinid foraminifera Rugose corals Tabulate corals Blastoids Trilobites (which had become extinct somewhat earlier during Permian)
Late Permian Extinctions Other groups of organisms were severely reduced in diversity, with some surviving species: Brachiopods Crinoids Bryozoa Ammonoids Organisms which inhabited warm waters shifted their distributions toward the equator. Cool conditions prevented construction of reefs and the formation of limestones.
Late Permian Extinctions Permian extinction also affected land dwellers. More than 70% of land animals disappeared or were severely reduced, including: Amphibian families Reptile families Synapsids (once called "mammal-like reptiles")
Late Permian Extinctions Among the plants, the spore-bearing plants that inhabited tropical coal swamps were replaced by seed-bearing gymnosperms, that could inhabit cooler, drier climatic conditions.
Contributing Factors Many factors may have contributed to the Permian mass extinction: 1. Climatic change associated with assembly of Pangea Global cooling and drying, along with interruption of equatorial circulation 2. Glaciation at both north and south ends of Pangea 3. Reduction in epicontinental seas as sea level dropped (habitat loss)
Contributing Factors 4. Unusually active volcanism releasing CO 2 (flood basalts in Siberia), leading to global warming, which may have triggered release of large stores of methane gas frozen in sediments on the sea floor, causing increased global warming. 5. Possibility of an extraterrestrial impact, as indicated by spherical carbon molecules containing an extraterrestrial helium-3 isotope
Diversity of marine animals, and extinction events over geologic time.