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. 9 PALEOZOIC LIFE Summary of invertebrate phyla 10 PALEOZOIC LIFE CONT. Summary of invertebrate phyla 11 ADAPTIVE RADIATIONS AND EXTINCTIONS Paleozoic was a time of several adaptive radiations and extinctions. Many geologic periods began with adaptive radiations (times of rapid evolution). Several periods ended with extinction events of varying severity. The extinction event at the end of Permian was the most extensive mass extinction in the history of life. 12 DIVERSITY DURING PALEOZOIC Red arrows mark extinction events. FIGURE 12-94 13 SOFT-BODIED ANIMALS Multicellular animals evolved during Precambrian. Soft-bodied Ediacaran-type organisms ranged into Cambrian. Soft-bodied fossils are infrequently preserved. Preservation improved with the origin of hard parts. 14 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 during the Early Cambrian. SMALL SHELLY FOSSILS FIGURE 12-2 15 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. FIGURE 12-1 Tiny fossils from the Late Precambrian and Early Cambrian in Siberia. 16 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.
93 PALEOZOIC ARTHROPODS AND THEIR GEOLOGIC RANGES Trilobites - Cambrian to Permian Horseshoe crabs - Silurian to Holocene Eurypterids - Ordovician to Permian Arachnids - Late Silurian to Holocene Ostracodes - Cambrian to Holocene Onychophorans - Cambrian to Holocene Insects - Devonian to Holocene 94 SUBPHYLUM TRILOBITA - TRILOBITES Chief characteristics: Body has three-lobes Skeleton composed of chitin, with calcium carbonate Body is divided into three segments: Rigid head segment - cephalon Jointed, flexible middle section - thorax Rigid tail piece - pygidium FIGURE 12-42 95 SUBPHYLUM TRILOBITA - TRILOBITES Name: Trilobite "three" (tri) + "lobed" (lobus). Geologic range: Cambrian to Permian Mode of life: Exclusively marine. Most were bottom dwellers living in shallow shelf environments. 96 CLASS EURYPTERIDA - EURYPTERIDS Extinct scorpion-like or lobster-like arthropods. Predators. Up to 10 ft long. Geologic Ordovician to Permian. Most are Silurian or Devonian. Mode of life: Inhabited brackish estuaries. 97 CLASS ARACHNIDA - ARACHNIDS Scorpions, spiders, ticks, and mites Scorpions are the oldest arachnids with a fossil record. Scorpions had evolved by Late Silurian. The earliest ones appear to have lived in the water, because their fossils have gills. Scorpions, spiders, and mites are found in Devonian rocks. Geologic Late Silurian to Holocene. 98 CLASS OSTRACODA -OSTRACODES The ostracodes are mainly microscopic in size. Tiny bivalved shell encasing a shrimp-like creature. Geologic range: Cambrian to Holocene. Mode of life: Both marine and freshwater. 99 CLASS ONYCHOPHORA
Behavior resembles that of a sponge. Body contracts abruptly expelling water, giving them the name "sea squirts." 5 PHYLUM CHORDATA SUBPHYLUM CEPHALOCHORDATA Primitive chordates. Lancelets, Amphioxus, Branchiostoma. Small marine animals with fish-like bodies and notochord. Geologic range: Cambrian to Holocene. Mode of life: Bottom dwellers. Lancelets spend much of their time burrowing in the sand in warm, coastal, marine environments. Filter feeders. Relatively sessile but capable of swimming. Significance: An ancestor to the vertebrates resembled a lancelet-like creature (Pikaia). 6 Chief characteristics: Lancelets resemble a small, colorless anchovy fillet. No obvious eyes or lateral fins. Worm-like. Has segmented axial muscles, gill slits, a dorsal hollow nerve cord, a notochord, and a post-anal tail. No solid skeleton. Nothing resembling a vertebral column. PHYLUM CHORDATA SUBPHYLUM CEPHALOCHORDATA 7 FIGURE 12-60 Branchiostoma, a fishlike member of the subphylum Cephalochordata. WHAT ARE CONODONTS? The conodonts were previously placed in a separate phylum (Phylum Conodonta), because their affinities were unknown. The current interpretation places the conodont-bearing animal with the Chordates in Phylum Chordata. The organism from which they came is not known with certainty. Examples of various shapes of conodont elements. Photographs courtesy of K. Chauff 8 CONODONTS characteristics: Microscopic in size Composed of calcium fluorapatite. Shape - cone-shaped teeth, or bars with rows of tooth-like denticles, or irregular knobby plates called platforms. Each conodont element is part of a larger organism. Most fossil occurrences are of disassociated elements, but occasionally they are found arranged in specific assemblages or “apparatuses." 9 CONODONTS Name: Conodont means "cone" + "teeth" (dont) Geologic Neoproterozoic to Late Triassic. Mode of life: Marine, free-swimming. 10 CONODONTS Significance: Useful in biostratigraphy
Types of marine algae: 1.Chlorophytes 2.Receptaculitids 67 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. 68 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 as well. 69 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 70 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. 71 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. 72 FIGURE 12-85 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)
73 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 reproductive structures. Familiar spore-bearing plants include mosses and ferns. 74 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) Water is required for fertilization. 75 THE FIRST 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 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. 76 INVASION OF THE LAND BY PLANTS The invasion of the land by plants profoundly altered the landscape. 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. 77 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 with woody tissues called xylem. 78 FIGURE 12-87 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. 79 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. 80