Bryozoan morphology
The hard parts of an individual zooid are called the zooecium plural zooecia , and the skeletal colony the zoarium Fig. 5.2 . The zooecia of stenolaemates are tube shaped and are often studied in thin section. In branching colonies, the mature parts of the zooecia usually grow at a high angle to the axis of colony growth. Zooecia may change in shape as they grow. They share common skeletal walls with adjacent zooids. In cross-section these tubes can be identified along with the shared hard...
Fish
The earliest vertebrates were fish, and all of them were marine, with fish not migrating into fresh water until the Devonian. Most of these early fish lacked jaws. Any mineralization was concentrated on the teeth or on armor plating outside the body. Jaws evolved in the Silurian and this group, sometimes known as gnathostomes, quickly came to dominate fossil fish assemblages. Primitive gnathostomes evolved sequentially into the two most common modern fish groups, cartilaginous and bony fish, as...
Tetrapod evolution and climate change
It is tempting to think of climate change as a recent phenomenon. However, in some ways the only predictable thing about climate is the certainty of change. There have been at least four major glaciations during the Phanerozoic icehouse periods and in between there is usually little or no evidence for permanent ice existing at the poles these are called greenhouse periods . In addition to climatic oscillations, there have been unique changes caused by tectonics or by biological evolution. These...
Seedbearing plants angiosperms
Angiosperms are the most diverse and widespread group of living plants Fig. 12.13 . Leaf impressions of angiosperm-like plants are known from the Triassic. The first true angiosperm fossils are from the Cretaceous Fig. 12.14 . During this period angiosperms diversified rapidly, particularly in low latitudes, and dominated most habitats by the end of the Cretaceous. Paralleling the rise of the angiosperms, spore-bearing plants and gymnosperms declined through the Cretaceous. Abundance and...
Ethological behavioral classification
This fundamental classification is founded on the supposed or inferred behavioral characteristics represented by the trace fossils Table 14.1 . The most important categories relate to feeding, dwelling, and locomotion. As the units are divided on the basis of activity there maybe some overlap between them if the organism performed more than one behavior for example, feeding and crawling at the same time. Also, different parts of the trace fossil structure may fall into different categories....
Discriminating between brachiopods and bivalves
Brachiopods look superficially very similar to bivalves Chapter 9 , with both organisms having two shells, usually made from calcite and frequently ornamented with radial ribs. This similarity is the consequence of sharing a similar lifestyle most species of each group are sessile filter feeders living in the shallow marine environment. As such they represent an example of evolutionary convergence. There is a simple way to distinguish between almost all brachiopods and bivalves, related to...
Land plant classification
A classification of land plants is given in Table 12.1. Informal groupings are used in this scheme. As an artificial classification it provides a working description of plant diversity rather than an explanation of the evolutionary relationships. Some of the groups are unnatural, for example seed ferns incorporates the seed plants that are not included in the other groups. Land plants are separated into those with a vascular system and those without. There are three important groups of...
What Are The Fossil Classification Of Man
Acanthodian lightly armored, jawed fish characterized by fins supported by a frontal spine. Acheulian tool suite associated with Homo erectus. Actinopterygian ray-finned, bony fish, including most modern fish. Anapsid primitive reptiles represented by modern turtles and tortoises. There are no holes in the skull behind the eye. Articular lower jaw bone in reptiles that articulates with the upper jaw, and an ear bone in mammals. Chondrichthyan group of fish characterized by a cartilaginous...
Trilobite evolution
Trilobites were a major part of the marine benthos for over 250 million years. During all of that time their basic body plan remained the same, and the changes that did occur through evolution tended to be in details rather than in serious shifts of shape. This lack of innovation in a successful group is known as evolutionary conservatism. However, despite this, trilobites inhabited a wide range of niches and explored a wide range of marine environments from their evolutionary origins in the...
Life and the evolution of continents
Life exists on a physically changing world, and these changes have both controlled the evolution of organisms and been recorded by their fossil record. Evolution operates rapidly on small populations, and so when a group of organisms becomes isolated through changes in the landscape around them, they quickly evolve to become different to their parent population. Organisms migrate across land bridges or along new seaways, as areas that were once isolated become accessible to one another. The...
Plants
The study of spores and pollen used to reconstruct long-term vegetative changes is called palynology. Spores and pollen are part of the plant reproductive system. As they are very resistant and vast numbers are dispersed over wide areas, they are important in biostratigraphy. They can also be useful paleo-environmental indicators, particularly for the Quaternary. Spores and pollen grains are very distinctive. In general, pollen grains are smaller than spores 25-35 lm compared with 100-200 m in...
Biases in the fossil record
The fossil record is extremely selective. The term preservation potential is used to describe the likelihood of a living organism being fossilized. Organisms with a high preservation potential are common fossils. The nature of their morphology and the environment in which the organisms lived are important factors in determining whether they will be preserved. These inherent biases skew our view of past life. In general, the fossil record is biased towards the following organisms with tissues...
Glossary Jbu
Archaeocyte the basic cell types found in sponges from which all specialist cells develop. Ascon simplest grade of sponge organization - the animal composes a single cup with perforated walls. Choanocyte specialist sponge cells with a long, active filament flagellum which can be used to move water through the body of the sponge and microvilli brush-like sets of small filaments to extract food from the water. Flagella whip-like appendage on a cell, allowing it to move or to generate currents....
Bryozoan evolution
There are five orders of stenolaemate bryozoans, and four of them evolved to their greatest diversity during the Palaeozoic. These include the well-known fan-shaped Fenestrata and the stony, usually stick-like, Trepostomata. These orders were severely affected by the end-Permian mass extinction event and all four were extinct by the end of the Triassic. The remaining order of stenolaemates, the Cyclostomata, were a minor component of Palaeozoic faunas but survived into the Mesozoic and radiated...
Bryozoans as environmental indicators
Bryozoans are potentially useful as environmental indicators, although their application to this topic is rarely straightforward. A major problem is comparing modern, cheilostome-dominated assemblages with older faunas. Rare bryozoan species are tolerant of most conditions, so statistical analyses of diversity or abundance tend to be applied. In post-Palaeozoic rocks and in the modern oceans, bryozoans are dominant members of shallow benthic communities in temperate latitudes, with normal...
Introduction Mlk
Vertebrates have been of immense importance in aquatic and terrestrial ecosystems from the Ordovician onwards. They are commonly present as predators and scavengers, becoming almost ubiquitous in modern faunas. However, their characteristic, multipart, internal skeleton fossilizes poorly, and they are under-represented in fossil assemblages. The vertebrates are the most important group of the phylum Chordata. The characteristic element of a chordate is its notochord, the strengthened rod...
Glossary Frd
Antennule front appendage in ostracodes, used for swimming or stability. Aperture opening in foraminifera through which most of the soft tissue projects. Autotroph organism that synthesizes organic compounds from inorganic materials. Such organisms are sometimes called producers. Calcite compensation depth CCD depth in the oceans at which calcite becomes unstable and may dissolve. Carapace term for shell used for ostracodes. Centrales circular diatoms with radial symmetry. Chamber one repeated...
Amphibians
Amphibians are tetrapods four-limbed vertebrates that lay eggs in water. They are the ancestral group to all of the other tetrapods, including reptiles, dinosaurs, and mammals, as well as birds. The most likely ancestors of amphibians, and all other tetrapods, are a group of extinct lobefin fish known as rhipidis-tians. These fish have a similiar skull morphology to the earliest amphibians and the pattern of limb bones common to all subsequent tetrapods, including humans Fig. 11.4 . This is the...
Brachiopod ecology and paleoecology
Brachiopods are exclusively benthic marine animals. As filter feeders they do not actively search for food and most brachiopods live on, or partially enclosed by, the substrate. They are dependent on currents to bring food and oxygen and carry away waste products. Most living brachiopods are attached to hard substrates, but fossil forms were much more diverse and exploited a range of benthic habitats, adapting their shell form and mechanism of attachment to suit the environment Table 6.2 ....
Evidence for early life
The search for life's origins and evidence for the pathways of its early evolution are two of the most important fields in paleontology, especially as this research informs the search for life on other planets. Evidence from a variety of sources is used to develop the debate, but as yet no consensus has emerged Table 15.1 . Molecular evidence points to a single common ancestor for all life on Earth, which makes it extremely likely that life evolved here, rather than being brought from...
Ensis
Characterized by an extremely elongated, thin, featureless shell approximately 12 cm in length with both posterior and anterior gapes. Ensis lives infaunally in muds and sands in the intertidal zone. During feeding, the anterior part of the shell is close to the sediment-water interface. During low tide, the animal burrows actively down into deeper sediments using the muscular foot. Teredo is a highly specialized bivalve able to bore into wood. The cylindrical shell is extremely reduced...
Autotropic protists
Acritarchs are hollow, organic-walled microfossils. They are believed to represent the cyst stages in the life cycles of planktic algae similar to a modern group, dinoflagellates, because both groups produce a characteristic molecule, dinosterane. They are one of the oldest groups of fossils and underwent a major radiation in the late Precambrian. Most acritarch vesicles range between 50 and 100 lm in size and are usually preserved as compressed films in black shales. Acritarchs are generally...
Life on land
The most significant event in the evolution of life during the Phanerozoic has been the colonization of land. Bacteria probably invaded fresh water and damp areas early in the Precambrian, and lichens were likely contributing to soil formation by 1000 million years ago. However, larger animals and plants all migrated from the sea onto land during the Palaeozoic. In doing so, they radically increased the living space available on the planet. The innovations that evolved to deal with this hostile...
Mass extinctions
Extinction happens all the time, but there are rare examples of short periods of time where extinction rates have been very high. The definition of the rate and duration of these events is subjective, but most researchers agree that five mass extinction events have occurred since the Cambrian Fig. 16.6 . These large faunal turnovers have been used by stratigraphers to define the boundaries of intervals of geological time Fig. 16.7 . They mostly occur at what we define as the end, or close to...
Tabulate corals
Tabulate corals were always colonial, and the individual polyps tended to be small. At various times in the past it has been suggested that they were not real corals, but recent work on their detailed skeletal structure shows that this is their true affinity. Preserved polyps from the tabulate genus Favosites have been discovered. Each polyp had 12 tentacles, and a similar overall appearance to the polyps of modern corals. Tabulate corals first appear in Lower Ordovician rocks from North...
Scleractinian corals
Scleractinian corals evolved from soft-bodied ancestors in the Middle Triassic period. By late Triassic times they had begun to form small patch reefs, and their importance as reef builders has been continuous since then. They are facilitated in this role by the following morphological adaptations they have a basal plate which acts as a holdfast, they build porous skeletons of aragonite which are more readily secreted than the massive calcite skeletons of more primitive corals , they are able...
Pterobranchs the living relatives of graptolites
There are only two living genera ofpterobranchs, Rhabdopleura and Cephalodiscus Fig. 10.2 . They have a fossil record that extends back to the Middle Cambrian, and it was probably then that both they and graptolites evolved from a common ancestor. Living pterobranchs are known worldwide, but are usually small and are easily overlooked. They are found from intertidal areas to abyssal depths, in water of normal salinity. Their preference is for areas with a rapid flow of water, and they often...
Diversification
Diversity is a measure of variety. It is usually assessed at a taxonomic level, for example, the number of species or families living at a particular time. It could also be applied to individual variation, or even to variations in DNA, but variation at this level is not generally used in the interpretation of the fossil record. All organisms share a single common ancestor that probably lived around 3.8 billion years ago. At this stage in evolution, diversity would have been extremely low by any...
Introduction 1
The Earth is the only planet we know to support life. Its long history shows that life and the planet it inhabits have a complicated relationship. Free oxygen in the atmosphere, the ozone shield, the movement of carbon into long-term reservoirs in the deep oceans, and the rapid weathering of rocks on the land surface are obvious examples of this relationship. The evolutionary history of life on Earth points to the development of a series of faunas that occupied the changing surfaces of the land...
Exceptionally preserved fossils
Remarkable fossil deposits are known as fossil lagerst tten. Lagerst tten is a German word that is applied to deposits of economic importance. The term fossil lagerst tten is used to describe fossiliferous formations particularly rich in paleonto-logical information. There are two types of fossil lagerst tten Konzentrat-Lagerst tten and Konservat-Lagerst tten Figs 1.6 and 1.7 . Occurrences where the number of fossils preserved is extraordinarily high are termed Konzentrat-Lagerst tten or...
Heterotrophic protists
Radiolaria are unicellular, marine microzooplankton characterized by an intricate, siliceous, internal skeleton. They are globally distributed and live at all levels of the water column. They have a long geological history, extending from the Cambrian to the present day, and their rapid evolution makes them useful biostratigraphic indicators. Living radiolarians may be considered as balls of protoplasm with an intricate internal skeleton, or test. Typically the test has a delicate, lattice-like...
Time and fossils
Geological time can be determined absolutely or relatively. The ages of rocks are estimated numerically using the radioactive elements that are present in minute amounts in particular rocks and minerals. Relative ages of different units of rocks are established using the sequence of rocks and zone fossils. Sediments are deposited in layers according to the principle of superposition, which simply states that in an undisturbed sequence, older rocks are overlain by younger rocks. Zone fossils are...
Classifying animals
A family tree for organisms implied in most systems of classification provides a series of events that must have happened in the past in a known order. Classification of the metazoa is therefore a key element in deducing information about their origin and early history. For example, it is now known that animals with a gut evolved relatively late in the history of metazoans. This information makes the discovery of possible fecal pellets produced from a gut-bearing animal in rocks up to 1.9...
Biogenic silica
Siliceous sponges were the main biological secretors of silica during the Cambrian, when they were mainly confined to shallow water. They formed the dominant biotic flux for this important geochemical cycle. However, since the Cambrian, two key factors have moved the site of this important flux from shallow water to deep water. These are the change in habitat of siliceous sponges and the evolution of plankton-building siliceous skeletons, the radiolarians and diatoms. The geological record of...
Phanerozoic diversity
The evolution of hard parts greatly improved the fossil record. The diversity patterns of the Phanerozoic seas were documented by Professor Jack Sepkoski, and the resulting diagram is usually referred to as Sepkoski's curves Fig. 16.2 . Diversity is the net product of the originations of species minus extinctions at any one time. This graph shows that species diversity has increased overall through the Phanerozoic. Over 800 families are now known, as opposed to around 200 in the Cambrian....
Land plants
The fossil record of plants is typically fragmentary. Generally, plants have a low preservation potential and assemblages are usually composed entirely of disarticulated material. During their life cycle plants may shed some of their component parts. Other plants become broken up or fragmented due to tapho-nomic processes. As a result, separate parts of the same plant are often assigned to different organ genera Fig. 12.1 . The extent of plant preservation is dependent on the morphology and...
Sporebearing plants
Advanced spore-bearing plants with true leaves and roots evolved during the Devonian lycopods club mosses , spheno-phytes horsetails , pteridophytes ferns , and progymnosperms precursors to the seed-bearing gymnosperms . Some plants developed specialized woody tissue enabling them to attain the stature of trees. Lycopods lycophytes formed a major part of the Devonian flora. Two distinct evolutionary lines developed from the lycophytes. One line, now extinct, evolved into the tall trees that...
Introduction Jrd
The cnidarians are a phylum that includes jellyfish, sea anemones, and corals. Cnidarians evolved in the Precambrian, and are amongst the earliest multicellular animals to be found in the fossil record. They are simple metazoans, with a primitive grade of organization. Although their bodies are organized into tissues, they lack organs. Their body plan is usually radial, although this has been modified in some groups. The cup-shaped body is composed of two layers of cells with a supportive...
Reconstructing the ecology of fossils
The information available to help in reconstructing a fossil and inferring its life habits come from three sources from modern relatives, from modern analogs, or from trace fossils Fig. 1.10 . Living relatives of a fossil are extremely useful in inferring information about that fossil's ecology. Living Nautilus, for example, uses a system of jet propulsion to power it through the water. Extinct ammonites share a common ancestor with this group and have a similar shell morphology. It therefore...
Carboniferous coal forests
Immense forests dominated by spore-bearing plants thrived in low-lying, swampy areas during the Carboniferous Fig. 12.8 . Extremely tall club mosses, Lepidodendron, and Sigillaria dominated the floodplain vegetation. Lepidodendron had a tall, unbranched trunk with a small canopy of branches at the top. Some plants exceeded 50 m in height and 2 m in diameter at the trunk base. Underground branched axes, Stigmaria, with root-like appendages, supported the massive trunk. The giant horsetail...
Seedbearing plants gymnosperms
Seed-bearing plants are divided into two groups. Those with exposed naked seeds, the gymnosperms, and plants that flower and produce seeds within a fruit, the angiosperms. Plants with seeds first appeared in late Devonian times and proliferated during the Upper Palaeozoic. Gymnosperm development peaked in the Mesozoic. Seeds have four main reproductive advantages over spores 1 A multicellular embryonic plant is held within the seed, whereas a spore is a single cell. 2 Seeds contain a food...
The origin of complexity
Tiny prokaryotes are still the most numerous life form on Earth. The generally larger eukaryotes, as single cells or larger multicellular organisms, evolved later. The origin of eukaryotic life is a source of intense debate. Eukaryotes contain organelles that perform specific functions, e.g. energy storage is undertaken by mitochondria and movement by cilia or a long flagellum, and reproduction and the storage ofgenetic information within a nucleus Fig. 15.2b . The presence of a nucleus is one...
Rugose corals
Rugose corals first appear in the geological record in Middle Ordovician rocks from North America. They diversified more slowly than tabulate corals, but their patterns of evolution are similar. They were important members of Palaeozoic reef communities, but their diversity declined during the end-Devonian extinction. At this time, and in the earlier extinction event at the end of the Ordovician, solitary corals and generalist colonies were more likely to survive than highly specialized...
Fossils at a Glance
A John Wiley amp Sons, Ltd., Publication This edition first published 2010, 2010 by Clare Milsom and Sue Rigby Previous edition 2004 Blackwell Publishing was acquired by John Wiley amp Sons in February 2007. Blackwell's publishing program has been merged with Wiley's global Scientific, Technical and Medical business to form Wiley-Blackwell. Registered office John Wiley amp Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK Editorial offices 9600 Garsington Road, Oxford,...
The Cambrian lagerstatten
At a variety of locations around the world, exceptionally preserved organisms of Cambrian age have been found, offering an unparalleled insight into this critical point in the evolution of life on Earth Table 1.1 . The most famous site is the Burgess Shale, in Canada, which records over 125 fossil genera, dominated by arthropods. A broadly similar fauna is found at Emu Bay in Australia. The older Chengjiang site, in China, records a similar variety of life from a different paleocontinent. The...
Bryozoan ecology
Bryozoans have variable colonial integration, with zooids tending to become more closely integrated through evolutionary time. Specialized zooids, such as the avicularia, do not feed and are provided for by other members of the colony. The extremely complicated and precise colony forms of many bryozoans suggest a close integration of the colony, with overall control being exerted on the activities of individual animals building the skeleton. The shape of the colony is often determined by the...
The earliest land plants
Plausible fossil green algae, dating back to 850 Ma, have been described from the Bitter Springs Chert, a siliceous deposit from Australia. Green algae may have colonized shallow water and shoreline habitats subject to periods of exposure. In this way algae living in marginal environments would have become adapted to periods of exposure and therefore life on land. Such plants would have had a selective advantage over plants living continually submerged. The first land plants were probably...
Ediacaran life
In 2004 a new period was added to the geological record. This is the Ediacaran period, which covers the timespan 635-542 million years ago. The period begins with a change from an icehouse to greenhouse state, and ends with the diversification of modern, skeletonized animals at the base of the Cambrian period Chapter 16 . During this time period, the first multi-celled animals appeared in the fossil record. Some of these animals appear to have no living relatives, and belong to an extinct group...
Crinoid morphology
Crinoids originated in the early Ordovician and persist to the present day. Their maximum abundance was in the Palaeozoic. Most fossil crinoids were attached to the substrate by a stalk and occupied shallow water environments Fig. 7.2 . Modern species are more widely distributed, living in habitats ranging from tropical reefs to cold, deep waters at polar latitudes. Reef-dwelling crinoids are stemless, are able to crawl Calyx connects the stem and the arms and contains the vital organs. The...
Sponge morphology
Sponges are characterized by four important cell types. Arch-aeocytes are cells shaped like amoebae, able to move within the colony and lacking a fixed shape. These cells are feeding cells and can also change into another cell type if required. Sclerocytes secrete mineralized elements of the skeleton, while spongocytes secrete the organic parts of the skeleton. Cho-anocytes are the cells that generate feeding currents through the sponge. They have a funnel-shaped end, with a long flagel-lum, or...