Introduction

Micropaleontology is the study of microscopic fossils. Because it is based only on fossil size, the term unites groups that are otherwise unrelated and includes microscopic organisms and microscopic parts of macroorganisms. Many sediments contain microfossils and they are important biostratigraphic, paleoenvironmental, and paleoceanographic indicators. Microfossils are important in biostratigraphy due to their abundance, global distribution, and durability. Their sensitivity to environmental...

Anapsids

Anapsids are a group that includes the earliest reptiles, a smattering of Permian and Triassic forms, and the modern turtles and tortoises, whose fossil record also extends back to the Triassic. Permian and Triassic anapsids fall into three families. The Permian millerettids are known from South Africa, which was at temperate southern latitudes during that time. They were small, active, insectivores of moderate size, with skulls typically around 5 cm long. Late Permian and Triassic...

Diapsids

In order to follow the evolution of the other major group of reptiles, the diapsids, we must return to the Triassic. Early diapsids had evolved into small or medium-sized carnivores, but had not been able to compete successfully with mammallike reptiles. However, following the end-Permian extinction event, they radiated significantly and during the Triassic replaced synapsids by active competition in almost all ecological niches. This successful group of diapsids is called archosaurs. It may be...

The Cambrian explosion

More and more data are helping to explain the event at the base of the Cambrian where mineralized skeletons evolved. A few sections worldwide record the full timespan from just before to just after the Precambrian-Cambrian boundary. As these are investigated, a detailed picture of events associated with this time period is emerging. The two most important questions about the boundary are 1 What caused the appearance of skeletons Was it a biological phenomenon or one related to changes in the...

Patella Dactylioceras

Patella is characterized by an uncoiled, conical, cap-like shell. Pronounced ribs that radiate from the apex strengthen the shell. The height of the cone is approximately 3 cm. Patella lives in the intertidal zone and clings to rocks using its foot. During low tide the animal clamps down to avoid desiccation. At high tide the gastropod grazes the rock surface for encrusting algae.

Magellania

Rhynchonelliform brachiopod Triassic-Recent This Recent brachiopod lives in Australian and Antartic waters at a depth of between 12 and 600 m. It measures approximately 3 cm from the pedicle opening to the anterior edge. Using its stout pedicle it attaches to hard substrates. The pedicle acts as a stalk and raises the brachiopod from the attachment surface. The lophophore is supported by a distinctive calcareous loop attached to the hinge area of the dorsal valve. This structure is only rarely...

Corals as climatic indicators

Corals have a long lifespan and record events that happened during their whole life in the incremental growth of their skeletons. Solitary rugose corals, such as the Silurian genus Kodono-phyllum, narrow and thicken along their length (Fig. 4.8). Wide patches represent times when the polyp was thriving. Narrow zones indicate times when the polyp was under stress and lost body mass, contracting towards the center of its calice, and only adding skeletal material to this central portion. Corals...

Figure acknowledgments

Figure 1.1 from Treatise on Invertebrate Paleontology, part O, Geol. Soc. Amer. and Univ. Kansas Press (Figure 159.6, O218) Crimes, T.P., Legg, I., Marcos, A. and Arboleya, M., 1977, in Crimes, T.P. and Harper, J.C. (eds) Trace Fossils 2, Seel House Press (Figure 10, p. 134). Figure 1.2 based on Williams, S.H., 1986, in Hughes, C.P. and Rickards, R.B. (eds) Palaeoecology and Biostratigraphy of Graptolites, Geological Society Special Publication 20 (Figure 1, pp. 166-7) and Barnes, C.R. and...

Dinosaur trackways

Trails of footprints preserved in the fossil record can reveal important information regarding the locomotion, morphology, and social behavior of the track maker. Trackways indicate if the dinosaur was bipedal or quadrupedal and whether the gait was narrow or sprawling. They can also be used to estimate the speed of travel. In general if the pace distance is greater than four times the footprint length the gait may be described as running. Speed is calculated using formulae developed by the...

Cypridina

Cypridina is distinguished by a thin, featureless, ovate carapace (approximately 1.5 mm in length). This ostracode is a marine, pelagic filter feeder, thriving in nutrient-rich waters associated with upwelling. The projection at the anterior of the carapace encloses elongated front limbs adapted for swimming. It has two stalked, compound eyes and a median simple eye. The most common coccolithophore in the modern oceans. The coccosphere is about 5 lm across. Cypris lives in freshwater...

Trilobite morphology

Trilobites were divided across the body into a head or cephalon , thorax, and tail or pygidium , and along the body into three lobes - a central axial lobe covering the main body cavity, and two pleural lobes covering the legs and gills on either side Fig. 8.3 . The cuticle from which the trilobite exoskeleton was constructed was layered, with a thin outer layer and a thicker inner one. Both were made from calcite, arranged in an organic matrix which has not yet been characterized. The head, or...

Early vascular plants

Horneophyton

The transition from aquatic to terrestrial habitats gradually took place over tens of millions of years. Plants steadily adapted to the environmental challenges of the land and became less dependent on aquatic habitats. The first true vascular plants are Middle Silurian, although resistant, cutinized spores are known from Upper Ordovician sediments, suggesting that they may have evolved earlier. Known from the mid-Silurian, early leafless and or rootless Sporangia borne on tips on terminal...

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

Fossil Angiosperm

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

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

Marsupials Southern 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

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...

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

Permian Sea Floor

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...

Synapsids

Jurassic Marsupials

Synapsid, mammal-like reptiles dominated the late Carboniferous and Permian land masses. The first radiation was of the group known as pelycosaurs Fig. 11.8 . This group moved into a range of dry habitats, and evolved to a large size, and in some cases to a herbivorous diet. The best known pelycosaur is Dimetrodon, with a skeleton characterized by a huge sail supported by extensions to its backbone. This sail probably helped the animal to maintain its preferred body temperature, and was one of...

Diversification

Diversity Extinction Graph

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...

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

Climate Greenhouse Icehouse Devonian

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

Lepidodendron Stem Anatomy

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...

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

Sigillaria

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

Gymnosperms Classification

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

Neoproterozoic Animal Names

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

Rugosa Septa

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

Devonian Plant

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

Cyclomedusa

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

Ordovician Crinoids

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

Basal Holdfast

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...

Trilobite mode of life

Trilobite Lifestyles

A great deal of work has been done on determining the mode of life of trilobites. Evidence for these deductions comes from the distribution of a particular species oftrilobites, modifications to their shape, and physical experiments conducted on model trilobites. The result is that many trilobites can be confidently located in terms of the depth of water in which they lived and the ecological role that they occupied. Several elements of trilobite morphology are useful in helping to infer life...

Pentacrinites

This crinoid has a small calyx and very long arms. The length of the figured specimen is approximately 13 cm. Exceptionally preserved specimens of Pentacrinites are found in the Lower Jurassic marls of Dorset, UK. These crinoids are commonly associated with fossil driftwood. It has been proposed that this species of Pentacrinites was pseudoplanktic, living attached to floating driftwood. Eventually the wood became waterlogged and sank into anoxic sediments that preserved the crinoids. This...

Deiphon

A very spiny trilobite about 4 cm in length when fully grown. The cheeks are reduced and both cephalon and pygidium are remarkable for their pair of large, robust spines. The lifestyle of this unusual form is disputed. It may have been pelagic, and the eyes point forwards, but they are rather smaller than other known open water forms. It may well have been an active trilobite living on soft mud, where the spines would have helped it stay on the sediment surface. This is known as a snowshoe...

Calymene

This is the trilobite most figured in this chapter. It is a small species, typically 2 cm in length. The cephalon is the widest part of the animal, and the thorax typically has 13 segments. The species was capable of complete enrollment, and is commonly preserved in this attitude. The fixed hypostome suggests that Calymene was predatory. A large-eyed trilobite with a streamlined thorax and pygidium. The species was small, typically 4 cm in length, and is usually found in black shales. It had a...

Brachiopod evolution

Brachiopods originated in the early Cambrian all three subphyla are known from this time and exist today. In the Cambrian, the Linguliformea and Craniiformea outnumbered the Rhynchonelliformea, although since this time the latter have dominated. In the early Ordovician the rhynchonelli-forms underwent a massive radiation, possibly in response to the opening up of new habitats associated with continental break-up. They continued to flourish until the end of the Ordovician, when glaciation...

Planorbis

Belonging to the subclass Prosobranchiata, order Mesogas-tropoda, this freshwater gastropod has an almost planispiral shell diameter approximately 1 cm . Although the morphology varies within the genera, most species have smooth shells. Living in a range of freshwater environments, Planorbis feeds on algae and plants. Some species live entirely within water, whilst others need to surface for air. This mesogastropod has a moderately high-spired shell with an oval aperture and short siphonal...

Neohibolites

This belemnite has a small, spindle-shaped guard approximately 4 cm in length with a long ventral groove in the area around the alveolus. The soft-body morphology of belemnites is known from exceptionally preserved individuals associated with fossil lagerstatten. Such specimens have long hooked tentacles and ink sacs.

Crinoid evolution

The first true crinoids appeared in the early Ordovician. Rapid diversification followed and all the main Palaeozoic crinoid groups were established by the Middle Ordovician. Most Palaeozoic crinoids were attached to the substrate by stems. Extinction at the end of the period resulted in a depleted crinoid fauna in early Silurian times. Subsequently, crinoids re-radiated, reaching their peak diversity in the early Carboniferous. By the beginning of the Mesozoic, crinoid abundance and diversity...

Spirifer

Rhynchonelliform brachiopod Devonian-Permian A triangular-shaped brachiopod with a long, straight hinge line 2-7 cm in length . The large delthyrium shows that the brachiopod lived attached to the substrate. The fold and sulcus enabled the brachiopod to separate the incoming nutrient-rich water from outgoing waste water. The triangular shape of the brachiopod is related to its internal morphology. The lophophore supports two symmetric spires with an axis parallel to the hinge line. These...

Trace fossils

Trace fossils are preserved impressions of biological activity that record fossil behavior. Trace fossils are classified on a behavioral ethological basis. Distinct trace fossil assemblages can be used in the interpretation of paleoenvironment. Traces are named according to the form of the trace rather than the trace maker. Trace fossils are important in the identification of the Precambrian-Cambrian boundary.

Bivalves

Bivalves are laterally compressed mollusks enclosed within a pair of hinged shells or valves. The valves are closed by the adductor muscles. The shell is opened by relaxing these muscles and water currents are drawn into the cavity. In the majority of bivalves the gill is modified for filter feeding, although the earliest bivalves may have been deposit feeders. Some bivalves retain this feeding strategy. Most forms are capable of limited movement and the foot can protrude into the sediment to...

External morphology of brachiopods

Mineralized material is secreted from the mantle lining the shell. Linguliforms are phosphatic, and craniiforms and rhynchonelliforms are calcareous. In the latter group the shell is multilayered and may have thin, tubular structures perpendicular to the layering. These are called punctae and are a useful diagnostic feature of brachiopods in thin section. Key aspects of the brachiopod external morphology are shell shape, shell sculpture, and the form of...

Microinvertebrates

Ostracodes are small crustaceans enclosed within a bean-shaped, two-part shell. They live in all aquatic environments, have a fossil record extending from the Cambrian, and are useful indicators of past salinity. Living ostracodes secrete a calcareous carapace formed of two slightly overlapping, ovate, hinged valves. Most ostracodes are less than 2 mm in length, although some Palaeozoic species reached 80 mm and a few living forms are 20-30 mm in length. Carapaces can be heavily calcified and...

Coral morphology and evolution

Morphology Soft Coral

The class Anthozoa includes soft-bodied sea anemones and corals that build calcareous skeletons. This ability to biominer-alize arose at least four times within the group, once for each of the major skeletal orders, and once for an unusual Silurian coral called Kilbuchophyllia Fig. 4.2 . Coral skeletons can be made from aragonite or calcite both CaCO3 . Most tabulate and rugose corals are built from the latter, most scleractinian skeletons from the former. Tabulate and rugose corals evolved...

Echinoid ecology and evolution

Echinoids exploit three main life habits represented by three very distinctive morphologies Table 7.3, Fig. 7.9 . Although regular echinoids are known from the Ordovician they are generally uncommon in the Palaeozoic. Lower Palaeozoic forms tended to be small. Size generally increased through the era. Echinoids declined significantly in the late Carboniferous and only a few taxa survived the end-Permian mass extinction event. Echinoid abundance increased in early Mesozoic times. There was a...

Sphenopteris

Part of the stem of the fossil lycopod Sigillaria a lycophyte . The external texture shows the former positions of the leaf bases. Sporangia were borne on the stem surface amongst them. The figured stem fragment is 6 cm in length. Part of the foliage of the extinct fern Sphenopteris a pteridophyte . Fronds have distinctive lobed pinnules. The figured section of frond is 6 cm in length.

Paradoxides

An extremely large trilobite, growing up to 60 cm in length, with up to 21 segments in the thorax. Each segment ends in a long spine. The cephalon also bears a pair of long spines called genal spines pointing towards the pygidium. The many spines on this trilobite may have helped it to stay on top of the soft sediment, or may have had a protective purpose, as this species was not able to enroll completely.

Sponges as reef builders

Fossil Sponge Paoli Septa

The best preserved fossil sponges tend to be reef formers, and the group has played an important role in building or colonizing reefs through the Phanerozoic. All reef-building sponges have a predominantly calcareous skeleton. Archaeocyathids Fig. 3.2 evolved into some of the first reef formers, during a brief period in the early Cambrian. They were small forms, generally around 10 cm in height, with a cup-like shape. Modular variations on this basic plan allowed them to increase in size and...

Climacograptus

Climacograptus

Diplograptid and early monograptid fauna Ordovician-Silurian A form genus - that is, a set of species that have a common shape rather than a common ancestry. These form genera are still usefUl for identifications in the field and at a preliminary level. Climacograptids have box-like thecae and are always biserial. They are typically 2-6 cm long. A spirally coiled graptoloid with unusual thecae, each with a spine at the aperture. These spines are capable of developing into branches, each made of...

Trilobite paleogeography

Trilobites evolved rapidly into easily distinguishable forms. Their species and genera can be used to aid in the reconstruction of both past continental positions and in unraveling one of the most puzzling events in the history of life - the Cambrian explosion. Trilobites lived most commonly on the continental shelves, and drifted around the Palaeozoic world as passengers on the tectonic plates. By reconstructing the distribution of provincial species, which only lived on one of these plates,...

Hemicidaris

This regular echinoid has a radially symmetric, hemispherical test approximately 3 cm in diameter . The ambulacra are narrow and the plates are ornamented with small tubercles. The interambulacral plates have a large, central tubercle surrounded by smaller, less prominent tubercles. A long, solid, primary spine was articulated on the central prominence and shorter spines attached to the minor tubercles. Spines were used for protection and locomotion. Such regular echinoids were epifaunal and...

Agnostus

A tiny trilobite, usually less than 5 mm in length, with an unusual head and tail and only two thoracic segments. The species had no eyes or facial suture. Rare occurrences of this animal with preserved soft parts suggest that it was an active swimmer, which usually adopted a partly enrolled shape see Fig. 8.4 . It likely fed on material suspended above very soft sea floors and was typical of deep water assemblages. A blind trilobite with a wide fringe developed around the front of the cephalon...

Micraster

Micraster is an infaunal echinoid with a distinctive heart-shaped test approximately 5 cm from posterior groove to anterior margin . The ambulacra are narrow and subpetaloid. The anterior ambulacrum is situated in a deep groove that leads towards the mouth. The anus is positioned on the anterior margin. Below the anus there is a small fasciole, a current-generating area that swept waste material into a sanitary tube. The mouth is on the lower surface, positioned towards the anterior margin. It...

Beyrichia

The carapace of this extinct marine ostracode has a long, straight hinge line about 1 mm in length and a distinctive granular or pitted external surface. This genus shows clear sexual dimorphism. The carapace was expanded in the female to accommodate the brood pouch. It has been suggested that this ostracode swam in shallow waters and fed on detritus, benthos, and plankton.

Echinoid morphology

Regular Echinoid Morphology

Echinoids, or sea urchins, have a robust, internal skeleton the test composed of numerous, fixed, calcite plates. Instead of arms the test has five narrow zones formed from perforated plates the ambulacra through which the tube feet emerge. These porous segments alternate with broader areas the inter-ambulacra that lack pores. The anus is on the upper aboral surface and is surrounded by a double ring of plates Fig. 7.7 . The mouth is on the underside oral surface . The external surface of the...

Gastrioceras

Gastrioceras

This Palaeozoic ammonoid has a goniatitic suture. The shell is inflated cadicone and the external surface is finely ribbed. The shell diameter is approximately 5 cm. Small tubercles line the margin of the moderately deep umbilicus. Gastrioceras is found in marine shales and is a useful zone fossil for the Upper Carboniferous. This ammonite is typically serpenticone and the external surface is ribbed the shell diameter is approximately 6.5 cm . The body cavity is tubular and elongated. Numerical...

Lepidodendron

Section of a branch showing the characteristic pattern of Lepidodendron leaf bases. Leaves of Lepidodendron were linear with a swollen attachment area. Leaf attachment sites leave a distinctive, rhombic impression leaf cushions on the stem surface. The close spacing of these markings shows that the foliage was dense. The leaf size varied between species and leaves were mainly restricted to smaller branches. The leaf cushions shown are approximately 3 cm in length. Frond of the seeded fern...

Cephalopods

Nautilus Fossil

Cephalopods are the most morphologically complex group of mollusks. They occupy the same ecological niche as fish and they are arguably the most sophisticated group of invertebrates. The class includes active, jet-propelled predators with highly developed sensory structures. All cephalopods are marine. The body of cephalopods is elongated so that the mantle cavity is anterior and the visceral mass is at the posterior end of the animal Fig. 9.8 . Living cephalopods swim using jet propulsion....

Graptolite mode of life

Graptolite zooids are thought to have been similar in appearance to modern pterobranch zooids, and in particular to those of Rhabdopleura. A cephalic shield would have been needed to secrete the collagenous bandages seen on the surface of grap-tolite rhabdosomes, and the fact that this surface was accessible to the zooids suggests the absence of external soft tissue. In planktic graptoloids one of the most noticeable adaptations is to an extremely regular colony shape and it seems likely that...

Annularia

Annutaria is foliage associated with the giant horsetail Catamites a sphenophyte . Slender leaflets were arranged in whorls around the smaller stems. Individual leaves were fused at their bases and had a single, unbranched vein running along the length of the leaf. Leaflets were approximately 4 cm in length. Horsetails were abundant in low-lying, marshy areas in the Carboniferous.

All Insects Pictures

Acanthopyge

Trilobites Figs 8.1 and 8.2 belong in the phylum Arthropoda, the most diverse phylum on the planet today. Arthropods include all insects, millipedes, centipedes, scorpions, and crus- Fig. 8.1 Trilobite Acanthopyge length 1.5 cm . Fig. 8.1 Trilobite Acanthopyge length 1.5 cm . taceans, such as crabs and lobsters, in addition to a range of more obscure forms. If estimates of10 million living species of insect are correct, then this phylum outnumbers vertebrates, for example, by a hundred times....

Evolution of trace fossils

As trace fossils are controlled by the nature of the depositional environment, they do not make good zone fossils. The only exception to this is at the Precambrian-Cambrian boundary. The base of the Cambrian is defined by the first appearance of the feeding trace of a worm-like animal, Treptichnus pedum. There is a significant increase in the diversity and complexity of trace fossil assemblages found in basal Cambrian rocks, contrasting with the simple burrows typical of late Precambrian times....

Stomatopora

Cyclostome gymnolaemate bryozoan Triassic-Recent An encrusting bryozoan, evolved to a growth form that spreads the colony over a wide area with a low density of zooids. By dispersing zooids widely, it is more likely that the colony will survive following the local destruction e.g., by predators of zooids occupying one part of the substrate. As a member of a pioneer community it would have encountered uncertain conditions, which might have been highly favorable or unfavorable.

Halysites

A colonial coral with a distinctive chain-shaped corallum. This cateniform shape is rare. Each corallite is connected to the next by a coenenchyme composed of a single tube cut horizontally by many small plates. Corallites are usually 2-6 mm across. The chain form of this coral had several advantages, especially in areas of high sedimentation rate. The holes between the polyps allowed them space to spread out for feeding, and also to dispose of unwanted sediment. They were able to colonize...

Amphoracrinus

This is the calyx of the Carboniferous crinoid Amphoracrinus height approximately 4 cm . Three basal, five radial, and five brachial plates form the lower part of the calyx. A plated, domed tegmen covers the calyx and there is a pronounced anal tube. Although only rarely preserved, the arms are known to branch many times. The whole calyx structure is rigid. Apiocrinites has a distinctive barrel-shaped calyx approximately 4 cm in height . The stem is formed from robust columnals and can be up to...

Ichnofacies

Fossil Trace Classification

Arguably the most important use of trace fossils is their application to paleoenvironmental interpretation. As the behavior of an organism is linked to certain environmental conditions, so the manifestation of this behavior i.e., the trace fossil is indicative of particular environments. Different types of trace fossils form distinct groupings that are generally stable through time. Four of the identified ichnofacies are primarily related to energy conditions, water depth, and deposition rates....

Molluskan shell growth

Each group has evolved a small range of the possible spiral shapes that can be generated, adopting those that function best for their mode of life. Spiral shells can be described simply using four variables Fig. 9.2 . Understanding the underlying symmetry of apparently very different mollusk shells is important because it gives an insight into the basic similarity of all of these forms. Gastropods usually have a low whorl expansion rate low W and a high rate...

Internal morphology of brachiopods

Brachiopod Internal Structure

The internal anatomy of articulated brachiopods can be divided simply into two sections. The pedicle, main internal organs, and muscles are packed together at the back of the shell whilst the lophophore dominates the mantle cavity in the central and anterior area Fig. 6.1a . Food particles are trapped by the lophophore's cilia, and passed back to the mouth and into the digestive tract. Waste products are emitted as small pellets from the anterior of the shell. The pedicle is the primary method...

Gastropods

Gastropods are the largest and most diverse class of mollusks. They live in marine, freshwater, and terrestrial environments and have exploited the widest variety of habitats and have developed a remarkable range of feeding strategies. Gastropods first appeared in the early Cambrian and reached their peak diversity in the Cenozoic. Gastropods may have a calcareous shell or be entirely soft bodied. They have a well-developed head and sensory organs and an expanded muscular foot Fig. 9.3 . In...

Ophiuroids

Ordovician Times And Its Animals

Ophiuroids, or brittle stars, are star-shaped echinoderms with five slender arms radiating from a distinct, circular, central disk Figs 7.5 and 7.6 . The arms are extremely flexible and are formed of specialized vertebrae-like plates. The mouth is on the lower surface at the center of the disk. Ophiuroids gather food with their arms. They are very mobile and are able to coordinate their arm movements to allow for relatively rapid crawling and swimming. Some species live in shallow water,...

Molluskan classification

The nature of the shell is an important characteristic in are the dominant classes of fossil and living mollusks. A more mollusk classification. Gastropods, bivalves, and cephalopods detailed description of each class is given in Table 9.1. Table 9.1 The main groups of mollusks. Table 9.1 The main groups of mollusks. Single, undivided, coiled shell or shell-less. Mantle cavity faces the front. Muscular foot is flattened and used for locomotion. Head is well developed with eyes and tentacles,...