Angiosperm origin
According to most traditional interpretations, as well as explicit phylogenetic analyses, angiosperms are a well-defined monophyletic group. Most morphology-based cladistic analyses including both extant and extinct taxa identify a monophyletic clade, often referred to as the anthophytes, comprising the angiosperms, Gnetales, Bennettitales, and Pentoxylon Fig. 1.4.2.1a . Several molecular phylogenetic studies also place Gnetales as the closest living relatives to the angiosperms. The anthophyte...
Bryozoans as a model system
Organisms that grow by budding morphologically variable but genetically homogeneous modules e.g. zooids within bryozoan colonies offer some special opportunities for the investigation of evolutionary tempo and mode. First, most characters whether metric, meristic, or coded behave as continuous variates, because zooids with different states of a character occur in varying proportions from colony to colony Cheetham 1987 . More significantly, breeding experiments with living bryozoan species have...
New data Panderichthys Acanthostega Ichthyostega and others
Panderichthyids include Panderichthys Fig. 1.3.7.1b and Elpistostege Clack 1997 from the Frasnian of Latvia and Canada, respectively. They possess tetrapod-like dor-sally placed orbits, flattened skulls, enlarged ribs, fin distribution, and details of humeral morphology Coates 1996 . However, these apparently advanced characters are associated with primitive features such as a jointed braincase resembling the generalized sarcopterygian condition Carroll 1996 , and many key skeletal features...
Coalswamp history
For over nine million years Westphalian coal swamps were dominated mainly by lycopsids and cordaites. The dominance of these groups reflects the commonness of the environments for which they were ecologically specialized wet to flooded in the case of most lycopsids and periodically dry in the case of cordaites. Medullosans and specialized lycopsids occupied fire and flood prone habitats ecotonal between peat and clastic swamps. Tree ferns were interstitial opportunists in all but the wettest...
Community response to the Mesozoic marine revolution
Various changes in benthic communities have been attributed to the increase in predation and grazing during the Mesozoic marine revolution. Communities of the Palaeozoic and early Mesozoic were dominated by Fig. 1.4.1.1 Number of families of marine durophagous predators, including eurypterid and crustacean arthropods, cephalopod molluscs, and vertebrates. Abbreviations from left to right LS, Late Silurian ED, Early Devonian MD, Middle Devonian LD, Late Devonian EC, Early Carboniferous LC, Late...
Major events in the evolution of Palaeozoic reef communities
Notwithstanding the great diversity of invertebrates that have contributed to reef-building over the course of the Phanerozoic, there appears to be a limited number of functional organizations that have evolved repeatedly and independently, suggesting that variations in life history as expressed by growth form have always been Fig. 1.3.3.3 Reconstruction of an Upper Devonian back-reef community, Canning Basin, Western Australia. Back-reef sediments show distinctive shallowing-upwards cycles...
What is a coal swamp
In broadest terms, coal swamps are mires wet environments in which organic matter accumulates. Mires can be classified broadly along a physical gradient that simultaneously describes their three-dimensional geometry, nutrient, and hydrological status. In planar mires the surface is below or at water table for much of the year and ground water includes mineral nutrients hence these mires are termed minerotrophic or rheotrophic. The Florida Everglades are a modern example. In domed, or...
Origin and earliest fossil records of hexapods
The sparse fossil record of mid-Palaeozoic hexapods, the pattern of colonization of land by Palaeozoic plant and arthropod groups, and temporal constraints on hexapod origins imposed by hypotheses of arthropod phylogeny on hexapod origins all suggest that the earliest hexapods probably appeared during the Late Silurian. Although often used as a synonym for 'Insecta', the term 'Hexa-poda' designates the more inclusive clade that consists of the Collembola springtails and Protura proturans ,...
Acanthodians
The oldest fishes with jaws and teeth preserved intact are the acanthodians, which date back to the Early Silurian. They are often represented in microscopic residues from dissolved limestone as isolated teeth, scales, and fin spines. Acanthodians have been likened to 'spiny sharks' in past literature, although their affinities appear to lie closer to the higher jawed fishes, such as osteichthyans true bony fishes , because of scale structure and the gross morphology of their braincase. The...
List of Contributors
L.C. AIELLO Department of Anthropology, University College London, Gower Street, London WC1E 6BT, UK. R.J. ALDRIDGE Department of Geology, University of Leicester, University Road, Leicester LEI 7RH, UK. P.A. ALLISON T.H. Huxley School for Environment, Earth Science amp Engineering, Imperial College of Science, Technology amp Medicine, Prince Consort Road, South Kensington, London SW75BP, UK. W.D. ALLMON Paleontological Research Institution, 1259 Trumansburg Road, Ithaca, New York 14850, USA....
Deciduous forests
The in situ tree stumps and litter layers of the Eocene fossil forests of Axel Heiberg Island Canadian Arctic Archipelago, palaeolatitude 75-80 N represent an excellent example of the Paleocene and Eocene vegetation of the high northern palaeolatitudes which has been termed polar broadleaved deciduous forest. These polar deciduous forests were of relatively low diversity and dominated by wind-pollinated, dry fruited, deciduous trees of the flowering plant families Betulaceae birch trees ,...
Problems and limitations of current knowledge
There are many lower-level taxonomic, stratigraphic, and biogeographical hypotheses upon which palaeonto-logical studies of speciation are based, and confirming their validity has often been very difficult. The specimens being studied must indeed belong to a single lineage or set of sister lineages, and all branches of such a clade of sister taxa must be included in the study. Micropalaeontological studies in particular have not always paid sufficient attention to these taxonomic prerequisites....
Origin of Primates
Whether the order Primates is restricted to extant forms and their undisputed extinct relatives Euprimates , or encompasses Plesiadapiformes as well, the origin of the group is enigmatic. The oldest euprimates appear abruptly in the fossil record in basal Eocene deposits of North America and Europe slightly later in Asia , with no clear indication of either their phylogenetic or geographical source. They seem to be part of an immigration event, also involving the ungulate orders Perissodactyla...
Plesiadapiformes
Plesiadapiforms were mouse- to marmot-sized arboreal animals that were among the most successful Paleocene-Eocene mammals. They were especially common and diverse in western North America, and are also known from Eurasia. Plesiadapiforms occupied an ecological niche approximating to that of Eocene rodents and euprimates. All three groups coexisted in the Eocene, but plesiadapiforms were considerably less spe-ciose and abundant then than during the Paleocene, a decline attributed to competition...
Ardipithecusthe earliest hominid
The hominoid fossil record for the period 8-5 Ma is poor, consisting of isolated specimens, most of which are too fragmentary to provide any reliable evidence about taxonomic affinity. The first creature with a more comprehensive fossil record, and which shows at least some rudimentary human specializations, is Ardipithecus ramidus, the 4.5 Ma remains of which were recovered at a site called Aramis, Ethiopia, in 1992 and thereafter. The fossils share some features with living species of Pan,...
Placoderms
The most successful of all the early jawed fishes were undoubtedly the placoderms, which appeared in the Early Silurian and reached a peak of diversity during the Middle-Late Devonian. Their name means 'plated skin', referring to a mosaic of bony armour plates that enveloped their heads and trunks. They possessed shark-like tails and in their overall anatomy were much akin to chondrichthyans. Placoderms have alternatively been placed as possible relatives of the bony fishes oste-ichthyans...
Introduction Pie
Living primates include monkeys, apes, and humans grouped as anthropoids , and their primitive cousins the lemurs, lorises, and tarsiers prosimians . This arrangement is gradistic but only partly phylogenetic Anthropoidea are considered monophyletic, whereas prosimians are not. Consequently, many authorities employ the cladistic terms Strepsirrhini for lemurs lorises Lemuriformes , and Haplorhini for Tarsi-iformes Anthropoidea Fig. 1.5.4.1 . A sister-taxon relationship between tarsiers and...
The role of continental drift and the isolation of mammalian faunas
Much of Tertiary and modern mammalian diversity is related to the isolation of different founder groups of mammals on different continents, and subsequent convergent evolution of similar ecomorphological types. The most obvious example today is the separate nature of the Australian marsupials, with their own iteration of various adaptive types such as 'moles', 'anteaters', and 'wolves', etc. Later Tertiary dispersals have muted or obliterated many differences in mammalian faunas between...
The earliest modern biome
Amongst modern land biomes tropical rain forests are familiar because of issues involving their fate due to human impact. However, asking palaeobiologists When was the earliest tropical rain forest ' may yield answers ranging from the Upper Carboniferous to only a few thousand years before present. None of these answers is incorrect, but all require further explanation. In the Upper Carboniferous, peat ultimately coal -forming and clastic swamp forests existed in equatorial latitudes, so these...
Introduction Qlb
Angiosperms flowering plants were the last major group of plants to appear in the fossil record their first scattered occurrences are reported from the earliest Cretaceous. Angiosperms diversified and increased dramatically in abundance through the Cretaceous, and by the mid-Cretaceous they had attained ecological prominence in most parts of the world. The radiation of angiosperms in the Cretaceous led to profound changes in the composition of terrestrial plant communities, which included...
Introduction Rkw
Although terrestrial ecosystems had begun by the Middle Ordovician Retallack 1990 Beerbower et al. 1992 , the typical growth plan of plants axis construction via apical meristems growing tips was uncommon before the Middle Silurian. The first plants were less than 0.5 m tall and simply constructed of progressively diminishing forked axes. Robust plant architectures are uncommon until near the end of the Early Devonian Pragian-Emsian Fig. 1.3.5.1a and result from more complex branching patterns...
121 Metazoan Origins and Early Evolution
The nature of the origin and early evolution of animals remains among the great conundrums of the history of life, despite incredible advances over the past decade. New fossil discoveries, a dramatically improved time scale, exciting new views of the relationships between major metazoan groups based on both molecular and morphological data, and a wealth of information from comparative studies of the developmental process have all contributed to our growing understanding of events during the...
Therapsids
The earliest therapsids, known from the Kazanian of Russia, South Africa, and possibly China, belong to three major groups Biarmosuchia, Dinocephalia, and Anomodontia. A fourth group, the Theriodontia, appears in slightly younger faunas. Biarmosuchians are very sphenacodontid-like in retaining a small temporal fenestra, though a slip of jaw musculature passed out through the fenestra to attach on its outer margin Fig. 1.3.10.3b . The upper canine is very long and the reflected lamina of the...
Comparison of basal synapsids with mammals
The magnitude of the differences in anatomy and physiology between a basal synapsid and a primitive living mammal may be inferred from an examination of their skulls Hopson 1994 . The pelycosaur Fig. 1.3.10.2a was an ectotherm, as are living reptiles, with a resting metabolic rate too low to generate sufficient heat to warm its body above ambient temperature. Therefore, its food and oxygen requirements were about one-tenth those of a mammal of comparable size. This is reflected in the simple...
References
Aldridge, R.J., Briggs, D.E.G., Smith, M.P., Clarkson, E.N.K. and Clark, N.D.L. 1993 The anatomy of conodonts. Philosophical Transactions of the Royal Society of London B 340, 403-421. Donoghue, P.C.J., Purnell, M.A. and Aldridge, R.J. 1998 Conodont anatomy, chordate phylogeny and vertebrate classification. Lethaia 31, 211-219. Forey, P. and Janvier, P. 1994 Evolution of early vertebrates. American Scientist 82, 554-565. Jefferies, R.P.S. 1986 The ancestry of vertebrates. British Museum Natural...
Timing of angiosperm origin and their first major radiation
The earliest angiosperm remains that can be recognized with certainty in the fossil record are dispersed, monoaperturate pollen grains with a reticulate-columellate outer pollen wall very similar to the pollen Fig. 1.4.2.3 Structural features of angiosperms leaves, wood, pollen . a Leaf of Cercidiphyllum with hierarchical reticulate venation. b,c Vessel elements of angiosperm wood. d,e Angiosperm pollen with reticulate-columellate pollen wall d monoaperturate grain of monocotyledon e tricolpate...
Angiosperm characteristics
Angiosperms exhibit exceptional morphological diversity, particularly among their flowers, and this diversity is also manifested among plants at the magnoliid grade. Both large bisexual floral structures, consisting of numerous tepals, stamens, and carpels in a spiral arrangement e.g. Magnoliaceae , and minute unisexual flowers consisting of just a single stamen or a single carpel e.g. Chloranthaceae , occur among basal magno-liid angiosperms Fig. 1.4.2.2 . Unique defining characters that unite...
Terrestrialization
The first records and ranges of all fossils thought relevant to terrestrialization are documented in Fig. 1.3.4.1. 1 Obligate permanent tetrads are so named because they do not split into four spores monads on dispersal. They possess durable, smooth, unornamented walls, thought to be impregnated with sporopollenin although this has not been chemically proven . Some are enclosed within a smooth or ornamented resilient envelope 'membrane' . Both forms are common in Llanvirn to late Llandovery...
PostPalaeozoic developments
During the Permian there was gradual supplementation of typical Late Carboniferous insect taxa by basal Fig. 1.3.9.4 Facing page The community of insect herbivores and detritivores on their late Pennsylvanian 300 Ma host plant, Psaronius, a tree fern that dominated peat-substrate swamp forests of the Illinois Basin. Members of the Psaronius component community are inferred from patterns of hostplant tissue damage and associated coprolite contents. All interactions are from insects, except j...
Insects in late Palaeozoic environments
During the early Late Carboniferous there was a dramatic appearance of diverse insect faunas at several major localities across equatorial Euramerica. A few middle Late Carboniferous to Early Permian localities yield faunas that are sufficiently diverse, abundant, and well preserved to have attracted considerable attention from palaeoentomologists. Two of the more notable insect fossil localities are in Illinois, USA. The first, Mazon Creek, is a celebrated body-fossil site in the north-central...
Introduction Vll
Mammals have been major components of terrestrial and aquatic environments for only the past 65 million years, even though the first mammal, defined as the common ancestor of the living monotremes, marsupials, and placentals, appears to have lived some 150 million years earlier, during the Late Triassic. More distant antecedents of mammals, the non-mammalian synap-sids or 'mammal-like reptiles', can be traced back an additional 100 million years, to the Late Carboniferous, when Synapsida and...
Info Ezg
Calcium carbonate, aragonlte Slllca Calcium carbonate, calcite Key dlvergences O Organlc, chltln etc. Calclum phosphate Fig. 1.2.2.1 Outline phylogeny of the Metazoa, emphasizing the distribution of biominerals. Only the principal biominerals are indicated, and subsidiary occurrences such as calcium sulphate in the statoconia of scyphozoans or ferric phosphate in holothurians see Lowenstam and Weiner 1989 are not included. Many aspects of this phylogeny, which is based on multiple lines of...
Mechanicalphysiological properties of early trees
Progymnosperms and gymnosperms lignophytes used the innovations of bifacial from both sides vascular cambium the growing layer producing wood cells inward and bark cells outward and cork cambium the growing layer repairing splits and wounds within bark to produce thick woody trunks and branches Beck 1988 Stewart and Roth well 1993 Taylor and Taylor 1993 . Wood and bark simultaneously accommodated the load bearing, fluid transport, and starch storage needs of perennially elongating and...
The major plant groups
Coal swamps were forested ecosystems composed of five major tree groups. The growth architectures Fig. 1.3.8.1 , biologies, and ecologies of these groups were distinctively different and contributed to plant assemblages that were strongly differentiated by habitat DiMichele and Phillips 1994 . The dominant plants of the wettest parts of West-phalian coal swamps were tree lycopsids, colloquially known as giant club mosses. Lycopsid trees reached 30 m in height and over 1 m in diameter at the...
The distinctive character of Palaeozoic reefs
Although some Palaeozoic reefs achieved rates of accretion similar to that shown by modern coral reefs e.g. 3-4mm year for the Permian Capitan Reef of Texas and New Mexico , both the community structure and relative contributions of inorganic and organic carbonate were often profoundly different. Palaeozoic reefs appear to have grown in the absence of photosymbiosis and, in some examples, much of the preservable biodiversity was housed within cryptic communities. Moreover, reef construction by...
Fossil evidence of terrestrialization
There are two main types of fossil evidence for terrestrial life body fossils and trace fossils direct and indirect evidence, respectively. Trace fossils include burrows and trackways in subaerial sediments, coprolites, and plant damage other evidence for terrestrial life, such as chemical fossils, could be included here. Trace fossils can provide evidence that animals were present on land, possibly what they were doing, but not necessarily what kind of animal left the traces. Body fossils give...
Agnathan diversity
Many kinds of jawless fishes evolved throughout the Silurian and Devonian Fig. 1.3.2.2 . These include armoured forms with a scoop-shaped solid bony shield like the osteostracans e.g. Cephalaspis , the naked lamprey-like anaspids e.g. Jaymoytius , and the heavily scaled thelodonts e.g. Thelodus . Finds from Canada indicate that some thelodonts, the Furcacaudiformes, had laterally compressed bodies with well-developed stomachs Wilson and Caldwell 1998 . Thelodonts in general had an internal soft...
5 Systematics Phylogeny and Stratigraphy
5.1 Morphology and Taxonomy, 489 5.1.1 Quantifying Morphology, 489 5.1.2 Morphometrics and Intraspecific Variation, 492 5.1.3 Disparity vs. Diversity, 495 m.a. wills 5.2.1 Estimating Completeness of the Fossil Record, 500 m.foote 5.2.2 Analysis of Diversity, 504 a.b. smith 5.3 Reconstructing Phylogeny, 509 5.3.1 Phylogenetic Analysis, 509 m. wilkinson 5.3.2 Fossils in the Reconstruction of Phylogeny, 515 p.l. forey and r.a. fortey 5.3.3 Stratigraphic Tests of Cladistic Hypotheses, 519 5.3.4...
123 Cambrian Food Webs
Food webs are descriptions of who eats whom within a community, thereby tracking energy flow through the system and, to an important degree, characterizing its ecological structure. Clearly any palaeoecological analysis would be greatly served by a detailed accounting of its food web. Nowhere is this more so than in the Early Cambrian when, following approximately three billion years of relatively simple microbially dominated ecologies, large energetic animals were suddenly thrust into the...
124 The Origin of Vertebrates
Although pre-Silurian vertebrates have been known since the late 1880s, they have generally been considered to be low in diversity and a relatively insignificant prelude to the principal radiation of the group in the Late Silurian and Devonian. Recent discoveries have demonstrated, however, that Ordovician vertebrate faunas are not only more abundant and widespread than hitherto suspected but also contain a far greater diversity of groups. Furthermore, there is now firm evidence that the fossil...
113 Life in the Archaean
When did life on Earth first appear What were primordial organisms like How and where did they live Though these are age-old philosophical and theological questions, they also have scientific significance. Clearly, Earth's history would have been different if abundant, diverse life had arisen when the crust solidified, perhaps 4.5 billion years ago, rather than halfway through geological time, at the end of the Archaean 2.5 Ga . To answer these questions empirically, palaeontolo-gical and...
114 Late Proterozoic Biogeochemical Cycles
The Proterozoic Eon 2500-540 Ma saw episodic increases in atmospheric oxygen, the evolution of multicellular life, and at its close, an enormous radiation of animal diversity. The rise of metazoans is marked by the Ediacara fauna see Section 1.2.1 , with body fossils evident in sediments as old as 594Ma, i.e. the end of the last Varanger glaciation. Evidence for metazoan activity is also present in the trace fossil record. Simple burrows and traces indicate sediment processing, and hence the...