334 Heterostraci
The heterostracans, a large group of some 300 species, radiated extensively in the Silurian and Early Devonian. Their head shields vary tremendously in shape among different species, and they are distinguished from the astraspids and arandaspids by having a single exhalant opening on each side into which the gills open. Heteros-tracans all have in common a broad ornamented plate on top, one or more plates on either side of this, and a large element covering the underside Halstead, 1973 Blieck,...
32 Vertebrate Hard Tissues
Bone is a key feature of vertebrates. There are different kinds of bone, and other bone-like hard tissues, and it is important for palaeontologists to understand these, especially when they are trying to classify isolated phos-phatic scales and teeth. Bone is made from mineral and protein components. In fine detail, living bone tissue consists of fibres of the protein collagen on which are deposited tiny hexagonal-prismatic crystals ofapatite. Cellular bone is a living tissue. Typical bone...
144 Development and vertebrate origins
The development of living vertebrates and basal chor-dates indicates a great deal about their ancestry. Embryos may be sliced thinly on a microtome, rather like a mini salami-slicer, and three-dimensional reconstructions are made from tracings of the thin-sections by computerized methods. In addition, and most importantly, studies of the genome allow developmental biologists to relate specific anatomical structures to genes. In many cases, they have found that genes that code for particular...
332 Conodonta
One of the longest-lived groups of early vertebrates, the conodonts, were identified with certainty as fishes only in 1983. Conodont elements, small 0.25-2 mm toothlike structures made from apatite, have been known since 1856, and they are so abundant in many marine rocks from the Late Cambrian to the end of the Triassic that they are used for stratigraphic dating. Particular conodont species, and groups of species, are characteristic of certain stratigraphic zones, and they form the basis of a...
26 Further Reading
There are many useful books that cover basic palaeon-tological, geological, and palaeobiological principles. Briggs and Crowther 2001 is an excellent compendium of short articles on all aspects of palaeobiology, and Benton and Harper 1997 is a useful short intro duction to all aspects of palaeontology. You can read more about excavating dinosaurs in an illustrated account by Benton 1989b ,whereas Buffetaut 1987 and Colbert 1968 are highly readable accounts about the history of vertebrate...
231 Functional morphology
The first question that people ask about any fossil vertebrate is 'what did it do ' Just how did the heavily armoured Devonian fishes manage to swim Why did some mammal-like reptiles have massively thick skull roofs What did Stegosaurus use its back plates for Why did sabre-toothed cats have such massive fangs These are all questions of functional morphology, the interpretation of function from morphology, the shape and form of an animal. The main assumption behind this approach is that...
Preface
Vertebrate palaeontology is always in the news astonishing, ancient basal chordate and vertebrate fossils are announced from China fossil hunters argue about which was the largest dinosaur of all, or the oldest dinosaur with feathers an ancient fossil bird is announced that adds 100 million years to their history ever-older specimens of human beings are unearthed in Africa. When I wrote this book in 1989, I felt that there was a need for an up-to-date account of what is known about the history...
222 Continental drift
One of the most dramatic changes that has taken place through geological time see Box 2.2 is continental drift, the movement of continents and oceans relative to each other. The idea that the present layout of continents had not always been the same was suggested in the 19th century, when some geographers noted how the Atlantic coasts of South America and Africa could be fitted together like giant jigsaw pieces. In 1912, Alfred Wegener marshalled a great deal of geological and palaeontological...
31 Cambrian Vertebrates
Until recently, the oldest putative vertebrates were isolated fragments of dermal armour from the Upper Cambrian of North America, and possibly also the superficially amphioxus-like Pikaia from the Mid-Cambrian Burgess Shale of Canada. New discoveries from the Chengjiang locality in China see Box 1.2 , the source also of many exceptionally preserved basal deuterostomes, have extended the range of vertebrates back to the Early Cambrian Shu, 2003 . Myllokunmingia, 28 mm long, is streamlined in...
112 Cephalochordata amphioxus
Another chordate generally reckoned to be related closely to the vertebrates is the amphioxus or lancelet, Branchiostoma, a representative of the Cephalochordata or Acraniata . The adult amphioxus is convincingly chordate-like, being a 50 mm long cigar-shaped animal which looks like a young lamprey or eel, yet lacking a head. Amphioxus swims freely by undulating its whole body from side to side, and it burrows in the sediment on the sea-floor Figure 1.3 a . Amphioxus feeds by filtering food...
221 Taphonomy
The mode of burial and preservation of fossils, their taphonomy, is important in their interpretation. The BBC series, Walking with Dinosaurs, was the most successful science documentary series ever made since 1997, it has been seen by over 200 million people in nearly every country in the world. The series of six programmes was conceived by Tim Haines a few years after he had seen Steven Spielberg's Jurassic Park 1993 , in which a clever mix of computer animation and models gave the first...
25 The Quality Of The Fossil Record
Key questions in palaeontology concern the quality of the fossil record. Is the sample of known fossils enough to justify detailed studies of the history of life Do palaeontologists know only 1 of all the species that ever lived, or 10 , or 70 Life originated 3500 million years ago, and countless millions of species have come and gone since then. Today there may be 10-30 million species on Earth, and no-one can begin to estimate how many have become extinct in the past. The history of life may...
111 Urochordatasea squirts
A typical sea squirt,or tunicate,is Ciona Figure 1.2 a , which lives attached to rocks in seas around the world. It is a 100-150 mm tall bag-shaped organism with a translucent outer skin the tunic and two openings, or siphons, at the top. The body is firmly fixed to a hard substrate. The internal structure is fairly complex Figure 1.2 b .A large pharynx fills most of the internal space, and its walls are perforated by hundreds of gill slits, each of which bears a fringe of cilia, fine hair-like...
13 Deuterostome Relationships
The relationships of chordates used to be rather problematic, but intensive analyses of morphological and molecular data have shown a clearer picture Eernisse and Peterson, in press Smith et al., in press . The Phylum Chordata is part of a larger clade, the Deuterosto-mia, which in turn is part of a yet larger clade of all the bilaterally symmetrical animals, the Bilateria see p. 2 . But what exactly diagnoses the Deuterostomia The clue comes from embryology, the study of the early phases of...
131 Embryology and the position of the anus
In early development each animal starts as a single cell. Soon this cell begins to divide, first into two cells, then four, then eight, sixteen, and so on Figure 1.5 a-c . Eventually a hollow ball of cells is produced, called the blastula stage Figure 1.5 d . A pocket of cells then moves inwards, forming the precursor of the gut and other internal structures. The opening of this deep pocket is called the blastopore.You can imagine pushing in the walls of a hollow rubber squash ball with your...
15 Vertebrates And The Head
The vertebrates, the major group of chordates, form the subject of this book. They have sometimes been termed craniates since all forms, including the hag- fishes and lampreys, have specialized head features the cranium, the skull . The term vertebrate is better known, so will be used here, following recommendations by Donoghue etal. 1998 . The basic vertebrate body plan Figure 1.9 shows all of the chordate characters so far described notochord, dorsal nerve cord, pharyngeal 'gill' slits,...
Box 11 Deuterostome Relationships
Three substantially different schemes for deuterostome relationships have been proposed. The 'traditional' view e.g. Maisey, 1986 Peterson, 1995 Donoghue et al., 1998 illustration a was to place the hemichordates as basal to chordates since they both share ciliated gill slits and giant nerve cells, as well as other features, which are not seen in echinoderms. Enteropneusts were sometimes said to be closer relatives of chordates since their gill slits are similar, they have a very short dorsal...
12 Phylum Hemichordata Pterobranchs And Acorn Worms
Another unusual group ofliving marine deuterostomes may offer further clues about the origin of the chor-dates. These are the hemichordates, a phylum that in- Phylum Hemichordata Pterobranchs and Acorn Worms 5 eludes two superficially very different kinds of marine animals. The first, the pterobranchs such as Cephalodis-cus Figure 1.4 a,b , are small animals that live in loose colonies on the sea-bed in the southern hemisphere and in equatorial waters. Cephalodiscus has a plate-like head...
Tree Of Life Controversy Boxes
Ch 1 Deuterostome relationships 8 Ch 3 Basal vertebrate relationships 41 Sarcopterygian relationships 68 Ch 4 Phylogeny of the Devonian tetrapods 80 Relationships of the basal tetrapods 98 Ch 5 Relationships of early amniotes 113 Relationships of the synapsid groups 122 Ch 6 Archosaur diversification 138 Ch 7 Chondrichthyan relationships 165 Relationships ofNeopterygii 178 Ch 8 Relationships of the dinosaurs 213 Relationships ofMesozoic reptiles 232 Ch 9 Bird fingers 1,2,3 or 2,3,4 262...