Note on Coloration

There is absolutely no way in which the colours of early fossil reptiles can be ascertained but, from what is known about animal coloration today, it is extremely likely that the same principles would have applied then. In all probability the larger dinosaurs would have been uniformly grey, like modern elephants, rhinoceroses and hippopotamuses. Marine reptiles were almost certainly dark above and whitish below, like modern sharks and whales. The effect of a pale ventral surface is that it...

Conclusions

The adaptive value of a permanent and high constant body temperature depends upon the action of enzymes. A complex, multi-enzyme system must evolve and function, because each individual enzyme system is constant and therefore predictable. Highly complex biological organisation depends upon multi-enzyme systems. No single characteristic that responded to numerous condition could evolve unless it were accompanied by all the other characteristics that were necessary. There must therefore have been...

Growth and Development

According to Paul (1997), dinosaurs would have grown extremely rapidly. The larger the adults, the greater the number of eggs that they would have laid -probably many tens of thousands during the life spans of the largest sauro-pods. The extreme ratio between size on hatching and at adulthood would have necessitated very rapid growth for sexual maturity to have been reached within two or three decades. Breeding would have had to begin within that time scale if sufficient juveniles were to...

Teeth Gastroliths and Digestion

Prosauropods such as Plateosaurus (Figs. 5, 65, 83e) and Massospondylus (Figs. 65,83f Sect. 7.3) had lightly built skulls and the jaws were articulated below the line of the teeth. Consequently, the teeth of the upper and lower jaws could be almost parallel as they approached each other when the mouth was closed. In addition, the biting force would have been distributed more evenly than it is when rows of teeth approach each other in a scissor-like fashion (King 1996). Galton (1985)...

Extinction

Extinction, resulting from competition and environmental change, is the inevitable fate of every species and taxon of living organisms. Only when mass extinctions occurred (Table 3) is there any call for explanation or comment. When many groups of organisms disappeared simultaneously within a relatively short space of time, the change recorded in the fossil records appears to have taken place so rapidly that some people are tempted to assume that a catastrophic event must have been responsible....

The Earliest Dinosaurs

Herrerasaurids

The Dinosauria arose in the Upper Triassic period, some 230 mya, and dominated the terrestrial faunas of the world for the next 165 my. The earliest genera were medium-sized, three-toed bipedal carnivores that grabbed their prey with the forelegs. A sister group is represented by the ornithosuchid or basal dino-sauromorph Marasuchus (Fig. 83a) (Sect. 8.4.3), a lightly-built flesh-eater that presumably caught small and speedy animals such as cynodonts and proco-lophonids, as well as feeding, no...

Anapsids

Procolophonids

The subclass Anapsida (Sect. 2.4) is represented by a number of early reptilian taxa including the mesosaurs (e.g. Mesosaurus, Fig. 7), the procolophonids and the Testudines. The family Procolophonidae ranged throughout the world from the Upper Permian to the Upper Triassic. Its early members were small and agile insectivores, with numerous peg-like teeth. Procolophon (Fig. 77) from the Lower Triassic of South Africa and Antarctica was probably herbivorous or insectivorous. Later members, from...

Longevity Injuries and Disease

Nothing, living or non-living, can persist indefinitely. In the days of the transatlantic liners, the average 'life' expectancy of a glass tumbler was about 1.5 crossings. Presumably, few tumblers would have survived for more than five or six crossings although potentially they could last for centuries. Whatever the potential life of a dinosaur, most individuals would have been killed by predators, injuries or disease long before they died of old age. Growth rings in certain bones and teeth...

Ceratopsians

Horned dinosaurs have already received considerable attention in these pages (Sect. 9.2.2). They were the last of the ornithischians to evolve before the final extinction of the dinosaurs and were extremely successful and numerous. Ad- Fig. 114a-c. Protoceratopsids (not to scale). a Microceratops (length ca. 60 cm), b Bagaceratops (length ca. 1 m), c Protoceratops (length ca. 3 m Upper Cretaceous). (After Palmer 1999) Fig. 114a-c. Protoceratopsids (not to scale). a Microceratops (length ca. 60...

Quadrupedal Locomotion

When reptiles first evolved from amphibians (Sect. 1.3), they inherited the short, stumpy legs of their ancestors. Modern newts and salamanders (Uro-dela) as well as modern reptiles such as lizards with elongated bodies and small laterally projecting legs show the most primitive form of tetrapod locomotion. If they are frightened and need to move exceptionally fast, urodeles and lizards usually wriggle along with the belly resting on the substrate, as though they were swimming, with their legs...

Mesozoic Reptiles Introduction

Extinction is the inevitable concomitant of evolution. As a result of natural selection in changing environments, all existing species must evolve into other chronologically distinct species, or else die out. None remains indefinitely without modification. Extinction is the consequence either of failure to adapt sufficiently rapidly, or else it occurs because the ecological niche of a species has disappeared. It can be caused by a combination of shortage of food, predation and disease,...

Thermal Effects

For more than 100 my before their demise, the dinosaurs enjoyed equable climatic conditions. At the end of the Mesozoic Era, however, the seasons became accentuated, as indicated by the rise of the angiosperms with their deciduous foliage and overwintering seeds. In 1965, the Canadian palaeontologist L.S. Russell proposed that winter temperatures might eventually have fallen low enough to kill such land animals as could not conserve their body warmth and did not hibernate. This might explain...

Courtship and Mating

In animals living today, courtship and mating involve a whole range of visual, acoustic, tactile and chemical signals. Fossils, by their very nature, can only provide unequivocal evidence for the first of these. It is generally assumed, however, that many of the morphological structures and ornaments, such as horns, frills, crests, spikes, thickened skulls, bosses, large teeth, big eyes and so on (Sect. 9.3.1), were not only used in combat but also in eliciting behavioural responses (Horner...

Life Styles

The pterosaurs were the first vertebrates fully to conquer the air. Although many fossilised examples have been collected, much of what is known about their modes of life is based on inference - as we have seen in the case of their locomotion on the ground (Sect. 6.4). Apart from a few small insectivorous forms such as Peteinosaurus, Batracho-gnathus and Anurognathus, most of the pterosaurs so far discovered have been specialised fish-eaters. Their long jaws and forwardly directed front teeth...

Basal Sauropodomorphs Prosauropods

Despite their similarity in appearance to the Sauropoda (Sect. 10.4) which radiated much later, in the Upper Jurassic and Cretaceous periods, the sauropodomorphs of the Upper Triassic were not related to them (Sect. 9.1). The apparent similarity must have resulted from parallel evolution which took place in similar environments at different periods of earth history. Plateosaurus (Figs. 65, 83e) is probably the best known of the prosauropods. Many well-preserved skeletons have been excavated...

Locomotion on the Ground

Palaeontologists generally concur that pterosaurs were capable of active flight even though the leverage of their pectoral muscles,in the absence of a keel,was less than it is in birds. But there is somewhat less agreement as to how they managed to walk on land. Indeed, the problem of how they moved on the ground, and took off into the air, dates almost from the discovery of the first fossil remains of the animals. The argument has often been polarised with two contrary views bipedal versus...

Introduction

The Mesozoic Era is popularly known as 'The Age of Reptiles'. It comprises three periods Triassic, Jurassic, and Cretaceous - but reptiles were already present during the preceding Carboniferous and Permian periods. These were the last periods of the Palaeozoic Era Table 1 . Palaeozoic means 'ancient life', Mesozoic 'middle life' and Cenozoic, which followed it and continues to the present, 'recent life'. Life probably began in the sea, and terrestrial plants and animals did not appear until...

The Origin of Birds

Birds are usually regarded as being archosaurs and, therefore, a sister group of the crocodiles Benton 2004 . This view originated with E. Haekel who, in 1866, claimed the mammals as the sister group of the remaining amniotes. Haekel was supported by T.H. Huxley and Ray Lankester in 1870. A contrary opinion, however, has been expressed by Brian Gardiner 1982,2002 who argued that crocodiles share their ancestry with both birds and mammals - having six synapomorphies with birds including an...

Hadrosaurids

The Hadrosauridae or duckbilled dinosaurs was the last family of Ornitho-poda to evolve. Hadrosaurids first appeared in the Middle Cretaceous and died out at the end of the period, about 30 my later. Although their bodies were all remarkably similar, like those of early iguanodontids, their heads differed a great deal. Figure 96 illustrates some crested types and a variety of other shapes are shown in Fig. 112.In their day, the duckbilled hadrosaurids were the most common and varied group of...

Pterosaur Flight

During the course of evolution, the oxygen content of the atmosphere has increased and decreased many times. When there was double the amount found today, this might possibly have allowed for the growth of giant plants and reptiles during the Mesozoic Era and also have contributed to the evolution of aerial reptiles. Some of these were very large indeed compared with modern birds. Three types of flight, which are by no means mutually exclusive, have evolved in the animal kingdom. These are...

Ankylosaurs

Nodosaurus Fossil

The remaining major group of armoured dinosaurs, the ankylosaurs, consisted of two families - Nodosauridae and Ankylosauridae. Ankylosaurs were characterised by a great variety of spikes and armour plating. Some genera possessed cranial horns, and the ankylosaurids were endowed with massive tail clubs Fig. 90 , which were probably used both in defence against predators and to combat rivals. In addition, the broad, flattened and armoured skulls might have been employed in head-to-head pushing...

Therapsids and the Origin of Mammals

Mammals And Reptiles

The synapsid order Therapsida Sect. 2.5 may have diverged from the pely-cosaurs during the Lower Permian, but the earliest fossils to be found were in the Upper Permian of Gondwanaland. Therapsids diversified greatly in the Triassic when they dominated the terrestrial vertebrate forms of the world but only one suborder, Cynodontia, persisted into the Lower Jurassic. The preceding Dicynodontia had been the most successful herbivorous therapsids of the Late Permian and Triassic - a span of almost...

Bibliography

The literature on Mesozoic reptiles is vast. The present list of publications includes by no means all those upon which the text has been based. For the sake of conciseness, reviews and recent books, particularly when well illustrated, have been cited in preference to original research publications. The names of artists are given when listed on title pages. Especially significant as sources of reference are the following Thomas and Olson 1980 Kemp 1982 Hotton et al. 1986 McGowan 1991 Wellnhofer...

Weapons of Attack

The offensive weapons of predatory dinosaurs, including the so-called carno-saurs Sects. 11.1,11.3.2 ,were primarily their sharp, inwardly curved, and serrated teeth Fig. 85 . Especially in the case of bipedal forms,however,the action of these teeth was often supplemented by forelimbs which grabbed the prey while it was being bitten. In numerous cases, curved jaws helped to hold the struggling prey securely. Many predators also had formidable claws that were used to slash the bodies of their...

Locomotion

Many aquatic reptiles use their limbs as paddles and swim relatively slowly. Turtles almost fly through the water with their front flippers but, even so, they are not as fast as most fishes and dolphins of comparative size. Some reptiles, however, especially the pliosaurs and ichthyosaurs, were streamlined and extremely fast Chap. 5 . They swam with the aid of flattened bodies and fish-like tails. When an eel swims, the inner sides of the curves on its sinuous body press against the water. The...

Early Diapsids

Chasmatosaurus Skeleton

The Diapsida, with two temporal fenestrae, includes the lizards and snakes, cro-codilians, pterosaurs, dinosaurs and birds. The crocodilians and pterosaurs have already been discussed. Here, we consider the ancestral lizards and snakes Fig. 78. Planocephalosaurus Rhynchocephalia Upper Triassic length ca. 20 cm . Based on Palmer 1999 Fig. 78. Planocephalosaurus Rhynchocephalia Upper Triassic length ca. 20 cm . Based on Palmer 1999 Squamata and Rhynchocephalia or Sphenodontida Table 2 , which are...

Gliding Reptiles

Triassic Reptiles

Apart from the pterosaurs, no reptiles have evolved flapping flight. Since the Upper Permian, however, small diapsid gliding reptiles have appeared in the fossil record. One of these, Daedalosaurus from Madagascar, was so named by Robert Carroll after Daedalus who, in Greek legend, escaped from Crete with the aid of wings which he had made for himself. Daedalosaurus is now considered to be a junior synonym of Coelurosauravus Figs. 47,50a , as is Weigelti-saurus from Germany and England. Fig....

Tachymetabolism

There is a fundamental difference between the metabolic rates ofhomeothermic or tachymetabolic fast rate of chemical change animals and those of heterothermal bradymetabolic slow rate of chemical change animals whose body temperatures tend to vary according to that of the environment. In today's mammals and birds the metabolic rate is about four times greater than that in extant reptiles. The occurrence of blood shunting from superficial to deep tissues as a means of conserving heat is now well...

Reptiles

Temporal Fossa Reptiles

The first reptiles - forms like Hylonomus Sect. 2.4 appeared in the Middle Carboniferous Benton 1996 . These shortly led to the three main divisions of reptiles, the anapsids, diapsids and synapsids, characterised by the temporal openings or fenestrae in their skulls Fig. 2 . Indeed, knowledge of the interrelationships of reptiles depends mainly upon their fossil skeletons, of which skulls are by far the most useful and important. They are of four different types Fig. 2 . In the subclass...

Ichthyosaurs

Stenopterygius

Ichthyosaurs first appeared in the Lower Triassic alongside the placodonts and nothosaurs. They were the most highly specialised of all aquatic reptiles, and evolved to become top marine predators, yet maintained essentially the same body shape throughout most of the Mesozoic Era - about 150 million years. Like nothosaurs, thalattosaurs, crocodilians and other amphibious reptiles, plesiosaurs would almost certainly have been ectothermal as are modern crocodiles. These usually sun themselves...

Swimming

Shark Swim Mechanics

The locomotion of the plesiosaurs has formed the subject of at least three different hypotheses, outlined by Taylor 1986 , Halstead 1989 , McGowan 1991 , Ellis 2003 and Benton 2004 . Because their tails were relatively small, their paddles large and powerful, it can reasonably be assumed that the latter were used for creating thrust. At first, it was thought that plesiosaurs swam by beating their limbs forward and backward as though they were oars. The paddles would, of course, have had to be...

Testudines

Classification Reptiles

Romer 1966 , once remarked that tortoises, terrapins and turtles are commonplace objects to us only because they are still living. Were they extinct, their shells would have been a cause of wonder, as they represent the most complete defensive armour found among tetrapod vertebrates. The Testudines or Chelonia is an ancient order of reptiles long considered to belong to the subclass Anapsida and therefore descended from the Captorhinidae or cotylosaurs...

Ceratosaurs

Sauronithoides

Whereas the Herrerasauridae Sect. 9.1 are known only from the Late Triassic of South America, the Ceratosauria was a much larger group that persisted from the Late Triassic to the Upper Cretaceous period. Possibly, the oldest ceratosaur genus known so far is Coelophysis Fig. 117 family Podokesauri-dae of which many well-preserved specimens have been found in Connecticut and New Mexico. They are of all ages - from newly hatched babies to full-grown adults. However, the latter only measured ca. 3...

Reptilian Ancestors

Triassic Period Dog

Although no definitive fossils have been found of the amphibian ancestors from which the reptiles evolved, they are usually considered to have been an early egg-laying offshoot of an amphibian group Batrachosauria of which Seymouria Fig. 4 is an example. Seymouria, Solenodonsaurus and the larger Diadectes Fig. 4 have sometimes been classified as basal reptiles - but the point at which reptilian characters dominated over those of amphibians is unclear. The remnants of lateral lines on the skull...

Rhamphorynchoids

Peteinosaurus

The rhamphorynchoids were the earliest and most primitive of the pterosaurs. Yet these had become already advanced fliers by Upper Triassic times ca. 228 mya . Eudimorphodon Figs. 45,56 Sect. 6.1 is a well-known example. Its long tail would have been held out rigidly during flight, counterbalancing the Fig. 56. Left Peteinosaurus Rhamphorhynchoidea Upper Triassic wingspan ca. 60 cm . Right Eudimorphodon Rhamphorhynchoidea Upper Triassic wingspan ca. 1 m Fig. 56. Left Peteinosaurus...

Weight and Size Limits

Apatosaurus Elephant Size Comparison

The body proportions of animals are affected by a number of considerations, probably the most important of which are the ratios of size to mass. If two individuals were to have exactly the same shape, but one was twice as long as the other, all other linear dimensions would be double those of the smaller individual. The surface area would, however, be the square of the surface area of the smaller individual, while its mass would be cubed. Thus, if a reptile 3 m in length with a surface area of...

Thermal Physiology

The thermal physiology of the dinosaurs and of other large reptiles has been the subject of animated discussion, not least because it is relevant to their extinction at the end of the Cretaceous period Chap. 12 . Temperature regulation in animals is either behavioural,autonomic self-governing or,more usually, a combination of the two. Like most day-active animals, Mesozoic reptiles would have basked in the sun when they were cold and sought the shade if they were too hot. Nocturnal species, on...

Reproduction

Horns Spikes Frills

Among higher animals, reproduction consists of a number of separate phases of activity. Courtship by the male is often preceded by the establishment of a territory and conflict with competing males. This agonistic or aggressive behaviour may consist primarily or even entirely of display Sect. 9.2.3 , and actual combat may be highly ritualised. Agonistic behaviour among dinosaurs probably resulted in the establishment of hierarchies, as it does in extant vertebrates. Interactions between...

Bradymetabolic Thermoregulation

In comparison with the reptiles of the Mesozoic Era, modern reptiles are mostly small and bradymetabolic. Their large surface-to-volume ratio would render tachymetabolism uneconomical. Furthermore, they are able to evade inclement weather by aestivating in summer or hibernating in sheltered retreats. Even so, in addition to behavioural temperature regulation, they are known to utilise a number of physiological thermoregulatory processes. These include the emergency cooling of the body of...