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
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
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
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
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....
Introduction Xui
The Mesozoic Era may indeed have been the 'age of dinosaurs' but, as we have seen Chap. 2 , there were many other dramatic reptiles inhabiting the land in those days - not to mention the amphibious Chap. 4 , marine Chap. 5 , and aerial Chap. 6 forms we have been discussing. Terrestrial Mesozoic reptiles included tortoises and turtles Anapsida Testudines , the mammal-like reptiles Synapsida Therapsida and various Diapsida. Among the latter were the sphenodontians, the squamata - lizards and...
Introduction Xcv
During much of the Mesozoic Era, the air was dominated by prehistoric reptiles of the order Pterosauria. These archosaurs Table 2 appeared during the Upper Triassic period, about 228 mya. This was some 70 million years before the first known birds Archaeopteryx spp. . The pterosaurs flourished until the end of the Cretaceous, 155 million years later. Two suborders of pterosaurs are recognised Rhamphorhynchoidea which had long, stiffened tails, and Ptero-dactyloidea with short tails. The...
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
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
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
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
The Harvard palaeontologist, A.S. 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
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
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
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
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...
Conclusions
In general, predatory animals are of two kinds ambush or sit-and-wait predators, many of which are capable of a sudden dart after their prey, and pursuit predators. Both types occurred among marine Mesozoic reptiles. Ambush predators dominated the large predator communities of the Middle Triassic and Upper Cretaceous periods, whilst pursuit predators were dominant in the Lower Jurassic, as they are among the fishes and whales of today's oceans. Between Late Middle and Upper Jurassic times there...
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
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...