Swimming 521
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...
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...
Continental Drift
In order to interpret the distribution and consequent diversification of the Mesozoic reptiles, one has to realise that continents are by no means static. During Cambrian times, some 500 mya million years ago , they were distributed along the equatorial belt of the world. They included Laurentia, Siberia, Baltica, Avalonia and the enormous Gondwanaland, the only one to extend into temperate latitudes. During the course of Silurian and Devonian periods, approximately 400 mya Table 1 ,...
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...
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...
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...
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...