7. The future of the world’s reptiles

The world’s reptile fauna is facing the threat of a considerable reduction in the number of species. One estimate is that by 2050 over 500 species, around 5 per cent, will have been lost. By 2080, the figure will have grown to 20 per cent, which is approximately 2,000 species. ‘The future of the world’s reptiles’ explains that the threats to reptiles are: commercial exploitation for food, medicines, and ornament; habitat destruction; global climate change; and pollution. Any comprehensive effort to conserve needs to address all of these. By far the most important way to conserve reptiles is setting up and regulating various kinds of protected area. Another important approach is legislation to control trade in reptiles.

5. Crocodiles

There are only about twenty-five species of living crocodilians, found in semi-aquatic habitats, mostly around freshwater rivers, lakes, and swamps, but also in marine areas. ‘Crocodiles’ explains how the crocodile body is very well adapted for the amphibious way of life; they can move quickly between the land, where they spend much of the day basking, and the water in which they mostly feed and to where they flee if threatened. It considers their skin; how they breathe, move, and feed; and their sense organs, including the unique integumentary sense organs. The social behaviour of crocodiles, especially courtship and the care of the young, is much more elaborate than in any other reptile group.

4. Snakes

The roughly 3,500 species of snakes are really a group of limbless lizards, although they are so distinctive, with so many unique features, that they are placed in their own reptile subclass, Ophidia or Serpentes. They have a worldwide distribution, occupying habitats from deserts to rainforests and seas. ‘Snakes’ describes how snakes feed, move, and make sense of their surroundings, as well as their social and reproductive behaviour. The main aspect of snake biology that accounts for their great success as hunting organisms is the way they acquire and ingest their food. The rear-fanged (colubrids) and front-fanged groups (elapids and viperids) are described along with their venom production.

3. Lizards

More than half of all reptiles alive today are lizards, with over 6,000 species. Lizards are truly worldwide in distribution, although like all reptiles they are most diverse and abundant in the tropics. ‘Lizards’ explains that evidence from the DNA sequences of genes has provided a pretty clear idea of how the modern lizards evolved. It describes the key features of ‘typical’ lizards—their predatory lifestyle, the specialized feeding mechanism called cranial kinesis, and their reproductive arrangements. It also discusses more specialized species such as limbless lizards; aquatic lizards; arboreal lizards such as chameleons; geckos; airborne lizards; and the large predators such as monitor lizards and the Gila monster.

2. History of reptiles

‘History of reptiles’ describes the origin and early evolution of reptiles, from the early ancestor-like Hylonomus and Petrolacosaurus 320 million years ago (mya) in the Carboniferous period. The end-Permian mass extinction, 250 mya, removed over 90 per cent of the world’s species of animals and plants, but one group—the archosaurs—began to expand and diversify. The archosaurs included the dinosaurs, made up of the Theropoda, the Sauropodomorphs, the Ornithischia, the pterosaurs, and the crocodiles. In the Mesozoic Era, several new kinds of reptiles evolved adaptations for life in the sea—plesiosaurs, ichthyosaurs, and others. The end-Cretaceous mass extinction, 66 mya, ended the dinosaurs, but many lizards, snakes, chelonians, and crocodiles survived.

6. Chelonians

Chelonians are the tortoises, terrapins, and turtles, with the single most characteristic feature being the shell, made up of a small number of very large scales, immovably joined to one another. Inside the shell, the number of vertebrae has been greatly reduced and all traces of the lateral undulation of the body typical of most reptiles have vanished. ‘Chelonians’ explains that this greatly affects other aspects of their anatomy and biology, such as how they walk, breathe, and feed. The roughly 320 species of living chelonians fall into two groups: the Pleurodira (the side-necked turtles) and the Cryptodira, far the most diverse of the two.

1. What is a reptile?

There are close to 10,000 different species of reptiles, with five different kinds of living animals making up the Class Reptilia: chelonians (turtles and tortoises); lizards; snakes; crocodilians; and the tuatara of New Zealand. ‘What is a reptile?’ explains that despite their huge range of body forms and ways of life, zoologists recognize them all as reptiles because of the fundamental characters that they all share, including dry and scaly skin, the ability to excrete urine waste as a solid, and the reproductive process of laying amniotic eggs on dry land. The evolutionary adaptations for moving to life on dry land, which began about 320 million years ago, are explained.