Eating Habits of Reptiles (Part 1)

Most animals are at least to some degree shaped by way they eat. Pursuers of live prey must be quick and agile, diggers and burrows have special tools to help them find their food. So it is with reptiles. The wide range of their feeding habits is reflected in the great diversity of their appearance. Reptiles, like the other classes of land vertebrates, include both carnivorous and herbivorous members, and there are others that eat almost anything nourishing which the environment affords.

It was not always like that, however. The reptile ancestors were carnivores and originally no doubt were adapted to stalking live prey in the form of insects. Insects constitute small meals of highly concentrated energy, and for many reptiles they are still the basic food, along with many other invertebrates such as spiders and earthworms. But there are numerous others that have radiated out in the great spectrum of feeding roles that the environment makes profitable. Their feeding adaptations fall into three basic categories: equipment for a herbivorous diet; adaptations making possible the swallowing of big objects; and equipment and behavior adapted to the taking of some one special kind of food, for instance eggs.

Some insight into the evolutionary history of the feeding habits of reptiles can be obtained from the study of their individual development. In the embryonic and larval development of an animal there is often a tendency to repeat, in a crude sort of outline form, the stages of evolution by which the race was produced. This is never a rigid, detailed process of repeating evolution, but simply a trend in which stages or structures repeat themselves in a broad and general way. Thus, human embryos go through a stage when they have gill-like pouches, which resemble our remote fish ancestors. Similarly, most young reptiles, whatever diet they may choose in later life, begin as insect eaters.

It might, of course, be said that this is a practical necessity, since developing young need just such an abundance of compact, highly concentrated food as insects represent. But even granting that insect eating at this stage is only a case of opportunism, the sequence of events is still a repetition of the evolutionary events that preceded it. It was the practical advantage afforded by wealth of insect food that originally brought the reptile ancestors ashore; and so today the young of reptiles not only return to the feeding habits of their ancestors, but do so for the same ecological reasons. The young of the big tree iguana, who will later spend their days browsing and picking fruit off trees, begin by stalking and catching insects. The green sea turtle, almost completely herbivorous at maturity, starts by eating practically any kind of animal food.

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