Field guide training: Reptiles – Part 2

The oldest fossil from a turtle which has been discovered until today is approximately 210 million years old and dates to the early age of the trias. This means that the first turtle species were living on the earth together with dinosaurs. Hence their nickname: Living fossil.

Turtles can be divided in three subtypes: Tortoise, sea turtle and terrapin. All three can be found in Southern Africa, with fourteen land-living species, five marine and six freshwater-based species. They all have one common characteristic: Their shell. The shell is not made of keratinised scales on their skin, but from bone plates which are an extension of their ribs. Depending on the species these bone plates can be either hard, soft or leathery. The fact that every turtle species owns a shell, can make it hard sometimes to distinguish between the different subtypes.

An important characteristic which helps to identify the right subtype is the form and function of the shell, also called carapace. Tortoise species have the ability to retract their tail and hindlegs into their shell thanks to a special joint which helps the tortoise to protect itself from predators. The head is protected by retracting both front legs. Terrapins on the other hand can retract their head and front legs but can only bend their hindlegs. Sea turtles do not have the ability to retract their extremities, which can be explained by evolution as their limbs can be used as flippers and help them to flee from their predators under water.

The carapace and its bone plates never stop growing during the lifespan of a turtle. Usually they grow quicker during the summer time than in winter time. These seasonal growing cycles can be used to determine the age of a turtle, because the bone structure shows annual rings, similar to trees.

All turtle species reproduce on land, which means the species which usually spend their life in water must come ashore to lay their eggs. The temperature which surrounds the eggs while they develop determines the sex of the young ones. If the temperature is between 30 and 34°C there will be more females and if the temperature is between 26 and 30°C there will be more males.

When you see a turtle during your time in Africa you should respect the following rules: Please avoid lifting the turtle up or to touching it, because this would cause a lot of stress for the animal. In this case it can happen that they urinate. During the dry season this can lead to dehydration and even cause the animal’s death.