Colossal tortoises

Most people are familiar with the famous giant tortoises of the Galapagos Islands – isolated oddities evolving in the absence of predators on a remote tropical paradise. However, as little as 5mya, continental landmasses (including Europe, Africa and India) also had their own species of giants. However, these were nearly three times the size of their modern cousins, probably close to the mass of a small car, and would have rivalled some dinosaurs for being among the most colossal reptiles of all time.

Fig 1_Kear&GeorgalisFig. 1. The near complete skeleton of Cheirogaster perpiniana (A, carapace; B, plastron) found near Perpignan, southern France (as displayed in the Muséum national d’Histoire naturelle, Paris). The carapace is 114cm long.

The best preserved gigantic tortoise fossils (as opposed to the merely ‘giant’ ones) have been found in Mediterranean Europe, particularly France, Greece and Spain, and were described in the scientific literature as early as 1877. Yet, despite an impressive chronicle of discoveries, the inter-relationships between these different kinds of gigantic tortoises are far from adequately understood. The present, albeit tentative, consensus is that there are at least three separate lineages, all of which achieved maximal body size at about the same point in geological time. Cheirogaster, the genus found in Europe, has a long fossil history stretching back some 50mys to the Eocene and includes up to 11 species. It is represented by a virtually complete skeleton (with a shell well over a metre long) unearthed from Pliocene deposits (about 5mys old) near Perpignan, in southern France. Also, several impressively big skulls, limb bones and other elements (suggesting animals of about 2m carapace length) from late Miocene and Pliocene sediments (around 5 to 8mys old) have been found on the eastern Aegean islands of Samos, Lesvos, and localities around Thessaloniki and Athens, in Greece. Together, these specimens provide a picture of what the extinct gigantic tortoises would have looked like – imagine a scaled up version of a Galapagos tortoise, but with a flatter shell, bony, armour-plated skin (presumably for protection against predators such as sabre-toothed cats) and a blunt-snouted head, with prominent forward facing eyes.

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