Vertebrate Zoology - V. M. Konstantinov 2011

Chordates
Terrestrial, or Four-Legged, Vertebrates — Vertebrates with Embryonic Membranes
Class Reptiles — Subclass Anapsida — Order Turtles — Suborder Cryptodira

Cryptodira represent a diverse group of turtles comprising 150 species, which accounts for two-thirds of all modern species. When withdrawing their HEAD into the shell, they bend their neck in a vertical S-shape. Consequently, the cervical vertebrae lack transverse processes or retain only rudimentary ones. The pelvis is not fused to the shell. The limbs vary in Structure depending on whether the turtle leads an aquatic or terrestrial lifestyle. The carapace is distinctly convex, particularly in terrestrial species.

They are widely distributed throughout the tropical and temperate Zones of the globe, with the exception of Australia. Most of them are herbivorous (Fig. 102).

Speaking of the tortoise family (Testudinidae), we should mention the Central Asian tortoise (Agrionemys horsfieldi), which is common in Central Asia and Kazakhstan. It inhabits sandy deserts and clay steppes, and is less frequently found in low-altitude mountains and oases. The carapace length reaches up to 25 cm in females, while it is noticeably smaller in males.

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Fig. 102. Turtles and tortoises:

1 — Galápagos giant tortoise; 2 — Central Asian tortoise; 3 — European pond turtle; 4 — loggerhead sea turtle; 5 — Amur softshell turtle

In spring, tortoises emerge from hibernation in March or early April. In April and May, females lay 2–5 eggs in a shallow pit dug in the sand and subsequently cover them up. Embryonic development lasts 70–80 days. Newly hatched tortoises often remain in their underground chambers for the winter, though they occasionally crawl out to the surface for brief periods. In mid-summer, when vegetation dries up, adult tortoises burrow into the sand and enter aestivation/hibernation. In sandy deserts, this dormancy can last up to 9–10 months.

In the past century, giant tortoises were abundant on uninhabited islands of the Indian and Pacific Oceans, particularly the Galápagos Islands. They were described in detail by Charles Darwin during his visit to these islands in 1835. Systematically, they are closely related to true land tortoises and lead a terrestrial life. The most famous is the Galápagos giant tortoise (Geochelone elephantopus), which reaches up to 2 m in length and weighs up to 200 kg. Most giant tortoises have been hunted to extinction. Efforts are currently underway to restore their populations and reintroduce them to their former habitats. All subspecies are listed on the IUCN Red List.

The European pond turtle (Emys orbicularis) is widespread across the steppe zone of the European part of Russia, Crimea, and the Caucasus. It inhabits stagnant or slow-flowing Water bodies and is an adept swimmer. Its diet consists primarily of terrestrial invertebrates. To bask, it frequently climbs onto tussocks and riverbanks, remaining there for hours. When threatened, it retreats into the water. It overwinters in hibernation and lays eggs in the sandy soil along the banks of water bodies. It belongs to the pond turtle family (Emydidae).