Vertebrate Zoology: Study Guide - T. A. Dauda 2014

Metazoans
Class Reptilia, or Reptiles
Order Testudines (Turtles)

There are approximately 200 known species of turtles. Their primary adaptation for passive defense is The Development of a shell that encloses the body and allows the neck, HEAD, limbs, and tail to be retracted. The shell develops from dermal bone formations as well as through the extensive expansion and fusion of several skeletal elements. In some turtles, a poorly developed bony shell is covered with soft, wrinkled Skin. Turtles lack Teeth. Their respiratory mechanism is unique: the Oral Cavity acts as a pump, with the floor rising and falling alternately. Air is drawn through the nostrils into the Oral Cavity and then forced into the Lungs.

The European pond turtle is found in the steppe zone of the Russian Federation, the Caucasus, and Crimea, inhabiting standing or slow-moving Water bodies. It climbs onto tussocks to bask and dives into the water when danger threatens. It spends the winter in hibernation and feeds on terrestrial invertebrates. Eggs are laid in the sand near water bodies. The steppe tortoise inhabits the sandy deserts of Central Asia and low mountain regions. Females have a shell length of up to 25 cm, while males are noticeably smaller. Turtles emerge from hibernation in March or early April. In April and May, females lay eggs, which take 70 to 80 days to develop. Due to the drying up of vegetation, adult turtles may enter estivation as early as June. For most individuals, summer dormancy transitions directly into winter hibernation, meaning turtles Sleep for 7 to 8 months out of the year.

The Chinese softshell turtle inhabits freshwater bodies of the Russian Far East. Its feet are webbed, and it features a long, mobile proboscis with nostrils opening at the tip. These turtles are swift swimmers capable of covering several kilometers, and they can remain submerged for 2 to 10 hours. They emerge onto land to reproduce and bask in the sun; they rarely stray far from the water, though instances have been recorded where a turtle encountered on land buried itself in the sand. They feed on fish, Mollusks, and crustaceans, and they overwinter underwater. Eggs are deposited in sandy depressions on shoals. When handled carelessly, these turtles can deliver a painful bite. The majority of turtle species inhabit tropical regions. The Galápagos tortoise, found on islands in the Indian and Pacific Oceans, reaches lengths of up to 2 m and weights of up to 200 kg. Even larger is the green sea turtle, widespread in tropical seas, which exceeds 1 m in length and can weigh up to 450 kg.

Giant tortoises, green sea turtles, and other species are harvested for their meat. The hawksbill sea turtle is hunted for its prized tortoiseshell, which is used to craft ornaments.

REVIEW AND SELF-Control Questions:

1. To what types of habitats are reptiles adapted?

2. What General Structural Features characterize the Class Reptilia?

3. Why are reptiles capable of developing without metamorphosis?

4. What structural and behavioral features are characteristic of Representatives of the orders Squamata, Crocodilia, and Testudines?

5. What is the Significance of Reptiles in nature and human life?

ORIGIN AND EVOLUTION of Reptiles

The remains of the earliest reptiles date back to the Upper Carboniferous period (approximately 300 million years ago). However, their divergence from amphibian ancestors—primitive stegocephalians—must have begun even earlier (around 320 million years ago). Like their ancestors, ancient reptiles were closely tied to moist biotopes and water bodies, but they possessed greater mobility and a slightly larger Brain; keratinization of their integument may have already begun.

Further evolution of primitive reptiles led to increased skeletal strength (through ossification), the transformation of the first two cervical vertebrae into the atlas and axis, the development of stronger limbs, and other traits that facilitated a fully terrestrial lifestyle.

It remains unclear precisely when their characteristic mode of reproduction and egg development in an aerial environment evolved. Reptiles achieved their greatest diversity in forms and ecological specialization during the Mesozoic Era.