Biology 10: Topic 12c: Class Reptilia (hüllők)

There are about 7000 species, include turtles, tortoises, alligators, crocodiles, lizards, snakes, etc

They are the 1^st really terrestrial vertebrates – they live and reproduce on land

They arose about 300 million years ago, probably because insects had spread into all land habitats and were a plentiful source of food

Dinosaurs were reptiles and they dominated on land from 250 million years ago until about 65 million years ago (representing the heyday of the reptiles). They showed extreme variations in size, habitat and lifestyle. Their extinction was most likely caused by climate change (in general), that was exacerbated by a meteor hitting the Earth (in what is now Mexico), which cause a huge dust cloud to rise and block sunlight for a very long period, leading to air pollution, drop in temperature and major plant death (herbivores’ food source)

BODY STRUCTURE

Skin: impermeable (vízálló), dry, covered with scales or bony plates

Various reptile skins

Movement: quadrupeds (4 legs, except the legless snakes, of course), with legs attached under the body allowing them for faster movement. Toes have claws for digging or climbing.

Respiration: lungs, larger than in amphibians, with infoldings. Can inhale with the help of rib muscles (except in turtles)

Circulation: 3-chambered heart, but the ventricle has a septum which partially separates it, resulting in less mixing of oxygenated and deoxygenated blood. They have double-circuit circulation. In crocodiles the septum almost completely separates the two ventricles, so they are sometimes said to have 4-chambered hearts.

Reproduction: entirely on land. They have internal fertilization, so they don’t need water to get the sperm to the egg. The female secretes a protective coverings over the eggs after fertilization and then lays them in a next (dug out of the ground). These eggs are amniotic eggs, which means there is an amniotic membrane surrounding the embryo and protecting it in a bubble of fluids. There is also a yolk that provides the growing embryo with nutrition. They don’t produce as many eggs as amphibians. Most species are oviparous, meaning they lay eggs, but some, like some vipers, are ovoviviparous, meaning they produce eggs, but they carry them around inside themselves until the eggs hatch

Excretory: this system is specialized to minimize water loss when getting rid of wastes, so they produce uric acid instead of ammonia (which is what we see in fish and amphibians)

CLASSIFICATION

O. Squamata – means scaly skinned

-includes snakes and lizards

1. Lizards – geckos, iguanas, skinks, chameleons, etc

- most have 4 legs

- have moveable eyelids

- have ear openings

Bearded Dragon

- exhibit autonomy: a lost tail can be regenerated

Green lizard

2. Snakes

Rákoczi viper

- all are legless

- excellent sense of smell: Jacobsen’s organ is found on the roof of their mouth (it contains chemical receptors). When the snake flicks its tongue in and out, it is “tasting” the air, or carrying chemicals picked up in the air, back to the Jacobsen’s organ in its mouth.

-poor vision: they have an eye covering, but no moveable eyelid. The eye covering moults with the rest of the skin

- poor hearing: no ear or ear drum (tympanic membrane) – can pick up vibrations in the ground

- pit vipers have the ability to detect heat using the pits found below their eyes, so they can see their “warm-blooded” prey, like an infrared image.

- predators: there is some variation in their hunting techniques. For example, constrictors squeeze their prey to death before eating them, while venomous snakes bite their prey to inject a venom (poison) that will paralyze or kill the prey before they eat them. Non-poisonous snakes will eat their prey alive. All snakes eat their prey whole and in order to do this they have hinged jaw bones that move independently and can open very wide. The lower jaw is actually two bones, so it can widen to the sides as well.

Jaw open wide

Note the large bump, a result of eating prey whole!

O. Chelonia – turtles (found in water) and tortoises (found on land)

- about 150 species

- unique in that they have a carapace (on top) and plastron (on the bottom)

- no teeth, use a horny beak to tear food

- they are omnivores (eat everything)

Red-eared slider (ékszerteknős)

European pond turtle

In Hungary, the release of red-eared sliders into ponds and other waterways has caused a decline in pond turtles, as the sliders are very aggressive competitors. Sliders are commonly kept as pets.

O. Crocodilia – crocodiles, alligators, caimans and gavials

- snouts allow us to tell them apart: alligators have short, wide snouts, crocodiles have longer, narrower snouts and their bottom teeth stick out when the animal’s mouth is closed. Gavials have a sort of “knob” on the end of their snout.