Reptiles and Birds

Biology I: Chapter 31-1

REPTILES

Reptile Characteristics

• Subphylum: Vertebrata

• Dry, scaly skin, and lungs

• Dry, scaly terrestrial eggs with several membranes

Reptile Characteristics

• Backbone

• Tail

• Two limb girdles

• Four limbs

• Example: iguana

Exceptions

• Snakes are limbless!

• Turtles have hard shells fused to their vertebrae!

Reptiles

• Dry body prevents water loss in a dry environment

• Disadvantage: the skin must be shed as it grows

• Can live across the globe, except in extremely cold environments

Evolution of Reptiles• Reptiles were the first animals

to adapt their eggs to dry habitats

• First reptiles are from 350 mya

• Did not become common until about 40-50 million years later when the conditions of Earth were drier

Mammal-Like Reptiles

• At the end of the Permian Period ~245 mya, a great variety of reptiles roamed the Earth

Mammal-Like Reptiles

• Displayed a mixture of mammalian and reptilian characteristics

• Dominated many land habitats

• Became extinct in just a few million years

• Replaced by another group of reptiles…

Enter the Dinosaurs• Late Triassic and Jurassic

periods

• Two groups of large aquatic reptiles swam in the seas

• Ancestors of modern turtles, crocodiles, lizards, and snakes populated many land habitats

Enter the Dinosaurs• Dinosaurs were

everywhere!

• Saurischia: lizard-hipped dinosaurs

• Ornithischia: bird-hipped dinosaurs

• Dinosaurs are the ancestors of modern birds

Exit the Dinosaurs• Mass Extinction 65 mya: the end of

the Cretaceous Period

• Caused by a dramatic series of natural disasters

• Volcanic eruptions, dropping in sea level, huge asteroid or comet smashing into the now Yucatan Peninsula in Mexico, etc.

• Opened up niches on land and in the sea, providing opportunities for other kinds of organisms to evolve

Form and Function in Reptiles• Adaptations that have

contributed to the success of reptiles on land:

• Well developed lungs

• Double-loop circulatory system

• Water-conserving excretory system

Form and Function in Reptiles• Adaptations that have contributed to the success of reptiles

on land (continued):

• Strong limbs

• Internal fertilization

• Shelled, terrestrial eggs

• Control of body temperature by changing environments

Body Temperature Control

• The ability to control body temperature is an enormous asset for active animals

• Ectotherm: animal that relies on interactions with the environment to help it control body temperature

• Turtles, snakes and other modern reptiles

Body Temperature Control

• To keep warm: bask in the sun during the day or stay under water at night

• To cool down: move into the shade, go for a swim, or take shelter in underground burrows

Body Temperature Control

Feeding• Eat a wide variety of foods

• Iguanas are herbivores and have long digestive systems to break down plant material

• Snakes, crocodiles and alligators are carnivores

• Chameleons have sticky tongues as long as their bodies to catch insects

Respiration• Lungs are spongy, providing more gas-exchange area

than those of amphibians

• Many have muscles around their ribs that expand the chest cavity to inhale and collapse the cavity to force air out

• To exchange gases with the environment, reptiles have two efficient lungs, or like some snakes, one lung

Circulation• Efficient double-loop circulatory system

– Blood to/from: lungs

– Blood to/from: body

• 2 atria and 1 or 2 ventricles

– Most have 1 ventricle with a partial septum, or wall, separating the oxygen-rich and oxygen-poor blood

Circulation

• Crocodiles and alligators have the most developed hearts of living reptiles

• 2 atria and 2 ventricles

• Arrangement also found in birds and mammals

Circulation

Excretion• Urine is produced in the kidneys

• Urine contains either ammonia or uric acid

• Ammonia: those reptiles that drink a lot of water; i.e. crocodiles and alligators

• Uric acid: those reptiles that need to conserve water, that live entirely on land; eliminated into a pasty white solid

Response

• Pattern of brain is similar to that of an amphibian

• The cerebrum and cerebellum are large compared to rest of the brain

• Active during the day

Response• Tend to have complex eyes

and can see color well

• Pair of nostrils: snakes have a good sense of smell

• Pair of sensory organs in the roof of the mouth: detect chemicals

• Simple ears with an external eardrum

Movement

• Reptiles with legs:– Run, walk, burrow,

swim or climb

• Reptiles without legs: – Squirm and twist

• Backbones of reptiles help accomplish much of their movement

Reproduction• All reproduce by internal

fertilization

• Most males have a penis that allows them to deliver sperm into the female’s cloaca

• The fertilized egg is covered with a leathery shell

Reproduction• Most are oviparous and lay the

eggs in nests

• Amniotic egg: egg composed of shell and membranes that create a protected environment in which the embryo can develop out of the water

• An important adaptation to land

Groups of Reptiles

• The four surviving groups of reptiles:

– Lizards and snakes

– Crocodilians

– Turtles and tortoises

– Tuatara

Lizards and Snakes• Order Squamata: scaly reptiles

Most lizards:

• Legs

• Clawed toes

• External ears

• Movable eyelids

Lizards and Snakes• Order Squamata: scaly reptiles

Most snakes:

• Lost both pairs of legs during their evolution

• Highly efficient predators

• Some can produce venom

Crocodilians

• Order Crocodilia

• Alligators, crocodiles, caimans, and gavials

• Long, broad snout and squat appearance

• Fierce carnivores

Crocodilians• Maternal care of young

• Live only in the tropics and subtropics

• Alligators: live only in fresh water, exclusively in North and South America

• Crocodiles: live in either fresh or salt water and are native to Africa, India and Southeast Asia

Turtles and Tortoises• Order Testudines

• Shell built into the skeleton

• Carapace: the dorsal part of the shell

• Plastron: ventral part of the shell

• Lacking teeth, these reptiles have horny ridges that cover the upper and lower jaws

Turtles and Tortoises

• Turtle: live in the water

• Tortoises: live on land

• Terrapin: turtle that is found in water that is somewhat salty

Tuataras• Order Sphenodonta

• Only member of its order

• Found in a few small islands off the coast of New Zealand

• Resemble lizards

• Lack external ears and retain primitive scales

• “Third eye”: part of a complex organ located on top of the brain…function still unknown

Ecology of Reptiles

• Many are in danger because of loss of habitat

• Humans also hunt them for food, to sell as pets, for their skins, etc.

• Some are now protected