A closer look at AAnmiotes Amniotes 26 1

A closer look at AAnmiotes

Amniotes 26 -1

KEY CONCEPT Reptiles, birds, and mammals are amniotes.

Amniote embryos develop in a fluidfilled sac. The amniotic sac contains everything an embryo needs to grow. some develop inside mother’s body some develop inside a tough, semipermeable shell

• The amniotic egg allowed vertebrates to reproduce on land. Embryo Allantois Holds waste materials as the embryo grows Amnion Protects and surrounds the embryo Chorion Allows gas exchange with outside environment Yolk sac Contains the nutrient supply for the growing embryo

Anatomy and circulation differ among amniotes. • The first animals walked in a sprawl. Other amniotes, including dinosaurs, evolved a more upright stance.

• All amniotes have two circuits of blood vessels. – pulmonary circuit moves blood from the heart to the lungs – systemic circuit moves blood from the heart to the rest of the body

• Amniotes have a three- or four-chambered heart. – reptiles hearts have three chambers – birds and mammals hearts have four chambers THREE-CHAMBERED HEART FOUR-CHAMBERED HEART

Amniotes can be ectothermic or endothermic. Amniotes manage body heat in different ways. Ectotherms have body temperatures determined by the surrounding environment. Endotherms use metabolic heat to keep tissues warm. Endotherms can live in a wider range of climates than ectotherms.

Reptiles

KEY CONCEPT Reptiles were the first amniotes.

Reptiles are a diverse group of amniotes. Reptiles share several characteristics. ectotherms covered with dry scales reproduce by laying or retaining amniotic eggs three-chambered heart cloaca

• Reptiles have two reproductive strategies. – Oviparous reptiles deposit eggs into an external nest. – Viviparous reptiles retain eggs and give birth to live offspring.

Reptiles have been evolving for millions of years. Over time, amniotes evolved into three different groups. synapsids anapsids diapsids

• The diversity of ancient reptiles led to the evolution of modern reptiles, birds, and mammals.

There are four modern groups of reptiles. Turtles, tortoises, and terrapins are the remaining anapsids. bony shell encases body 200 species

• Sphenodonts are closely related to lizards. – diapsids – primitive characteristics – two species

• Snakes and lizards are very closely related and share a number of features. – diapsids – shed skin at regular intervals – flexible skull – Jacobson’s organ brain Jacobson’s organ tongue

• Crocodilians are more closely related to birds than other diapsids. – diapsids – semi-aquatic predators – 23 species

KEY CONCEPT Birds have many adaptations for flight.

Birds

Birds evolved from theropod dinosaurs. Birds and many theropods share anatomical features. hollow bones fused collarbones that form V-shaped wishbone rearranged muscles in the hips and legs “hands” that have lost their fourth and fifth fingers feathers

• The oldest undisputed fossilized bird is Archaeopteryx.

A bird’s body is specialized for flight. Birds have several unique features that allow them to fly. wings to produce flight strong flight muscles to move the wings active metabolism that provides energy to the muscles lung gizzard kidney crop small intestine pectoral muscle hollow bone structure to minimize weight gonads active during only part of year large intestine cloaca sternum (keel) heart liver

• Wings are structures that enable birds to fly. – airfoil shape – covered with feathers

• Air sacs help a bird meet its oxygen demand during flight.

Birds have spread to many ecological niches. The shape of a bird’s wing reflects the way it flies. short and broad long and narrow

• The shape of a bird’s wing reflects the way it flies. wide and broad lung – stout and tapered gizzard kidney crop small intestine large intestine pectoral muscle cloaca sternum (keel) heart liver

• Differences in the shape of a bird’s beak reflects how it eats. – spearlike – hooked – chisel-shaped blue-footed booby Bald eagle green woodpecker

• Birds show great diversity in their foot shape. – webbed – heavy claws – different toe location blue-footed booby bald eagle green woodpecker

Mammals

KEY CONCEPT Evolutionary adaptations allowed mammals to succeed dinosaurs as a dominant terrestrial vertebrate.

All mammals share several Mammals are active, large-brained, endotherms with complex social, feeding, and reproductive behaviors. common characteristics.

• All mammals share four anatomical characteristics. – hair to retain heat – mammary glands to produce milk

• All mammals share four anatomical characteristics. – a middle ear with three bones to hear higher-pitched sounds – chewing jaw to break up food quicker

• A set of adaptations in the mammalian jaw makes chewing possible. – secondary palate closes off air passages – muscles move jaw side-to-side

Modern mammals are divided into three main groups. Monotremes lay eggs. duck-billed platypus echidna

• Marsupials give birth to live young that grow to maturity inside a pouch. – opossum – kangaroo – wombat – koala

• Eutherians give birth to live young that have completed fetal development. – most familiar mammals – humans • Eutherians filled many niches after the extinction of the dinosaurs.