Ch 26 A Closer Look at Amniotes 26.1 Amniotes 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.

Anatomy Differences: 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 FOUR-CHAMBERED HEART THREE-CHAMBERED HEART

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.

26.2 Reptiles Reptiles were the first 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.

Over time, amniotes evolved into three different groups. synapsids anapsids diapsids

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

26.3 Birds Birds and many theropod dinosaurs 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.

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 hollow bone structure to minimize weight gonads active during only part of year

Wings are structures that enable birds to fly. airfoil shape covered with feathers Air sacs help a bird meet its oxygen demand during flight. The shape of a bird’s wing reflects the way it flies. wide and broad stout and tapered

Differences in the shape of a bird’s beak reflects how it eats. Spearlike Hooked chisel-shaped Birds show great diversity in their foot shape. Webbed heavy claws different toe location

26.4 Mammals Evolutionary adaptations allowed mammals to succeed dinosaurs as a dominant terrestrial Mammals are: active large-brained, endotherms with complex social, feeding, and reproductive behaviors.

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

3 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.