26 1 Amniotes KEY CONCEPT Reptiles birds and

26. 1 Amniotes KEY CONCEPT Reptiles, birds, and mammals are amniotes.

26. 1 Amniotes Amniote embryos develop in a fluid-filled sac. • The amniotic sac contains everything an embryo needs to grow. – some develop inside mother’s body – some develop inside a tough, semipermeable shell

26. 1 Amniotes • 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

26. 1 Amniotes Anatomy and circulation differ among amniotes. • The first animals walked in a sprawl. • Other amniotes, including dinosaurs, evolved a more upright stance.

26. 1 Amniotes • 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

26. 1 Amniotes • 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

26. 1 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.

26. 1 Amniotes KEY CONCEPT 26. 2 Reptiles were the first amniotes.

26. 1 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

26. 1 Amniotes • Reptiles have two reproductive strategies. – Oviparous reptiles deposit eggs into an external nest. – Viviparous reptiles retain eggs and give birth to live offspring.

26. 1 Amniotes Reptiles have been evolving for millions of years. • Over time, amniotes evolved into three different groups. – synapsids – anapsids – diapsids

26. 1 Amniotes • The diversity of ancient reptiles led to the evolution of modern reptiles, birds, and mammals.

26. 1 Amniotes There are four modern groups of reptiles. • Turtles, tortoises, and terrapins are the remaining anapsids. – bony shell encases body – 200 species

26. 1 Amniotes • Sphenodonts are closely related to lizards. – diapsids – primitive characteristics – two species

26. 1 Amniotes • 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

26. 1 Amniotes • Crocodilians are more closely related to birds than other diapsids. – diapsids – semi-aquatic predators – 23 species

26. 1 Amniotes KEY CONCEPT 26. 3 Birds have many adaptations for flight.

26. 1 Amniotes 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

26. 1 Amniotes • The oldest undisputed fossilized bird is Archaeopteryx.

26. 1 Amniotes 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 crop – active metabolism that pectoral muscle provides energy to the muscles – hollow bone structure to sternum (keel) minimize weight – gonads active during only part of year lung gizzard kidney small intestine large intestine cloaca heart liver

26. 1 Amniotes • Wings are structures that enable birds to fly. – airfoil shape – covered with feathers

26. 1 Amniotes • Air sacs help a bird meet its oxygen demand during flight.

26. 1 Amniotes 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

26. 1 Amniotes • 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

26. 1 Amniotes • Differences in the shape of a bird’s beak reflects how it eats. – spearlike – hooked – chisel-shaped blue-footed booby Bald eagle green woodpecker

26. 1 Amniotes • Birds show great diversity in their foot shape. – webbed – heavy claws – different toe location blue-footed booby bald eagle green woodpecker

26. 1 Amniotes KEY CONCEPT 26. 4 Evolutionary adaptations allowed mammals to succeed dinosaurs as a dominant terrestrial vertebrate.

26. 1 Amniotes All mammals share several common characteristics. • Mammals are active, large-brained, endotherms with complex social, feeding, and reproductive behaviors.

26. 1 Amniotes • All mammals share four anatomical characteristics. – hair to retain heat – mammary glands to produce milk

26. 1 Amniotes • All mammals share four anatomical characteristics. – a middle ear with three bones to hear higher-pitched sounds – chewing jaw to break up food quicker

26. 1 Amniotes • A set of adaptations in the mammalian jaw makes chewing possible. – secondary palate closes off air passages – muscles move jaw side-to-side

26. 1 Amniotes Modern mammals are divided into three main groups. • Monotremes lay eggs. – duck-billed platypus – echidna

26. 1 Amniotes • Marsupials give birth to live young that grow to maturity inside a pouch. – opossum – kangaroo – wombat – koala

26. 1 Amniotes • 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.