26 A Closer Look at Amniotes

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FIGURE 26.7 Phylogenetic Tree of ReptilesThe diversification of ancient reptiles eventually led to the evolution of modern animals.lizards, snakes,mammals turtles and tuataras crocodiliansbirdsMillions ofyears agoCenozoicCretaceousichthyosaursplesiosaurspterosaursdinosaurs50100150Jurassic200TriassicPermianpelycosaurs250300Carboniferousanapsidsdiapsids350synapsidsreptilesAnalyze Are there any diapsid mammals? Explain your answer using the diagram.Dinosaurs were the second great radiation of the amniote family. Theyappeared 230 million years ago and were the dominant land vertebrates forthe next 150 million years. Many kinds of dinosaurs evolved during that time.Herbivorous species included huge sauropods, tanklike ceratopsians, andduck-billed dinosaurs. They were hunted by carnivorous theropod dinosaurs,which eventually gave rise to birds. All of the nonavian, or walking, dinosaurswent extinct 65 million years ago.Pterosaurs were the first vertebrates to evolve powered flight. Their wingsconsisted of skin supported by an extremely elongated fourth finger. Theearliest species, from the end of the Triassic, were small animals with longtails. Later species, such as Pteranodon lost their tails and grew as large as smallairplanes. Recent fossils show that pterosaurs may have been covered withhair, suggesting that they were endothermic. They went extinct at the endof the Cretaceous along with the dinosaurs.Apply How did the discovery of temporal skull holes help scientists determinephylogeny of amniotes?ConnectingCONCEPTSPhylogeny Recall from Chapter17 that a phylogeny is a type ofevolutionary tree that illustrateshow different species are relatedto each other. The relationshipsbetween modern animals andancient reptiles help scientistsunderstand evolution.Chapter 26: A Closer Look at Amniotes 795
MAIN IDEAThere are four modern groups of reptiles.Of all the reptiles that evolved during the Mesozoic era, only four groupsare alive today: turtles, sphenodonts, snakes and lizards, and crocodilians.FIGURE 26.8 Sea turtles live intropical ocean waters all over theworld.TurtlesThere are about 200 living species of turtles today. Turtles, tortoises, andterrapins are the only remaining anapsid group of amniotes. The distinctiveshape of a turtle is actually a bony shell that encases the reptile’s body. Thedomed back of a turtle’s shell is called the carapace, while the smooth ventralpart is called the plastron. This shell is covered with tough, flattened platesmade of keratin that are fused to the turtle’s rib cage and vertebrae. Manyturtles can pull their head and limbs into the shell for protection.Turtles are toothless and have sharp, horny beaks. Most turtles are omnivorous—theyeat plants as well as animals. They are found in terrestrial, freshwater,and marine environments. Fully terrestrial turtles are called tortoises.They have high domed shells and thick stumpy limbs. Freshwater turtles haveflatter shells. Some species have lost the bone in their shells to become “softshell” turtles. The sea turtle in FIGURE 26.8, like most marine turtles, has forelimbsthat are large flippers that let it “fly” underwater.FIGURE 26.9 Snakes and lizardsprotrude a forked tongue to collecttiny molecules out of the air.These molecules are interpretedby the Jacobson’s organ to informthe reptile about its surroundings.braintongueJacobson’sorganSphenodontsThe only living sphenodonts are two species of tuatara that live on a few smallislands off the coast of New Zealand. They are closely related to lizards andsnakes, and look similar to a spiny iguana. Tuataras have primitive characteristics,such as a diapsid skull and an eyespot in the center of their head.Snakes and LizardsSnakes and lizards are very closely related and share a number offeatures. Snakes and lizards all shed their skin at regular intervals.They also have flexible skulls that let them capture and swallowprey larger than their head. All snakes and lizards use a highlydeveloped organ that allows them to “taste” the air. As shown inFIGURE 26.9, when a snake or lizard flicks its forked tongue out ofits mouth, the tongue collects particles out of the air. Particles areinterpreted by a sensory receptor called the Jacobson’s organ,which is found in the top of the reptile’s mouth. This organallows lizards and snakes to locate prey and avoid predators.Most lizards are carnivorous. Small species hunt insects,but large species such as the Komodo dragon prey on mammals.Some species, such as iguanas, are strict herbivores. Snakes are agroup of legless lizards. All snakes are predators. Some snakes killtheir prey by constriction, wrapping their body around their preyand squeezing. Others use poisons that are injected into theirprey through modified teeth.796 Unit 8: Animals
Page 1 and 2: 26CHAPTERA Closer Lookat AmniotesKE
Page 3 and 4: 26.1 AmniotesKEY CONCEPT Reptiles,
Page 5 and 6: ConnectingCONCEPTSCirculatory Syste
Page 7 and 8: DATA ANALYSISCHOOSING GRAPHSChoosin
Page 9: FIGURE 26.6 Turtles and tortoisesar
Page 13 and 14: 26.3 BirdsKEY CONCEPT Birds have ma
Page 15 and 16: FIGURE 26.13 Bird AnatomyBird anato
Page 17 and 18: QUICK LABOBSERVINGComparing Feather
Page 19 and 20: CHAPTER 26MATERIALS• balance• 1
Page 21 and 22: ConnectingCONCEPTSNatural Selection
Page 23 and 24: FIGURE 26.18 The shovel-likebill of
Page 25 and 26: CHAPTER 26OPTIONS FOR INQUIRYUse th
Page 27 and 28: CHAPTER26@ CLASSZONE.COMKEY CONCEPT
Page 29 and 30: Critical Thinking23. Analyze A pers

26 A Closer Look at Amniotes

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