Copyright Pearson Prentice Hall Biology Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 33-1 Chordate Evolution Photo Credit: Nigel J. Dennis/Photo Researchers, Inc. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chordate Origins Chordate Origins Much of what scientists know about the origins of chordates comes from studying the embryos of living organisms. Studies suggest that ancient chordates were closely related to echinoderms. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chordate Origins Fossils preserved in Canada's Burgess Shale include a peculiar organism called Pikaia. Notochord Tentacle This is a reconstruction of Pikaia, a soft-bodied animal that lived during the Cambrian Period. Photo Credit: S. Conway Morris, University of Cambridge Paired muscle blocks Tail fin Head region Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chordate Origins Pikaia had a notochord—a long, supporting rod that runs through a chordate’s body just below the nerve cord. It also had paired serial muscles. Because of these characteristics, scientists now classify Pikaia as an early chordate. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chordate Origins Tunicates are the simplest living animals to have key characteristics of chordates: a notochord a dorsal hollow nerve cord a tail that extends posterior to the anus pharyngeal pouches Copyright Pearson Prentice Hall

The Chordate Family Tree What are the roots of the chordate family tree? Copyright Pearson Prentice Hall

The Chordate Family Tree The chordate family tree has its roots in ancestors that vertebrates share with tunicates and lancelets. Copyright Pearson Prentice Hall

The Chordate Family Tree Tunicates and lancelets Sharks and their relatives Ray-finned fishes Frogs and toads Turtles, tortoises Lizards, snakes Lungfishes Salamanders Crocodilians Coelacanth Caecilians Mammals Hagfishes Lamprey Birds Nonvertebrate chordates Endothermy Jawless fishes Amniotic egg Cartilaginous fishes Four limbs Bony fishes The phylum Chordata includes both vertebrates and nonvertebrate chordates. All of these subphyla share a common invertebrate ancestor. This cladogram shows the phylogenetic relationship of modern chordate groups to that common ancestor. The different colored lines represent the traditional groupings of these animals, as listed in the key. The red circles indicate some of the important chordate adaptations. Such adaptations are the results of evolutionary processes, including natural selection. Lungs Amphibians Reptiles Jaws and paired appendages Birds Mammals Vertebrae Invertebrate ancestor Copyright Pearson Prentice Hall

Evolutionary Trends in Vertebrates The hard body structures of many vertebrates have left behind an excellent fossil record. Scientists also infer evolutionary trends by studying characteristics of living chordates. Copyright Pearson Prentice Hall

Evolutionary Trends in Vertebrates What is a main trend in the evolution of chordates? Copyright Pearson Prentice Hall

Evolutionary Trends in Vertebrates Adaptive Radiations  Over the course of evolution, the appearance of new adaptations—such as jaws and paired appendages—has launched adaptive radiations in chordate groups. Adaptive radiation is the rapid diversification of species as they adapt to new conditions. Copyright Pearson Prentice Hall

Evolutionary Trends in Vertebrates Convergent Evolution Adaptive radiations can produce species that are similar in appearance and behavior, but not closely related. This is called convergent evolution. Convergent evolution has produced flying vertebrates as different as birds and bats. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chordate Diversity Chordate Diversity Living chordates are diverse: nonvertebrate chordates, which include tunicates and lancelets vertebrates, which include fishes, amphibians, reptiles, birds, and mammals Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chordate Diversity Nonvertebrate chordates (4%) Mammals (8%) Fishes (49%) Birds (17%) Reptiles (13%) Amphibians (9%) Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chordate Diversity Tunicates and lancelets (2022) Mammals (4500) Hagfishes and lampreys (80) Sharks and their relatives (900) Birds (9100) Ray-finned fishes (25,000) Crocodilians (22) Lizards, snakes, tuatara (6800) Turtles and tortoises (260) Coelacanth and lungfishes (8) Caecilians (165) Salamanders (415) Frogs and toads (4300) Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 33-1 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 33-1 Species that are similar in appearance and behavior but are not closely related are sometimes the result of convergent evolution. adaptive diversity. divergent evolution. disruptive selection. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 33-1 The fossil Pikaia found in Cambrian rocks is thought to be an ancestor of chordates because it shows evidence of a notochord and paired blocks of muscle. vertebrae. bilateral symmetry. fins. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 33-1 In some chordates, pharyngeal pouches develop into paired skeletal muscles. wings. paired appendages. gills. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 33-1 The largest group of chordates is the mammals. fishes. birds. reptiles. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 33-1 In the current understanding of the evolution of the chordates, which of the following appeared most recently? jaws and paired appendages lungs endothermy vertebrae Copyright Pearson Prentice Hall

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