Animals The Vertebrates Chapter 26 Something Old Something
Animals: The Vertebrates Chapter 26
Something Old, Something New n Every animal is a combination of traits n Some traits are conserved from remote ancestors n Other traits are unique to its branch of the family tree
Chordate Features n Deuterostomes n All share four features: – Notochord supports body – Nervous system develops from dorsal nerve cord – Embryos have pharynx with slits – Embryos have tail that extends past anus
Chordate Groups n Urochordata – Salps and tunicates n Cephalochordata – Lancelets n Craniates – Fishes, amphibians, reptiles, birds, mammals
Tunicates (Urochordates) n Larva is free-swimming n Adult is sessile and baglike with no coelom n Both stages are filter feeders n Pharynx serves in both feeding and respiration
Tunicate Life History Larva undergoes metamorphosis to adult form pharynx Tunicate larva nerve cord gut oral opening atrial opening pharynx with gill slits Tunicate adult notochord Figure 26. 3 Page 446
Lancelets (Cephalochordates) n Fish-shaped filter feeders n Simple brain n Segmented muscles n Chordate characteristics of adult: – Notochord lies under dorsal nerve cord – Pharynx has gill slits – Tail extends past anus
Lancelet Body Plan dorsal, tubular nerve cord pharynx with gill slits tail extending past anus notochord tentaclelike structures around mouth segmented muscles aorta gonad midgut pore of anus atrial cavity hindgut Figure 26. 4 a Page 447
Early Craniates • Brain inside chamber of cartilage or bone • Arose before 530 million years ago • Resemble lancelets, lamprey larva Do not post on Internet Reconstruction of one of the earliest known craniates Figure 26. 4 Page 447
Trends in the Evolution of Vertebrates n Shift from notochord to vertebral column n Nerve cord expanded into brain n Evolution n Paired n Gills of jaws fins evolved, gave rise to limbs evolved, gave rise to lungs
Evolution of Jaws n First supporting structures gill slit fishes lacked Early jawed fish (placoderm) jaws n Jaws Early jawless fish (agnathan) are modifications of jaw spiracle jaw support Modern jawed fish (shark) anterior gill supports jaw Figure 26. 5 Page 448
Existing Jawless Fishes n Cylindrical body n Cartilaginous n No paired fins skeleton Hagfish tentacles Lamprey gill slits (twelve pairs) gill openings (seven pairs) mucous glands
Jawed Fishes n Most diverse and numerous group of vertebrates n Two classes: – Chondrichthyes (cartilaginous fishes) – Osteichthyes (bony fishes)
Cartilaginous Fishes: Class Chondrichthyes n Most are marine predators n Cartilaginous n Main skeleton groups: – Skates and rays – Sharks – Chimaeras (ratfishes)
Bony Fishes: Class Osteichthyes n Includes 96 percent of living fish species n Three subclasses: – Ray-finned fishes – Lobe-finned fishes – Lung fishes
Body Plan of a Bony Fish fin supports muscle segments brain olfactory bulb urinary bladder heart anus kidney swim bladder liver gallbladder stomach intestine Figure 26. 9 b Page 451
Lobe-Finned Fishes n Coelocanths n Lunglike sacs do not function in gas exchange
Lungfishes n Have gills and one lung or a pair n Must surface to gulp air Do not post on Internet Figure 26. 9 f Page 451
Early Amphibians n Fishlike skull and tail n Four Ichthyostega limbs with digits n Short neck Acanthostega Do not post on Internet Figure 26. 10 a Page 452
Modern Amphibians n All require water at some stage in the life cycle; most lay eggs in water n Lungs are less efficient than those of other vertebrates n Skin serves as respiratory organ
From Fins to Limbs n Genetic enhancer controls genes involved in formation of digits on limb bones n Change in a single master gene can drastically alter morphology
Living Amphibian Groups n Frogs and toads n Salamanders n Caecilians
Rise of Amniotes n Arose during Carboniferous n Adaptations to life on land – Tough, scaly skin – Internal fertilization – Amniote eggs – Water-conserving kidneys
Adaptive Radiation n Produced n Extinct numerous lineages groups include: – Therapsids (ancestors of mammals) – Marine plesiosaurs & ichthyosaurs – Dinosaurs and pterosaurs
Living Reptiles Not a monophyletic group Crocodilians Turtles Tuataras Snakes and lizards
Evolutionary History of Amniotes snakes lizards stem reptiles tuataras ichthyosaurs pterosaurs birds dinosaurs plesiosaurs archosaurs crocodilians turtles anapsids therapsids synapsids Carboniferous Paleozoic era (mammals) Permian Triassic Jurassic Mesozoic era Cretaceous Figure 26. 14 Page 455
Crocodile Body Plan olfactory lobe snout vertebral column gonad spinal cord kidney hindbrain, midbrain, forebrain heart esophagus stomach liver cloaca intestine Figure 26. 13 c Page 454
Turtles n Armorlike n Horny n Lay shell plates instead of teeth eggs on land Figure 26. 15 Page 456
Lizards and Snakes n Largest order (95 percent of living reptiles) n Most lizards are insectivores with small peglike teeth n venom gland hollow fang All snakes are carnivores with highly movable jaws Figure 26. 15 d Page 457
Tuataras n Only two living species n Live on islands off coast of New Zealand n Look like lizards, but resemble amphibians in some aspects of their brain and in their way of walking
Birds n Diverged from small theropod dinosaurs during the Mesozoic n Feathers are a unique trait – Derived from reptilian scales – Serve in insulation and flight
Amniote Egg yolk sac embryo amnion allantois chorion albumin hardened shell Figure 26. 16 a Page 458
Adapted for Flight n Four-chambered heart n Highly efficient respiratory system n Lightweight bones with air spaces n Powerful muscles attach to the keel Figure 26. 17 Page 458
Mammals: Phylum Mammalia n Hair n Mammary glands n Distinctive teeth n Highly developed brain n Extended care for the young Figure 26. 19 c Page 460
Mammal Origins & Radiation n During Triassic, synapsids gave rise to therapsids (ancestors of mammals) n By Jurassic, mouselike therians had evolved n Therians coexisted with dinosaurs through Cretaceous n Radiated after dinosaur extinction
Three Mammalian Lineages n Monotremes – Egg-laying mammals n Marsupials – Pouched mammals n Eutherians – Placental mammals
Role of Geologic Change n Monotremes and marsupials evolved while Pangea was intact n Placental mammals evolved after what would become Australia had split off n No placental mammals in Australia n Elsewhere, placental mammals replaced most marsupials
Living Monotremes n Three species – Duck-billed platypus – Two kinds of spiny anteater n All lay eggs
Living Marsupials n Most of the 260 species are native to Australia and nearby islands n Only the opossums are found in North America n Young are born in an undeveloped state and complete development in a permanent pouch on mother
Living Placental Mammals n Most diverse mammalian group n Young develop in mother’s uterus n Placenta composed of maternal and fetal tissues; nourishes fetus, delivers oxygen, and removes wastes n Placental mammals develop more quickly than marsupials
Earliest Primates n Primates evolved more than 60 million years ago during the Paleocene n First primates resembled tree shrews – Long snouts – Poor daytime vision
From Primates to Humans “Uniquely” human traits evolved through modification of traits that evolved earlier, in ancestral forms
Hominoids n Apes, humans, and extinct species of their lineages n In biochemistry and body form, humans are closer to apes than to monkeys n Hominids – Subgroup that includes humans and extinct humanlike species
Trends in Lineage Leading to Humans n Less reliance on smell, more on vision n Skeletal changes to allow bipedalism n Modifications of hand allow fine movements n Bow-shaped jaw and smaller teeth n Longer lifespan and period of dependency
Adaptations to an Arboreal Lifestyle n Better daytime vision n Shorter n Larger snout brain n Forward-directed n Capacity eyes for grasping motions
The First Hominoids n Appeared n Arose during Miocene in Central Africa n Spread through Africa, Asia, Europe n Climate was changing, becoming cooler and drier
The First Hominids n Sahelanthropus tchadensis arose 6 -7 million years ago n Bipedal australopiths evolved during Miocene into Pliocene A. anamensis A. afarensis A. africanus n A. garhi A. boisei A. robustus Exact relationships are not known
Homo Habilis 1. 9 -1. 6 million years ago n May have been the first member of genus n Lived in woodlands Do not post on Internet of eastern and southern Africa H. habilis Figure 26. 31 Page 468
Homo erectus 2 million-53, 000? years ago n Evolved in Africa n Migrated n Larger brain than H. habilis n Creative n Built into Europe and Asia toolmaker fires and used furs for clothing
Homo sapiens n Modern man evolved by 100, 000 years ago n Compared to Homo erectus: – Smaller teeth and jaws – Chin – Smaller facial bones – Larger-volume brain case
Neanderthals n Early humans that lived in Europe and Near East n Massively built, with large brains n Disappeared n DNA when H. sapiens appeared evidence suggests that they did not contribute to modern European populations
Earliest Fossils Are African n Africa appears to be the cradle of human evolution n No human fossils older than 2 million years exist anywhere but Africa n Homo erectus left Africa in waves from 2 million to 500, 000 years ago
Where Did H. sapiens Arise? n Two hypotheses: – Multiregional model – African emergence model n Both attempt to address biochemical and fossil evidence
Multiregional Model that H. erectus migrated to many locations by about 1 million years ago n Argues n Geographically separated populations gave rise to phenotypically different races of H. sapiens in different locations n Gene flow prevented races from becoming species
African Emergence Model that H. sapiens arose in sub. Saharan Africa n Argues n H. sapiens migrated out of Africa and into regions where H. erectus had preceded them n Only after leaving Africa did phenotypic differences arise
Genetic Distance Data NEW GUINEA, AUSTRALIA PACIFIC ISLANDS SOUTHEAST ASIA ARCTIC, NORTHEAST ASIA NORTH, SOUTH AMERICA NORTHEAST ASIA EUROPE, MIDDLE EAST AFRICA 0. 2 0. 1 Genetic distance (percent) 0 Figure 26. 37 Page 471
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