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3-30-05 IB 202 Agnathan Vertebrate diversity Fig. 34.7 • Amphibian Reproduction • Non-amniotes - eggs lack a shell and dehydrate quickly in dry air. – Mostly external fertilization; eggs shed in ponds or swamps, or other moist environments. – Vast numbers of eggs in temporary pools where mortality is high. – Some species – parental care. • Males or females house eggs on their back, in the mouth, or even in the stomach. • A few ovoviviparous or viviparous. • Why didn’t amphibians evolve an amniotic egg ( a water proof egg) like the reptiles and birds ?????? Evolutionarydevelopmental barrier???? • Inside the shell of the amniotic egg are several extraembryonic membranes that function in gas exchange, waste storage, and the transfer of stored nutrients to the embryo. – These develop from tissues layers that grow out from the embryo. Fig. 34.19 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Evolution of Amniotes • Monophyletic group (clade), with all modern reptiles, birds, and mammals sharing a common ancestor. • An evolutionary radiation of amniotes during the early Mesozoic era (~200mya) gave rise to 3 main groups, - anapsids, synapsids and diapsids. (holes in temporal region of skull, none,one and two). Two Great Waves of Adaptive Radiation of Amniotes Extant taxa Late Triassic (206 mya) Permian (290-245mya) Fig. 34.20 • Synapsids - mammal-like reptiles therapsids mammals. • Anapsids - extinct. – Turtles – may be anapsid, may be diapsid descendant. • Diapsids - extinct and modern reptiles. • Early Mesozoic (245 mya) two lineages: • lepidosaurs (lizards, snakes, and tuataras) • archosaurs (crocodiles and alligators, dinosaurs, and birds) • Birds’ closest relatives are the extinct dinosaurs – the saurischian dinosaurs. • Read about the uncertain taxonomy of amniotes – not in exam and use of reptile as a taxonomic unit. Fig. 34.21 Reptile Adaptations for Terrestrial Life – Amniotic egg (leathery). – Scales containing the protein keratin waterproof the skin. – Reptiles obtain all their oxygen with lungs; no cutaneous respiration unlike amphibians. • Ectotherm vs Endotherm • Modern reptiles are ectotherms – i.e rely on external heat (solar) and shade for adjusting body temperatures. • (Endothermy – ability to maintain high body temp by metabolic heat production). • Were their reptilian ancestors (dinosaurs) ectotherms? • Some anatomical evidence supports endothermy. • Large dinosaurs have low surface-to-volume ratios low body temp fluctuation; functional enothermy. • The dinosaur that gave rise to birds was certainly endothermic, as are all birds and feathers on fossil dinosaurs may have been for insulation. • Extant Reptiles • ~ 6,500 species; four groups: •Testudines (turtles) •Sphenodontia (tuataras) •Squamata (lizards, snakes) •Crocodilia (alligators,crocodiles) Birds Began as Feathered Reptiles • Theropod ancestor - small, bipedal, carnivorous dinosaurs, e.g. velociraptor. • The famous Mesozoic Archeopteryx. • ~150 mya, during Jurassic. • Had clawed forelimbs, teeth, and a long tail containing vertebrae. Too heavy to fly. • Not precursor to modern birds. • Cladistic analyses of fossilized skeletons support the hypothesis that the closest reptilian ancestors of birds were theropods. – These were relatively small, bipedal, carnivorous dinosaurs (such as the velociraptors of Jurassic Park). – While most researchers agree that the ancestor of birds was a feathered theropod, others place the origin of birds much earlier, from an ancestor common to both birds and dinosaurs. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Without its feathers, Archeopteryx would probably be classified as a theropod dinosaur. • Its skeletal anatomy indicates that it was a weak flyer, perhaps a tree-dwelling glider. • Archeopteryx is not considered to be the ancestor of modern birds, but probably an extinct side branch. – The evolutionary side branch that includes Archeopteryx probably stemmed from a common ancestor that also produced the lineage from which modern birds evolved. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • In 1998, paleontologists described a diversity of Chinese fossils that may fill in the gap between dinosaurs and early birds such as Archeopteryx. – These include feathered but flightless dinosaurs which may have evolved feathers for thermoregulation or courtship displays. – Others have a much closer kinship to modern birds with a lack of teeth, a horny bill, and a short stubby tail (a few fakes, money!). Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 34.28 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Extant Birds • ~ 8,600 species (~ 28 orders); two major groups. • Ratites - flightless; lack a breastbone and large pectoral muscles (except penguins). Eg. ostrich, kiwi, and emu (recent extinct large birds-moa). • Carinates – flight birds; have a carina, or sternal keel, which anchors the large pectoral muscles. • Nearly 60% of birds are passeriformes, or perching birds. Avian Adaptations to Flight • Reduction of weight: – The bones are honeycombed to reduce weight without sacrificing much strength. – Female has one ovary. – Air sacs. Frigate bird skeleton 4 oz (2 m wing) • Wings and feathers. • Large strong pectoral muscles to power flight. • Endothermic – constant high body temperature for efficient function. • Efficient circulatory system – 4 chambered heart. • Efficient respiratory system – lung with one pass gas exchange. • Feathers are among the most remarkable of vertebrate adaptations. – They are both extremely light and strong. – Feathers are made of the protein keratin, the same material in reptile scales and mammalian hair and nails. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Feathers may have functioned first as insulation during the evolution of endothermy and were later co-opted as flight equipment. – Birds have downy feathers and contour feathers. – The downy feathers of birds lack hooks on barbules, producing a fluffiness that provides excellent insulation because of the trapped air. – Contour feathers are the stiff ones that contribute to the aerodynamic shapes of the wing and body. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The evolution of flight required radical alteration in body form but provided many benefits. – Flight enhanced hunting and scavenging. • It enabled many birds to exploit flying insects, an abundant, highly nutritious food resource. – Flight provides a ready escape from earthbound predators. – It enables many birds to migrate great distances to exploit different food resources and seasonal breeding areas (Arctic seashores major nesting areas). • The Arctic tern migrates round-trip between the Arctic to Antarctic each year. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Rise of Mammals Permian (290-245mya) Fig. 34.20 • Evolution of Mammals • Dinosaurs became extinct at the CretaceousTertiary (K-T)boundary ~ 65 mya (end of Mesozoic). • Mammalian evolution began over 220 mya from reptilian stock – the therapsids. • Remained small, and “out of the lime light” until dinosaurs became extinct. • Extensive diversification in Cenozoic. • Extant mammals - ~ 4,500 species. • Characteristics of Mammals • Amniotes; offsprings born rather than hatched (except monotremes) • Presence of mammary glands – mothers produce milk and nurse newborns. • Long periods of parental care; long period of learning by offspring. • Have hair made of keratin (protein). • Endothermy. • Active metabolism supported by efficient respiratory and circulatory systems. • Brains larger than other vertebrates of equivalent size; capacity for learning. • More complex jaws and teeth types than reptiles. • 3 ear bones instead of one. Fig. 34.30 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Cladogram of Mammals African branch “Afrotherian” Endentates Fig. 34.33 • Monotremes – duck bill playtpus, spiny echindas are the only living mammals that lay eggs. • Females produce milk in specialized glands, but no nipples • Baby sucks milk from the mother’s fur. • Found only in Oz and New Guinea. • Marsupials - opossums, kangaroos, bandicoots, and koalas. • Born very early, and completes its embryonic development while nursing within a maternal pouch, the marsupium. • In Australia, marsupials have radiated and filled niches occupied by eutherian mammals in other parts of the world. • Through convergent evolution, these diverse marsupials resemble eutherian mammals that occupy similar ecological roles. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 34.32 • Eutherian (placentals) mammals • Complete embryonic development within the uterus joined to the mother by the placenta. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Which animal is the closest relative to whales? Primates and the Evolution of Homo sapiens • Primates - two subgroups. – The Prosimii (prosimians) - lemurs of Madagascar and the lorises, pottos, and tarsiers of tropical Africa and southern Asia. – The Anthropoidea (anthropoids) - monkeys, apes, and humans. Fig. 34.34 Fig. 34.35 Africa, Asia S. America • The oldest known anthropoid fossils, from about 45 million years ago, support the hypothesis that tarsiers are the prosimians most closed related to anthropoids. • Anthropoid -Monkeys • ~ 40 million years ago, monkeys were established in Africa, Asia, and South America. • The Old World and New World monkeys underwent separate adaptive radiations • New world monkeys - arboreal, prehensile tail, nostrils open to side • Old world monkeys - arboreal and ground-dwelling species, NO prehensile tail, nostrils open downwards ?? New world?? ?? Old world?? bald uakari • Anthropoid – Apes • Hylobates (gibbons), Pongo (orangutans), Gorilla (gorillas), and Pan (chimpanzees and bonobos). – Modern apes are confined exclusively to the tropical regions of the Old World. ?? Which is which?? – They evolved from Old World monkeys about 25-30 million years ago. Fig. 34.37 • • • • • Characteristics of Apes With the exception of gibbons, modern apes are larger than monkeys, with relatively long arms and short legs, and no tails, Although all apes are capable of brachiating, only gibbons and orangutans are primarily arboreal. Social organization varies among the genera, with gorilla and chimpanzees highly social. Apes have relatively larger brains than monkeys, and their behavior is more flexible. Humanity is one very young twig on the vertebrate tree • Paleoanthropology - the study of human origins and evolution. – Hominoid is a term referring to great apes and humans collectively – Hominid has a narrow meaning, confined to those twigs of the evolutionary tree that are more closely related to us than any other living species. Two main groups of hominids: Australopithecus – early hominids; extinct Homo - all extinct except Homo sapiens • Human evolution is marked by the evolution of several major features. – Brain Size - brain size in hominoids tripled over the past 6 million years. – Jaw Shape - hominoid ancestors had longer jaws prognathic jaws - than those of modern humans. • Bipedal Posture - hominoid ancestors walked on all four limbs when on the ground, like modern apes. • Reduced Size Differences Between the Sexes – Gorillas and orangutans, male 2X female by weight. Chimps and bonobos, 1.35X females. Humans, males 1.2X females. Read the rest on paleoanthropology of hominids – not in exam Fig. 34.38