The Origin and Evolution of Vertebrates • Vertebrates: • derive their name from vertebrae, the series of bones that make up the vertebral column, or backbone. • For more than 150 million years after 530 mya, vertebrates were restricted to the oceans, but about 365 million years ago, the evolution of limbs in one lineage of vertebrates set the stage for these vertebrates to colonize land. • There they diversified into amphibians, reptiles (including birds), and mammals. • There are about 52,000 species of vertebrates, including the largest organisms ever to live on the Earth 1-Chordates have a notochord and a dorsal, hollow nerve cord • Chordates (phylum Chordata) are bilaterian animals that belong to the clade of animals known as Deuterostomia • Chordates comprise all vertebrates and two groups of invertebrates, the urochordates and cephalochordates • Vertebrates have a backbone, made up of vertebrae, part of their internal skeleton. Chordates have a dorsal nerve chord instead of a spine. All vertebrates are chordates, but not all chordates are vertebrates. Echinodermata Chordates Cephalochordata ANCESTRAL DEUTEROSTOME Urochordata Notochord Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Myxini Common ancestor of chordates Head Petromyzontida Chondrichthyes Vertebral column Actinopterygii Jaws, mineralized skeleton Actinistia Lungs or lung derivatives Dipnoi Lobed fins Reptilia Limbs with digits Amniotic egg Mammalia Milk Figure. Phylogeny of living chordates. Tetrapods Amniotes Amphibia 4 Derived Characters of Chordates Dorsal, hollow nerve cord Muscle segments Notochord (sırt ipliği) Mouth Anus Muscular, post-anal tail Pharyngeal slits or clefts-farinks Figure. Chordate characteristics. 4 Derived Characters of Chordates the notochord; - present in all chordate embryos as well as in some adult chordates - longitudinal, flexible rod located between the digestive tube and the nerve cord. - composed of large, fluid-filled cells encased in fairly stiff, fibrous tissue. -provides skeletal support throughout most of the length of a chordate. -In humans, the notochord is reduced and forms part of the gelatinous disks sandwiched between the vertebrae. Dorsal, Hollow Nerve Cord; -develops from a plate of ectoderm that rolls into a tube located dorsal to the notochord. -unique to chordates. -The nerve cord of a chordate embryo develops into the central nervous system: the brain and spinal cord. 4 Derived Characters of Chordates Pharyngeal Slits or Clefts; - posterior to the mouth is the pharynx. -In all chordate embryos, a series of pouches separated by grooves forms along the sides of the pharynx. In most chordates, these grooves (known as pharyngeal clefts) develop into slits that open to the outside of the body. -These pharyngeal slits allow water entering the mouth to exit the body without passing through the entire digestive tract. - function as suspension-feeding devices in many invertebrate chordates. In vertebrates (with the exception of vertebrates with limbs, the tetrapods), these slits and the structures that support them have been modified for gas exchange and are known as gill slits. In tetrapods, the pharyngeal clefts do not develop into slits. Instead, they play an important role in the development of parts of the ear and other structures in the head and neck. Muscular, Post-Anal Tail -in many species it is greatly reduced during embryonic development. - contains skeletal elements and muscles, and it helps propel many aquatic species in the water. Echinodermata Chordates Cephalochordata ANCESTRAL DEUTEROSTOME Urochordata Notochord Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Myxini Common ancestor of chordates Head Petromyzontida Chondrichthyes Vertebral column Actinopterygii Jaws, mineralized skeleton Actinistia Lungs or lung derivatives Dipnoi Lobed fins Reptilia Limbs with digits Amniotic egg Mammalia Milk Figure. Phylogeny of living chordates. Tetrapods Amniotes Amphibia Cephalochordata • Lancelets (Cephalochordata) are named for their bladelike shape They are marine suspension feeders that retain characteristics of the chordate body plan as adults • Urochordata • • Tunicates (Urochordata) are more closely related to other chordates than are lancelets When attacked, tunicates, or “sea squirts,” shoot water through their excurrent siphon The lancelet Branchiostoma, a cephalochordate. Early Chordate Evolution • Findings suggest that the ancestral chordate may have looked something like a lancelet • —that is, it had an anterior end with a mouth; • a notochord; a dorsal, hollow nerved cord; • pharyngeal slits; and a post-anal tail. 5 mm Segmented muscles Pharyngeal slits Figure. Fossil of an early chordate. Echinodermata Chordates Cephalochordata ANCESTRAL DEUTEROSTOME Urochordata Notochord Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Myxini Common ancestor of chordates Head Petromyzontida Chondrichthyes Vertebral column Actinopterygii Jaws, mineralized skeleton Actinistia Lungs or lung derivatives Dipnoi Lobed fins Reptilia Limbs with digits Amniotic egg Mammalia Milk Figure. Phylogeny of living chordates. Tetrapods Amniotes Amphibia 2-Craniates are chordates that have a head Chordates with a head are known as craniates (from the word cranium, skull). The origin of a head; —consisting of a brain at the anterior end of the dorsal nerve cord, eyes and other sensory organs, and a skull —enabled chordates to coordinate more complex movement and feeding behaviors. Hagfishes • The most basal group of craniates is Myxini, the hagfishes • Hagfishes have a cartilaginous skull and axial rod of cartilage derived from the notochord, but lack jaws and vertebrae • They have a small brain, eyes, ears, and tooth-like formations • Hagfishes are marine; most are bottom-dwelling scavengers 3-Vertebrates are Craniates that have a backbone composed of vertebrae During the Cambrian period, a lineage of craniates gave rise to vertebrates. With a more complex nervous system and a more elaborate skeleton than those of their ancestors, vertebrates became more efficient at two essential tasks: capturing food and avoiding being eaten. Echinodermata Chordates Cephalochordata ANCESTRAL DEUTEROSTOME Urochordata Notochord Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Myxini Common ancestor of chordates Head Petromyzontida Chondrichthyes Vertebral column Actinopterygii Jaws, mineralized skeleton Actinistia Lungs or lung derivatives Dipnoi Lobed fins Reptilia Limbs with digits Amniotic egg Mammalia Milk Figure. Phylogeny of living chordates. Tetrapods Amniotes Amphibia Lampreys • Lampreys (Petromyzontida) represent the oldest living lineage of vertebrates • jawless vertebrates that feed by clamping their mouth onto a live fish, suck blood Conodonts: were the first vertebrates with mineralized skeletal elements Origin of bone and teeth The human skeleton is heavily mineralized bone, whereas cartilage plays a fairly minor role. But a bony skeleton was a relatively late development in the history of vertebrates. The vertebrate skeleton evolved initially as a structure made of unmineralized cartilage. What initiated the process of mineralization in vertebrates? One hypothesis is that: mineralization was associated with a transition in feeding mechanisms. Early chordates probably were suspension feeders, like lancelets, but over time they became larger and were able to ingest larger particles, including some small animals. The earliest known mineralized structures in vertebrates—conodont dental elements—were an adaptation that may have allowed these animals to become scavengers and predators. 4-Gnathostomes are vertebrates that have jaws • Today, jawed vertebrates, or gnathostomes, outnumber jawless vertebrates • Gnathostomes include sharks and their relatives, ray-finned fishes (kıkırdaklı), • lobe-finned fishes, • amphibians, • reptiles (including birds), • and mammals Echinodermata Chordates Cephalochordata ANCESTRAL DEUTEROSTOME Urochordata Notochord Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Myxini Common ancestor of chordates Head Petromyzontida Chondrichthyes Vertebral column Actinopterygii Jaws, mineralized skeleton Actinistia Lungs or lung derivatives Dipnoi Lobed fins Reptilia Limbs with digits Amniotic egg Mammalia Milk Figure. Phylogeny of living chordates. Tetrapods Amniotes Amphibia Gill slits Cranium Mouth Skeletal rods Figure. Hypothesis for the evolution of vertebrate jaws. 0.5 m Figure. Fossil of an early gnathostome. Chondrichthyans (Sharks, Rays, and Their Relatives) • Chondrichthyans (Chondrichthyes) have a skeleton composed primarily of cartilage • The largest and most diverse group of chondrichthyans includes the sharks, rays, and skates Cartilage is a type of dense connective tissue. It is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix composed of collagen fibers, abundant ground substance rich in proteoglycan, and elastin fibers. Bones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals. Dorsal fins Chondrichthyans (Sharks, Rays, and Their Relatives) Pectoral Pelvic fins fins (a) Blacktip reef shark (Carcharhinus melanopterus) (b) Southern stingray (Dasyatis americana) Figure. Chondrichthyans (c) Spotted ratfish (Hydrolagus colliei) • Shark eggs are fertilized internally but embryos can develop in different ways – Oviparous: Eggs hatch outside the mother’s body – Ovoviviparous: The embryo develops within the uterus and is nourished by the egg yolk – Viviparous: The embryo develops within the uterus and is nourished through a yolk sac placenta from the mother’s blood Ray-Finned Fishes and Lobe-Fins • The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes • Osteichthyans include the bony fish and tetrapods – Aquatic osteichthyans are the vertebrates we informally call fishes*** Echinodermata Chordates Cephalochordata ANCESTRAL DEUTEROSTOME Urochordata Notochord Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Myxini Common ancestor of chordates Head Petromyzontida Chondrichthyes Vertebral column Actinopterygii Jaws, mineralized skeleton Actinistia Lungs or lung derivatives Dipnoi Lobed fins Reptilia Limbs with digits Amniotic egg Mammalia Milk Figure. Phylogeny of living chordates. Tetrapods Amniotes Amphibia Spinal cord Swim bladder Dorsal fin Adipose fin Brain Caudal fin Nostril Cut edge of operculum Anal fin Liver Gills Anus Stomach Kidney Intestine Heart Lateral line Gonad Pelvic fin Urinary bladder Figure. Anatomy of a trout, a ray-finned fish. Ray-Finned Fishes • Actinopterygii, the ray-finned fishes, include nearly all the familiar aquatic osteichthyans • Ray-finned fishes originated during the Silurian period (444 to 416 million years ago) • The fins, supported mainly by long, flexible rays, are modified for maneuvering, defense, and other functions Figure. Ray-finned fishes (Actinopterygii). Yellowfin tuna (Thunnus albacares) Red lionfish (Pterois volitans) Common sea horse (Hippocampus ramulosus) Fine-spotted moray eel (Gymnothorax dovii) Lobe-Fins 5 cm Lower jaw Scaly covering Dorsal spine • The lobe-fins (Sarcopterygii) have muscular pelvic and pectoral fins • Lobe-fins also originated in the Silurian period Figure. A coelacanth (Latimeria). 5- Tetrapods are gnathostomes that have limbs • One of the most significant events in vertebrate history was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods Echinodermata Chordates Cephalochordata ANCESTRAL DEUTEROSTOME Urochordata Notochord Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Myxini Common ancestor of chordates Head Petromyzontida Chondrichthyes Vertebral column Actinopterygii Jaws, mineralized skeleton Actinistia Lungs or lung derivatives Dipnoi Lobed fins Reptilia Limbs with digits Amniotic egg Mammalia Milk Figure. Phylogeny of living chordates. Tetrapods Amniotes Amphibia Derived Characters of Tetrapods • Tetrapods have some specific adaptations – Four limbs, and feet with digits – A neck, which allows separate movement of the head – Fusion of the pelvic girdle (leğen kemeri) to the backbone – The absence of gills (except some aquatic species) – Ears for detecting airborne sounds Fish Characters Scales Fins Gills and lungs Figure. Impact: Discovery of a “Fishapod”: Tiktaalik. 375 mya Tetrapod Characters Neck Ribs Fin skeleton Flat skull Eyes on top of skull Shoulder bones Ribs Neck Scales Head Eyes on top of skull Humerus Ulna Flat skull Elbow Radius Fin “Wrist” Fin skeleton Lungfishes Eusthenopteron Panderichthys Tiktaalik Figure. Steps in the origin of limbs with digits. Acanthostega Limbs with digits Tulerpeton Amphibians Amniotes Silurian PALEOZOIC Permian Carboniferous Devonian 415 400 385 370 355 340 325 310 295 280 265 0 Time (millions of years ago) Key to limb bones Ulna Radius Humerus Amphibians • Amphibians (class Amphibia) are represented by about (a) Order Urodela (salamanders) 6,150 species • Order Urodela (b) Order Anura includes salamanders, (frogs) which have tails (c) Order Apoda (caecilians) Echinodermata Chordates Cephalochordata ANCESTRAL DEUTEROSTOME Urochordata Notochord Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Myxini Common ancestor of chordates Head Petromyzontida Chondrichthyes Vertebral column Actinopterygii Jaws, mineralized skeleton Actinistia Lungs or lung derivatives Dipnoi Lobed fins Reptilia Limbs with digits Amniotic egg Mammalia Milk Figure. Phylogeny of living chordates. Tetrapods Amniotes Amphibia (a) Tadpole Figure. The “dual life” of a frog (Rana temporaria). (b) During metamorphosis (c) Mating adults • Amphibian means “both ways of life,” referring to the metamorphosis of an aquatic larva into a terrestrial adult • Most amphibians have moist skin that complements the lungs in gas exchange • Amphibian populations have been declining in recent decades…why are they so vulnerable? • Fertilization is external in most species, and the eggs require a moist environment • In some species, males or females care for the eggs on their back, in their mouth, or in their stomach 6- Amniotes are tetrapods that have a terrestrially adapted egg • Amniotes are a group of tetrapods whose living members are the reptiles, including birds, and mammals Echinodermata Chordates Cephalochordata ANCESTRAL DEUTEROSTOME Urochordata Notochord Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Myxini Common ancestor of chordates Head Petromyzontida Chondrichthyes Vertebral column Actinopterygii Jaws, mineralized skeleton Actinistia Lungs or lung derivatives Dipnoi Lobed fins Reptilia Limbs with digits Amniotic egg Mammalia Milk Figure. Phylogeny of living chordates. Tetrapods Amniotes Amphibia Parareptiles Turtles Reptiles Archosaurs Crocodilians Pterosaurs Saurischians Dinosaurs Diapsids Ornithischian dinosaurs Saurischian dinosaurs other than birds Birds Plesiosaurs ANCESTRAL AMNIOTE Ichthyosaurs Synapsids Lepidosaurs Tuataras Squamates Mammals Figure. A phylogeny of amniotes. Figure. The amniotic egg. Reptiles • The reptile clade includes the tuataras, lizards, snakes, turtles, crocodilians, birds, and some extinct groups • Reptiles have scales that create a waterproof barrier • Most reptiles lay shelled eggs on land • Most reptiles are ectothermic, absorbing external heat as the main source of body heat • Birds are endothermic, capable of keeping the body warm through metabolism (a) Tuatara (Sphenodon punctatus) (b) Australian thorny devil lizard (Moloch horridus) Figure. Extant reptiles (other than birds). (c) Wagler’s pit viper (Tropidolaemus wagleri) (e) American alligator (Alligator mississippiensis) (d) Eastern box turtle (Terrapene carolina carolina) Birds • Birds are archosaurs, but almost every feature of their reptilian anatomy has undergone modification in their adaptation to flight Derived Characters of Birds • Many characters of birds are adaptations that facilitate flight • The major adaptation is wings with keratin feathers • Other adaptations include lack of a urinary bladder, females with only one ovary, small gonads, and loss of teeth Finger 1 (b) Bone structure Palm Finger 2 (a) Wing Forearm Shaft Vane Wrist Finger 3 Shaft Barb Barbule Hook (c) Feather structure Figure. Form fits function: the avian wing and feather. Figure. Artist’s Toothed beak reconstruction of Archaeopteryx, the earliest known bird. Airfoil wing with contour feathers Wing claw Long tail with many vertebrae • The demands of flight have rendered the general body form of many flying birds similar to one another Behavior and morphology has adapted to fulfill distinct niches Figure. A king penguin (Aptenodytes patagonicus) “flying” underwater. Figure. Hummingbird feeding while hovering. Figure. Specialized beaks. Figure. Feet adapted to perching. 7-Mammals are amniotes that have hair and produce milk • Mammals, class Mammalia, are represented by more than 5,300 species • Derived characters of mammals: – Mammary glands, which produce milk – Hair – A high metabolic rate, due to endothermy – A larger brain than other vertebrates of equivalent size – Differentiated teeth • Monotremes Marsupials (324 species) (5 species) ANCESTRAL MAMMAL Monotremata Marsupialia Eutherians (5,010 species) Proboscidea Sirenia Tubulidentata Hyracoidea Afrosoricida Macroscelidea Xenarthra Rodentia Lagomorpha Primates Dermoptera Scandentia Figure. Exploring: Mammalian Diversity. Carnivora Cetartiodactyla Perissodactyla Chiroptera Eulipotyphia Pholidota Monotremes • Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus Marsupials • Marsupials include opossums, kangaroos, and koalas • The embryo develops within a placenta in the mother’s uterus • A marsupial is born very early in its development • It completes its embryonic development while nursing in a maternal pouch called a marsupium Figure. Australian marsupials. (a) A young brushtail possum (b) Long-nosed bandicoot Marsupial mammals Plantigale Convergent evolution of marsupials and eutherians (placental mammals). Eutherian mammals Deer mouse Mole Marsupial mole Sugar glider Flying squirrel Wombat Tasmanian devil Kangaroo Woodchuck Wolverine Patagonian cavy Orders and Examples Main Characteristics Lay eggs; no nipples; young suck milk from fur of mother Monotremata Platypuses, echidnas Orders and Examples Completes embryonic development in pouch on mother’s body Marsupialia Kangaroos, opossums, koalas Echidna Proboscidea Elephants Koala Long, muscular trunk; thick, loose skin; upper incisors elongated as tusks Tubulidentata Aardvarks Teeth consisting of many thin tubes cemented together; eats ants and termites Aardvark African elephant Sirenia Manatees, dugongs Aquatic; finlike forelimbs and no hind limbs; herbivorous Hyracoidea Hyraxes Manatee Xenarthra Sloths, anteaters, armadillos Tamandua Lagomorpha Rabbits, hares, picas Jackrabbit Carnivora Dogs, wolves, bears, cats, weasels, otters, seals, walruses Rock hyrax Short legs; stumpy tail; herbivorous; complex, multichambered stomach Reduced teeth or no teeth; herbivorous (sloths) or carnivorous (anteaters, armadillos) Rodentia Squirrels, beavers, rats, porcupines, mice Chisel-like incisors; hind legs longer than forelegs and adapted for running and jumping; herbivorous Primates Lemurs, monkeys, chimpanzees, gorillas, Golden lion humans tamarin Sharp, pointed canine teeth and molars for shearing; carnivorous Perissodactyla Hooves with an odd Horses, zebras, number of toes on tapirs, each foot; herbivorous rhinoceroses Indian rhinoceros Hooves with an even number of toes on each foot; herbivorous Chiroptera Bats Coyote Cetartiodactyla Artiodactyls Sheep, pigs, cattle, deer, Bighorn sheep giraffes Cetaceans Whales, dolphins, porpoises Pacific whitesided porpoise Main Characteristics Red squirrel Frog-eating bat Aquatic; streamlined body; paddle-like fore-limbs and no hind limbs; thick layer of insulating blubber; carnivorous Eulipotyphla “Core insectivores”: some moles, some shrews Chisel-like, continuously growing incisors worn down by gnawing; herbivorous Opposable thumbs; forward-facing eyes; well-developed cerebral cortex; omnivorous Adapted for flight; broad skinfold that extends from elongated fingers to body and legs; carnivorous or herbivorous Eat mainly insects and other small invertebrates Star-nosed mole Derived Characters of Primates – Hands, feet for grasping – Flat nails – A large brain and short jaws – Forward-looking eyes close together on the face, providing depth perception – Complex social behavior and parental care – A fully opposable thumb (in monkeys and apes) Living Primates • There are three main groups of living primates – Lemurs, lorises, and pottos – Tarsiers – Anthropoids (monkeys and apes) Figure. Coquerel’s sifakas (Propithecus verreauxi coquereli), a type of lemur. Lemurs, lorises, and bush babies Tarsiers ANCESTRAL PRIMATE Old World monkeys Gibbons Orangutans Gorillas Chimpanzees and bonobos Humans 60 50 20 30 40 Time (millions of years ago) 10 0 Figure. A phylogenetic tree of primates. Anthropoids New World monkeys (a) New World monkey: spider monkey with prehensile tail (b) Old World monkey: macaque Figure. New World monkeys and Old World monkeys. (a) Gibbon (b) Orangutan (c) Gorilla (d) Chimpanzees (e) Bonobos Figure. Nonhuman apes. Humans are mammals that have a large brain and bipedal locomotion • The species Homo sapiens is about 200,000 years old, which is very young, considering that life has existed on Earth for at least 3.5 billion years Derived Characters of Humans • A number of characters distinguish humans from other apes – Upright posture and bipedal locomotion – Larger brains capable of language, symbolic thought, artistic expression, the manufacture and use of complex tools – Reduced jawbones and jaw muscles – Shorter digestive tract • The human and chimpanzee genomes are 99% identical • How can we be this close, yet so different? Paranthropus robustus 0 ? Paranthropus boisei 0.5 Homo Homo neanderthalensis sapiens Homo ergaster 1.0 Australopithecus africanus Millions of years ago 1.5 2.0 2.5 Kenyanthropus platyops Australopithecus garhi Australo3.0 pithecus anamensis 3.5 Homo habilis 4.0 4.5 6.0 6.5 7.0 Homo rudolfensis Australopithecus afarensis 5.0 5.5 Homo erectus Ardipithecus ramidus Orrorin tugensis Sahelanthropus tchadensis • Hominins originated in Africa about 6– 7 million years ago • Early hominins show evidence of small brains and increasing bipedalism Figure. The skeleton of “Ardi,” a 4.4million-year-old hominin, Ardipithecus ramidus. • Misconception: Early hominins were chimpanzees – Correction: Hominins and chimpanzees shared a common ancestor • Misconception: Human evolution is like a ladder leading directly to Homo sapiens – Correction: Hominin evolution included many branches or coexisting species, though only humans survive today Australopiths • Australopiths are a paraphyletic assemblage of hominins living between 4 and 2 million years ago • Some species, such as Australopithecus afarensis walked fully erect Figure. Evidence that hominins walked upright 3.5 million years ago. (a) The Laetoli footprints (b) Artist’s reconstruction of A. afarensis • Homo erectus originated in Africa by 1.8 million years ago • It was the first hominin to leave Africa Neanderthals • Neanderthals, Homo neanderthalensis, lived in Europe and the Near East from 350,000 to 28,000 years ago • They were thick-boned with a larger brain, they buried their dead, and they made hunting tools • Debate is ongoing about the extent to which genetic material was exchanged between neanderthals and Homo sapiens Homo Sapiens • Homo sapiens appeared in Africa by 195,000 years ago • All living humans are descended from these African ancestors Figure. A 160,000-year-old fossil of Homo sapiens. • The oldest fossils of Homo sapiens outside Africa date back about 115,000 years and are from the Middle East • Humans first arrived in the New World sometime before 15,000 years ago • In 2004, 18,000-year-old fossils were found in Indonesia, and a new small hominin was named: Homo floresiensis • Homo sapiens were the first group to show evidence of symbolic and sophisticated thought • In 2002, a 77,000-year-old artistic carving was found in South Africa REFERENCE CAMPBELL BIOLOGY 9th ed.
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