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During embryonic development, blastopore becomes anus
Phylum Echinodermata
– sea stars, sea cucumbers, sea urchins
Phylum Chordata
– acorn worms, sea squirts, lancelets, vertebrates
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• Sea stars, sea cucumbers, sea urchins, sea lilies, brittle stars
Pentameric symmetry in adults
Characteristics
– calcareous endoskeleton
– bilaterally symmetrical larvae
– water vascular system
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Class Crinoidea (sea lilies, feather stars)
Class Asteroidea (sea stars)
Class Concentricycloidea (sea daisies)
Class Ophiuroidea (brittle stars)
Class Echinoidea (sea urchins, heart urchins, sand dollars)
Class Holothuroidea (sea cucumbers)
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Endoskeleton
– calcite (CaCO
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Larva
– free-swimming, bilaterally symmetrical
– pentameric symmetry develops at metamorphosis
Water vascular system
– coelomic canals
– gas exchange and locomotion
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Water enters through sieve-like madreporite
Stone canal → ring canal → radial canals
Stone canal
– calcified tube, connects madreporite to ring canal
Ring canal
– runs around base of arms
Radial canals
– run along arms; tube feet and ampullae for locomotion
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Acorn worms, sea squirts, lancelets, vertebrates
Bilateral symmetry
Characteristics
– notochord
– pharyngeal slits
– dorsal hollow nerve cord
Oldest fossils from Cambrian (530 million years ago)
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• Subphylum Hemichordata (acorn worms, pterobranchs)
Subphylum Urochordata (sea squirts, tunicates)
Subphylum Cephalochordata (lancelets)
Subphylum Craniata (fish, amphibians, reptiles, birds, mammals)
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Characteristics of chordates are present at some stage of the life cycle
Notochord
– dorsal rod between nerve cord and gut, attachment point for blocks of muscles (myotomes)
Pharyngeal slits
– paired openings in pharynx, used for filter feeding in some chordates
Dorsal nerve cord
– hollow nerve cord above notochord, expanded anteriorly to form brain in some chordates
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Acorn worms, pterobranchs
Characteristics
– tripartite body: proboscis, collar, trunk
– pharyngeal slits filter food particles from water
– mouth in groove between proboscis and collar
– dorsal nerve cord in collar
Marine, solitary (acorn worms) or colonial
(pterobranchs)
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Sea squirts, tunicates, salps
Characteristics
– notochord and dorsal nerve cord in pelagic forms (larvae and adults)
– incurrent and excurrent siphon for water intake and expulsion
– pharyngeal slits filter food particles from water
– adult body encased in tunic composed of tunicin (form of cellulose)
Marine, solitary or colonial, sessile or pelagic
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Lancelets
Characteristics
– notochord extends for full length of body
– muscle blocks (myotomes) along body
– pharyngeal slits filter food particles from water
– oral hood with buccal cirri around mouth
– dorsal and tail fins, paired metapleural folds
Marine, solitary, benthic
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Jawless fish and vertebrates
– oldest fossil craniates are lower Cambrian (530 million years ago)
Characteristics
– head with cranium (skull) of cartilage or bone
– brain with cranial nerves
Marine, freshwater or terrestrial, solitary, mobile
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Lampreys and hagfish
Characteristics
– cartilaginous skeleton
– notochord persists in adults
– lack jaws
Extinct jawless fish were bottom-dwelling filter or detritus feeders
Modern jawless fish are blood-feeding ectoparasites or scavengers
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Vertebrates (fish, amphibians, birds, reptiles and mammals)
Characteristics
– vertebrae replace notochord in adult
– projections from vertebrae protect nerve cord and aorta
– neural crest cells give rise to many structures in the head and other parts of the body
– dentine and enamel often form teeth or denticles
Evolution of jaws from gill-arches allowed vertebrates to exploit a range of diets
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Cartilaginous fish: sharks, rays, skates, chimaeras
Characteristics
– skeleton of cartilage (frequently calcified)
– fins with broad bases
– lack swim bladder
– denticles in skin and along jaws
Marine or freshwater (few species), benthic or pelagic
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Ray-finned fish: sturgeons, paddlefish, barramundi, eels, seahorses, butterflyfish etc.
Characteristics
– skeleton of bone
– fins with narrow bases, supported bony rays
– swim bladder present
– jaw formed of teeth-bearing dermal bone
Marine or freshwater, benthic or pelagic
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Lobe-finned fish: coelacanths and lungfish
Characteristics
– fins with broad, fleshy bases
Sarcopterygians are the closest relatives of tetrapods (amphibians, sauropsids and mammals)
– similarities in pelvic girdle, pectoral and pelvic appendages, dermal bones and heart
Marine or freshwater, benthic or pelagic
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Frogs, toads, newts, salamanders, caecilians
Characteristics
– skull with occipital condyles that articulate with vertebrae
– single sacral vertebra
– glandular skin without epidermal structures
– eggs lack shells
– lungs and skin used in gas exchange
Freshwater and terrestrial
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Vertebrates (sauropsids, mammals)
Characteristics
– extra-embryonic amnion encloses embryo in fluid-filled sac
– embryonic allantois (outgrowth of hindgut) is used for excretion during development
– thick, waterproof skin with scales, hair or feathers
– intervertebral disc
– atlas and axis are first two cervical vertebrae
Amniotes include Sauropsida (birds, ‘reptiles’) and
Mammalia
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• Turtles, tortoises and terrapins
Characteristics
– body protected by dorsal and ventral shields (carapace and plastron respectively)
– shoulder (pectoral) girdle lies inside rib cage
– skull anapsid (lacks openings to accommodate jaw muscles)
– jaws toothless
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Snakes, lizards and tuatara
Characteristics
– teeth fused to edges of jaws
– some species can shed tail at pre-formed fracture points
(autotomy)
– snakes can disarticulate jaws to accommodate large prey
Tuataras ( Sphenodon ) of New Zealand are ‘living fossils’
– only surviving members of order Rhynchocephalia
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Crocodiles, birds, dinosaurs
Characteristics
– diapsid skull with additional preorbital opening
– moveable membrane over eye
– muscular gizzard
Most of the diagnostic characteristics of birds are adaptations to flight
– birds are descendants of the dinosaur lineage
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Characteristics
– epidermal hair
– milk production from mammary glands
– left aortic arch carries systemic circulation
Subclass Prototheria
– Order Monotremata (egg-layers)
Subclass Theria
– Order Metatheria (marsupials)
– Order Eutheria (placentals)
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Lemurs, tarsiers, monkeys, apes (including humans)
Characteristics include
– prehensile digits and opposable thumb
– bicuspid premolars, molars with three to five cusps
– binocular vision, large brain
Strepsirhini (lemurs, lorises, galagos, pottos)
– rhinarium (nose pad) with slit-like nostrils
Haplorhini (tarsiers, monkeys, apes)
– nose with rounded nostrils
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Characteristic bipedal gait of hominids frees hands for grasping food, holding young, nest-building and tool-making
Sahelanthropus tchadensis ( 7 to 6 million years ago)
– Djurab Desert, Chad, Africa
– apelike brain case, short face and ‘human’ teeth
Australopithecus (4.4 to 2.5 million years ago)
– Ethiopia to South Africa
– forward-jutting face, browridge, ‘human’ hands and molar teeth
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Tool-making hominids coexisted with Homo in
Africa
Paranthropus (2.8 to 1.6 million years ago)
– skulls with sagittal crests
– powerful jaw with large premolars
– vegetarian, used digging tools (probably for collecting tubers and other plant material)
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Oldest fossils of Homo are c. 2.5 million years old
– H. rudolfensis and H. habilis coexisted with
Australopithecus in Africa
Differences between Homo and Australopithecus
– brain capacity of Homo larger than Australopithecus
– reduction in jaw and tooth size
– evidence of tool-making ( H. habilis )
More modern species with larger brain capacity
– H. ergaster from Africa
– H. erectus from Java (‘Java Man’) and China (‘Peking
Man’) made more sophisticated tools than H. habilis
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Competing theories of origin of Homo sapiens
Out-of-Africa theory
– migration of anatomically modern humans from Africa, replacing all other populations of Homo
– mtDNA evidence suggests a common ancestor 170 000 years ago
Multiregional theory
– anatomically modern humans evolved semiindependently from H. erectus -like ancestors simultaneously in different region
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