Chapter 34 Origin and Evolution of Vertebrates 34 2 good to know for the final Echinodermata is the sister taxon to vertebrates Cephalochordata are the basal taxon Chordates Characteristics o These characteristics were seen in the earliest chordate fossils marine o Seen today in embryos but not always in adults o Notochord Endoskeleton forms from the tough stiff cells but they are not cartilage o Dorsal hollow nerve cord Tube forms from the fold of ectoderm on the dorsal side to the notochord 34 7 o Pharyngeal slits or clefts Ancestral use filter feeding and gas exchange gills o Muscular post anal tail Better locomotion Invertebrates Cephalochordata Lancelets All key chordate features retained in the adult Minnow like but burrows and filter feeds Most basal and only a few species left Urochordata Tunicates Sea Squirts Highly derived sessile adult filter feeds with a basket like pharynx 34 5 Swimming larva have all key chordate features Uro tail where most of the notochord is Craniates Craniate Characteristics Chordates with a head o Cranium holds the brain o Centralization of paired sensory organs Neural crest cells 34 7 o Gist rise to parts of the skull and more Gills with muscular supports for gas exchange 42 23 Heart with 2 4 chambers o Closed circulatory system with hemoglobin in blood cells Myxini Hagfish 34 9 Eel like marine scavenger o No fins o Skull made of cartilage o No jaws o No vertebrae use the notochord for support Make slime as a defense mechanism Basal craniate Vertebrates Characteristics Craniates with vertebrae enclosing the spinal cord o Replaced the notochord as the main body support o First made of cartilage and then later bone Early Vertebrates o All jawless fish like filter feeders or scavengers o Later jawless parasite on fish Petromyzontida Lampreys Most basal extant vertebrate o Vertebrae are made of cartilage Jawless parasite on fish Jaws Gnathostomes Gnathostomes Vertebrates with jaws o Likely derived from gill slit supports o Usually with teeth for predation Larger forebrain smell and sight Paired lateral fins limbs usually 2 pairs o Pectoral and pelvic fins limbs Lateral line system aquatic only o Detects pressure of nearby prey enemy Fossil Gnathostomes o Placoderms early jawed fish 34 14 Body armored skin about 450mya o Later fish with mineralized bones Diverged into 3 lines about 420mya Cartilaginous sharks and rays Ray fin fish trout Lobe fin fish coelacanth Chondricthyes Sharks and Rays Skeleton mostly cartilage derived characteristic o Bony teeth and tooth like scales Buoyancy controlled by liver oils and active swimming Most are active predators marine 34 15 Internal fertilization development varies o Oviparous egg laid embryo develops within the egg o Ovoviviparous egg retained within the mother embryo fed by yolk live birth o Viviparous embryo fed directly by maternal tissue live birth Osteichtyes Bony Fish Ray Fin Coelacanth Lungfish All have a lung o Paraphyletic taxon omits tetrapods Ray fin and lobe fins coelacanths and lungfish Characteristics o Aquatic gnathostomes with an ossified skeleton Bones with calcium phosphate o Lungs first evolved in this group From the out pocketing of the esophagus Used to gulp air in oxygen poor shallow water Later modified to a swim bladder for buoyancy 34 16 Operculum gill cover protects and pumps water o Flat scales and slime protected and reduce drag o Usually external fertilization and oviparous Actinopterygii Ray fin fish 34 17 o Thin fins supported by long flexible rays o Most diverse group of all vertebrates Both marine and fresh water Herbivores predators and scavengers o Almost all living bony fish are in this group Seahorse lionfish eel and tuna Lobe fin fish o Pelvic and pectoral fins supported with bones and muscles o Actinistia coelacanths o Dipnoi lungfish Gulps air into the lungs in stagnant ponds Tetrapods Evolution of tetrapods Characteristics o 4 limbs with digits o Neck Head moves independently of body o Pelvic girdle fused to the backbone o Lung breathing as adults Lobe fin fish line lead to the first tetrapod o Tiktaalik fossil 34 20 was a freshwater fish with tetrapod like freatures Fish scales fins gills and lungs Tetrapod neck ribs fin skeleton flat skull eyes on top of skull o Later the Acanthostega fossil fishlike tetrapod 34 21 Large and diverse group of amphibians by the mid to late Paleozoic o Went from 8 to 5 digits all extant tetrapods have 5 digits Amphibians Most basal and extant tetrapod group o Thin moist skin loses water easily no scales Gas exchange occurs across the skin as well as in lungs Three chambered heart for better oxygen supplu o Dual circulation leads to higher blood pressure 42 4 5 Reproduction closely related to freshwater o Diverse mating behaviors o External fertilization Most are oviparous with fish like eggs Larval stage common o Herbivorous and fish like o Metamorphosis into carniborous adult 3 groups orders o Salamanders 4 legs and tail as adult Newts Most primitive Freshwater larva with external gills o Frogs and toads 4 legs and no tail as adults Toads mostly terrestrial with thicker skin o Caecilians no legs as adults Highly derived Mostly terrestrial burrowing Amniotes Characteristics Amniotic egg o Embryo enclosed in watery amniotic sac o Other extraembryonic membranes sustain the embryo with little water loss o Amnion coushins the embryo o Yolk sac delivers nutrients source of blood system o Chorion for gas exchange o Allantois for waste disposal and gas exchange o Eggshell protects and reduces water loss Leathery egg shells in lizards snakes and turtles Calcified shell in birds Fertilization must be internal In mammals almost all the eggshell in absent Membranes still function Waterproof skin o Dead skin with keratin and lipids o No gas exchange across the skin Water conserving kidneys o Concentrate nitrogenous wastes urea or uric acid for excretion o Fish excrete diliuted ammonia Breath by expanding rib cage o Negative pressure breathing more efficient fish and amphibians only gulp air More efficient dual circulation 42 5 o Septate or completely divided ventricle Control body temperature o Ectothermic the animal uses the environment to warm the body behavior thermoregulation basking o Endothermic the high metabolic rate warms the body physiological thermoregulation shivering Phylogeny 34 25 Earliest ammniotes gave rise to both reptiles and mammals 25 6 Reptiles include 3 major lines o Turtles relationships are uncertain o Archosaurs