Chapter 34 Origin and Evolution of Vertebrates34.2 good to know for the finalEchinodermata is the sister taxon to vertebratesCephalochordata are the basal taxonChordates- Characteristicso These characteristics were seen in the earliest chordate fossils (marine)o Seen today in embryos but not always in adultso Notochord Endoskeleton forms from the tough stiff cells but they are not cartilageo 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 InvertebratesCephalochordata: Lancelets- All key chordate features retained in the adult- Minnow like but burrows and filter feeds- Most basal and only a few species leftUrochordata: 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 isCraniatesCraniate Characteristics- Chordates with a heado Cranium holds the braino 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 chamberso Closed circulatory system with hemoglobin in blood cellsMyxini: Hagfish (34.9)- Eel like marine scavengero No finso Skull made of cartilageo No jawso No vertebrae: use the notochord for support- Make slime as a defense mechanism- Basal craniateVertebratesCharacteristics- Craniates with vertebrae enclosing the spinal cordo Replaced the notochord as the main body supporto First made of cartilage and then later bone- Early Vertebrateso All jawless fish like filter feeders or scavengerso Later jawless parasite on fishPetromyzontida: Lampreys- Most basal extant vertebrateo Vertebrae are made of cartilage- Jawless parasite on fishJaws-GnathostomesGnathostomes- Vertebrates with jawso Likely derived from gill slit supportso 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 Gnathostomeso Placoderms= early jawed fish (34.14) Body armored skin- about 450myao Later fish with mineralized bones Diverged into 3 lines about 420mya- Cartilaginous= sharks and rays- Ray fin fish= trout- Lobe fin fish= coelacanthChondricthyes: 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 varieso Oviparous= egg laid; embryo develops within the eggo Ovoviviparous: egg retained within the mother; embryo fed by yolk; live birtho Viviparous= embryo fed directly by maternal tissue; live birthOsteichtyes: Bony Fish, Ray Fin, Coelacanth, Lungfish- All have a lungo Paraphyletic taxon (omits tetrapods) Ray fin and lobe fins (coelacanths and lungfish)- Characteristicso Aquatic gnathostomes with an ossified skeleton Bones with calcium phosphateo 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 watero Flat scales and slime protected and reduce drago Usually external fertilization and oviparous- Actinopterygii: Ray-fin fish (34.17)o Thin fins supported by long flexible rayso Most diverse group of all vertebrates Both marine and fresh water Herbivores, predators, and scavengerso Almost all living bony fish are in this group Seahorse, lionfish, eel and tuna- Lobe-fin fisho Pelvic and pectoral fins supported with bones and muscleso Actinistia= coelacanthso Dipnoi: lungfish Gulps air into the lungs in stagnant pondsTetrapodsEvolution of tetrapods- Characteristicso 4 limbs with digitso Neck Head moves independently of bodyo Pelvic girdle fused to the backboneo Lung breathing as adults- Lobe fin fish line lead to the first tetrapodo 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 skullo Later the Acanthostega fossil= fishlike tetrapod- 34.21- Large and diverse group of amphibians by the mid to late Paleozoico Went from 8 to 5 digits, all extant tetrapods have 5 digitsAmphibians- Most basal and extant tetrapod groupo 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 suppluo Dual circulation leads to higher blood pressure (42.4-5)- Reproduction closely related to freshwatero Diverse mating behaviorso External fertilization- Most are oviparous with fish like eggs- Larval stage commono Herbivorous and fish likeo Metamorphosis into carniborous adult- 3 groups (orders)o Salamanders: 4 legs and tail as adult Newts Most primitive Freshwater larva with external gillso Frogs and toads: 4 legs and no tail as adults Toads mostly terrestrial with thicker skino Caecilians: no legs as adults Highly derived Mostly terrestrial, burrowingAmniotesCharacteristics- Amniotic eggo Embryo enclosed in watery amniotic saco Other extraembryonic membranes sustain the embryo with little water losso Amnion coushins the embryoo Yolk sac delivers nutrients (source of blood system)o Chorion for gas exchangeo Allantois for waste disposal and gas exchangeo 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 skino Dead skin with keratin and lipidso No gas exchange across the skin- Water conserving kidneyso Concentrate nitrogenous wastes (urea or uric acid) for excretiono Fish excrete diliuted ammonia- Breath by expanding rib cageo 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 temperatureo Ectothermic: the animal uses the environment to warm the body (behavior