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27 Cards in this Set
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what is paedomorphosis and how does it apply to the evolution of vertebrates?
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a phylogenetic change in which juvenile characteristics are maintained into adulthood. it is thought that vertebrates evolved through the failure to metamorphose into an adult and instead reach sexual maturity as a larva (paedomorphis)
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what are the critical adaptations in vertebrate evolution?
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- musculoskeletal modifications
- pharynx evolved as feeding aparatus - respiration became efficient - new head, brain and sensory features -formation of appendeges that allow for terrestrial life -jaws |
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sub-phylum vertebrata - what are the basic chordate characteristics?
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-dorsal hollow nerve cord
-notochord -7x pharyngeal gill slits -post anal tail -endostyle (thyroid) |
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vertebrata - what is the importance of musculoskeletal modifications?
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- attachment site for muscles
-bony case protecting brain adn internal organs - provides support structure and framework of body - grows with animal therefore allows for very large size |
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vertebrata - how did respiration become more efficient
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- allows for efficient transfer of o2 into blood
- increased surface area means higher o2 and more energy, which allows for a more active lifestyle. lead to developement of highly active predatory lifestyle |
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vertebrata - what are the features of the evoluved brain
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- larger and more complex
- hind, mid and forebrain - allows for much greater response to stimuli - assist with development of predation - concentration of censory organs in head |
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compare vertebrate with invertebrate
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invertebrates- ventral nerve cord, no ceolom and an external/hydrostatic skeleton
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vertebrata - what are thought to be the 2 evolutionary ancestors of vertebrata and why
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- urochordata (jawless ostracoderm) as it's larval stage exhibits all chordate features. it is assumed larva failed to metamorphose and developed adult features in larval stage (paedomorphosis)
- cephlachordates (amphioxus) retained primative pattern to pre-vertebrate condition. most likely sister group to ancestor |
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Superclass Agnatha -
what are the two classes of agnatha and what are their characteristics? |
- mynixi (hagfish) blind
- petromyzontida (lamprey) undergo metamorphosis both contain: notochord all life, fins- no paired appendages, cartilaginous internal skeleton, dorsal nerve cord and differentiated brain |
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Class Condricythes (cartilaginous fishes)- what are the subclasses within this class?
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elasmobranchii - true sharks and rays
holocephali - chimaeras |
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how were jaws important to evolution of vertebrata?
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- it allowed for biting off larger chunks of organisms, providing more energy and thus can sustain larger forms
-it allows for the manipulation of objects (picking things up, hholding in place) |
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what is a heterocercal tail and what class does it belong to
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a heterocercal tail is an asymmetrical tail with a larger top lobe. provides very strong horizontal thrust. it belongs to sharks
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class Condricythes - respiration and circulation. how many chambers does the shark heart have?
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- most sharks need to continue swimming to ventilate gills
-most water drawn in through mouth rather than spiricule - have a 2 chambered heart |
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what are the characteristics of the elasmobranchii - rays
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-dorsoventrally flattened
-pectoral fins enlarged (wings) - water drawn in through spiricules not mouth -5-6 gills on ventral surface |
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sharks - how many sections of the stomach do they have and what are they called
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they have 2
-cardiac and pyloric stomachs |
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sharks - what are the functions of the spiricules
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located just above the gills, they take in water and help to pump water over gills
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what was the first creature to exhibit jaws?
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class condricythes
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how did the evolution of jaws come about?
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-due to modifications of the first two gill arches
-developed ability to squeeze 2 gill arches together - 2nd arch attaches to skull for stability |
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what are the characteristics of the class elasmobranchii - sharks?
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- approx 400mya
-cartilaginous skeleton - notocord replaced by vertebrate -thought to have evolved AWAY from bone as cartlidge is lighter and more bouyant -one or two dorsal fins -paired pectoral appendages -5-7 gill slits each side |
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list what makes sharks bouyant
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-heavy bone has been replaced with light cartilidge
-the liver is filled with oil -does not have a swim bladder |
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describe the skin layers of a shark
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-thin epidermis (outermost layer)
-dermis which secretes placoid scales that pierce through the epidermis |
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list features of the teeth in a shark
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pulp cavity surrounded by dentine with enamel outer layer.
It is as hard as steel. teeth are replaced continuously throughout life |
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what do sharks and rays feed on and what type of teeth do they use for this?
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sharks feed on mammals and fish (mostly) and have sharp triangular teeth for cutting.
rays feed on benthos and have small blunt teeth for grinding. NOTE there are a few filter feeders |
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describe the sensory systems of a shark including sight, hearing, smell, pressure and electreception
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-poor hearing.
-eyesight is best in low light though still not great - very good sense of smell -lateral line system along the head sense shifts in pressure (water movement due to prey) -ampullae of Lorenzini are able to detect electrical feilds given off by prey |
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what is the apullae of Lorenzini, what does it do and which class does it belong to?
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it is the system in sharks (cl chondricythes) that allow for the sensory perception of electric feilds given off by prey
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describe the reproduction within sharks
-type of fertilisation - copulatory organs |
-diecious
-internal fertilisation -male has clasps on penis to help keep it in -produce a few large offspring -oviporous (egg bearing) and viviporous |
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how are shark young prodcued?
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they can be birthed through eggs containing yolk sacs for nourishment or birthed live straight from the mother
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