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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?
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)
what are the critical adaptations in vertebrate evolution?
- 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
sub-phylum vertebrata - what are the basic chordate characteristics?
-dorsal hollow nerve cord
-notochord
-7x pharyngeal gill slits
-post anal tail
-endostyle (thyroid)
vertebrata - what is the importance of musculoskeletal modifications?
- 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
vertebrata - how did respiration become more efficient
- 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
vertebrata - what are the features of the evoluved brain
- 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
compare vertebrate with invertebrate
invertebrates- ventral nerve cord, no ceolom and an external/hydrostatic skeleton
vertebrata - what are thought to be the 2 evolutionary ancestors of vertebrata and why
- 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
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
Class Condricythes (cartilaginous fishes)- what are the subclasses within this class?
elasmobranchii - true sharks and rays
holocephali - chimaeras
how were jaws important to evolution of vertebrata?
- 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)
what is a heterocercal tail and what class does it belong to
a heterocercal tail is an asymmetrical tail with a larger top lobe. provides very strong horizontal thrust. it belongs to sharks
class Condricythes - respiration and circulation. how many chambers does the shark heart have?
- most sharks need to continue swimming to ventilate gills
-most water drawn in through mouth rather than spiricule
- have a 2 chambered heart
what are the characteristics of the elasmobranchii - rays
-dorsoventrally flattened
-pectoral fins enlarged (wings)
- water drawn in through spiricules not mouth
-5-6 gills on ventral surface
sharks - how many sections of the stomach do they have and what are they called
they have 2
-cardiac and pyloric stomachs
sharks - what are the functions of the spiricules
located just above the gills, they take in water and help to pump water over gills
what was the first creature to exhibit jaws?
class condricythes
how did the evolution of jaws come about?
-due to modifications of the first two gill arches
-developed ability to squeeze 2 gill arches together
- 2nd arch attaches to skull for stability
what are the characteristics of the class elasmobranchii - sharks?
- 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
list what makes sharks bouyant
-heavy bone has been replaced with light cartilidge
-the liver is filled with oil
-does not have a swim bladder
describe the skin layers of a shark
-thin epidermis (outermost layer)
-dermis which secretes placoid scales that pierce through the epidermis
list features of the teeth in a shark
pulp cavity surrounded by dentine with enamel outer layer.
It is as hard as steel.
teeth are replaced continuously throughout life
what do sharks and rays feed on and what type of teeth do they use for this?
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
describe the sensory systems of a shark including sight, hearing, smell, pressure and electreception
-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
what is the apullae of Lorenzini, what does it do and which class does it belong to?
it is the system in sharks (cl chondricythes) that allow for the sensory perception of electric feilds given off by prey
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
how are shark young prodcued?
they can be birthed through eggs containing yolk sacs for nourishment or birthed live straight from the mother