Gnathostomes Flashcards
What are gnathostomes?
animals with jaws have 2 pairs of fins (extinct agnathans so jawless had only 1 pair of fins –> still surviving have no pairs of fins)
- they have a bigger brain than jawless vertebrates
what happens to the hox genes of animals with jaws (gnathostomes)
THEY DUPLICATE… BECOME 4 CLUSTERS OF HOX GENES WHICH ADDS GENETIC DIVERSITY BC OF JAWS, LARGER BRAIN AND IMPROVED VISION AND SMELL
Where did jaws come from?
they came from the modification of 2 skeletal rods that had supported the anterior pharyngeal slits
posterior slits became specialized for gas exchange (gill slits)
What groups of species involves the Class chondrichthyes?
- includes sharks, rays and chimeras
what are the bone features of chondrichthyes
they are cartilaginous fishes and their endoskeleton is made out of cartilage
but they have teeth made out BONES
how did their cartilaginous skeleton develop?
it was not a primitive character states, it was derived from ancestors with bony skeletons
- in the development of most vertebrates, the skeleton is first cartilage and then becomes ossified but sharks skip this
How do sharks swim and move?
- their propulsions come from their tails
- they don’t have a gas filled swim bladder for buoyancy
but their buoyancy comes from storing oil in their liver and because oil is denser than water, they sink when they are not swimming
how do sharks breathe?
- they have to use muscles to gulp water and aerate their gills to help them breathe
Describe the shark’s skin and teeth?
- they have rough skin with dermal placoid scales (scales are like bones and looks like their teeth)
- their scales are structurally homologous with vertebrate teeth (which means that vertebrate teeth is derived from same ancestor as shark scales!)
- shark teeth are continuously replaced like a conveyor belt
How do sharks sense movement and smell?
- they have nostrils that sense smelling not for gas exchange
- they detect changes in electrical fields generated by the muscular movement of other animals through their pores around their heads
- they detect vibrates in water using their lateral line that runs across the length of their body and they use that for hearing … the hairs pick up vibrations and amplify it in their lateral lines
How do sharks reproduce?
- sharks reproduce by copulation … males use their pelvic fins as claspers to hold onto the female and guide sperm
- fertilization is also internal
- they are oviparous (they lay eggs) and their eggs are protected in a leathery egg case for protection
what are the 3 progeny productions?
- oviparous –> egg laying
- ovoviviparous –> eggs hatch in utero
- viviparous –> live birth
