Amniotes - Reptiles Flashcards
What two groups did the reptilomorphs diverge into during the Permian?
Sauropsids and synapsids
Give some features of the amniotic egg
3 extraembryonic membranes:
- chorion encloses everything
- allantois for waste storage and becomes site for bladder
- amnion
Have a shell - leathery in the ancestor
Albium - source of water and adds additional protection
Yolk - food source for the embryo
Chalaza - suspends the yolk and keeps the embryo in position
What are the reasons for a shell to cover the amniotic egg?
Defence
Gas and water exchange
Where does the embryo start to develop?
Germinal disc
What are some features of amniotic reproduction?
Internal fertilisation
Most males have intromittent organs - birds dont tend to have them
Females have clitorises/hemiclitores - these are homologous with male intromittent organ
Some have envrionmental sex determination
No larvae stage
Egg has to be laid on land
Why may have the amniotic egg evolve?
Increased surface area for gaseous exchange
Shell provides support - means can maybe have larger eggs which causes larger adults
What are some derived features of the amniotes?
Have an axis and atlas - connection of these allows for head rotation
Reduced skin permability - it is thicker, keratinised and has more lipids
Have skin elaborations - scales, hair, feathers (these are homologous with epidermal placodes)
All have alpha kertain (probably ancestral feature) and sauropsids have beta keratin
Costal ventilation - rib movement is more powerful so air can be pulled over longer distances
Longer necks
More complex nerves controlling forelimb
What are the different types of temporal fenestration?
Anapsid = no fenestra
Synapsid = one fenestra
Diapsid = two fenestra
Can have modified diapsids = where they had two fenestra but have lost one or both
Was temporal fenestration in ancestor forms?
No
Not found in early sauropsids
So must have evolved independently in both synapsids and sauropsids
What temporal fenestration do turtles have?
Diapsid but look anapsid
Give some features of the turtles (Chelonia)
Ribs and vertebrae are fused to the carapace
Plastron is hard shell on belly
Keratin scutes cover carapce and plastron
No teeth - ancestors had teeth
Have a flexible and retractable neck - dont think ancestral form could
Kertain beak
How do turtles (Chelonia) breathe?
To breathe in:
Contract muscles to move gut/visceral downwards
Gut movement causes lung to also move down which allows air in
To breathe out:
Contract muscles that force gut upwards
Gut movement causes lung to move up
Expels air
Aquatic turtles use hydrostatic pressure and use pharynx and cloaca for gas exchange
What is envrionmental sex determination?
Envrionmental temperatures determines the sex of the embryo
Very common reptiles
Probably due to an advantage of size:
- the sex which is larger in size will be produced at higher temperatures (on average)
Give some features of the Tuatara (Sphenodonta)
Only group in the Sphenodonta
Sister group to snakes and lizards
Nocturnal
Low body temperature
Live in burrows with seabirds
Feed on arthropods - possibly what causes them to become nocturnal
Diapsids
Thought to have lost the 2nd bar in skull and reformed it later on - possibly made jaws stronger
What groups come under the Lepidosaurs?
Lizards and snakes - known as the squamates
What bars have the squamates lost on their skull?
Lizards have lost their bottom bar
Snakes have lost both bars
This has allowed them to have kinetic jaws
Give some features of the lizards
80% are < 20g
Small lizards are insectivores
Large lizards tend to be herbivorous with some exceptions e.g. monitors
Many are arboreal
What is the problem with fast moving in the monitors?
Causes conflict with locomotion and ventilation - as use the same muscles
Some have evolved gular pumping - the mouth pumps to ventilate the lungs
What unique features do chameleons have?
Zygodactylous feet
Eyes move independently
How many times has limb reduction evolved in lizards?
> 60
Give some features of the snakes
Very specialised legless lizards - they are the sister group to them
Branched from lizards during the cretaceous
Had a digging/underground stage where they lost their eyes. Came back to the surface and reformed eyes - possibly why their eyes are different to lizards
Mostly thorax
Change in gene expression leads to more thoracic vertebrae - Oct4
In mice they found a reduction in ZRS decreases the production of Shh (responsible for limb formation) so get no limbs - maybe the same in snakes?
Lack pectoral and pelvic girdles - these are vestigial in pythons and boas
Eupodophis is an earlier form of snake and was found to have rear limbs - so possibly lost forelimbs first and then rearlimbs
What are the problems with the elongation of the body? How have snakes overcome this?
Causes a reduced body diameter and a smaller mouth
Snakes evolved a very flexible jaw by losing both temporal bars and having many points of articulation in the skull - can have up to 8
Teeth face backwards to help push prey down throat
Give some features of the Crocodylia
Belong to the Archosaurs
Diapsid skull
Teeth found in sockets (thecodont) - evolved independently to the mammals
Have a secondary palate - evolved independently to the mammals
Semi-aquatic but primarily aquatic predators
Have integumentary sensory organs - pressure receptors on jaw
Have multiple form of movement - swim, crawl, walk, gallop
Use liver movement to ventilate lungs
Use sound in social behaviour - territorial, mating, parental care
Lay eggs that are ESD
Some show play behaviour
