Lecture 15: The Amniotes Flashcards
Amniotes:
Reptiles and birds + mammal
The amniotes…
- a self-contained waterproof chamber for development, eliminates the larval stage.
- contains 4 membrane layers that are not part of the embryo.
Yolk sac…
Surrounds the yolk nutrients, which is accumulation of nutrients that surrounds the embryo.
Allantois…
stores nitrogenous waste, stores all waste from the embryo. Lies against the chorion so also involved in gas exchange.
3 types of Amniote based on..
number of fenestra (windows) in the skull
No fenestra, turtles, extinct reptiles..
Anapsid
Two fenestra, other reptiles, birds…
Diapsid
One fenestra, mammals…
synapsid
Reptiles:
- 7000 species, many extinct lineages
- paraphyletic (multiple lineages) [isnt a single ancestor from all the reptiles]
- lack of single defining characteristic, other than have an amniotic egg, no feathers (not birds)
- inc. turtles, lizard, snakes, crocodiles, tuatara
Reptile features:
-dry scaly keratinised skin, prevents desiccation and UV
-internal fertilisation, eggs laid on land
-ectothermal -regulate their temp through solar energy
-heavier more ossified skeleton than amphibia, stronger joints, clawed toes
-more complex muscle and nervous systems
4 chambered heart separates oxygenated and deoxygenated blood
ectotherm + & -
pos
-eat less than endotherm (10% of what endotherm eat)
neg
- slow in cold weather therefore vulnerable
Evolution history of reptiles..
- oldest fossile date to the carboniferous (300mya)
- early forms probably fed on invertebrates
- penetrated further inland than amphibians
(reptiles) first amniote radiation in the Permian led to…
anapsid, synapsids and diapsids; diapsids led to lepidosauria (lizards and snakes) and archosauria (crocodiles&dinosaurs)
(reptiles) Second radiation of archosauria led to..
dinosaurs etc
Most reptiles of sustained rapid motion..
- stride is short
- proximal limb segments move on the horizontal plane
- ectothermic, glycolysis rather than oxidative metabolism
Dinosaurs endothermic?
- legs beneath body
- long strides
- vascularised bones (blood in bones)
- predator prey ratios (similar to present day mammal)
dinosaurs ectothermic?
- warm Mesozoic
- surface area to volume ratio (high temp maintained by storing heat in there bodies, lost heat relatively slowly)
dinosaurs extinction theories?
- rise of the mammals
- explosion (volcano?) lots of particulate matter and not enough sunlight.
- asteroid impact
Now scientists believe asteroid impact caused change in climate (climate change)
Modern reptiles 3 main orders
- chelonia (turtles)
- squamata (ilzards and snakes)
- crocodilia (alligators and crocodiles)
Order chelonia (turtles)
- 250sp
- includes marine, freshwater and terrestrial types
- teeth replaced by sharp horny plates
- bony dermal plates fuse to form carapace and plastron
- flexibile neck
Order squamata (ilzards and snakes)
- lizards (4000 sp)
- snakes (2500sp), highly specialised
- loss of limbs, elongate body form,likely burrowing ancestor
- loss of eyelids, have clear spectacle
- many specialisations for finding prey
- jacobson’s organs senses smell
- pit organs sense heat (endothermic prey)
- jaws extremely flexible with moveable joints for large prey.
Order crocodilia (alligators and crocodiles)..
- 22spp
- all extant species …………….
Class Aves (birds)
- how they defined
- phyletic group?
- reptile features that are present
- defined by the presence of feathers
- monophyletic group
- reptile features include scaly legs, amniote eggs (reduces water loss, calcium carbonate)
Aves characteristics…
- honeycombed bones with cross struts
- reduced organs (e.g. females have 1 ovary)
- no teeth, food ground in gizzard
- keratin bill (modified, hooke bill for tearing flesh, humming bird long thing bill for nectar)
- large pectoral muscle anchored to keel with rigid fused vertebrae gives power for flight
