8. Key adaptations in vertebrate evolution.pdf

Key adaptations in vertebrate evolution Aarni Auerniitty First land animals Circulation  Single cycle circulation (left): fishes  Double circulatory system, three chambers (middle): amphibians, most reptiles  Oxygen...

Key adaptations in vertebrate evolution Aarni Auerniitty First land animals Circulation  Single cycle circulation (left): fishes  Double circulatory system, three chambers (middle): amphibians, most reptiles  Oxygen deprived and highly oxygenated blood mix in the heart  Double circulatory system, four chambers (right): mammals, birds, crocodilians  Oxygen rich and poor blood do not mix  Fishes  Endoskeleton doesn’t limit growth and movement as much as exoskeleton  Jawless lampreys (ympyräsuiset) were the first animals with endoskeleton, 500 mya  Jawed fishes: lungfishes, coelacanths (varsieväkalat), cartilaginous fishes and and bony fishes evolved later  Single cycle circulation  Bony fishes and lung fishes have swim bladder  Breathing through gills (exception of lungfishes)  Lateral-line sense  Scales for protection  Fins for swimming  Sexual reproduction  External Amphibians  First vertebrate land animal fossils are amphibians from 400 million years ago  Key adaptations  Legs for easier movement on land  Located on the side  better in aquatic environment  Lungs for breathing air  Still need moist skin to help in gas exchange  Double circulation (three chambers)  External fertilization dependant on water  Metamorphosis of offspring  Exothermic (vaihtolämpöinen) = body temperature depends on the environment Reptiles  Around 300 million years ago the climate of Earth became increasingly arid  Reptiles were the first vertebrates fully adapted to life on land  Adaptations  Limbs under the body and better adapted endoskeleton for easier movement on land  Thick skin resistant to dry conditions  Internal fertilisation and laying eggs  reproduction is not dependant on water  Offspring develop inside eggs  no stages of metamorphosis  Highly developed nervous system and senses  More stimuli to react to from the environment  More efficient circulation and respiration (still three chambered heart)  Mammals  First mammals appeared around 200 million years ago, but only got more common after the extinction of dinosaurs  Adaptations  Double circulation with four chambers  Very efficient circulation and gas exchange  Endothermic (tasalämpöinen) = body temperature is controlled internally  Fur helps in maintaining temperature and protects against UV-radiation  Giving birth to live offspring (except platypus)  Placenta (except marsupials)  Lactation and commonly taking care of the offspring Birds  Evolved from reptiles 170 million years ago  Newest class of vertebrates  Adaptations  Flight  Feathers (also great heat insulator)  Hollow bones  Toothless beak  Similar to mammals birds have double circulation with four chambered heart and they are endothermic  They retained some features from reptiles  Laying eggs  Internal fertilisation  Unlike reptiles birds take care of their brood