Lecture 29 Flashcards
What are the defining features of vertebrates?
-vertebrae (backbone) forms around notochord -internal and elaborate skeleton (cartilage or bone) -defined head with braincase (skull) and sensory organ
When did legs and jaws evolve in vertebrates?
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What did the jaws evolve from and when?
-jaws derived from gill arches of chordates -earliest jawed fishes -late Silurian (420Mya) -some had dental armour=placoderm t-he gill arches move forward= first jaws, after that evolution of teeth
What did the first legs evolve from?
-most bony fishes have fins made of long rays of bone (ray finned fishes -some fishes developed more substantial bones in the fins (lobe-finned fishes) eg. lungfish=can breathe air
Who were the first Tetrapods? (able to walk animals)
-class Amphibia -about 350 Mya some of the lobe-finned fishes, living in shallow lagoons, developed these bones to be able ˇwalkˇ(paddle in shallow water) -had both gills and lungs (lungfish) -still needed water -had unusual limbs (eight digits!)
What are the characteristics of the class reptiles (vertebrae class)?
-tetrapod vertebrates -evolved from advanced reptile-like amphibians -adapted to life on dry land -many extinct groups (dinosaurs, pterosaurs etc.) -modern reptiles inhabit all continents except Antarctica key features: -have scutes or scales -“cold-blodded” -most lay eggs -no aquatic larval stage -could do without constant access to water= the major advance in reptiles -need to warm up to move
When did the major groups of tetrapods appear? (amphibians, reptiles,mammals, dinosaurs and crocodiles, birds)
-Amphibians: 350Mya -Reptiles: 330Mya -Mammals: 190Mya (mammals lineage-mammal-like reptiles=320Mya) -Dinosaurs and crocodiles= 230Mya (after Permian extinction) -Birds= 150Mya
What lineage do the dinosaurs come from?
-same as crocodiles (archosaurs!) -but walked upright!
What is the origin of birds?
-one group of small dinosaurs= dromaeosaurs -discovered in 1861 Germany= fossil of that with feathers and wings= first evidence for evolutionary origin of birds from dinosaurs -birds are part of archosaurs -archaeopterx= what the fossil was named
How did mammals evolve?
-first mammal-like reptiles =320Mya -at first very reptile-like -many were large and carnivorous(powerful jaws) -smaller mammal like reptiles evolved (possibly with fur) -upright stance(legs tucked under body) eg. Thrinaxodon
What did it mean for mammals the change of stance?
-hip joints and upper limb bones changed in mammals and dinosaurs enabled quicker locomotion -fish move their bodies from side to side when they swim -sprawling animals like crocodiles and lizards do the same -the change =mammals move their back half of body forward and back (bend in a different plane) -dolphins and whales-mammals so move in that way too
How did the jaw evolve in mammals?
-mammal-like reptiles became more mammal-like -jaw articulation changed —reptiles=quadrate and articular —mammals=squamosal and dentary -cynognathus had two joints -jaw bones become ear bones
What are the characteristics of the class Mammalia?
-terrestrial, aquatic, flying, subterrean -about 5000 species -key features: —fur —warm-blooded —milk —3 inner ear bones -split into three sub-classes –Prototheria (platypus, echidna) –Metatheria (marsupials) –Eutheria (placental mammals)
What are the characteristics of the Mammalia subclass Eutheria?
-prolonged gestation period -fed internally via a placenta -massive range of body size (2g to 200 000 000g) -about 20 orders (inculding primates) -some unexpected relationships -some unexpected relationships between mammals discovered by DNA analysis elephants and dugongs to golden moles!
What are the characteristics of the order Primates?
-fourth largest order of mammals (after rodents,bats and insectivores) -includes great apes, humans - more than 250 species -most arboreal (live in trees)
