Mesozoic Dinosars (final exam) Flashcards
What are the 2 evolutionary groups following from dinosaurs?
dinosaurs > theropod dinosaurs > birds
What are the dinosaur characteristics?
- teeth in individual sockets
- reduced lower leg bone (fibula)
- pelvis anchored to vertebral column with three vertebrae
- ball and socket hip joint
- antorbital fenestra (archosaur character)
- upright posture
- terrestrial (controversial, but all dinos live on the land - no marine and no flying)
What are the two distinct orders of dinosaurs (distinguishing feature?)
Saurischia (typically meat eaters):
*pubis points forward
Ornithischia (herbivores):
*pubis points backwards
so distinguishing feature is shape of hip
Name the 5 dinos in the Ornithischian group and the 2 in the Saurischia group
Ornithischian:
- Ornithopod
- Pachycephalosaur
- Ceratopsia
- Stegosaur
- Anklosaur
Saurischia:
- Sauropod
- Theropod
Describe the Ornithopods (Ornithischian dinos) (characteristics? teeth?)
- bipedal herbivores
- abundant in Cretaceous
- had hollow crests on heads > for communication probably
- well developed forelimbs > facultatively bipedal (not restricted to it)
- cared for young in nests
- have massive tails > tendons turn into bones in order to support the tail
- specialized teeth and jaws > co-evolution with flowering plants? > efficient herbivores
- always replacing worn-out teeth and could chew their food
Describe the Pachycephalosaurs (Ornithischian dinos) (characteristics? location?)
- bipedal herbivores
- thick-boned, domed skulls
- only in N. hemisphere during Cretaceous
- butted heads for dominant and mating displays? > or just for showing off? dome changes size through growth
> it’s proposed that they use their tails in the same way kangaroos do with their fighting style - not confirmed
Describe the Ceratopsians (Ornithischian dinos)
- large head with bony frill at top of neck
- earliest (late Jurassic) were small, some may have been bipedal
- quadrupedal herbivores in Cretaceous
- one or more horn on nose and brows
- extremely diverse groups in terms of the horns and frills > these couldn’t been for hiding or defence but probably just for sexual display
What does evidence from Alberta tell us about Ceratopsians?
There is evidence from bonebeds (mass death assemblages) in Alberta which show that babies lived with adults in HERDS
- bonebeds have thousands of bones
- evidence of drowning in flash floods or river crossings
Describe the Stegosauria (Ornithischian dinos) (main characteristics? time?)
- medium sized quadrupedal herbivores
- Jurassic (did not live with Tyrannosaurus rex! went extinct earlier on)
- plates on back: for head regulation? defence? mating? to scare off predators? camouflage?
- spikes on end of tail for defence
- some earlier species had spikes, not plates on back
Describe the Ankylosauria (Ornithischian dinos)
- bony armour on head, back, and flanks (sides between ribs and hip) - so basically all over
- some had club on end of tail
- most heavily armoured dinosaurs > likely slow moving
What is the most well preserved dinosaur ever?
The Borealopelta - from Anklyosauria group
- slow moving dino that would just stand around and eat all day because it was well protected with all the armour and spikes
Describe the Sauropods (Saurischian dinos)
- quadrupedal herbivores
- includes largest land animal ever (Brachiosaurus > preceded by late Triassic to early Jurassic prosauropods)
- most abundant in Jurassic, fewer present in Cretaceous
- moved in herds: trackway evidence
- terrestrial animals
- ver hollow bones to lighten their skeleton so that they could be so large and still move around on land
- lots of eggs with little embryos preserved - so we have information about growth
Describe the Theropods (Saurischian dinos)
- bipedal carnivores
- many had feathers
- large range in size
What are the two main thermoregulation modes in vertebrates? others?
Ecothermy: cold-blooded
> reptiles and amphibians
Endothermy: warm-blooded
> mammals and birds
others: Gigantothermy, mesothermy, poikilothermy
What is the evidence that supports dinosaurs being endothermic? what’s the consensus?
- large brain in relation to body size
- fast growth and maturity > from bone microstructure
- upright posture
- four-chambered hear (maybe?)
- some dinosaurs had feathers > act as insulators
- modern birds are endotherms (but crocodiles are ectothermic?)
*in reality there was probably a mix of different thermoregulatory styles in dinosaurs
What did birds evolve from? Explain some of the evolutionary changes from these to birds
they evolved from small theropods which evolved from dinosaurs
- decrease in body size through Mesozoic and Cenozoic
- loss of teeth with development of beak
- loss of flight feathers on hindlimbs, loss of bony tail
- huge diversification after K-Pg extinction
What was the first bird (and when)
Archaeopteryx (*Jurassic)
- feathers and a wishbone
- teeth, clawed wings and a long tail
What are the two main controversies about the Saurischian dinos?
Mouth/Lips:
- past image of dinos like Tyrannosaurus rex has been with mouth open or with mouth closed and big teeth showing over lip
- really it was determined that dinosaurs probably had a lizard like mouth with fleshy lips covering the teeth (dino fandom doesn’t love this bc it doesn’t look as cool)
Theory that Spinosaurus were Aquatic dinos:
- their original fossils were bombed in WW2
- with new skeletal material the scaling is off - trying to interpret lifestyle
- proposed that they had penguin-like bones which shows signs of hunting underwater
- determined that they are NOT an aquatic dinosaur - they were semiaquatic and just waded in the water
