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Mid Triassic

-dinosaurs appear
-angiosperms allowed for a whole different set of dinosaurs



-competitors of dinosaurs
-our ancestors
-some synapsids gave rise to therapsids and ultimately to mammals



-warm blooded present because they had hair
-gave rise to mammals



-don't become mammals because they have live births (this doesn't happen till much later)
-retain some characteristics of today's reptiles like small brains



-plunged in Triassic period
-when dinosaurs have evolved their more effective mode of breathing
-could be the switch between proto-mammals and dinosaurs


Antorbital Fenestra

-all dinosaurs have this
-it's an opening in front of the eye orbit
-makes skull lighter



-great big guys with long necks and itty bitty heads
-head so little because neck is so long and can't support too much weight
-vertebrae themselves are built very lightly


How do these Sauropods live?

-thought that they lived in water so that it could support their massive weight and then they just ate from the banks and such
-not actually how they lived they were entirely terrestrial and forages vegetation from trees
-largest ever known land animals


Elephants vs. Diplodocus

-6 tons vs. 12 tons
-elephants spend 16 hours grazing
-their teeth are like bricks to facilitate constant grazing
-Sauropods' teeth are not for chewing-very weak
-believed that they raked foliage in without chewing it and without moving
-had huge fermentation chamber that operated at warm body temperature to digest un-chewed plant material


Sauropods breathing

-system present in birds today
-has lungs but also has additional air sacs so it not only fills lungs but also air sacs
-air comes in and doesn't all go directly to lungs but into air sacs and some is routed back out and through the lungs and then back into some of the sacs
-breathing out pushes it out through the sacks into the lungs and then out of the body
-position of the sacs is seen on the body of the dinosaurs on the vertebrae



-possible they arose twice-once in each lineage or more parsimoniously arose once in the Triassic
-present in both bird hipped dinosaurs (ornithischians) and lizard hipped dinosaurs (saurischians)
-non-avian dinosaurs also had feathers
-what about feathers for display like peacocks
-used for insulation, flight, and sexula display
-one of dinosaur evolution's great novel features


Chickens vs. TRex

-eerily similar
-have little hook on back foot
-dinosaurs sit on nests the same way birds do with their legs tucked up underneath


Discovery of dinosaur feather colors

-some cases so well preserved you can see pigment cells that have been preserved in the feathers
-modern birds: shape of pigment cell roughly corresponds to color


Dinosaur success

-not just big cold blooded lizards
-success (which continues to present day) stems from morphological and physionlogical adaptations


Dinosaur time line

-evolve from a bipedal archosaur ancestor in the mid Triassic
-radiate into huge forms in the Jurassic
-with evolution of angiosperms in the lower Cretaceous a different set of dinosaurs become dominant
-we know one of those lineages as birds
-catastrophic K/T mass extinction ends all non-avian dinosaurs



-triassic therapsids evolved into the first of these
-shift toward mammalian jaw
-egg laying
-reptilian brain size


Why did dinos win out in Triassic?

-large mammals did not come to dominate Earth's ecosystems until after non-avian dinosaurs became extinct at the end of cretaceous
-until then no mammal larger than a raccoon


Dino physiological advantages

-Triassic oxygen levels low
-dinos had much more efficient flow-through breathing
-dinos combined this with independently evolved warm-blooded physiology and highly effective locomotion


How do you know it's a dino?

-all have a skull with an opening in front of eye sockets
-have hip with five fused sacral vertebrae, an opening in the hip where the femur articulates and a distinct ankle


Sauropods unique adaptatiosn

-not matched since
-uniquely efficient mode of harvesting vegetation
-huge size-largest known land animals
-unique anatomy and physiology involving new features as well as pre-adaptive features shared by all dinosaurs


What did selection work for

-body size to resist predation
-weight support and locomotion
-efficiency of feeding and digestion
-reproduction, development and care of progeny


Responses to selection

-increased size, hollowed out and lightweight bones; heart and circulatory system had to withstand high pressure
-novel feeding system that allows a light-weight head and does away with chewing
-life history unlike that of giant


Reproduction in mammals vs. sauropods

-mammals: single large offspring, intensive maternal care, slow maturation
-sauropods: egg size limited by physics, so lots of small eggs, little maternal care, fast growth


Dino sex?

-no direct evidence only analogs and imagination
-imaginative reconstruction
-perhaps very large and mobile penises like whales and a specific duck


Triceratops horns

-optimal horn and shield design for defense from T. rex?
-no seem better built for sexual display like antelopes spar for females


Berlin Archaeopteryx

-actual specimen on exhibit at the Natural HIstory Museum in Berlin
-famous feathered dinosaur "missing link" between reptiles and birds
-not actually a missing link but a continuum of trends in theropod evolution


Discoveries from China that revolutionized our understand of dinosaurs and evolution of birds

-non-flying dinosaurs with feathers for insulation
-simple through complex feathers
-diversity of forms spanning dino-bird transition
-bird-like gliders among dinosaurs-feathers for flight
-dinosaurs sat on nests like birds
-feathers for sexual display and sexual selection


Non-avian dinos: Microraptor

-also had feathers and wing-like arms
-Microraptor-related to Velociraptor
-newly discovered fossil that shows major stage in evolution of flight-using feathers for gliding
-intermediates int he fossil record


Stages of evolution of feathers in dinos as seen in fossil record

-from simple filament
-to down feathers
-to body covering feathers
-to contoured wing feathers
-see images