Chapter 9 Dinosaur Life Death and Rebirth For the first century and a half dinosaurs were viewed as giant dimwitted sluggish reptilian tail draggers o Clich s like dead dumb as a dinosaur were in common use and people were only interested in mammals Deinonychus found in 1964 by John Ostrom This dinosaur was the so called velociraptor in the Jurassic Park movies Robert Baker stimulated a reanalysis of our perceptions of dinosaurs Clearly dinosaurs were a group unto themselves NOT like other reptiles o There has been a lot of interest in dinosaur metabolism We don t know for sure about their metabolism Were they very active like us or in a state of torpor for much of the time like living reptiles o Nevertheless growth rates correlate with metabolic growth and dinosaur growth rates have been determined Using histology which shows a blend of fast growing bones like mammals but growth lines when it stopped each year like reptiles growth line counts revealed ages Size estimates allowed rates of growth to be calculated throughout development o Maximal growth rates were calculated for the tiniest and largest dinosaurs and compared to living animals o The results all dinosaurs grew considerably faster than living reptiles This was determined from FSU research In fact they grew like marsupial mammals They were endothermic but grew like possums and kangaroos o Dinosaurs lived fast lives even the giant Sauropods reached adult size in just twenty years and lived no longer than fifty years Similar to the maximum age of elephants of today o Whatever they were like biologically there is no escaping the fact that dinosaurs were one of the most successful groups of animals ever dominating a 172 million year span o So what happened to dinosaurs What we think of as dinosaurs went extinct 65 5 million years ago during one of several major extinctions that have occurred in Earth s history NOT ONLY DINOSAURS PERISHED 40 to 80 of all life on the planet died too Pterosaurs mosasaurs plesiosaurs many clams plankton corals a few mammals and some plants all bit the dust Survivors included most birds mammals amphibians frogs and salamanders and reptiles lizards snakes turtles and crocodiles These animals existed during the time of the dinosaurs and still exist today What caused the demise of the dinosaurs is a huge mystery Over one hundred theories many crazy have been posited as to what happened The three most plausible theories of dinosaur demise include the following o Volcanism the activity of volcanoes in India altered the Earth s climate Evidence Deccan Basalts in India o Drastic lowering in sea levels led to ecological changes that affected the dinosaurs Evidence seaway sediments o A ten kilometer wide asteroid hit the Gulf of Mexico and sent debris high into the air causing major climate changes nuclear winter global warming you name it Evidence the rare material radium is found in ash layers known marking the KT boundary Cretaceous Tertiary boundary rare on Earth but found in meteorites Asteroid theory is the most sexy and commonly accepted Most people believe that it was just the asteroid or a combination of all things Some argued that o Iridium can come from volcanoes o The Chicxulub crater may be a volcano caldera o There have been lots of other similar sized asteroid impacts that didn t kill anything But why didn t the asteroid kill birds mammals crocodiles salamanders frogs creatures that are extremely environmentally sensitive o For whatever reason dinosaurs as we know them went extinct sixty five million years ago Archaeopteryx meaning ancient wing the first bird as we define birds that In 1860 a feather from a bird was found in Jurassic Period sediments existed This was proof that birds were living with dinosaurs There were funny things with this bird though the specimen was very primitive in that it had teeth fingers with claws and a long bony tail like that of a reptile British scientist Thomas Huxley was very quick to note the similarities between the first bird and dinosaurs namely the theropods Birds are essentially evolved theropod dinosaurs As Huxley noted aside from the lack of feathers on dinosaurs the resemblance between birds and dinosaurs is uncanny Most paleontologists believe that birds are theropod dionsuars Until just a few years ago some argued that there were still problems with this theory they argued that dinosaurs didn t have wishbones and feathers that they were too big to be relatives of the Archaeopteryx o All of these agreements have since been laid to rest especially owing to several incredible finds from China China is currently a big hotbed for dinosaur research One thing that was discovered in China was that dinosaurs also had wishbones just like birds do Twelve different species of theropods with feathers have been found clearly though the first feathers were for display and not for flight So we can now say that BIRDS ARE THEROPODS Already the raptors from Jurassic Park the purported most accurate depictions of dinosaurs ever are outdated paleobiology is on the move All dinosaurs except for the really big ones were probably covered in fuzz the precursor of feathers The Tyrannosaurs may also have a few feathers There is only dinosaur we known accurate color for for its feathers What about the size claw age problems The tiniest dinosaurs were seven ounces Curiously some Archaeopteryx s found had four wings they had a gliding stage before birds took to powered flight Precursor to bats o So there you have the evidence can the bird like skeletal and feather anatomy the non reptilian advanced nesting behavior and gregarious behavior be explained by some unfathomably amazing convergence from some undiscovered lineage of fossil animals or is it time for the world to realize that birds are dinosaurs For this class dinosaurs went extinct 65 5 million years ago but did they ever really do extinct at all Birds are still flying around outside today iClicker question What does this illustration reveal about the T rex It had a great sense of smell Illustration shows olfactory bulbs inside the dinosaur s skull
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