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 Clichés 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 throughoutdevelopment. 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 duringthe 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 highinto 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. In 1860, a feather from a bird was found in Jurassic Period sediments. Archaeopteryx (meaning ancient wing) – the first bird (as we define birds) that 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
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