Chapter 5 – Cerapoda, aka the Marginocephalia(The Giant Buffalos and the Head-Bangers)- Question a student e-mailed Dr. Erickson:o How do we know the color of dinosaurs? For the most part, we don’t – we just see artists’ renditions with our best guesses. Only two dinosaurs have been discovered with strips that indicated different, banded colors. - The distinguishing feature of the Marginocephalia was a margin or rim of bone protruding from the back of their skulls over the neck. - The Marginocephalia consists of two groups:o Pachycephalosauria The Pachycephalosaurs are an enigmatic group – we don’t know too much about them. They were bipedal, herbivores (non-chewing teeth), had a head that looked like a bowling ball. The distinguishing feature of these animals was, of course, their thickened skull bones(up to 1 foot), with knobby protuberances. - As a consequence, we have often found only heads that had rolled for miles on thebottom of rivers. The first heads found in this manner were mistaken for dinosaur knee-caps! (Although dinosaurs did not have knee caps…)- We now know that some of the heads were so beaten up because Pachycephalosaurs lived in highland regions, not out on floodplains. Their bodies were broken up by the time they reached the floodplains where they are usually found. - Why did they have these big, dome-shaped heads?o Competing theories include – Structures for head butting reminiscent of big-horn sheep, musk, oxen Structures for flank-butting like many mammals do today – the knobs are driven into the sides of rivals in competition. - THESE TWO THEORIES ARE THE MAIN ONES – THIS WILL BE ASKED ON THE TEST. Structures for thermoregulation – for the same reason as ankylosaur domes, this is unlikely. Domes are poor heat dissipaters, and microstructural studies show that the blood vessels closed during later life,becoming solid bone, which would not radiate heat. A team of paleontologists and engineers have been working to model and test the utility of the domes for head- and flank-butting. - Skulls have been sectioned and computerized renditions called finite-element models have been made. With these models, dissipations of force can be assessed. That is, if you put the properties of bone into thecomputer, you can electronically test it to see how much weight it would be able to withstand. TEST QUESTION – WHAT IS FINITE-ELEMENT MODELING?o Ceratopsia They are also known as horned dinosaurs, but NOT ALL OF THEM ACTUALLY HAD HORNS. They were some of the most diverse dinosaurs. They were gregarious, so we often find them present in great numbers. The distinguishing feature of these dinosaurs was a beak shaped like that of a parrot on the upper and lower jaws. - Psittacosaurs – the first ceratopsianso As with all the major dinosaur groups, they started out small and evolved to become bigger over time. o Bipedalo Did not have dental batteries, but did, however, have gastroliths to grind up plants (Rocks that they ingested). o They may have been bristly. o How did dinosaurs grow? If you cut up the bones, place them on a glass slide, and grind and polish itto microscope thickness, you can count growth lines in the bones and figure out how old the animal is. This led to the very first growth curve of dinosaurs. Dr. Erickson and a Russian scientist were the people who created this veryfirst growth curve. Comparison with living animals shows that they grew at rates father than living reptiles, slower than birds, and just like moderately-fast-growing marsupials like kangaroos and possums. - Neoceratopsians were advanced ceratopsians that were quadrapedal and had big neck frills. THIS DINOSAUR HAS BEEN VERY IMPORTANT TO THE FIELD. o The first ones were small and hornless. o This animal lived in a desert environment and has been found buried in prehistoric sand dunes. Their skulls show sexual dimorphism. o In the 1920s, explorer Roy Champan Andrews, the model for Indiana Jones, was looking for ancient humans when his crew came across lots of Protoceratops and nearby egg nests. It was concluded that here were the actual nests of dinosaurs! They supposedly belonged to Protoceratops. - Andrews played up the find and became extremely famous. o The crew also found the supposed predator of the eggs – it was aptly named Oviraptor (the egg-stealer). One was even found atop a nest, apparently caught in the act!o Recently, colleagues from the American Natural History Museum returned to Mongolia and found four more oviraptors atop the nests and even found embryos in the eggs. It was found that the nests were actually the nests of oviraptors – the embryos in the eggs were oviraptor babies. The supposed egg stealers were really the egg layers! They were incubating the eggs like birds, a very unreptilian behavior. Advanced neoceratopsians were large (about thirty feet long), horned. - There were two types of advanced neoceratopsians. o Those with big eye horns and small nose hornso Those with big nose horns and small eye horns There were triceratops, teraceratops. Then, there was the crazy Pachyrhinosaur, which had a huge “boss” on its head. - Some think that the Pachyrhinosaur base was for shoving matches; others think it was the base for the largest horn ever. o There is more evidence for the shoving match theory. Lots of evidence for evolution in these dinosaurs – the nose horn forms in infants and then turns down like in the Einiosaurus and fuses into a boss. The largest and most-famous ceratopsians was the Triceratops (three-horned face). - The horns from the Triceratops were discovered by Marsh and his assistance. He initially thought that the horns were from a giant buffalo, and, despite protests from his crew, named it Bison alticornis. At five tons, that would be one huge buffalo! Later, a triceratops skull with the horns was found, causing Marsh to correct his mistake. - During Cope and Marsh’s race to name dinosaurs, Triceratops was oversplit into no less than sixteen species.o The confusion came from the naming of young, scraps, males, females, and variation in the species – this is called oversplitting. TEST QUESTION – WHAT IS OVERSPLITTING?- It is likely that Triceratops used its horns for defense at times, but one must keep in mind that horns in most animals today are used primarily for display and fighting with one another, not for killing
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