Note: Content may be edited for style and length. Science News. Story Source: Materials provided by Brown University. Journal Reference : Jessica H. Whiteside, Paul E. Olsen, Timothy Eglinton, Michael E. Brookfield, and Raymond N. Compound-specific carbon isotopes from Earth's largest flood basalt eruptions directly linked to the end-Triassic mass extinction.
ScienceDaily, 23 March Brown University. How dinosaurs rose to prominence. All sorts of large, bizarre reptiles disappeared for ever. The Late Triassic was the heyday of the archosaurs.
The illusion of dinosaur dominance stemmed from the fact that fossils of Triassic land animals are rare and usually incomplete.
When scientists found Triassic fossils that looked like they came from dinosaurs, they logically assumed that they were dinosaurs. That included the rauisuchians, long-legged predators shaped like bears or lions. The largest stretched 7 metres. Some were bizarre, such as the sail-backed Arizonasaurus. Another dominant group of predators were the phytosaurs, long-bodied reptiles with narrow crocodilian jaws that looked a bit like modern gharials. The most common plant-eaters were aetosaurs, low-slung animals up to 5 metres long with small heads and armoured bodies, built like the ankylosaurs of the dinosaur age.
For the next 10 million years the world belonged to these little-known animals, with dinosaurs playing bit parts. Then along came the Triassic—Jurassic mass extinction of million years ago. It was one of the five most devastating extinctions of the past million years but has attracted little attention , partly because there is no obvious trigger and partly because it claimed no charismatic victims.
This unique anatomy helped dinosaurs become successful. Having an upright posture also freed the hands, allowing dinosaurs such as iguanodonts to grasp branches and carnivorous dinosaurs to claw and kill prey, noted Gregory Erickson, a paleobiologist at Florida State University. Ultimately, having free arms "allowed gliding then flight in birds," he said.
Moreover, dinosaurs were likely warm blooded, according to research on their growth rates. Initially, dinosaurs were not as diverse as the crocodile-like archosaurs they were living alongside, Brusatte noted. In fact, dinosaurs "didn't become too successful right away; the crocs ruled the Triassic, then the end-Triassic extinction hit and the dinosaurs survived and took over. As of , there were 1, scientifically described dinosaur species, according to the Paleobiology Database.
About 50 previously unknown species are described each year, meaning there's roughly one newfound species described each week, Brusatte said. All of these dinosaurs fit into one of three groups: Ornithischia, Sauropodomorpha and Theropoda. Ornithischia dinosaurs include beaked plant-eaters, such as Stegosaurus , duck-billed dinosaurs also called hadrosaurs , as well as horned dinosaurs like Triceratops and armored dinosaurs like Ankylosaurus. Some ornithischians walked on four legs, while others walked on two.
Sauropodomorpha dinosaurs were long-necked, pot-bellied dinosaurs that had tiny heads and column-like limbs.
This group includes sauropods such as Diplodocus , their smaller antecedents including Chromogisaurus and extra-large sauropods known as titanosaurs such as Dreadnoughtus and Argentinosaurus , which are among the largest land animals that have ever existed.
Theropoda is a group of meat-eating dinosaurs, although some such as Chilesaurus diegosuarezi changed their diet to be herbivorous or omnivorous. Theropods include Tyrannosaurus rex and Velociraptor , as well as birds, which evolved from small theropods.
So, how are these groups related? It's up for debate. Ornithischian dinosaurs have a backward-pointing pubis bone in the hip, earning them the name bird-hipped dinosaurs. However, they are not the ancestors of birds; theropods are. Meanwhile, theropods and sauropodomorphs have saurischian or "reptile hips," which are also seen in modern crocodiles and lizards, according to the book "Dinosaurs Rediscovered. Historically, it was thought that the reptile-hipped theropods and sauropodomorphs were more closely related to each other than to ornithischians.
However, a study in the journal Nature uprooted the dinosaur family tree by suggesting that ornithischians and theropods were more closely related, based on analyses of 74 dinosaur species, Live Science previously reported.
Shortly after, another study in the journal Nature found that neither family tree, as well as a third that is rarely considered, is statistically significant from the other, meaning all the suggested family trees are equally plausible until more evidence comes forth. Dinosaurs lived during most of the Mesozoic era, a geological age that lasted from million to 66 million years ago. The Mesozoic era includes the Triassic, Jurassic and Cretaceous periods. Dinosaurs arose from small dinosauromorph ancestors in the Triassic period, when the climate was harsh and dry.
They faced "competition from the croc-line archosaurs for tens of millions of years, [but] finally prevailed when Pangea began to split," Brusatte told Live Science. At this time, volcanoes erupted along the cracks of the supercontinent, causing global warming and mass extinction, he said. During the Jurassic period million to million years ago , dinosaurs rose to dominance and some grew to huge sizes.
For example, Vouivria damparisensis , the earliest titanosaur, dates to million years ago. It weighed about 33, lbs. Iconic dinosaurs from this period include Brontosaurus , Brachiosaurus , Diplodocus and Stegosaurus. Whether dinosaurs rose to fame from fitness or a roll of the dice should become clearer as paleontologists discover more fossils to fill in the sparse record of dinosaurs' early history and elucidate what caused the extinctions at the end of the Triassic.
Rogers says that Brusatte's analysis will probably challenge people to support their claims of dinosaur superiority with stronger evidence. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue.
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