Wanna-Be Dino? Prehistoric Reptile Looked Like a Dinosaur
Not all prehistoric animals that looked like dinosaurs were actually dinos, suggests a new fossil.
A reptile that lived before the Dinosaur Age resembled a dino, suggesting that iconic dinosaur body shapes were present long before the dinosaurs themselves actually emerged.
The newly identified reptile, described in the journal Current Biology, resembled pachycephalosaur dinosaurs that lived more than 100 million years later. Other extinct animals found with the reptile looked like later dinos too.
The reptile has been named Triopticus primus, meaning the "First of Three Eyes" because the natural pit at the top of its skull lends the appearance of an extra eye.
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"Triopticus is an extraordinary example of evolutionary convergence between the relatives of dinosaurs and crocodylians and later dinosaurs that is much more common than anyone ever expected," co-author and project leader Michelle Stocker, a Virgnia Tech College of Science researcher, said in a press release. "What we thought were unique body shapes in many dinosaurs actually evolved millions of years before in the Triassic Period, about 225 million years ago."
Convergence refers to when distantly related animals evolve to look very similar to each other. A classic example of this is a bird wing and a bat wing. Both animals use their wings for flight, yet the inner details of their wings are different and evolved independently.
Three Eyes dates to about 230 million years ago, according to the researchers. The reptile's partial skull was originally collected at a site called Otis Chalk near Big Spring, Texas, by the Works Progress Administration in 1940.
President Franklin Roosevelt had initiated a monumental effort to put Americans back to work at end the Great Depression. With so much digging going on, numerous fossils were unearthed. In fact, so many fossils were found during such a short time span that several of them were just put into storage uncleaned.
Such was the case for Three Eyes, whose skull was eventually sent to the Texas Vertebrate Paleontology Collections in 2010. It is there that Stocker and her team rediscovered and analyzed the specimen.
They determined that the reptile had an extremely thickened skull roof, just like the very distantly related pachycephalosaur dinosaurs that lived more than 100 million years after the lifetime of Three Eyes.
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"CT scanning showed us that the similarity of Triopticus with the much later dome-headed pachycephalosaur dinosaurs was more than skin deep, extending to the structure of the bone and even the brain." co-author Lawrence Witmer of Ohio University's Heritage College of Osteopathic Medicine said.
It was not a coincidence that the reptile and dinosaurs resembled each other.
"After the enormous mass extinction 250 million years ago, reptiles exploded onto the scene and almost immediately diversified into many different sizes and shapes," co-author Sterling Nesbitt of Virginia Tech said. "These early body shapes were later mimicked by dinosaurs."
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Dinosaurs did not consciously do this, of course, but their ancestors and environment must have prompted the evolved similarities.
Many of the other Triassic reptiles originally buried with Triopticus at Otis Chalk display features that are easily recognized in later dinosaurs as well. These include the long snouts of Spinosaurus, the toothless beaks of ornithomimids (aka ostrich dinosaurs), and the armor plates of ankylosaurs.
"The Otis Chalk fauna is an amazing single snapshot of geologic time where you have this extraordinary range of animal body plans all present at the same time living together," Stocker said. "Among the animals preserved in the Otis Chalk fauna, Triopticus exemplifies this phenomenon of body-shape convergence because its skull shape was repeated by very distantly-related dome-headed dinosaurs more than 100 million years later."
Other studies over the past several years indicate that dinosaurs, like these distant cousins from the Triassic Period, were all reptiles. Reptiles rapidly evolved in terms of numbers of species soon after the greatest mass extinction of all time on Earth, at the end of the Permian Period.
You can manipulate 3D models of Three Eyes' skull at two different sites: one showing the partial skull alone and another showing the likely size and shape of the reptile's brain.
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Paleontologists have just assembled the most comprehensive family tree of meat-eating dinosaurs. Published in the journal Current Biology, the family tree reveals how diverse carnivorous dinosaurs were and how birds eventually evolved from them. Tyrannosaurs, including Tyrannosaurus rex, are one key group on the meat-loving dino family tree.
Lead author Steve Brusatte of the University of Edinburgh's School of GeoSciences told Discovery News, "The most iconic dinosaurs of all, tyrannosaurs were more than just the 13-meter-long (nearly 43 feet long), 5-ton monster predator T. rex. Tyrannosaurs were an ancient group that originated more than 100 million years before T. rex, and for almost all of their evolutionary history they were small carnivores not much bigger than a human in size."
"Some of the rarest theropods (two-legged carnivorous dinos) of all, compsognathids are represented by about half a dozen species," Brusatte said. "They were small, sleek meat-eaters which ate small prey like lizards." One of the more recent finds, Juravenator from Germany, is known from a nearly complete fossil.
Ornithomimosaurs were theropods called "ostrich mimic" dinosaurs -- for a reason. "Like living ostriches, they could run fast on their long legs and used their sharp, toothless beaks to eat a varied diet of small prey, plants, and perhaps even small shrimps in the water just like living flamingos," Brusatte explained. "A recent find in Canada showed that not only were ornithomimosaurs feathered, but they also had complex feathers on their arms that would have formed something of a wing, although they couldn't fly."
Brusatte describes therizinosaurs as "perhaps the weirdest theropods of all." "These were big, bulky, cumbersome dinosaurs that ate plants. They had fat barrel-shaped chests, stocky legs, and big claws on their arms," Brusatte said. For many years paleontologists argued about which group this dinosaur belonged to, only recently settling on theropods. This means they were fairly closely related to birds, despite their weird anatomy.
Alvarezsaurs were among the smallest dinosaurs of all, measuring just a few feet long and weighing less than 5 kilograms (10 pounds). "Some of them had only a single functional finger on their hand, which they probably used to prod deep into the nests of bugs, which were one of their main food sources," Brusatte said.
Oviraptorosaurs, were a group of small omnivores that were lightweight, lacked teeth and had tall, hollow crests on their skulls. The recently discovered Anzu -- the so-called " chicken from hell" -- came by its nickname honestly. It towered more than five feet tall, weighed more than 400 pounds, and was covered in a coat of feathers.
"Troodontids were probably the smartest dinosaurs of all, as they had the largest brains relative to their body size of any dinosaur group," Brusatte said. "Most troodontids were small, fast-running dinosaurs that probably ate both meat and plants." Among the most recently discovered of this group are the small, feathered Anchiornis and Xiaotingia, which lived in China about 160 million years ago. "They look eerily similar to birds, so much so that some researchers think they could be primitive birds rather than troodontids with wings and feathers," Brusatte said.
Dromaeosaurids were "raptor dinosaurs" that include Velociraptor from "Jurassic Park" fame. These dinosaurs were pack hunters who wielded a sharp, hyper-extendable "killer claw" on their second toe. "One of the most recently discovered dromaeosaurids is Balaur, a poodle-sized terror from Romania which had not one, but two 'killer claws' on each foot."
"The oldest birds, like Archaeopteryx that lived 150 million years ago in Germany, are very hard to distinguish from their closest dinosaurian relatives," Brusatte said. "Unlike living birds, they had teeth, sharp claws on their wings, and long tails." "Over the past two decades," he continued, "over 50 new species of Mesozoic birds have been discovered in northeastern China, in the same rock units as the famous 'feathered dinosaurs.' So many birds are preserved here because entire ecosystems were buried by volcanic eruptions, turning animals to stone like a dinosaur version of Pompeii."
"The 10,000 species of birds that live today -- from hummingbirds to ostriches -- are modern dinosaurs," Brusatte said. "They are dinosaurs in the same way that humans are mammals. The classic body plan of living birds -- feathers, wings, wishbones, air sacs extending into hollow bones -- did not evolve suddenly but was gradually assembled over tens of millions of years of evolution. But, when this body plan finally came together completely, it unlocked great evolutionary potential that allowed birds to evolve at a super-charged rate." "They underwent a burst of evolution early in their history, which eventually led to the 10,000 species alive today -- more than twice the number of mammals."