FAMILIAR FACE: Although no soft tissue or coverings were found on the Triassic Tawa hallae specimens, researchers speculate that these primitive dinosaurs were likely covered with some sort of coat, similar to the protofeathers found on some Cretaceous period theropods.
Image: JORGE GONZALEZ
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The earliest stages of dinosaur evolution remain buried under eons of rock, but the discovery of a new primitive carnivore fossil in the U.S. Southwest promises to dispel some of the debate about how these beasts spread across the globe—and about the origins of the group that eventually led to modern birds.
"It gives us new information about early evolution of dinosaurs," Sterling Nesbitt, a postdoctoral researcher at the University of Texas at Austin's Jackson School of Geosciences, said about the discovery during a Web cast with reporters on Wednesday. The diminutive, two-meter-long Tawa hallae fills a big gap in the fossil record between the earliest carnivores, such as Herrerasaurus, and later theropod lines that include Tyrannosaurus rex and the first birds. "Tawa helps us reconstruct those relationships," Nesbitt said. The findings were published online Thursday in Science.
"Discovering these really basal forms are always one of the most important things," says Mark Norell, chairman of the Division of Paleontology at the American Museum of Natural History in New York City and senior author of a paper on the discovery also co-authored by Nesbitt.
Dinosaurs first appear in the fossil record in the late Triassic period (which ranges from about 250 million to 200 million years ago), so the unearthing of the 214 million-year-old Tawa in New Mexico brings a new understanding about where many of the earliest dinosaurs evolved. Found in the fossil-rich Hayden Quarry at Ghost Ranch, Tawa and some of its contemporaries actually appear to be more closely related to different dinosaur relatives in South America—rather than each other. This finding suggests that early dinosaur lineages likely diverged in what is now South America (as the supercontinent Pangaea was breaking up) before moving to North America, a conclusion that Norell calls "rather unexpected." Previous theories about this poorly understood period had assumed a North American origin for some of these earlier lines.
Even though the new meat-eater lived some 139 million years before the vicious Velociraptor, Tawa already looked quite a bit like it, with a big tail, long, sharp claws and serrated, meat-ripping teeth, revealing the speed with which the earliest dinosaurs evolved. Despite its familiar body, however, Tawa retains some primitive features—including its hips and parts of its forearms—surprising the researchers when it turned up at such a late date in New Mexico. It seemed to be living "about 15 million years later than it should have been," Nesbitt said.
Although Tawa is not part of the precise lineage that led directly to birds, it appears to be the first dinosaur known to have specialized hollow air sacs in its neck vertebrae, a version of which can still be found in modern birds. The purpose of these structures is still unknown, but, says Norell, "it shows us how primitive air sacs are." Tawa also already had open hip sockets that remain characteristic in birds we see today—right down to a holiday turkey, Nesbitt noted in the Webcast.
Nesbitt asserts that this new theropod will also at last settle a debate about the even older Herrerasaurus, which some paleontologists had thought belonged to a separate non-theropod early line, or was not even a dinosaur. Nesbitt and his colleagues examined Tawa's pelvis, claws and teeth and found they were similar enough those of Herrerasaurus that the latter was indeed a very early theropod.
Tawa hallae is represented by fossils from some five to seven well-articulated individuals of different sizes, all unearthed at Ghost Ranch over the course of four years. "The preservation of Tawa is exquisite," Nesbitt said, noting that the level of detail found in the bones and other surrounding fossils is "unprecedented [from] the late Triassic." That the bones and skeletons were well preserved allows the researchers to examine many of the specimens in three dimensions. As Norell notes, any Triassic find is exciting but the condition of these discoveries, he says, is especially exhilarating.
Tawa also helps to trace the evolution of some morphological features back to the very first dinosaurs. It provides a much clearer picture of the basal theropods, Norell says. And, as Nesbitt noted, it "looks more like what we think the common ancestor of dinosaurs looked like."
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Add CommentIt s fake...
Reply | Report Abuse | Link to thisIt s fake...
Reply | Report Abuse | Link to this@guner: Really? Well, thank you for pointing that out and substantiating your claims with reams of factual evidence and quantitative analysis. You know, someone really needs to stand up to these "experts", and we're proud you've volunteered to do so. Kudos to you!
Reply | Report Abuse | Link to thissorry,this is not about this topic...I HAVE A ORIGENAL COPY OF SCIENTIFIC AMERICAN FROM AUGUST28,1845 VOLLUME 1 NUMBER 1 A MINT ...IF SOMEONE IS INTERESTED CALL DAVE 1847 -532-3238 ONLY SERIOUS REPLY...
Reply | Report Abuse | Link to thisSciAm-bay Nice work there daveyboy!
Reply | Report Abuse | Link to thisYou've expanded our universe, enhanced our knowledge and enriched our experiences!
Now, be a good little boy and go away. Please.
Thanks Quinn for saying it before i did !
Reply | Report Abuse | Link to thisThanks Quinn for saying what i was about to !
Reply | Report Abuse | Link to thisSomeone proclaimed to me a few months ago that they "knew" that a lower form of humans started evolving into the millions of IDIOTS we have today.
Reply | Report Abuse | Link to thisI have a simpler theory with observations to support it: These millions of IDIOTS are simply the suckers who believe the mass of right-wing propaganda flooding every outlet today.
Since this fellow is a right-winger, he insisted that HIS theory was about the "left-wing idiots" who've evolved from higher humans who existed during "the Enlightenment" period.
Thereby "enlightened" I asked him when he was going to launch expeditions and form a research institute to prove his "theory." (That's because he didn't have any research supporting his theory - kinda getting the cart before the horse.) Well - despite my checking in on his progress, he's never responded to my questions about what would surely be break-through research. Maybe he's out of touch - digging up evidence the the remote wilds of France.
"The diminutive, two-meter-long Tawa hallae". Diminutive? Maybe compared to the famous descendant TRex. But compared to a full-grown human male, and as one at about that size, in a freak time transportation incident I would have no wish to meet Mr Tawa face-to-face thank you very much. But then again, no wish to meet with people who are so off-topic either .... Now I warmed some years back to the notion that birds might well be dinosaurs (the notion of TRex astride a branch saying "Who's a pretty boy then?" tickled my fancy). Such a concept is all the more important because it would show the implications of natural selection so very clearly. Where did all the dinos go? Did some survive the Big Nasty 65m years back, evolve through adaptation to changing environment to sing songs at dawn? Salutary. It isn't for certain yet but the idea has gained ground based on a lot of discoveries in the past decade or so. What strikes me about what we call the Age of the Dinosaur is that it displayed such a vast range and richness of adaptation and evolution - and maybe, just maybe, it ain't over yet .... Puts us in perspective perhaps? To see it all as part of a continuum of change. In 60 million years will our descendants sing at dawn?
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