Mini Me:
T. rex dwarfs the newly described Raptorex, a pint-size tyrannosaur from Inner Mongolia that had many of the hallmarks of its larger successors.
Image: Courtesy of Paul C. Sereno, University of Chicago
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Looming larger than a double-decker bus and baring teeth that have been likened to serrated bananas, Tyrannosaurus rex has long been considered one of the most fearsome creatures ever to have walked the earth. Other familiar tyrannosaurs, such as Albertosaurus and Tarbosaurus, were likewise terrifying in their size and bite—despite those absurd-looking but characteristic arms. But it turns out that not all tyrannosaurs have these hallmark features.
This past fall paleontologists unveiled two tyrannosaurs new to science that are shaking up long-standing ideas about everyone’s favorite mega-predator. The finds are forcing researchers to reevaluate the origin of the tyrannosaur body plan and reconsider what they thought they knew about the diversity of this well-studied group. “Our view of tyrannosaur evolution has changed dramatically,” says doctoral student Stephen L. Brusatte of the American Museum of Natural History in New York City.
Over the past decade researchers have established that behemoth tyrannosaurs such as T. rex evolved from smaller ancestors. And they thought that the signature features of T. rex—including a huge skull built for tearing into flesh and bone, puny arms, and running legs and feet—were inextricably linked to the evolution of large body size. But in the October 16 Science, Paul C. Sereno of the University of Chicago and his colleagues, including Brusatte, described a new tyrannosaur, Raptorex kriegsteini, that upends this idea.
Unearthed in Inner Mongolia, Raptorex lived 125 million years ago—60 million years before T. rex terrorized North America. The fossil shows that, in fact, the T. rex body design debuted in a dainty dino, one that weighed little more than a human and was about 1/100th the size of T. rex. As such, Raptorex clears up some puzzling aspects of T. rex anatomy, observes Thomas R. Holtz, Jr., of the University of Maryland, a tyrannosaur authority who was not involved in the research. For example, paleontologists have long wondered why T. rex had lower limbs engineered for speed when the animal’s sheer heft would have precluded swift locomotion. But the presence of fleet legs and feet in the much older Raptorex indicates that T. rex’s lower limb architecture is just an evolutionary holdover from a smaller, faster ancestor.
The fact that the Raptorex body plan was simply scaled up in later tyrannosaurs such as T. rex attests to the adaptive value of those trademark traits. But not all members of this group went that evolutionary route, as Brusatte and his colleagues revealed in a paper published in the October 13 Proceedings of the National Academy of Sciences USA that describes the second new tyrannosaur.
Discovered in 2001 on an expedition in Mongolia’s Gobi Desert, the 65-million-year-old specimen, named Alioramus altai, has a suite of features that deviate sharply from the tyrannosaur norm. Tipping the scales at an estimated 350 kilograms, this dinosaur—believed to have been about nine years old when it died—is larger than Raptorex but still only half the size of a nine-year-old T. rex (which reached full size in 18 years). Furthermore, it has a “totally weird skull shape,” Brusatte asserts. Among other bizarre traits, the skull is long and slender, somewhat like a crocodile’s, and it lacks the banana-shaped teeth and enlarged browridges that enabled T. rex and other tyrannosaurs to bite with bone-crushing force.
The skull of A. altai also exhibits eight small horns, including one on each cheek that stuck out to the side. Though modest compared with the horns of dinosaurs like Triceratops, the horns of Alioramus are quite extravagant for a tyrannosaur. They would not have done much good in combat, so Brusatte surmises that they served to attract mates once the animal reached sexual maturity.
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7 Comments
Add CommentT-Rex = Scavenger.
Reply | Report Abuse | Link to thisIs it really a "re-thinking" to suggest that T-Rex descended from a smaller animal with similar features instead of a similar size animal with different features? Why would it be assumed that the size came before the distinct features?
Reply | Report Abuse | Link to thisI take issue with the "certainty" that is usually portrayed in this type of article. Note the following quote:
Reply | Report Abuse | Link to thisUnearthed in Inner Mongolia, Raptorex lived 125 million years ago—60 million years before T. rex terrorized North America.
In reality, the author does NOT know for sure if Raptorex lived 125 million years ago. Also, there is NO certainty that T-Rex terrorized anything more than local plant leaves. Remember the Panda Bear's actual canine-like teeth and its actual vegetarian diet.
"T-Rex=Scavenger"
Reply | Report Abuse | Link to thisThere is no particular reason to think that T-rex was just a scavenger. Surely they would steel food from lesser species just as lions do today; that makes sense from an energy expenditure point of view.
My theory about T-rex and the like though, whether big or small, is that the strange little forearms are not an adaptation to running, because none of the mammalian top predators have this feature and most of them can run very fast. No I think those small forelimbs are an adaptation to the hideous side-sweeping tail hammers of ankylosaurs and the like. If enough herbivores developed means of damaging the forelimbs of their predators then advantage would go to the predators which could balance on their hind legs and lean over the defense to bite the neck of the prey or grab onto the front of its face to smother it.
ok, guys...first of all, dating fossils is very accurate now...down to the hundreds of thousands of years or so, which, geologically speaking, is akin to us speaking in days. second, T rex was absolutly NOT a scavenger, but like all predators would be an opportunistic feeder. The article is not saying that noone thought the huge Tyrannosaurs evolved from smaller ancestors, it is illustrating the similarity of body design and tracing the evolution of the family...all large dinosaur families had ancestors on the "small" side. as far as the arms, um, in modern predatory mammals it is absolutly an adaptation for speed. cats and canines rely on a combination of coordination of 4 legs and trunk muscles to achieve high speed. large Tyrannosaur arms were probably an adaptation to compensate for their larger heads (relative to body size) and to reduce weight. modern cats rely on their arms for holding prey as do some members of the canine family, although not as much...Tyrannosaurs did not need this function to be present as they relied on their superior bite force and enlarged neck muscles for bringing down prey...this article is interesting because it is interesting to see how T rex's relatives developed similar adaptations thru time as they went from minor to apex predators and their food source changed.
Reply | Report Abuse | Link to thisTo say T-Rex was not a scavenger is naieve at best . The function of bone crushing jaws like in the modern Hyeana is tatamount to it's survival .Once a pack drives away the killing animal they eat everything , including the bones , just like a T- Rex would have done .
Reply | Report Abuse | Link to thisAs cows in the meadows are the biggest threat to life ,or rather the end of life on our planet because of the methane they produce by farting. I tgot me thinking,if cows alone are such a threat, when we include wildebeast,antelope,deer,zebra and so on and so forth this must multiply the methane problem considerably.
Reply | Report Abuse | Link to thisMy question is, huge Dinosaurs and many of them roamed the earth for millions of years would their methane contribution perhaps been their downfall which led to their extinction.