RESEARCH NEWS

PALEONTOLOGY known only from a single titanic vertebra discovered more than 100 yearsago in Colo- rado ARGENTINA-"I work weighed seven tons. The bones of the new with the biggest dinosaurs in the smallest theropod, excavated last year from a 110- museum,"paleontologist Rodolfo Coria likes million-year-old deposit by Coria and to say. Coria may be exaggerating slightly Leonardo Salgado of the University of about the size of the municipal museum in Comahue in the nearby city of Neuquen, this little town in northern Patagonia, but he include a thigh bone and an upper jaw that isn't kidding about the bones that crowd the are a few centimeters longer than matching halls there: They're the sizeofsmallrefrigera- bones of the South Dakota behemoth. But tors. These seven vertebrae belonged to because this theropod belonged to a different Argentinosaurus, a long-necked vegetarian lineage than Sue and had a heavier build, dinosaur, or sauropod, that may have out- Showing~oniespine. Vertebrae of Argentino- says Holtz, a theropod specialist, "I would weighed other giants by 40 metric tons. esutus, the largest a meter and a half high. expect this animal may have been several Move over, Seismosauius, Supersaurus, and tons heavier than Sue." Uuxasausus, contenders from the American Bonaparte of the MuseumofN atural History But whether the animal is truly the big- West. Argentinosaurus, which lived 100 mil- in Buenos Aires, was a titanosaurian, a type gest or merely very big, its dimensions raise lion years ago in the middle of the Creta- of sauropod that flourished in South sizablequestions. One is about the metabo- ceous period, could be the new dinosaur America during the Cretaceous period. By lism that could have sustained such a giant. heavyweight champion. comparing thedirriensions of the fossilswith For two decades, researchers have been "Argentinosaurus isunquestionablythe larg- those of the matching bones in more com- wranglingover whether dinosaurswerewarm- est sauropod for which we have good mate- plete titanosaurian skeletons, Bonaparte and . or cold-blooded. The warm-blooded, or en- rial," says paleontologist Thomas Holtz of Coria estimate that the creature had a hind dothermic, view gained support 2 years ago, I /the u.s. Geological Survey in Reston, Vir- limb 4.5 meters-long and measured 7 meters when an analysis of oxygen isotopes in the ginia, who discussed it with Coria at the Oc- from shoulder to hip. Add a tail and neck of bones ofseveral dinosaurs, including a tyran- tober meeting of the Society of Vertebrate the uSual (titanosaurian) proportions, and nosaur, implied that these creatures kept Paleontology in-Seattle. Not everyone is Argentinosaurus would have been some 30 their extremities nearly aswarm astheir body readyto grant this new contender the crown, meters long. cores-s-a hallmark of warm-bloodedness. though; David Gillette of the Utah Geologi- There are longer dinosaurs, but perhaps But James Farlow of-Indiana University- cal Survey thinks it was probably no heavier no heavier ones. One sauropod from New Purdue argues that a warm-blooded giant than the American ground-shakers. And Mexico, called Seismosaurus, may have mea- wouldhave needed an implausibleamount of sauropod specialist John McIntosh of sured 40 meters or more from tip to tail. But food. If giant theropods had food require- Wesleyan University in Middletown, Con- it was long and lean-as dinosaurs go. Gil- ments resembling those of large mammalian necticut, points out that estimating sizeand lette, itsdiscoverer,estimatesthatSeismosaur- predators, he says, the total population weight from incomplete skeletons alwaysin- us probably weighed between 40 and 80 tons. wouldhave been so small that chance events volves "lots of if's, and's, and but's." Argentinosaurus, shorter' but stockier, prob- could easily have wiped it out. "I don't see But there's no doubt, Mclntosh allows, ably matched Seismosaurus in weight, he says. how they could have attained these large "that [Argentinosaurus] is a very, verylarge But Gregory Paul, a respected dinosaur body sizes and been endothermic," he says. animal." Along with the bones of another illustrator in Baltimore who has made sys- Peter Dodson of the University of Pennsyl- giant that are crammed into Coria's hall- tematic estimates of the largest dinosaurs' vania has reached a similar conclusion for ways-an unnamed meat-eater, or theropod, sizeand weight, thinks the difference in build the giant sauropods, although his reasoning that maybe bigenough to dethrone Tyranno- tips the scales decisively in favor of Argen- is different. Larger animals have a harder saurus rex as king of the carnivores-it raises tinosaurus. He puts its weight at between 80 time shedding internal heat, he explains, and a lot ofquestions about dinosaur size.Paleon- and 100 tons-heavier than two fullyloaded an animal the size of a giant sauropod that tologists wonder how such huge creatures semi trucks. Paleontologist Dale Russell of had a mammalian metabolism would have found enough to eat, cooled their bodies, and the Canadian Museum of Nature in Ottawa, baked itself from the inside out. coped with the force of gravity. who has seenjhe bones, agrees with that Whatever metabolic style these dinosaurs Argentinosaurus, which has estimate. "That is the only dinosaur that I had, it willnot explain the evolutionary pres- been excavated since the late feel secure might, have approached 100 sures that drove them to get so big. Nor will 1980s by Coria and Jose metric tons," he says. The only thing that it explain how they solved the bioengineer- might have outweighed it, say paleontolo- ing problems posed by enormous size. How gists, is a beast called Am- did a creature as big asArgentinosaurus pump phicoelias fragiUimus, blood up to its lofty head, for example? "When you get to the really giant ones," Dodson says,"youcan only scratch yourhead in wonderment." Coria's South American contenders are not just pushing the limits of What a beast. Reconstruction of his hallway space-they're also testing the Argentinosaurus, showing the bones excavated so far (dark areas). limits of scientific explanation. -Tim Appenzeller

SCIENCE • VOL. 266 • 16 DECEMBER 1994 1805