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July 02, 2012

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Feathers may have been common on dinosaurs

July 2, 2012
Courtesy of the American 
Museum of Natural History
and World Science staff

A new­found fos­sil sug­gests feath­ers were more wide­spread on di­no­saurs than pre­vi­ously thought—grac­ing all pred­a­to­ry di­no­saurs, and per­haps oth­ers, sci­en­tists say.

The new fos­sil comes from a line­age of di­no­saurs, the­ro­pods, con­sid­ered the an­ces­tors of birds, but is the first ev­i­dence of a feath­ered the­ro­pod not closely re­lat­ed to birds, re­search­ers ex­plain.

Skeleton of Sciurumimus as found on a lime­stone slab (H. Tisch­ling­er/\Ju­ra Mu­seum Eich­statt)

A de­scrip­tion of the an­i­mal, dubbed Sci­u­ru­mimus al­bers­do­er­feri, is pub­lished in this week’s early on­line edi­tion of the jour­nal Pro­ceed­ings of the Na­t­ional Acad­e­my of Sci­ences.

Theropods, which in­clude the fa­mous Ty­ran­no­saur­us rex, are mostly car­niv­o­rous di­no­saurs that walked on two legs. Fos­sils have re­vealed many of them had feath­ers, but the feath­er­ing was only been found in the­ro­pods that are clas­si­fied as coel­ur­o­saurs, a di­verse group in­clud­ing an­i­mals like T. rex and birds. 

Sci­u­ru­mimus—identified as a meg­a­lo­saur, not a coe­luro­saur — is the first ex­cep­tion to this rule. The new spe­cies al­so sits deep with­in the ev­o­lu­tion­ary tree of the­ro­pods, much more so than coelurosaurs, sug­gest­ing to sci­en­tists that its own de­scen­dants had si­m­i­lar char­ac­ter­is­tics.

“All of the feath­ered pred­a­to­ry di­no­saurs known so far rep­re­sent close rel­a­tives of birds,” said study co-author and pa­lae­on­tol­ogist Ol­i­ver Rauhut, of the Bay­erische Staatssamm­lung für Paläon­tolo­gie un­d Ge­olo­gie in Mu­nich, Germany. “Sci­u­ru­mi­mus is much more ba­sal [deep] with­in the di­no­saur family tree and thus in­di­cates that all pred­a­to­ry di­no­saurs had feath­ers.”

Mid-tail sec­tion of Sci­u­ru­mimus un­der ultra­violet light, show­ing patches of pre­served skin (yel­low) and fi­ne fil­a­ments (blu­ish lines above the ver­te­brae) (H. Tis­chlinger/Jura Mu­se­um Eich­statt)

The fos­sil, which is of a ba­by Sci­u­ru­mi­mus, was found in the lime­stones of north­ern Ba­var­ia and pre­serves re­mains of a fil­a­men­tous plum­age, in­di­cat­ing feath­ers cov­ered the whole body, re­search­ers said. “Un­der ul­tra­vi­o­let light, re­mains of the skin and feath­ers show up as lu­mi­nous patches around the skele­ton,” said co-author Hel­mut Tis­chlinger, from the Ju­ra Mu­se­um Eich­statt in Ger­many.

Sci­u­ru­mimus is not only re­mark­a­ble for its feath­ers, the re­search­ers said: the skel­e­ton, which rep­re­sents the most com­plete pred­a­to­ry di­no­saur ev­er found in Eu­rope, al­lows a rare glimpse at a young di­no­saur. “It has been sug­gested for some time that the lifestyle of pred­a­to­ry di­no­saurs changed con­sid­erably dur­ing their growth,” Rauhut said. “Sci­u­ru­mi­mus shows a re­mark­a­ble dif­fer­ence to adult meg­a­lo­saurs in the den­ti­tion [teeth], which clearly in­di­cates that it had a dif­fer­ent di­et.”

Adult meg­a­lo­saurs reached about 20 feet in length and of­ten weighed more than a ton. They were ac­tive preda­tors, which probably al­so hunt­ed oth­er large di­no­saurs. The ju­ve­nile spec­i­men of Sci­u­ru­mi­mus, which was only about 28 inches in length, is thought to have hunt­ed in­sects and oth­er small prey, judg­ing by slen­der, point­ed teeth in the tip of the jaws.

“Ev­ery­thing we find these days shows just how deep in the family tree many char­ac­ter­is­tics of mod­ern birds go, and just how bird-like these an­i­mals were,” Norell said. “At this point it will sur­prise no one if feath­er-like struc­tures were pre­s­ent in the an­ces­tors of all di­no­saurs.”

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A newfound fossil suggests feathers were more widespread on dinosaurs than previously thought—gracing all predatory dinosaurs, and perhaps others, scientists say. The new fossil comes from a lineage of dinosaurs, theropods, considered the ancestors of birds, but is the first evidence of a feathered theropod not closely related to birds, researchers explain. A description of the animal, dubbed Sciurumimus albersdoerferi, is published in this week’s early online edition of the journal Proceedings of the National Academy of Sciences. Theropods, which include the famous Tyrannosaurus rex, are mostly carnivorous dinosaurs that walked on two legs. Fossils have revealed many of them had feathers, but the feathering was only been found in theropods that are classified as coelurosaurs, a diverse group including animals like T. rex and birds. Sciurumimus—identified as a megalosaur, not a coelurosaur— is the first exception to this rule. The new species also sits deep within the evolutionary tree of theropods, much more so than coelurosaurs, suggesting to scientists that its own descendants had similar characteristics. “All of the feathered predatory dinosaurs known so far represent close relatives of birds,” said study co-author and palaeontologist Oliver Rauhut, of the Bayerische Staatssammlung für Paläontologie und Geologie in Munich, Germany. “Sciurumimus is much more basal [deep] within the dinosaur family tree and thus indicates that all predatory dinosaurs had feathers.” The fossil, which is of a baby Sciurumimus, was found in the limestones of northern Bavaria and preserves remains of a filamentous plumage, indicating that the whole body was covered with feathers. “Under ultraviolet light, remains of the skin and feathers show up as luminous patches around the skeleton,” said co-author Helmut Tischlinger, from the Jura Museum Eichstatt. Sciurumimusis not only remarkable for its feathers, the researchers said: the skeleton, which represents the most complete predatory dinosaur ever found in Europe, allows a rare glimpse at a young dinosaur. Apart from other known juvenile features, such as large eyes, the new find also confirmed other hypotheses. “It has been suggested for some time that the lifestyle of predatory dinosaurs changed considerably during their growth,” Rauhut said. “Sciurumimus shows a remarkable difference to adult megalosaurs in the dentition [teeth], which clearly indicates that it had a different diet.” Adult megalosaurs reached about 20 feet in length and often weighed more than a ton. They were active predators, which probably also hunted other large dinosaurs. The juvenile specimen of Sciurumimus, which was only about 28 inches in length, is thought to have hunted insects and other small prey, judging by slender, pointed teeth in the tip of the jaws. “Everything we find these days shows just how deep in the family tree many characteristics of modern birds go, and just how bird-like these animals were,” Norell said. “At this point it will surprise no one if feather like structures were present in the ancestors of all dinosaurs.”