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Allosaurus ate more like a falcon, T. rex more like a croc, study finds

May 22, 2013
Courtesy of Ohio University
and World Science staff

Mighty T. rex may have thrashed its huge head side­ways to dis­mem­ber prey, but a new study sug­gests its smaller cous­in Al­lo­saur­us was a more dex­ter­ous hunt­er and tugged at prey more like a fal­con.

“Ap­par­ently one size does­n’t fit all when it comes to di­no­saur feed­ing styles,” said Ohio Uni­vers­ity pa­le­on­tol­ogist Er­ic Sniv­ely, lead au­thor of the stu­dy, pub­lished May 21 in the on­line jour­nal Palaeon­tolo­gia Elec­tron­ica

Ske­l­e­ton and recon­structed soft tis­sues in the late Ju­ras­sic pred­a­to­r Al­lo­saur­us. (Cour­tesy Ohio U.)


“Many peo­ple think of Al­lo­saur­us as a smaller and ear­li­er ver­sion of T. rex, but our en­gi­neer­ing an­al­y­ses show that they were very dif­fer­ent preda­tors”—though both mem­bers of a line­age called theropods, widely con­sid­ered the an­ces­tors of birds.

Al­lo­saur­us’s mus­cu­la­ture, he added, “unique­ly equip­ped” it “to drive its head down in­to prey, hold it there, and then pull the head straight up and back with the neck and body, tear­ing flesh from the car­cass … kind of like how a pow­er shov­el or back­hoe rips in­to the ground.”

Snively led a team of Ohio Uni­vers­ity re­search­ers who started with a high-resolution cast of the five-foot-long skull plus neck of the 150-million-year-old Al­lo­saur­us, one of the best-known di­no­saurs. They CT-scanned the bones, ob­tain­ing da­ta they could ma­ni­pu­late in a com­put­er.

Snively and me­chan­i­cal en­gi­neer John Cot­ton ap­plied a spe­cial­ized en­gi­neer­ing anal­y­sis bor­rowed from robotics called mul­ti­body dy­nam­ics. This let the sci­en­tists run sim­ula­t­ions of the head and neck move­ments Al­lo­saur­us made when at­tack­ing prey, strip­ping flesh from a car­cass or even just look­ing around.

“The en­gi­neer­ing ap­proach com­bines all the bi­o­log­i­cal da­ta—things like where the mus­cle forc­es at­tach and where the joints stop motion—in­to a sin­gle mod­el. We can then sim­ulate the phys­ics,” said Cot­ton.

To learn how Al­lo­saur­us de-fleshed prey such as Steg­o­saur­us, the team had to “re-flesh” Al­lo­saur­us. The ana­tom­i­cal struc­ture of modern-day di­no­saur rel­a­tives, such as birds and crocodil­ians, com­bined with tell-tale clues on the di­no­saur bones, let Snively and an­atomists Law­rence Wit­mer and Ryan Ridgely build in­to their com­put­er Al­lo­saur­us neck and jaw mus­cles, air si­nus­es, the wind­pipe and oth­er soft tis­sues.

A key find­ing was an un­usu­ally placed neck mus­cle called long­is­simus capi­tis su­per­fi­cialis. In most pred­a­to­ry di­no­saurs, such as T. rex, which Snively had stud­ied, this mus­cle passed from the side of the neck to a bony wing on the out­er back corners of the skull. It “acts like a rid­er pulling on the reins of a horse’s bri­dle,” he said. “If the mus­cle on one side con­tracts, it would turn the head in that di­rec­tion, but if the mus­cles on both sides pull, it pulls the head straight back.” 

But the anal­y­sis of Al­lo­saur­us re­vealed that the longis­simus mus­cle at­tached much low­er on the skull, which, ac­cord­ing to the en­gi­neer­ing an­al­y­ses, would have caused “head ven­troflex­ion fol­lowed by re­trac­tion,” the thrust-and-pull ac­tion.

Small fal­cons, such as kestrels, use this same de-fleshing tech­nique. Tyran­nosaurs like T. rex, on the oth­er hand, were en­gi­neered to use a grab-and-shake tech­nique to tear off hunks of flesh, more like a croc­o­dile, Snive­ly said.

The team’s en­gi­neer­ing an­al­y­ses re­vealed a cost to T. rex’s feed­ing style: high rota­t­ional in­er­tia. That large bony and toothy skull perched at the end of the neck made it hard for T. rex to speed up or slow down its head or to change its course as it swung its head around. Al­lo­saur­us, how­ev­er, had a rel­a­tively very light head, which the team found as they re­stored the soft tis­sues and air si­nus­es.

Al­lo­saur­us, with its light­er head and neck, was like a skat­er who starts spin­ning with her arms tucked in,” al­low­ing her to spin fast, said Sniv­ely. “T. rex, with its mas­sive head and neck and heavy teeth out front, was more like the skat­er with her arms fully ex­tend­ed … and hold­ing bowl­ing balls in her hands. She and the T. rex need a lot more mus­cle force to get go­ing.”

As a re­sult, he added, Al­lo­saur­us was a much more flex­i­ble hunt­er that could move its head and neck fast and with good con­trol. That con­trol, how­ev­er, came at the cost of brute-force pow­er, re­quir­ing a de-fleshing style that, like a fal­con, re­cruited the whole neck and body to strip flesh from the bones.


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The mighty T. rex may have thrashed its huge head sideways to dismember prey, but a new study suggests its smaller cousin Allosaurus was a more dexterous hunter and tugged at prey more like a falcon. “Apparently one size doesn’t fit all when it comes to dinosaur feeding styles,” said Ohio University paleontologist Eric Snively, lead author of the study, published May 21 in the online journal Palaeontologia Electronica. “Many people think of Allosaurus as a smaller and earlier version of T. rex, but our engineering analyses show that they were very different predators”—though both members of a lineage called theropods, widely considered to be the ancestors of birds. Allosaurus’s musculature, he added, “uniquely equipped” it “to drive its head down into prey, hold it there, and then pull the head straight up and back with the neck and body, tearing flesh from the carcass … kind of like how a power shovel or backhoe rips into the ground.” Snively led a team of Ohio University researchers including experts in mechanical engineering, computer visualization and dinosaur anatomy. They started with a high-resolution cast of the five-foot-long skull plus neck of the 150-million-year-old Allosaurus, one of the best-known dinosaurs. They CT-scanned the bones at O’Bleness Memorial Hospital in Athens, which produced data the authors could manipulate in a computer. Snively and mechanical engineer John Cotton applied a specialized engineering analysis borrowed from robotics called multibody dynamics. This let the scientists run simulations of the head and neck movements Allosaurus made when attacking prey, stripping flesh from a carcass or even just looking around. “The engineering approach combines all the biological data—things like where the muscle forces attach and where the joints stop motion—into a single model. We can then simulate the physics and predict what Allosaurus was actually capable of doing,” said Cotton. To learn how Allosaurus de-fleshed prey such as Stegosaurus, the team had to “re-flesh” Allosaurus. The anatomical structure of modern-day dinosaur relatives, such as birds and crocodilians, combined with tell-tale clues on the dinosaur bones, let Snively and anatomists Lawrence Witmer and Ryan Ridgely build into their computer Allosaurus neck and jaw muscles, air sinuses, the windpipe and other soft tissues. A key finding was an unusually placed neck muscle called longissimus capitis superficialis. In most predatory dinosaurs, such as T. rex, which Snively had studied, this muscle passed from the side of the neck to a bony wing on the outer back corners of the skull. It “acts like a rider pulling on the reins of a horse’s bridle,” he said. “If the muscle on one side contracts, it would turn the head in that direction, but if the muscles on both sides pull, it pulls the head straight back.” But the analysis of Allosaurus revealed that the longissimus muscle attached much lower on the skull, which, according to the engineering analyses, would have caused “head ventroflexion followed by retraction,” the thrust-and-pull action. Small falcons, such as kestrels, use this same de-fleshing technique. Tyrannosaurs like T. rex, on the other hand, were engineered to use a grab-and-shake technique to tear off hunks of flesh, more like a crocodile. But the team’s engineering analyses revealed a cost to T. rex’s feeding style: high rotational inertia. That large bony and toothy skull perched at the end of the neck made it hard for T. rex to speed up or slow down its head or to change its course as it swung its head around. Allosaurus, however, had a relatively very light head, which the team found as they restored the soft tissues and air sinuses. “Allosaurus, with its lighter head and neck, was like a skater who starts spinning with her arms tucked in,” allowing her to spin fast, said Snively. “T. rex, with its massive head and neck and heavy teeth out front, was more like the skater with her arms fully extended … and holding bowling balls in her hands. She and the T. rex need a lot more muscle force to get going.” The end result, he added, is that Allosaurus was a much more flexible hunter that could move its head and neck around relatively rapidly and with considerable control. That control, however, came at the cost of brute-force power, requiring a de-fleshing style that, like a falcon, recruited the whole neck and body to strip flesh from the bones.