SAY 鈥渢yrannosaur鈥� and most people picture a clunky, heavy-set beast with huge teeth and a brutish character. But the latest member of the team was built more like a ballerina.
The largely intact skeleton of Alioramus altai was excavated from 65-million-year-old rocks in the Gobi desert in Mongolia (Proceedings of the National Academy of Sciences, ).
All the other tyrannosaurs discovered to date conform to the familiar chunky body plan with short, deep skulls, massive jaws and heavily built bodies. Alioramus broke the mould with its long thin head, weak jaws and slender, air-filled body. Were it not for the eight small horns protruding from its snout and head, it might have been dino-elegance personified.
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Fully grown individuals would probably have been up to 8 metres long to T. Rex鈥榮 13 metres. Its long head and puny bite didn鈥檛 equip it for crunching through bones in the way other tyrannosaurs could.
But what it lacked in strength and power it made up for in speed and agility. Alioramus had air sacs running through the vertebrae in its neck and spine which it used for ultra-efficient breathing. Modern birds which are descendants of the order of dinosaurs to which tyrannosaurs belong, are similarly designed. Air fills these cavities when birds inhale, and then flows from the bones into the lungs when they exhale. This means that the lungs have a constant stream of fresh air and can extract up to two-and-a half times as much oxygen per breath as a mammal.
Highly 鈥減neumatic鈥� bones would have also made Alioramus remarkably light for its size. Growth rings show that the Gobi desert specimen was a 9-year-old juvenile, weighing in at around 370 kilograms when it died. Its close cousin Tarbosaurus would have weighed twice as much at that age. T. Rex, would probably have weighed at least 5 tonnes.
鈥�Alioramus was more of a ballerina than Tarbosaurus,鈥� says Steve Brusatte of the American Museum of Natural History in New York. 鈥淚t surely went after smaller prey and relied more on speed and stealth than on brute strength.鈥�
鈥淚t surely went after smaller prey and relied more on speed and stealth than on brute strength鈥�