THE biggest, and possibly the baddest predatory dinosaur of them all was not the fabled Tyrannosaurus rex, or even its slightly larger rival Giganotosaurus, but a long-jawed, sail-backed creature called Spinosaurus.
An examination of some newly obtained fossils shows that Spinosaurus stretched an impressive 17 metres from nose to tail, dwarfing its meat-eating relatives. As well as being longer than its rivals, Spinosaurus also had stronger arms with which to catch its prey, unlike the puny-armed T. rex and its ilk.
Until 10 years ago, T. rex held the mantle of the biggest predatory dinosaur. Of the 30 specimens collected so far, the largest and most complete is a fossil called Sue, kept at the Field Museum of Natural History in Chicago. She measures 12.8 metres long and is thought to have weighed 6.4 tonnes when alive 67 million years ago.
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Enter Giganotosaurus, a meat-eating dinosaur that lived in what is now Argentina. Reconstruction of a partial skeleton indicated that it stretched 13.7 metres. It lived about 100 million years ago at around the same time as two other huge predatory dinosaurs were stalking other continents. The slightly smaller Carcharodontosaurus lived in Africa while Acanthosaurus lived in North America, the only one of the three dinosaurs for which we have more than a handful of fragmentary fossils. All three predators were closely related to Allosaurus, a 9 to 12-metre-long predator of a lighter build than T. rex which was common in North America 150 million years ago.
However, Spinosaurus has been casting its fearsome shadow over all these beasts for some time. German palaeontologist Ernst Stromer discovered the first and best specimen in 1912 in Egypt. He identified it as a long-snouted giant predator which he believed was bigger than T. rex, and published a detailed study of the bones, including a partial backbone with long spines on the vertebrae, which may have supported a sail. Stromer鈥檚 fossils were obliterated when allied bombers hit a Munich museum in 1944. Since then, all that has been discovered are some specimens of related smaller spinosaurs, as well as some isolated bones of Spinosaurus itself.
But a new examination of two skull fragments of Spinosaurus has confirmed its early reputation. Cristiano Dal Sasso of the Civic Natural History Museum in Milan, Italy, and his colleagues analysed a snout the museum acquired from an Italian collector, and previously unidentified bones from the upper rear of the skull collected by the University of Chicago, both of which were originally unearthed in Morocco.
鈥淲ith their long, slender snouts and interlocking teeth, spinosaurs were like theropods with crocodile mouths鈥�
After measuring their sizes, he estimates that the 99-centimetre-long snout came from a skull 1.75 metres long. From what we know of the body shapes of other spinosaurs, Dal Sasso calculates that the new Spinosaurus was 17 metres long and weighed 7 to 9 tonnes (Journal of Vertebrate Paleontology, vol 25, p 888).
Spinosaurus lived alongside Carcharodontosaurus in Africa 100 million years ago, and like T. rex and Giganotosaurus was a theropod, the group of dinosaurs that gave rise to birds. But Dal Sasso says spinosaurs, with their very long and slender snouts are more like 鈥渢heropods with crocodile mouths鈥�. Their long teeth interlocked to catch prey, and a sawfish vertebra stuck between a tooth socket and an emerging tooth in one fossil specimen supports the idea that Spinosaurus preyed largely on fish. Other specimens also suggest that spinosaurs had arms 鈥渟trong enough to be used in catching prey鈥�, says Eric Buffetaut of France鈥檚 National Centre for Scientific Research in Paris, who collaborated with Dal Sasso.
T. rex and Giganotosaurus 鈥渨ere doing very different things鈥�, says palaeontologist Larry Witmer of Ohio University in Athens. T. rex had puny arms, but its stout skull had massive banana-shaped teeth that could crunch through bone, where Giganotosaurus had a much more slender skull, with blade-like teeth to slice through flesh.
Earliest Tyrannosaur
A 鈥渃rowned dragon鈥� that lived 160 million years ago was the great-grandaddy of the tyrant lizard king T. rex.
Two skeletons of the oldest known tyrannosauroid have been discovered in what used to be wetland in the Gobi desert of western China. The beast has been named Guanlong, or 鈥渃rowned dragon鈥�, not because of its ferocity or its kinship with T. rex, but because it had an unusual prominent nasal crest on its head, which was probably an ornament used to display sexual prowess.
Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and colleagues uncovered the nearly complete skeleton of a juvenile and the partial skeleton of a 3-metre long adult. The juvenile had died first and its skeleton sank into the mud of the wetland, where it may have been trampled by the adult before it too died (Nature, vol 439, p 715).
Tyrannosaurs only became giants late in their evolution. They spent the early part of their history as secondary predators in the shadow of allosaurs and spinosaurs, says Tom Holtz of the University of Maryland in College Park. Nine-metre-long giant tyrannosaurs didn鈥檛 appear until about 80 million years ago, just 15 million years before an asteroid impact ended the reign of the dinosaurs.
