Dino with camel hump
Some dinosaur fossils are characterized by long vertebral processes previously thought to support flat flaps of skin. However, according to a new analysis, some posterior flaps resemble more protuberances, suggesting that these dinosaurs were more adaptable than previously thought. Skin flaps are believed to have originally evolved about 270 million years ago in the dinosaur ancestors, the pelycosaurs, which include Dimetrodon. The sails probably served as heat collectors for these small, cold-blooded reptiles. For about the last 10 years or so, the pelycosaur model has been extended to include various large dinosaurs with spiny structures that lived in Africa about 100 million years ago and may have had skin flaps to warm or cool their blood. However, according to Western Illinois University paleontologist Jack Bowman Bailey at Macomb, the need for such structures has been questioned. For large animals living in hot climates, sails could cause overheating, says Bailey.
Bailey did an analysis which he believes shows that such dinos resembled humpbacked buffalo more than spiny lizards. He related the vertebral length of the Ouranosaurus, a herbivore, and the Spinosaurus, a carnivore, to two other parameters: the chest depth and the height of an intervertebral disc. He then measured the same ratio in various pelycosaurs with sails on their backs, and in humped-backed buffalo, and in two extinct animals: a huge humped stag and an equally gigantic camel, which, unlike today's camel, had an array of spines to support its humps. The ratio in spiny dinosaurs is much more like that in mammals than in pelycosaurs, reports Bailey in the Journal of Paleontology (Winter 1997 issue). He therefore believes that dinosaur spines, like buffalo spines, supported protuberances of fatty tissue. The back fat would then have acted both as an energy reserve in times of food shortages and as a heat shield, says Bailey. He adds that this would have enabled the animals to travel great distances.
According to dinosaur expert Paul Barrett of the University of Cambridge in the UK, Bailey's interpretation is both new and plausible. Barrett is glad that the notion of sails in spiny dinosaurs "has been discarded and muscles have taken their place." But he believes the new notion will be difficult to prove because soft tissue structures are rarely preserved in fossils.