Feathers in their caps
Awellreceived recent paper published in the journal Nature has shown that extinct flying reptiles, pterosaurs (‘‘pterodactyls’’), while mostly covered with short hairlike filaments, bore on some parts of their heads at least a few true branched feathers, which were brightly coloured and probably used for communication.
This may indicate they were more closely related to dinosaurs than previously thought.
The work by a group of Belgian and Brazilian scientists at University College Cork, Ireland, analysed the head crest of a 115millionyearold Brazilian pterosaur, Tupandactylus imperator. Its huge head crest bore a basal ring of fuzzy, branched true feathers which had melanophores of different sizes and shapes to produce different bright colours, under genetic control.
Pterosaurs, comprising the order Pterosauria (Owen, 1842), flew throughout the Mesozoic era and, like dinosaurs, became extinct about 65.5 million years ago in the endCretaceous event. Prodigiously adapted for flight, pterosaurs were characterised by extreme elongation of the fourth finger of the ‘‘hand’’ to support a membranous wing that extended back to the ankle of the hind leg, and by a reduction of the hind limb. The fifth finger was vestigial and the first three fingers were free of the wing, enabling grasping and terrestrial locomotion on all four limbs.
Pterosaur bones were very thin — only 1mm2mm thick, even in giant species. This immediately distinguishes pterosaur fossil bones from those of other vertebrates with hollow bones, such as birds and some dinosaurs, whose bones had thicker walls. Very thin walls lighten bones for flight, and walls only 1mm or 2mm wide enable the identification even of damaged, isolated fossil pterosaur bones. Other features unique to pterosaurs are the rodlike pteroid bone in the wrist and the long clawless first toe of the foot, not found in any other reptile. They were likely warm blooded. The overall shape of pterosaurs was unique and distinctive.
Pterosaurs were mostly brightly coloured and possessed physiologically sophisticated wings, the wingspan ranging from 20cm to 12.2m. On the ground, they walked on all fours.
Although there are no known fossils outside the Mesozoic era, it is likely that pterosaurs arose just before the Mesozoic, because even the earliest known pterosaur fossils from the early Triassic period had fully developed wings and many sophisticated adaptations for sustained flight. Pterosaurs had air tubes through their very light bones like those of birds, with which they shared a great many other flight adaptations evolved through convergent evolution. For example, like flying birds, pterosaurs had a large breastbone for attachment of powerful flight muscles.
The oldest known pterosaurs had fully toothed jaws and long tails. Some later ones were walking along a beach.
toothless and the jaws were adapted into a beak, while the tail became modified into a stump. They ranged in size from a few centimetres to that of a modernday fighter jet.
Many probably moved over water, bending their long necks to pluck fish from below the surface as they flew in the air above.
Pterosaur fossils only became numerous halfway through the Mesozoic era in the Jurassic period, when pterosaurs had a worldwide distribution.
Although close cousins of the dinosaurs, pterosaurs evolved on a separate branch of the reptile family tree. They were the first vertebrates and the first animals after insects to evolve powered flight — not simply leaping and gliding, but flapping their wings to generate lift and travel through the air. (Note that birds, class Aves, are classified in the Dinosauria and within the Theropoda, having evolved from theropod dinosaurs.)
Among fossils from the early Triassic period, possible ancestors of both pterosaurs and dinosaurs have been found, such as Scleromochlus taylori (family Scleromochlidae), a 20cmlong reptile from Scotland with a large head, short neck, slender body and long hind limbs, which likely ate insects. Other candidates, similar in size and appearance to Scleromochlus, are placed in the family Lagerpetidae. The chain of events that led to fully powered flight in pterosaurs, however, is unknown.