Gliding Reptiles

Apart from the pterosaurs, no reptiles have evolved flapping flight. Since the Upper Permian, however, small diapsid gliding reptiles have appeared in the fossil record. One of these, Daedalosaurus from Madagascar, was so named by Robert Carroll after Daedalus who, in Greek legend, escaped from Crete with the aid of wings which he had made for himself. Daedalosaurus is now considered to be a junior synonym of Coelurosauravus (Figs. 47,50a), as is Weigelti-saurus from Germany and England.

Kuehneosaurus Skeleton
■ Fig. 47. Coelurosauravus (Squamata; Upper Permian ; length ca. 60 cm ). (After Evans 1982)
Triassic Reptiles
■ Fig. 48. Kuehneosaurus (Squamata; Upper Triassic; length ca. 75 cm). (Cloudsley-Thompson 1994 after Charig 1979)

The specialised postcranial skeleton of these reptiles had very long ribs that undoubtedly supported a membrane of skin. This would have been opened to enable the animal to glide, and folded back against the body when it was moving through vegetation or on the ground (Evans 1982). Wellnhofer (1991) and Norman and Wellnhofer (2000) described several similar forms, including Kuehneosaurus (Figs. 48,50b) and Icarosaurus (Figs. 49,50c) from the Upper Triassic strata of what are now Britain and USA respectively. The latter was named after Icarus, the son of Daedalus. Like those of Coelurosauravus, the membranes with which these animals glided was supported on elongated ribs - of which there were only 10 or 11 pairs, compared with 21 in the case of the

■ Fig. 49. Icarosaurus (Squamata; Upper Triassic; length ca. 30 cm). (After Wellnhofer 1991)

Coelurosauravidae. The wings would, therefore, have been relatively narrower in these Mesozoic forms,than they were in the Upper Permian gliding reptiles.

A similar development of the ribs to support a gliding membrane or pata-gium is seen in the modern Draco volans (Agamidae) and related species. In Draco, the five to seven pairs of elongated limbs are usually kept folded, but are spread apart when the animals are gliding. These lizards inhabit the rainforests of Indonesia and feed upon ants and other insects living on the trunks of the tall trees: they eat whilst climbing up one tree and then glide, swiftly and safely, to another. Distances of up to 60 m, have been recorded from a starting height of only 10 m (Evans 1982).Not only does gliding flight save energy,but it enables the lizards to avoid walking across the potentially dangerous floor of the forest. Moreover, the patagium is brightly coloured, and aids camouflage by disrupting the outlines of the creatures. The same was probably true in the case of the Permian and Triassic forms discussed above.

Fossils of an Upper Triassic reptile, Sharovipteryx mirabilis (Fig. 50d) (Squa-mata) show that this, too, was a glider - although somewhat different in form from those already described. It was slender, with a relatively long neck and extremely elongated hind legs and tail. Its hind limbs were more than three times the length of the forelegs. Their proportions exceeded those of modern agamid lizards which run and jump with the trunk elevated so that the front legs may, or may not, touch the ground between strides (Cloudsley-Thompson 1999). This gives a clue as to the probable evolutionary origin of the flight mechanism. The main gliding membrane stretched between the hind limbs and the tail. The long

■ Fig. 50a-d. Gliding lizards (Squamata). a Coelurosauravis (Upper Permian; length ca. 60 cm), b Kuehneosaurus (Upper Jurassic; length ca. 75 cm), c Icarosaurus (Upper Triassic; length ca. 30 cm), d Sharovipteryx (Lower Triassic; length ca. 25 cm). (After Wellnhofer 1991)
■ Fig. 51. Longisquama (?Pseudosuchia; Upper Triassic; length ca. 15 cm)

tail would have balanced that part of the body extending in front of the membrane. Narrow gliding membranes may well have also been present behind the forelimbs. Although Sharovipteryx would not have been able to flap its leg membranes like wings, it could well have glided with the forelimbs stretched slightly forward and the back legs spread out at right angles to the body.

Another curious gliding reptile, described by A.B. Sharov in 1970 from the Late Triassic of Kirghistan, was Longisquama (Fig. 51). The enormously elongated, scale-like appendages along its back were actually longer than the body and were arranged in a double row. They could apparently have been held upwards like the wings of a butterfly, or folded down along the sides of the body to form horizontal gliding surfaces. Each individual appendage consisted of a long, thin shaft that broadened towards the distal end and bent backwards. Each pair of these appendages probably corresponded to a dorsal vertebra. The ten pairs of appendages, overlapping at their edges, would have created continuous wing surfaces. Longisquama appears to have been a pseudosu-chian, and was therefore completely unrelated to the other Mesozoic gliding reptiles discussed above. It acquired its aerial abilities by parallel evolution. The suggestion has been made that the appendages might also have been thermoregulatory devices like those of some pelycosaurs (Sect. 2.5), or display structures that were used to attract mates and threaten rivals. Evans (1982) commented that, if Sharov's description is correct, then any resemblances between Longisquama and the Upper Permian flying reptiles must be due to con vergence, as indeed is the resemblance between them and Sharovipteryx, the other Triassic gliding reptiles, and modern Draco spp.

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  • rossana piazza
    What did kuehneosaurus eat?
    9 years ago

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