Mythunga camara

Introduction

Mythunga camara was a primitive, Early Cretaceous pterodactyl from north-central Queensland. Pterodactyls, including the crested, toothless Pteranodon, were one of two pterosaur suborders. Mythunga, Australia's only named pterosaur and one of the largest from Australasia, is represented by the most complete pterosaur skull known from the region. Mythunga had an unusual skull, with a hollow, box-like snout and large, widely spaced teeth.

Identification

Pterosaurs were winged diapsid reptiles that developed powered flight independently of birds and bats. Characteristic openings in their skulls place them within Archosauria, the group that also includes dinosaurs, crocodiles and thecodonts. Pterosaurs had large skulls (with bony bars or struts), well developed cervical (neck) vertebrae, greatly enlarged pectoral (shoulder) girdles, enlarged forelimbs developed into wings, small trunks and weakly developed hind limbs. Eyes were generally large and protected by bony (sclerotic) rings. Pterosaurs must have had excellent eyesight, but evidence from brain casts indicates a poor sense of smell. The primary difference between pterodactyloids and the older rhamphorhynchoids (the other subclass of pterosaurs) is tail length: pterodactyloids were short-tailed and rhamphorhynchoids were long-tailed.

Mythunga was a large pterodactyl known only from the anterior part of an unusual toothed skull. Unique features include large posterior dentary teeth, dentary and maxillary teeth spaced widely apart that would have interlocked in life (there are just three maxillary teeth between the last enlarged tooth and the nasopreorbital opening), and a unique combination of other anatomical characters. The top of the snout is lost, and it is not known whether Mythunga had a crest as in Pteranodon. The internal structure of the snout is hollow and box-like, with thin-walled chambers separated by struts. The jaws are hollow, evidence that pterosaur skulls and jaws were made up of hollow boxes and tubes. Few pterosaur fossils are preserved because of their extremely light, hollow bones. Mythunga is not an advanced pterodactyl; it was not edentulous (toothless) and did not have a deep or curved snout, features seen in more advanced members of the group.

Although there are no postcranial fossils of Mythunga, it would have had wings formed by a thin skin membrane supported by a greatly elongated fourth finger, as in other pterosaurs, and a short tail, as in other pterodactyls.

Its name is derived from a western Queensland Aboriginal word for star and hunter of the skies.

Habitat

Mythunga lived near the coast of the epicontinental Eromanga Sea, gliding on the air currents above the coast and diving down to snap up fish, as some large sea birds do today. This inland sea was a cool, clear body of water covering vast areas of central Australia during the Early Cretaceous. Adjacent land was forested with araucarian conifers and podocarps, and the climate was cool-temperate and seasonal. Associated with the skull of Mythunga were fragmentary ichthyosaur remains, ammonites and other molluscs.

Distribution

Mythunga was found on Dunluce Station near Hughenden, north-central Queensland. Other Australasian pterosaurs have been discovered in Queensland, Victoria, New South Wales, Western Australia and New Zealand.

Feeding and diet

The interlocking teeth of Mythunga are typical of pterosaurs that fed on fish. The wide spacing between the teeth may have been an adaptation to feed on large fish.

Life history cycle

Pterosaurs are thought to have roosted and nested on rocks or cliffs near water bodies (often near the ocean or on islands), feeding mainly on fish or marine invertebrates (including tiny crustaceans) that were caught on the wing. Flight was accomplished by powered, flapping flight. The large, short-tailed Cretaceous pterosaurs were capable of gliding or soaring over long distances. Locomotory studies show that pterosaurs probably used all four limbs when moving on the ground, rather than using the back legs in a bipedal manner.

Fossils description

The partial skull of Mythunga wasdiscovered in 1991 by Philip Gilmore on Dunluce Station (part of the Toolebuc Formation, a marine formation that once formed the shallow floor of the Eromanga Sea). One-third to one-half of the skull and lower jaws is preserved. Although it represents a large individual, the material may be that of a juvenile; if so, adult Mythunga would have been even larger. The holotype skull of Mythunga is held by the Queensland Museum in Brisbane.

In spite of its fragmentary nature, Mythunga is the most complete pterosaur known from Australasia, in large part because the lightly built pterosaurs did not fossilize well. There are now three pterosaurs from the Early Cretaceous of Queensland: in addition to Mythunga, there is a possible anhanguerid and a pterosaur similar in form to Lonchodectes, both from the Toolebuc Formation near Boulia (Warra Station and Elizabeth Springs). Fragmentary pterosaur fossils from the Early Cretaceous of Victoria (Dinosaur Cove) and from the Late Cretaceous of Western Australia (Giralia Range) and New Zealand (Mangahuanga Stream, Hawkes Bay) have also been found.

Evolutionary relationships

The relationships of pterosaurs are difficult to determine because pterosaur material is usually fragmentary and often incomplete. Pterosaurs are archosaurs, the group to which dinosaurs (and therefore birds), crocodiles and thecodonts also belong. The first pterosaurs may have evolved from a small, tree-dwelling reptile that developed a gliding membrane and elongated fingers (the fourth digit) to support the membrane (the hypothetical 'propterosaur'). This view takes a 'trees-down' view of pterosaur evolution. The alternate view is that pterosaurs evolved from a ground-dwelling reptile (the 'ground-up' hypothesis). The debate is thus much like that surrounding the evolution of flight in birds. Both sides generally agree that archosaurs were descended from an eosuchian (a small reptile from the Permian era). Like bats, pterosaurs first appear in the fossil record filly fledged; there are no 'missing links' or transitional fossils. Pterodactyloidea probably descended from a branch of the Rhamphorhynchoidea (the earlier Triassic-Jurassic subclass of pterosaurs) during the Jurassic.

An analysis of the fragmentary skull of Mythunga camara suggests that it represents a unique new group, not closely related to known pterodactyls like Pteranodon or Ornithocheirus. It is provisionally placed as an archaeopterodactyloid, the most primitive members of the suborder Pterodactyloidea. This group is not generally known from the Early Cretaceous although they have recently been found in Early Cretaceous deposits from Liaoning, China.

References

• Bennett, S. C. and Long, J. A., 1991a. A large pterodactyloid from the Late Cretaceous (Late Maastrichtian) of Western Australia. Records of the Western Australian Museum 15, 435-443.
• Molnar, R. E., 1987. A pterosaur pelvis from Western Australia. Alcheringa 11, 87-94.
• Molnar, R. E. and Thulborn, R. A. 1980. First pterosaur from Australia. Nature 288, 361-363.
• Molnar, R. E. and Wiffen, J. 1994. A Late Cretaceous polar dinosaur fauna from New Zealand. Cretaceous Research 15, 689-706.
• Molnar, R. E. and Thulborn, R. A. 2007. An incomplete pterosaur skull from the Cretaceous of north-central Queensland, Australia. Arquivos so Museo Nacional, Rio de Janeiro, v. 65, No. 4, 461-470.
• Padian, K. 1984. The origin of pterosaurs. Pp. 163-168 in Third Symposium on Mesozoic Terrestrial Ecosystems. Reif, W. E. and Westphal, F. (eds). Tübingen, Attempto Verlag.
• Rich, T. H. and Rich, P. V., 1989. Polar dinosaurs and biotas of the Early Cretaceous of southeastern Australia. National Geographic Research 5, 15-53.
• Wiffen, J. and Molnar, R. E., 1988. First pterosaur from New Zealand. Alcheringa12, 53-59.

Further reading

• P. Wellenhofer. 1991. The Illustrated Encyclopedia of Pterosaurs by Salamander Books, London, 191 pp.
• Evolution and Paleobiology of Pterosaurs. E. Buffetaut and J. M. Martin (eds). Geological Society Special Publications 217, London.
• J. A. Long. 1998. Dinosaurs of Australia and New Zealand and Other Animals of the Mesozoic Era. New South Wales University Press, Sydney.