Gondwana: A Dinosaur Eden?



Although dinosaur remains from Australia are nowhere near as numerous or as well preserved as some other countries, what has been discovered has provided a tantalising glimpse of what Australia's Mesozoic past may have been like. For much of the latter parts of the Mesozoic Era Australia was a relatively isolated peninsular connected to the rest of Gondwana only in the extreme polar regions. During much of the Early Cretaceous period high sea levels had separated the Australian continent further into a series of large island landmasses, adding further to it's geographic isolation. Both islands and peninsulars are known for their effects in isolating animal populations and resulting in strange and unique groups of animals evolving. Once the Australian continent broke free of Antarctica towards the end of the reign of dinosaurs it became even more isolated. Being surrounded by sea and cut off biologically from the rest of the world has resulted in Australia's unique modern flora and fauna - a land of pouched marsupials and egg-laying monotremes.

Continental Plates 106 MYA
Land bridges connected many of these continental plates together

It would seem that even in Mesozoic times the Australian fauna was just as unusual, except that hundreds of millions of years ago it was a range of strange and unique dinosaurs that dominated the land instead of strange and unique mammals. Several, albeit fragmentary, finds from Australia's Mesozoic past have challenged theories on the origins and extinction of various Mesozoic animal groups.

"Too Early - and in the Wrong Place"


Nomingia The oviraptorosaurs were a group of strange-looking theropod dinosaurs that are mostly known from the Late Cretaceous, and almost exclusively from the Northern Hemisphere. With their strange beaked parrot-like heads, coupled with large curved predatory claws on often long forelimbs, researchers are still unsure exactly what these dinosaurs ate or how they lived. Their sharp claws suggest a predatory nature, but toothless beaked mouths would seem to be ill equipped for tearing off or chewing chunks of meat. One oviraptorosaur, named Nomingia gobiensis from Mongolia, even had a hyper-reduced tail that ended with a fused pygostyle-like section reminiscent of the shortened, stiffened tail of birds. It would seem that oviraptorosaurs in general were a strange lot indeed.

Traditional theories have the oviraptorosaurs arising some time during the Early Cretaceous in the Northern Hemisphere, and diversifying by the Late Cretaceous. However evidence from Australia and South America, predating almost all other known oviraptorosaur material, are beginning to suggest that these theropod dinosaurs may have had a Gondwanan, Southern Hemisphere origin.

Caenagnathid A possible caenagnathid lower jaw fragment (right surangular, NMV P186386) and an oviraptorosaur vertebra (NMV P186302) were found at Dinosaur Cove in Southern Victoria (Otway ranges), dating to around 106 MYA. The jaw fragment shows similarities with that of dromaeosaurs, but is closer to that of caenagnathid oviraptorosaurs due to a pronounced medial inflection of the coronoid process. The isolated vertebra also shares some dromaeosaur and oviraptorosaur features, such as single pleurocoels on each side of the dorsal centrum (most other theropod groups have paired pleurocoels).

The poorly known theropod Kakuru kujani, known only from a single tibia (lower leg bone) from the Early Cretaceous of South Australia, may also have been related to the oviraptorosaurs. Re-evaluation of the material suggests a marked similarity to that of Ingenia yanshi, an oviraptorosaur from the Late Cretaceous of Mongolia. Although all of the possible Australian oviraptorosaur material is fragmentary at best, the animals being known only by isolated bones, it would seem that the evidence for a Gondwanan origin for these dinosaurs is becoming more compelling with each new find (which now includes early oviraptorosaur-like material from South America, another Gondwanan country).

Leptoceratops The Ceratopians are another group of mostly Late Cretaceous Northern Hemisphere dinosaurs that may also prove to be of Gondwanan origin. The traditional theory sees them evolving from the Early Cretaceous Psittacosaurids in Asia, into forms such as Protoceratops, and onward into the larger horned ceratopian species such as Triceratops. Both advanced ceratopians and their more primitive protoceratopian cousins migrated from Asia into North America via the Berring Strait land bridge. This theory fit nicely with the Psittacosaurus-Protoceratops-"advanced ceratopian" fossil sequence. Unfortunately Australia has once again yielded evidence that could shatter this nice neat theory.

In 1994 a fossil ulna (lower arm bone) was described by Drs Tom Rich and Patricia Vickers-Rich, after having been found in Early Cretaceous (115 MYA) deposits in the Strzelecki group in Victoria a few years earlier. While in North America the two palaeontologists showed the ulna to several ceratopian experts. When laid next to the ulna of Leptoceratops gracilis from the Late Cretaceous (Maastrichtian) of Canada, it was generally agreed that the two bore a striking resemblence.


Click the image for a close-up of the Australian bone

The bone itself is about 16 centimetres long and is missing the olecranon process (otherwise known as the "funny bone"). Like all ceratopian ulnae it is short and deep, and is mediolaterally flattened. No other known type of dinosaur has an ulna like this, although it can not be ruled out that the Australian specimen may represent an as-yet unknown type of dinosaur that was found only in Australia, and that came to resemble ceratopians in at least this particular bone by chance. This latter explanation, although possible, would be an extreme case of evolutionary convergence.

The Australian bone, if it is ceratopian, presents a problem. The earliest neoceratopian, Protoceratops andrewsi from Monglia, first appears in the fossil record about 30 million years after the date for the Australian material. Leptoceratops itself, which this bone most closely resembles, comes from the latest Late Cretaceous about 65 million years ago, which is around 50 million years later than the Australian bone. If the Australian material is accepted as ceratopian then it would place the origins of the neoceratopia much earlier than once thought, on the opposite side of the planet, and may cast doubt on the Psittacosaurid origin of these horned dinosaurs (since Psittacosaurus lived at the same time as the Australian animal).

Old Timimus reconstruction Ornithomimid-like material has also surfaced within Early Cretaceous Australian deposits. Timimus hermani was once thought to have been an ornithomimid, however its status is now uncertain. Despite this, several extremely ornithomimid-like fragments have been discovered within the Early Cretaceous Victorian rocks. So far a claw, part of a pelvis, and a caudal vertebra from the Flat Rocks site near the town of Inverloch in southern Victoria have been discovered, their ornithomimid status perhaps more certain than the Timimus material.

It was once thought that ornithomimosaurs were another mostly Late Cretaceous Northern Hemisphere group of dinosaurs. However earlier evidence from several Gondwanan countries (such as Australia and Africa) is beginning to suggest a Southern Hemisphere Gondwanan origin for these dinosaurs as well. Recent evidence however may throw this theory into doubt. An undescribed ornithomimosaur from Thailand may well turn out to be Jurassic in age. Possible ornithomimosaur material from both England (Kimmeridge clays) and the United States (Morrison formation) both dated to the Jurassic may indicate that ornithomimosaurs developed earlier than was once thought. If so, then they may pre-date the splitting of Pangaea into Gondwana and Laurasia. This would explain their presence in both Gondwana and Laurasia before their hey-day in the Late Cretaceous, but it would mean that ornithomimosaurs were not strictly of Gondwanan origin (since Gondwana had yet to form at the time).

In 1997 a mammal jaw was found at the Flat Rocks site near the town of Inverloch in south-eastern Victoria. It was subsequently named Ausktribosphenos niktos, and since then the number of lower jaws known has risen to seven, indicating that it was probably a quite common animal. Studies have suggested that the mammal may have belonged to the Erinaceidae, a family of placental mammals that includes modern hedgehogs. If so it is nearly twice as old as the next oldest remains for this family, known only from the Northern Hemisphere. It has been suggested that erinaceids may have rafted northwards on micro-continental plates as they split off from the main Gondwanan continents, suggesting that at least this group of placental mammals may have originated in Gondwana. Another suggestion is that the teeth of these animals came to resemble those of placentals independantly, and they are actually more closely related to monotremes.

It was once thought that placentals originated solely in the Northern Hemisphere, reaching more southerly areas of the planet much later. With Ausktribosphenos dating to around 115 MYA, it suggests that the origin of placental mammals may not have been a strictly Northern Hemisphere event.

"Aren't You Supposed to be Extinct?"

The evidence for early oviraptorosaurs and ceratopians from Australia is based only on isolated, and often poorly preserved, fossils. However there is plenty of evidence that some dinosaur groups, and other animals that lived along side them, were able to continue living in parts of Australia when they had become rare or even extinct in other parts of the world. Hypsilophodontids, small bipedal herbivores, were a common component of the dinosaur fauna during the Jurassic in many parts of the world, however by the Early Cretaceous had become much rarer. In contrast, the Early Cretaceous of Australia was teeming with hypsilophodontid species.

Leaellynasaura Several species have been named so far, including Leaellynasaura, Fulgarotherium, and Qantassaurus. A close relative, Atlascopcosaurus, may prove to be more closely related to the much larger Muttaburrasaurus from Queensland in northern Australia. There are also several other types of hypsilophodontid dinosaur known from the southern Victorian deposits that are so far unnamed. Fulgarotherium itself may contain three or four distinct taxa. So far it seems that there were at least six or more distinct genera of hypsilophodontids in Victoria during the Early Cretaceous, with perhaps several species in each. Whereas hypsies in general were becoming a much rarer component of the dinosaur fauna in other parts of the world after the Jurassic, they seemed to thrive in Australia.

The Mesozoic world didn't just consist of dinosaurs. A whole host of other animals lived along side them, such as crocodiles, the flying pterosaurs, amphibians, and even mammals. One group of amphibians, known as labyrinthodontids, were large crocodile-like animals related to salamanders. They were thought to have become extinct during the Late Permian or Early Triassic periods, even before the first dinosaurs and mammals appeared. However discoveries in Australia proved that here they managed to live on - for a further 120 million years!

Koolasuchus

Siderops is a labyrinthodont amphibian known from the Late Jurassic of Queensland in northern Australia. However the latest survivors appear to have held out until the Early Cretaceous in the southern reaches of Australia. Koolasuchus is known from two large jaw fragments 80 cm long from an animal that would have been around 5 metres in total length - somewhat more fearsome than your average frog. It was found near the town of San Remo in southern Victoria, in rocks that have been dated to around 120 MYA. It is thought that in other parts of the world competition from crocodiles wiped out most labyrinthodont species. However during the Early Cretaceous southern Victoria would have been within the Antarctic circle, making it too cold for crocodiles. The climate seems to have warmed up a tad by 110 MYA though. The remains of crocodiles have been found in these deposits - but no labyrinthodontids. It seems they made their last stand in southern Victoria, some 120 million years after most of their kind became extinct elsewhere. The ever adaptable crocs seem to have won out in the end though, and are still with us today, as diverse a group as ever.

It has been suggested that, given the adaptations that Australian (and New Zealand, Antarctic, etc...) dinosaurs probably had to cold conditions and extended periods of darkness, they may well have hung on in the southern polar regions at a time when dinosaurs in other parts of the world were becoming (or had become) extinct. Certainly, it has been hypothesised that some modern birds may be descended from Gondwanan species that radiated to other parts of the world after the Cretaceous Period. Given that the likely culprit for the Cretaceous-Paleogene extinction event (the "K/Pg extinction") was in the northern hemisphere (the impact crater at Chicxulub, on the Yucatan Peninsular), the extreme south may have remained a haven for dinosaurs, at least for a while. Unfortunately there are few, if any, Late Maastrichtian deposits found in these areas, and what few Late Late Cretaceous material is known usually takes the form of isolated and fragmented pieces.

"Strange and Unique"

There are several types of dinosaur that have so far been found only in Australia, and nowhere else on earth. They are so unique that researchers are having a hard time finding out exactly where they fit on the dinosaur family tree. In some cases it seems that they had no relatives outside of the Australasian region, probably a result of their isolation from the rest of the world. It seems that Australia hasn't changed all that much since then - we still have many animals that are found nowhere else on earth.

Muttaburrasaurus Muttaburrasaurus langdoni was a large seven metre long ornithopod from the Early Cretaceous of Queensland. At first it was classified as an iguanodontid, a group of large spike-thumbed herbivores common during the Early Cretaceous throughout the world. However further study has failed to reveal any characters that would unite Muttaburrasaurus with the likes of Iguanodon.

Muttaburrasaurus had several unusual features. At the front of its snout was an enlarged hollow chamber that may have been used as a resonating chamber for making trumpet-like calls. The back of its skull suggest that it had an unusually strong bite for an ornithopod of this size. Its teeth seem to have been designed for sheering rather than the grinding teeth of most large ornithopods. The entire tooth row seems to have been replaced all at once, rather than teeth being shed and replaced individually as the need arose. The nature of the teeth and jaws has prompted some researchers to suggest that Muttaburrasaurus may have been partially carnivorous, something extremely unusual for an ornithopod dinosaur. It has been suggested that Muttaburrasaurus, and perhaps the smaller (2-3 metre) Atlascopcosaurus loadsi from Victoria, could have belonged to an endemic "Muttaburrasauridae" that was found nowhere else on earth.

Minmi In 1964 a small, three metre long armored dinosaur was discovered in Early Cretaceous rocks in Queensland. In 1980 it was scientifically described, and given the name Minmi paravertebra. Another more complete specimen was discovered in 1990, lacking only parts of the pelvis, the lower parts of both left limbs, and the tip of the tail. The armored spikes, plates and scutes that were embedded in its skin were also preserved.

Minmi has two features not found in any other dinosaur. Firstly, although many armored dinosaurs had bony scutes embedded within their skin, Minmi is the only one known to have had armor across its belly. Secondly, the spine of Minmi was interlocked and reinforced by bony projections called paravertebrae. Not only is Minmi the only well known armored dinosaur found in the southern hemisphere, it is also one of the smallest. No-one quite knows how Minmi fits in with the other armored dinosaurs. It has features in common with both the ankylosaurs and the nodosaurs, and some features that neither of the two existing groups had. It is likely that it will be assigned to a group all of its own, perhaps somewhat closer to ankylosaurs than nodosaurs. Remains of similar dinosaurs have been found in New Zealand and Antarctica, both of which were close Gondwanan neighbours.

Ozraptor subutaii was a two metre long theropod dinosaur known from the Mid Jurassic of Western Australia. It is known only from the end of the tibia (the "shin bone"), although the articular surface at the bottom is unique enough to warrant its own scientific name. Some researchers feel that Ozraptor may have been a primitive dromaeosaur, the family of dinosaurs that includes Velociraptor mongoliensis. If so it would not only make this dinosaur the oldest known dromaeosaur, but also one of the oldest known coelurosaurs.

"Business as Usual"

Modern Australia is now an island continent, even more cut off from the rest of the world that it was during the Cretaceous period. As a result it still remains a refuge for animals and plants that have become rare or extinct in other parts of the world. Whereas marsupials, mammals that give birth to extremely under developed young and nurse them in a pouch, are rare in other parts of the world, they are the dominant mammalian form in Australia. Of the three known species of monotremes (egg laying mammals) in the world, two live only in Australia: the platypus and the echidna. A third species, a giant form of long-haired echidna, lives in Papua New Guinea, a close neighbour that only became detached from the continent when sea levels rose about 10,000 years ago. Platypus fossils are known to date back to the Early Cretaceous, some 100 million years ago or more, making it one of the oldest known mammal families still alive today.

The lungfish Neoceratodus that still inhabits rivers in Queensland today is virtually unchanged from its ancient ancestors. Lungfish tooth plates are known from several Early Cretaceous fossil sites in Australia, alongside the remains of dinosaurs. It has changed little in form for about 500 million years.

During the early 1990s a tree was discovered in the Blue Mountains of New South Wales that has no living relatives today. The Wollemi pine is virtually identicle to Wollemia nobilis, an ancient species of tree that was thought to have become extinct some 120 million years ago. It now grows naturally in only three moist, shaded canyons at a secret location in the Blue Mountains. All of the forty known adult trees are genetically identical, perhaps suggesting that at one point there was only one left. As well as reproducing via seed, they can also send out suckers from their roots, that grow to become adult trees of their own. The Royal Botanic Gardens in Sydney did test planting's in the open plain to see if it could exist outside of a moist shaded canyon atmosphere and confirmed in Sydney Newspapers it will grow in a drier open climate. In years to come the rare tree may well become a common feature in parks and gardens around the world. It has already become established in several parks around Sydney, with commercial release of the plant to the public expected around 2005. The tree itself may also be a haven for ancient lifeforms that live nowhere else. Already two new strains of fungus have been discovered growing on its leaves, one of which produces a potent anti-cancer drug. Dr Tim Flannery of the Australian Museum has suggested that there may be ancient species of invertebrates (such as insects) living in the tree that are unknown to science.

A survey in Western Port Bay, in Victoria, during March 2002 discovered a living colony of brachiopod shellfish known as "lamp shells", due to their resemblance to Roman oil lamps. One of the last few living colonies, these shellfish have a 500 million year history in the fossil record. They were discovered in an area that has been proposed as a protected marine park. Their discovery will pretty much ensure the protected status of the waters in the area from now on.

References

Currie, P.J., P.Vickers-Rich and T.H.Rich 1996 Possible oviraptorosaur (Theropoda, Dinosauria) specimens from the Early Cretaceous Otway Group of Dinosaur Cove, Victoria. Alcheringa 20:73-79

Frankfurt, N.G. and L.M.Chiappe 1999 A possible oviraptorosaur from the Late Cretaceous of Northwestern Argentina. Journal of Vertebrate Palaeontology 19(1):101-105.

Long, J.A. 1998 Dinosaurs of Australia and New Zealand, and other animals of the Mesozoic Era. University of New South Wales Press, Sydney.

Long, J.A. and R.E.Molnar 1998 Ozraptor, gen. nov., a new Jurassic theropod dinosaur from Western Australia. Records of the Western Australian Museum 19.

Mackovicky, P.J. 1997 A new small theropod from the Morrison Formation of Como Bluff, Wyoming. Journal of Vertebrate Palaeontology 17:755-757.

Molnar, R.E. 1995 Possible convergence in the jaw mechanisms of ceratopians and Murraburrasaurus. In A.Sun and Y.Wang (eds) Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota, short papers. China Ocean Press, Beijing. pp.115-117.

Molnar, R.E. 1996 Observations on the Australian ornithopod dinosaur, Muttaburrasaurus. Memoirs of the Queensland Museum 39(3):639-652

Molnar, R.E. 1996 Preliminary report on a new ankylosaur from the Early Cretaceous of Queensland, Australia. Memoirs of the Queensland Museum 39(3):653-668

Molnar, R.E. and N.S.Pledge 1980 A new theropod dinosaur from South Australia. Alcheringa 4:281-287.

Rich, P.V. and T.H.Rich 1999 Wildlife of Gondwana. The 500-million year history of vertebrate animals from the ancient southern supercontinent. Second Edition. Reed books, Sydney.

Rich, T.H. 1996 Significance of Polar Dinosaurs in Gondwana. Memoirs of the Queensland Museum 39(3):711-717

Rich, T.H. and P.Vickers-Rich 1994 Neoceratopsians and ornithomimosaurs: dinosaurs of Gondwanan origin? Research and Exploration 10:129-131.

Vickers-Rich, P. and T.H.Rich 1991. The dinosaurs of winter. Natural History, 32-37.

Vickers-Rich, P., and T.H.Rich 1993 Australia's polar dinosaurs. Scientific American 269(1):50-55.

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