Lower Cretaceous Dinosaurs

Australia: The Land Where Time Began

Lower Cretaceous Dinosaurs

Footprints, a few partial skeletons and many isolated bones are all the dinosaur remains that are known from the Early Cretaceous of Australia. The known remains, though patchy, have been sufficient to indicate a considerable degree of faunal diversity and what the authors¹ describe as 'enigmatic biogeographical relationships'. On eroded wave-cut platforms of the Broome Sandstone, in the Carnarvon Basin, along the west coast near Broome, northwestern Western Australia, there are exposed dinosaur trackways from the Berriasian. The tracks were made in the sediments of a wetland that became the Broome Sandstone. There are many footprints that represent a variety of dinosaurs such as sauropods, such as Brontopus, that the authors³ suggest maybe attributable to brachisaurids, ornithopods that were large, iguanodontian, and small ornithopods (Wintonopus), large theropods (Megalosauropus broomensis), and footprints from an animal with 5-toed forefeet and 3-toed hindfeet that in North America would indicate a stegosaurus, this pattern being characteristic of stegosaurs. The Broome Sandstone is considered to be highly significant because of the extreme rarity of stegosaurus from the Cretaceous. Some of the herbivorous dinosaurs making the footprints were very large, the sauropod footprints being up to 1.5 m wide, suggesting an animal more than 40 m long. The ornithopod footprints are up to 800 mm long.

A single phalanx (toe bone) of a theropod has been found in the Birdrong Sandstone. In the Gippsland Basin in southern Victoria an array of taxa that was much more diverse was found in the Wonthaggi Formation that included:

Many small herbivorous ornithopods such as Quantassaurus intrepidus, Atlascopcosaurus loadsi, Fulgurotherium australae and Leaellynasaura amicagraphica, of which the last 3 survived until the Albian;

An astragalus (ankle bone) that the authors¹ suggest could be from Australovenator, a recently described theropod from Australia;

a possible ornithomimid - an herbivorous dinosaur that had an ostrich-like appearance;

The ulna of an apparent neoceratopsian, Serendipaceratops arthurcclarkei, dinosaurs with horns such as the Protoceratops from Mongolia;

The authors¹ suggest that as the ornithomimids and neoceratopsians are mostly known from the Jurassic-Cretaceous in North America and Asia their presence in Australia would imply faunal exchanges occurred periodically during the Mesozoic between Australia and North America and between Asia and Australia. There are doubts about the affinities of some of these isolated bones, alternative interpretations suggesting similarities with dinosaurs from Gondwana, South America in particular.

In the Wallumbilla Formation at White Cliffs, New South Wales, the Bulldog Shale and the Bungil Formation near Roma, southern Queensland, Aptian age dinosaur fossils have been found. In the Wallumbilla Formation and Bulldog Shale indeterminate ornithopods (ankle and toe bones, Coober Pedy) of medium size have been found, and at Andamooka, small theropods (limb bones, vertebra, phalanx) and at White Cliffs a phalanx. Kakuru kujani, the only taxon to be named, was a theropod that was very bird-like based on an opalised tibia and fibula (shinbone) and phalanx from Andamooka. The holotype of Minmi paravertebra was found in the Bungil Formation. M. paravertebra, an endemic species, was a primitive ankylosaur about 2-3 m long that had a characteristic dermal armour of spines across the neck and imbedded in the skin of its back, and on its belly small circular ossicles in the form a of a pavement.

Small herbivorous ornithopods apparently dominated the dinosaur assemblages of Australia during the Albian. These included Atlascopcosaurus loadsi, Fulgurotherium australae, Leaellynasaura amicagraphica, as well as several species that are yet to be identified, have been reported from the Eumeralla Formation and Griman Creek Formation. In the Griman Creek Formation, Toolebuc Formation, Allaru Mudstone and Mackunda Formation, a large primitive 7 m long iguanodontian, Muttaburrasaurus, was among the ornithopods found. Muttaburrasaurus langdoni is the only species of this genus to be described at the time of writing. An inflated bony nasal structure on its snout is a distinguishing feature that has been suggested to have been used to amplify its vocalisations. It has also been suggested by the authors¹ that the size of this structure may have varied between the sexes. Muttaburrasaurus is believed to have primarily been a quadruped, though it has been suggested to probably reared up on its hind legs to reach higher vegetation. The teeth of this species were blade-like for shearing, unlike those of more advanced iguanodontians that had teeth that formed broad grinding surfaces.

Minmi remains have been found in the Toolebuc Formation and Allaru Mudstone, including a specimen that was extremely well preserved that still had the skull and the chewed fragments of twigs and leaves of it last meal in the area of its stomach. In the Griman Creek Formation and the Eumeralla Formation isolated bones and scutes of ankylosaur armour have been found that are not sufficiently complete to identify them more specifically. A second possible neoceratopsian ulna has been found in the Eumeralla Formation that is more gracile and smaller than that of Serendipaceratops

In the Toolebuc Formation, the Allaru Mudstone and the Griman Creek Formation there are sauropods of Albian age. Austrosaurus mckillopi an ambiguous titanosaurian, based on a few dorsal vertebrae that were incomplete, is the species to which the material in the Allaru Formation, i have been assigned. Isolated teeth and tail vertebrae in the Griman Creek Formation, Lightning Ridge, also indicate the presence of titanosauriforms. In the Toolebuc Formation a partial vertebra from the neck that was found near Hughenden, central Queensland, has been suggested by the authors¹ to possibly be from a brachiosaurid.

Isolated bones from the Albian of a possible oviraptorosaur (ceanagnathid) have been found in Australia, as have an ulna that resembles that of Megaraptor, a theropod from South America, and a femur (thighbone) of Timimus hermani, a putative ornithomimid were all found in the area around Dinosaur Cove in the Eumeralla Formation. These are all controversial, as are a number of dinosaurs from Victoria with some workers preferring they be assigned as indeterminate members of higher-level groups. In the Eumeralla Formation and the Griman Creek Formation many teeth and large claws have been found that have been attributed to dinosaurs that are dromaeosaurid-like being very similar to the well-known Velociraptor. An opalised theropod metatarsal about 250 mm long, the tail vertebra of Walgettosuchus woodwardi, that is now considered to be taxonomically invalid, and an unusual metacarpal (finger bone) that has been assigned to Raptor ornitholestoides, from a predator estimated to be about 5 m long have been found in the Griman Creek Formation. It was given its specific name based on its structural similarity to Ornitholestes, a coelurosaurian from North America.

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