Australia: The Land Where Time Began
Winton Formation - Early Cretaceous - 98-95 Ma
This consists of sedimentary rocks, sandstone, siltstone and claystone that cover large areas of central western Queensland between Boulia in the west to Maxwelton in the east and south into northeastern South Australia and northern New South Wales. The rocks were formed on a riverine plane in the Eromanga Basin as the Eromanga Sea retreated. The different type of sediments were deposited in different environments on the plain, large meandering rivers, lakes, forest pools, swamps, coastal estuaries. It has been estimated that the rivers must have been huge, on the scale of the Amazon or the Mississippi, to deposit so much sediment in this part of the Eromanga Basin, sufficient to fill the basin with so much sediments that by 95 million years ago the Eromanga Sea was forced to retreat for the last time. In places the deposits are as much as 400 m thick. It is one of the richest areas for dinosaur fossils in Australia, because of the environmental conditions present when the deposits were laid down.
As the sea retreated river systems from the south and east formed vast floodplains. The waters of this delta system left fossils of lungfish, sharks, crocodiles, many teeth of which have been found in the sediments associated with the remains of Eliot. Near Isisford, south of Longreach, crocodilian fossils have been found. Because of the hard lime-rich sandstone the bones are preserved in, cleaning the fossil is slow and difficult.
The first remains of this animal were found on Clutha Station near Maxwelton in western Queensland. The remains are fragmentary, but it is estimated to have been more than about 15 m long. It appears to have been a typical sauropod with a small head on a long neck, with a large body on the typical sauropod trunk-like legs. It's hand was unusually elongated, suggesting it may have walked almost on its finger tips, leading to the speculation that it had great vertical reach, possibly feeding high in the trees. It has a similar arrangement of front legs and neck to brachiosaurids, but it is believed to have been more closely related to titanosaurids.
The remains of a sauropod about 20 m long have been found on a sheep station near Winton, central western Queensland, nicknamed Elliot. Nearby was a smaller dinosaur of the the same type, but a juvenile, suggesting Eliot may have been its mother, but further excavation is needed to make the situation clearer. Some teeth from carnivorous dinosaurs were found among the remains of Eliot, possibly from scavengers.
Also found at the site were seed cones from Redwood trees and the leaves of Auaucaria pines, some ginkgo leaves and flowering plants.
A fossil beetle was also found.
Metaceratodus wollastoni, Upper Cretaceous
Isisfordia duncani, at 98-95 million years ago, is the oldest known modern crocodile (eusuchian crocodyliform). It is believed to be a semi-aquatic ambush predator about 1.1 m long, living in the swamps and lakes of the vast riverine plains that formed following the retreat of the Eromanga Sea. It is 20 million years older than the first known appearance of alligators and gharials in the fossil record, and more than 30 million years older than the next oldest known true crocodile. Before the discovery of Isisfordia it had been believed that crocodiles first appeared in Europe or North America. It now seems they may have actually arisen in Gondwana. It is believed that Isisfordia probably ate any type of animal up to its own size, as do modern crocodiles.
There were also dinosaurs, titanosauriform sauropods, theropods, and small ornithopods. Their tracks can be seen at Lark Quarry.
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading|