Australia: The Land Where Time Began

A biography of the Australian continent 

Lower Cretaceous Sea Turtles

In the Toolebuc Formation and Allaru Mudstone sea turtles, chelonioidea, from the Lower Cretaceous have been found, being among the commonest of the reptile fossils in these deposits. Of the 3 distinct types that have been named all appear to be members of the Protostegidae, a widespread family in the Cretaceous.

Notochelone costata was the first to be described. Based on a partial carapace, plastron, and elements of limb girdle from an unknown locality Sir Richard Owen described it in 1882. Small body size, less than 1 m, and a low keel along the midline of the carapace characterise the Notochelone.

Bouliachelys suteri, that was slightly larger than N. costata, was found in the deposits of the Toolebuc Formation around Boulia in western Queensland. Bouliachelys has been determined to be a primitive chelonioid that is believed to be close to the base of the radiation of the protostegids, based on several skulls and some complete shells with associated limb elements. It is suggested to have eaten hard-shelled prey as it had prominent crushing ridges on the palate of its robust skull and a hooked beak that was serrated. In the gut area of several fossils of Bouliachelys what is believed to be the gut contents of the animals have consisted almost entirely of the crushed shell fragments of the inoceramid bivalves.

Cratochelone berneyi, the rarest known sea turtle from the Early Cretaceous of Australia was also the largest of the known Australian sea turtles from this time. It was named based on an associated humerus that was fragmentary, a plastron and pectoral limb girdle that were found on Sylvania Station near Hughenden in central-northern Queensland. It was estimated to be about 4 m long when its remains were compared to those of large sea turtles from North America of Late Cretaceous age. It has been suggested that Cratochelone probably had metabolic levels that were augmented as are those of the modern leatherback turtles and probably had similar pelagic habits to them.

As the known Australian fossil of Cratochelone is the only Australian sea turtle that has been found as a single specimen it has been suggested that it was probably not a normal inhabitant the shallow Australian inland sea, possibly occasionally straying into this environment from open ocean.

Sources & Further reading

1. Kear, B.P. & Hamilton-Bruce, R.J., 2011, Dinosaurs in Australia, Mesozoic life from the southern continent, CSIRO Publishing.