Fossils of the Winton Formation

Queensland Museum

The Winton Formation has revealed much about other animals living in Queensland’s Cretaceous environment. The freshwater lake and stream deposits have yielded lungfish, turtles and the bony fish, Cladocyclus. A crocodile skeleton found near the town of Isisford, in central western Queensland, is the oldest and most complete known from Australia.  Named for the town where it was discovered, Isisfordia duncani, is among the most complete fossil crocodiles known.

Isisfordia duncani
Isisfordia duncani is a small crocodile from the Cretaceous Period. Its fossil was discovered in the town of Isisford in western Queensland. The Winton Formation has reveled much about animals living in Queensland's Cretaceous environment.

A fossilised skull of Isisfordia duncani, a small crocodile from the Cretaceous Period of western Queensland. The snout is more elongated than the modern crocodiles and the skull structure is also different, however, Isisfordia belonged to a group that was ancestral to all modern crocodiles.

Lungfish

Lungfish have existed since the Age of the Fishes during the Devonian Period, more than 400 million years ago, when these animals underwent a rapid radiation. As a group, lungfish are considered to be closely related to coelacanths (rare, lobe-finned fish dating to the Devonian), and to tetrapods, the group of vertebrates that gave rise to land-based animals.

Image: Toothplate of the lungfish, Metaceratodus wollastoni. Lungfish are a common element in the freshwater fauna of the Winton Formation.

There are three living genera of lungfish – Protopterus in Africa, Lepidosiren in South America, and Neoceratodus in Australia. Analysis of molecular data and fossil evidence suggests the South American and African groups split during the Cretaceous Period and this is consistent with the time that geologists believe these two land masses separated.

Early in their evolutionary history, lungfish evolved a successful body plan and life strategy. As a result, their basic body plan has remained relatively consistent, leading to their being described as 'living fossils'.

During their long history, lungfish have been well adapted to their environments. The main evidence of evolutionary change is in their fan-like tooth plates, which they use to crush food. Depending on the time period and species, lungfish tooth plates vary in appearance and can be used to distinguish different species.

Lungfish have highly distinctive teeth and this is often the only part of the animal that is found in the fossil record. This specimen is from sedimentary rocks at Riversleigh, and dates to the Miocene in the Cenozoic Period.

Turtles

Three turtles – Bouliachelys suteri, Notochelone costata, and Cratochelone berneyi are known from Queensland’s Cretaceous seas. The largest, Cratochelone was similar in size to a modern Leatherback Turtle at more than 2m long. Notochelone costata was about the size of a modern Green Turtle, and Bouliachelys suteri was similar to a modern Loggerhead Turtle. Fossil droppings (coprolites) found within the body cavity of Notochelone indicate that it ate Inoceramus bivalves.

Image: Skull and lower jaw of Notochelone costata.
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Skull Notochelone sp.
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Skull of Bouliachelys suteri. The early Cretaceous seas of Queensland have some of the earliest sea turtles known. This turtle was first discovered near Hughenden, in north Queensland.
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Bony fish

More than 11 genera of bony fish have been identified from fossil deposits and species from Queensland include: Pachyrhizodus marathonensis and Cooyoo australis.

Image: Cooyoo australis, skull and skeleton. This specimen is in resin, which supports the fragile bones during extraction and also preserves the original alignment of the fish in the rock.

The largest known bony fish is the marlin-like, Cooyoo australis, a powerful predator that grew up to about 3m, but the most common pelagic fish was probably the tuna-like Pachyrhizodus. The largest species of this genus was Pachyrhizodus marathonensis, which exceeded 1.5m in length.

Bony fishes, which have evolved in the Paleozoic Era, radiated strongly through the Mesozoic, along side sharks which have skeletons of cartilage. Many new species evolved in the shallow seas produced by the global sea level changes and this also occurred in the Cretaceous seas of Queensland.

Image: Unidentified bony fish
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Credits: Story

Images and text from: In Search of Ancient Queensland.
Principal Authors: Dr Alex Cook and Dr Andrew Rozefelds.
Published by the Queensland Museum, 2015.
Photographer: Peter Waddington

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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