Dinosaur Trackways in Western Australia (2)

In late June and early July 1997, Tony Thulborn, Giuseppe Leonardi (Naples) and Tim Hamley (Dr Thulborn's part-time student-assistant) made a trip to Broome, Western Australia, where they discovered thousands of dinosaur footprints in the Lower Cretaceous Broome sandstone along the coastline.

The stretch of coastline had been swept clean by the last cyclone (called a hurricane in the Northern Hemisphere) to reveal an Early Cretaceous land-surface virtually intact, with the original topography, channels and hillocks, tree-stumps and root systems in their position of growth. Footprints included sauropods, ornithopods, theropods and some mystery items including supposed ?stegosaur tracks. Photographs and latex peels were made where possible, although only on a small scale.

A brief summary of the previously known Broome tracks, with emphasis on sauropods, was published in the journal Gaia, volume 10, 1994. Some scientists thought that aspects of the account were exaggerated, such as unusually big sauropod prints (up to 1.5 m long), the exceptional diversity (at least 10 different types of track-makers), and the co-occurrence of sauropod and ornithopod tracks (sometimes thought to be ecologically separated).

On returning to Broome they told Paul Foulkes (a naturalist) of the sites, who set off to see for himself. He returned, reporting that he'd found even more newly-uncovered tracks.

At a conference in Perth, the following week, the discovery was discussed within earshot of a stray reporter. As a result newspaper reports had the find as a single unbroken dinosaur "highway" 80km long. Although the footprint sites (plural) do extend over 80 to 100 km of coast, it is NOT a single exposure or one continuous trackway surface. It is a series of sites, many of them rather small, with (sometimes vast) stretches of beach between them. The sites don't all seem to be at the same stratigraphic level and they appear to represent a variety of environments (forest, swamp, lagoon, fluviatile/deltaic) each with its own distinctive suite of dinosaur track types. The newly-exposed sites seem to represent fairly well-vegetated forest or swamp environments. Sauropod tracks seem to dominate the lagoonal settings.

Here is a brief rundown of track types present at the sites:

Ornithopod tracks - large and small. Some small ones resemble Wintonopus, others don't. The big ones are commonly 60-65 cm pes length, and Giuseppe Leonardi found one measuring 80 cm.

Theropod tracks - large and moderate in size. Some are definitely Megalosauropus, some definitely aren't. One of the biggest found has a pes (foot) length of 51 cm. There are some small tridactyl prints too (5-10 cm range), which may or may not be theropod.

Sauropod tracks. Some of moderate size, but plenty with pes length greater than 60 cm. The biggest to date is 1.7 m pes length. Some have manus (fore limb) prints, others don't. Some fit easily into ichnogenus Brontopodus, but there is a vast range that don't - in all shapes and sizes, with and without indications of digits. There are at least three or four different type of sauropod prints, which have not necessarily come from different species. There are some nice trackway sequences, though none of them very lengthy, and at least two 'stomping grounds' - one of which Dr Thulborn describes as "so breath-taking that it deserves to be lifted bodily (or replicated as high-fidelity cast) and put into a museum".

There are at least three odd types of footprints - one with a curious rectangular outline, another including the so-called ?stegosaur tracks; and, maybe, some swimming/paddling traces. Overall the sauropod and ornithischian tracks vastly outnumber theropod tracks.

(Edited from a posting by Dr Tony Thulborn to the Dinosaur mailing list, dated 29 August 1997.)

Thulborn, R.A., T.Hamley and P.Foulkes 1994 Preliminary report on sauropod dinosaur tracks in the Broome sandstone (Lower Cretaceous) of Western Australia. Gaia 10:85-96

Index of Trackways