Leaves reveal ancient Queensland was warm
Warmer and wetter Dinosaurs at Lark Quarry in Queensland stomped around a warm, wet and seasonal climate bursting with flowering plants, a new study reveals.
The analysis of plant fossils, led by PhD student Tamara Fletcher from the University of Queensland, shows the climate in this area during the late Cretaceous period was warmer and wetter than previously thought.
According to their study, published in the latest issue of Australian Journal of Botany, the area had a mean annual rainfall of 1646 millimetres and a mean annual temperature of 16 degrees. It also found the area had a nine-month plant growth season.
The Lark Quarry conservation area, 110 kilometres south of Winton in central Queensland, is part of the Winton Formation, a rocky land network that sprawls across parts of South Australia, New South Wales and Queensland.
Previous studies of plant fossils reveal a landscape dominated by conifers and flowering plants from the Early to Late Cretaceous, 145 million to 66 million years ago.
But despite this wealth of material, not a lot is known about the climate that existed at the time.
"A source of interest is what's going to happen if [the climate] gets warm," Fletcher says.
"[My research] supports broader ideas of trying to get a better model of the climate at the time. What the climate does during globally warm periods."
The study is based on the premise that leaf characteristics such as size, shape, and margin type represent adaptive strategies to a plant's evolutionary environment.
For example, leaves tend to be larger in wetter environments.
Fossil field work
Fletcher and colleagues analysed leaf characteristics from fossils collected at two sites at Lark Quarry dated 92 to 94.5 million years ago.
The three-dimensional preservation of the leaves in a single sedimentary layer suggests they were deposited quite quickly.
The researchers then compared their data with plant fossil records from the Queensland Museum, which were deposited at different times right across the Winton Formation.
They found the leaves collected from Lark Quarry indicated the climate was warmer and wetter than the museum's collection suggests.
Fletcher says this difference maybe because the museum collection is biased towards intact fossils, which tend to be smaller.
"That's what we call a taphonomic bias," she says.
"What they have as a collection represents the diversity of plants there and the characteristics you need to identify those plants.
"But that doesn't necessarily capture [a plant species'] full size range for example.
"If we had large leaves for a tree, and they fossilised, and we go out and dig them up, they're more likely to be torn apart during that process; so they are an incomplete leaf compared to a smaller leaf."
Flora and fauna
Fletcher says her findings are consistent with oceanic and terrestrial data.
In addition to floral methods, Fletcher says the diverse fauna of the Winton Formation, also offers climate information.
"You don't get crocodilians when mean annual temperatures are less than 16 degrees in a locality," she says.
"And we know Isisfordia duncani [a species of crocodile] existed in the area at the time."
Fletcher plans to continue to look at places across the Winton Formation and build knowledge about the flora, fauna and climate in the area during the late Cretaceous period.
Andrew Rozefelds, curator for Lost Creatures: Stories from Ancient Queensland at the Queensland Museum, says the study is important in providing more information about Australian palaeobotany.
"New knowledge changes our perceptions and understandings," says Rozefelds says.
"(The) museum's role is to ensure information is as up to date as possible; once work is published we can look into how we update information."