Friday, September 25, 2015

Large monitor lizards and early Australians

At least three large species of monitor lizards lived in prehistoric Australia, an undescribed fossil species known from one location, the Komodo dragon (Varanus  komodoensis), and the Megalania (Varanus priscus). Komodo dragons are an extant relic species confined to a few islands in the Lesser Sundas, Indonesia.  Megalania is extinct, attained a length of about 7 m and like other Varanus probably had a venomous bite.  Megalania remains have been excavated from five locations.  Humans arrived in Australia about 50,000 years ago and the megalania remains from two sites may be less than 50,000 years old, but the dating at these sites has been considered unreliable.  In a new paper, Price et al. (2015) report remains of giant monitor that overlapped with the humans.

As if life wasn't hard enough during the last Ice Age, research led by the University of Queensland has found Australia's first human inhabitants had to contend with giant killer (=monitor) lizards.

UQ vertebrate palaeoecologist Dr Gilbert Price said researchers working in Central Queensland were amazed when they unearthed the first evidence that Australia's early human inhabitants and giant apex predator lizards had overlapped.

"Our jaws dropped when we found a tiny fossil from a giant lizard during a two metre deep excavation in one of the Capricorn Caves, near Rockhampton," Dr Price said.

"The one-centimetre bone, an osteoderm, came from under the lizard's skin and is the youngest record of a giant lizard on the entire continent."

Dr Price and his colleagues used radiocarbon and uranium thorium techniques to date the bone as about 50,000 years old, coinciding with the arrival of Australia's Aboriginal inhabitants.

"We can't tell if the bone is from a Komodo dragon -- which once roamed Australia -- or an even bigger species like the extinct Megalania prisica, which weighed about 500 kg and grew up to six metres long," Dr Price said.

"The find is pretty significant, especially for the timeframe that it dates."

The largest living lizard in Australia today is the perentie, which can grow up to two metres long.

Dr Price, from UQ's School of Earth Sciences, said massive lizards and even nine-metre long inland crocodiles roamed Australia during the last Ice Age in the Pleistocene geological period.

"It's been long-debated whether or not humans or climate change knocked off the giant lizards, alongside the rest of the megafauna," he said.

"Humans can only now be considered as potential drivers of their extinction."

The bone was found in what could be Australia's most fossil-rich site, with the Capricorn Caves housing millions of bones of many species.

Dr Price said scientists could only hypothesise how the giant lizard bone made its way inside the cave, which contains bones of many rodents regurgitated by owls.

He said a crew of volunteer citizen scientists helped with the research by sorting and sieving specimens.

Capricorn Caves manager Ann Augusteyn said the find highlighted her team's "huge responsibility" to care for the caves.

"This study also begs the question -- what else is entombed in our caves and what else can we learn?"


Citation
Price GJ,  Louys J,  Cramb J, Feng Y-X,  Zhao J-X,  Hocknull SA, . Webb GE,  Nguyen AD, Joannes-Boyau R. 2015. Temporal overlap of humans and giant lizards (Varanidae; Squamata) in Pleistocene Australia. Quaternary Science Reviews, 2015; 125: 98 DOI: 10.1016/j.quascirev.2015.08.013

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