Life before Humans.....

Skyrail Nature Diary: June 2015

This month we will be looking at some interesting animals believed to have been extinct before humans arrived in Australia. Many of the animals which are known to have existed in our prehistoric tropical rainforests, were discovered as fossils in the famous Riversleigh fossil field within Queensland’s Lawn Hill National Park on the border of the Northern Territory. This fossil field is possibly the richest collection of mammal fossils in the world and as such, is inscribed on UNESCO’s World Heritage list together with the Naracoorte Caves in South Australia. Riversleigh’s fossils have expanded our knowledge of the prehistoric Australian animals that lived here following the extinction of the dinosaurs. The Riversleigh site consisted of a rainforest habitat up to 15 million years ago, and is then thought to have transitionally changed to dry forest and todays savannah (with fluctuations experienced during episodes of glacial maximums).

One typical discovery ast Riversleigh is of large mammalian predators which were completely unknown. Today, goannas and raptor birds are the main land predators of Australia. Another important discovery was the existence of what is known as mega-fauna. This simply means a suite of large animals that no longer exist. Today’s mammals and reptiles are mostly fairly small, the Red Kangaroo being the largest. A goanna, occasionally known by the Aboriginal name of Mungoon-gali, was the size of a saltwater crocodile once roamed over most of Australia. Today the perentie is the largest goanna. There were also some huge grazing and browsing marsupials, most notably the Giant Wombat that was the size of a cow and the Diprotodon that was the size of a hippo, making it the largest marsupial that ever lived.

Three metre kangaroos with a flattened face and a single giant claw on each of its hindlegs were around when humans reached Australia, as were gigantic flightless birds related to ducks (known as mihirungs), a small kangaroo with fangs (Balbaroo) and an enormous snake known as Wonambi in the Dreamtime stories. Earlier there was a large toothed platypus and a huge Marsupial Tapir with large claws and a short trunk. South America also had some unusual relatives of the marsupials which were excellent hunters. It is believed that the more recent of the above extinctions, especially of the mega-fauna, was at least partly caused by humans living in Australia at the time. The practice of burning, combined with the presence of comparatively few serious predators and a drying climate may have contributed to pushing these amazing creatures to extinction. 

Australia used to have crocodiles that lived on land, known as Quinkan Crocodiles! As a result of living their entire lives on land they couldn’t drown their victims like modern crocodiles can. This led to them have serrated knife like teeth rather than the conical ones Salties have. The other three species of Quinkan Crocodiles were less than half this size. These crocodiles lived as recently as 40,000 years ago. An earlier land croc was the Drop Croc, a two metre croc that climbed trees!

Horned Turtles are an interesting group of reptiles in that they are the only turtles from Australia that actually lived on land. All modern turtles in Australia are aquatic, which is curious when you consider how dry this continent is! These turtles have been around for quite some time. The last known specimens died on Lord Howe Island about 2,000 years ago. It’s assumed that the Ice Age was at least partially responsible for their extinction. As their name suggests, Horned Turtles had two large horns on their heads. They also sported some formidable spines on their tails. Most experts believe Horned Turtles were herbivorous like modern day tortoises. It was once thought that these large land turtles were exclusively Australian but new finds in South America from just before, or after the extinction of the dinosaurs, suggest that they have been around since before Gondwanaland was created. 

By Tore Lien Linde