Text and photos by Dr. Bob Fleming
On our first day in northeastern Australia, in the Centennial Lakes Park in Cairns, we found an arrow pointing to the Gondwanan Evolution Garden.
A Gondwana Garden? I’d never heard of such a thing.
Gondwana, the southern part of the ancient supercontinent of Pangea, is a name well-known name in geological circles, but a garden? This was a first.
Then, on our last day in Australia, this time on Bruny Island off Tasmania’s east coast, we again came upon the concept of a Gondwana garden. Here on the 600 hectare (1,500 acre) Inala Private Reserve we explored their Jurassic Garden dotted with plants whose ancestors once grew on Gondwana.
As Australia is a continent isolated from others, it is quite understandable that many Australians are aware of the concept of plate tectonics and that continents move, ideas that were considered rubbish during my university days in the 1950s-1960s.
But how to explain the presence of kangaroos in Australia when they are not seen anywhere else in the world? The answer lies in the history of our planet.
Earth’s geological record shows that some 250 million years ago (mya) most of the world’s landmasses were melded into one supercontinent, now referred to as Pangea. Later, beginning around 185 mya, rifts appeared in Pangea and the huge landmass gradually split into two divisions, the southern section named Gondwana. In the ensuing millions of years Gondwana also fractured into parts and Australia is one of those remnants.
Today, much of the flora and fauna found south of the equator speaks of Gondwana. For example the Southern Beech, Nothofagus, survives today in an arc from southern Chile around to New Zealand, Tasmania and north into the mountains of New Guinea. Another example is the early cone-bearing Araucaria ‘pines,’ the distribution of which traces a similar arc from Chile around to New Guinea. Thus one now encounters the Monkey Puzzle tree in southern Chile (and as a garden ornamental commonly planted round the world), the Hoop Pine in Australia, and the Klinki Pine in New Guinea.
Both Nothofagus and Araucaria likely evolved in what was western Gondwana as an Araucaria fossil dating to 185 mya and Nothofagus fossil dating to about 135 mya have been found in beds from that region. Later, due to favorable conditions they continued to evolve and today survive on far-flung remnants of Gondwana.
Another Gondwana connection is seen in the Proteaceae family, illustrated by the colorful Banksias in Australia and the related Proteas from southern Africa. The parrot family is yet an additional link as members proliferate primarily in two areas of the world – Australia and South America. And then there are spiders. The closest relatives of the primitive Tasmanian Cave Spider (Hickmania troglodytes) are seen in Chile.
Species that evolved early may be driven extinct by climate change or out-competed by later arrivals but on isolated continents and islands with favorable conditions, protection may allow them to proliferate. As an example, 13 of the 19 recognized Araucaria species grow only on remote New Caledonia Island.
Kangaroos are the pride of Australia, the symbol of the Qantas, the national airline, and pictured on the Australian Coat of Arms. These pouched mammals (marsupials) speak not so much of a Gondwana connection but of continental isolation. Indeed, the flora and fauna we find today on whatever continent is the result of a combination of factors including genetic and geological history as well as both ancient and modern climates.
On our last morning in Australia, while admiring the plantings in the Inala Jurassic Garden, all arranged in family clusters, and thinking about the biological threads that connect these southern lands, we were watched all the while (albeit from a distance) by a Bennet’s Wallaby and a Forty-spotted Pardalote, representatives of families found only in Australia. The natural history of this continent is very special indeed.