Taxonomy and prehistory
Taxonomists study the breadth of life through the depths of time, from the beginning of life on Earth over 3.5 billion years ago to the present.
And while taxonomy is important in understanding prehistoric life, prehistory is equally important for a taxonomic understanding of life today. The structure of today's life, a structure that taxonomists attempt to capture in their classifications, is the result of billions of years of evolution, and cannot be understood outside the context of its history. For this reason, taxonomy and prehistory are intimately connected.
Australia is a great place to study some aspects of prehistory, and a relatively poor place to study others. Ours is one of the oldest and most stable continents on Earth. In other more active continents, most ancient rocks have been uplifted, eroded and redeposited as younger sedimentary rocks, or subducted, melted and erupted as younger volcanics. Both these processes have been more subdued in Australia.
For this reason we have some of the oldest rocks, sediments and land surfaces on Earth, and hold an important fossil record of the earliest living organisms, including the bacterial structures called stromatolites, enigmatic organisms from the Ediacaran Period when soft-bodied, macroscopic organisms first became common and widespread, and trilobites and other members of the so-called Cambrian Explosion, when organisms with hard, readily-fossilised exoskeletons became dominant.
A specimen of Dickinsonia costata, first named by Australian geologist and palaeontologist Reg Sprigg from the Ediacara Sandstone formation of the Flinders Ranges. Dickinsonia is one of the most prominent and famous members of the so-called Ediacaran Fauna, soft-bodied creatures that flourished around 550 million years ago. Scientific debate continues about the nature and relationships of Ediacaran organisms such as Dickinsonia.
The trilobite Redlichia takooensis from the Emu Bay shales of Kangaroo Island. Like the more famous Burgess Shales, the Emu Bay Shales preserve specimens of trilobites and other organisms from the Cambrian Explosion, sometimes in exquisite detail. Source: South Australian Museum http://www.samuseum.sa.gov.au/media/unlocked/layers-of-treasure-to-be-uncovered-on-kangaroo-island
Equally important in a global context are the well-preserved Devonian fish fossils at Gogo in the Kimberley region of northern Western Australia and at Canowindra in New South Wales. At Gogo dead fishes fell into oxygen-poor, deep waters and were covered with fine sediments shortly after they died, resulting in exquisite details of preservation including tissues, nerves, and the world's oldest-known example of an embryo connected by an umbilical cord to a yolk sac inside its mother.
An artist's reconstruction of Materpiscis attenboroughii, discovered as an exquisitely preserved fossil in the Gogo formation, live-bearing a young one. Source: Long, Trinajstic, Young & Senden (2008). Live Birth in the Devonian Period. Nature. 453; 650-652. DOI: 10.1038/nature06966
Unfortunately, the very conditions that have led to the preservation of Australia's significant Cambrian and Devonian fossils, our geological stability, have worked against good exposures of later Mesozoic rocks, formed during the period when dinosaurs were dominant. The relatively low relief and absence of significant recent mountain-building in drier parts of Australia means that good outcrops of rocks of this age are very few compared with other regions such as western USA and China. Nevertheless, significant dinosaur finds have been made in south-western Queensland, and on the coast of Victoria.
More recent fossils of more familiar animals are often spectacular, including mammalian and bird megafaunas, some of which became extinct as recently as 50,000 years ago. Important earlier fossil sites include Queensland's remarkable Riversleigh deposits from the Oligo-Miocene around 20 million years ago. The beautifully preserved fossil animals and plants from Riversleigh allow a detailed insight into a strangely different Australia, when the rainforests that covered much of the continent were inhabited by diverse ancestors of today's marsupials, monotremes, birds, frogs and bats.
An artist's impression of the many fossil mammals, birds, reptiles and plants discovered at the Riversleigh fossil site in Queensland, which together tell a story of a strangely familiar yet remarkably different Australia. Source: https://www.sbs.com.au/topics/science/nature/article/2016/06/10/carnivorous-kangaroo-and-4-other-animals-were-almost-glad-are-fossils
Of course, while animal fossils often capture public interest, plant fossils are equally important, providing key insights into both the evolution of the plants we're familiar with today, and helping us understand prehistoric habitats and environmental change. In particular, a rich trawl of plant fossils including leaves, flowers, fruits and pollen helps track the remarkable changes that have occurred in Australia's transition from a warm, wet, rainforested landscape to the mostly semi-arid one of today. Understanding these changes is key also to understanding the likely future of Australia in a rapidly warming world.
Fossil animals and dinosaurs may capture the imagination, but fossil plants, especially fossil pollen grains shown here, provide in some ways the richest and most detailed understanding of the prehistory of Australia.
Taxonomy allows us to make sense of fossil finds and of the fossil record. The classification of fossils by taxonomists provides the framework for research by others, including ecologists, palaeoclimatologists and geologists seeking to understand the evolution of Earth and its environment, as well as providing the only direct evidence of the evolution of life.