Sunday, 5 February 2017

Lake Kariba dinosaur expedition: Part 1

Our knowledge of dinosaur evolution is based on a series of snapshots provided by the fossil record, with a handful of key regions providing the lion’s share of information for any particular time period. This relies on serendipity – rocks of the right age and type need to be preserved in a way where they are accessible for collection – and the distribution of these deposits is essentially random, due to numerous geological processes acting to different extents in different areas at different times. For example, our most detailed insights on the last dinosaurs currently come from the western USA and Canada, whereas presently our information on the earliest dinosaurs is confined to Argentina and Brazil.

Southern Africa provides an important piece in this puzzle, with a series of sandstone and mudstone deposits laid down on broad river floodplains, that were laid down at a time when dinosaurs were first starting their rise to numerical and ecological dominance. These environments became more arid through time, culminating in vast dune seas, where dinosaur fossils could still be found. This series of rocks is referred to as the Stormberg Group in South Africa and reveals not only the dinosaurs but also the other members of a series of terrestrial faunas that lived during the Late Triassic and Early Jurassic, spanning a period when several pulses of extinction rocked the world at the Triassic/Jurassic boundary. The Stormberg Group has been (and continues to be) the focus of much attention and has yielded some of the best-known African dinosaurs, which are often known from abundant and beautiful material. These include the ornithischians Heterodontosaurus and Lesothosaurus, the theropods Dracovenator and Coelophysis, and (most abundantly) the sauropodomorphs, including Antetonitrus, Massospondylus, Pulanesaura and many others.

Adjacent regions of southern Africa, including Botswana, Lesotho, Zambia and Zimbabwe, have similar sedimentary series that are thought to correlate with those in South Africa, but for various reasons these deposits are have been less thoroughly explored. Nevertheless, some important material is known from these areas, with rich localities in Lesotho (which have supplied beautiful early mammal and Lesothosaurus material, as well as dinosaur footprints) and Zimbabwe. Many sites are known in Zimbabwe, with well-known taxa such as Coelophysis and Massospondylus known from the south of the country, while the early sauropod Vulcanodon was found on the shores of Lake Kariba on its northern border. Several field crews have worked on sites in the south of Zimbabwe more recently, finding new and important material, but the potentially rich dinosaur sites around the shores of Lake Kariba have not been prospected by palaeontologsts since the time of Vulcanodon’s discovery in 1969.

More recently, a small band of dedicated amateur palaeontologists and geologists, including local safari camp owner Steve Edwards and geologist Tim Broderick, have had their eyes to the ground along the shores of Lake Kariba and have found interesting new material of their own. Steve and Tim mentioned this material to various dinosaur specialists around the world, including my colleague Jonah Choiniere (based at the Evolutionary Studies Institute in Johannesburg) and I. The presence of Vulcanodon, and other Early Jurassic dinosaurs elsewhere in Zimbabwe, as well as the exciting news that new material was being found, suggested to Jonah and I that a trip to area would be fruitful and exciting. After months of background research, building new contacts with colleagues in Zimbabwe, and raising the money, Jonah was able to organise an expedition to the Lake Kariba area, in which I was lucky enough to participate, along with several other Zimbabwean and South African colleagues. So, on the 5th January 2017 Jonah, his postdoc Pia Viglietti, our joint PhD student Kimi Chapelle and I left Johannesburg, bound for Harare …

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