A famous palaeontologist once remarked that most of the early history of mammals could be written as generations of teeth. This view, though perhaps over-stated, has some basis in fact. The enamel that clothes teeth is the hardest organic substance known, and is likely to bear the burdens of fossilization far better than mere bones. But even teeth have their limitations as bearers of information about evolutionary history. This explains the excitement in palaeontological circles about several recent and spectacular discoveries of teeth attached to whole fossil skulls and skeletons, allowing light of unprecedented sharpness to be shone into hitherto shadowy corners of mammalian evolution.
One such corner is illuminated in a report in Nature from Guillermo W. Rougier of the University of Louisville, Kentucky and colleagues. They describe two newly found specimens of a tiny mammal called Deltatheridium pretrituberculare that lived in the shadow of the dinosaurs, around 70 million years ago. Known since the early 1920s from teeth and a few fragmentary remains, the position of Deltatheridium in evolution has long been debated. But the new specimens provide enough information to show that this creature was related to the present-day marsupials (kangaroos, koala bears and their relatives.) This discovery enriches our understanding of the early evolution of marsupials, and mammals in general.
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