Zheng and Zhou – Just So

Rudyard Kipling was born in India and wrote short stories for children explaining why and how animals originated. The first of the Just So Stories was published in 1902 and five years later Kipling had received the Nobel Prize for literature.

th-4                        220px-JustSoStories

Little did he realise just how near and yet how far he was to clues about the origin of mammals, for real fossil evidence is published this week (Nature 500, 8th August, pages 160, 163 and 199). The new discoveries come from just across the Himalayas in China’s Mongolia and Hebei Provinces.

The oldest of these is from the 215 million years old Triassic of Hebei, a rodent-like creature about 6cms long that lived in trees –

nature12353-f1  – the work of Zheng et al

The Mongolian specimens are also from small herbivores and only 165 million years old, from the Early Jurassic. They walked with an ambulatory gait like an armadillo –

nature12429-f1 – the work of Zhou et al.

This difference  of 50 Myr for the age of the first mammal is a lot, even by geological standards, and it leads Zheng and Zhou to suggest very different genealogies.

The difference is really about what a mammal actually was, around 200 million years ago. The features that show up well in these fossils, such as teeth and bones of the middle ear, give clues too obscure to answer that question.

Just so.

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