A fossil unearthed from 540-million-year-old sediments in China enriches and challenges our understanding of past life on Earth. The fossil animal is called Xidazoon stephanus, and it is described in the 19 August issue of Nature by Degan Shu of Northwest University, Xi'an, China, with Simon Conway Morris of the University of Cambridge, UK, and their colleagues. It fits into no known animal category, showing the surprises that still await us in the fossil record.
The researchers recovered two, or possibly three specimens of Xidazoon, preserved on a single slab. The animal was around ten centimetres long in life, and looked, if anything, like the dust bag from inside a vacuum cleaner. At one end was a prominent, circular mouth ringed with two concentric circles of plates. This led to a large, swollen anterior section, separated by a waist from a more flaccid-looking but prominently segmented posterior region. The animal finished, with a flourish, with a set of terminal spines. The researchers think that the creature lived in the seabed, like a burrowing worm, ingesting sediment in its ring-like mouth.
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