<figcaption> Credit: Left: David Hall / Photo Researchers, Inc</figcaption>
Credit: Left: David Hall / Photo Researchers, Inc

The paper:
F. Delsuc et al., "Tunicates and not cephalochordates are the closest living relatives of vertebrates," Nature, 439:965-8, 2006. (Cited in 116 papers)

The finding:
Using a data set of 146 nuclear genes, including tunicate data from the Oikopleura dioica genome project, Frédéric Delsuc and his colleagues from the University of Montreal and the University of Bergen, Norway, applied new data and techniques to reclassify tunicates (urochordates, also known as sea squirts) as the closest living relatives to vertebrates - and not cephalochordates, as previously believed.

The evidence:
Before the Delsuc paper, researchers had found neural crest cells, a necessary component of vertebrate embryonic development, in urochordates but not in cephalochordates (Nature, 431:696-9, 2004). "This was a problem because tunicates weren't the closest to vertebrates," says Ronald Jenner at the UK's University of Bath. Now, he says, "everybody...

Changing understanding of vertebrates' closest relatives:

Before 2006 Delsuc Telford
Closest Cephalochordata Urochordata Urochordata
2nd Closest Urochordata Cephalochordata Cephalochordata
3rd Closest Echinodermata Echinodermata Hemichordata

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