The fossils of many arthropods — invertebrates with hard, external skeletons and segmented bodies — from 540 million to 250 million years ago have a large pair of 'great appendages' that they probably used to grasp and handle food. Euarthropods had shorter versions of the appendage, whereas many of the now-extinct anomalocaridids had longer, leg-like structures.
The position of these animals in the arthropod family tree is controversial. Martin Stein, now at the University of Kansas in Lawrence, reports a new arthropod species that bridges a gap between the two groups.
The new species, Kiisortoqia soperi (reconstruction pictured), discovered in Greenland, was clearly a euarthropod but had the longer type of appendage.
Stein says this supports a shared ancestry of the long and short 'great appendages' and suggests that both evolved from the limbs of a particular segment of the arthropod body.
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Palaeontology: The long and the short. Nature 464, 144 (2010). https://doi.org/10.1038/464144a
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DOI: https://doi.org/10.1038/464144a
