Re: Common Ancestor?


kramer.newsreader@xxxxxxxxx wrote:
Hi. This may be kind of a difficult question to answer, but what sort
of animal would have been the common ancestor between vertabrates and
arthropods? Do we have fossil evidence of such a creature? What
living creature is most closely related to such an ancestor?

The LCA of vertebrates and arthropods would be "Urbilateria", the
ancestral bilaterian. In cladistic terms, any modern bilaterian (ant,
squid, starfish, you, earthworm, ...) is equally close to it.

Morphologically, Urbilateria probably was a worm-like critter crawling
around on the sea bottom sometime in the later Precambrian. We've got
trace fossils from crawling worms from about the right period, but
identifying any specific as Urbilateria isn't realistically possible.


.

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