A better tree?

I keep telling my zoology students that I don't dwell too much on taxonomy, and don't expect them to either, because it's in such a state of flux. As soon as I make them memorize a taxonomic scheme, it gets changed. That's probably going to accelerate as we train our genetic artillery on more and more groups. Evidence here, and this is pretty big.

A group of researchers led by Jeff Schultz and Jerry Regier at the Center for Biosystems Research at the University of Maryland Biotechnology Institute have compared genetic sequences among 85 different species of arthropods with the goal of redrawing the phylogenetic tree for this largest (by far) of the animal phyla. They've come up with some very unexpected results. Maybe the most surprising nugget is the placement of the little-known Xenocarida as a sister group to the the Hexapoda. Hexapoda? That's the insects, comprising some 80% of the earth's named animal species. The figure at left is from an earlier publication by the group that appeared in Systematic Biology in 2008. The placement of the insects squarely in among things like ostracods and copepods means that the crustaceans do not represent a monophyletic group, i.e. one containing all the descendants of a common ancestor. Time to rewrite that chapter in Hickman.

Another interesting result involves Triops. You may recognize this guy - they're marketed as "dinosaur shrimp", a throwback to the Triassic Period. My daughter gave me some to rear a couple of Christmases ago (if you know my daughter, you know that this is completely in character). They were actually pretty interesting little guys, pre-flush (sorry, Jess). Anyway, the new work indicates that Triops has a much more recent origin than was previously believed. I expect the good folks at Triops.com will keep that little piece of information under wraps.

The work is reported online at Nature, and summarized here by Science Daily.