Tuesday, May 19, 2009

About That Adapid. . .Or, Hype In the Digital Age

Today's PLoS ONE includes an article on a new primate from the Eocene of Germany, Darwinius masillae. Poor Darwinius has suffered heaps of abuse over her existence (we know the specimen is probably a she, based on the lack of a baculum). She died young, possibly suffocating during a belch of noxious gas from a volcanic lake. She got squashed ("lightly crushed," as her describers euphemistically say) under tons of rock, and then was rudely given a split personality upon her discovery. Each half of Darwinius was sold privately to a different collector, and eventually one half made it as far as a museum in Wyoming. This half received a little bit of creative restoration somewhere in between. The other, more intact half eventually made it to a museum in Norway. But, the fun was only beginning!

Our friend was described by a multi-national team of scientists, who teamed up with the History Channel, BBC, and other outlets to create a media blitz the likes of which the world has never seen before. Not only a peer-reviewed article, but press conferences, book deals, television programs, interviews, and much more.

Why is there such a fuss over such a little specimen (weighing in at approximately a kilogram while alive)?

First off, this is a spectacular fossil. The Messel Beds of Germany have produced truckloads of spectacular specimens with exquisite soft tissue preservation (everything from bats to birds to rodents), but primates are exceedingly, exceedingly rare. Nobody would debate the tremendous scientific value of the find. People are debating the authors' interpretation of the find.

The authors claim that Darwinius is a haplorhine primate. That is, Darwinius (and other members of its clade, the adapoid primates) is more closely related to anthropoid primates (including monkeys of all sorts, apes, humans, etc.) than to strepsirrhine primates (the group including lemurs). It's hard to believe for those of us who study dinosaurs, but this is a ridiculously contentious claim. To put it into context for you dinosaur nerds, this would be similar to someone claiming that Compsognathus is more closely related to birds than Velociraptor. Oh, the humanity!

The claim of Darwinius and other adapoids as a haplorhine is contentious for two reasons: 1) most recent, widely accepted cladistic analyses place adapoids as closer to lemurs (strepsirrhines) than to monkeys (haplorhines); and 2) there is no real cladistic analysis to support the claim made by the present paper. Instead, the authors give a list of characters that they believe to support the assignment to the haplorhine clade. Unfortunately, there is little or no discussion as to what these characters (including absence of a "toilet-claw" and "tooth comb," features found within, but not universally across, lemurs and kin) mean, including the possibility of convergence or mosaic evolution.

So, it appears that some extraordinary claims are made about Darwinius, but the supporting analyses are spartan. Given the wonderful preservation of the skeleton, it should be relatively straight-forward to code this specimen and present a cladistic hypothesis (because this will resolve all questions, right?!). Darwinius is an important fossil. The problem is that the interpretation of this specimen is highly debateable. The authors may very well be correct. . .but the burden of proof is still upon them.

As always with articles in PLoS ONE, the paper is free for everyone. Judging by the blogosphere today, there are some very strong opinions about this specimen - if you have thoughts on the little critter, please post a comment or note over at PLoS ONE!

Further Reading in the Blogosphere
Brian presents an excellent, in-depth analysis of Darwinius over at Laelaps.
Bora provides a nice list of blog coverage over at Blog Around the Clock.
Carl writes another excellent critique at The Loom.

Franzen, J., Gingerich, P., Habersetzer, J., Hurum, J., von Koenigswald, W., & Smith, B. (2009). Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology PLoS ONE, 4 (5) DOI: 10.1371/journal.pone.0005723

Image at top from the original article at PLoS ONE (Franzen et al., 2009).


Mike Taylor said...

Andy, I am looking at the comments at:
but I can't see yours.

Andy said...

I put my comment in the "ratings" section (where I outlined my rationale for how I rated the paper).