Living observers of continental drift

OK, so the title of this post might be a little misleading, but I wanted to point out this article that I found in the New York Times Science section.

Some of the strongest evidence Alfred Wegener put forward in support of continental drift was the existence of identical plant and animal fossils on land masses that were now separated by great distances. For example, fossils of mesosaurus, a freshwater reptile, can be found in both Africa and South America. It seemed highly unlikely that mesosaurus could have swum the open ocean, so Wegener's idea was that the species evolved and lived during a time when the continents were joined, and they have since been pulled apart. There were many other fossil links between now distant continents, as well as distinctive rock units and successions, and glacial deposits.

This article uses a living species, the mite harvestman, a tiny relative of the daddy longlegs, to do the same thing. The mite harvestman has been around in an identifiable form since the Devonian (see Dunlop J.A, Anderson L.I, Kerp H, Hass H. Preserved organs of Devonian harvestmen. Nature,2003;425:916), roughly 400 million years ago. Harvestman now include about 5000 species living on every continent except Antarctica. DNA sequencing of some of these species shows when they split off from various common ancestors, and the timing of those evolutionary splits is consistent with various continental collisions and rifting events. In other words, the DNA in a variety of mite species whose individual range is rarely over 50 miles actually traces 400 million years worth of plate tectonics.

I am not surprised by the findings, but I really enjoy studies like this. It is always amazing to me when very different approaches to the same problem come up with the same answer. Different techniques, different goals, different scientists, same result.

For those interested, the data was formally presented in

Sarah L. Boyer, Ronald M. Clouse, Ligia R. Benavides, P. Sharma, Peter J. Schwendinger, I. Karunarathna, G. Giribet: Biogeography of the world: a case study from cyphophthalmid Opiliones, a globally distributed group of arachnids. Journal of Biogeography (OnlineEarly Articles). doi:10.1111/j.1365-2699.2007.01755.x (here).


And. for your continued enjoyment, some images of mite harvestman fossils from Cretaceous amber.

Halitherses grimaldii new genus and species. The first fossil harvestman from Burmese amber, Lower Cretaceous (amber). (a) Lateral aspect of holotype Bu-1583a; scale bar, 1mm. (b) Detailed lateral view of holotype Bu-1583a; scale bar, 0.5mm. (c) Front end of lateral view of holotype Bu-1583a showing extended right pedipalp; scale bar, 0.5mm. (d) Detail of Bu-1583a tarsus and tibia of right pedipalp showing the clavete setae; scale bar, 0.1mm. (e) Ventrolateral view of paratype Bu-1583b; scale bar, 0.5mm. (f) Posterodorsal view of paratype Bu-1583b; scale bar, 0.5mm.

Image and figure caption are stolen shamelessly from

Giribet, G., and Dunlop, J.A., 2005, First Identifiable Mesozoic harvestman (Opiliones: Dyspnoi) from Cretaceous Burmese amber. Proceedings of the Biological Society, v. 272, n. 1567, pp. 1007-1013.