Earth Science

Land Ho

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Science  10 May 2002:
Vol. 296, Issue 5570, pp. 983
DOI: 10.1126/science.296.5570.983c

Major changes are required to move from life under water to life on land. The first clear terrestrial animal fossils are early arachnids and centipedes from about 420 million years ago. These fossilized arthropods show sufficiently developed features that it is likely that an earlier evolution occurred.

Now MacNaughton et al. describe tracks in wind-derived sandstone from near the Cambrian-Ordovician boundary (about 505 million years ago). The tracks appear to have been made by large amphibious arthropods several centimeters across. Although the dunes forming the sandstone were probably close to a seashore and these tracks are likely to represent only temporary excursions on land, they do indicate that colonization of the nonmarine environment may have proceeded fairly rapidly after complex animal life evolved in the oceans.—BH

Geology30, 391 (2002).

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