When animals first crawled onto land, one of the greatest obstacles they had to contend with was figuring out how to breathe. No longer bathed in oxygen-rich marine waters, their gills would surely have dried out.
Hagadorn and Seilacher have analyzed fossils from 500-million-year-old rocks that show one way these early pioneers may have dealt with this problem--the first terrestrial animals carried a shell on their backs.
Like modern hermit crabs, these ancient pioneers had a scorpion-like body, and could stuff their abdomen into a coiled snail shell. One advantage of doing this was that the shell may have acted as a humid chamber to keep their gills moist.
This would have allowed brief forays out of the water, to explore the beaches and tidal flats, and to graze in environments where there was no competition from other animals or predators.
These fossils represent the first usage of "tools," and provide insights into how some animals may have made the leap from living in water to living on land.
The article by James W. Hagadorn and Adolf Seilacher, Dept. of Geology, Amherst College, Amherst, Massachusetts, was published in the April issue of Geology.
- James W. Hagadorn and Adolf Seilacher. Hermit arthropods 500 million years ago? Geology, 2009; 37 (4): 295-298 DOI: 10.1130/G25181A.1
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