A rapid warming about 55.5 million years ago led to the brief proliferation of smaller-bodied insects and earthworms, say scientists, who predict that the same phenomenon may be underway today. During the Palaeocene-Eocene thermal maximum, temperatures soared for a period of about 100,000 years, as did atmospheric carbon dioxide concentrations.
Jon Smith of the Kansas Geological Survey and colleagues analyzed trace fossils left behind by burrowing insects in the Bighorn Basin, Wyoming, before, during and after this ancient warming episode. During the period of peak warmth, the average body size of burrowing creatures was significantly smaller than during cooler periods. The authors infer that the hot, dry climate — brought on by the spike in atmospheric carbon dioxide levels — suppressed adult body size, probably by shortening lifespans and altering patterns of juvenile development. In addition, say the authors, high CO2 levels may have lowered the nutritional value of plants favoured by insects for feeding, thereby limiting growth.
The team points out that if modern insects respond similarly to climate change, body size could already be decreasing. Living organisms could be compared with museum collections and archaeological specimens to monitor such changes, they say.
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Newton, A. All creatures small. Nature Clim Change 1, 125 (2009). https://doi.org/10.1038/climate.2009.109
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DOI: https://doi.org/10.1038/climate.2009.109
