Mammals might respond to global warming by shrinking in size.
During a large warming event called the Palaeocene–Eocene Thermal Maximum (PETM), some 56 million years ago, mammals became smaller. To see how common this climate-driven dwarfing might have been, Abigail D'Ambrosia of the University of New Hampshire in Durham and her colleagues measured the size of fossil teeth from four common mammal species from the Bighorn Basin in Wyoming, as a proxy for body size. The fossils, including those of an ancestral horse and a rabbit-sized, hoofed animal, spanned a time period that included a climate-warming event called the Eocene Thermal Maximum 2, which occurred 53 million years ago and was less hot than the PETM.
The team found that the rabbit-sized animal shrank by about 15% during the later warming event. The ancient horse species decreased in size by about 14%, whereas previous research suggested that a closely related horse shrank by roughly 30% during the PETM.
The authors hypothesize that reduced size could have helped the animals to disperse heat by increasing their surface-to-volume ratio, or could be due to dietary changes or climate-change-related drought.
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Heat could lead to tiny mammals. Nature 543, 467 (2017). https://doi.org/10.1038/543467b