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Mesozoic birds made insects shrink

From: Ben Creisler

A new online paper:

Matthew E. Clapham and Jered A. Karr  (2012)
Environmental and biotic controls on the evolutionary history of
insect body size.
Proceedings of the National Academy of Sciences (advance online publication)
doi: 10.1073/pnas.1204026109

Giant insects, with wingspans as large as 70 cm, ruled the
Carboniferous and Permian skies. Gigantism has been linked to
hyperoxic conditions because oxygen concentration is a key
physiological control on body size, particularly in groups like flying
insects that have high metabolic oxygen demands. Here we show, using a
dataset of more than 10,500 fossil insect wing lengths, that size
tracked atmospheric oxygen concentrations only for the first 150 Myr
of insect evolution. The data are best explained by a model relating
maximum size to atmospheric environmental oxygen concentration (pO2)
until the end of the Jurassic, and then at constant sizes, independent
of oxygen fluctuations, during the Cretaceous and, at a smaller size,
the Cenozoic. Maximum insect size decreased even as atmospheric pO2
rose in the Early Cretaceous following the evolution and radiation of
early birds, particularly as birds acquired adaptations that allowed
more agile flight. A further decrease in maximum size during the
Cenozoic may relate to the evolution of bats, the Cretaceous mass
extinction, or further specialization of flying birds. The decoupling
of insect size and atmospheric pO2 coincident with the radiation of
birds suggests that biotic interactions, such as predation and
competition, superseded oxygen as the most important constraint on
maximum body size of the largest insects.

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