Updating the fungal infection-mammalian selection hypothesis at the end of the Cretaceous Period
Arturo Casadevall, Chris Damman
Abstract
In 2005, one of us proposed that a fungal bloom at the end of the Cretaceous Period would have favored the selection of the endothermic mammals over ectothermic reptiles, which eventually led to the great mammalian radiation and the replacement of the Cretaceous reptilian megafauna with the mammalian megafauna of the Tertiary or Paleogene Period [1]. This idea, which we now name the "fungal infection-mammalian selection" (FIMS) hypothesis, suggested a new explanation for how the mammals came to replace reptiles as the dominant large animals after the Cretaceous Period [2], which ended 66 million years ago with a planetary cataclysm known as the Cretaceous-Paleogene extinction event. At the time, this extinction event was attributed to volcanism, a bolide impact, or some combination of both. In the ensuing decade and a half since FIMS was first proposed, considerable progress was made in understanding the events following the cataclysm at the end of the Cretaceous Period, which provide the opportunity to add refinements to this hypothesis. For example, in 2005, there was uncertainty on the temporal relationship between the bolide impact and the mass extinction event, with some estimates placing it 300,000 years earlier Today there is a growing consensus for a temporal and causative relationship between a bolide impact at Chicxulub, Mexico, in the Yucatan peninsula and the mass extinction event at the end of the Cretaceous Period [4]. This together with a greater appreciation of the planetary effects following this cataclysm [5] allow refinements and updates to the FIMS hypothesis.