Did avian-like pulmonary anatomy increase the susceptibility of dinosaurs to fungal diseases? Extending the "fungal infection mammalian selection" hypothesis.

The Cretaceous-Paleogene (K-Pg) bolide impact caused the extinction of over half of all plant and animal species. The "fungal infection mammalian-selection" (FIMS) hypothesis, first proposed in 2005, suggested that a post-K-Pg fungal bloom created selective pressures that favored the survival and evolutionary radiation of warm-blooded mammals due to their resistance to fungal diseases, while cold-blooded dinosaurs were at an evolutionary disadvantage. Evidence now indicates that dinosaurs were also endotherms; hence, body temperature alone was unlikely to have predisposed all dinosaurs to fungal infection. The fossil record suggests that avian-like respiratory anatomy was present in archosaurs, the ancestors of all dinosaurs. Here, we update the FIMS hypothesis, drawing on insights from modern bird anatomy and physiology, to suggest that dinosaurs may have been more susceptible to respiratory diseases, including fungal infections, perhaps sufficiently to tip the scales away from a second dinosaur age in a world replete with fungal spores.