Skeleton of a Cretaceous mammal from Madagascar reflects long-term insularity

The tendency of mammals to increase or decrease body size with respect to geography or time depends on the abundance, availability, and size of resources. This dependency accounts for a change in mass with respect to geography, including latitude (Bergmann's rule), a desert existence, and life on oceanic islands (the island rule), as well as in a seasonal anticipation of winter (Dehnel's phenomenon) and a tendency for some lineages to increase in mass through time (Cope's rule). Such a generalized pattern could be called the "resource rule," reflecting the controlling effect of resource availability on body mass and energy expenditure. The correlation of mammalian size with geography and time reflects the impact of temperature, rainfall, and season on primary production, as well as the necessity in the case of some species to share resources with competitors. The inability of the constituent "rules" to account for all size trends often results from unique patterns of resource availability.

Temporal correlation between some continental flood basalt eruptions and mass extinctions has been proposed to indicate causality, with eruptive volatile release driving environmental degradation and extinction. We tested this model for the Deccan Traps flood basalt province, which, along with the Chicxulub bolide impact, is implicated in the Cretaceous-Paleogene (K-Pg) extinction approximately 66 million years ago. We estimated Deccan eruption rates with uranium-lead (U-Pb) zircon geochronology and resolved four high-volume eruptive periods. According to this model, maximum eruption rates occurred before and after the K-Pg extinction, with one such pulse initiating tens of thousands of years prior to both the bolide impact and extinction. These findings support extinction models that incorporate both catastrophic events as drivers of environmental deterioration associated with the K-Pg extinction and its aftermath.