Earth's wobble killed off mammal species -

Mammalian species are known to last an average of 2.5 million years before being snuffed out, but nobody had been able to figure out why. The reason, it turns out, may be linked to regular wobbles in Earth's orbit.
Jan van Dam from Utrecht University in the Netherlands and colleagues reached this conclusion after studying the fossil record of rodents from central Spain over a 22-million-year span. This showed a link between rodent extinction events and the climate record.
Changes in the Earth's tilt and the shape of its orbit lead to climate cycles of around 1.2 and 2.4 million years. At their extremes both these cycles cause global cooling, expansion of polar ice sheets and changes in rainfall patterns. The extinction peaks coincided with global cooling maxima, while new appearance peaks coincided with periods of stable climate (Nature, DOI: 10.1038/nature05163).
"Changes in seasonality associated with the astronomical variations - harsh winters, dry summers - are really a matter of life and death to mammals," van Dam points out.
From issue 2573 of New Scientist magazine, 11 October 2006, page 17