Pants variety grew, Animal Variety Died

A long, long time ago, actually about 100 000 000 years ago, during the Cretaceous era, suddenly a great variety of plants started appearing. Until now scientists thought that would also have increased the mammal variety of specie as it would have increased their survival chances. But actually a new study shows that animal variety declined during the great angiosperm radiation of mid-Cretaceous period. A former high school biology teacher, Grossnickle, was the first one to make this discovery. He wrote a paper on this subject called  "Mammal disparity decreases during the Cretaceous angiosperm radiation,". Here is an abstract of it:

Fossil discoveries over the past 30 years have radically transformed traditional views of Mesozoic mammal evolution. In addition, recent research provides a more detailed account of the Cretaceous diversification of flowering plants. Here, we examine patterns of morphological disparity and functional morphology associated with diet in early mammals. Two analyses were performed: (i) an examination of diversity based on functional dental type rather than higher-level taxonomy, and (ii) a morphometric analysis of jaws, which made use of modern analogues, to assess changes in mammalian morphological and dietary disparity. Results demonstrate a decline in diversity of molar types during the mid-Cretaceous as abundances of triconodonts, symmetrodonts, docodonts and eupantotherians diminished. Multituberculates experience a turnover in functional molar types during the mid-Cretaceous and a shift towards plant-dominated diets during the late Late Cretaceous. Although therians undergo a taxonomic expansion coinciding with the angiosperm radiation, they display small body sizes and a low level of morphological disparity, suggesting an evolutionary shift favouring small insectivores. It is concluded that during the mid-Cretaceous, the period of rapid angiosperm radiation, mammals experienced both a decrease in morphological disparity and a functional shift in dietary morphology that were probably related to changing ecosystems.

 Grosspeckle discovered that it is true that the great increase of food did increase the amount the number of mammals on earth but also decreased the variety of mammal species, leaving almost only small, insect eating, animals.  Most of his research was made by studying the jaws of different mammals of this time period. He also noticed that the animals with quite small jaws and bodies, were the ones that did the best during this time period, we think that those were the ancestors of the therians (also ancestor of the humans).