骨格譽讚 Who designed the Gorgeous Anatomical Structure!!??, Image Processed with Photos taken at ROM: Royal Ontario Musium Toronto May 30 2009

The hostile environment hardly to survive might have made them bigger, faster, sharper and stronger.. though the things totally went upside down at the end of their time by external force caused by bombardment of comets on earth..
Ironically only tiny & hairy marsupials survived in the end maybe because they were more enduring against freezing weather and they were more efficient in digesting & converting food into energy and even they were tiny enough to survive with small amount of food..