by Aaron G. Filler, MD, PhD
Figure 6-2 – The Dinosaur Mammal Transition Alternate Scenarios
A – Catastrophic: abrupt extinction of all dinosaurs at 65 million years ago from meteorite strike – followed by the rise of mammals (ciii). B – Non-competitive: dinosaurs declined gradually over twenty million years (bi, bii, biii) opening the niches that mammals then filled (ciii). C - Competitive: gradual decline of dinosaurs (bi, bii, biii) takes place simultaneously with the rise of the mammals (cii) during a 20 million year period of competition. D – Competitive2: major diversification of the mammals (ci) before the dinosaurs decline.
Dinosaur decline: (bi) – decrease in origin of new dinosaurs species, (bii) -gradual extinction of small dinosaurs (biii) – gradual extinction of large dinosaurs.
Penny, D. and M. J. Phillips (2004). The rise of birds and mammals: are microevolutionary processes sufficient for macroevolution? Trends in Ecology and Evolution 19(10): 516-22. Figure reproduced by permission of Elsevier.