John W. Wilson
May 1, 1975
Integrative and Comparative Biology
The ratio of species per family in North American local mammal faunas is lowest in Eocene time due to increased phyletic separation between surviving species. In respect to changes in adaptive zone, morphology may be relatively slow to change when an organism is using several different resources. If an organism's fitness set is concave, morphology may not change to adapt to the new resource until it has become a significant proportion of its resource set. Even when a resource has been important to the organism for some time, there may be little morphologic adaptation to the resource.