Evidence for a Mid-Jurassic Adaptive Radiation in Mammals

Evidence for a Mid-Jurassic Adaptive Radiation in Mammals

Authors:

Close et al

Abstract:

A series of spectacular discoveries have transformed our understanding of Mesozoic mammals in recent years. These finds reveal hitherto-unsuspected ecomorphological diversity that suggests that mammals experienced a major adaptive radiation during the Middle to Late Jurassic [ 1 ]. Patterns of mammalian macroevolution must be reinterpreted in light of these new discoveries [ 1–3 ], but only taxonomic diversity and limited aspects of morphological disparity have been quantified [ 4, 5 ]. We assess rates of morphological evolution and temporal patterns of disparity using large datasets of discrete characters. Rates of morphological evolution were significantly elevated prior to the Late Jurassic, with a pronounced peak occurring during the Early to Middle Jurassic. This intense burst of phenotypic innovation coincided with a stepwise increase in apparent long-term standing diversity [ 4 ] and the attainment of maximum disparity, supporting a “short-fuse” model of early mammalian diversification [ 2, 3 ]. Rates then declined sharply, and remained significantly low until the end of the Mesozoic, even among therians. This supports the “long-fuse” model of diversification in Mesozoic therians. Our findings demonstrate that sustained morphological innovation in Triassic stem-group mammals culminated in a global adaptive radiation of crown-group members during the Early to Middle Jurassic.