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Mid-Jurassic adaptive radiation in mammals

Ben Creisler

A new online paper:

Roger A. Close, Matt Friedman, Graeme T. Lloyd & Roger B.J. Benson (2015)
Evidence for a Mid-Jurassic Adaptive Radiation in Mammals.
Current Biology (advance online publication)
DOI: http://dx.doi.org/10.1016/j.cub.2015.06.047


•Rates of morphological evolution and disparity are quantified in
Mesozoic mammals
•Elevated rates prior to the Late Jurassic support a mid-Jurassic
adaptive radiation
•Slower rates characterized the Late Jurassic to the end-Cretaceous
•Early evolution in Theria was exceptionally rapid, but then slowed dramatically


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 . Patterns of mammalian macroevolution must be
reinterpreted in light of these new discoverie, but only taxonomic
diversity and limited aspects of morphological disparity have been
quantified. 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 and the attainment of maximum disparity, supporting a
“short-fuse” model of early mammalian diversification. 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.