Abstract

Ichthyosaurs were important marine predators in the Early Jurassic,
and an abundant and diverse component of Mesozoic marine
ecosystems. Despite their ecological importance, however, the
Early Jurassic species represent a reduced remnant of their former
significance in the Triassic. Ichthyosaurs passed through an evolutionary
bottleneck at, or close to, the Triassic-Jurassic boundary,
which reduced their diversity to as few as three or four lineages.
Diversity bounced back to some extent in the aftermath of the
end-Triassic mass extinction, but disparity remained at less than
one-tenth of pre-extinction levels, and never recovered. The group
remained at low diversity and disparity for its final 100 Myr. The
end-Triassic mass extinction had a previously unsuspected profound
effect in resetting the evolution of apex marine predators
of the Mesozoic.