Resetting the evolution of marine reptiles at the Triassic-Jurassic boundary

Abstract

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

Ichthyosaurs from the French Rhaetian indicate a severe turnover across the Triassic–Jurassic boundary

“…A very large portion of ichthyosaur diversity and disparity vanished in the course of LT extinction; only the open ocean-adapted parvipelvians survived (McGowan 1997; Thorne et al 2011), and then rapidly radiated at the Triassic-Jurassic boundary and during the Jurassic (Fischer et al 2013). However, the last unambiguous record of nonparvipelvian ichthyosaurs is middle Norian (e.g.…”

“…Whereas the JCB extinction is now regarded as a minor event for ichthyosaurs (Fischer et al 2012;Fischer et al 2013), the LT and CTB extinctions are considered as severe (Thorne et al 2011;Fischer et al 2014). A very large portion of ichthyosaur diversity and disparity vanished in the course of LT extinction; only the open ocean-adapted parvipelvians survived (McGowan 1997; Thorne et al 2011), and then rapidly radiated at the Triassic-Jurassic boundary and during the Jurassic (Fischer et al 2013).…”

“…Storrs and Gower 1993). Thorne et al 2011) and the rapid radiation of Neoichthyosauria (Fischer et al 2013) are restricted to the Rhaetian stage, which is about 7.2 Ma in duration (Gradstein et al 2012) and form a rather short-lived turnover that profoundly affected the evolutionary history of ichthyosaurs.…”

Microvertebrates from the classic Rhaetian bone beds of Manor Farm Quarry, near Aust (Bristol, UK)

“…Extinctions occurred at different points through the Late Triassic, including during the end-Triassic mass extinction itself, and there were major extinctions and turnovers among sharks (Cappetta, 1987;Friedman and Sallan, 2012) and marine reptiles (Thorne et al, 2011). Bony fishes, on the other hand, were apparently little affected by the end-Triassic event, with all families crossing the boundary into the Jurassic (Friedman and Sallan, 2012;Romano et al, 2014).…”

The Rhaetian (Late Triassic) vertebrates of Hampstead Farm Quarry, Gloucestershire, UK

“…The other main terrestrial tetrapod clades, including crocodylomorphs, lepidosaurs, and mammals also diversified to some extent after the ETME. In the seas, there were major extinctions and turnovers among sharks (Cappetta, 1987(Cappetta, , 2012 and marine reptiles (Thorne et al, 2011), whereas bony fishes were apparently unaffected by the ETME, with all families passing into the Jurassic (Friedman and Sallan, 2012). Many details of the ETME are still much debated, not least the timing, duration, and magnitude of the event (e.g.…”