Ten years of databasing Trigoniida – an advanced status report

The order Trigoniida is a major clade in the Bivalvia, dating back to the Silurian and surviving with a single relic genus, Neotrigonia, in Australian waters today. During the Mesozoic, Trigoniida were cosmopolitan, highly diversified and abundant, particularly in shallow marine environments. While this has long been established, evolutionary dynamics and species-level diversity fluctuations including the effects of extinction events were never studied in detail. We have databased trigoniids offline since 2013 and online via MolluscaBase since 2014. Out of 2250 marine nominal species-level taxa currently recorded by us, approximately 150 are Palaeozoic, 1850 are Mesozoic and only 30 are Cenozoic. Some 200 names are as yet unassigned stratigraphically or are unavailable. Marine Trigoniida are currently distributed over three superfamilies and 18 families. Among these, the Myophoriidae and Trigoniidae, in particular, are in need of revision. We assess spatial and stratigraphic distributions of trigoniid families and superfamilies during the Mesozoic and identify patterns of evolution and expansion. At present, distribution is based on type localities only. However, given that the majority of species-level taxa occur at a single locality or in a single country or region, we assume that global patterns are readily captured. It is evident that the Trigoniida, being predominantly shallow-water, shallow-infaunal filter feeders, were affected by the three major ‘Mesozoic’ extinction events: end-Permian, end-Triassic and end-Cretaceous. While their diversity and morphologic disparity increased significantly following the first two of these events, they barely survived the K–Pg crisis and remain reduced to simplified cardiid-like morphologies today. Our data document the rapid expansion of Trigoniida in the Triassic and again after the Triassic–Jurassic extinction. Furthermore, increasing provincialism at family level during the Jurassic and Early Cretaceous, as well as the gradual demise of several clades during the Late Cretaceous are evident. Further cleaning and updating of the database will specifically improve synonymies as well as spatial and temporal distributions. As a result, phylogenetic and biogeographic hypotheses within one of the largest clades of Mesozoic bivalves will become testable.