Changes in predator-prey interactions are often implicated as drivers of major evolutionary change. A prominent example is the dramatic changes in shallow marine assemblages during the Mesozoic Marine Revolution (MMR) when major clades, including rhynchonelliform brachiopods, became restricted and less diverse. Currently, shallow water temperate and polar brachiopods can be large, but in the tropics, they are all small. By contrast, we demonstrate that throughout the Jurassic large brachiopods occurred in shallow sites, from polar to tropical latitudes, but are absent in later periods from tropical areas. These changes occurred in parallel in both major orders (Rhynchonellida and Terebratulida) and also independently within the two sub-ordinal lineages within the Terebratulida (terebratulinids and terebratellinids). Increases in both grazing and predation pressures associated with the MMR might account for this pattern. However, we note that many current environments support both large brachiopods and high densities of grazing species and suggest that the pattern fits more closely to the intensification of durophagous predation in shallow tropical waters.

We collected data on the maximum size attained by modern brachiopod taxa. This database of 442 terebratulide and 58 rhynchonellide taxa was assembled from published accounts (70 papers and monographs) and direct measurements made from museum samples (including a large set from the wet collections of the Smithsonian Institution National Museum of Natural History (Washington D.C., USA), the Naturhistoriska riksmuseet (Stockholm, Sweden) and our field collections. The following were recorded: taxon (making no attempt to revise the generic or specific systematics), longitude and latitude of collection site, depth of collection, and length of the ventral valve of the largest individual encountered (in mm). For trawl data, we used the minimum depth recorded. Taxonomic coverage of the database is good with 95% of extant genera of both terebratulides and rhynchonellides captured and including c.90% of the type species. Our database was then filtered by depth to capture sub-samples representing collection depths of less than 80m (N=122 for terebratulides and N = 12 for rhynchonellides).

Palaeontological data were collected using 170 published papers and monographs, supplemented by direct measurements of specimens in museum collections of the Sedgwick Museum of Earth Sciences (Cambridge University, UK), the Oxford University Museum of Natural History (UK), the Natural History Museum (London, UK), the Naturhistoriska riksmuseet (Stockholm, Sweden) and the Smithsonian Institution National Museum of Natural History (Washington D.C., USA). For every fauna (i.e., taxa collected from the same locality and time interval) only the maximum-sized individual of the largest each of the terebratulide or rhynchonellide taxa present was recorded. The following data for the largest individual from each order (and for Jurassic terebratulides for each of the suborders Terebratellinida and Terebratulinida) were recorded: locality, precise age of deposit and length of the ventral valve (in mm). Only those samples collected with clear evidence of occurrence in the photic zone were included. Palaeolatitudes were derived either using the established value on the Paleobiology Database or from published local palaeogeographic reconstructions.