The mid-Paleozoic precursor to the Mesozoic marine revolution

Abstract

The mid-Paleozoic was punctuated by a rapid radiation of durophagous (shell-crushing) predators. These new predators were primarily placoderm and chondrichthyan fishes but probably also included phyllocarid and eumalacostracan arthropods. Coincident with the radiation of these durophages, beginning in the mid-Devonian, there was an increase in the frequency of predation-resistant morphologies in a variety of marine invertebrate taxa. Among bellerophontid molluscs, disjunct coiling disappeared and umbilici became less common while the frequency of genera with sculpture increased. The abundance of brachiopod genera with spines on one or both valves increased dramatically. Sculpture became more pronounced and common among genera of coiled nautiloids. Inadunate and camerate crinoids showed a marked increase in spinosity, and all three crinoid subclasses tended to develop thicker thecal plates.Trends toward increasing relative frequencies of predation-resistant features were formed in different ways. Bellerophontid genera lacking predation-resistant features tended to go extinct, leaving the sculptured, tighdy coiled forms as the predominant forms. Among Brachiopoda, the radiation of productids provided the tremendous increase in numbers of spinose genera. Among crinoids, predation-resistant features were acquired through evolution within established clades.These observations suggest that predation by shell-crushing predators has been an important control on the morphology and composition of the marine invertebrate fauna since at least the Middle Devonian. The mid-Paleozoic radiation of durophages and response of the marine fauna was in many respects similar to events of the Mesozoic Marine Revolution, in effect, the Paleozoic precursor to that event.

Strong coupling of predation intensity and diversity in the Phanerozoic fossil record

“…This phenomenon can be described as a passive diffusion of realized behaviors resulting from a true biological signal of increasing taxonomic diversity: trace-producing predatory strategies, such as drilling and peeling, become more common when taxonomic diversity increases. This explanation fits well with the proliferation of drilling predation and repair scars concurrent with the Ordovician radiation and the subsequent diversity high of the Paleozoic Plateau (14). Similarly, this model can explain why the Mesozoic Marine Revolution (16) coincided with the post-Jurassic taxonomic diversification of the marine metazoans.…”

“…1). However, our Paleozoic estimates indicate that predation intensity increased already by the late Ordovician/early Silurian, predating notably (by Ϸ70 million years) the midPaleozoic Marine Revolution, an interval of intense escalation postulated initially on the functional morphology of presumed predators and prey (14) and subsequently supported by trends in predation on brachiopods and sessile echinoderms (12,23). Similarly, although the Mesozoic Marine Revolution was initially proposed as a period of intense escalation in the mid-to-late Mesozoic (16), our results highlight the dearth of species-level predation estimates until the late Mesozoic (12) [see supporting information (SI) Text] and also suggest that the further increase in predation intensity occurred throughout the late Cenozoic.…”

“…In fact, the previous quantitative projects focused mainly on reconstructing predation records, but did not compare those records to long-term diversity patterns or, at best, addressed the issue marginally in qualitative and anecdotal terms. This may not be so surprising, when considering that the patterns revealed in those studies hinted at discordance rather than concordance between trends in diversity and predation intensity: mid Paleozoic spike in predation (12,14,17) occurred in the middle of the Paleozoic diversity plateau long after the Great Ordovician Radiation and the Mesozoic Marine Revolution took place in mid-late Mesozoic/early Cenozoic (16), while diversity may have continued to increase throughout the late Cenozoic (20-22) as well.To test for correlation between diversity and predation intensity, we have assembled a predation database for marine invertebrates that (i) provides methodologically consistent species-level estimates of trace fossil frequencies; (ii) spans the entire recorded history of marine metazoans (Ediacaran-Holocene); and (iii) includes a sufficient number of estimates based on bulk samples to assemble a time series of predation intensity estimates that can be contrasted against the fossil record of diversity. …”

“…In fact, the previous quantitative projects focused mainly on reconstructing predation records, but did not compare those records to long-term diversity patterns or, at best, addressed the issue marginally in qualitative and anecdotal terms. This may not be so surprising, when considering that the patterns revealed in those studies hinted at discordance rather than concordance between trends in diversity and predation intensity: mid Paleozoic spike in predation (12,14,17) occurred in the middle of the Paleozoic diversity plateau long after the Great Ordovician Radiation and the Mesozoic Marine Revolution took place in mid-late Mesozoic/early Cenozoic (16), while diversity may have continued to increase throughout the late Cenozoic (20)(21)(22) as well.…”

“…When evaluating the importance of ecological interactions in driving the Phanerozoic evolution of metazoans, predation has received particular attention, both because it has been invoked repeatedly as an evolutionary force (10,(14)(15)(16) and because quantitative data on the geological history of predator-prey interactions are accessible by studying trace fossils left on prey skeletons.…”