paleozoic-a few centimeters to tens of centimeters: post-Paleozoic >1meter
||Smith et al., Body size evolution across the Geozoic, Annual Review of Earth and Planetary Sciences, Vol. 44 :523-553, 2016 DOI: 10.1146/annurev-earth-060115-012147 link p.544 2nd paragraph
||Kidwell SM, Brenchley PJ. 1994. Patterns in bioclastic accumulation through the Phanerozoic: changes in input or in destruction?Geology 22: 1139–43 link AND Li X, Droser ML. 1999. Lower and Middle Ordovician shell beds from the Basin and Range province of the western United States (California, Nevada, and Utah). Palaios 14: 215–33 link
||P.544 2nd paragraph: "The evolution of physically and chemically robust structural elements to support large organisms has also impacted the nature of the sedimentary rock record. In addition to being bioturbated, Phanerozoic sedimentary rock sequences are identifiable by the accumulations of biogenic sediments, including coal, phosphorites, and shell beds in the form of shallow-marine accumulations of animal shells to deeper-marine accumulations of protistan tests of carbonate and silica. The oldest shell beds occur in Neoproterozoic carbonate rocks, comprising shells of Cloudina and Namacalathus, two genera of calcified metazoans with uncertain phylogenetic affinities (Grotzinger et al. 2000). The thickness of shell beds, like the depth and prevalence of bioturbation, has generally increased across the Phanerozoic along with the sizes of shell-producing animals. Paleozoic shell beds are typically a few centimeters to tens of centimeters thick, whereas post-Paleozoic shell beds commonly exceed one meter in thickness (primary sources)."