AUTHOR=Sedorko Daniel , de Barros Gabriel E. B. , Netto Renata Guimarães , Ghilardi Renato Pirani , Agostinho Sônia , Ramos Kimberly Silva , Franco Neto Emmanuel , Moreira Junior Carlos Alves , Borghi Leonardo 

TITLE=Multiple-Rusophycus assemblage from the Parnaíba Basin (NE Brazil) reflects trilobites as tracemakers and molting behavior

JOURNAL=Frontiers in Ecology and Evolution

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2023.1117947

DOI=10.3389/fevo.2023.1117947

ISSN=2296-701X

ABSTRACT=Trilobites inhabited all environments of Paleozoic seas, ranging from estuaries to continental slopes, and were globally distributed. Although their functional morphology and phylogenetic relations are established by well-preserved body fossils, the behavior of trilobites has received less attention. Three well-known trace fossils are interpreted to be produced by trilobitomorphs when preserved in Paleozoic rocks, Rusophycus (a resting trace), Cruziana (a furrowing trace), and Diplichnites (a locomotion trace). Those trace fossils unveil some aspects of trilobite behavior, but they were not investigated to test paleoecologic strategies based on morphometric parameters. This study uses Rusophycus to access the paleoecologic strategies of trilobites in storm-dominated shallow marine deposits of the Pimenteira and Cabeças formations (Middle to Upper Devonian, Parnaíba Basin, Brazil). Relatively small-sized Rusophycus are dominant in such deposits, suggesting the dominance of young tracemakers and inferred r-strategist populations. The here reported multiple-Rusophycus assemblage reveals paleoecologic strategies of the population, and tiers relationship (cross-cutting epistratal and shallow-tier trace fossils such as Bergaueria, Palaeophycus, and Protopaleodictyon) indicate deep Rusophycus. The main reason for those burrowing activities deep in the substrate might be protection during ecdysis, probably by calmoniids or homalonotids. A carnivorous behavior to excavate deep within the substrate cannot be discarded, but Brazilian sedimentary basins have no record of carnivorous trilobites, which is an argument against this hypothesis.