How benthic animals responded to the Paleozoic plant terrestrialization: Evidence from trace fossils and their ecosystem engineering reconstruction

The Paleozoic plant terrestrialization (PPT) represents a significant evolutionary event in geological history, documenting the colonization of terrestrial environments by plants and animals as well as the establishment of terrestrial ecosystems. Trace fossils, as a reliable interaction proxy between organisms and environments, not only provide a comprehensive record of the activities of early terrestrial organisms, but also offer valuable insights into the reconstruction of terrestrial ecosystems during the mid-late Paleozoic. This study presents a novel, systematic compilation of trace fossils across fully marine, marginal-marine and alluvial facies from the mid-late Paleozoic in three major blocks of China, that is, North China, South China, and Tarim, which occupied different latitudes during that time. This comprehensive compilation encompasses 427 stratigraphic units, and a total of 101 ichnogenera and 54 architecture designs. The study also reassessed several ichnological parameters, including ichnodiversity, ichnodisparity, tiering, as proxies for assessing the pacing of benthic ecosystem reconstruction following the PPT. The evolutionary trend of ichnodiversity and ichnodisparity across different regions and sedimentary environments was revealed and compared. Notably, decoupling ichnodiversity and ichnodisparity show a step-wise increasing trend during the Silurian–Devonian transition, reaching maximum values in siliciclastic supratidal to intertidal, marginal-marine, and alluvial settings during the Lochkovian, Pragian, and Emsian, respectively. Interestingly, along with the PPT, benthic animals were able to colonize new niches in shallow- and deep-marine environments from the nearshore and offshore settings. Environmental factors such as the fluctuations of paleoclimate changes and enhancement of continental weathering caused by PPT had probably triggered the transformative changes in the marine-terrestrial environment. The migration of Zoophycos from shallow-marine environment to marginal-marine and deep-marine environments during the mid-late Paleozoic, nominated as the Zoophycos diversification event, is presented as a proxy of PPT. From a macroevolutionary perspective, a global increase in seawater nutrients is anticipated to drive biological adaptations in organisms, allowing trace makers that are more adapted to the low-oxygen environments to prosper. This study provides novel insights into the innovation of benthic animal behaviors and PPT during the Paleozoic era.