The Last Stand of an Ordovician Heritage: Daedalus from the Upper Silurian of the Yangtze Platform, South China

The widely documented ichnogenus Daedalus is a relatively short-ranged, facies-constrained trace fossil, with enigmatic paleoecology interpretations and potential paleoclimate and evolutionary significance. Here, we conduct an integrated study involving facies analysis, redox conditions, paleoclimate and paleoproductivity parameters, as well as spatio-temporal distribution of Daedalus in the geological record. D. archimedes was firstly reported from the upper offshore and lower shoreface settings of the upper Silurian of South China, which represents the highest stratigraphic level of this ichnogenus. These trace fossils represent deposit-feeding structures that occurred in the well-oxidized, fine-grained sediments with low primary productivity, formed in a humid-warm paleoclimate zone. The substrate characteristics and referred trophic mode of the last Daedalus deviate from previous occurrences, potentially suggesting adaptive evolution, including a changed feeding strategy and a possible elevated respiration rate in the context of higher atmospheric oxygen levels. Against a backdrop of intensified competitions from more advanced life styles and progressively complexified tiering structures initiated during the Floian-Dapingian nearshore innovation, Daedalus experienced an abrupt post-Middle Ordovician decline, culminating in their complete disappearance from the geological record following the Silurian. While the Silurian Daedalus display a distinct tropical provincialism, their Ordovician counterparts were restricted to temperate to cold waters in the Southern Hemisphere. The changed latitudinal distribution gradient of Daedalus, from high and middle paleolatitude regions during the Early Ordovician, to middle and low paleolatitude regions during the Middle and Late Ordovician coincides with a critical shift from greenhouse to icehouse conditions during the Early Paleozoic. This correlation highlights the potential of short-ranged, widespread trace fossils as independent proxies for major climatic perturbations in deep time.