Bioerosional innovation for living in carbonate hardgrounds in the Early Ordovician of Sweden

Some of the world's oldest macroborings occur in hardgrounds in lower Ordov ician (Arenig) limestones exposed on the island of Gland, southern Sweden. The trace fossils, which are described here as Gastrochaenolites oelandicus isp. nov., appear to be dwelling structures excavated in the indurated sub strate by invertebrates of unknown taxonomic affinity. They are the oldest examples of this ichnogenus. The appearance of a macroboring life habit at this early time represents a revolutionary new adaptive strategy for inhabi ting carbonate hardgrounds. However, this innovative strategy apparently wa s not successful for the long term, because this particular macroboring tax on seems to have disappeared shortly after its early Ordovician appearance.