Bioerosion of Lower Ordovician Hardgrounds in Southern Scandinavia and Western North America.

Trace fossils produced by macroboring invertebrates can be found in carbonate hardgrounds of early Ordovician age in southern Sweden, southern Norway and western Utah (U.S.A.). The bioeroded rocks are highly fossiliferous, thinly bedded, shallow-marine li-mestones. The macroborings in each of the three localities are vase-shaped cavities with diameters and lengths ranging from one to a few centimeters. At least some of the Swedish specimens apparently belong to the ichnogenus Gastrochaenolites LEYMERIE. These bioerosion trace fossils appear to be the oldest macroborings in carbonate hardgrounds, and they indicate that the macroboring niche was firmly established in shallow-marine carbonate shelf environments at least by Arenig time in the Ordovician Period