The trace fossil Thalassinoides from the Upper Ordovician of the eastern Great Basin; deep burrowing in the early Paleozoic

Upper Ordovician Thalassinoides burrows are common in carbonate rocks in the eastern Great Basin. The unidentified bulldozers that caused these burrows behaved much like the Cretaceous-Recent shrimp, Callianassa, as is seen by the similarity of their burrows. Ordovician Thalassinoides formed burrow galleries that reached a depth of up to one meter. Suggestions that organisms were not capable of burrowing deeper than 6 cm in open marine, soft substrata until the end of the Paleozoic must be revised.--Modified journal abstract.