When did malacostracans first appear in the fossil record?

The fossil record of the Malacostraca extends back to the early Paleozoic Era, specifically the Early Ordovician Epoch, approximately 488 million to 472 million years ago.1

While some earlier arthropods from the Cambrian Period (542 million to 488 million years ago) resembled malacostracans in body form, they are not considered direct ancestors because they lacked key characteristics of true Crustacea, such as mandibles and maxillae. The first eucaridan malacostracans appear later in the fossil record during the middle Paleozoic, specifically the Late Devonian Epoch (385 million to 359 million years ago).1