Widespread fossil freshwater gobies (Teleostei, Gobioidei): true distributions or wastebasket taxa?

Fossil remains of gobies are well known from Miocene freshwater deposits in the North Alpine Foreland Basin (NAFB) and Central Paratethys. Some of those have reportedly large distributions almost akin to extant invasive gobies. One example is “Gobius” (now Eleogobius) brevis (Agassiz, 1839), known from six localities across Western and Central Europe. Given this rather large distribution, the question stands whether this is the actual distribution of a single species or a wastebasket taxon.

Here, we reassess the taxonomic diversity of fossil remains known as Eleogobius brevis by focusing on two Middle Miocene palaeolakes from southern Germany (Ries crater, Oehningen) using historical material from museum collections (97 skeletons, many with otoliths preserved in situ). Based on comparative morphology using both osteological traits and otoliths, we show that the material comprises an unexpected taxonomic diversity of at least five previously unrecognized species.

Notably, none of the Ries gobies correspond to previously described species from the NAFB or Central Paratethys. Given the short time span of life-sustaining environmental conditions in the Ries crater lake and its isolation from major river systems, we thus infer a rapid goby radiation.

In contrast, otoliths preserved in situ in the Oehningen goby species indicate that these species had a broader distribution across the Middle Miocene freshwater systems of the NAFB.

Thus, E. brevis can be considered a wastebasket taxon. A careful re-examination of all specimens that were previously assigned to E. brevis is needed to confirm their taxonomic assignment.