Abstract
The modern Gobioidei (Teleostei) comprise eight families, but the extinct †Pirskeniidae from the lower Oligocene of the Czech Republic indicate that further families may have existed in the past. However, the validity of the †Pirskeniidae has been questioned and its single genus †Pirskenius has been assigned to the extant family Eleotridae in previous works. The objective of this study is to clarify the status of the †Pirskeniidae. Whether or not the †Pirskeniidae should be synonymised with the Eleotridae is also interesting from a biogeographical point of view as Eleotridae is not present in Europe or the Mediterranean Sea today. We present new specimens and re-examine the material on which the two known species of †Pirskenius are based (†P. diatomaceus Obrhelová, 1961; †P. radoni Přikryl, 2014). To provide a context for phylogenetically informative characters related to the palatine and the branchiostegal rays, three early-branching gobioids (Rhyacichthys, Protogobius, Perccottus), an eleotrid (Eleotris) and a gobiid (Gobius) were subjected to micro-CT analysis. The new data justify revalidation of the family †Pirskeniidae, and a revised diagnosis is presented for both †Pirskenius and †Pirskeniidae. Moreover, we provide for the first time an attempt to relate a fossil gobioid to extant taxa based on phylogenetic analysis. The results indicate a sister-group relationship of †Pirskeniidae to the Thalasseleotrididae + Gobiidae + Oxudercidae clade. Considering the fossil record, the arrival of gobioids in freshwater habitats in the early Oligocene apparently had generated new lineages that finally were not successful and became extinct shortly after they had diverged. There is currently no evidence that the Eleotridae was present in the European ichthyofauna in the past.
Highlights
Living gobioids are distributed worldwide and constitute one of the most species-rich vertebrate suborders, with approximately 2,200 species belonging to > 270 genera [1]
The specimens of Protogobius attiti, Perccottus glenii and Eleotris pisonis each display six branchiostegal rays (Fig 5A3, 5A4, 5B3 and 5C3), while the specimen of Gobius incognitus reveals a number of five branchiostegal rays (Fig 5D3)
In R. guilberti the penultimate branchiostegal ray is associated with the posterior ceratohyal (Fig 4A3, 4A4, 4B3 and 4B4), while in P. attiti the penultimate branchiostegal ray articulates at the anterior ceratohyal, but close to the gap that separates this part of the bone from the posterior part (Fig 5A3 and 5A4)
Summary
Living gobioids are distributed worldwide and constitute one of the most species-rich vertebrate suborders, with approximately 2,200 species belonging to > 270 genera [1] They are small, mostly benthic fishes that form a significant faunal component of reefs and other shallow marine ecosystems, and are abundant in brackish and freshwater habitats [2]. The oldest gobioid species known from clearly freshwater environments are based on skeletons dated to the early Oligocene [14,15,16,17] They are represented by four species, †Pirskenius diatomaceus Obrhelova, 1961, †P. radoni Přikryl, 2014, ’Gobius' gracilis Laube, 1901 (which probably represents an extinct genus) and †Lepidocottus papyraceus (Agassiz, 1832).
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