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Abstract
Margaritiferidae is an ancient freshwater bivalve family originated in the Jurassic in East Asia. Here, we revise several nominal taxa of fossil freshwater pearl mussels that were recovered from the Upper Pliocene and Pleistocene deposits of the Dniester and Prut river valleys. Based on morphological and stratigraphic data, we found that these nominal taxa belong to the genus Pseudunio and are junior synonyms of P. flabellatiformis (Grigorowitch-Beresowski, 1915). The new synonymy is proposed as follows: Margaritifera (Pseudunio) moldavica Chepalyga, 1964 syn. nov., Margaritifera (Pseudunio) robusta robusta Chepalyga, 1964 syn. nov., Margaritifera (Pseudunio) robusta speensis Chepalyga, 1964 syn. nov., and Margaritifera (Pseudunio) robusta tirassica Chepalyga, 1964 syn. nov. All these fossil nominal taxa were described based on minor differences in the shell shape and size, hinge structure, and stratigraphic position. Finally, we suggest an updated phylogenetic scheme of the genus Pseudunio, which contains five valid species: P. marocanus (Pallary, 1918) [Eocene – Recent, Morocco], P. auricularius (Spengler, 1793) [Pliocene – Recent, Southern and Western Europe], P. homsensis (Lea, 1865) [Pliocene – Recent, Orontes and Nahr al-Kabir basins], P. flabellatiformis (Grigorowitch-Beresowski, 1915) comb. rev. [Pliocene – Late Pleistocene, paleo-Dniester and paleo-Danube basins, an extinct lineage related to P. auricularius and P. homsensis], and P. flabellatus (Goldfuss, 1837) comb. rev. [Miocene, paleo-Danube Basin, a stem lineage, MRCA of P. auricularius - P. homsensis clade].
Highlights
Numerous fossil nominal taxa of freshwater pearl mussels (Bivalvia: Unionoida: Margaritiferidae) were introduced by paleontologists based on the differences in shell shape, size, umbo position, shape of adductor scars, and hinge structure (Bogatchev, 1961; Chepalyga, 1964, 1965, 1967; Devyatkin et al, 1971)
This study aims to revise several fossil taxa of Margaritiferidae described from the Pleistocene deposits of the Dniester and Prut river valleys in Moldova (Table 1) and to discuss the speciation in the genus Pseudunio using paleontological, biogeographic, and molecular evidences
Our sample of subfossil Pseudunio shells from the Middle Pleistocene deposits near the Sucleia village can be considered M. (P.) robusta speensis or M. (P.) robusta tirassica based on the stratigraphic position (Figs. 1-4)
Summary
Numerous fossil nominal taxa of freshwater pearl mussels (Bivalvia: Unionoida: Margaritiferidae) were introduced by paleontologists based on the differences in shell shape, size, umbo position, shape of adductor scars, and hinge structure (Bogatchev, 1961; Chepalyga, 1964, 1965, 1967; Devyatkin et al, 1971). Studies of recent taxa reveal that freshwater pearl mussels share high levels of intraspecific morphological variability and that minute morphological differences cannot be used as species-level diagnostic characters (Bolotov et al, 2015; Vikhrev et al, 2017; Lopes-Lima et al, 2018). The phylogenetic position of several fossil taxa related to this genus remains unclear, while paleontologists repeatedly suggested to use Pseudunio as generic or subgeneric name for fossil taxa with fully developed dentition, e.g. Margaritifera flabellata (Goldfuss, 1837) and M. flabellatiformis (Grigorowitch-Beresowski, 1915) (Scholz et al, 2007; Schneider and Prieto, 2011). Nesemann (1993) has already placed these fossil taxa within the genus Pseudunio
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