Ferussina Grateloup, 1827 is a European Paleogene land snail genus, which is currently classified in its own family, the Ferussinidae Wenz, 1923 (1915), in the superfamily Cyclophoroidea. The shell of this genus is remarkable by its last quarter whorl turning towards the apex instead of away from it, which is an unusual trait in terrestrial snails. We show, however, that this trait has evolved at least nine times in terrestrial Eupulmonata and Caenogastropoda, and it does not justify distinction at the family level in any of the reported cases. This observation suggests the systematic position of Ferussina should not be based on the apexward-turning last quarter whorl alone but instead on the general morphology of the shell. As a result, we re-evaluate the systematic position of the Ferussinidae and treat it as a subfamily of the Cyclophoridae.

character evolution, Eocene, Oligocene, parallel evolution, terrestrial Gastropoda, unique trait

Ferussina Grateloup, 1827 (and its synonym Strophostoma Deshayes, 1828; see Wenz 1923; Kadolsky 2008) is a genus reported from middle Eocene (Lutetian) to upper Oligocene (Chattian) deposits of France, Germany, Italy, and Switzerland (Fig. 1); a dubious record comes from presumably lower Miocene strata of southern France (Degrange-Touzin 1892). It is currently classified in its own family, the Ferussinidae Wenz, 1923 (1915) (Bouchet et al. 2017) in the superfamily Cyclophoroidea Gray, 1847. Ferussina is characterized by a relatively large (ca 1–3 cm), depressed-globular shell with an obtusely conical spire, a round aperture, and a last quarter whorl turning towards the apex (Sandberger 1870–1875; Roman 1899; Rey 1968; Kadolsky 2008; Salvador et al. 2016). As a result, the aperture opens in the adapical direction of the shell, orientating the umbilicus of the shell upwards while the animal was crawling.

Figure 1. 

Geographic and stratigraphic distribution of Ferussina in central and western Europe. Records that are questionable in terms of stratigraphic horizon or species identification are indicated with a question mark (see Suppl. material 1: Table S1 for more information). The map was created with ESRI ArcGIS 10.4.

In his catalogue of fossil non-marine gastropods, Wenz (1923) included seven species in the genus Ferussina, i.e. F. anomphalus (Sandberger, 1871), F. anostomaeformis Grateloup, 1827 (the type species by monotypy), F. globosa Dumas, 1876, F. lapicida Leufroy, 1828, F. praeglobosa (Roman, 1904), F. striata (Deshayes, 1828), and F. tricarinata (Braun, 1838). These are distinguished by the relative height of the spire, presence of an inflation on the last whorl, presence of a keel or angulation on the last whorl, and presence and width of an umbilicus, as well as surface ornamentation (Fig. 2; compare also Deshayes 1828; Sandberger 1870–1875; Roman 1899, 1904; Kadolsky 2008). Sculpture ranges from fine to distinct, riblet-like growth lines and, in the case of F. tricarinata, narrow spiral keels on base and periphery.

Figure 2. 

Representatives of the genus Ferussina. A–C Ferussina anostomaeformis Grateloup, 1827, Gaas (Larrat), France, lower Oligocene; syntype, UBRG, Grateloup collection, no. 65-2-150 D Ferussina anostomaeformis, St-Paul-lès-Dax (Abesse, “Château”), France, upper Oligocene; MNHN.F.A72133 E–H Ferussina anomphalus capellinii (Sandberger, 1873), Blaustein (Arnegg), Germany, lower Oligocene; syntype, SMNS 22180 I–L Ferussina tricarinata (Braun, 1838), Hochheim, Germany, upper Oligocene (Hochheim Formation, “Landschneckenkalk”); NHMW 75000/E/1778. Photos: Laurent Charles (A–C), Pierre Lozouet (D), Rodrigo Salvador (E–H), Barna Páll-Gergely (I–L). Scale bars: 1 cm.

An “upright” turning last whorl (termed “anostomy” by Nordsieck 1986) is unusual in terrestrial snails but has repeatedly evolved in both the Eupulmonata (“pulmonates”) (at least six times) and Caenogastropoda (at least three times) (Schileyko 1998, 1999, 2000; Egorov 2009, 2013), and even in a Devonian marine gastropod (Braun 1838). This trait has not been considered a justification for the distinction at the family level in any of the reported cases. This observation suggests the systematic position of Ferussina should not be based on the apexward-turning last quarter whorl alone but instead on the general morphology of the shell. As a result, we re-evaluate the systematic position of the Ferussinidae and treat it as a subfamily of the Cyclophoridae Gray, 1847.

Abbreviations used:

MNHN – Muséum National d’Histoire Naturelle, Paris; NHMW – Natural History Museum Vienna; SMNS – State Museum of Natural History Stuttgart; UBRG – Université du Bordeaux.

While the apexward-turning last whorls are unique among fossil European land snails, we found this trait in a number of unrelated extant and fossil clades, including 12 pulmonate (Wenz 1940; Schileyko 1998, 1999, 2000) and four caenogastropod genera (Egorov 2009, 2013), representing at least nine independent events. Table 1 summarises the key information.

The list above shows that shells with the last whorl turned apexward are present in numerous unrelated lineages of pulmonate and operculate terrestrial snails. In all cases, the species and genera with this peculiar shape have normally coiled relatives. Similarly, the fossil Ferussina certainly evolved from normally coiled ancestors, and we should not give too great importance to this trait when determining its systematic position. Moreover, the closest relatives of these genera are often species with high-spired shells. This suggests that we cannot exclude high-spired cyclophoroideans from the possible relatives of Ferussina.

We can exclude the Pomatiidae as possible relatives, as members of this family have calcareous opercula that are often found as fossils. No such opercula have been documented for Ferussina. The Cochlostomatinae, also with numerous extant and fossil members, are smaller than Ferussina and are characterized by high, conical shells, and some members have calcareous opercula (Fehér 2004; Zallot et al. 2015). The cyclophoroid family Craspedopomatidae, represented by several fossil species in Europe, comprises only very small, globular forms of only a few millimetres in diameter (Wenz 1923; Harzhauser and Neubauer 2018).

The most probable group of relatives is the Cyclophoridae. Most members of this family have broadly conical shells similar to that of Ferussina, except for the apexwards turn of the last quarter whorl. Extant Cyclophoridae have non-calcareous opercula, which are not preserved as fossils. So far, 14 species of Cyclophoridae are known from the Cenozoic sedimentary record of Europe (WWenz 1923; Steklov 1966; Schütt 1991, 1997; Stworzewicz 1995). The oldest records derive from the upper Paleocene (Thanetian) of France. Earlier mentions of European cyclophoroids from the Jurassic and Cretaceous belong to the families Diplommatinidae, Megalostomatidae, and Pupinidae, or are unassigned cyclophoroids (Hrubesch 1965; Bandel 1991, 1993; Neubauer et al. 2019). The genus Ventriculus Wenz in Fischer & Wenz, 1914 was classified in the family Cyclophoridae, subfamily Pupinellinae by Wenz (1923), a group now included in Pupinidae (Bouchet et al. 2017). The Pupinidae presently inhabits Asia from India to the oceanic islands (Egorov 2013).

Cyclophoridae are otherwise mostly restricted to south-eastern Asia, and the European fossils represent a rare exception of biogeographic affinity between both regions. Only a few other taxa that are widespread in East Asia today are also found in the European Cenozoic fossil record, such as Diplommatinidae, Strobilopsidae, and Pupinidae (e.g. Wenz 1923; Manganelli et al. 2008; Páll-Gergely et al. 2015; Harzhauser and Neubauer 2018).

In summary, we suggest a revised systematic position of the genus Ferussina in the Cyclophoridae. Given the distinct biogeographic and stratigraphic setting and morphological differences to extant Cyclophoridae, we suggest to maintain the genus in a distinct subfamily, Ferussininae.

The extant genera with apexward-turning body whorl listed above inhabit various habitats, with about half of them being obligatory rock-dwellers, indicating that this peculiar trait can be developed under various environmental conditions. Ferussina lived in a period when the regions it occurred in central and western Europe (France, Switzerland, Germany, Austria, and northern Italy) were dominated by warm-temperate to subtropical evergreen forests (Pound and Salzmann 2017). The Late Oligocene Ferussina tricarinata was thriving in semiarid conditions in the Mainz Basin on the shores of a brackish to hypersaline lake (Kadolsky 1989). Other Ferussina species may have dwelled in more humid climates among leaf litter and under decaying logs, but we have insufficient data about the taphonomy and paleoecology of their occurrences.

We are grateful to Bruno Cahuzac, Laurent Charles, Anita Eschner, Pierre Lozouet, Hartmut Nordsieck, Emmanuel Robert, and Rodrigo Salvador for sending photos and/or providing valuable literature and information. Dietrich Kadolsky and Mathias Harzhauser are thanked for their constructive reviews. We are indebted to The Biodiversity Heritage Library for the multitude of rare literature made available to us (http://www.biodiversitylibrary.org). This study was supported by the MTA (Hungarian Academy of Sciences) Premium Post Doctorate Research Program granted to B. Páll-Gergely. T.A. Neubauer was supported by a DFG grant (no. NE 2268/2-1).