Neomys, KAUP, 1829

Genus Neomys View in CoL during the Early and Middle Pleistocene

Most of the European fossil record from late Biharian (Q 2) and early Toringian (Q 3) ( Fejfar 1961, 1966, Maul 1990, Rzebik-Kowalska 1991, Rzebik-Kowalska 1994, Zaitsev and Baryshnikov 2002, Agadjanian and Kondrashov 2007, Maul and Parfitt 2010, Rzebik-Kowalska 2013, van Kolfschoten 2014, Rzebik-Kowalska and Rekovets 2016, Pazonyi et al. 2018) is ascribed to Neomys newtoni , a fossil species described from Upper Freshwater Beds at West Runton, type locality of the Cromerian fauna (Q 2). The chronological span of these records and the Neomys newtoni stage of the Neomys history can be estimated by the interval 1.2–0.4 Ma (MIS 28–12). In any case, Neomys newtoni represents the oldest form clearly affiliated to Neomys . After a detailed analysis of material from the Austrian Q 3 locality Hundsheim, Rabeder (1972) highlights the resemblance of this taxon with extant N. anomalus / milleri , even suggesting putative identicality of newtoni and N. anomalus / milleri . Examining that (at first sight quite robustly supported) alternative, we confirmed that despite the overall resemblance, N. newtoni differs from milleri in more respects. A particularly broad phenotype variation seems to be a quite characteristic feature of this form. Demonstrating a normal statistical distribution in almost all characters in the entire set of respective specimens, we consider that all the items belong to a single clade, different from the extant milleri , i.e., N. newtoni . The span of phenotype variation suggests that Neomys newtoni may represent the source taxon of all recent species. The phylogenetic morphocline of N. anomalus / milleri would then be characterized by stabilization of phenotype of the ancestor species, while that of N. fodiens was driven by enlarging of skull and dentition, extension of molariform teeth and strengthening of the distal part of the mandible.

Apart from N. newtoni , further three fossil species of the genus Neomys were reported from biozones Q 2 and Q 3: N. intermedius BRUNER, 1952 , N. hintoni ZAITSEV et BARYSHNIKOV, 2002 , and N. browni HINTON, 1911 . Neomys intermedius is reported from two localities in Germany (Breitenberghöhle – Q 3 (Bruner 1957), Markgrabenhöhle – Q 3 (Bruner 1952)) and followed by an uninformative description that is not sufficient for exact diagnosis. Neomys hintoni is reported from three localities from Caucasus: Treugolnaya Cave – Q 3 (Zaitsev a Baryshnikov 2002), Mezmaiskaya Cave – Q 3 (Zaitsev a Osipova 2004), Haykadzor – Q 2 ( Tesakov et al. 2019). Even though the description is detailed and exactly defines the traits of this taxon, its taxonomic relevance should be further confronted with detailed information on phenotype variation of related species and dynamics of their local divergences, which are unfortunately still not available in a proper extent. The same can be said about Neomys browni , reported from two localities in the United Kingdom (Grays Thurrock – Q 3 ( Hinton 1911), Cudmore – Q 3 ( Roe et al. 2009)), and diagnosed by a narrow and low coronoid process. With regards to a broad phenotype variation (also demonstrated in the present paper) as a characteristic feature of N. newtoni , we tend to consider N. hintoni , N. intermedius as the local forms of Neomys newtoni , alternatively Neomys milleri (pertinent in the case of N. browni ).

Numerous hypotheses regarding history and range dynamics of Neomys were proposed based on methods of molecular phylogenetics and phylogeography, palaeontology and morphological similarities. Molecular phylogenetics establishes the interval of divergence of the extant species between 0.4 and 1.6 Ma.

According to Igea et al. (2015), Neomys fodiens was the first species to diverge (around 1.22 Ma), being the sister group of the rest of the species. Colonization of Europe during the Early Pleistocene followed by rapid expansion to northern and central European regions is presumed by Rzebik-Kowalska (1998) and Castiglia et al. (2007). According to Igea et al. (2015), Neomys teres separated from the common ancestor of N. milleri and N. anomalus 0.56 Ma. N. teres and N. anomalus / milleri could represent two lineages that survived Quaternary climatic oscillations in southern refugia: N. teres in Anatolia and N. anomalus on the Iberian Peninsula ( Castiglia et al. 2007). This agrees with one of the hypotheses presented by Kryštufek et al. (2000), who assume that the common ancestor of Neomys milleri and Neomys anomalus crossed the Bosporus and colonized Anatolia during one of the glacials. Part of the population stayed in the region south from the Black Sea and later evolved in Neomys teres . An alternative hypothesis assumes expansion of Neomys fodiens during a cold period southwards across Balkan-Anatolian bridge, followed by a return northward during an interglacial. The authors presume that one population was isolated in the Pontic mountains, where it evolved into N. teres . The population living along the land bridge evolved into the ancestor of N. milleri / teres ( Kryštufek et al. 2000) . Based on morphologic features, the same authors present a third hypothesis: the possibility of expansion of N. fodiens along the shore of the Black Sea to Caucasus and the Pontic mountains, where as a result of allopatric speciation, it evolves into N. teres . However, this hypothesis does not correspond to the results of molecular genetics, hence Kryštufek et al. (2000) as well as Castiglia et al. (2007) and Igea et al. (2015) consider the possibility of N. fodiens diverging first and being the sister taxon of the rest of the species the most probable. On the contrary, Neomys milleri would be a relatively recent taxon.

According to Castiglia et al. (2007), expansion of Neomys fodiens was faster in comparison to Neomys anomalus / milleri , due to N. fodiens possessing more developed adaptations to a challenging environment. Climatic oscillations would have had a more serious impact on the latter species. According to Castiglia et al. (2007), the N. anomalus-milleri clade shows a considerably higher degree of divergence. According to mitochondrial phylogenetics, N. anomalus comprises the population inhabiting the central region of the Iberian Peninsula, and N. milleri the rest of European population, including northeast of the Iberian Peninsula. These two lineages would have diverged 0.4 Ma, with a deviation 0.26–0.86 million years – in other words, during the Middle or Late Pleistocene ( Igea et al. 2015). According to the authors, it is probable that N. anomalus evolved on the Iberian Peninsula during one of the Middle Pleistocene glacials, while N. milleri colonized the Pyrenees only during the latest Pleistocene or Holocene.

The fossil record does not support hypotheses about older origins of N. fodiens and later divergence of N. milleri . The presence of N. fodiens in Europe is not proved until the Middle Pleistocene age (a few records, biozone Q 3); most of the records are dated to the present cycle (biozone Q 4). The hypothesis by Rzebik-Kowalska (1998) assuming colonization of Europe by N. fodiens during the Early Pleistocene still lacks any support from the actual fossil record. Considering its phenotype constitution, N. milleri can undoubtedly be regarded as the form retaining plesiomorhic patterns of the genus (comp. e.g., less reduced distal molars), while N. fodiens exhibits a derived state in most of the phenotype variables.

It cannot be ruled out that the increase of N. fodiens size was related to the disappearance of another large shrew, Macroneomys brachygnathus , during early Toringian. The earliest records positively representing Neomys fodiens are reported from the Iberian Peninsula (TD 10 in Atapuerca, 370 ka; Moya-Costa et al. 2023). The respective specimens exceed the limits of our extant samples, particularly with the specimens (from the same layer) identified as “ Neomyini cf. Macroneomys ”. These extremely large phenotypes correspond to the extant Iberian form, Neomys fodiens niethammeri , which shows – against expectancy – only shallow genetic differences from other extant populations of the species (Balmori-de La Puente et al. 2019).