Ischymomys, ZAZHIGIN, 1977

Ischymomys

The name of the genus Ischymomys was first published in Gromov (1972: 16) as a mentioned information from a letter of the year preceding the publication date (“ Ischymomys ZAJIGIN, 1971 (in litt.)”), with morphological notes ( Gromov 1972: 19), but without illustration of the molars. The so-called Hipparion fauna of the Pri-Irtysh was indicated as the stratigraphic age of the find horizon ( Gromov 1972: 19). In later literature, the date of the genus was cited either as 1972 (according to Gromov’s article), as for example in Savinov (1982, 1988), or as 1971 (according to Zazhigin’s letter), as for example in Kordos (1994) or McKenna and Bell (1997: 150).

However, neither date is correct, because the first mention of the name Ischymomys in Gromov (1972) does not follow the rules of ICZN (International Code of Zoological Nomenclature), and is therefore a nomen nudum. This naming did not conform because it lacks a diagnosis and is not based on a type species (cf. Articles 13.3 and 42.3). Regarding genus-group names, it says: “The application of each genus-group name is determined by reference to the type species of the nominal taxon that it denotes.” According to Articles 13.3.1–3 and 42.3.2 of the ICZN (1999), the only exceptions from this rule are nominal taxa of the genus group established before 1931, which is not the case here.

The species Ischimomys kalbica, has been established one year later by Mos’kina (1973) from the Makovka locality in Kazakhstan in unpublished thesis, and therefore it also must be regarded as nomen nudum (for the usage of the genus name Ischimomys instead of Ischymomys , see comment below).

In 1977, Ischymomys , the former nomen nudum, was used again in the context of a description of the corresponding finds. In the description and diagnosis (Zazhigin in Gromov and Polyakov 1977), the explicit designations Ischymomys gen. nov. and I. qudriradicatus sp. nov. were applied. This is a legitimate procedure, permitted by the ICZN rules, which leads to valid genus and species names: “A nomen nudum is not an available name, and therefore the same name may be made available later for the same or a different concept; in such a case it would take authorship and date from that act of establishment, not from any earlier publication as a nomen nudum ” ( ICZN 1999).

Therefore, in Gromov and Polyakov’s (1977) monograph on Microtinae (= Arvicolinae ), this new genus Ischymomys was first described with the type species I. quadriradicatus (designated by monotypy) from Petropavlovsk (now Petropavl) from the Upper Miocene deposits of the Ishim Formation. Holotype is the right m1, No. 952/ 51 in collection of Geological Institute, Russian Academy of Sciences. It was diagnosed as follows ( Gromov and Polyakov 1977: 210; translation from the English version Gromov and Polyakov 1992): “Voles with cementless molars. M1 with three roots and M2, M3 with four ones. Posterior “island” may be present on all upper molars, rapidly disappears on anterior molars, but always present on M3. Anterior “island” absent on M3. Paraconid section of m1 with an “island” that forms during closure of first medial fold and disappears before roots reach half-crown height. True prismatic fold absent; false (juvenile) fold often observed instead. Enamel equally thick throughout periphery of tooth. Position of roots of posterior lower molars relative to incisor not known.” However, no illustrations were provided in this publication either.

Over the years, literature has sometimes inconsistently used the name Ischymomys or Ischimomys . Although the river on the bank of which the site is located is called Ишим (in Cyrillic) and would be letter by letter transliterated as Ishim, the genus was given the name Ischymomys . A. Tesakov (reviewer of this paper) provides the following explanation: “Ishim in Russian is pronounced using the sonant of the middle row transliterated [actually transcribed into English as «y».]”. The spelling Ischymomys is the case in both the first (invalid) mention by Zazhigin cited in Gromov (1972), and the second (valid) description and diagnosis of Zazhigin in Gromov and Polyakov (1977), i.e., correct original spelling. This is also quoted in Gromov and Baranova (1981): Ischymomys quadriradicatus ZAZHIGIN, 1977 . On the other hand, Savinov (1982, 1988) named the genus Ischimomys ZAZHIGIN, 1972 . This spelling was also used by Kordos (1994), although he noted in a footnote “P.S.: The name of Ischimomys and Ischymomys are mixed in different publications.” Interestingly, even Zazhigin himself once wrote in Zazhigin et al. (2002) the genus name as Ischimomys .

The correct designation is therefore Ischymomys quadriradicatus ZAZHIGIN, 1977 . Finally, it should be mentioned that MEIN (2003: 414) incorrectly stated the year of the first description as Ischymomys ZAZHIGIN, 1992 , which is obviously based on the translated version of the book of Gromov and Polyakov from 1977 into English in 1992 ( Gromov and Polyakov 1992).

It always helps the reader when illustrations of the dentition of a newly described species are published as well. However, according to ICZN (1999), illustrations of the species are only recommended for species described after 1999 (cf. Article 16. Names published after 1999: Recommendation 16F. “… to add information about the type specimens and illustrate holotype or syntypes ”). However, the first illustrations of Ischymomys were not provided for the type species I. quadriradicatus , but for the species I. ponticus TOPACHEVSKIY, SKORIK et REKOVETS, 1978 , which was discovered at the Ukrainian site Frunzovka (now Frunzivka) 2, and described in 1978 with clear drawings of these specimens. The new species was diagnosed ( Topachevskiy et al. 1978: 39; translated from Russian with some terms slightly modified according to the current usage): “The middle pair of salient angles (paracone and hypocone) of M3 are almost completely separated: the width of the connection between the dentine fields is smaller or approximately similar to the thickness of the enamel. The linea sinuosa and, apparently, the enamel islet on M1, are more strongly developed than in the type species I. quadriradicatus ZAZHIGIN. ”

Only Savinov (1982) provided descriptions with illustrations and measurements of the type species Ischymomys quadriradicatus from the type locality Petropavlovsk, but based on different material than that of Zazhigin. The illustrations show some examples of all molar positions in occlusal and lateral view. However, some of the figures are small drawings in which the features (confluence, shape of re-entrant and salient angles) are not particularly easy to recognise. Better illustrations of this material can be found in a later work by Savinov (1988) (for m2s and m3s, see Text-figs 4 and 5 of this paper).

Over the years, the number of originally rare finds of the genus Ischymomys has increased significantly, and now includes (1) the material from the type locality of I. quadriradicatus Petropavlovsk , for which Zazhigin (in Gromov and Polyakov 1977) reported more than 60 isolated molars, and Savinov (1982) nearly 300 isolated molars of all tooth positions and 10 mandible fragments; (2) the finds from Makovka in Kazakhstan ( Mos’kina 1973, Savinov 1988, Zazhigin et al. 2002); (3) the finds from Frunzivka 2 ( Topachevskiy et al. 1978, Nesin and Topachevskiy 1991, Topachevskiy and Nesin 1992) and other Ukrainian localities ( Rekovets and Pashkov 2009, Nesin 2013, Rekovets et al. 2014, Kovalchuk 2017, Nesin and Kovalchuk 2017) such as (4) Popove 3 (formerly Popovo), (5) Lysa Gora 2, (6) Mykhailivka-on-Bug 1, (7) Mykhailivka-on-Bug 2 (formerly Mikhailovka 1 and 2), and (8) Verkhnya Krynytsia; (9) Kohfidisch (mandible with m2, originally determined as Promimomys (Prosomys) sp.) in Austria ( Bachmayer and Wilson 1978, but as Ischymomys sp. in Daxner-Höck and Höck 2015); (10) Shala in Chia (a single m1 fragment) ( Qiu and Li 2016); and (11) Leordoaia in Moldova (1 M1) ( Nicoara and Lungu 2008, Nicoara 2013: pl. IX, fig. 2). It also seems very likely that the finds from (12) Nyarad (1 M1) ( Kretzoi 1976, Kordos 1994, Fejfar et al. 2011: 11) and (13) Sümegprága (2 m 1, 1 m 3) ( Kordos 1994, Fejfar et al. 2011: 11) are actually not Pannonicola , but Ischymomys remains (see below).