Nomenclatural review of Polyptychoceras and 18 related taxa (Ammonoidea: Diplomoceratidae)

Abstract

The nomenclature of Polyptychoceras, a Late Cretaceous heteromorph ammonite genus, and 18 related taxa is examined with a view to clarifying their nomenclatural availability, authors, dates of publication, and name-bearing types, on the basis of the International Code of Zoological Nomenclature (Fourth Edition). It is concluded that one family-group name, four genus-group names, and 12 species-group names are currently available. In contrast, the names Po. subundatum and Po. jimboi are unavailable. We also showed that Po. yubarense had been established by Shimizu (J Shanghai Sci Inst, Sect II, 1(11):159–226, 1935a).

Introduction

Polyptychoceras is a genus of heteromorph ammonites from the Upper Cretaceous, a member of the family Diplomoceratidae Spath, 1926. Due in part to its unique paper clip-like shell (Fig. 1), many studies have examined the paleoecology, taphonomy, and shell morphology of this genus (e.g., Matsumoto and Nihongi 1979; Okamoto and Shibata 1997; Okamoto and Asami 2002; Kruta et al. 2009; Ifrim et al. 2013; Okamoto et al. 2013). However, several pieces of nomenclatural information for each name in this genus remain unclear. For example, the name Po. yubarense, which has been attributed to Yabe (1927) or Jimbō (1894), was not established in these works. As a result, the true author and date of publication of this species are unknown.

Fig. 1

A well-preserved specimen of Polyptychoceras pseudogaultinum (Yokoyama, 1890), UMUT-MM19881a from Hokkaido Island, Japan, coated with ammonium chloride. In this individual, the paper clip-like shell is composed of four straight shafts running almost in parallel connected with U-shaped tubes. Scale bar represents 10 mm. The repository of this specimen is the University Museum, University of Tokyo. For detailed locality, see Okamoto and Shibata (1997)

Hayakawa and Tashiro (1994) and Okamoto and Shibata (1997) have identified taxonomic issues within Polyptychoceras. For instance, several individuals that had been initially described as distinct species were later interpreted as different ontogenetic stages of the same species by Okamoto and Shibata (1997). Most such problems remain unresolved today. Owing to this, restudying the taxonomy of Polyptychoceras in the future will contribute to revising the diversity of heteromorph ammonites in the Late Cretaceous.

In the present study, we examined the nomenclature of members of the genus Polyptychoceras and related taxa and clarified their nomenclatural availability, authors, and dates of publication according to the current International Code of Zoological Nomenclature Fourth Edition (International Commission on Zoological Nomenclature 1999; partly amended in ICZN 2003, 2012), hereafter referred to as the Code. In addition, we treat name-bearing types of each taxon.

Polyptychoceratinae Matumoto, 1938

Subfamily Polyptychoceratinae was originally proposed by Matumoto (1938) as the family “Polyptychoceratidae”. This name is not accompanied by a description, definition, bibliographic reference, or proposal for a new replacement name, but it is assumed to have formed from an available generic name, Polyptychoceras Yabe, 1927, by inference from its stem and the context of the original publication. Although this name does not satisfy the provisions of the Code’s Article 13.1, as mentioned above, it is available from its original publication because (1) Polyptychoceratinae was used as a valid taxon name before 2000 (e.g., Wright et al. 1996) and (2) it has not been rejected by an author who, after 1960 and before 2000, expressly applied Article 13 of the then current edition of the Code (Art. 13.2.1).

The type genus of this family-group taxon is Polyptychoceras Yabe, 1927 (Art. 63). Moreover, the rank of this name was changed from family to subfamily by Wiedmann (1962).

Polyptychoceras Yabe, 1927

Polyptychoceras was originally proposed by Yabe (1927) as a subgenus of the genus Hamites in a list of fossils from Hokkaido Island, Japan. The name Polyptychoceras is available, though it is not accompanied by a description or definition. This is because, from context, the specific names listed can be unambiguously assigned to nominal species (e.g., “pseudogaultinus Yok.”: Ptychoceras pseudogaultinum Yokoyama, 1890), though no bibliographic references were provided (Art. 12.2.5).

Shimizu (1935a, p. 178) reported that Polyptychoceras pseudogaultinum (Yokoyama) had been designated as a “subgenotype” [type species of subgenus] of subgenus Polyptychoceras by Yabe (1927); however, this designation has not been confirmed. In the same year, Shimizu (1935b, p. 271) stated that the “genotype” [type species] of the genus Polyptychoceras is “Anisoceras pseudogaultinum Yokoyama, Palaeontographica, XXXVI, 1890, 181, pl. XX, Figs. 1–3”. He states that the species is the type species and clearly accepts the species as the type species; thus Shimizu (1935b) is deemed to have subsequently designated Ptychoceras pseudogaultinum Yokoyama, 1890 as a type species (Art. 69.1.1).

According to Wright et al. (1996), the genus Polyptychoceras is subdivided into three subgenera: Polyptychoceras (s. s.), Subptychoceras, and Phylloptychoceras. In contrast, Jagt et al. (2006) treat Phylloptychoceras as an independent genus because of its characteristic ornamentation and suture line (see also Shigeta and Nishimura 2013). In the present study, we follow Jagt et al. (2006) and exclude Phylloptychoceras from Polyptychoceras.

Polyptychoceras vancouverense (Whiteaves, 1879)

Polyptychoceras vancouverense was originally proposed by Whiteaves (1879) as “Ptychoceras Vancouverense”. This name is available because it is accompanied by a description (Art. 12.1). The spelling of the specific name was emended by Usher (1952) as “vancouverense” (Art. 32.5.2.5).

Usher (1952) designated one of the illustrated specimens in the original publication of this name (Whiteaves 1879, pl. XIV, Fig. 3) as the lectotype (Art. 74). The specimen illustrated in Whiteaves (1879, pl. XIV, Fig. 3a), is a paralectotype (Art. 74.1.3).

Polyptychoceras pseudogaultinum (Yokoyama, 1890)

Polyptychoceras pseudogaultinum was originally proposed by Yokoyama (1890) as “Ptychoceras pseudo-gaultinum”. This name is accompanied by a description of the denoted species and is available (Art. 12.1). The spelling of the specific name was emended by Jimbō (1894) as “pseudogaultinum” (Art. 32.5.2.3).

Because neither a holotype nor a lectotype has been fixed for the species, the specimens illustrated in Yokoyama (1890, pl. XX, Figs. 1–3) are syntypes.

Polyptychoceras subquadratum (Yokoyama, 1890)

Polyptychoceras subquadratum was originally proposed with a description by Yokoyama (1890) as “Anisoceras subquadratum”. Therefore, this name is available (Art. 12.1). The illustrated specimen (Yokoyama 1890, pl. XX, Fig. 4) is the holotype fixed by monotypy (Art. 73.1.2).

Okamoto and Shibata (1997) interpreted this species as a junior subjective synonym of Po. pseudogaultinum. They acted as First Revisers and gave precedence to the name Po. pseudogaultinum (Art. 24.2.1).

Polyptychoceras haradanum (Yokoyama, 1890)

Polyptychoceras haradanum was originally proposed by Yokoyama (1890) as “Anisoceras Haradanum” based on several specimens. This name is available because it is accompanied by a description (Art. 12.1). The spelling of the specific name was emended by Yabe (1927) as “haradanus” (Art. 32.5.2.5) in which the ending was changed because of an agreement in gender.

Matsumoto et al. (1963) designated the specimen illustrated in the original publication of this name (Yokoyama 1890, pl. XX, Fig. 5) as the lectotype (Art. 74.4).

Polyptychoceras subundulatum (Yokoyama, 1890)

Polyptychoceras subundulatum was originally proposed by Yokoyama (1890) as “Anisoceras subundulatum”. This name is accompanied by a description and is available (Art. 12.1).

Matsumoto et al. (1963) designated the specimen illustrated by Yokoyama (1890, pl. XX, Fig. 6) as the lectotype. This designation is invalid because it was conducted for an unavailable name as mentioned in the next section (Art. 74.3). The specimens illustrated in Yokoyama (1890, pl. XX, Figs. 6–7) are, therefore, syntypes.

Polyptychoceras subundatum (unavailable name)

In Matsumoto et al. (1963, p. 30), the above species (Polyptychoceras subundulatum) was spelled incorrectly as “Polyptychoceras subundatum” more than once. Because this change in the spelling of the specific name can be interpreted as “demonstrably intentional” (Art. 33.2.1), the latter name is an “unjustified emendation” (Art. 33.2.3). If the unjustified emendation meets the other requirements for availability, this name is itself an available name (Art. 19.1). However, this name was also written as “Anisoceras subundatum”. The generic combination of this “species” is ambiguous and this name is thus unavailable (Art. 11.9.3.4).

Polyptychoceras obstrictum (Jimbō, 1894)

Polyptychoceras obstrictum was originally proposed with a description by Jimbō (1894) as “Hamites obstrictus”. Therefore, this name is available (Art. 12.1).

Matsumoto (1963) designated a specimen illustrated in the original publication of the species (Jimbō 1894, pl. VII [XXIII], Fig. 2) as the lectotype. This designation is invalid because it was conducted for the incorrect subsequent spelling “Hamites obstrictum” (unavailable name), which is without agreement in gender. All specimens of the type series are syntypes and collectively constitute the name-bearing type (Art. 73.2), because neither a holotype nor a lectotype has been fixed for the species. Therefore, the specimen illustrated in Jimbō (1894, pl. VII [XXIII], Fig. 2) is a syntype.

Polyptychoceras yabei (Nagao, 1931)

Polyptychoceras yabei was originally proposed by Nagao (1931a) as “Hamites yabei”. This name is accompanied by a description of the characters purported to differentiate the species and is available (Art. 13.1). The same name was used by Nagao (1931b, c) in a description of an aptychus from Hokkaido Island, Japan. In Nagao (1931b), the name is not accompanied by a description, definition, bibliographic reference, or proposal for a new replacement name. Thus, the name does not satisfy the provisions of Article 13.1. In Nagao (1931c), the name is accompanied by a description of the characters purported to differentiate the species and satisfies the provisions of Article 13.1. However, Nagao (1931c) was published in September 1931, whereas Nagao (1931a) was published in April 1931. Therefore, the name Hamites yabei is attributed to Nagao (1931a) (Art. 50.1).

Neither a holotype nor a lectotype has been fixed for the species. Accordingly, the specimen illustrated in Nagao (1931a, p. 168, Figs. 1, 1a) is a syntype.

Polyptychoceras mihoense Shimizu, 1935

Polyptychoceras mihoense was originally proposed by Shimizu (1935a) as a species of the genus Polyptychoceras. This name is accompanied by a description and is available (Art. 13.1). The name was also proposed by Shimizu (1935b), but this publication does not satisfy the provisions of Article 13.1 in terms of listing only the species name.

No holotype or lectotype has been fixed for the species.

Subptychoceras Shimizu, 1935

Subptychoceras was established by Shimizu (1935a), with a description and Subptychoceras yubarense Shimizu, 1935, fixed as the type species by monotypy (Art. 68.3). The name was also proposed by Shimizu (1935b) in the same manner. However, Shimizu (1935b) was published in July 1935, whereas Shimizu (1935a) was published in February 1935. Therefore, Subptychoceras is attributed to Shimizu (1935a).

Polyptychoceras yubarense (Shimizu, 1935)

Polyptychoceras yubarense was established by Shimizu (1935a) as “Subptychoceras yubarense”. Shimizu (1935a) incorrectly attributed this name to Yabe (1927); however, the name “Hamites yûbaresis” [sic][recte yûbarensis], proposed by Yabe (1927, p. 44 [18]), is a nomen nudum (with no original description, or indication). In contrast, Hamites sp. in Jimbō (1894), which is referred to in the explanation by Shimizu (1935a), is accompanied by a description of the species denoted by the name. For this reason, Subptychoceras yubarense proposed by Shimizu (1935a) is available (Art. 13.1.2).

Because neither a holotype nor a lectotype has been fixed for the species, the specimen illustrated in Jimbō (1894, pl. VII [XXIII], Fig. 6) is a syntype.

Polyptychoceras jimboi (nomen nudum)

Polyptychoceras jimboi was originally proposed as a species of the genus Polyptychoceras by Matumoto (1938) in a table of stratigraphic distributions of Cretaceous fossils without a description. Therefore, Po. jimboi is unavailable (Art. 13.1).

Dihamites Matsumoto, 1977

Dihamites was originally proposed by Matsumoto (1977). This name is accompanied by a description, diagnosis (Art. 13.1), and fixation of a type species (Art. 13.3). Therefore, Dihamites is available. The type species of the genus-group taxon is Dihamites obiraensis Matsumoto, 1977, fixed by Matsumoto (1977) by original designation (Art. 68.2).

Polyptychoceras obiraense (Matsumoto, 1977)

Polyptychoceras obiraense was established by Matsumoto (1977) as “Dihamites obiraensis”. The specimen illustrated in Matsumoto (1977, pl. 59, Fig. 2; text-Fig. 12) is a holotype fixed by original designation (Art. 73.1.1).

Heteroptychoceras Matsumoto, 1977

Heteroptychoceras was originally proposed by Matsumoto (1977). This name is accompanied by a description that is purported to differentiate the genus (Art. 13.1) and is further accompanied by the fixation of a type species (Art. 13.3). Hence, the name Heteroptychoceras is available. The type species of the genus-group taxon is Heteroptychoceras obatai Matsumoto, 1977, fixed by Matsumoto (1977) by original designation (Art. 68.2).

Polyptychoceras obatai (Matsumoto, 1977)

Polyptychoceras obatai was originally proposed by Matsumoto (1977) as “Heteroptychoceras obatai”. This name is accompanied by a description that is purported to differentiate the species and is therefore available (Art. 13.1). One of the specimens illustrated in Matsumoto (1977, pl. 58, Fig. 4) is a holotype fixed by original designation (Art. 73.1.1). The specimen illustrated in Matsumoto (1977, pl. 60, Fig. 1) is a paratype (Art. 72.4.5).

Polyptychoceras sakhalinum Alabushev and Wiedmann, 1997

Polyptychoceras sakhalinum was established by Alabushev and Wiedmann (1997). One of the specimens illustrated in Alabushev and Wiedmann (1997, pl. 4, Fig. 4) is a holotype fixed by original designation (Art. 73.1.1). Therefore, all specimens of the type series other than the holotype, such as that illustrated in Alabushev and Wiedmann (1997, Figs. 5–7 in pl. 4 and text-Fig. 4D), are paratypes (Art. 72.4.5).

Conclusion

Toward a taxonomic revision, we examined the nomenclature of the genus Polyptychoceras and 18 related taxa on the basis of the current Code to clarify their nomenclatural availability, authors, dates of publication, and name-bearing types. We conclude that one family-group name, four genus-group names, and 12 species-group names are available, whereas two species-group names are unavailable (summarized in Table 1).

Table 1 Summary of the nomenclatural availability of the genus Polyptychoceras and 18 related taxa