Misunithyris, Baeza-Carratalá & Pérez-Valera & Pérez-Valera, 2018

Baeza-Carratalá, José Francisco, Pérez-Valera, Fernando & Pérez-Valera, Juan Alberto, 2018, The oldest post-Paleozoic (Ladinian, Triassic) brachiopods from the Betic Range, SE Spain, Acta Palaeontologica Polonica 63 (1), pp. 71-85 : 75-76

Genus Misunithyris nov.

Etymology: From Mīšūnīš, ancient name of the current Mundo River; in the Mundo River valley, the most significant outcrops of specimens from which this genus is erected are found.

Type species: Misunithyris goyi sp. nov. (by monotypy); see below.

Diagnosis.—As for the type species by monotypy.

Remarks.—The supra-generic systematic arrangement of Misunithyris is debatable, depending on the diagnostic criteria selected. Exceptional concurrence of several internal and external features can make attributable this genus to different groups within Terebratulida . On the one hand, the new genus herein erected shows common features with the superfamily Dielasmatoidea Schuchert, 1913 , which includes some genera with enveloped dental plates and cardinal process. However, the assignment to Dielasmatoidea can be problematic because Misunithyris does not evidence a dielasmoid-type brachidium (sensu Dagys 1974 or Smirnova 2008). In this sense, supplementary elements such as median ridges or vertical plates (even not forming part in the development of brachidium, as stated by Dagys 1974 and Smirnova 2008) have not been observed in the internal structure of Misunithyris . Furthermore, some Dielasmatoidea representatives show septum-supported architectures and often short-looped developments (e.g., Adygella Dagys, 1959 ; Dielasmina Waagen, 1882 ; Tunethyris Calzada, Peybernes, Kamoun, and Youssef, 1994 ). In addition, crural bases are given off dorsally instead the distinctive crural progress revealed in Misunithyris .

Within Dielasmatoidea , higher similarity was expected with the anteriorly multicostate stock attributed to the Permian Dielasmina Waagen, 1882 and Hemiptychina Waagen, 1882 and the Permian–Triassic Costoconcha Jin, Sun, and Ye, 1979 , since besides the anterior ribbed pattern, all genera share quite a few beak features and the presence of cardinal process, but the rest of the internal structure is totally different, mainly referred to the dental plates and the crural development, which is clearly a brachidium-supported structure in the first stages.

Another dielasmatoid morphotype, widely distributed and to some extent contemporary with Misunithyris is represented by Coenothyris Douvillé, 1879 . The species of this Triassic genus display comparable dental plates, undeveloped or fused with the thickened shell wall, evident cardinal process, and long loop. Conversely, it evidences an initial septum-supported structure, notable septalium and, especially, the external features (such as smooth shell, often with strong uniplication) are entirely different (e.g., Popiel-Barczyk and Senkowiczowa 1989; Török 1993; Senkowiczowa and Popiel-Barczyk 1996; Kaim 1997; Pálfy 2003; Feldman 2005).

Arrangement within Zeillerioidea Allan, 1940 is the most plausible option, mainly because of the presence of dental lamellae, the well-developed and large dorsal median septum, and a clear zeilleroid-type brachidium (sensu Smirnova 2008) with a long-looped development, not connected to the median septum. However, some characters do not fully agree with the various families up to now determined in Zeillerioidea .

Misunithyris shares with the family Eudessidae Muir-Wood, 1965 the envelopment of dental plates, the presence of a cardinal process and most of the beak features. The most remarkable difference to Eudessidae are in a short dorsal median septum and the crural bases given off dorsally, as well as the usual growth of a median cardinal plate of the later group and not perceived in Misunithyris . Some external diagnostic criteria are very different as well, since even showing Eudessidae multicostate shells, Misunithyris shows a marginal ribbing pattern instead the entire multicostate shell-length of Eudessidae . Folding pattern is also unrelated as the conspicuous dorsal sulcus developed by Misunithyris is not shared with any Eudessidae representatives.

The affinities with the family Zeilleridae are found in several subfamilies. Some representatives of the subfamily Vectellinae Baker, 2006 exhibit a long-looped development and cardinal process as a knob or poorly developed callus. However, Middle–Late Triassic representatives of this subfamily are very different in both external and internal features to the new established genus. It is the case of Fletcherithyroides Dagys, 1977 , Aulacothyroides Dagys, 1965 , and Parantiptychia Xu and Liu, 1983 , consisting on smooth morphotypes, also showing a long stage of crura supported by septal pillars. Probably the clearest affinity in this subfamily is found in the Upper Triassic?–lowermost Jurassic Tauromenia Seguenza, 1885 , due to comparable anterior ribbing pattern and the beak features, as well as the well-developed dorsal median septum ( Alméras et al. 2007; Baeza-Carratalá and García Joral 2012) and long-looped brachidium ( Alméras et al. 2007).

Finally, there are several arguments for and against assigning Misunithyris to the subfamily Zeilleriinae Schuchert, 1929 as was defined in Kaesler and Selden (1997–2007). The septum is clearly well-developed and the brachidium evidences a long-looped progression. Conversely, the presence of cardinal process is atypical in this subfamily, although some genera show primitive lobes as massive callus or small knobs (e.g., Antiptychina Zittel, 1880 ; Kolymithyris Dagys, 1965 ). On the other hand, some of them also reveal enveloped dental lamellae instead the typical strong and unenveloped dental plates characteristic of this subfamily. As for Tauromenia , the closer external affinities are found in the anteriorly ribbed representatives of this subfamily, i.e., Calpella Owen and Rose, 1997 and Parathyridina Schuchert and Le Vene, 1929 , the internal structure of which remains poorly known except for the presence of a prominent median septum (e.g., Cooper 1983; Baker 2006; Alméras et al. 2010b). In this sense, very close internal and external affinities have been recognized with the recent erected multicostate genus Menathyris Feldman, 2013 , except for the cardinal process and the anterior folding pattern.

It must be kept in mind that the subfamily Zeilleriinae Schuchert, 1929 was recently split into several subfamilies by Baeza-Carratalá and García Joral (2014) on the basis of the hinge plates-crural bases relationship, thus resulting three subfamilies (Aulacothyrinae Babanova, 1964, Zeilleriinae Schuchert, 1929 , and Securininae Baeza-Carratalá and García Joral, 2014). Attending to this criterion, Misunithyris clearly shows a Bakonyithyris - type pattern and might be arranged into Aulacothyrinae. However, the representatives of Aulacothyrinae (sensu Baeza-Carratalá and García Joral 2014) have not evidenced cardinal process so far, and the progress of dental plates is rather different.

Summarizing, the arrangement of Misunithyris into family Zeilleridae is the best plausible determination, but does not fully agree with the currently defined subfamilies. Combining external and internal features, it seems to be closer to the multicostate zeilleriid stock, such as Menathyris Feldman, 2013 , Calpella Owen and Rose, 1997 , or Tauromenia Seguenza, 1885 . A new subfamily might be erected, either with Misunithyris as monotypic taxon, or together with the aforementioned genera, but further studies of internal structures in their representatives will be required to establish the validity of this approach, emphasizing examination of cardinal process and brachidium architecture in addition to the already known shared features.

Stratigraphic and geographic range.— Misunithyris is so far a monospecific genus recorded in the Gevanites epigonus Chronozone of the Fassanian (lower Ladinian, Middle Triassic) from the Betic Range (Fig. 2).