INTRODUCTION

The Early Permian ammonoid family Perrinitidae Miller and Furnish, 1940 includes eight genera with a strongly dissected suture. The shell shape in all representatives is pachyconic (thickly discoidal), differing in different genera in small variations in the whorl and umbilical widths (Leonova, 2002).

Perrinitids were first found in the Permian deposits of the southwestern states of the United States, and the type genus Perrinites was described by Böse (1917) over 100 years ago. At approximately the same time, another representative of this family was found on Timor Island. It was identified and described by Haniel (1915) as Cyclolobus subcumminsi. A few years later John Perrin Smith (Smith, 1927), in whose honor the genus Perrinites was named, described a new species Perrinites brouweri from Timor and redescribed Haniel’s species as Perrinites subcumminsi. Thereby he established the presence of perrinitids in the eastern hemisphere. Nevertheless, for quite a long time perrinitids were considered to be a family characteristic exclusively of the western states of the USA and Mexico, and the genozones Properrinites and Perrinites were widely used in the Lower Permian biostratigraphy of these regions (Böse, 1917; Plummer and Scott, 1937; Miller and Furnish, 1940 et al.).

Toumanskaya (1937) was the first to report perrinitids from the territory of the USSR. She described these specimens in a new genus, Paraperrinites with the type species Paraperrinites subcumminsi (Haniel). More complete data on the Pamir and Darvaz perrinitids were published by Toumanskaya (1963) and Leonova (Leonova, 1983; Leonova and Dmitriev, 1989; Leven et al., 1992)

In the 1980s, Tharalson (1984) thoroughly studied perrinitids, found clear morphological distinctions between the inner portion of the suture in two phylogenetic lineages, and on this basis recognized two subfamilies Perrinitinae and Paraperrinitinae. A subsequent biogeographical analysis showed that the representatives of the former subfamily were characteristic only of the western hemisphere, and members of the latter subfamily are found in both hemispheres (earlier in their phylogenetic history), and restricted to the eastern hemisphere (later in their phylogenetic history) (Leonova, 1996). Zhou and Liengjarern (2004) disagreed with this concept, while Ehiro et al. (2005) supported it in general, but with some reservations.

All researchers generally agree that ammonoids of the family Perrinitidae were inhabitants of equatorial basins, and did not live in boreal basins (Tharalson, 1984; Zhou and Liengjarern, 2004; Ehiro et al., 2005; Leonova, 2011; Korn and Baets, 2015, etc.). Nassichuk (1971) who described Properrinites from the Yukon Territory, later wrote on this occurrence (Nassichuk, 1995, p. 232): “This is the most northerly occurrence of Properrinites and tends to support the hypothesis that lower Sakmarian strata in the northern Yukon were deposited in an equatorial setting.”

RESULTS AND DISCUSSION

During field work in 2017, colleagues from the laboratory of mollusks of the Paleontological Institute, Russian Academy of Sciences A.V. Mazaev and M.S. Boiko discovered for the first time a specimen of the Asselian–Sakmarian genus Properrinites in the Early Permian Shakh-Tau Shikhan near the city of Sterlitamak in Bashkortostan (Fig. 1). The Shikhans are a series of several isolated fossil reefs (mounds) that have formed mountains in the Sterlitamak District, Bashkortostan. This find was totally unexpected, because until recently it was universally believed that the family was restricted biogeographically, and no perrinitids had ever been found in the Urals or Cisuralia.

Fig. 1.
figure 1

Properrinites locality in Bashkortostan, South Urals. The asterisk marks the location of the Shakh-Tau Shikhan.

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The single specimen of Properrinites sp. is represented by a fragment of a relatively large shell (about 60 mm in diameter) with a well-preserved external portion of the suture, in a quarry developed in place of the Shakh-Tau Shikhan. The shell is pachyconic, typical for the genus. The preserved portion of the external portion of the suture is an important diagnostic character. It consists of a ventral and three lateral, complexly dissected lobes and a bipartite umbilical lobe (Fig. 2). The degree of the lobe dissection in this group indicates a particular evolutionary stage of the genus Properrinites. The closest taxon, both in age and geographic position is Properrinites dmitrievi Ruzhencev, 1978 from the Asselian–Sakmarian of Pamir.

Fig. 2.
figure 2

Properrinites sp. (a) shell, natural size; (b) external portion of the suture; specimen PIN, no. 5615/1, Shakh-Tau Shikhan, Bashkortostan, Upper Asselian (after Leonova and Boiko, 2018).

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The taxonomic composition of the Late Asselian ammonoid community inhabiting the reef area studied differs from the synchronous marine communities of the Uralian Paleoocean. Previous findings from this reef included such extreme endemics as Shikhanites singularis Ruzhencev, 1938 and Protopopanoceras sublahuseni Gerassimov, 1937, which have never been recorded from other localities.

The following ammonoid species have been found in the Asselian–Sakmarian limestones of the Shakh-Tau and Tra-Tau Shikhans from the 1930s until the present: Neopronorites rotundus (Maximova, 1938), Sakmarites asaphus (Ruzhencev, 1938), S. postcarbonarius tetragonus (Karpinsky, 1889), Artinskia subartiensis (Gerassimov, 1937), Medlicottia subdorbignyi Gerassimov, 1937, Shikhanites singularis Ruzhencev, 1938, Agathiceras uralicum (Karpinsky, 1874), Prothalassoceras biforme (Gerassimov, 1937), Somoholites shikhanensis Ruzhencev, 1938, Paragastrioceras sterlitamakense Gerassimov, 1937, Protopopanoceras sublahuseni Gerassimov, 1937 (Gerassimov, 1937; Ruzhencev, 1951; Korolyuk, 1985). This list is now supplemented by: Properrinites sp., Neopronorites tenuis (Karpinsky, 1889) and many nautiloids, around 20 species (Barskov and Boiko, 2016; Leonova and Boiko, 2018).

Thus, the Uralian Late Asselian–Early Sakmarian reef ammonoid assemblage includes 13 species of 11 genera. Its comparison to assemblages with the primitive perrinitids Properrinites and Subperrinites Tharalson, 1984 from other regions reveals that the closest generic composition is observed in the Early Sakmarian assemblage found in Yukon (Nassichuk, 1971). The species of the genera Medlicottia Waagen, 1880, Prothalassoceras Böse, 1917, Eoasianites Ruzhencev, 1933, Uraloceras Ruzhencev, 1936, Somoholites Ruzhencev, 1938, Tabantalites Ruzhencev, 1952, and also nautiloids Liroceras Teichert, 1940 and Titanoceras Hyatt, 1884 in association with Subperrinites furnishi (Nassichuk, 1971). It should be noted that representatives of the genus Tabantalites are relatively frequently found in the Asselian–Sakmarian of the South Urals (Ruzhencev, 1951). The main argument supporting the Early Sakmarian age of that locality according to Nassichuk (1971; 1995) was the presence of the primitive member of Medlicottia, since previously this genus was only known beginning from the Late Sakmarian. The most recent occurrence of a similarly primitive representative of Medlicottia in the Urals suggests that the Yukon and Shakh-Tau occurrences are of the same age.

The assemblage with Properrinites dmitrievi Ruzhencev, 1978 from the Tashkazyk Formation of Pamir (Late Asselian–Early Sakmarian) also contains species of the genera Boesites Miller and Furnish, 1940, Metapronorites Librovitch, 1938, Vanartinskia Ruzhencev, 1978, Agathiceras Gemmellaro, 1887, Prothalassoceras, Glaphyrites Ruzhencev, 1936, Eoasianites, Svetlanoceras Ruzhencev, 1974, Somoholites, Almites Toumanskaya, 1941, Cardiella Pavlov, 1967, Emilites Ruzhencev, 1939, Tabantalites, Prostacheoceras Ruzhencev, 1937, and Martoceras Toumanskaya, 1938 (Ruzhencev, 1978). In that case the generic composition is more diverse, as it contains more prolecanitids and vidrioceratids, as well as marathonitids, apart from the species known from Bashkortostan.

In TimorProperrinites deroeveri Gerth, 1950 was found in association with species of the genera Metapronorites, Akmilleria Ruzhencev, 1940, Agathiceras, Somoholites, Juresanites Maximova, 1940, Metalegoceras Plummer et Scott, 1937, Kargalites Ruzhencev, 1938, and Propopanoceras Toumanskaya, 1938 (Haniel, 1915; Smith, 1927; Gerth, 1950). This assemblage is distinct in the presence of metalegoceratids, which are known from other regions, but in assemblages lacking perrinitids.

In Texas, New Mexico, Kansas, and Nevada, the assemblage contains primitive perrinitids: Subperrinites bakeri (Plummer and Scott, 1937), S. denhami (Miller and Furnish, 1940), S. plummeri (Elias, 1938), S. moorae (Miller and Furnish, 1940), Properrinites boesei (Plummer and Scott, 1937), and P. nevadaensis Miller, Furnish and Clark, 1957, which are found in the Bursum, Neal Ranch, Putnam, Wolfcamp, Alta, Lenox Hills, and Council Grove formations, in the lower part of the Hueco Formation and lower part of the Cibolo Formation together with representatives of the genera Akmilleria, Aristoceras Ruzhencev, 1940, ”Stenolobulites” Mikesh, Glenister et Furnish, 1988, Kargalites, Crimites Toumanskaya, 1937, and Propopanoceras (Böse, 1917; Plummer and Scott, 1937; Miller and Furnish, 1940; Miller, Furnish and Clark, 1957, etc.).

In South ChinaProperrinites dmitrievi Ruzhencev was found in the Maping Formation together with species of the genera Boesites, Metapronorites, Agathiceras, Eoasianites , Subkargalites Ruzhencev,1938, Kargalites, Almites, and Emilites (Zhou, 1987). In his recent paper Zhou (2017) re-identified Properrinites dmitrievi as Properrinites gigantus Zhou, 2017, but this does not change the general pattern, especially that the material was very poorly preserved. In general this assemblage is very similar to that of the Tashkazyk Formation of Pamir, even at the species level.

In all the above regions, the younger Artinskian–Roadian deposits contain more derived perrinitid genera: Metaperrinites Ruzhencev, 1950 and Perrinites Böse, 1917 (sections of Texas, New-Mexico, Kansas, Oklahoma, and also Mexico, Guatemala, Venezuela, and Colombia), and Metaperrinites, Paraperrinites, Perrimetanites Leonova, 1983, and the Pamir genera-endemics in the Eastern Hemisphere. In other regions (Crimea, Thailand, and Japan), perrinitids are found in the Artinskian and Kungurian stages and are represented by the genera Metaperrinites, Perrimetanites and possibly, Perrinites (Glenister et al., 1990; Leonova, 1996; Zhou and Liengjarern, 2004; Ehiro et al., 2005). In Thailand Ishibashi et al. (1996) reported Properrinitesbosei, after re-examination this specimen was re-identified as Metaperrinites ishibashii (Zhou and Liengjarern, 2004).

Zhou (in Zhou and Liengjarern, 2004) wrote on the possible migration of perrinitids to the territory of modern Thailand via seaways along the linear belts across the northeastern Pacific, Inner Mongolia, and Far East (Nei Mongolia and Far East Primoria linear belts). This can be correct only partly. It should be emphasized that no primitive perrinitids are found in the Asselian–Sakmarian of Japan, i.e., the first perrinitids of the Tethyan Realms appeared in the central regions of the Tethyan Realm, rather than in its northeastern or eastern regions. Zhou argues that the absence of perrinitids in some other basins, including the Uralian Basin, is evidence that these ammonoids live only in zones of active linear belts—geosynclines, the “open-sea.” In addition, Zhou considers that finds of perrinitids in the western American Midcontinent are related to post-mortem shell dispersal, rather than to their inhabitation of these basins. It is difficult to agree with this statement. Firstly, these regions (northern Texas, Kansas, and Oklahoma) are known to have occurrences of Shumardites Smith,1903, which is considered to be ancestral to the family Perrinitidae (Ruzhencev, 1950), and also occurrences of its oldest representative (Subperrinites bakeri) (Tharalson, 1884). Secondly, perrinitids were found there in association with other characteristic ammonoids, similar to those in the geosyncline regions. Thirdly, recent finding of Properrinites in the reef facies of the Uralian Basin also refutes Zhou’s hypothesis (Zhou and Liengjarern, 2004). There are also some reservations with regard to the seaway exchange between the American Biogeographic Province and Tethyan Ocean across the northern regions of Paleopacifica. Perrinitids have never been found either in Inner Mongolia, or in Primorye, but conversely the Lower Permian sections of these regions contain typical Arctic ammonoid assemblages (Ehiro et al., 2005; Leonova, 2007).

According to Ehiro et al. (2005), faunal exchange between equatorial American regions (or the East Pacific Realm according to the biogeographical scheme proposed by Korn and Baets (2015) occurred across the Pacific due to warm currents, which reached the eastern borders of the Tethys Ocean, i.e., the locations of the Thailand and Japan basins. This scheme is difficult to implement because faunas in these regions contain only Artinskian–Kungurian perrinitids, whereas earlier, Asselian–Sakmarian taxa are reported from the central regions of the Tethys (Timor, South China, Pamir), rather than from the eastern regions.

Taking into account all the above data, I propose the following scheme. Species of Properrinites migrated from America (the center of origin of perrinitids, where the geochronologically oldest members are recorded, e.g., Subperrinites bakeri from the Bursum Formation (Furnish and Glenister, 1971), as well as their supposed ancestors), across Paleopacifica to the central part of the Tethys Ocean and became established in the basins of Timor, South China, and Pamir. There, their evolution continued and more advanced descendants appeared (Fig. 3). In the Timor region, Properrinites gave rise to Paraperrinites, while in the South China and Pamir regions, Properrinites gave rise to Metaperrinites and Perrimetanites, as well as to the endemic Pamir taxa. Perrimetanites was apparently as evolutionary derived as Perrinites, and occupied the place of Perrinites in the Tethys communities.

Fig. 3.
figure 3

Migrations of Perrinitidae in the early Permian (paleogeographic reconstruction after Ziegler et al., 1996). Distribution of Asselian–Sakmarian perrinitids shown by gray ammonite symbols and arrows, and distribution of Artinskian–Kungurian perrinitids shown by black ammonite symbols and arrows.

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The presence of species of Perrinites in the Kungurian of Thailand or South China has not been confirmed. Since the paper by Zhou and Liengjarern (2004) lacks necessary information for genus identification, i.e., there is no illustration of the internal part of the suture, and according to the text it was not studied, so the identification cannot be confirmed. From the published outline of the external portion of the suture (Zhou and Liengjarern, 2004, fig.17, 3–4), it is possible to conclude that the third external lateral lobe was incompletely subdivided into two lobes, which is characteristic of the genus Perrimetanites. Glenister and Furnish (in Glenister et al., 1990) pointed to a considerable similarity of the perrinitid from Thailand to Perrimetanitesprogressus Leonova from Pamir. It is likely that Perrinites is correctly recorded from Japan (Southern Kitakami Massif), which is supported by the studies of Ehiro et al. (2005). Irrespective of the presence or absence of the genus in localities of the Eastern Hemisphere, it is possible to consider two possible ways of perrinitid migration and distribution in these basins in the second half of the Early Permian.

On the one hand, there is undeniable evidence of the presence of Late Asselian–Early Sakmarian members of Properrinites in localities of Timor, Pamir, South China, and now the Urals, which appeared in these basins at the very beginning of the Early Permian, and existed there throughout several geological epochs. Perrinitids reached their maximum diversity in the second half of the early Permian (in the Late Artinskian–Kungurian time), hence it is logical to conclude that at that time they spread to other regions of the Tethys Ocean: to the west (localities in Crimea) and to the east (localities in Japan and Thailand). On the other hand, in my opinion, at the end of the Early Permian Perrinites could also migrate with warm currents from equatorial waters of America to the eastern borders of the Tethys Ocean, as suggested by Ehiro et al. (2005).

The presence of Properrinites in the Late Asselian–Early Sakmarian limestone of the Shakh-Tau Shikhan supports the hypothesis that, by the beginning of the Permian, marine connections between the Tethys Ocean and Uralian basin were well established (Leonova, 2018). Strictly speaking, the Uralian basin cannot be considered part of the Boreal biogeographic realm as had originally been thought by many authors. Migrations between the Urals and Tethys were not only southward, but also towards the Urals. The Urals and Tethyan basins were completely interrupted due to the total closure of the southern part of the Uralian Paleoocean. In the second half of the Early Permian, perrinitids only migrated within equatorial regions.