Introduction

The analysis of patterns of paleobiogeography depends on a global data set. Efforts to collect information on the age and location of disparate fossil species, such as the Paleobiology Database and the Geobiodiversity Database, among others, are critical in defining global patterns, but these depend on a robust primary literature describing occurrences of fossil taxa.

Reports of Paleozoic crinoids from Mongolia are infrequent, and many of the earliest papers described only stems (Stukalina, 1973, 1994, 1997; Tungalag, 1998). Webster and Ariunchimeg (2004) described a Lower Devonian (Emsian) fauna from Shine Jinst in southern Mongolia, including the first crinoid cups and thecae from Mongolia. They recognized five distinct taxa but named only Cyathocrinites because of poor preservation. Waters et al. (2021) described a Late Devonian (Famennian) echinoderm fauna of twelve crinoid genera and two blastoid genera from southwestern Mongolia. Recently, Carboniferous (Serpukhovian) crinoids have been collected from southwestern Mongolia, but they are too fragmentary for identification (Waters, personal observation, 2020).

In this paper, we describe the new periechocrinitid Gennaeocrinus tariatensis new species from the Emsian of Mongolia. Gennaeocrinus is well known from multiple species from the Devonian of North America and is questionable from western Europe. In terms of Devonian plate tectonics, it is well known from cratonic settings on east/southeast Laurentia and questionably known from similar settings on southwest Baltica and Iberia in the reconstructions of Domeier and Torsvik (2014). However, G. tariatensis was collected from a collage of small terranes and active island arc complexes in the Central Asian Orogenic Belt on the southeastern margin of Siberia. Thus, its tectonic, paleogeographic, sedimentological, and paleolatitudinal occurrence differs from all other species of the genus.

Geological setting

Mongolia is a very large country and occupies a primary position in the Central Asian Orogenic Belt (Fig. 1), the largest Paleozoic orogenic belt that evolved in a manner similar to the modern Indonesia and western Pacific. Mongolia comprises 44 terranes (Badarch et al., 2002), including cratonic, metamorphic, passive margin, island arc, forearc/backarc, accretionary complex, and ophiolitic terranes (Fig. 2).

The crinoid described herein was collected from the Tariat Formation, which is part of the Tarvagatay Terrane of Badarch et al. (2002). The Tarvagatay Terrane occurs in the northern Hangay mountains. The Terrane consists of Precambrian basement overlain by lower Cambrian stromatolitic limestone and volcaniclastic rocks. Devonian and Mississippian conglomerate, sandstone, and siltstone containing marine fossils complete the sequence. Alekseeva (1993) described the Tariat Formation as a terrigenous sequence with 70 m of basal conglomerates overlain by 150 m of green sandstones, siltstones, and mudstones with abundant brachiopods and plant fossils in darker siltstones. An overlying terrigenous sequence contains 250 m dark-gray to greenish siltstones and sandstones also with abundant brachiopods. The Tariat Formation is unconformably overlain by lower Carboniferous conglomerates. The Tariat Formation is Emsian in age according to the presence of the strophomenoid Maoristrophia kailensis Shishkina, 1990, a brachiopod that defines the Mongolian Chulun Horizon (Alekseeva, 1993). This horizon correlates with the Salairka Horizon in Siberia and the Polygnathus kitabicus Conodont Biozone in the basal Emsian (Yolkin et al., 2000).

Figure 1.

The Central Asian Orogenic Belt accretionary zone located between the European and Siberian cratons to the north and the Tarim and North China cratons to the south. Map after Ju and Hou (2014).

Paleobiogeography

The tectono-stratigraphic compilations of Mongolia by Badarch et al. (2002) and Windley et al. (2007) recognized the Main Mongolian Lineament, which divides the country into an early Paleozoic domain in the north and a late Paleozoic domain in the south. The Tarvagatay Terrane is part of the Mongol–Okhotsk Belt north of the Main Mongolian Lineament. The Tariat Formation was deposited in a trench–accretionary wedge environment in the Mongol–Okhotsk Ocean to the south (in current orientation) of the Siberian Craton (Bussien et al., 2011).

Emsian paleobiogeography is based primarily on brachiopods and shows differentiation into the Rhenish–Bohemian Realm, the Appalachian Realm, and the high-latitude Malvinokaffric Realm. Some Devonian workers combine the Rhenish–Bohemian Realm into the Appalachian Realm. Brachiopods with a cosmopolitan distribution from the Mongol–Okhotsk fauna support the conclusions of Hou and Boucot (1990) that they are part of the Old World Realm even though geographic distances between the areas are quite large. Paleobiogeographic reconstructions by Torsvik and Cocks (2017) placed the Mongolian terranes, including the Tarvagatay Terrane, along the southern margin of the Siberian Craton at a latitude of approximately 50°N. The Old World Realm is primarily equatorial to mid-latitudes, and the Malvinokaffric Realm is located in the high latitudes of the Southern Hemisphere (Torsvik and Cocks, 2017).

Emsian faunas have a high degree of cosmopolitan distribution of taxa where adequate data are available. The Emsian marked the acme of a remarkable spread of reefs, the largest known and most latitudinally widespread reefs in the Phanerozoic according to Copper and Scotese (2003). Judging from the distribution of reefs, they concluded that the Middle Devonian (Emsian–Givetian) had a supergreenhouse climate. However, Joachimski et al. (2009), concluded that the Middle Devonian had sea surface temperatures closer to 23–25°C and was not a supergreenhouse climate according to oxygen isotopes in conodont apatite. Regardless of which temperature model is correct, Emsian sea levels were high, and geographically disparate faunas contained many similar, cosmopolitan genera.

Materials and methods

The holotype of Gennaeocrinus tariatensis n. sp. was collected from an outcrop of the Tariat Formation at 48°12′23″N, 100°1′49″E (measured by GPS) in Arkhangai Aimag, Tariat Somon, Mongolia (Fig. 3). The specimen was a mold preserved in a greenish–gray fossiliferous siltstone. Descriptions of the specimen are based on a latex cast prepared at the Paleontological Center of the Mongolian Academy of Science and photographed with ammonium chloride sublimate.

Repository and institutional abbreviation.—The latex cast of the holotype is reposited in the collections of the Mongolian University of Science and Technology (MUST) research collections in Ulaanbaatar, Mongolia.

Systematic paleontology

The superfamilial classification used here follows Cole (2017), Wright (2017), and Wright et al. (2017); family-level classifications follow Moore and Teichert (1978). Morphologic terminology follows Ubaghs (1978) and Ausich et al. (2020). The plating of interrays is given by the number of plates in each range from proximalmost plate to the last range before the tegmen. In the posterior interray, the primanal is indicated by “P,” and the first interradial plate in regular interrays is indicated by “1.”

Figure 2.

Map of the 44 tectonic terranes of Mongolia (after Badarch et al., 2002). The crinoid locality, indicated by the arrow, is located on the Tarvagatay Terrane, an arc terrane that accreted to the southern margin of the Siberian Craton.

Figure 3.

Field photo of outcrops of the Tariat Formation located in the Arkhangai Aimag, Tariat Somon, Mongolia. The Tariat is an Emsian fossiliferous unit composed primarily of conglomerates, sandstones, and siltstones. The arrow points to the crinoid locality.

Figure 4.

Gennaeocrinus tariatensis n. sp. (1) Photograph of the holotype of Gennaeocrinus tariatensis preserved as a mold in a greenish-gray siltstone. (2) Latex cast of the holotype showing prominent ornament of radiating ridges that cross plate boundaries. (3) Plate diagram of Gennaeocrinus tariatensis prepared by W.I.A. (4) Enlargement of the latex cast of Gennaeocrinus tariatensis showing subtle plate boundaries largely obscured by strong radiating ridges. Scale bars = 1 cm.

Discussion

Gennaeocrinus is a monobathrid crinoid that is well known from the Emsian and Givetian of North America with possible occurrences from Germany and Spain. By contrast, G. tariatensis n. sp. is the first species of the genus found in the Central Asian Orogenic Belt (CAOB). It was collected from Emsian terrigenous sediments on a convergent margin terrane in the Mongol–Okhotsk Belt, which accreted onto the Siberian Craton. In terms of paleolatitude, previously known species of Gennaeocrinus have an equatorial distribution, but Gennaeocrinus tariatensis occurs at 50°N. The occurrence of Gennaeocrinus tariatensis significantly increases the paleogeographic range of Gennaeocrinus, but information is still lacking to hypothesize on patterns of migration. The occurrence of Gennaeocrinus in the Mongol–Okhotsk fauna is not completely unexpected as Emsian brachiopods have a high degree of cosmopolitanism and significant similarity between taxa in the Old World Realm and the Mongol–Okhotsk fauna (Hou and Boucot, 1990).

Webster and Arunichimeg (2004) described an Emsian crinoid fauna from the Chuluun Formation in the Shine Jinst area of Mongolia. In contrast to the terrigenous nature of the Tariat Formation, the Chuluun Formation is dominated by carbonates with mound- and reef-forming stromatoporoids and corals in addition to crinoidal grainstones. This locality is south of the Main Mongolian Lineament and is located on either the Mandavooloo or Gobi Altai Terrane. In contrast to assertions by Webster and Arunichimeg (2004) that the Chuluun crinoids were the most northerly known Emsian crinoid fauna, recent paleogeographic reconstructions (Torsvik and Cocks, 2017) of the CAOB place the Mandavooloo and Gobi Altai Terranes at a latitude of 25–30°N. Gennaeocrinus tariatensis is the most northerly known Emsian crinoid, with a paleolatitude of approximately 50°N.