New Permian radiolarians from east Asia and the quantitative reconstruction of their evolutionary and ecological significances

The biostratigraphically important Permian radiolarian genera Pseudoalbaillella sensu stricto and Follicucullus (Follicucullidae, Polycystinea) are discriminated by morphological gaps in their wings and segmentation. Previous statistical analyses demonstrated that Longtanella fills morphological gaps between these two genera. Longtanella has long been regarded as a junior synonym of Parafollicucullus, and only a few species have been described. Herein several true Longtanella species are recognized from South China, and eight new species and five indeterminate species are described and illustrated to prove the validity of the genus Longtanella. In addition, a new genus, Parafollicucullinoides gen. nov., is described. Their palaeogeographic distributions and living environments are explored by applying correspondence analysis (CA), with occurrence datasets of selected fusulinacean genera from the Japanese Islands, China and Sundaland. CA results indicate that Longtanella was present to a limited extent in warmer conditions in the fusulinacean Province B and C during Kungurian–Roadian time, and possibly lived above the thermocline and below the deepest limit of fusulinaceans. The Pseudoalbaillella and the Follicucullus group preferred open ocean conditions, living below the thermocline and distributed not only in the ‘Equatorial Warm Water Province’, but also the northern peri-Gondwana Cool Water Province and the southern North Cool Water Province.

Palaeobioprovincial scheme. The most appropriate palaeobioprovincial scheme for these radiolarian genera (Longtanella, Pseudoalbaillella sensu stricto and the Follicucullus group) is the fusulinacean scheme. As radiolarians have never occurred with fusulinaceans in the same samples, this tendency is of interest.
Palaeobioprovincial analyses combining different taxa have rarely been performed for Permian marine organisms. It is generally understood that tropical bioprovinces were widely developed around the equator and expanded to higher latitudes in Greenhouse times such as the Eocene and Cretaceous 25 . The Permian, however, regardless of age and Greenhouse mode, experienced palaeobioprovinces that were partitioned by www.nature.com/scientificreports/ both latitude and longitude 26 ; this phenomenon is shown by nektonic animals like conodonts, ammonoids and marine fishes [27][28][29] , and planktonic organisms are predicted to follow the similar patterns. Fossilized planktonic organisms in the Palaeozoic are limited to groups such as radiolarians whose skeleton is siliceous. We know that Cisuralian (Early Permian) radiolarian faunas were significantly different among the South Urals 30 , South China-Japan 2 , and North American midcontinent 31 . Lopingian (Late Permian) radiolarian faunas also showed strong provincialism between the Delaware Basin 32 and the South China-Japan regions 33,34 . According to previous correlations, Longtanella ranges from UAZ 2 (middle Asselian) to the end of UAZ 14 (the Changhsingian) with relatively higher occurrence probability (p ≥ 0.20) in UAZ 6 (Kungurian) and UAZ 7 (Roadian) 6 . The metadatabase from our studies demonstrates that locations yielding Longtanella overlap with those of Pseudoalbaillella and the Follicucullus group in different ways in different palaeobioprovinces. The palaeogeographic distribution map shows that Longtanella are restricted to the fusulinacean Provinces B (Eastern Tethyan Province) and C (Panthalassan Province), whereas both Pseudoalbaillella and the Follicucullus group are reported not only in Provinces B and C, but also in Provinces A (Western Tethyan Province) and D (Cratonic North American Realm) (Fig. 2).
Selected fusulinacean genera. The palaeogeography of fusulinaceans in east to southeast Asia including China and Japan has been well documented [36][37][38] . The Permian fusulinoidean palaeogeographic provinces in China are divided into the Cathaysia Tethys Province (CTP), Angara Tethys Province (ATP) and Gondwana Tethys Province (GTP) 39 . All these provinces constitute the Eastern Tethyan Province (Province B) 6,7 . In consideration of this knowledge, locality maps of fusulinaceans (occurrences of fusulinaceans are listed in supplement 3) were prepared for the selected seven genera (Table 1). These genera were chosen based on the facts that their taxonomic concepts are very stable, marked by obvious characters, and they are reliable guides to geographic distribution 26,40,41 .
The faunal affinity between 'cold-water' Monodiexodina and 'warm-water' Misellina is often reported 37,38,42 , although these affinities seem to apply only for the Eastern Tethyan and Panthalassa provinces 43 in the sense of Kobayashi 7 . Chusenella is helpful to indicate fusulinacean-bearing strata because this genus is commonly found in east and southeast Asia. Additional localities of Permian fusulinacean-bearing strata are provided by the distribution maps of Biwaella and Rauserella. Differing from the major fusulinacean province of Japan, the Panthalassan Province (Province C)  The age of the samples was determined by their coexistent species using the statistical likelihood UAZ ranges proposed recently 6 . Most samples were correlated with UAZ 6 or UAZ 7 without contradiction in faunal association, except for samples ST9, ST8 and 13ST4-2. UAZ 6 and UAZ 7 are also correlated with the Kungurian and Roadian, respectively (supplement 2). All the Longtanella specimens are found in UAZ 6 or UAZ 7 .
Occurrences of related radiolarian genera. Japanese Islands (supplement 1 Fig. S6). The basement rocks of the Japanese Islands comprise mainly Palaeozoic-Cenozoic accretionary complexes with island arcrelated rocks 50,51 . Permian radiolarians occur in several Palaeozoic-Mesozoic geological units of the Japanese Islands: North Kitakami Belt, Mino-Tamba-Ashio Belt, Ultra-Tamba Belt, Maizuru Belt, Akiyoshi Belt, Hidagaien Belt, North and South Chichibu belts and Kurosegawa Belt. Pseudoalbaillella and the Follicucullus group have been reported from everywhere in these tectonic belts except in the North Kitakami Belt, so the occurrences of Longtanella only are mapped herein. Occurrences of Pseudoalbaillella and Longtanella have been reported 52 from the North Kitakami Belt of the Northeast Japan Zone. However, confirmed occurrences of the Follicucullus group have not been recognized yet, probably because of thermal metamorphism by Early Cretaceous granite 53 . There are no reliable Permian fusulinacean data, so we exclude the North Kitakami Belt from further discussion.
In the Inner Southwest Japan Zone, occurrences of Longtanella are restricted compared to Pseudoalbaillella and the Follicucullus group. Pseudoalbaillella and Follicucullus occur abundantly in the Mino-Tamba-Ashio Belt, but only a few occurrences of Longtanella have been reported 54 . Longtanella and Pseudoalbaillella were reported 55 from the Hida-gaien Belt. No obvious Longtanella has been discovered from the Ultra-Tamba, Maizuru and Akiyoshi belts. However, Longtanella was noted 56 in tuffaceous mudstone and chert of the Nagato Tectonic Zone. According to these authors, these rocks are possibly derived from the Akiyoshi Belt.
Relatively abundant Longtanella occur in the Outer Southwest Japan Zone. Longtanella, Pseudoalbaillella and the Follicucullus group co-occur in some sites of the Northern and Southern Chichibu belts 57,58 . The cooccurrence of Longtanella, Pseudoalbaillella and the Follicucullus group has been noted 59 in the Kurosegawa Belt, which is located between the Northern and Southern Chichibu belts. Finally, Longtanella was discovered 60 from Permian chert pebbles in the Lower Cretaceous Choshi Group of the Kurosegawa Belt.
Mainland China (exclusive of the Changning-Menglian Suture Zone) (supplement 1 Fig. S7). The three radiolarian groups are quite common in the northern and western parts of South China, including Guangxi, Sichuan, Guizhou, Jiangsu, Hubei, and Anhui provinces, mainly from the Gufeng and Bancheng formations. Other occurrences are from accretionary complexes, such as the Xijinulan-Gangqiqu ophiolite complex and East Kunlun tectonic complex. Longtanella is found mostly from the 'stable continental region' in South China and less than Pseudoalbaillella and the Follicucullus group in numbers and distributions. The Follicucullus group is distributed www.nature.com/scientificreports/ widely, even in eastern Nei Mongol. Generally, these three groups are not so significantly different in distribution and are often associated with each other.
Sundaland and the Changning-Menglian Suture Zone (supplement 1 Fig. S8). The tectonic continuity of the Changning-Menglian Suture Zone is closely related to tectonic zones in Sundaland (the continental core of SE Asia which is comprised of the Sunda shelf and parts of the Asian continental shelf), so the Changning-Menglian suture zone is considered here. Longtanella is not found in the Changning-Menglian Suture Zone where Pseudoalbaillella and the Follicucullus group exist 61,62 , but present in the Inthanon Suture Zone, the Sra Kaeo Suture and the Bentong-Raub Subzone. As discussed later, radiolarians are more limited in distribution than fusulinaceans. They almost all occur in suture zones except for Pseudoalbaillella, which is exclusively found from the Sukhothai Terrane and the Indochina Terrane. As with the distributions in South China, Longtanella, Pseudoalbaillella and the Follicucullus group often co-occurred, but there are more records of the latter two than Longtanella.
Occurrences of selected fusulinacean genera. Japanese Islands (supplement 1 Fig. S6). Occurrences of fusulinaceans in the Japanese Islands have been thoroughly plotted 63    Correspondence analysis (CA). The combinations of radiolarian and fusulinacean occurrences at the scale of tectonic divisions is so complex that we used CA to analyse the data. The analysis reduced the data to nine axes, of which the first three explain 69.2% of the variance (33.5%, 19.3% and 16.4% in ascending order; Table 2). On Axis 1, all the fusulinacean genera except Monodiexodina receive positive scores, whereas all the radiolarian genera receive negative scores (Fig. 4, Table 3). The highest absolute score on Axis 1 is negative, for Monodiexodina (− 1.77), and the highest positive scores are for Pisolina (0.90) and Biwaella (0.75). Values on Axis 2 are high (> 1.00) for Pisolina and low (< − 1.00) for Rauserella (Fig. 4). The inertia scores (

Discussion
Longtanella occurrence in references. Xiao et al. 6 noted that Longtanella spp. was found between UAZ 2 (middle Asselian) and UAZ 13 (Wuchiapingian). Once Ito 11 documented detailed morphological characters for Longtanella, the source data in Xiao et al. 6 must be rechecked for Longtanella. Referring to Supplementary data 5 in Xiao et al. 6 , the most reliable range for Longtanella is revised as UAZ 6 (Kungurian) to UAZ 8 (Wordian). This difference was caused from our earlier incomplete knowledge of the 'broken wing' . We conclude that the genus Longtanella is a good marker for the Kungurian to the Wordian. www.nature.com/scientificreports/ Interpretation of correspondence analysis. Axis 1. The positive direction of Axis 1 is largely contributed by Pisolina whereas the negative direction is contributed by Monodiexodina (Fig. 4, Table 3). The preferred palaeoenvironment of Pisolina is 'semi-restricted platform facies' which represents a low hydrodynamic environment 66 or 'inner gentle slope benthic biofacies' 67 . The preferred palaeoenvironment of Monodiexodina has been subject to two interpretations. One is an anti-tropical distribution 37 although the suggested preferred temperatures are different from cold water 68 , middle latitude between high latitudinal cool/cold-water and tropical warm-water realms 37 , and temperate cool-water zone between temperate-and warm-water zones 43 to warm water 69 . The other interpretation is high energy water conditions like clastic lithofacies 44 and wave-and stormreworked, transgressive lag deposits 70 . Considering the inner gentle slope benthic biofacies of Pisolina, the most likely interpretation of Axis 1 is a range from gentle water conditions (positive) to high-energy water conditions (negative). All three radiolarian genera are plotted in the negative area of Axis 1 (Table 3), probably reflecting open ocean conditions. Pseudoalbaillella and the Follicucullus-group are significant in Cos2 score (Table 3) although their contributions are not significant (Table 3). This also implies that open ocean conditions are not the most important factor for the distribution of the Longtanella.
Axis 2. The preferred palaeoenvironments of Rauserella have not been discussed; it occurs with abundant small foraminifers in intercoralite sediments 71 , abundant bryozoans with rare corals 72 , abundant non-colonial  www.nature.com/scientificreports/ corals 73 , common calcareous algae 74 and variable fragments of fossils 75 . Following this information, Axis 2 is defined by Pisolina-bearing limestone facies in the positive direction and Rauserella-bearing limestone facies in the negative direction. The selected three radiolarian genera have never been found from such limestones, and thus coordinates, contributions and Cos2 (Table 3) all are small scores, and not related to Axis 2.
Axes 3 and 4. As discussed above, Monodiexodina may have had an anti-tropical distribution. Preferred palaeoenvironments for Afghanella are poorly described in previous papers, but Afghanella in Zagros, Iran, occurs in a warming event 43 . The most likely interpretation of Axis 3 is an anti-tropical distribution in the positive direction and warmer conditions in the negative direction. The distribution of Longtanella is mainly described by Axis 3 (14.74 in Contribution, 0.269 in Cos2, Table 3) but also Axis 4 (21.79 in Contribution and 0.277 in Cos2), but the interpretation of Axis 4 is difficult. The coordinate score of Axis 3 for Longtanella is -0.409 (Table 3), suggesting warmer conditions on the line of anti-tropical to warmer conditions axis. Low values for Pseudoalbaillella and Follicucullus show that these two radiolarian genera were not related to this anti-tropical to warmer conditions axis.

Summary of interpretations for selected radiolarian genera. The distributions of Pseudoalbaillella
and Follicucullus correspond to open ocean conditions, but such conditions were not important for Longtanella. Instead, Longtanella preferred warmer condition along the anti-tropical to warmer conditions axis, but this condition did not impact on the distributions of Pseudoalbaillella and the Follicucullus group. Therefore, Longtanella appears to have been well adapted to warmer conditions, differing from the widespread ancestral Pseudoalbaillella as well as its widespread descendant the Follicucullus group. Compared to Pseudoalbaillella, Longtanella shows atrophied pseudothoracic wings and reduced pseudothorax and increased test height, and it evolved into the Follicucullus group by complete reduction of undulated segmentation of pseudoabdomen.
Revisiting the palaeogeographic map. The fusulinacean palaeogeographic map shows different palaeo-provinces among the western Palaeo-Tethys (Province A), eastern Meso-Tethys and Meso-Tethys (Province B), Panthalassa (Province C) and the eastern margin of Panthalassa (Province D) 7 (Fig. 1). Our CA analysis shows the combination of Provinces B and C with a common distribution over this area for Pseudoalbaillella and the Follicucullus group. This result also supports the earlier recognition 6 of the same low-latitudinal standard Permian radiolarian biostratigraphy between Provinces B and C. The relatively restricted distribution of Longtanella in Provinces B and C is explained by the preferred warmer conditions in our CA. This seems to contradict the higher latitudinal distribution in British Columbia and Far East Russia. However, the original depositional position of parts of the British Columbia blocks or terranes were at a northern middle latitude 200 Ma age (earliest Jurassic) 76 and the original position in the Permian was probably at a lower latitude. Permian radiolarian and fusulinacean localities in Far East Russia are a northern extension of the tectonic divisions of the Japanese Islands 50 and thus the original depositional positions were also at low latitudes. The Permian radiolarian faunas are the same between Japan and Far East Russia 6 . The fusulinacean faunal similarity among British Columbia, Far East Russia (= Primorye, Sikhote-Alin) and the Japanese Islands is already known 77 and was identified as the 'Tethyan-Panthalassa fauna' or 'Yabeina territory' in subsequent studies 71,78,79 . In consideration of these tectonic and faunal affinities, Longtanella may be present in a limited way in warmer conditions in the fusulinacean Provinces B and C. For conodonts, the Permian 'Equatorial Warm Water Province' along the zone between northern and southern mid-latitudes 27 (Fig. 1) includes all of fusulinacean Provinces A, B and C. Both Pseudoalbaillella and the Follicucullus group are distributed not only in the 'Equatorial Warm Water Province' but also in the northern peri-Gondwana Cool Water Province and southern North Cool Water Province. By contrast, Longtanella is distributed in a very limited way, as explained above. The terrestrial and oceanic realms were mapped in the latest Permian 80 . Because the Middle Permian was cooler than the latest Permian 81 , the tropical ocean zone was narrower in the Middle Permian 80 . Waters above the thermocline are variable whereas water below the thermocline is homogenously cold in low to middle latitudes 82,83 . This oceanic rule requires the warm-water-dependent Longtanella to live above the thermocline, which means that it cannot be associated with fusulinaceans because they lived in deep-water environments. In the maps of Middle Permian palaeoprovinces with brachiopods 84 , the distributions of both Pseudoalbaillella and the Follicucullus group cover not only the Cathayasian realm but also the southern part of the Sino-Mongolian realm and part of the Cimmerian realm, just like the conodont palaeoprovinces 27 . The distributions of brachiopods and conodonts are largely controlled by latitudinal surface water temperature (SST), but the differences in distribution of Pseudoalbaillella and the Follicucullus group suggest that their distribution did not depend on SST. These two genera are found in the Middle Permian limestone in the Guadalupe and Apache mountains of West Texas. Noble et al. 85 explained that a stimulatory response to increased runoff is related to abundance changes in Follicucullus ventricosus. Such runoff conditions generate a similar oceanographic situation to an upwelling region in terms of oceanic physiology 86 and deep-water radiolarians can then be found in the intermediate zone 87 . Xiao et al. 88 defined water depths scheme for the Permian referred from the modern oceanography. The thermocline is roughly situated in similar water depth to the deep chlorophyll maximum (DCM)" and we defined the very shallow and shallow zones by the DCM. As Longtanella lived in different water conditions from Pseudoalbaillella and the Follicucullus group, the latter would have lived below the thermocline. Evolutionary perspectives. Xiao et al. 6 showed mathematically that Longtanella evolved from Pseudoalbaillella, whereas the Follicucullus group was divergent from Longtanella (Fig. 5). Our study herein first recognized that Longtanella was limited to Provinces B and C in the Kungurian to Wordian, differing from provinces where its ancestor (Pseudoalbaillella) and descendant (Follicucullus) lived. The short range and limited distri- www.nature.com/scientificreports/ bution of Longtanella might be related to some climatic changes. Although our data are insufficient to specify this prediction, the early Kungurian is known for the end of late Artinskian-early Kungurian warming and maximum marine flooding event in east Gondwana 89 and the early Capitanian is the time of diversification of Follicucullus species 90 . We hypothesized that Longtanella evolved near east Gondwana to adapt to warmer waters with less input of fresh water around the early Kungurian and lost the competition for survival against the newly diversified Follicucullus species around the early-middle Capitanian.

Conclusions
Eight new species and five indeterminate species of Longtanella are described, which greatly expands knowledge of this genus. Correspondence analysis was applied to occurrences of Longtanella, its sister taxa (Pseudoalbaillella and the Follicucullus group), and seven fusulinacean genera. The most likely interpretation of the CA output Axis 1 is gentle (positive) to high-energy water conditions (negative). Axis 2 is defined by Rauserella-bearing (negative) to Pisolina-bearing limestone facies (positive). Axis 3 is warmer conditions (negative) to anti-tropical distribution (positive). Comparisons with fusulinacean palaeoenvironmental interpretations based on CA suggest that there are some differences in the distributions of Longtanella, Pseudoalbaillella and the Follicucullus group. Pseudoalbaillella and the Follicucullus group favour open ocean conditions, but this condition is not important for Longtanella. Longtanella may be present in a limited way in warmer conditions in the fusulinacean Provinces B and C. Pseudoalbaillella and the Follicucullus group are distributed in not only the 'Equatorial Warm Water Province' but also in the northern peri-Gondwana Cool Water Province and southern North Cool Water Province in the conodont scheme. Longtanella lived above the thermocline and below the deepest limitation of fusulinaceans. Pseudoalbaillella and the Follicucullus group lived below the thermocline.
This leads to the suggestion that Longtanella was well adapted to warmer conditions, differing from the widespread ancestral Pseudoalbaillella and the widespread descendant Follicucullus. The evolutionary appearance of Longtanella contributed to the atrophy of pseudothoraxic wings and size of the pseudothorax and lengthening of the total height of the test from Pseudoalbaillella and evolved to the Follicucullus group by complete reduction of undulated segmentation of the pseudoabdomen. The appearance of Longtanella may relate to a regional warmer event after the early Kungurian glacial period in East Gondwana and its extinction is likely related with diversification of the Follicucullus group in the early-middle Capitanian.  11 , the character data set is provided in supplement 6). The species name is written as the original described name.

Methods
Sampling and analysis procedures. Forty-six samples were collected from all slices of the Bancheng Formation in the Shiti section. The fragmented samples were soaked in a 4% HF solution for 10 h at room temperature. After discarding the supernatant liquid, the acid residues were transferred to other containers, then water was added until the residues were greatly diluted. After this step, the same steps were repeated more than 40 times for each sample. Disaggregated particles were wet-sieved through a 54 µm mesh sieve and dried at the end of 40 time steps. By preliminary observation under a binocular microscope, 38 samples with rich identifiable radiolarians were selected. Individuals with distinguishable morphological characters were picked for species identification under a binocular microscope, and then better-preserved specimens (over 800 specimens in total) were photographed under the scanning electron microscope (Hitachi SU8010 in State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences) for further morphological examination and species identification.
Meta-database. Detailed occurrences of selected fusulinacean and radiolarian genera were mapped in the Japanese Islands, China and Sundaland. Sundaland includes the southern to southwestern parts of China, Vietnam, Thailand, eastern Myanmar, Indonesia and Malaysia. Global distribution maps for the selected radiolarian genera include all other regions in the world. Following the current concepts of radiolarian genera, Longtanella, Pseudoalbaillella sensu stricto and the Follicucullus-group (Follicucullus and Cariver) 12 were re-identified from illustrated specimens in publications that are archived in Tohoku University (ca. 5800 papers). The world palaeogeographic map was drawn based on the Middle to Late Permian tectonic reconstruction map (Fig. 2). Both the Pseudoalbaillella and Follicucullus group are widely distributed in the western and eastern margins of Palaeo-Tethys (Sicily 91 ; Turkey 92 ; South China 2 ; Malaysia 93 ), east of the Meso-Tethys (Thailand 94 ), western Panthalassan Ocean (Far East Russia 95 ; Japan 58 ; New Zealand 96 ), eastern Panthalassan Ocean (British Columbia 97 ; Alaska 48 ; South America 98 ). By contrast, known occurrences of Longtanella are limited to the western Panthalassan Ocean, eastern margin of Palaeo-Tethys, east of Meso-Tethys, and part of the eastern Panthalassan Ocean. This suggests a more limited distribution for Longtanella than its ancestral Pseudoalbaillella or descendent Follicucullus group. The middle to upper Permian marine deposits with radiolarians in the Japanese Islands, China and Sundaland have been well studied since the 1980s. In these areas, any identifiable morphotypes without a taxonomic name are regularly illustrated, and study of these indicates the occurrence of Longtanella at the level of tectonic divisions. Statistical analysis. Statistical analyses of radiolarian palaeobioprovinces were performed with the occurrence or absence dataset (binary data) of co-occurrences of radiolarian and fusulinacean genera at the level of tectonic belts. Questionable occurrences or questionable identifications were not included in the occurrence list. The tectonic divisional scheme comes from published work for the Japanese Islands 51 , China 13 , and Sundaland 99 .
For the present studies, we used CA (the dataset for CA is in supplement 7). CA is one of the most useful multivariate statistical methods to explore occurrence and absence data 88 . In consideration of taxonomic stability at the genus level, the occurrences of seven fusulinacean genera in the Early-Middle Permian from China, Japan and Sundaland were compiled to analyze possible factors in the distribution of Longtanella. The CA suggests that Longtanella differs from the Pseudoalbaillella and the Follicucullus group not only in palaeogeographic distribution, but also in its preferred temperature living conditions. The CA, in short, can output independent factors that describe distributions.
The CA was performed with the statistical software R (R ver. 4.0.2) and plugins (RStudio ver. www.nature.com/scientificreports/