Luyi Miao

Xu Dai

Dieter Korn

Arnaud Brayard

Jing Chen

Xiaokang Liu

Haijun Song
email: haijunsong@cug.edu.cn

A Changhsingian (Late Permian) nautiloid assemblage from Gujiao, South China

Keywords: Nautiloidea, Cephalopoda, Permian, Changhsingian, Guizhou, China

A ca. 0.30 m thick cherty limestone bed in the Dalong Formation at Gujiao (Guizhou) yielded a highly diverse Changhsingian nautiloid assemblage. Its age is late Changhsingian, indicated by the co-occurring ammonoid Pseudotirolites sp. This assemblage is composed of nine species and five taxa in open nomenclature in nine genera, including one new genus and three new species:

Neotainoceras zhaoi sp. nov., Nodopleuroceras gujiaoense sp. nov., and Gujiaonautilus longliensis gen. nov., sp. nov. Sholakoceras is for the first time recorded in South China. Compared with literature data from 52 sites in various regions worldwide, the material described here presents the most diverse Changhsingian nautiloid assemblage. Among the genera of the Gujiao assemblage, Pleuronautilus, Tainoceras and Liroceras are cosmopolitan, while the others are more endemic or genera known so far only from South China.

INTRODUCTION

The greatest Phanerozoic mass extinction at the Permian-Triassic boundary (PTB) extirpated more than 80% of marine species [START_REF] Erwin | The Permo-Triassic extinction[END_REF][START_REF] Song | Two pulses of extinction during the Permian-Triassic crisis[END_REF]; see last estimates in [START_REF] Stanley | Estimates of the magnitudes of major marine mass extinctions in earth history[END_REF]. Many groups such as ammonoids (e.g., [START_REF] Villier | Morphological disparity of ammonoids and the mark of Permian mass extinctions[END_REF][START_REF] Brayard | Good genes and good luck: Ammonoid diversity and the end-Permian mass extinction[END_REF], brachiopods (e.g., [START_REF] Shen | Paleobiogeographical extinction patterns of Permian brachiopods in the Asian western Pacific region[END_REF][START_REF] He | Late Permian marine ecosystem collapse began in deeper waters: evidence from brachiopod diversity and body size changes[END_REF], conodonts (e.g., [START_REF] Orchard | Conodont diversity and evolution through the latest Permian and Early Triassic upheavals[END_REF][START_REF] Lai | A review of the Late Permian-Early Triassic conodont record and its significance for the end-Permian mass extinction[END_REF], foraminifers (e.g., [START_REF] Groves | Extinction, survival, and recovery of lagenide foraminifers in the Permian-Triassic boundary interval, Central Taurides, Turkey[END_REF][START_REF] Song | Evolutionary dynamics of the Permian-Triassic foraminifer size: Evidence for Lilliput effect in the end-Permian mass extinction and its aftermath[END_REF]) and calcareous algae (e.g., Jia & Song 2018) suffered a significant drop in diversity during the PTB mass extinction. However, timing and pattern of nautiloid extinction during this event and their subsequent recovery are still not well-understood, owing to the relative paucity of reported occurrences and detailed taxonomic, biostratigraphic and phylogenetic studies of this fossil group (e.g., [START_REF] Kummel | American Triassic coiled nautiloids[END_REF].

Changhsingian nautiloids are known from various places; they had been reported from the Bellerophon Formation in the Dolomites, North Italy [START_REF] Posenato | Orizzonti a nautiloidi e a brachiopodi della Formazione a Bellerophon (Permiano Superiore) in Val Gardena (Dolomiti)[END_REF][START_REF] Prinoth | Late Permian Nautiloids from the Bellerophon Formation of the Dolomites (Italy)[END_REF], the Akhura Formation of Armenia and Azerbaijan [START_REF] Shimansky | Podotryad Nautiloidea[END_REF][START_REF] Kotlyar | Posdnepermskiy etap evolyutsii organicheskogo mira. Dzhulficheskiy i dorashamskiy yarusy SSSR[END_REF], the Ali Bashi Formation of NW Iran [START_REF] Teichert | Nautiloid cephalopods from the Julfa Beds, Upper Permian, Northwest Iran[END_REF], the Khuff Formation of Saudi Arabia [START_REF] Chirat | Nautiloids of the Permian-Triassic Khuff Formation, central Saudi Arabia[END_REF][START_REF] Posenato | Marine biotic events in the Lopingian succession and latest Permian extinction in the Southern Alps (Italy)[END_REF], the Chhidru Formation of the Salt Range in Pakistan [START_REF] Waagen | Salt Range fossils, 1. Productus Limestone fossils[END_REF]Reed 1944;[START_REF] Kummel | Stratigraphy and paleontology of the Permian-Triassic boundary beds, Salt Range and Trans-Indus Ranges[END_REF], the Urushten Formation of Psebay, Krasnodarskiy Kray in Russia [START_REF] Kotlyar | Posdnepermskiy etap evolyutsii organicheskogo mira[END_REF], the Takhtabulak of Tajikistan [START_REF] Shimansky | Permskie Nautilida Pamira (Permian nautilids of the Pamirs). Byulleten Moskovskogo Obshchestva Ispytatelei Prirody[END_REF], the Changxing and Dalong formations of South China [START_REF] Zhao | Late Permian cephalopods of south China[END_REF]Liang 1984;[START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF]) and the Huai Tak Formation of Thailand [START_REF] Ishibashi | Permian-Triassic boundary and fauna at Doi Pha Phlung, northern Thailand[END_REF]. The nautiloids from these localities can be attributed to ten families, of which the Grypoceratidae, Liroceratidae and Tainoceratidae are dominant.

The earliest report of Lopingian (Late Permian) nautiloids from South China was that of Tainoceras orientale ("Nautilus orientalis") and T. mingshanense ("Nautilus mingshanensis"), described by [START_REF] Kayser | Obercarbonische Fauna von Lo-ping[END_REF] from the Jiangxi Province. After a long interruption, [START_REF] Zhao | Late Permian cephalopods of south China[END_REF] illustrated very diverse Changhsingian cephalopod assemblages in their monograph, but they described only a few nautiloids from Anhui, Zhejiang, Guangxi and Guizhou. Following this study, [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] investigated a Changhsingian nautiloid assemblage from Guizhou. Liang (1984) reported on a few nautiloids from several scattered sections in Hunan and Guangxi. A nautiloid assemblage from a reef environment in Lichuan (Hubei) was studied by [START_REF] Wu | Study of Nautiloids in the upper Permian Changxingian Reefs from Lichuan, West Hubei[END_REF].

Additional to these occurrences, nautiloid material was mentioned from other places, e.g. Fujian [START_REF] Yang | Permian-Triassic boundary stratigraphy and fauna of South China[END_REF], Chongqing and Sichuan [START_REF] Wang | Late Permian and early Early Triassic ammonoid fauna of Fenghai, Yong'an, Fujian and their stratigraphic significance[END_REF]).

Here we document a new diverse nautiloid assemblage from the Changhsingian Dalong Formation at the Gujiao section (Guizhou) that corresponds to deeper-water facies. As nautiloids are generally only minor components in the fossil record, this rather rich assemblage may improve our knowledge of the Changhsingian nautiloids not only of South China, but it might also provide important data for future studies on the nautiloid extinction and recovery as well as their evolution at the PTB.

GEOLOGICAL SETTING

The Gujiao section is located ca. 20 km south-east of Guiyang, the capital of Guizhou. During the PTB interval, this area had an equatorial position at the interface between the Panthalassa ocean and the Tethys (Fig. 1A). It belonged to the transitional zone between the upper Yangtze Platform and the Nanpanjiang Basin [START_REF] Feng | Lithofacies Palaeogeography of Early and Middle Triassic of South China[END_REF]. The studied section is an outcrop along a new road; it shows well-exposed Permian and Triassic strata ranging from the Late Permian Changxing and Dalong formations to the Early Triassic Daye Formation (Fig. 1B).

The Changxing Formation is composed of bioclastic and cherty limestones. It yielded abundant and diverse Late Permian fossils, e.g. brachiopods, bryozoans, gastropods, corals and dasycladacean algae [START_REF] Dai | A new Griesbachian-Dienerian (Induan, Early Triassic) ammonoid fauna from Gujiao, South China[END_REF]. This bioclastic limestone-dominated succession with abundant calcareous algae and corals suggests deposition on a carbonate platform. One volcanic ash bed has a position near the top of the formation (Fig. 1D).

The Dalong Formation consists mainly of cherty limestone, cherts and black shales, which are alternating with volcanic ash beds (Fig. 1D; [START_REF] Dai | A new Griesbachian-Dienerian (Induan, Early Triassic) ammonoid fauna from Gujiao, South China[END_REF]. Abundant radiolarians were documented in the cherty limestone and cherts, suggesting a deep basin setting [START_REF] Feng | Uppermost Changxingian (Permian) radiolarian fauna from southern Guizhou, southwestern China[END_REF]. A cherty limestone bed of ca. 30 cm thickness in the lower part of the Dalong Formation yielded abundant and well-preserved nautiloids (n = 103) and ammonoids (n >300). The occurrence of the ammonoid genus Pseudotirolites (Fig. 2) indicates a late Changhsingian age [START_REF] Dai | A new Griesbachian-Dienerian (Induan, Early Triassic) ammonoid fauna from Gujiao, South China[END_REF].

The overlying Triassic Daye Formation is characterized by alternations of thin-to medium-bedded limestones and shales corresponding to a basin or basin margin setting. A diverse fauna, including bivalves, nautiloids, gastropods and foraminifers was found in the lower Daye Formation, with several successive ammonoid assemblages indicating an Induan age [START_REF] Dai | Rapid biotic rebound during the late Griesbachian indicates heterogeneous recovery patterns after the Permian-Triassic mass extinction[END_REF][START_REF] Dai | A new Griesbachian-Dienerian (Induan, Early Triassic) ammonoid fauna from Gujiao, South China[END_REF].

MATERIAL AND METHODS

A total of 103 nautiloid specimens were collected from a single cherty limestone bed with~ 30 cm thickness in the lower Dalong Formation (bed 7 in Fig. 1D). Most of the specimens are internal moulds; only some of them possess remnants of the recrystallized shell. Despite of this, they are relatively often well-preserved. All the specimens were prepared in the laboratory using air scribe to work out anatomy details to facilitate species level identification. Well-preserved nautiloid specimens were photographed using a Canon 70D camera with a macro lens EF 100 mm f/2.8.

SIGNIFICANCE FOR PALAEOBIOGEOGRAPHY

Changhsingian nautiloids in South China: a regional signal linked to depth?

Changhsingian nautiloids are abundant and widespread in South China [START_REF] Zhao | Late Permian cephalopods of south China[END_REF]Liang 1984;[START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF][START_REF] Wu | Study of Nautiloids in the upper Permian Changxingian Reefs from Lichuan, West Hubei[END_REF]. They were mainly reported from Guizhou, Zhejiang and Hubei and are distributed in three main depositional environments, i.e. reefs, slopes and basin settings. The compositional similarity of the Changhsingian assemblages from Meishan (Zhejiang), Qinglong and Langdai (West Guizhou) is rather high. Material of these three regions was recorded from slope and basinal environments. All these deep or slope-environment sites show relatively similar assemblages with the predominant tainoceratid genera Tainoceras, Neotainoceras and Pleuronautilus. [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] documented several sections with diverse nautiloids from the deeper-water Dalong Formation in western Guizhou. These assemblages from the Zhongying and Langdai sections are dominated by the families Tainoceratidae (Tainoceras, Neotainoceras, Pleuronautilus) and Trigonoceratidae (Aulagonoceras), accompanied by a few representatives of the Liroceratidae (Liroceras) and Gzheloceratidae (Tylonautilus).

Diverse nautiloids were reported from the Changxing Formation of the Meishan section (slope facies; [START_REF] Zhao | Late Permian cephalopods of south China[END_REF]. This community is composed of the Tainoceratidae (Tainoceras, Neotainoceras, Pleuronautilus, and Metacoceras), Liroceratidae (Liroceras), and Gzheloceratidae (Parametacoceras).

In contrast to these common assemblages from slope and basin settings, the nautiloids from the Jiantianba reefs in Lichuan [START_REF] Wu | Study of Nautiloids in the upper Permian Changxingian Reefs from Lichuan, West Hubei[END_REF] show a low taxonomic diversity. This assemblage is dominated by Liroceras and Permonautilus and includes nine species in eight genera. Unlike the abundant Tainoceratidae in the deep-water facies of Guizhou and Zhejiang, this family is rather rare and only the single genus Pleuronautilus was found in the Jiantianba reefs.

The taxonomic composition of the Gujiao assemblage is very similar to those from western Guizhou (Langdai and Qinglong). Sholakoceras and the new genus Gujiaonautilus are here described for the first time. The Gujiao nautiloid assemblage is therefore overall congruent with other deep-water Chinese nautiloid faunas, which are dominated by the family Tainoceratidae, and includes only a few genera of the Liroceratidae, Trigonoceratidae, Grypoceratidae, and Rhiphaeoceratidae.

Changhsingian nautiloids in other regions

Most localities yielding Changhsingian nautiloids are restricted to low Tethyan palaeolatitudes (Fig. 3; Table S1), e.g. Iran [START_REF] Teichert | Nautiloid cephalopods from the Julfa Beds, Upper Permian, Northwest Iran[END_REF], Armenia and Azerbaijan [START_REF] Shimansky | Podotryad Nautiloidea[END_REF][START_REF] Kotlyar | Posdnepermskiy etap evolyutsii organicheskogo mira. Dzhulficheskiy i dorashamskiy yarusy SSSR[END_REF], Italy [START_REF] Posenato | Orizzonti a nautiloidi e a brachiopodi della Formazione a Bellerophon (Permiano Superiore) in Val Gardena (Dolomiti)[END_REF][START_REF] Prinoth | Late Permian Nautiloids from the Bellerophon Formation of the Dolomites (Italy)[END_REF], Saudi Arabia [START_REF] Chirat | Nautiloids of the Permian-Triassic Khuff Formation, central Saudi Arabia[END_REF][START_REF] Posenato | Marine biotic events in the Lopingian succession and latest Permian extinction in the Southern Alps (Italy)[END_REF], Thailand [START_REF] Ishibashi | Permian-Triassic boundary and fauna at Doi Pha Phlung, northern Thailand[END_REF]. Only the nautiloids from Tajikistan [START_REF] Shimansky | Permskie Nautilida Pamira (Permian nautilids of the Pamirs). Byulleten Moskovskogo Obshchestva Ispytatelei Prirody[END_REF] and Pakistan [START_REF] Waagen | Salt Range fossils, 1. Productus Limestone fossils[END_REF][START_REF] Reed | New fossils from the Productus Limestones of the Salt Range, with notes on other species. Memoirs of the Geological Survey of India[END_REF]Reed , 1944;;[START_REF] Kummel | Stratigraphy and paleontology of the Permian-Triassic boundary beds, Salt Range and Trans-Indus Ranges[END_REF]) are closer to middle palaeolatitudes. Iran, Armenia and Azerbaijan are adjacent regions, so that we combined them into the Transcaucasia-Iran region. The nautiloid composition of the Transcaucasia-Iran region is most similar to that in South China. Nautiloid assemblages from Northwest and Central Iran [START_REF] Teichert | Nautiloid cephalopods from the Julfa Beds, Upper Permian, Northwest Iran[END_REF]Taraz et al. 1981) contain Metacoceras, Tainoceras, Liroceras, and Pleuronautilus. [START_REF] Shimansky | Podotryad Nautiloidea[END_REF] and [START_REF] Kotlyar | Posdnepermskiy etap evolyutsii organicheskogo mira. Dzhulficheskiy i dorashamskiy yarusy SSSR[END_REF] reported several nautiloid assemblages from Transcaucasia (Armenia and Azerbaijan), including Syringonautilus, Tainionautilus, Pleuronautilus, Domatoceras, and Foordiceras. Most of these genera were also documented in South China except Syringonautilus and Temnocheilus.

Another location with abundant nautiloids is the Salt Range Pakistan, which is dominated by Tainoceratidae with a few Grypoceratidae and Koninckioceratidae [START_REF] Waagen | Salt Range fossils, 1. Productus Limestone fossils[END_REF]Reed 1944;[START_REF] Kummel | Stratigraphy and paleontology of the Permian-Triassic boundary beds, Salt Range and Trans-Indus Ranges[END_REF]. Most of the nautiloids of the Salt Range were also reported in the Transcaucasia-Iran region, e.g. Metacoceras, Pleuronautilus, Tainionautilus, Tainoceras, Domatoceras, Temnocheilus. Aside from these genera, two representatives of the Grypoceratidae appear to be restricted to the Salt Range, i.e. Stearoceras and Pselioceras (Reed 1944).

The Dolomites in northern Italy are another region with nautiloids in a subequatorial region [START_REF] Posenato | Orizzonti a nautiloidi e a brachiopodi della Formazione a Bellerophon (Permiano Superiore) in Val Gardena (Dolomiti)[END_REF][START_REF] Prinoth | Late Permian Nautiloids from the Bellerophon Formation of the Dolomites (Italy)[END_REF]). However, this community is different from that of the Transcaucasia-Iran basin; it is dominated by the Liroceratidae (Liroceras and Peripetoceras) and Tainoceratidae (Foordiceras, Tirolonautilus and Tainoceras).

Besides these larger nautiloid assemblages, some low-diverse Changhsingian nautiloid occurrences are known from other regions. In the Urushten Formation of Psebay (Krasnodarskiy Kray, Russia), only the two genera Pseudotemnocheilus and Pleuronautilus were reported [START_REF] Kulikov | Find of Claraia (Bivalvia) in the Upper Permian of the northern Caucasus[END_REF][START_REF] Kotlyar | Posdnepermskiy etap evolyutsii organicheskogo mira[END_REF] . Only one genus Tirolonautilus was reported in the Khuff Formation of Ad Dawadimi, central Saudi Arabia [START_REF] Chirat | Nautiloids of the Permian-Triassic Khuff Formation, central Saudi Arabia[END_REF]. In Tajikistan, only the single genus Pararhiphaeoceras was recorded from Changhsingian strata by [START_REF] Shimansky | Permskie Nautilida Pamira (Permian nautilids of the Pamirs). Byulleten Moskovskogo Obshchestva Ispytatelei Prirody[END_REF]. Only Siamnautilus was documented in the Huai Tak Formation of Thailand by [START_REF] Ishibashi | Permian-Triassic boundary and fauna at Doi Pha Phlung, northern Thailand[END_REF]. The nautiloids in Tajikistan and Thailand were all endemic taxa.

SYSTEMATIC PALAEONTOLOGY

Systematic descriptions mainly follow the classifications proposed by Kummel (1964) and[START_REF] Dzik | Phylogeny of the Nautiloidea[END_REF]. Synonymy lists and taxa in open nomenclature are annotated following the recommendations of [START_REF] Matthews | The life-cycle of Bucephalus haimeanus Lacaze-Duthiers, 1854 from Cardium edule[END_REF] and [START_REF] Bengtson | Open nomenclature[END_REF]; 'v' implies that the authors have checked the original material of the reference; 'p' indicates that the reference applies only in part to the species under discussion. The morphological range of each taxon has been quantified using the four classic geometrical parameters of the nautiloid conch: diameter (dm), whorl height (wh), whorl width (ww), umbilical diameter (uw) and the distance between two rows of ventral nodes (Dn). Descriptive terminology for the conch morphology is after [START_REF] Korn | A key for the description of Palaeozoic ammonoids[END_REF]. All specimens described here are housed in the Yifu Museum of China University of Geosciences, Wuhan, China (YFMCUG 00201-YFMCUG 00303). Diagnosis. Tainoceratidae with subinvolute to subevolute conch and subquadrate whorl profile, venter with central groove and sometimes two additional, shallower grooves. Sculpture with a double row of nodes on the venter. Suture line with a narrow ventral lobe in the area of the ventral groove and shallow lateral lobes.

Remarks. Tainoceras is a long-ranging genus from the Gzhelian to the Late Permian. In the Changhsingian, Tainoceras is diverse and widely distributed with at least five valid species [START_REF] Yao | On the biostratigraphy of the Permian and the boundary between the Permian and Triassic in western Guizhou-eastern Yunnan. Late Permian coal bearing strata and biota from western Guizhou and eastern Yunnan[END_REF][START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF][START_REF] Prinoth | Late Permian Nautiloids from the Bellerophon Formation of the Dolomites (Italy)[END_REF]. Tainoceras is similar to Metacoceras Hyatt, 1883 (which does not possess a ventral groove), Tirolonautilus [START_REF] Mojsisovics | Das Gebirge um Hallstatt. Die Cephalopoden der Hallstätter Kalke. 1. Band[END_REF] (which possesses a depressed to slightly compressed conch with a median ventral groove and occasionally oblique ribs on the venter), Pleuronautilus Mojsisovics, 1882 (which has a smooth venter), and Tainionautilus [START_REF] Mojsisovics | Das Gebirge um Hallstatt. Die Cephalopoden der Hallstätter Kalke. 1. Band[END_REF] (which has strongly oblique ribs on flanks and venter).

Tainoceras guizhouense [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF]Figure 4A, B v. 1984 Tainoceras guizhouense;Zheng, p. 242, pl. 2, figs. 1-5. Holotype. Specimen NIGPAS 34364; illustrated by Zheng (1984, pl. 2, fig. 5).

Type locality and horizon. Zhongying, Qinglong; Changhsingian.

Material. Only one well-preserved phragmocone (YFMCUG 00201).

Diagnosis. Tainoceras with subevolute conch and subrectangular and depressed whorl profile; broad and arched venter with rounded ventrolateral shoulders; the flanks converge towards the subangular umbilical margin with . Venter with central groove and sometimes two further, shallower grooves.

Sculpture with a double row of transversely elongated nodes on both sides of the ventral groove; a row of larger nodes were located on the ventrolateral shoulder and rise to shallow ribs on flanks.

Suture line with a narrow external lobe in the area of the ventral groove and broad ventral saddles, broad and shallow lateral lobes on the flank.

Description. Specimen YFMCUG 00201 is 89 mm in maximum diameter. It is pachyconic and subevolute (ww/dm = 0.62; uw/dm = 0.34) with subrectangular and moderately depressed whorl profile; the width is much larger than the height (ww/wh = 1.56). The very broad and slightly convex venter bears a marked central groove; it has a width of 4.7 mm on the last portion of the phragmocone (at dm = 89 mm). One additional, shallow ventral groove is located on each side at the ventral margin near the rounded ventrolateral shoulder. The flanks converge slowly towards the umbilical margin and the maximum whorl width is located at the ventrolateral shoulder. The umbilicus has a subangular margin and a vertical wall.

The conch bears a very conspicuous sculpture. Two rows of transversely elongated nodes are arranged on both sides of the ventral groove. These ventral nodes are approximately 15 mm long and spaced regularly 7.5 mm apart (at dm = 89 mm). Another two rows of nodes are located on the ventrolateral shoulders; they give rise to shallow ribs that extend across the flanks and disappear near the umbilical shoulder. The umbilical shoulders bear two rows of small and elongated nodes. The suture line shows a narrow, deep ventral lobe in the area of the ventral groove and broad and shallow lateral lobes.

Remarks. Numerous species of Tainoceras have been separated on the basis of differences in the shape and characteristics of sculpture. T. guizhouense is distinguished from almost all other species of the genus by its coarse and elongated nodes and three grooves on the venter. T. unklesbayi Miller & Youngquist, 1949 from the Early Permian Toroweap Formation of the Grand Canyon is similar to T. guizhouense with its elongated nodes on each side of the ventral groove, but its ventral nodes are obliquely elongate (transversely elongate in T. guizhouense).

Occurrence. Dalong Formation, Guizhou; late Changhsingian. T. guizhouense has so far only been reported from Changhsingian strata of Guizhou [START_REF] Yao | On the biostratigraphy of the Permian and the boundary between the Permian and Triassic in western Guizhou-eastern Yunnan. Late Permian coal bearing strata and biota from western Guizhou and eastern Yunnan[END_REF][START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF].

Tainoceras sp.

Figure 4C

Description. Only one fragment (YFMCUG 00202) of a phragmocone with weakly depressed subrectangular whorl profile (ww/wh = 1.20) is available. The venter is arched with a narrow and shallow longitudinal central groove. Two rows of regularly spaced nodes are arranged adjacent to the ventral groove. The angular ventrolateral shoulders show a row of elongated nodes, which are larger than the ventral nodes. The flank converges towards the umbilical shoulder with the maximum width at the ventrolateral shoulders.

Remarks. This specimen exhibits characteristic features of Tainoceras, e.g. the depressed subrectangular whorl profile, two rows of nodes on the venter and two rows of nodes on the ventrolateral shoulders. However, the smooth flanks have never been documented in any species of Tainoceras. Therefore, our specimen might represent a new species. We prefer to keep it in open nomenclature because only one fragment is available.

Genus Neotainoceras Zhao, Liang & Zheng, 1978 Type species. Neotainoceras pachydiscum Zhao, Liang & Zheng, 1978;Meishan (Zhejiang, South China), Changhsingian. Paratypes. The five specimens, YFMCUG 00204 (Fig. 4D), YFMCUG 00205 (Fig. 4E), YFMCUG Type locality and horizon. Gujiao section (Guizhou); bed GJ-7 in the Dalong Formation (late Changhsingian).

Material. A total of nine specimens (YFMCUG 00203-YFMCUG 00211) were collected from the type horizon: six well-preserved fragments are included in the type series (YFMCUG 00203-YFMCUG 00208); additionally three internal moulds or squashed fragments.

Diagnosis. Neotainoceras with subinvolute conch and depressed subrectangular whorl profile.

Slightly convex venter with narrow ventral groove and rounded ventrolateral shoulders, convex flanks and angular umbilical margin. Sculpture with two rows of elongate ventral nodes symmetrically positioned on both sides of the ventral groove, one row of obtuse nodes on the ventrolateral shoulder, two rows of weak nodes on the flank and one row of elongate and low nodes on the umbilical shoulder. Ventral nodes slightly oblique. Subcentral siphuncle. Suture line with rather deep and narrow lobe at the ventral groove, a shallow rounded lobe as it crosses another groove and a low saddle as it crosses a row of nodes on the ventral area; lateral lobe broad and shallow.

Description. The rather well-preserved holotype (specimen YFMCUG 00203, Fig. 4F) has a maximum diameter of 72 mm. The conch is thinly pachyconic and subinvolute (ww/dm = 0.66; uw/dm = 0.29) with a weakly depressed subrectangular whorl profile (ww/wh = 1.47). The venter is broadly arched and bears a narrow ventral groove; it is separated from the convex, almost parallel flanks by a rounded ventrolateral shoulder. The umbilicus is deep with vertical wall and is separated from the flanks by a weakly angular margin. Two rows of blunt ventral nodes are symmetrically located on each side of the ventral groove. These nodes are weakly elongated and slightly oblique.

The flanks show two additional rows of low nodes, and the umbilical margin bears one row of rather small and elongated nodes.

The suture line forms a narrow ventral lobe at the central groove, a rather shallow and rounded lobe as it crosses the second groove between the ventral nodes, a small rounded saddle as it crosses a row of nodes and broad and shallow lateral lobes. The siphuncle has a near-central position.

Remarks. Among the four other species assigned to the genus Neotainoceras, N. pachydiscum closely resembles N. zhaoi, but the ventral nodes of N. zhaoi are sharper than in N. pachydiscum and other species. Aside from ventral nodes, the flanks of N. zhaoi with two rows of nodes differ from other species of Neotainoceras. While the flanks of N. pachydiscum and N. liuchengense are decorated with a row of small tubercles near the umbilical margin, the flanks of N. gigantum are smooth without tubercles. N. zhaoi has also a more rectangular whorl profile than N. pachydiscum, N. Remarks. Pleuronautilus is one of the most diverse genera of the Tainoceratidae. It was a long-living genus, ranging from the Asselian to the Norian (e.g. [START_REF] Dzik | Phylogeny of the Nautiloidea[END_REF]. [START_REF] Mojsisovics | Die Cephalopoden der mediterranen Triasprovinz[END_REF] erected this genus based on Triassic specimens from Northern Alps. Following this work, [START_REF] Foord | Catalogue of the Fossil Cephalopoda in the British Museum (Natural History), Part 2, containing the remainder of the suborder Nautiloidea, consisting of the families Lituitidae, Trochoceratidae, and Nautilidae, with a supplement[END_REF] emended Pleuronautilus to include a variety of Permian forms. Arthaber (1896) established more additional species and Hyatt (1900) established the family Pleuronautilidae. However, through multiple revisions, [START_REF] Kummel | American Triassic coiled nautiloids[END_REF] attributed Pleuronautilus to the Tainoceratidae and added five subgenera (Encoiloceras, Anoploceras, Holconautilus, Enoploceras, Trachynautilus), now regarded as genera, to Pleuronautilus, which altogether contains approximately 95 species. [START_REF] Dzik | Phylogeny of the Nautiloidea[END_REF] discussed the phylogeny of Pleuronautilus and the possibility that it is a polyphyletic taxon composed of several evolutionary lineages that branched independently. More than eight Changhsingian species of Pleuronautilus were reported so far [START_REF] Waagen | Salt Range fossils, 1. Productus Limestone fossils[END_REF]Reed 1944;[START_REF] Shimansky | Podotryad Nautiloidea[END_REF][START_REF] Zhao | Late Permian cephalopods of south China[END_REF][START_REF] Kulikov | Find of Claraia (Bivalvia) in the Upper Permian of the northern Caucasus[END_REF][START_REF] Yao | On the biostratigraphy of the Permian and the boundary between the Permian and Triassic in western Guizhou-eastern Yunnan. Late Permian coal bearing strata and biota from western Guizhou and eastern Yunnan[END_REF][START_REF] Kotlyar | Posdnepermskiy etap evolyutsii organicheskogo mira. Dzhulficheskiy i dorashamskiy yarusy SSSR[END_REF][START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF]. It mainly differs from Anoploceras and Encoiloceras by its compressed whorl profile and from Metacoceras and Mojsvaroceras by the node-bearing ribs on the flanks.

During the last 60 years, Late Permian representatives of Pleuronautilus were sporadically reported from sites that were mainly located in the equatorial area of Tethys. From the Wuchiapingian, numerous Pleuronautilus specimens were discovered in Azerbaijan and NW Iran [START_REF] Shimansky | Podotryad Nautiloidea[END_REF][START_REF] Teichert | Nautiloid cephalopods from the Julfa Beds, Upper Permian, Northwest Iran[END_REF]. From South China, Changhsingian material was reported from Zhejiang [START_REF] Zhao | Late Permian cephalopods of south China[END_REF] and Guizhou [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF]. Pleuronautilus has so far not been recorded from Induan strata immediately after the PT mass extinction, but from the Olenekian, the genus is known from Chernyshev Bay, Russkiy Island, Russia [START_REF] Zakharov | Rannetriasovye ammonoidei vostoka SSSR[END_REF] Pleuronautilus zhongyingensis [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF]Figure 7A, B v. 1984 Pleuronautilus zhongyingensis Zheng,p. 245,pl. 2,figs. 12,13;pl. 3,fig. 1;.

Holotype. Specimen NIGPAS 34379; illustrated by Zheng (1984, pl. 2, fig. 12-13).

Type locality and horizon. Zhongying section in Qinglong, Guizhou; Dalong Formation (Changhsingian).

Diagnosis. Pleuronautilus with subevolute conch and depressed subtrapezoidal whorl profile. Venter smooth and arched with subangular ventrolateral shoulders; flanks converge towards the rounded umbilical margin. Sculpture with robust and prorsiradiate ribs on the lateral area. Subcentral siphuncle, suture line with broad ventral and lateral lobes.

Material. Three strongly recrystallized (YFMCUG 00215-YFMCUG 00217) fragments.

Description. Specimen YFMCUG 00215 is subevolute (uw/dm = 0.40 at 81 mm diameter) and has a subtrapezoidal, weakly depressed whorl profile (ww/wh = 1.21) with a smooth venter and a subangular ventrolateral shoulder. The flanks are slightly convex and convergent towards the umbilical margin; the maximum whorl width is at the ventrolateral shoulder. They are ornamented with robust and prorsiradiate ribs, becoming wider towards the ventrolateral shoulder. The umbilicus has a vertical wall and a rounded umbilical shoulder. The suture line is not visible.

Remarks. Our specimens are perfectly fitting with the Changhsingian specimens of Pleuronautilus zhongyingensis described and illustrated by [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] from the Zhongying section of Qinglong, West Guizhou. [START_REF] Wu | Study of Nautiloids in the upper Permian Changxingian Reefs from Lichuan, West Hubei[END_REF] found Pleuronautilus cf. zhongyingensis in a Changhsingian reef at Lichuan. When comparing the material of the two sites, it is obvious that the ribs of the holotype of P. zhongyingensis are coarser. P. changxingensis [START_REF] Zhao | Late Permian cephalopods of south China[END_REF] from the Changxing Formation of Meishan section differs from P. zhongyingensis by the presence of prorsiradiate ribs on the flanks and a wider umbilicus.

Occurrence. Dalong Formation (late Changhsingian) of the Jianzishan and Zhongying sections, South China [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF].

Pleuronautilus sp.

Figure 7C-G

Material. Seven specimens (YFMCUG 00218-YFMCUG 00224).

Description. The best-preserved specimen YFMCUG 00220 (Fig. 7F,G) has a maximum diameter of 50 mm and is thinly discoidal and subevolute (ww/dm = 0.34; uw/dm = 0.42) with an almost quadratic whorl profile (ww/wh = 1.01) and a subtabulate venter. The convex flanks converge slowly towards the rounded ventrolateral shoulder; the maximum whorl width is near the rounded umbilical margin. The umbilical wall is vertical. The flanks are ornamented with dense, rectiradiate ribs starting from the umbilical margin and disappearing at the ventrolateral shoulder. The suture line has a broad shallow ventral lobe and broad lateral lobes.

Remarks. Compared with other Late Permian material of Pleuronautilus, the ribs of these specimens are more closely arranged and gracile. The similar Changhsingian species P. magnus [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] from Liuzhi in Guizhou has ribbed inner whorls, but its outer whorls bear large nodes near the ventrolateral shoulders. As only a few specimens were sampled, we prefer to keep this taxon in open nomenclature.

Genus Nodopleuroceras [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] Type species. Nodopleuroceras guizhouense [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF]; Liuzhi and Guiyang (Guizhou); Changhsingian.

Diagnosis. Tainoceratidae with subevolute conch and subquadrate whorl profile, slightly convex venter and flattened flanks; subangular to rounded ventrolateral and umbilical margin. Sculpture with closely spaced, prorsiradiate ribs on the lateral area; ribs backward projected and extending sideways to the venter, intersect with a V-shaped sinus on the venter or discontinue at the shallow ventral groove. The ribs always bear several spiral rows of nodes on the lateral area. Suture line with a shallow ventral lobe and two broad lateral lobes.

Remarks. Nodopleuroceras was erected by [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] based on rather poorly preserved specimens of the single species N. guizhouense from Guizhou. The ornamentation of Nodopleuroceras shows several spiral rows of nodes and sinuous ribs similar to Tainonautilus, but the ribs of Nodopleuroceras are denser and more elongated on the venter. Nodopleuroceras is similar to Wuchiapingian Nodonautilus of Anhui (Liang 1984) by sharing some common features, e.g. a subevolute conch and closely arranged ribs. However, Nodopleuroceras can be distinguished from Nodonautilus by its subquadrate whorl profilewith convex venter, rather shallow and narrow ventral grooves, while Nodonautilus is characterized by the thick ribs and a broad deep ventral groove. It differs from Pleuronautilus and Eulomacoceras [START_REF] Zhao | Late Permian cephalopods of south China[END_REF] by its denser ribs on the venter, from the Wuchiapingian Paratainonautilus from Jiangxi by [START_REF] Qin | New Material of Early Late Permian Cephalopods in Fengcheng-Gaoan Area, Jiangxi[END_REF] by its nodes on the ribs, and from Clavinautilus from the Changxing Formation of West Guizhou [START_REF] Zhao | Late Permian cephalopods of south China[END_REF]) by the slightly arched venter without nodes.

Nodopleuroceras gujiaoense sp. nov. Type locality and horizon. Gujiao section (Guizhou); bed GJ-7 in the Dalong Formation (late Changhsingian).

Material. Eleven specimens (YFMCUG 00225-YFMCUG 00236) from bed GJ-7.

Diagnosis. Nodopleuroceras with subevolute conch and subquadrate whorl profile. Ornament with closely spaced ribs which extend with shallow sinus across the flank, form a projection at the ventrolateral shoulder and a V-shaped ventral sinus. Eight spiral rows of nodes from umbilicus to mid-venter. Suture line with shallow ventral lobe and broad lateral lobes.

Description. The holotype (specimen YFMCUG 00225, Fig. 8A) has a maximum diameter of 56 mm; it is thinly discoidal and subevolute (ww/dm = 0.37; uw/dm = 0.39) with a nearly square-shaped whorl profile (ww/wh = 1.04). The venter is rounded, while the flanks are weakly flattened with the maximum width in the midflank area; the umbilical margin is rounded and the umbilical wall is vertical. The shell is ornamented with a combination of ribs and additional nodes, which are placed in spiral rows on the ribs. The ribs extend with a concavo-convex course, forming a shallow lateral sinus, a moderately high ventrolateral projections and a narrow, V-shaped ventral sinus. In most cases, these ribs are beginning at the umbilical margin, but occasionally, ribs are intercalated on the inner flank in some distance from the umbilicus. Eight rows of small nodes are developed on the flanks, becoming coarser towards the venter. The suture line shows a shallow ventral lobe as well as broader and deeper lateral lobes. The siphuncle has near-central position.

Remarks. When compared with Nodopleuroceras guizhouense, N. gujiaoense sp. nov. differs by its eight rows of nodes on the flanks, while the flank of N. guizhouense shows only three rows of nodes near the umbilical margin. Additionally, N. guizhouense shows a well-developed ventral groove, which is absent in the new species.

Occurrence. Dalong Formation (late Changhsingian), Gujiao section (Guizhou).

Genus Gujiaonautilus gen. nov. Derivation of name. Named after the Gujiao section, the type locality.

Type species. Gujiaonautilus longliensis sp. nov.; Gujiao section (Guizhou), Changhsingian.

Included species. Gujiaonautilus longliensis sp. nov. Description. The holotype (specimen YFMCUG 00248, Fig. 10D) is 72.5 mm in maximum diameter; it is thinly discoidal and subevolute (uw/dm = 0.37, uw/dm = 0.34) with weakly compressed subquadrate to nearly oval whorl profile (ww/wh = 0.85). The venter is weakly convex with rounded ventrolateral shoulders; the flanks are convex with the maximum whorl width near the umbilical margin; with rounded umbilical shoulders and vertical umbilical wall. The venter bears a narrow and shallow ventral groove, bordered by two rows of slightly elongate and oblique tubercles on each side. This species displays a remarkable variation in the distances between rows of ventral nodes; the Dn/ww value range from 0.14 to 0.24 among the specimens, but is constant during ontogeny. The flanks exhibit dense and intercalary ribs. These ribs are in general weakly sinuous and sometimes two ribs develop from a single node on the umbilical shoulder; they disappear near the ventrolateral shoulder. When preserved, the shell shows conspicuous growth lines that are best visible on the venter (specimens YFMCUG 00243, YFMCUG 00250-00251); they curve backward between the ventral nodes and the end of the ribs. The suture line displays a shallow ventral lobe between the two rows of ventral nodes and broad, deeper lateral lobes.

This species shows some growth allometry. Whorls of preadult individuals display a subtabulate venter and a depressed rectangular whorl profile (ww/wh = 1.26 at dm = 27.7 mm in specimen YFMCUG 00247), while in the adult stage, the whorl profile is slightly compressed with a convex venter and rounded ventrolateral shoulders. The whorl width/diameter ratio decreases from 0.5 to ca. 0.3 during ontogeny (see Fig. 11). Changes in ontogeny can also be seen in the sculpture; in large-sized individuals, the ribs are more sinuous, slightly extended towards the venter and connected with ventral nodes.

Measurements. See online resource and Fig. 11.

Occurrence. Dalong Formation (late Changhsingian), Gujiao section (Guizhou).

Family Rhiphaeoceratidae [START_REF] Ruzhencev | Nizhnepermskie svernutye i sognutie nautiloidei yuzhnogo Urala[END_REF] Genus Sholakoceras [START_REF] Ruzhencev | Nizhnepermskie svernutye i sognutie nautiloidei yuzhnogo Urala[END_REF] Type species. Sholakoceras bisulcatum [START_REF] Ruzhencev | Nizhnepermskie svernutye i sognutie nautiloidei yuzhnogo Urala[END_REF]; Ural Mountains of Kazakhstan; Sakmarian.

Diagnosis. Rhiphaeoceratidae with subevolute conch; whorl profile subquadrate, with nearly flattened ventral and flanks, rounded ventrolateral and umbilical shoulders. The flanks bear short and prorsiradiate ribs. The suture line is characterized by a very shallow ventral lobe, shallow lateral lobes and a deep funnel-shaped dorsal lobe.

Remarks. [START_REF] Ruzhencev | Nizhnepermskie svernutye i sognutie nautiloidei yuzhnogo Urala[END_REF] introduced this genus, including three species, and concluded that Sholakoceras, Rhiphaeonautilus, Rhiphaeoceras and Pararhiphaeoceras are sister genera in the same family: the Rhiphaeoceratidae. Genera belonging to this family are all widely perforate and bear plicate ribs on the flanks. A large variation among genera is also observed, especially for the whorl profile. It is characteristically subquadrate in Sholakoceras, low elliptical in Rhiphaeoceras, subtrapezoidal with a broad arched venter and narrow flanks bearing short inflated ribs in Rhiphaeonautilus, and subtrapezoidal with rounded ventrolateral shoulders and short, oblique ribs in Pararhiphaeoceras. [START_REF] Liang | Early Permian Cephalopods from Northwestern Gansu and Western Nei Monggol[END_REF] reported the Roadian Sholakoceras transforme from Gansu (North China). Mapes

Figure 12A-B

Description. A single well-preserved internal mould of one and a half whorls with complete protoconch is available. The conch is subevolute (dm/uw = 0.40 at 33 mm diameter), with a subquadrate whorl profile (ww/wh = 1.10). The subtabulate venter bears a double row of small elongated nodes in centre. The Dn/ww ratio is 0.24 at wh = 12.1 mm. The flanks converge slightly towards the subangular ventrolateral shoulders with the maximum whorl width at the umbilical shoulders. The flanks are ornamented with prorsiradiate ribs. The umbilical perforation is rather large (8.1 mm in diameter) with a conical protoconch. The adapical ornament is conspicuous with densely arranged transverse plications. The suture line is almost straight with an inconspicuous ventral lobe and broad shallow lateral lobes.

Remarks. This specimen is perforate and bears plicate ribs on the flanks, with a subquadrate whorl profile, which are all features of Sholakoceras. Nevertheless, elongated ventral nodes were not reported so far for any species of this genus. As only one rather small internal mould is available, we prefer to keep this taxon in open nomenclature.

Family Liroceratidae Miller & Youngquist, 1949Genus Liroceras Teichert, 1940 Type species. Coloceras liratum [START_REF] Girty | On some new genera and species of Pennsylvanian fossils from the Wewoka Formation of Oklahoma[END_REF]Oklahoma (Unites States).

Diagnosis. Liroceratidae characterized by involute, globular and smooth conch with depressed whorl profile. Umbilicus is small or occluded. The suture line is almost straight.

Remarks.

A detailed discussion of this genus is available in [START_REF] Barskov | Middle Permian cephalopods of the Volga-Ural Region[END_REF]. Liroceras differs as follows from other genera of the Liroceratidae: Paranautilus has a depressed whorl profile (which is rather depressed whorl in Liroceras), Peripetoceras shows a more quadrate whorl profile with subangular umbilical shoulders and Coelogasteroceras differs from Liroceras by the presence of a ventral groove. Permonautilus exhibits coarse growth lines and often spiral lines, as well as long umbilical projections of the shell in the adult stage. [START_REF] Wu | Study of Nautiloids in the upper Permian Changxingian Reefs from Lichuan, West Hubei[END_REF]Figure 13A, B v. 1992 Liroceras lichuanense Wu & Kuang,p. 291,pl. 1,figs. 2,3,5. Lectotype. Specimen LJ242; illustrated by Wu & Kuang (1992, pl. 1, fig. 3.) Diagnosis. Liroceras with subglobular and smooth conch and slightly depressed horseshoe-shaped whorl profile; arched venter and flanks without ventrolateral shoulders. Umbilicus occluded. Suture line almost straight.

Liroceras lichuanense

Material. Two large phragmocones (YFMCUG 00292-YFMCUG 00293) from the GJ-7 are available.

Description. The larger specimen YFMCUG 00292 is slightly squashed and measures 108 mm in maximum diameter. It has a weakly depressed horseshoe-shaped whorl profile that is wider than high (ww/wh = 1.37). The venter is broadly arched without ventrolateral shoulders and the umbilicus is occluded. The shell is smooth with obvious growth lines, which bend in a broad and shallow U-shape sinus on the venter. The suture line is almost straight without obvious lobes and saddles.

Remarks. The specimens of Liroceras lichuanense from the Gujiao section are much larger than those from Lichuan [START_REF] Wu | Study of Nautiloids in the upper Permian Changxingian Reefs from Lichuan, West Hubei[END_REF]. L. lichuanense is characterized by its occluded umbilicus and a depressed crescent whorl profile, which makes it different from many species that possess an open umbilicus. This species differs from L. chenxianense (Liang 1984) by its depressed whorl profile, while the whorl profile of L. chenxianense is oval with the maximum whorl width at middle of the flanks.

Occurrence. Reefs of Lichuan (Hubei, South China), Dalong Formation (late Changhsingian) at Gujiao section (Guizhou). [START_REF] Zhao | Permian Cephalopods from Tanjiashan, Hunan[END_REF] Figures 13C, 14A-C 1954 Liroceras orientale Zhao,p.13,pl. 5,figs. 1,2. Holotype. Specimen 7133 illustrated by Zhao (1954, pl. 5, fig. 1, 2).

Liroceras orientale

Diagnosis. Liroceras with subinvolute, globular, smooth conch with depressed kidney-shaped whorl whorl profile; arched venter and flanks without ventrolateral shoulders; umbilical shoulders narrowly rounded. Umbilicus deep and broad with a vertical umbilical wall. Suture line almost straight.

Material. Two large internal moulds (YFMCUG 00294 and YFMCUG 00298) and three well-preserved small individuals (YFMCUG 00295-YFMCUG 00297) from the Gujiao section GJ-7 are available.

Description. Specimen YFMCUG 00294 is the largest one available with 84 mm in maximum diameter. It displays a globular and subinvolute conch (uw/dm = 0.93; uw/dm = 0.19 at maximum diameter) associated with a moderately depressed kidney-shaped whorl profile (ww/wh = 1.81 at maximum diameter). The venter is broadly rounded without ventrolateral shoulders. The flanks are also broadly arched. The umbilical shoulder is narrowly rounded in juvenile whorls and becomes more broadly rounded during ontogeny. One small phragmocone (specimen YFMCUG 00296) with preserved shell on the umbilical wall of the outer whorl, shows a small and deep umbilicus with a vertical umbilical wall. The suture line is almost straight with a broad and inconspicuous ventral lobe.

Remarks. Liroceras orientale is similar to the Kungurian L. sinense [START_REF] Zhao | Permian Cephalopods from Tanjiashan, Hunan[END_REF] with its depressed crescent-shaped whorl profile, but L. orientale has a higher expansion rate with a deeper and larger umbilicus. The umbilical shoulder of L. hunanense [START_REF] Zhao | Permian Cephalopods from Tanjiashan, Hunan[END_REF]) is more rounded. L. orientale differs from L. lichuanense by the deeper and larger umbilicus.

Occurrence. Kungurian at Tanjiashan (Hunan, South China); Dalong Formation (late Changhsingian) at Gujiao section (Guizhou).

Family Trigonoceratidae Hyatt, 1884 Genus Aulagonoceras [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] Type species. Aulagonoceras plicatum [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] Zhongying section (Guizhou); Dalong Formation (Changhsingian).

Diagnosis. Trigonoceratidae with almost subevolute conch and compressed subtrapezoidal or reniform whorl profile. Concave venter with one or more ventral grooves. Flanks variously convex.

Ventrolateral and umbilical shoulders subangular to angular with sharp margins. Sculpture with four or more rows of ridges located on the venter, ventrolateral shoulders and flanks. Suture line with narrow ventral lobes in ventral grooves, rather broad lateral lobes. Growth lines well visible and forming a in the broad and deep U-shape sinus on the venter.

Remarks. Aulagonoceras is only known from Changhsingian sediments of South China and includes three species: A. plicatum, A. spirale and A. bispirale [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF]. This genus is characterized by a reniform whorl profile, coarse growth lines and four or more ridges located on the venter, ventrolateral shoulders and flanks. Aphelaeceras, from the same family and only found in Changhsingian strata of West Guizhou [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF], is close to Aulagonoceras. However, it has a much more compressed conch with fewer ridges; it also exhibits a deeper ventral groove. [START_REF] Wu | Study of Nautiloids in the upper Permian Changxingian Reefs from Lichuan, West Hubei[END_REF] described Aulagonoceras jiantianbaense from a Changhsingian reef at Lichuan. However, according to the definition of Aulagonoceras, A. jiantianbaense should be excluded from this genus, because it has a compressed and oval whorl profile with rounded ventrolateral shoulders, ribs and a ventral strigation, all these features differing from Aulagonoceras.

Aulagonoceras plicatum [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF]Figure 15A-C v. 1984 Aulagonoceras plicatum Zheng, p. 249, pl. 4, figs. 7-9, 16-22, 28, text-figs. 12d, 13a. Holotype. Specimen NIGPAS 34393 illustrated by Zheng (1984, pl. 4, figs. 4-6).

Type locality and horizon. Zhongying section in Qinglong, Guizhou; Dalong Formation (Changhsingian).

Diagnosis. Aulagonoceras with subevolute conch and compressed subtrapezoidal whorl profile.

Concave venter incised with three grooves, of which the central one is deepest; flanks convex.

Ventrolateral and umbilical shoulders subangular to angular. Sculpture with four rows of ridges located on venter. Suture line with narrow ventral lobes in ventral grooves, rather broad lateral lobes.

Material. This species is rare in the sampled fauna; only two specimens (YFMCUG 00299 and YFMCUG 00300) were excavated.

Description. Specimen YFMCUG 00299 shows a subevolute conch (uw/dm = 0.32 at wh = 9.5 mm) and a weakly depressed, subtrapezoidal whorl profile. The ww/wh ratio shows a large intraspecific variation, ranging from 0.32 to 0.74. The venter is concave with three grooves, of which the central one is the deepest; the grooves are separated by four ridges on the venter and the subangular ventrolateral shoulders. The flanks are slightly convex and converge towards the venter with the maximum whorl width at the umbilical shoulders. The flank is slightly concave between the ventrolateral margin and flank ridge. Umbilical shoulder is broadly subangular and bears carinas.

The growth lines bent forward on the flanks, turn backward rapidly from the flank ridges and bend forward to form projections on the venter between two ventrolateral keels. The suture line shows a narrow shallow ventral lobe, saddles on the ventrolateral keel, broad lateral lobes.

Remarks. The number of ridges on the conch is the essential difference among the species of Aulagonoceras. A. plicatum [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] is characterized by four ridges on the venter and the ventrolateral shoulders and has marked growth lines, while A. spirale [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] has eight ridges on the venter and the flank without obvious growth lines. A. bispirale [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] bears two ridges on the flank and has a total of ten ridges on conch.

Occurrence. Dalong Formation, Zhongying section [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] and Gujiao section (Guizhou); late Changhsingian.

Family Grypoceratidae Hyatt, 1900 Genus Pseudotitanoceras [START_REF] Shimansky | Podotryad Nautiloidea[END_REF] Type species. Pseudotitanoceras armeniacum [START_REF] Shimansky | Podotryad Nautiloidea[END_REF]; Azerbaijan; 'Dzhulfian Stage' (Wuchiapingian).

Diagnosis. Grypoceratidae with smooth, moderately subevolute conch and subtrapezoidal whorl profile. Venter flattened to concave; flanks slightly convex and converging towards the rounded ventrolateral shoulders with the maximum width at the rounded umbilical margin. Small and deep umbilicus with almost vertical wall. Sculpture with double row of elongated and low nodes on ventrolateral shoulders.

Remarks. [START_REF] Shimansky | Podotryad Nautiloidea[END_REF] erected Pseudotitanoceras based on Nautilus armeniacus [START_REF] Abich | Geologische Forschungen in den Kaukasischen Ländern. Theil 1. Eine Bergkalkfauna aus der Araxesenge bei Djoulfa in Armenien[END_REF] as its type species. Following the work of [START_REF] Shimansky | Podotryad Nautiloidea[END_REF], [START_REF] Teichert | Nautiloid cephalopods from the Julfa Beds, Upper Permian, Northwest Iran[END_REF] reported Pseudotitanoceras armeniacum from the Julfa Formation of Iran. Pseudotitanoceras was also documented in the Akhura Formation of Azerbaijan and Armenia [START_REF] Kotlyar | Posdnepermskiy etap evolyutsii organicheskogo mira. Dzhulficheskiy i dorashamskiy yarusy SSSR[END_REF]) and the Hambast Formation of Central Iran [START_REF] Taraz | Uppermost Permian and Permian-Triassic Transition beds in Central Iran[END_REF]) and the Dalong Formation of Guizhou [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF].

Pseudotitanoceras sp.

Figure 15D

Description. The single small sampled specimen (YFMCUG 00301) is subinvolute (uw/dm = 0.27 at 28 mm diameter) with a nearly quadrate, subtrapezoidal whorl profile (ww/wh = 0.96). The ventral area is smooth and almost flat. The ventrolateral shoulder is subangular to angular and bearing a row of elongate nodes. The flanks are flattened and convergent to the ventrolateral shoulders with the maximum width at the umbilical margins. The umbilical wall is flattened. The suture line is not visible on the specimen.

Remarks. The tabulate venter and the elongate ventrolateral nodes are typical features of

Pseudotitanoceras. This specimen differs from P. armeniacum by distinct ventrolateral shoulders. It is much similar to Pseudotitanoceras sp. from the Changhsingian of Liuzhi and Qinglong [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF], with its subtrapezoidal whorl profile and small elongate nodes on the angular ventrolateral shoulders. With only one small specimen, we prefer to leave it in open nomenclature. [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] from Gujiao (Guizhou). A, YFMCUG 00215. B, YFMCUG 00216. C-G, Pleuronautilus sp. from Gujiao (Guizhou). C, YFMCUG 00218. E, YFMCUG 00219. D, suture line of YFMCUG 00219, at wh = 20.6 mm. G, YFMCUG 00220. F, suture line of YFMCUG 00220, at wh = 10.9 mm. Scale bars = 10 mm. [START_REF] Wu | Study of Nautiloids in the upper Permian Changxingian Reefs from Lichuan, West Hubei[END_REF] from Gujiao (Guizhou). A, YFMCUG 00292. B, YFMCUG 00293. C, Liroceras orientale [START_REF] Zhao | Permian Cephalopods from Tanjiashan, Hunan[END_REF] from Gujiao (Guizhou), YFMCUG 00294.

CONCLUSIONS

FIG. 7. A-B, Pleuronautilus zhongyingensis

Scale bars = 10 mm. [START_REF] Zhao | Permian Cephalopods from Tanjiashan, Hunan[END_REF] from Gujiao (Guizhou). A, YFMCUG 00295. B, YFMCUG 00296. C, YFMCUG 00297. Scale bars = 10 mm. [START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF] from Gujiao (Guizhou). A, YFMCUG 00300. B, YFMCUG 00299.C, suture line of YFMCUG 00299, at wh = 13.3 mm. D, Pseudotitanoceras sp. from Gujiao (Guizhou), YFMCUG 00301. Scale bars = 10 mm.

FIG. 14. Liroceras orientale

FIG. 15. A-C, Aulagonoceras plicatum

Further

  Type species. Nautilus quadrangulus McChesney, 1860; Pennsylvanian at Grayville, White County (Illinois, United States).

Diagnosis.

  Figures 4D-G, 5A-C

  Figure5D-E

  , and Utah (McGowan et al. 2009). Middle and Late Triassic material of Pleuronautilus was rarely documented. Except for undefined species from the late Norian of Nevada (Laws 1982), Vörös (2001) described one Anisian species from Hungary and Jurkovšek et al. (2002) described the Ladinian Pleuronautilus gaudryi from Slovenia.

Figure

  Figure8A-D

Diagnosis.

  Figures 8E-F, 9A-C, 10A-G

  et al. (2007) provided a detailed embryological discussion based on a hatched specimen of Sholakoceras pleuronautiloides from the Sosio Limestone of Sicily (Italy) and they transferred the Wordian Trematodiscus pleuronautiloides (Gemmellaro 1890) to Sholakoceras. Sholakoceras was until now, reported only from Early and Middle Permian strata; this is the first time that Sholakoceras is documented from Changhsingian beds. Sholakoceras sp.

A

  FIGURE CAPTIONSFIG. 1. A, Changhsingian palaeogeographic reconstruction, modified from Scotese (2001). The star indicates the Gujiao locality. B. Changhsingian palaeogeographic map of South China showing location of the studied site, modified from Feng et al. (1997) and Lehrmann et al. (1998). NPJB, Nanpanjiang Basin. C. Field view of the Gujiao section. D. Simplified lithology of the Changxing and Dalong formations at the Gujiao section.

FIG. 3 .

 3 FIG. 3. Palaeo-positions of known Changhsingian nautiloid occurrences worldwide; palaeogeographic map modified from Scotese (2014). PK, Pakistan; SA, Saudi Arabia; TH, Thailand; TI, Transcaucasia-Iran basin (including Armenia, Azerbaijan, Iran); IT, Italy; SC, South China; RU, Psebay (Russia); TJ, Tajikistan.

FIG. 8 .

 8 FIG. 8.A-D, Nodopleuroceras gujiaoense sp. nov. from Gujiao (Guizhou). A, YFMCUG 00225 (holotype). B, YFMCUG 00226 (paratype). D, YFMCUG 00227 (paratype). C, suture line of YFMCUG 00227, at wh = 23.2 mm. E-F, Gujiaonautilus longliensis gen. nov., sp. nov. from Gujiao (Guizhou). E, YFMCUG 00242. F, YFMCUG 00243. Scale bars = 10 mm.

  This nautiloid assemblage consists of nine species and five taxa in open nomenclature in nine genera: Tainoceras guizhouense Zheng, 1984, Tainoceras sp., Neotainoceras zhaoi sp. nov., Neotainoceras sp. A, Neotainoceras sp. B, Pleuronautilus

zhongyingensis

[START_REF] Zheng | Late Permian Nautiloids from Western Guizhou[END_REF]

, Pleuronautilus sp., Nodopleuroceras gujiaoense sp. nov., Gujiaonautilus longliensis gen. nov., sp. nov., Sholakoceras sp., Liroceras lichuanense Wu, 1992, Liroceras orientale Zhao, 1954, Aulagonoceras plicatum Zheng, 1984 and Pseudotitanoceras sp.

ACKNOWLEDGMENTS

We are indebted to We greatly acknowledge an anonymous reviewer and Jerzy Dzik (Warsaw) for their valuable comments on an earlier version of the manuscript and Sally Thomas (London) as well as Michael Hautmann (Zurich) for their suggestions.. We acknowledge Yi Wang for his help in the field. Jia Yan, Zhipu Qiu, Mingtao Li, Fengyu Wang and Enhao Jia is thanked for her support with photographic work and interior work. This work benefited from the help of Cheng Ji and Qiulai Wang (Nanjing) to access comparable specimens. This study is supported by the National Natural Science Foundation of China (grant no. 41622207, 41672016). Dieter Korn acknowledges the support by the German Research Foundation (DFG projects Ko1829/12-1, Ko1829/17-1) and the National Natural Science Foundation of China (grant no. 41630101). Arnaud Brayard acknowledges the support by the ANR project AFTER (ANR-13-JS06-0001-01) and the French "Investissements d'Avenir" program, project ISITE-BFC (ANR-15-IDEX-03). The project was supported by the Fundamental Research Founds for National University, China University of Geosciences (Wuhan).

DATA ARCHIVING STATEMENT

This published work and the nomenclatural acts it contains, have been registered in ZooBank: http://zoobank.org/References/E74B2E81-6DCF-4199-98C8-B51EF6A5173F


Dr Loïc Habert

Dr Kevin Cariou
email: kevin.cariou@cnrs.fr

Kilian Muñiz

Photoinduced Aerobic Iodoarene-Catalyzed Spirocyclization of N-Oxy-Amides to N-Fused Spirolactams

Keywords: hypervalent iodine, pyrylium, aerobic photoredox reaction, dual organocatalysis

Iodoarene catalysis is a powerful methodology that usually requires an excess of oxidant, or of redox mediator if the terminal oxidant is dioxygen, to generate the key hypervalent iodine intermediate to proceed efficiently. We report that, using the spirocyclization of amides as a benchmark reaction, aerobic iodoarene catalysis can be enabled by relying on a pyrylium photocatalyst under blue light irradiation. This unprecedented dual organocatalytic system allows the use of low catalytic loading of both catalysts under very mild operating conditions.

Hypervalent iodine(III) compounds have been known for 130 years, [1] yet interest in their reactivity was very modest until the 80's, before witnessing a dramatic surge in the 2000's. [2][3][4] They possess many advantages in terms of versatility, high selectivity and lack of toxicity; however, their use as a stoichiometric reagent remains a drawback. Indeed, the driving force behind their reactivity is the final release of one equivalent of iodoarene (Scheme 1a), such as iodobenzene. The liberation of a stoichiometric amount of organic waste is in total contradiction with the need for greener and more responsible processes. In order to circumvent these hurdles, the more general and sought after strategy is based on the in situ re-oxidation of the iodoarene into a reactive iodine(III) species. This approach, pioneered by Ochiai & Miyamoto [5] and by Kita [6] in 2005, de facto establishes iodoarenes as a particular subclass of organocatalysts, [7][8][9] with many synthetic applications, including asymmetric versions. [10,11] Scheme 1. Stoichiometric iodoarene oxidative transformation (a), iodoarene catalysis (b) and aerobic iodoarene catalysis (c).

Apart from anodic oxidation, which, more than 20 years after the pioneering studies by Fujita, [12] currently receives increasing attention, [13][14][15][16][17][18][19] iodoarene catalysis requires the use of a stoichiometric oxidant, [8] thus generating an equimolar quantity of inorganic or organic waste (Scheme 1b). A more desirable alternative is the use of molecular oxygen as a widely available and cheap stoichiometric oxidant that would only generate aqueous waste (Scheme 1c). Since the single electron oxidation potential of iodobenzene is much higher (half peak potential: Ep/2 = 2.17 V vs SCE) [20] than the reduction potential of oxygen (-0.33 V vs SHE, for single electron reduction at pH = 7 ), [21] resorting to an electron-transfer mediator [22] (ETM) is mandatory. This strategy was eventually implemented in 2017 by Miyamoto & Uchiyama [23] and Powers [24] who independently reported the first examples of aerobic oxidation of iodoarenes. Both approaches are based on the formation of a suitable oxidant during the O2mediated autoxidation of aldehydes, [25][26][27] although the protocols slightly differ. The Miyamoto-Uchiyama protocol requires a sterically hindered aldehyde and was applied to the glycol scission of 1,2-diols and the Hofmann rearrangement of primary amides with only 3 to 5 equivalents of iso-butyraldehyde and 5 to 20 mol% of pentamethyliodobenzene. [23] Powers' method, which was further refined for the formation of iodine(V) reagents, [28] uses 10 equivalents of acetaldehyde and 1 mol% of CoCl2 as the initiator to promote the synthesis of (diacetoxy)iodoarenes from the corresponding aryl iodides in acetic acid. This system was named "oxidase catalysis" by the authors. [29] Five distinct examples of catalytic applications were presented, necessitating between 10 to 20 mol% of diiodobenzene and one equivalent of iodobenzene to work efficiently. Despite the spectacular improvement that these aerobic strategies bring to iodoarene catalysis, yet they still require a rather large excess of aldehyde and, in some cases, even a stoichiometric amount of the iodobenzene catalyst. With the goal of developing an aerobic system that would only require a substoichiometric amount of the O2-mediator we sought to employ a visible-light photoredox catalyst to reoxidize the iodoarene into an iodine(III) derivative. Since the 2011 study by Lalevée on the use of a ruthenium photocatalyst with a diphenyliodonium to form phenyl radicals, [30] the interplay between visible-light photoredox catalysis and hypervalent iodine(III) derivatives has been increasingly studied. [31] However, all these studies rely on the reduction of iodine(III) reagents to give an aryliodide by-product while there is no report of a photoredox oxidation of an iodoarene into an iodine(III) derivative. The oxidation potential of aryliodides quite high, [20] it precludes the use of most Ru-and Ir-based complexes [32] in favor of organic dyes [33][34][35] such as acridinium (Fukuzumi's catalyst Acr + ) or pyrylium (pyry + ) salts. To explore this dual (iodoarene/photocatalyst) catalytic system, the spirocyclization of amides into N-fused spirolactams was chosen as a benchmark reaction. After their initial work on the generation of nitrenium ions from chloramides, [36] this transformation was then developed by Kikugawa in 2003 using a stoichiometric amount bis(trifluoroacetoxy)iodo]benzene (PIFA) in trifluoroethanol (TFE) (Scheme 2a). [37] This reaction was later reported using anodically generated iodine(III) by Nishiyama. [38] In 2007, Kita described a catalytic version, using 10 mol% of iodotoluene in the presence of 1.5 equivalents of m-CPBA (Scheme 2b) [39] while Togo used Oxone. [40] Kita later refined this method using 2 mol% of a diiodobiaryl with 2 equivalents of peracetic acid. [41] Finally, this reaction was one of the examples that Powers [24] implemented in an aerobic fashion with 20 mol% of diiiodobenzene and 10 equivalents of acetaldehyde (Scheme 2c). For our part, we set to establish the feasibility of this transformation under aerobic conditions with an iodoarene catalyst, which would be oxidized using an organic photocatalyst (phot + ) under irradiation (Scheme 2d). The reaction was first studied with N-Methoxy amide 1a as the starting material using a high catalyst loading of iodobenzene (50 mol%) in the presence of 2.5 mol% of 2,4,6-triphenylpyrylium tetrafluoroborate (TPT, E1/2 P*/P• = 2.30 V vs. SCE) [42] as the photocatalyst, under one atmosphere of dioxygen and irradiation at 455 nm (Table 1). The influence of the solvent was dramatic as no reaction was observed in dichloroethane (DCE) or acetonitrile, while trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) enabled the formation of the desired spiro-adduct in 10% and 18%, respectively. Doubling or tripling the reaction time allowed to double the yield to 37%. As the TPT catalyst is known for its poor photo-stability, we used the more robust and more oxidizing mesityl-2,6-diphenylpyrylium tetrafluoroborate (MDPT, E1/2 P*/P• = 2.62 V vs. SCE) recently developed by Beeler. [43] This led to a slight improvement of the yield to 43%. On the contrary, the use of 9-mesityl-10-phenylacridinium tetrafluoroborate (Ph-Acr, E1/2 P*/P• = 2.20 V vs. SCE) [44] did not permit the reaction to proceed. Table 1. Optimization of the reaction conditions [a] Iodoarene (mol%) Photocatalyst (mol%) Solvent Time (h) Yield 2 (%) [b] PhI (50) TPT (2.5) DCE 24 N. R. [c] PhI ( 50 To favor the oxidation of the iodoarene, derivatives bearing a substituent in ortho were then assayed. Using 20 mol% of iodobenzoic acid (IBA), which could lead to a transient benziodoxole intermediate, [45][46][47] spiro adduct 2a could be isolated with a 58% yield. 1,2-Diiodobenzene, that can form µ-oxo intermediates, [48] was less effective and a 46% yield was obtained. Finally, Kita's bis iodoarene catalyst [41] was employed (DCE was added to HFIP to increase its solubility) and a 55% yield could be obtained with a catalyst loading of only 2.5 mol%. Being almost as efficient as with 20 mol% of IBA, these conditions were selected as optimal since only mol% of the iodoarene catalyst and 5 mol% of the photocatalyst are needed to promote the spirocyclization.

When the N-methoxy group was changed for an ethoxy, or a benzyloxy group the corresponding spiro-adducts 2b and 2c were obtained with 59% and 63% yield, respectively (Scheme 3a).While electron-rich groups were not suitable for the reaction (vide infra), electron-poor benzyloxy groups such as pentafluorobenzyl and para-nitrobenzyl groups were compatible and yielded 2d (39%) and 2e (51%). The spirocyclization also proceeded smoothly with various N-acyloxy amides, whether an acetate (2f, 61%), a pivalate (2g, 52%), a phenyl acetate (2h, 53%), a benzoate (2i, 46%) or a meta-nitrobenzoate (2j, 47%). More diversely substituted N-alkoxy derivatives also underwent the spirocyclization, including the propargyl and allyl derivatives (2k, 46% and 2l, 50%) and the chloropentanyl compound (2m, 45%

). Yet for several substrates the reaction only led to a complex mixture, although it could not be determined if it was due to a decomposition of the starting material, the final product or both (Scheme 3b). These included N-oxy derivatives with an electronrich group (1n), a hydroxyl functionality (1o), a silyl group (1p) or a tertiary ether (1q). In contrast with what was observed by Kita, Scheme 3. Scope and limitations of the spirocyclization of amides to N-fused spirolactams under photoinduced aerobic iodoarene catalysis.

substrates 1r and 1s, which would have furnished the 4membered and 6-membered spiro derivatives, respectively, only led to decomposition. Other types of substituent that could help stabilize a putative radical intermediate on the nitrogen such as a phthalimidate (1t), [39,41] a tosyl (1u) or a phenyl (1v) were also ineffective, and so was an alkyl group (1w) or an unprotected amide (1x). Control experiments (Scheme 4) showed that the reaction did no proceed in the absence of either catalyst, oxygen or light, nor in the presence of 20 mol% of a radical quench such as BHT and TEMPO. When air was used instead of pure dioxygen, the reaction only yielded 12% of 2a. Finally, acetic acid was used as a highly polar and protic solvent but no reaction took place. These observations led us to propose a plausible mechanism based on a dual organocatalytic system (Scheme 5). Photoexcitation of the pyrylium Pyry + would generate the highly oxidizing Pyry + * (E*red vs SCE= 2.62 V) [43] that could promote the oxidation of iodoarene A into iodoaryl radical cation B and form Pyry • . Oxidation of the latter into Pyry + by the dioxygen would close the photoredox catalytic cycle and generate the superoxide ion. [49] Iodoaryl radical cation B has been proposed as an intermediate in the anodic generation of iodine(III) reagents [19] and could serve as a precursor to iodanyl radical C, [27] upon reaction with the solvent. After combination with the superoxide and protonation peroxy-iodinane D could be formed. Eventually, full solvolysis could occur leading to iodinane E. [13,14] This spirocyclization has been proposed to occur through the initial formation of a nitrenium ion [39] but a N-centered radical, stabilized by the alkoxy group, [50] could also be operative. This means that all three species C, D and E could promote the transformation of 1 into 2, by triggering the formation of a reactive nitrogen intermediate. In all cases, this would regenerate the starting iodoarene, thus closing the second catalytic cycle. Control experiments demonstrate that several factors are essential for this dual catalytic system to be operative. As evidenced by the absence of reactivity in non-fluorinated solvent, including the highly polar and protic AcOH, HFIP solvent is essential, a feature that has already been noted for electrochemical generation of iodine(III) species, [17][18][19] presumably via multiple roles. First, its superior solvatation properties for charged species [51] such as arene radical cations generated in photoredox process, [52] would favor the formation of B and C. Moreover, when apically bound to the iodine in λ 3 -iodanes D or E, its strong electron-withdrawing character would enhance the stabilization of the 3-center 4electron hypervalent bond. [53] Scheme 5. Mechanistic proposal: (a) dual catalytic cycles and (b) structure of the solvolyzed ArI(III) species.

The stability of the can also be further enhanced by The substituents on the aryl group of A, can play a crucial role in the stabilization of the hypervalent iodine(III) reagents generated.

From IBA, the formation of a cyclic benziodoxole would occur for both the peroxy-λ 3 -iodane D [54] and HFIP-derived E (Scheme 5b). For Kita's bis iodoarene catalyst, [41] the stabilization would come from the formation of µ-oxo species, here depicted for the fully solvolyzed adduct E.

Using the spiro-cyclization of amides as a model reaction, we have thus demonstrated that aerobic iodoarene catalysis can be enabled by relying on a pyrylium photocatalyst under blue light irradiation. This unprecedented dual organocatalytic system allows the use of low catalytic loading of both catalyst under very mild operating conditions. We are currently pursuing more thorough study of this dual catalyst system to gain a deeper understanding of the reaction pathway by experimental and theoretical methods, with a particular focus on determining the nature of the oxidized iodoarene species. This will allow to expand the range of transformations that can be accomplished using this strategy, including the development of asymmetric reactions.

Scheme 2 .

 2 Scheme 2. Spirocyclization of amides to N-fused spirolactams using a stoichiometric iodine(III) reagent (a), iodoarene catalysis (b), aerobic iodoarene catalysis (c) and dual aerobic photo-and iodoarene catalysis (d, this work).

Scheme 4 .

 4 Scheme 4. Control experiments.

Acknowledgements K.C. thank Prof. S. Quideau (Université de Bordeaux), Dr L. Grimaud (ENS, Paris), Dr I. Ciofini (Chimie ParisTech), Dr N. Hoffmann (Université de Reims) and Pr G. Gasser (Chimie ParisTech) for insightful dicussions. The authors also thank CNRS, ICSN and Chimie ParisTech, for financial support. This work was supported by a grant from the CNRS (Emergence@INC 2019 program).

Conflict of interest

The authors declare no conflict of interest.

Entry for the Table of Contents

Lighting up iodoarene catalysis: Using the spiro-cyclization of amides as a benchmark reaction, the feasibility of photocatalytic aerobic iodoarene catalysis was demonstrated by relying on a pyrylium photocatalyst under blue light irradiation. This unprecedented dual organocatalytic system allows the use of low catalytic loading of both catalysts under very mild operating conditions.

Institute and researcher Twitter usernames: Dr Kevin Cariou: @CariouK; Chimie ParisTech | PSL: @ChimieParisTech; ICSN: @ICSN_lab.