Early Jurassic Belemnites from the Gondwana Margin of the Southern Hemisphere —Sinemurian Record from South Tibet

Gondwana Research 28 (2015) 882–887

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Early Jurassic belemnites from the Gondwana margin of the Southern Hemisphere —Sinemurian record from South Tibet

Yasuhiro Iba a,⁎, Shin-ichi Sano b, Xin Rao c, Dirk Fuchs a,TingenChenc, Robert Weis d, Jingeng Sha c a Department of Natural History Sciences, Hokkaido University, N10W8, Kitaku, Sapporo, Hokkaido 060-0810, Japan b Fukui Prefectural Dinosaur Museum, Fukui 911-8601, Japan c State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China d Musée National D'Histoire Naturelle, 25 Rue Münster, 2169 Luxembourg, Luxembourg article info abstract

Article history: Belemnites (Order Belemnitida), a very successful group of Mesozoic coleoid cephalopods, dominated fossil Received 11 February 2014 coleoid assemblages throughout the Jurassic and Cretaceous. According to the current view, the phylogenetically Received in revised form 10 June 2014 earliest known belemnites have been reported from the lowermost Jurassic (Hettangian) of northern Europe. The Accepted 13 June 2014 earliest belemnites are characterized by low diversity and small-sized rostra. Their distribution has until recently Available online 11 July 2014 been assumed to be restricted to northern Europe until the Pliensbachian. Early belemnites (the Sinobelemnitidae – Handling Editor: I.D. Somerville and the Belemnitina) are now also known from the Late Triassic of China and the Hettangian Sinemurian of Japan, and therefore from the eastern Tethys and western Paleo-Pacific oceans. It has been suggested that the distribu- Keywords: tion of belemnites became more widespread and expanded to the Southern Hemisphere for the first time in the Belemnites Toarcian. Here we re-describe a Sinemurian belemnite from South Tibet, which was located at the Gondwana Sinemurian margin at that time. The specimen is characterized by a long rostrum with one deep and long alveolar Tibet groove with a splitting surface, whose position cannot be determined as being either dorsal or ventral. Gondwana This morphological feature allows an assignment of the re-described rostrum to either the Sinobelemnitidae Southern Hemisphere or the Pachybelemnopseina. The Sinemurian belemnite from Tibet represents the earliest firm record of the Paleobiogeography Belemnitida from the Southern Hemisphere, suggesting that the wide distribution and diversification of this order was established much earlier than previously thought. © 2014 Published by Elsevier B.V. on behalf of International Association for Gondwana Research.

1. Introduction 2006). In order to solve this enigma, the swimming ability of early belemnites, which certainly controls their biogeographic patterns, has been Belemnites (Order Belemnitida) are an extinct group of coleoid discussed recently (e.g., Weis et al., 2012). cephalopods, which had signiﬁcant biomass and occur abundantly and Hettangian records from Japan recently reported by Iba et al. (2012) worldwide in the Late Mesozoic. Belemnites therefore likely played an shed new light on the neglected existence of early Jurassic belemnites important role in Jurassic–Cretaceous marine environments as both pred- outside Europe (Yokoyama, 1904). The observations by Iba et al. (2012) ators and prey (e.g., Doyle and Macdonald, 1993; Rexfort and Mutterlose, moreover re-opened the discussion on the presence of Late Triassic 2006). The understanding of the rise, radiation and fall of belemnites is (Carnian) belemnites in South China (Zhu and Bian, 1984). Considering therefore crucial for unraveling the evolution of the Mesozoic marine these East Asian belemnites were attributed to the Sinobelemnitidae. ecosystems. Distribution and diversity patterns of belemnites in Middle Iba et al. (2012) argued that the earliest belemnites originated in the Jurassic to Cretaceous times have been well recognized (e.g., Doyle, 1987; eastern Tethys and western Paleo-Paciﬁc rather than in Europe. Conse- Mutterlose, 1998; Christensen, 2002; Košt'ák, 2004; Iba et al., 2011). Their quently, the early evolutionary history of the Belemnitida now needs a evolutionary history in the Early Jurassic is, however, not fully understood complete revision that requests a new focus on records outside of (e.g., Doyle, 1994; Doyle et al., 1997; Sanders et al., in press). Previously, it Europe. was thought that belemnites originated during the earliest Jurassic In the light of this, it is necessary to reassess observations made (Hettangian) and their distribution was restricted to Europe until the by Chen (1982), who described belemnites from the Sinemurian Pliensbachian. The causes for this paleogeographically limited distribution (Early Jurassic) to Cretaceous of South Tibet. Chen (1982) reported on remains open (Doyle, 1993, 1994; Doyle et al., 1994; Weis and Delsate, the occurrence of three Sinemurian belemnite taxa, Salpingoteuthis sp., Belemnopsis sp. and Passaloteuthinae gen. et sp. indet. Doyle et al. (1997) reviewed all published records of Early Jurassic belemnites in ⁎ Corresponding author at: Department of Natural History Sciences, Hokkaido University, N10W8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan. Tel.: +81 11 706 3538. the world, and concluded that true belemnites did not expand into E-mail address: [email protected] (Y. Iba). the Southern Hemisphere in pre-Toarcian time. Doyle et al. (1997)

http://dx.doi.org/10.1016/j.gr.2014.06.007 1342-937X/© 2014 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. Y. Iba et al. / Gondwana Research 28 (2015) 882–887 883 rejected therefore the affinity of the Tibetan material to the 3. Geological setting Belemnitida and included the material under discussion in the Order Aulacocerida, another coleoid group that was common in the Salpingoteuthis sp. of Chen (1982) co-occurred with ammonites Triassic but declined in the Early Jurassic. To overcome these incon- Euagassiceras sp. and Gleviceras sp. in the Ridang Formation in sistencies in taxonomy and to find new evidence for Early Jurassic Guomachong, Ridang, Lhunze County, South Tibet (Fig. 1)(Chen, non-European belemnites, we re-studied the “Salpingoteuthis” specimen 1982). Both Eugassiceras and Gleviceras indicate the Sinemurian age, of Chen (1982) from the Sinemurian of South Tibet. The rostrum repre- and show wide distribution: Eugassiceras occurs from Europe, Mexico, sents the earliest belemnite record in the Southern Hemisphere at that Argentina, Ecuador, Colombia, and Gleviceras from Europe, Morocco, time. Its paleobiogeographical and evolutionary significance is discussed Canada, Alaska, Mexico, and Peru (Howarth, 2013). Wang and He in the present study. (1981) also reported these two Sinemurian ammonites from the same formation and area. The co-occurrence of ammonites suggests that the belemnite specimen described here can be assigned to the Sinemurian. 2. Material The area where the specimen has been found is located in the south of the Yarlung Zangbo Suture Zone, and thus belongs to the northern The material of Chen (1982), which is stored in the collection of the Himalaya region (Fig. 1). Since the Yarlung Zangbo Suture Zone repre- Nanjing Institute of Geology and Palaeontology (NIGP), has been stud- sents the collisional tectonic boundary between the Eurasian Plate and ied. The single specimen described and figured as Salpingoteuthis sp. in the Indian Plate, the Northern Himalaya represents a part of northern Chen (1982) comes from Guomachong, Ridang, Lhunze County, South Indian Plate. This area was therefore located in the Southern Hemi- Tibet (Fig. 1) and consists of an incomplete belemnite rostrum (NIGP sphere, namely the Gondwana margin, in Jurassic times. no. 58844). Two other Sinemurian belemnites listed by Chen (1982), Belemnopsis sp. and Passaloteuthinae gen. et sp. indet., were not found 4. Systematic paleontology in the collections in Nanjing. Subclass Coleoidea Bather, 1888 Order Belemnitida Zittel, 1895 gen. et sp. indet.

4.1. Description

The medium-sized, slender conical rostrum exhibits both a symmet- rical outline and proﬁle (Fig. 2a–e). The apex and alveolar region are missing. Most of the rostrum is still covered with sediments (Fig. 2b). Its external shape, especially that in the apical region (Fig. 2a, and b6–8), does not represent its original morphology (Fig. 2a, b). The total length of the preserved rostrum is 66.3 mm. The maximum dorso-ventral diameter and lateral diameter, which is located at the anterior end is 7.3 mm and 7.8 mm, respectively (Fig. 2b1). The transverse section is dorso-ventrally depressed in the stem region (Fig. 2b1–5) and circular in the apical region (Fig. 2b6–8). The ratio of the dorso-ventral diameter/lateral diameter is ranges from 1.0 (Fig. 2b8) to 1.2 (Fig. 2b1). A single alveolar groove is visible on the external surface of the rostrum, which was shown in Chen (1982, plate 20-16). Unfortunately, this part of the rostrum was cut longitu- dinally in subsequent scientiﬁcworksandhalfoftherostrumofthe alveolar part was lost. The transverse sections (Fig. 2b) suggest that the alveolar groove extends up to the apical part (Fig. 2a, b7), but it does not reach the apex (Fig. 2a, b8). The groove is deep and V-shaped in the anterior part, it cuts the growth lines, accompanied by a well- developed splitting surface (Fig. 2a, b1–3, f, g). Posteriorly, the groove becomes gradually shallower until it peters out in the apical region (Fig. 2b4–6). Unfortunately, it cannot be determined whether the alveolar groove is situated on the ventral or dorsal side, because the phragmocone is missing. Also, there is no evidence of either an apical groove or striae.

4.2. Comparison with selected belemnite genera of the Early–Middle Jurassic

The present specimen (NIGP no. 58844; Salpingoteuthis sp. of Chen (1982))isdeﬁnitely not congeneric with Salpingoteuthis (Doyle, 1992), because of the lack of diagnostic characters such as multiple, elongated ventral and dorsal grooves along the rostrum. It is even doubtful to include the specimen in the Suborder Belemnitina due to the presence of an alveolar groove and the absence of an apical groove. With respect to the existence of an alveolar groove, the Fig. 1. Map showing the locality of the Sinemurian belemnite in South Tibet. Geological map is modiﬁed from the Bureau of Geology and Mineral Resources of Xizang Autono- Family Sinobelemnitidae (suborder uncertain) and the Suborder mous Region (1993). Abbreviations: Ca: Cambrian, Tr: Triassic, Ju: Jurassic, Cr: Cretaceous, Pachybelemnopseina (=Belemnopseina) must be taken into consid- Eo: Eocene, Ce: Cenozoic. eration. The rostra of both taxa can be distinguished by the position 884 Y. Iba et al. / Gondwana Research 28 (2015) 882–887

Fig. 2. Belemnite with an alveolar groove (Belemnitida gen. et sp. indet.; NIGP no. 58844) from the Sinemurian of Guomacong, Ridang, Lhunze County, South Tibet.a,Groovesideview. White dotted lines indicate its original morphology without sediment matrix. b, Transverse sections of rostrum. Groove side to the top. c, Opposite side of groove. d, Lateral view. Groove to the right. e, Lateral view. Groove to the left. f, Macrophotograph of transverse section of b1, indicating concentric growth lines and deep and V-shaped groove. g, Longitudinal section of stem region. Abbreviations: sr: stem region, ar: apical region, ge: groove end, m: matrix, gr: groove, gl: growth line. ss: remains of organic layer of splitting surface. of the groove, which is dorsal in the Sinobelemnitidae and, with the considered as early members of the Pachybelemnopseina, whose earliest exception of the Duvaliidae, Dicoelitidae, Pseudodicoelitidae, ventral records were recognized in the Toarcian of Arctic Canada and South Tibet in the Pachybelemnopseina (Iba et al., 2012)(Table 1). Since it is (Jeletzky, 1980; Wu, 1982). Dicoeilites rostra have both a ventral and a difficult to determine whether the alveolar groove in our present dorsal alveolar groove (Stevens, 1964; Jeletzky, 1980). These morpholog- specimen is located dorsally or ventrally, the assignment to either the ical features are clearly different from those of our Sinemurian rostrum Sinobelemnitidae or the Pachybelemnopseina is difficult to assess. (Table 1). The Pseudodicoelitidae has a ventral and a dorsal alveolar The Sinobelemnitidae, which has a dorsal alveolar groove with a dis- groove and also an apical groove (Jeletzky, 1980). A dorsal alveolar tinct splitting surface, include only two genera, Sinobelemnites (Carnian) groove accompanies a splitting surface (Jeletzky, 1980). These mor- and Sichuanobelus (Carnian–Sinemurian) (Zhu and Bian, 1984; Iba et al., phological characters are absent in the Tibetan specimen (Table 1). 2012; Iba, in press). The rostrum of Sinobelemnites is characterized by Weis et al. (2012) considered the Holcobelidae (Early laterally compressed rostra with well-developed multiple lateral Aalenian to Early Bajocian) to be the earliest representative of the lines. Since these morphological characters are absent in our Tibetan Pachybelemnopseina. Calabribelus has an alveolar groove, which is specimen, it can be clearly differentiated from Sinobelemnites.The U-shaped in transverse section. In contrast, Holcobelus has an interme- Sichuanobelus rostrum is characterized as a laterally compressed ros- diate groove with a rudimentary developed splitting surface (Weis trum without lateral lines (Table 1). There is a minor difference between et al., 2012). These morphological characters of the Holcobelidae are rostrum shape of Sichuanobelus and Tibetan specimen (i.e., laterally not developed in the specimen from Tibet (Table 1). compressed or dorso-ventaly depressed rostrum) (Table 1). Other stratigraphically early genera of the Pachybelemnopseina The Duvaliidae, which occurs worldwide from Bathonian–Aptian such as Hibolithes and Pachybelemnopsis (Bajocian to Early Creta- has no splitting surface along its dorsal alveolar groove (Doyle and ceous for both genera) possess a ventral alveolar groove with well- Mariotti, 1991 and our own observations). The lack of splitting surface developed splitting surface (e.g., Weis et al., 2012). The former genus in the Duvaliidae shows large morphological differences with the Tibetan differs significantly from the Tibetan belemnite by the hastate shape specimen (Table 1). The dicoelitid belemnites, such as Dicoelites can be of the rostrum, and by its alveolar groove that is usually restricted to Y. Iba et al. / Gondwana Research 28 (2015) 882–887 885

the alveolar region. The rostrum of Pachybelemnopsis is similar to that of the Tibetan specimen in having a comparatively long alveolar groove, ; ; and by a generally dorso-ventrally depressed rostrum (Riegraf, 1980; Mariotti et al., 2007; Weis et al., 2012). The Tibetan specimen, however, shows minor differences, such as circular shape in transverse section in the apical region. Though the morphology of the specimen NIGP no. 58844 closely Present Subcircular in the alveolar region and depressed in the stem and apical region Mariotti et al. (2007) Weis et al. (2012) resembles that of Sichuanobelus (Sinobelemnitidae) or Pachybelemnopsis (Pachybelemnopseina), studied belemnite, cannot properly be assigned to either of these two families, because of the unknown position of the alveolar groove. The specimen is, therefore, tentatively determined as Belemnitida gen. et sp. indet. in this paper. A more reﬁned taxonomic assignment of the material from Tibet should be discussed in future studies based on additional material. Single (ventral)Rudimentaly developed Single (ventral) subcircular 5. Discussion and conclusions

5.1. Paleobiogeographical signiﬁcance Bajocian Early Bajocian Bajocian-Early Cretaceous – The current hypothesis about the distribution of early belemnites is brieﬂy summarized below. The earliest known belemnites are Intermediate groove (ventral) developed Weis et al. (2012) Weis et al. (2012) Riegraf (1980, 1999) sinobelemnitids, which were discovered in sediments of Late Triassic age (Carnian) in the Sichuan Province, South China (Zhu and Bian, 1984; Iba et al., 2012; Iba, in press). A possible Permian record also from South

Jeletzky China (Chen and Sun, 1982) still needs to be re-investigated. Apart from ; the South Tibetan record described here, Early Jurassic (Hettangian– Pliensbachian) belemnites have been described only from Europe and Japan (e.g., Doyle, 1994; Iba et al., 2012, 2014, in press). Both areas were located at the northern Tethys margin at that time. Small forms of (dorsal and ventral) Toarcian-Kimmeridgian Aalenian Stevens (1964) (1980) the Belemnitina occur in Europe. On the other hand, large endemic ; forms of the Belemnitina, and also sinobelemnitids were recovered from Japan (Fig. 3). Doyle et al. (1997) presumed that all belemnite records in the South- ern Hemisphere from pre-Toarcian Jurassic sediments are members of Single (dorsal) Two AbsentCompressed Absent Circular to compressed CompressedAptian Compressed to Absent Absent Absent Mariotti(1991) present study (splitting surface) the Aulacocerida. Following this, aulacocerids were common compo- nents of the coleoid faunas of the Southern Hemisphere at that time. Doyle et al. (1997) concluded that a global turnover from aulacocerids to belemnites occurred in the Toarcian. It has been considered that the distribution of belemnites became more widespread and expanded to the Southern Hemisphere for the first time in the Toarcian (e.g., Doyle et al., 1997). The oldest (Toarcian) specimens confirming this hypothe- (dorsal and ventral) (apical groove or striae) depressed Jeletzky (1980) Doyle and sis are 1) Brevibelus and “Cylindroteuthis” from Chile, New Caledonia and New Zealand, 2) Acrocoelites-related forms from Argentina and possibly Iba ; Antarctica, which show clear affinity to European taxa, and 3) Dicoelites Iba, in ; from South Tibet. Dicoelites specimens of Toarcian age are unknown from Europe, but present in Arctic Canada (Jeletzky, 1980). In the ; present paper, however, the occurrence of a Sinemurian belemnite fi Iba et al. (2012) et al. (2014) Zhu and Bian (1984) press from South Tibet has been con rmed. This region was located at the Gondwana margin at that time, and thus the Tibetan Sinemurian belemnite represents the earliest firm record of belemnites from the Southern fi

Iba, in Hemisphere. This nding suggests that the worldwide distribution of ; the Belemnitida was established much earlier than previously thought (Fig. 3). The paleobiogeography of early belemnites needs a complete Zhu and Bian (1984) press SinobelemnitidaeSinobelemnitesSingle Sichuanobelus (dorsal) Single (dorsal) Pseudodicoelites Two Pseudodicoelitidae DuvaliaCompressed Duvaliidae Compressed Dicoelitidae Dicoelites Compressed to Holcobelidae Holcobelus Calabribelusrevision Pachybelemnopsis Mesohibolithidae considering their worldwide distribution since the Sinemurian at the latest. It is therefore suggested that records of putative belemnite in the Early Jurassic and even Triassic times, especially from the Southern Hemisphere and eastern Tethys, need to be re-investigated in order to reassess the coleoid paleobiogeography and turnover in Triassic–Early Jurassic times. specimen (position unknown) stem region and circular in the apical region 5.2. Evolutionary signiﬁcance and importance of the Tibetan belemnite records

The Tibetan Sinemurian rostrum (NIGP no. 58844) is characterized by the presence of a single alveolar groove and the absence of apical References Present study Family Present Tibetan Genus Alveolar grooves Single Splitting surface PresentApical groovesLateral lines AbsentTransverse section Depressed in the Present AbsentGeological age Absent Present Sinemurian Present Absent Carnian Present in dorsal Absent groove Absent Carnian-Sinemurian Present Toarcian-Bajocian Present in ventral groove Present Bathonian- Rudimentaly Present Present Present Present Present (rare)

Table 1 Character states of belemnite rostrum of selected taxa. grooves. These morphological characters have never been observed in 886 Y. Iba et al. / Gondwana Research 28 (2015) 882–887

Fig. 3. Wide distribution of belemnites in the early phase of their evolution. Paleomap (200 Ma) based on Blakey (2010).

Early Jurassic belemnites (the Belemnitina) from Europe. Two belem- in Zhada County, South Tibet, has been confirmed by our own obser- nite groups, the Sinobelemnitidae and the Pachybelemnopseina have vations. These Calabribelus specimens had been described by Chen developed an alveolar groove similar to the Tibetan specimen, either (1982) as Hastites sp. (NIGP no. 58837) and Holcobelus cf. blainvillei dorsally or ventrally. As already discussed above, the systematic assign- (NIGP no. 58839). These specimens are characterized by a small- to ment either to the Sinobelemnitidae or the Pachybelemnopseina is still medium-sized rostrum, a cylindro-conical shape, a rounded lateral uncertain. In both cases, however, the evolutionary history of belem- margin, the presence of a single, long (reaching to near apex) and nites with alveolar grooves needs revisions, and thus will brieflybe deep (u-shaped in transverse section), ventral alveolar groove with discussed here. rudimentary splitting surface, and the absence of an apical groove. The sinobelemnitids have been described from the Carnian of China Although Calabribelus is usually considered to be endemic to Europe and the Hettangian–Sinemurian of Japan (Iba et al., 2012; Iba, in press). and the Mediterranean region (Weis et al., 2012), its coeval occurrence These stratigraphic ranges are concordant with those of the Tibetan in South Tibet clearly indicates that this taxon is present at the Gondwana specimen. The sinobelemnitids are, so far, known only from the eastern margin of the Southern Hemisphere. Thus, the evolutionary history Tethys or the western Paleo-Pacific, thus they are considered endemic of the Holcobelidae, including the supposed Holcobelus–Calabribelus– to this region. If the Tibetan Sinemurian specimen belongs to the Pachybelemnopsis lineage, needs revision. These considerations need to Sinobelemnitidae, the paleobiogeographic distribution of this belemnite account for records in the Southern Hemisphere and also the enigmatic family is much wider than previously thought, perhaps even global. records in northern Siberia and northeastern Russia (northern part of The early evolutionary history of the Pachybelemnopseina is still northwestern Paleo-Pacific) (Sachs and Nalnjaeva, 1975). The second uncertain, though its earliest records have been considered to be of hypothesis therefore also needs serious thought. The new observations Toarcian–Aalenian age. The Sinemurian age of the Tibetan specimen discussed in this paper provide useful information for the future discus- is remarkably older than these records. If the Tibetan Sinemurian sion of the early evolution of the Pachybelemnopseina. specimen belongs to the Pachybelemnopseina, the origin of this sub- It should be noted that another early Pachybelemnopseina related order must be dated back by at least 15 m.y. into the Sinemurian. genus Dicoelites was also recovered from the possibly Early Jurassic Recently, Weis et al. (2012) proposed a new hypothesis explaining Pupuga Formation in Nyalam, western Tibet (Wu, 1982). However, the early evolution of the Pachybelemnopseina. They suggest that this the age of the Pupuga Formation is still debatable. Wu (1982) suggested belemnite lineage started accordingly in the early Middle Jurassic with a Toarcian age, based on the occurrence of several Early to Middle Juras- Holcobelus (intermediate groove with rudimentary splitting surface), sic ammonites. Later these ammonite records were completely revised, evolved via Calabribelus (alveolar groove with rudimentary splitting some of the specimens were re-assigned to an Early Cretaceous (Aptian) surface), and finally reached Pachybelemnopsis (alveolar groove with genus (Zhang, 1985). Other specimens are too poorly preserved to dis- well-developed splitting surface). The center of origin was located in cuss their systematic assignment. Some parts of the Pupuga Formation Europe and the Mediterranean region. The Tibetan Sinemurian record were, however, re-considered to be of Toarcian age based on the occur- challenges this hypothesis since this specimen already has an alveolar rences of new ammonite findings (Polyplectus discoides, Dumortieria sp. groove with a well-developed splitting surface. Two different phyloge- and Phymatoceras cf. crassicosta (Yin and Zhang, 1996; Yin, 2010)). The netic scenarios are possible: 1) the rostrum of the Sinemurian Tibetan complex geological structure of this area, and the difficulty to date the belemnite independently developed the morphological character Tibetan Dicoelites precisely, allow no further interpretation at the “alveolar groove with well-developed splitting surface” much earlier moment. If a Toarcian age is confirmed, the Tibetan record represents than the Holcobelus–Calabribelus–Pachybelemnopsis lineage, or 2) one of the earliest records of the Dicoelitidae and possibly the earliest this character is homologous and the Sinemurian Tibetan belemnite record of the Pachybelemnopseina in the world along with the Arctic represents an earlier representative or even the root-stock of the Canadian ones (Jeletzky, 1980; Doyle et al., 1997). The phylogenetic Holcobelus–Calabribelus–Pachybelemnopsis lineage. relationship between the Tibetan Sinemurian belemnite and the Toarcian Since the sinobelemnitids had acquired the character of a “single Dicoelites needs to be clarified, in order to better understand the early dorsal alveolar groove with well-developed splitting surface” already evolution of the Pachybelemnopseina. Future studies should pay more in the Late Triassic, much earlier than the Holcobelus–Calabribelus– attention to the Toarcian Dicoelites, including a re-investigation of the Pachybelemnopsis lineage that has a single ventral groove with rudi- Tibetan Dicoelites specimen and its age assignment. mentary or well-developed splitting surface, the first explanation The early evolution of belemnites with an alveolar groove has not yet sounds possible. On the other hand, the occurrence of Calabribelus sp. been fully understood. The presence of such belemnites in the Sinemurian in the Nieniexiongla Formation (Aalenian–Bajocian after Yin (2010)) of South Tibet indicates that belemnites had already diversified at this Y. Iba et al. / Gondwana Research 28 (2015) 882–887 887 time, much earlier than has been previously thought. Important belem- Iba,Y.,Sano,S.,Mutterlose,J.,Kondo,Y.,2012.Belemnites originated in the Triassic—a – – new look at an old group. 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