Chiosella timorensis (Nogami, 1968)

GRADINARU, EUGEN, 2022, The Olenekian-Anisian / Early-Middle Triassic Boundary, And Assessment Of The Potential Of Conodonts For Chronostratigraphic Calibration Of The Triassic Timescale, Acta Palaeontologica Romaniae 18 (2), pp. 3-51 : 13-27

Chiosella timorensis , a conodont having a highly controversial taxonomy and definition

With regard to the definition of the conodont species Chiosella timorensis , for a long time the conodont researchers adopted a broader concept, with Spathognathodus gondolelloides Bender, 1970 in the synonymy of Gondolella timorensis Nogami, 1968 , the first being interpreted as a juvenile of the latter (e.g., Sweet, 1970 a, 1973; Kozur, 1973b; McTavish, 1973; Mirăuţă, 1974; Kemper et al., 1976; Buryi, 1979, 1989; Assereto et al., 1980; Chhabra & Sahni, 1981; Matsuda, 1983; Gaetani et al., 1992; Klets, 1995; Kiliç, 2021).

However, Budurov (1976b), Buryi (1979, 1989), Buryi et al. (1980), Budurov et al. (1983, 1985, 1987, 1988 a, 1989) and Budurov & Trifonova (1991) considered that Neospathodus gondolelloide s is a senior synonym of Chiosella timorensis . The above-cited authors based their conclusion by only commenting on the disputed dates when the monographs by Nogami (1968) and Bender (1970b) were published, instead of properly addressing the distinct morphologies of the two conodont species.

Later, Kozur (1989b) and Orchard (1995) stated that gondolelloides is a distinct conodont species, and thus not a juvenile synonym of timorensis , and also that it begins earlier than the latter species, in the upper Spathian, and that the two species co-occur in the Aegean. This has been further agreed on by Kozur et al. (1995), Budurov & Sudar (1995), Orchard (1995), Meço (1999, 2010), Kozur (2003a, b), Krystyn et al. (2004), Kozur & Bachmann (2005), Ovtcharova et al. (2006), Orchard et al. (2007 a, b), Klets (2008), Orchard (2010) and Goudemand et al. (2012).

Even the generic assignement of the conodont species timorensis has been variously interpreted over time, as Gondolella ( Nogami, 1968; Kozur, 1973 b, 1980 a-b; Gaetani et al., 1992; Jacobshagen et al., 1993), Paragondolella ? ( Koike et al., 1971), Neospathodus ( Sweet, 1970 a, 1973; McTavish, 1973; Kemper et al., 1976; Goel, 1977; Ishida, 1979; Koike, 1979 a-b; Watanabe et al., 1979; Buryi, 1979, 1989; Tanaka, 1980; Wang Z-H, 1982; Matsuda, 1983; Dagys, 1984; Klets, 1995), Neogondollela ( Nicora, 1977; Collinson & Hasenmueller, 1978; Assereto et al., 1980; Koike, 1981; Sweet & Bergström, 1986; Paull, 1988; Paull & Paull, 1998), Kashmirella ( Budurov et al., 1988b, 1989; Budurov & Trifonova, 1991, 1995; Budurov & Sudar, 1995; Kiliç et al., 2016), or Chiosella ( Kozur, 1989b, 1999, 2003a-b; Orchard & Bucher, 1992; Orchard, 1992, 1994 a, 1995, 2005, 2010; Koike, 1999; Klets, 2006, 2008; Goudemand et al., 2012; Plasencia et al., 2013; Yan et al., 2015; Chen Y-L et al., 2016; Muto et al., 2019, 2020; Chen Y et al., 2020).

The generic assignement of the species gondolelloides has also been interpreted either as Spathognathodus ( Bender, 1970) , Neospathodus ( Sweet, 1970 a, 1973; Orchard, 1995), Gondolella ( Kozur, 1973b; Gaetani et al., 1992), Kashmirella ( Budurov et al., 1988b, 1989; Budurov & Trifonova, 1991, 1995; Budurov & Sudar, 1995; Kiliç et al., 2016) or Chiosella ( Kozur, 1989b; Orchard & Bucher, 1992). More recently, the assignement of the species gondolelloides was limited to Chiosella (e.g., Klets, 2008; Orchard, 2010; Plasencia et al., 2013; Muto et al., 2019).

Furthermore, Nicora (1977), Kozur (1989b) and Gaetani et al. (1992) treated Neogondolella aegaea Bender, 1970 as a junior synonym of Chiosella timorensis , thus implying the equivalence between the Timorensis Zone of Sweet (1970a), placed in the top of the Spathian, with “Die aegaea – Zone” of Bender (1970b), placed in the Anisian. Lastly, the two morphotypes of timorensis that were discrimated by Nicora, Neogondolella timorensis timorensis ( Nogami, 1968) and Neogondolella timorensis benderi Nicora, 1977 , respectively, together with Spathognathodus gondolelloides Bender, 1970 , interpreted as a juvenile of timorensis , are all allocated to Godolella timorensis by Gaetani et al. (1992, p. 195, pl. 17), thus complicating once again the definition of this conodont species.

As seen from the above references, the definition of timorensis versus gondolelloides , in which aegaea was also involved, represented a long disputed issue, and it remains still unresolved, being mostly a problem of subjective criteria agreed by the conodont researchers.

During the Triassic Symposium held at St Christina/Val Gardena, Italy, September 2003, an ad-hoc group meeting including Heinz Kozur, Mike Orchard, Alda Nicora, Leopold Krystyn and Eugen Grădinaru examined the conodont material from the Deşli Caira section, in Romania, and concluded that gondolelloides and timorensis are distinct species of Chiosella , the timorensis species having a narrow platform that surrounds the posterior end of the carina. It was also concluded based on the ammonoid data at hand at that time in the Deşli Caira section that Ch. gondolelloides is common in the uppermost Spathian, whereas Ch. timorensis began later, at the base of the Aegeiceras ugra fauna. This conclusion was adopted by Grădinaru et al. (2006, 2007) and Orchard et al. (2007a) for the Deşli Caira section, and closely mimicked by Orchard et al. (2007b) and Lehrmann et al. (2006, 2015a-b) for the Guandao section in China.

Discussing this matter, Golding (2021a) underlies that recently “ Additional issues with Ch. timorensis center on the definition of the species, and its differentiation from related species such as Ch. gondolelloides, Ch. n. sp. A and Ch. n. sp. B (see discussion in Goudemand et al., 2012) ”, whereas “ At Wantou Chen et al. (2020) recognized the new species of Chiosella identified by Goudemand et al. (2012), but retained the name Ch. gondolelloides for several specimens considered to be Ch. timorensis by Goudemand et al. (2012), making correlation of the Chiosella faunas between Wantou, Deşli Caira and Guandao difficult at this time ”.

Lastly, besides the controversial definitions of the two leading species of the conodont Chiosella , the lineage gondolelloides - timorensis has also been for a long time interpreted variously. Early initiated by Sweet (1970a), Kozur (1973b, 1989b, 2003b), Kozur et al. (1995) and Budurov (1976b), this remained along-disputed issue, being even actually controversially discussed by Orchard (1995), Goudemand et al. (2012), Yan et al. (2015), Chen Y-L et al. (2016), Chen Y et al. (2020) and Kiliç et al. (2016).

Thus, one may conclude that the conodont species Chiosella timorensis for a long time had a disputed taxonomic status and also very unstable morphological definitions, and these remain still unresolved. For sure, the issue of the conodont species Chiosella timorensis was and still is one of the most controversial among the Triassic conodonts as regards its definition and taxonomic assignement. All these aspects cast major and reasonable doubts about the reliability of this conodont species as a potential primary biotic proxy for the Olenekian-Anisian/Early-Middle Triassic boundary.

Chiosella timorensis , a conodont having a long-disputed first occurrence and chronostratigraphic range

The first occurrence ( FO), implying the distinction or coincidence between the first appearance datum ( FAD) versus the lowest occurrence ( LO), and the chronostratigraphic range of the conodont Chiosella timorensis have been a long-disputed issue for the Triassic conodont researchers. On the other side, with regard to the coincidence of the LO and the FAD of the conodont Ch. timorensis , i.e., the coincidence of its lowest biostratigraphicum datum with its earliest biochronological event, in almost all cases this was not properly tied to the ammonoid bio-chronostratigraphy.

When Nogami (1968, p.117) described from the Portuguese Timor the new conodont species Gondolella timorensis , from the beginning an uncertainity with regard to the dating of its occurrence was raised. Although this species was found in “ dunkelgrauerer Kalk mit vielen Ammoniten sowie Leiophyllites timorensis Bando, L. sp. und Procarnites aff. kokeni (Arthaber) ”, its occurrence was dated by Nogami (1968, p.128) as ” oberstes Skyth (oder unterstes Anis) ”. This is at odds with the qualified opinion of Nakazawa & Bando (1968, p. 87), who stated that “ Judging from the ammonites, the age of the limestone refers to the Latest Skythian, rather than the Early Anisian ”. Unfortunately, in spite of the expert dating done by Nakazawa & Bando (1968), many of the Triassic conodont researchers gave credit to the uncertain dating advanced by Nogami (1968), and by this all subsequent discussions regarding the age of the first occurrence of the conodont species Chiosella timorensis were placed on a uncertain, long-disputed path.

Chronologically, the next reference to Gondolella timorensis Nogami, 1968 was by Sweet (1970a), who described this conodont species as Neospathodus timorensis ( Nogami, 1968) from the Narmia Member of Mianwali Formation at Narmia, in West Pakistan. Sweet (1970a, p.217) nominated for the first time this conodont species “ as the index for a distinctive, if poorly known, Zone of Neospathodus timorensis ”. Sweet (1970a) further stated that “ An Anisian age is suggested (but by no means established) by noting that conodonts from Anisian (= “Hydaspian”) rocks on Chios, Greece, that Bender (1967?) named Spathognathodus gondolelloides are probably closely related to the ones herein referred to N. timorensis ”, and “ If this is so, and Nogami’s uncertainity as to the age of the rocks yielding the types of N. timorensis is well founded, it may be that the uppermost bed of the Narmia (and the Zone of N. timorensis ) are Anisian in age ”.

Subsequently, Sweet et al. (1971, fig. 1) errected 22 Triassic conodont zones tied to the Triassic ammonoid zones, with Zone 13 ( Neospathodus timorensis Zone ) being placed at the top of the Spathian Substage.

Clark (1977), Clark et al. (1979), Solien (1979), Paull (1988), and other authors, closely adopted the conodont zonation of Sweet et al. (1971).

Contradictory data to the first occurrence of timorensis have been provided by Nicora (1977) and Collinson & Hasenmueller (1978). Nicora (1977, p. 97) concluded in her well-known monograph on the Lower Anisian platform-conodonts from the Tethys and Nevada that “ data from Chios and Nevada suggest that N. t. timorensis makes its appearance at the base of the Anisian and characterizes the lower part of the Aegean Substage of Asssereto (1974) ”. This statement of Nicora (1977) was based on a re-interpretation, which remains, however, disputable in view of the previous chronostratigraphic interpretation made by Nakazawa & Bando (1968) of the taxonomic assignement of the ammonoids mentioned by Nogami (1968) at the type locality of Gondolella timorensis . Consequently, Nicora (1977, p. 97) stated that “ it is possible to say that N. t. timorensis , in the type locality, represents an uncertain interval between the Upper Scythian and Lowermost Anisian ”. Nicora (1977, p. 97) also stated that ” the biostratigraphic position of N. t. timorensis in West Pakistan is uncertain ”, but concluded that “ it occurs there above rocks that yielded Upper Scythian ammonoids ”. Ultimately, Nicora (1977, p. 97) based her assertion on finds in the Star Canyon and Coyote-Bloody Canyon sections of Nevada, where the author mentioned that N. t. timorensis occurs with Lower Anisian ammonoids, and also on the interpretation of ammonoid-conodont associations in Chios, stating that it “ is the only place in which it is possible to fix the biostratigraphic level of first occurrence of N. t. timorensis ”.

On the contrary, Collinson & Hasenmueller (1978, p. 187) reported Neospathodus homeri and Neospathodus timorensis in samples from the Haugi ammonoid zone in Nevada, which Silberling & Tozer (1968) regarded as highest Spathian. Anticipating these controversial findings by Nicora (1977) and Collinson & Hasenmueller (1978), we must mention that Orchard & Bucher (1992) and Orchard (1994a) stated that Chiosella timorensis is unconfirmed at the level of the latest Spathian Haugi Zone (Yatesi beds) in Nevada, in which Orchard (1994a, p.108) found that conodont faunas are dominated by N. ex gr. homeri , with some elements approaching Chiosella gondolelloides (Bender) . This controversy is now finally resolved by the undisputed find of Chiosella timorensis in the latest Spathian Haugi ammonoid zone in Nevada ( Goudemand et al., 2012).

Sweet & Bergström (1986, p.108 and fig. 9), although they have contended that “ the Timorensis Zone may span the Scythian-Anisian boundary ”, stated, however, that “ this boundary is drawn at the base of the Timorensis Zone , but with no particular conviction ”.

Finally, Sweet (1988, p. 269 and p. 271) gave credit to the statements given by Nicora (1977) and by this overcame his non-conviction, and concluded that “ The Timorensis Zone is regarded as Anisian (Aegean), and it is suggested that the base of this zone closely approximates the Spathian/Anisian boundary and may be used regionally to mark the boundary between the Lower and Middle Triassic ”.

Later, Sweet’s statement that “ the positions in Pakistani sections of common late Spathian ammonoids project to levels in the Composite Standard ( CS) just below the first occurrence of Neospathodus [or Neogondolella] timorensis ” has not been supported by the ammonoid succesion provided by Guex (1978, fig. 4), as the topmost interval of the Spathian Substage in the Salt Range, Pakistan, corresponding to the Haugi ammonoid zone in Nevada, is not documented by ammonoids.

Chronologically, Nicora (1977) and Assereto et al. (1980) made for the first time the formal proposal that the FO of the conodont Gondolella timorensis Nogami, 1968 may be used for the definition of the lower boundary of the Anisian Stage in a clearly named section and locality, i.e., the section at Chios, Greece. The historical premises on which these authors prompted their proposal are unfolded in a foregoing section in the present paper where it is outlined that the Chios section lacks conclusive ammonoid data to properly fix the Spathian-Aegean/Olenekian-Anisian boundary.

Besides the above mentioned references that historically are the most relevant for the issue discussed in the present section, there are many other references in which the first occurrence of Chiosella timorensis and its chronostratigraphic range have been discussed for a long time, which are also highly controversial. One relevant reference, which demonstrates the still existing uncertainity around the above discussed issue by the end of the 1980 s, is Lozovsky et al. (1989), who stated that Neospathodus timorensis Zone appers to be early Anisian, but the lower part of its range may slightly correlate with the uppermost Lower Triassic.

The issue of first occurrence and chronostratigraphic range of the timorensis / gondolelloides / aegaea group has been largely and controversially discussed by Kozur and Budurov, who repeatedly modified over time their opinions in conjunction with the diffuse taxonomic assignement and definition of timorensis versus gondolelloides , and with the successively changing current views on their chronostratigraphic range.

Kozur (1972, 1974, 1975) and Kozur & Mostler (1972) advanced a Triassic conodont zonation, in which the “ timorensis Assemblage-Zone ” is placed in the upper Spathian ( Keyserlingites subrobustus -Zone), followed by “ aegaea S.-Z.” of the “ aegaea A.-Z” placed in the Lower Anisian. Shortly afterthat, Kozur (1973a, b) began to advocate that the Keyserlingites subrobustus -Zone should be placed at the base of the Anisian, by taking into consideration the evolution of the gondolellid conodonts, and based on the inadequate interpretation, as proved later, of the chronostratigraphic significance of ammonoid faunas around the Olenekian-Anisian boundary. Consequently, Kozur (1980 a-b) and Kovács & Kozur (1980) placed the Keyserlingites subrobustus -Zone (= Neopopanoceras haugi -Zone) and the “ timorensis -zone” at the base of the Aegean, by inadequately interpreting the mixed ammonoid assemblage from Ziyun, China, discussed by Wang Y-G (1978), and on which, later, even Wang Y-G (1985) completely changed his interpretation. Finally, by adopting the ammonoid succession in Nevada and British Columbia published by Bucher (1989, 1992, 2002), Kozur (1989a, 1999, 2003 a-b) and Kozur & Bachmann (2005) adopted a new zonation scheme, with Chiosella timorensis -Zone placed at the base of the Aegean ( Japonites welteri -Zone), following upward by the Chiosella gondolelloides -Zone placed at the top of the Neopopanoceras haugi -Zone of the latest Spathian, and where the former lower Anisian “ aegaea -A.-Z.” is missing.

Budurov, in Budurov & Trifonova (1974), and Budurov (1976a, b) advanced a Triassic conodont zonation where the “ gondolelloides Zone aIβ” is placed in “obere Teile des Hydasp” of Bender (1970), the chronostratigraphic equivalent of the lower Anisian of Assereto (1974). In the next publications, Budurov et al. (1983, 1985, 1987) and Budurov & Trifonova (1984) placed the Neospathodus gondolelloides R.-Z. either on the top of the Spathian or straddling the upper Spathian-lower Anisian boundary, where gondolelloides is interpreted as the senior synonym of timorensis . When the new genus Kashmirella was introduced by Budurov et al. (1988b) to replace the generic assignment of Neospathodus gondolelloides Bender 1970 (= G. timorensis Nogami 1968 ), the newly named K. gondolelloides R.-Z. is straddling the upper Spathian-lower Anisian boundary (e.g., Budurov et al., 1989; Budurov & Trifonova, 1991), subsequently replaced by K. timorensis R.-Z. ( Budurov & Trifonova, 1994). When stated that gondolelloides and timorensis are distinct conodont species, Budurov & Sudar (1995) and Budurov & Trifonova (1995) have split the former K. gondolelloides R.-Z. and introduced a new zonation with the K. timorensis R.-Z. at the top of the Spathian, and the K. gondolelloides R.-Z. at the base of the Anisian. One may observe that this new proposed conodont zonation is opposite to that promoted by Kozur (1999, 2003a, b) and Kozur & Bachmann (2005), with the two zones placed in a reversed chronostratigraphic order.

In Europe, the conodont species timorensis is reported from several localities ( Fig. 3 /1 to 6), as follows, in the chronological order of their reports: Chios Island, Greece ( Nicora, 1977; Assereto et al., 1980; Gaetani et al., 1992; Jacobshagen et al., 1993); Perşani Mountains, Romania ( Mirăuţă & Gheorghian, 1978; Patrulius et al., 1996); Capelluzzo, Southern Apennines, Italy ( Mietto et al., 1991); Sosio Valley, Sicilia, Italy ( Kozur et al., 1995) ; Kçira, Albania ( Muttoni et al., 1996, 2019; Germani, 1997); Deşli Caira, Romania ( Grădinaru et al., 2000, 2006, 2007; Orchard et al., 2007a).

The status of the conodont species timorensis in the Chios and Kçira sections, and its relevance for the OAB, were already discussed in a previous section of the present paper. Mietto et al. (1991) reported the finding of Gondolella timorensis (sensu Sweet, 1970 a, 1973; Nicora, 1977; Kozur, 1989b), with gondolelloides in the synonymy of timorensis , in the Southern Apennines, and asserted that the Timorensis conodont zone characterizes the lowest Aegean Substage of Assereto (1974), thus following the Triassic conodont zonation of Sweet et al. (1971) and the conclusions of studies done by Nicora (1977) in Chios. For the Sosio Valley, Kozur et al. (1995) identified the conodont species timorensis as the index for the base of the Anisian. As regards the Deşli Caira section, the new ammonoid biostratigraphy achieved in this locality documents that the FO of the conodont species timorensis is well below the OAB (Grădinaru, in Grădinaru & Gaetani, 2019). Mirăuţă (1974), Mirăuţă & Gheorghian (1978) and Mirăuţă et al. (1984) mentioned the occurrence of gondolelloides / timorensis group in the lower Anisian of North Dobrogea and the Eastern Carpathians. Later, Mirăuţă (in Patrulius et al., 1996) noted that Gondolella timorensis persisted longer than G. regalis , till the Pelsonian, in the Schreyeralm Limestone from the Pleașa Lupșei Outlier, in the Perșani Mountains. It must be underlined that Mirăuţă followed Sweet’s concept of the gondolelloides / timorensis group, with gondolleloides in the synonymy of timorensis , and this is entirely proved by the illustrated specimens, among which no one can be assigned to the true timorensis .

From Southwest Asia, the occurrence of Ch. timorensis is known in Turkey and Oman. The most recent record of the conodont species timorensis is from Gebze, in Turkey ( Fig. 3 /7), and it was published by Kiliç (2021). Although this author noted the range of this species appears to be late Spathian to Aegean, he refers, however, in his paper to the Timorensis Zone as early Anisian in the Kokaeli Triassic succession. As regards the definition of timorensis species, Kiliç (2021, p. 627) is adopting the concept of Sweet and Budurov, with gondolelloides in the synonymy of timorensis . From Wadi Alwa, in Oman ( Fig. 3 /8), the occurrence of the conodont species timorensis is reported by Orchard (1994a), who stated it correlates to the basal Lower Anisian Japonites welteri beds of Nevada.

In the Himalayas region, Fucks & Mostler (1969) early reported from northern Nepal, in the area north of Dhaulagiri (Dolpo), a conodont assemblage equivalent to the latest Spathian-earliest Anisian Timorensis conodont assemblage of Nogami (1968). Subsequently, a succession of articles have been published by Sweet (1970 a, 1973) on the occurrence of the conodont species timorensis in the Salt Range, western Pakistan, from the Narmia Member of the Mianwali Formation ( Fig. 3 /9). In a previous section of the present paper, the twisting options of Sweet (1970 a, 1973, 1988) and Sweet et al. (1971) on the first occurrence and stratigraphic range of the conodont species timorensis , having gondolelloides in its synonymy, are underlined, which jumped from the latest Spathian-earliest Anisian to the latest Spathian, and finally to the earliest Anisian. Nakazawa et al. (1975) made reference to the conodont zonation done in Pakistan by Sweet (1970 a, 1973), with the Timorensis Zone placed in the uppermost Lower Triassic.

Kovács & Kozur (1980, pl. 1, figs 1, 2, 4) illustrated Gondolella? timorensis Nogami from Dolpo Gebiet, west Nepal ( Fig. 3 /10), and its occurrence is dated to the Keyserlingites subrobustus-Zone. The conodont Timorensis A-Z defined by Kovács & Kozur (1980, tab. 1) is overlapping the Keyserlingites subrobustus-Zone and the basal part of the Paracrochordiceras anodosum-Zone, both ammonoid zones being assigned to the Aegean Substage/base Anisian Stage. Garzanti et al. (1995) recorded the occurrence of Gondolella timorensis ( Nogami, 1968) from Manang, in Nepal, in the topmost Tamba Kurkur Formation, as indicating the earliest Anisian ( Timorensis Zone ).

From Spiti, India ( Fig. 3 /11), the conodont species timorensis is reported in several localities. Goel (1977) reported the abundant occurrence of Neospathodus timorensis (Nogami) , with gondolelloides in its synonymy, at Guling, in Spiti, from dark shales and grey limestones with Keyserlingites dieneri and Spiriferina stracheyi , dated as Spathian.

Gupta & Budurov (1981) and Gupta (1983) reported the occurrence of Neospathodus timorensis (Nogami) from the shaly limestones with Rhynchonella griesbachi , below the Nodular Limestone, at the base of the Anisian, in the Lilang section, Spiti, the conodont species timorensis being considered by Gupta & Budurov (1981, p. 24) “ an index species for the zone of the same name in the Upper Aegean ”.

Balini & Krystyn (1997) definitely documented the Anisian age of the Durgaites dieneri Beds in Spiti Himalayas, thus ending a long-lasting discussion on their Lower or Middle Triassic position (see also Wang Y-G, 1985; Dagys & Ermakova, 1986; Dagys, 1988; Bucher, 1989; Tozer, 1994c). Krystyn et al. (2004), based on the FO of Chiosella timorensis , placed the Olenekian-Anisian boundary in the upper part of the Niti Limestone, from which the occurrence of the ammonoid genus Preflorianitoides is reported, and considered this to be the only cephalopod found within the lowermost Anisian of the Muth section. It is to be noted that the ammonoid genus Preflorianitoides described by Wang Y-G (1978) from Zyiun, in China, in presumed Scythian-Anisian “mixed ammonoid faunas”, is considered a Spathian ammonoid by Wang Y-G (1985), Tozer (1980) and Shevyrev (1990). In the Deşli Caira section, this ammonoid occurs in the latest Spathian ( Grădinaru et al., 2007), besides Procarnites , Proptychitoides , Albanites , and also the ammonoid genus Procladiscites . In a previous section of the present paper, it is underlined that the occurrences of Procladiscites at Chios prompted the untenable assumption of Assereto et al. (1980, p.731) that the beginning of the Anisian is marked by the first appearance of cladiscitids, and that this would also coincide with the first occurrence of Neogondolella timorensis . Although in the Spiti section the appearance of the conodont Chiosella timorensis is reported lower than the base Aegean Durgaites dieneri ammonoid zone in the Himalayan Muschelkalk Member, the FO of the oft-cited boundary marker conodont Chiosella timorensis is nevertheless preferred by Krystyn et al. (2004) and Sue et al. (2021) as fixing the Olenekian-Anisian boundary in the uppermost part of the Niti Limestone Member, even if its Aegean age is not confidently documented by ammonoids. In conclusion, for Krystyn et al. (2004) and Sue et al. (2021) the Chiosella timorensis conodont zone is coincident with the base Aegean Durgaites dieneri ammonoid zone, although its FO is well below the first occurrence of distinct Anisian ammonoids, i.e., in the upper part of the Niti Limestone in an undefined stratigraphic interval placed between the Spathian/late Olenekian and the Aegean/early Anisian.

From Kashmir, India (Fig. 13/12), Chhabra (1981) reported the Neospathodus homeri - Neospathodus timorensis assemblage in the upper part of the Nodular Limestone dated as early Anisian, with gondolelloides as a junior synonym of timorensis . Chhabra & Sahni (1981) suggested that the placement of the Scythian-Anisian boundary at the base of the Neospathodus timorensis Zone is in agreement with the data of Nicora (1977) from Chios and Nevada, and that this zone characterizes the lower part of the Aegean Substage as defined by Assereto (1974).

Matsuda (1983, 1985) reported the occurrence of Neospathodus timorensis and figured specimens from the latest Spathian in Kashmir, but the definition follows Sweet’s taxonomic concept of the timorensis / gondolelloides group. Pakistani-Japanese Research Group (1985) confirmed the presence of Neospathodus timorensis Zone in Pakistan, from the Narmia Member of Mianwali Formation, and placed this in the uppermost Spathian.

From Central Asia, Bragin et al. (2016) have mentioned occurrences of early Anisian conodonts, among them Neospathodus sp. aff. N. timorensis (Nogami) , from the top of the Zougan Formation in the southeastern Pamirs, Tajikistan ( Fig. 3 /13).

In Eastern Asia, the most important occurrences of Ch. timorensis come from China. The first record of Neospathodus timorensis is only from the early 1980s, when Wang Z-H (1982) reported its occurrence from the Guizhou Province, South China, and dated it as Spathian based on the conodont zonation of Sweet et al. (1971). Concomitantly, N. timorensis was reported by Tian (1982) from Tulong, Tibet ( Fig. 3 /14), and dated as late Olenekian, but the figured specimen (pl. 13, fig. 22) is presumably a gondolelloides specimen. Wang & Wang (1983), when summarizing the Triassic conodont biostratigraphy in China, advocated the placement of the Neospathodus timorensis Zone at the top of the Olenekian. The newest report on the occurrence of Ch. timorensis at Tulong, located in the Himalaya Terrane of Tibet, is by Chen A-F et al. (2021), and the first occurrence ( FO) of Chiosella timorensis is credited to fix the Olenekian–Anisian boundary ( OAB) at Bed 25, upper part of the Kangshare Formation, only on the basis of the data provided in the references commonly used in this matter ( Grădinaru et al., 2006; Orchard et al., 2007a, 2007b; Orchard, 2010; Chen Y et al., 2020). Wu G-C et al. (2007) reported the occurrence of Ch. timorensis from Dibucuo, in the Lhasa Terrane of Tibet ( Fig. 3 /14), and this in placed also at the base of the Anisian.

When the conodont species Chiosella timorensis was agreed by the ICS in 2002 as a primary biotic proxy for the Olenekian-Anisian boundary (cf. Kozur 2003a), a suite of articles concentrated on the conodont biostratigraphy around the OAB in the Triassic successions from several localities in Guizhou Province, South China ( Lehrmann et al., 2002, 2015 a-b; Yao et al., 2004, 2011; Wang et al., 2005; Orchard et al., 2007b; Ji et al., 2011; Yan et al., 2015; Liang et al., 2016; Chen Y et al., 2020).

The section of Guandao ( Fig. 3 /15) has been advanced as a reference GSSP for the base of the Anisian Stage/Middle Triassic Series (cf. Gradstein et al., 2004). The chronostratigraphic interpretation of the conodont biostratigraphy in the Guandao section ( Orchard et al., 2007b), for which there are no ammonoid data to properly document the Olenekian-Anisian boundary, is purely mimicking the chronostratigraphic interpretation given to the ammonoid/conodont record in the Deşli Caira section ( Grădinaru et al., 2007; Orchard et al., 2007a). On this basis, Ji et al. (2011, and Chinese references therein) furthermore support the conodont Ch. timorensis as a proxy for the Lower-Middle Triassic boundary in the Guandao section. When Tong et al. (2019) discussed the Anisian Stage in China, it was confirmed once more that the Guandao section lacks ammonoids around the OAB boundary.

Two other localities in the Guizhou Province, Wantou and Youping ( Fig. 3 /16), are recently advanced by Ogg (2019) and Chen Y et al. (2020) as potential GSSP candidates for the Olenekian-Anisian/Early-Middle Triassic boundary, further supporting the conodont Chiosella timorensis as a proxy for this boundary. Even more, the taxonomic definition by Chen Y et al. (2020) of the conodont species Chiosella timorensis is consistently different when compared to the definition given by Goudemand et al. (2012), thus making more complicated the taxonomy and the lineage of the gondolelloides / timorensis group. Intentionally, or not, in the stratigraphic diagrams of the two “exceptional” Chinese localities, the Olenekian-Anisian/Early-Middle Triassic boundary is not properly indicated. It seems the placement of the Olenekian-Anisian boundary in the “exceptional” Chinese sections represented a great dilemma even for the mentioned authors, and such an undecision is astonishing to the readers of their article. The two “exceptional” Chinese localities are devoid of ammonoids just in the stratigraphic interval of their sections that is critical to fix the Early-Middle Triassic boundary. Additionally, the two “exceptional” Chinese sections have rapid lithological changes, just in the stratigraphic interval where potentially the boundary could be placed, and this represents a major bias for the ammonoid occurrence in the two “exceptional” Chinese sections. As already showed in a previous section of the present paper, Ogg (2019) and Chen Y et al. (2020) centered their discussion mostly on the Early-Middle Triassic boundary interval, as is indicated explicitly in the titles of their articles, and not properly on the boundary itself. This may explain why the boundary location is not shown in the two “exceptional” Chinese sections, for which Chen Y et al. (2020, p. 12) amazingly concluded to have great potential as important GSSP reference sections for the Early-Middle Triassic boundary and can enable precise global correlation.

Recently, Ogg et al. (2020b) noted that “ The lowest occurrence of the Chiosella timorensis (or its sensu stricto morphotype on its early lineage) conodont slightly precedes the Anisian ammonoid level and can be correlated to North American and Asian stratigraphy ”. Furthermore, with the desire to find a solution for this incongruence, Ogg et al. (2020b) stated “ If the lowest occurrence of Ch. timorensis is selected as the global marker, then the uppermost part of the ammonoid Neopopanoceras haugi Zone of “latest Olenekian” in theTethyan realm will slightly overlap the basal Anisian ”.

Ogg et al. (2020b), in their obsession to further suport the conodont species timorensis as a primary biotic proxy for the base of the Anisian, intentionally ignore that the Neopopanoceras haugi zone is the penultimate ammonoid zone in the late Spathian of Nevada, being followed by the Courtilloticeras stevensi ammonoid zone (e.g., Monnet et al., 2013, fig. 2), and also ignore that the classic Neopopanoceras haugi ammonoid zone from western Nevada, as defined by Silberling & Tozer (1968), correlates with the Keyserlingites subrobustus ammonoid zone in British Columbia, Arctic Canada and Arctic Europe, and with the Olenekites spiniplicatus ammonoid zone in Arctic Siberia (e.g., Dagys & Tozer, 1989; Dagys & Weitschat, 1993; Tozer, 1994a; Dagys & Sobolev, 1995). By adopting the suggestion of Ogg et al. (2020b), then a major instability in the standard Triassic timescale would be introduced as regards the Olenekian-Anisian boundary. Although on a recent Research Gate Forum it has been endorsed once more that the ammonoids are the taxonomic group with the highest power of temporal resolution within the Triassic (see also Jenks et al., 2015), the conodont workers continue their offensive in promoting the conodonts as primary biotic proxies to define or redefine the boundaries in the standard Triassic timescale (see Ogg et al., 2020b).

In Southeast Asia, the occurrence of the conodont species timorensis was early reported by Koike (1973) from Kodiang, Malaysia ( Fig. 3 /17), and the author dated it as “early (or middle) Anisic”, but the illustrated specimen (pl. 16, fig. 15) is an indeterminate fragment. Kemper et al. (1976) reported the occurrence of timorensis from western Thailand ( Fig. 3 /18), and dated it as late Spathian to early Anisian, but the figured specimens (pl. 6, figs. 3a-b) likely belong to the conodont species gondolelloides . It must be underlined, Koike (1973) and Kemper et al. (1976) have treated gondolelloides as the junior synonym of timorensis , by adopting Sweet’s taxonomic concept on the gondolelloides / timorensis group.

In the Japanese Islands, the occurrence of the conodont species timorensis was reported starting from the earliest 1970s. Data have been summarized by Koike (1979 a-b, 1981), Ishida (1979), Watanabe et al. (1979), Tanaka (1980), Igo & Koike (1983) and Nakazawa et al. (1994), who stated that the Neogondolella (= Chiosella ) timorensis Zone , both in the Triassic pelagic carbonate and cherty successions, indicates the uppermost Spathian to the lowermost Anisian, which reflects the opinion current at that time on the first occurrence and stratigraphic range of the conodont species timorensis . In the last decades, several authors reported on the occurrence and stratigraphic range of the conodont species timorensis in Japan. Hirsch & Ishida (2002) and Maekawa et al. (2018), summarizing the conodont data from the Chichibu terrane pelagic carbonates, at Kamura, Kyushu Island, and Taho, Shikoku Island ( Fig. 3 /19), placed the conodont fauna with Ch. timorensis in the lowermost Aegean (Lower Anisian). To calibrate the Lower Triassic d 13 C isotope curve from shallow-marine pelagic carbonates in the classic Kamura section, Horacek et al. (2009) placed the Chiosella timorensis Zone in the lower Anisian, following the current concept with this conodont species as a primary biotic proxy for the base of the Anisian. Subsequently, Zhang L et al. (2019a), referring to the same section from Kamura, to overcome the unrealibility of Chiosella timorensis as a primary biotic proxy for the OAB due to the new data on the ammonoid-conodont succession in Nevada, which demonstrated that its FAD is in the late Spathian, asserted that the earliest Anisian age is coincident to the Chiosella ex gr. timorensis - Cratognathus Zone. By this, the authors assumed that the coexistance of Ch. timorensis, Ch. n. sp. B and Cratognathus sp. B at Kamura suggests an earliest Anisian age by reference to the conodont succession in the Deşli Caira, Romania and Guandao, South China sections.

Ha et al. (2021) report on the occurrence of Ch. timorensis in the Triassic carbonate succession from the Taho Formation in western Shikoku Island. By referring to Goudemand et al. (2012), who revised the conodont succession of the Deșli Caira section (candidate section of OAB) and proposed that the FO of Chiosella n. sp. A indicates the OAB for conodont successions, Ha et al. (2021) stated that Chiosella n. sp. A occurs in the study area slightly above the FO of C. timorensis and continues upwards, and asserted that the Ch. timorensis Zone probably contains the ammonoid-based OAB.

For the chronostratigraphic calibration of the Panthalassic Triassic pelagic deep-sea chert stacked in the Jurassic accretionary complex of southwestern Japan, located mainly on Honshu Island ( Fig. 3 /20), Muto et al. (2018, 2019, 2020) and Muto (2021) assumed that the horizon corresponding to the traditional OAB, due to lower biostratigraphic resolution, should essentially be the same as the first occurrence ( FO) of Ch. timorensis , based on comparison with conodont occurrences in Tethyan pericontinental sections, although they noted, however, that in Nevada the ammonoid-conodont succession documents the first appearance of this conodont species in the late Spathian.

In Northeast Asia, the issue of the first occurrence and chronostratigraphic range of the timorensis / gondolelloides group received particular attention from the Russian conodont researchers. Some of the formerly reported occurrences were updated or revised. For example, Neospathodus timorensis (Nogami) mentioned by Dagys (1984) in the upper Olenekian from eastern Taimyr is interpreted by Sobolev & Klets (2009) as Chiosella gondolelloides (Bender) , and it is part of the latest Olenekian Paragondolella (= Neogondolella ) paragondolellaeformis conodont zone.

The lower Anisian occurrence of Neospathodus timorensis is reported by Bragin (1991) in the Ekonai terrane of the Koryak Upland ( Fig. 3 /21), in association with radiolarian assemblages. Neospathodus aff. timorensis is reported from Zyryanka, Kolyma ( Fig. 3 /22) by Konstantinov et al. (1997) and Klets (1998), subsequently being assigned by Klets & Kopylova (2008) to the new species Chiosella omulyovika Kopylova and Klets. This occurs in a conodont assemblage together with Neogondolella taimyrensis Dagys , N. jubata Sweet , Paragondolella paragondolellaeformis (Dagys) , and Chiosella crepidica Klets and Kopylova , and is assigned to the upper Olenekian according to Klets & Kopylova (2008) and Konstantinov & Klets (2009).

Buryi (1989) and Klets (1995) described and figured N. timorensis from Sikhote-Alin ( Fig. 3 /23) and stated that its stratigraphic range corresponds to the latest Olenekian-lowest Anisian boundary interval. Buryi (1997) reported the occurrence of the conodont species timorensis in cherts along the Rudnaya River, Dalnegorsk region, Sikhote-Alin, which are exotic enclosures in the Early Cretaceous turbidites of the Taukha allochthonous terrane. In the opinion of Buryi (1997, p. 49), Neospathodus timorensis Zone defines the interval of Aegean, Bithynian and lower Pelsonian.

Burij et al. (1976) stated early that N. timorensis is absent in South Primorye ( Fig. 3 /24) due to the erosion of the uppermost layers of the Lower Triassic in pre-Anisian time. Later, Buryi (1979) reported the occurrence of N. timorensis in South Primorye in allochthonous late Olenekian limestone blocks, which are embedded in Ladinian terrigenous deposits occurring in the basin of the Chernaya River (Sobolev, pers. commun.).

Klets (2005, 2006, 2008) synthesized all information and the current views on the Triassic conodont occurrences and conodont-based geochronology in Northeast Asia.

Konstantinov & Klets (2009, p. 179), when discussing the Anisian Stage in Northeast Asia, stated that conodonts, in particular the FO of Chiosella timorensis (Nogami) , appear to be inappropriate biomarkers. Firstly, because the content of the Chiosella timorensis group and its stratigraphic distribution are ambiguously understood, and secondly, because undoubtfully-defined Chiosella timorensis has not been found as yet in the Triassic sections of Northeast Asia. The statement of Konstantinov & Klets (2009) is fully justified in view of the problems relating to the definition of timorensis versus gondolelloides , as proved by the synonymies, descriptions and illustrations done by Buryi (1979, 1989) and Klets (1995).

In Timor, the conodont species timorensis was first described by Nogami (1968) from Mount Lilu ( Fig. 3 /25), in Timor-Leste (cf. Charlton et al., 2009). In a previous section of the present paper the subsequent consequences resulting from the uncertain dating of its occurrence and stratigraphic range were underlined. Orchard (1994a) reported the occurrence of the conodont species Chiosella timorensis , together with fewer Gladigondolella tethydis and a single specimen of Neogondolella ex gr. regale, from Nifukoko ( Fig. 3 /26), in West Timor (cf. Charlton et al., 2009), from an allochthonous Hallstatt limestone block, and dated it as Early Anisian based on his current concept on the FO of Ch. timorensis . The assertions of Orchard (1994a, p. 110) with regard to the age of the conodont timorensis in the West Timor block are opposed to the assertions by Tozer (1994c), who assumed the late Spathian to earliest Anisian dating of the ammonoids in the condensed Hallstatt-type limestone in the studied block. However, the dating of ammonoids, also of the associated conodont fauna, in the West Timor block, is not yet clearly defined, as the assertions of Tozer (1994c) about the ammonoids Keyserlingites versus Durgaites and their stratigraphic ages are not fully justified by the actual data (e.g., Balini & Krystyn, 1997; Krystyn et al., 2004).

From Western Australia, the occurrence of the conodont species timorensis was early reported by McTavish (1973, 1975), who adopted Sweet’s taxonomic concept, with gondolelloides in the synonymy of timorensis , and placed the Neospathodus timorensis Zone in the late Spathian. Subsequently, the conodont Chiosella timorensis Zone was treated as early Anisian by Nicoll & Foster (1998), Nicoll (2002) and Nicoll et al. (2007). Subsequently, Gorter et al. (2008, 2019) reported the occurrence of the conodont species timorensis in the offshore Carnarvon, Perth & Canning basins ( Fig. 3 /27), and asserted it is a good approximation of the OAB, although the authors noted, however, this conodont species occurs first with upper Spathian Haugi Zone ammonoids in Nevada.

From the western United States, significant data on the discussed issue in the present section originated, and it must be noted from the very beginning these generated major controversies regarding the first occurrence and chronostratigraphic range of the timorensis / gondolelloides group. Collinson & Hasenmueller (1978) reported Neospathodus homeri and Neogondolella timorensis from the Haugi ammonoid zone in the lower Prida Formation of the Humboldt Range in northwestern Nevada ( Fig. 3 /28), which is documented as latest Spathian by Silberling & Wallace (1969). Subsequently, the occurrence of timorensis in the western United States was reported by Clark et al. (1979), Wardlaw & Jones (1980), Carey (1984) and Paull (1988). Carey (1984) classed the occurrence of Ch. timorensis in northwestern Nevada as latest Spathian to earliest Anisian. Instead, Paull (1988, and reference therein), by following the conodont zonal scheme of Sweet & Bergström (1986), noted that the Timorensis zone , the uppermost zone of the Lower Triassic, is commonly reported from Nevada, where Neospathodus (or Neogondolella ) timorensis is often present in abundance.

Wardlaw & Jones (1980) reported the occurrence of Neospathodus timorensis , presumably straddling the Spathian-Anisian boundary, from Great Valley , California Coast Ranges ( Fig. 3 /29). From east-central California, Stone et al. (1991) reported Chiosella sp. cf. Ch. timorensis found at a presumably stratigraphic level above the Haugi Zone . The occurrence of the conodont species timorensis is also reported from Sheep Creek, southeastern Idaho ( Fig. 3 /30) by Carr (1981, unpubl. PhD thesis), as noted by Paull (1988). Clark & Carr (1984, fig. 9) interpreted the occurrence of Neogondolella timorensis as diagnostic of the latest Early or earliest Middle Triassic, as a distinct zone in their Idaho Lower Triassic conodont zonation.

Orchard & Bucher (1992, p. 136) and Orchard (1994a, p.108) revised Collinson’s material, and based on new conodont faunas from the Haugi Zone (Yatesi beds) in the same area, concluded that the conodont species timorensis is unconfirmed in the respective conodont fauna that is dominated by N. ex gr. homeri , with some elements approaching Chiosella gondolelloides (Bender) . Instead, Orchard & Bucher (1992, p. 136) and Orchard (1994a, p. 108) documented that only the basal Anisian Japonites welteri beds of Bucher (1989) include Chiosella timorensis . Based on the above data, Orchard (1994a, pp. 108 and 111) concluded that “ C. timorensis has a worldwide occurrence and appears to be a suitable index for the base of the Middle Triassic, as has been suggested by several authors (e.g., Assereto et al., 1980) ”, and stated that “ On the basis of Nevadan and Canadian data the appearance of Chiosella timorensis provides a suitable datum for defining the Lower-Middle Triassic boundary ”.

Paull & Paull (1998) reported the occurrence of Neogondolella timorensis unaccompanied by neospathodid species from O’Neil Pass in northeastern Nevada, and these authors agreed with Orchard (1995) that “ Chiosella timorensis (Nogami), although it closely predates known Anisian ammonoids ( Gaetani et al., 1992), represents the best conodont datum for definition of the base of the Middle Triassic ”.

In a previous section in the present paper, there were already underlined the shortcomings in the statements of Assereto et al. (1980) with regard to the dating of the first occurrence of Ch. timorensis , and its relevance for the base of the Lower-Middle Triassic boundary. In the same section, it was emphasized that Gaetani et al. (1992, p. 197) in opposition stated that the conodont Gondolella timorensis (= Chiosella timorensis ), which appears before the appearance of the first Anisian ammonoid fauna in the Chios section, cannot be used to define the base of the stage exactly, because its appearance approximates the beginning of the Anisian only in a broad sense.

Finally, the issue of the FAD of Chiosella timorensis in Nevada has been definitely resolved by Goudemand et al. (2012), who documented that this conodont species occurs in the Haugi Zone in the northern Humboldt Range (Nevada, USA), which has been classically placed by Silberling & Tozer (1968), Silberling & Nichols (1982), Bucher (1989) and Guex et al. (2010) in the late Spathian Substage, i.e., the last substage of the Spathian/late Olenekian/Early Triassic in the North American Triassic chronostratigraphy. So, for the first time the inadequacy of the FAD of Chiosella timorensis as a marker of the Olenekian-Anisian boundary is fairly documented by the ammonoid chronostratigraphy. The data provided by Goudemand et al. (2012) have been later supplemented by Ovtcharova et al. (2015), and these authors firmly demonstrated that Chiosella timorensis occurs in the conodont faunas of the latest Spathian of Nevada, including the Haugi and Stevensi zones, the penultimate and ultimate ammonoid zones of the latest Spathian, respectively, as documented by the comprehensive study of the Spathian ammonoid faunas from the western USA done by Guex et al. (2010). As a result, Goudemand et al. (2012) and Ovtcharova et al. (2015) reasonably questioned, based on undeniable ammonoid data, the usefulness of the FAD of Ch. timorensis as an index for the Olenekian-Anisian boundary. Ovtcharova et al. (2015), through the application of Unitary Association, defined a succession of two laterally reproducible maximal associations/conodont biozones between which the Olenekian-Anisian boundary falls, where the residual maximal horizon including Ch. timorensis is placed below the OAB. It has been concluded that the chronostratigraphic location of the OAB remains to be resolved at a later date in a succession having a complete ammonoid record around the Olenekian-Anisian boundary, to which the conodont record has to be closely tied.

In Western Canada, the timorensis fauna is differentiated by Orchard & Bucher (1992) and Orchard & Tozer (1997a, fig. 4) as a basal Anisian interval at Ursula Creek, northeast British Columbia ( Fig. 3 /31), belonging to the North American craton-bound Triassic, and also in the western Cordilleran allochthonous terranes of Canada, i.e., in Quesnellia ( Fig. 3 /32) and in Stikinia ( Fig. 3 /33), by correlation with the basal Anisian Japonites welteri beds of Nevada. However, Orchard (1994, p. 107) and Orchard & Tozer (1997a, fig. 4) noted Ch. timorensis , potentially defining the base of the Middle Triassic, is known from otherwise undated strata in Canada. Golding (2014) mentions Chiosella timorensis from the Montney Formation in the subsurface of northeast British Columbia, as indicating the uppermost Spathian or the Anisian. Pointing out that the first occurrence of Chiosella timorensis is known to occur with Spathian (upper Olenekian) ammonoids of the Neopopanoceras haugi Zone in Nevada and China, as stated by Goudemand et al. (2012), Golding et al. (2014) concluded that its use as a definitive index species for the base of the Anisian is questionable, as this would require the Neopopanoceras haugi Zone to be re-defined as Anisian in part. Subsequently, specimens of Ch. timorensis have been described by Golding et al. (2015) from the subsurface of British Columbia in the Petro-Canada Kobes d-048-A/094-B-09 and Shell Groundbirch 16–02- 078-22 W6 wells. Golding (2021b) reported the finding of Ch. timorensis in the subsurface of British Columbia, with only one specimen, and the author concluded, having in view the co-occurrence of the conodont Neogondolella bifurcata , that this suggests the Anisian.

In Arctic North America, Wardlaw & Jones (1980) reported the occurrence of Neospathodus timorensis in the Brooks Range, Alaska ( Fig. 3 /34), but the single illustrated specimen is of doubtful identity. It may be assigned to the Spathian conodont genus Borinella (Golding, pers. commun.).

In Arctic Europe, Nakrem et al. (2008) and Hounslow et al. (2008), in their attempt to elaborate an integrated biomagnetostratigraphic intercalibration of the Boreal and Tethyan timescales, reported the occurrence of a single specimen of Chiosella cf. timorensis in the lower Botneheia Formation in the Milne Edwardsfjellet section in central Svalbard ( Fig. 3 /35), the authors implying an early Anisian age by reference to Kçira, Albania and Deşli Caira, Romania sections.

As may be seen, the FO of the occurrences conodont species timoresis have been dated either as late Spathian (e.g., Nogami, 1968; Sweet et al., 1971; Kozur, 1972, 1974, 1975; Kozur & Mostler, 1974; McTavish, 1973, 1975; Goel, 1977; Collinson & Hasenmueller, 1979; Tian, 1982; Wang & Wang, 1983; Matsuda, 1983, 1985; Paull, 1988; Budurov & Sudar, 1995; Budurov & Trifonova, 1995), either as early Anisian (e.g., Sweet, 1970a; Koike, 1973; Budurov, 1976 a-b; Nicora, 1977; Kozur, 1980 a-b, 1989 a, 1999, 2003a-b; Gupta & Budurov, 1981; Chhabra, 1981; Gupta, 1983; Sweet, 1988; Mietto et al., 1991; Orchard, 1994 a, 1995; Orchard & Bucher, 1992; Orchard & Tozer, 1997a; Garzanti et al., 1995; Kozur et al., 1995; Krystyn et al., 2004; Wu G-C et al., 2007; Grădinaru et al., 2007; Orchard et al., 2007 a-b; Nicoll et al., 2007; Horacek et al., 2009; Gorter et al., 2019; Yao et al., 2011; Yan et al., 2015; Liang et al., 2016; Bai et al., 2017; Li M et al., 2018b; Zhang L et al., 2019a; Chen Y et al., 2020; Muto et al., 2020; Muto, 2021; Sue et al., 2021; Song et al., 2021; Kiliç, 2021; Ha et al., 2021; Chen A-F et al., 2021), or straddling the late Spathian-early Anisian boundary interval (e.g., Kemper et al., 1976; Koike, 1981; Igo & Koike, 1983; Sweet & Bergström, 1986; Lozovsky et al., 1989; Buryi, 1989; Budurov et al., 1989; Budurov & Trifonova, 1991, 1994; Nakazawa et al., 1994; Klets, 1995).

Also, one may observe that many conodont workers have changed through time their options with regard to the stratigraphic range of the conodont species timorensis . It is related either to the changing of the taxonomic interpretation of the timorensis versus gondolelloides or to the uncertainities in chronostratigraphic dating of the occurrences of these two conodont species. In most of the older reported occurrences, gondolelloides was placed in the synonymy of timorensis (e.g., Sweet, 1970 a, 1973; McTavish, 1973; Kozur, 1973b; Mirăuţă, 1974; Kemper et al., 1976; Matsuda, 1983; Assereto et al., 1980; Gaetani et al., 1992; Buryi, 1979, 1989; Budurov & Trifonova, 1994; Klets, 1995), or timorensis was placed in the synonymy of gondolelloides (e.g., Budurov, 1976b; Buryi et al., 1980; Budurov et al., 1983, 1985, 1987, 1988a-b, 1989; Budurov & Trifonova, 1991). This gives rise to uncertainties with regard to many of the older reported occurrences of the true conodont species timorensis .

Plasencia et al. (2013), based on a comprehensive revision of the Triassic conodont literature, found that the stratigraphic range of Ch. timorensis is from the late Spathian to the early Pelsonian. Qin et al. (2021) noted, like Buryi (1997), that in Sikhote-Alin, Far East Russia, Ch. timorensis has its youngest occurrences in the lower part of the Illyrian in the Shaiwa section, Guizhou, South China.

The above data cast major doubt on the defintion of the OAB by having the conodont species timorensis as a primary biotic proxy, and also with regard to its suitability as an index species to define an Aegean /lower Anisian Timorensis conodont zone. As the conodont species timorensis has its FO in the late Spathian and the HO in the lower part of the Illyrian, if the last is proved true, and having in view also its isolated occurrences, in most cases not properly tied chronostratigraphically to other index fossils, this conodont species has no credible potential to define the OAB.

One may conclude that Chiosella timorensis , in most cases having uncertain or controversial definitions, or having scarce or doubtful occurrences in many regions, is not qualified to be a primary biotic proxy for the base of the Middle Triassic Series. There is no unitary definition yet, unanimously accepted, of the condont species timorensis , whereas its stratigraphic range remains very diffuse.

Chiosella timorensis , a conodont species without a cosmopolitan occurrence

The known occurrences of the conodont species timorensis in Europe and Southwest Asia are all located in the western Tethys realm ( Fig. 4 /1-7), i.e., Chios Island, in Greece, Kçira, in Albania, Capelluzzo and Sosio, in Italy, Perşani Mts and Deşli Caira, in Romania, Gebze, in Turkey. Its occurrence in the Boreal realm of Europe ( Fig. 4 /35) is questionable.

In the western United States, the conodont species timorensis has confirmed occurrences in Nevada ( Fig. 4 /28), which was located at a low-latitude during the Triassic on the eastern rim of Panthalassa ( Orchard & Bucher, 1992). In northeast British Columbia, Canada ( Fig. 4 /31), the conodont species timorensis has a high-latitude North American craton-bounded occurrence. Its occurrence is reported also from the western Cordilleran allochthonous terranes of Canada ( Fig. 4 /32-33) and these were positioned at low-latitudes during the Triassic, being tectonically transported to higher latitudes during the Cenozoic oblique subduction of the Pacific oceanic plate under the North American continental plate ( Tozer, 1982; Silberling et al., 1984, 1992, 1997; Orchard, 1991). Orchard & Bucher (1992) underlined “ the relatively common occurrence of Chiosella in the accreted terranes may represent remanants of a fauna that was particularly widespread in low-latitudes ”, suggesting a ‘Tethyan’ affinity. Paull (1988, p. 602), when discussing Early Triassic diversity and paleoceanography, stated that the distribution of conodonts, with the Timorensis zone placed at the top of the Lower Triassic, is remarkable, with an equatorial span of about 20,000 km from the east Tethys embayment to western North America. In agreement with the Triassic paleogeographic reconstruction done by Tozer (1982), Paull (1988) noted that the west coasts of Pangaea were bounded by vast regions of scattered islands and shoals-suspect terranes “in waiting”, lying well offshore of what is present-day western North America, some 5,000 km south and westward into the open ocean.

The occurrence of the conodont timorensis in Boreal realm of North America is uncertain ( Fig. 4 /34). In Arctic Siberia the occurrence of the conodont species timorensis is not confirmed (see Sobolev & Klets, 2009).

In Central and East Asia, most occurrences of timorensis are reported from the Himalayan region, from South China, and from the Japanese Islands. Isolated timorensis occurrences are reported from Southeast Asia. Most of these regions were located in the eastern Tethyan realm, and were welded to Eurasia by the closure of the Paleo-Tethys (see Metcalfe, 1990 a-b, 1998, 2013; Wakita & Metcalfe, 2005; Hirsch et al., 2006; Ishida & Hirsch, 2011, fig. 11). The Japanese terranes with Triassic pelagic deep-sea cherts and shallow-marine atoll carbonates bearing timorensis occurrences ( Fig. 4 /19-20) originated from low-latitude and equatorial Panthalassa (see Matsuda & Isozaki, 1991; Hirsch & Ishida, 2002, fig. 5; Muto et al., 2018, fig. 1; Muto, 2021, fig. 1; Zhang L et al., 2019a, fig. 2), being tectonically accreted during the scraping-off process of ocean-derived materials at the Japanese convergent margin (e.g., Isozaki et al., 1990; Wakita & Metcalfe, 2005).

With regard to Far East Russia, it is to be noted that most of the regions where timorensis occurrences have been reported, although many of them are doubtful and not properly dated by ammonoid biostratigraphy, are in allochthonous terranes ( Nokleberg et al., 1994; Vishnevskaya & Filatova, 1994; Parfenov et al., 2009), which during the Triassic were positioned in low-latitudes in the eastern Panthalassa ( Fig. 4 /21-24), as documented by the occurrence of Monotis bivalves, conodonts, radiolarians, and of Rhabdoceras ammonoids ( Chekhov, 1982; Dagys et al., 1983; Bragin, 1991; Klets, 2008; Grădinaru & Sobolev, 2010). Liu K et al. (2021), based on detrital zircon U-Pb data and also on geochronological data, argued that in Sikhote-Alin different sedimentary rocks were juxtaposed by syn- and post-subduction sinistral displacements along the NE Asian continental margin during the late Mesozoic.

With regard to the occurrences of the conodont species timorensis in offshore Western Australia, McTavish (1975) and Nicoll (2002) placed the occurrences of Chiosella timorensis on the Gondwana margin of the Tethys Ocean ( Fig. 4 /27). Paleogeographically, the timorensis occurrence in offshore Western Australia, together with all occurrences in Oman ( Fig. 4 /8), Himalayan regions ( Fig. 4 /9-12), Malaysia ( Fig. 4 /17-18) and Timor ( Fig. 4 /25-26), some of them being positioned around south 300 latitude by McTavish (1975, fig. 36), were located mainly in the southern Tethys realm.

With regard to the provincialism in the geographic distribution of the Triassic conodonts, Huckriede (1958) was the first to note a distinction between faunas of the Alpine and Germanic Muschelkalk areas. Mosher (1968) added the western North America province, and underlined that connections between the Germanic Muschelkalk and western North American areas may have been either polar or to the southeast through the Tethys seaway.

Kozur & Mostler (1972) and Kozur (1973c, 1980b) distinguished three main faunal provinces, the Northern Boreal province, the Southern Boreal province and the Tethyan province between the former. Within the Tethyan main province several regional provinces were segregated, i.e., Nevadian, Asiatic, Dinaric, Austroalpine, West Mediterranean (= Sephardic) and Germanic, some of them having subprovinces. For the mentioned authors, the occurrences of the conodont species timorensis are confined only to the Tethyan province starting from Nevada through Japan, South China, Primorye, Southeast Asia, Timor, Western Australia, Tibet, and from Himalayas until the east of the Mediterranean region, with the occurrence from Chios, the only one known at that time (see Kozur, 1980b, fig. 1).

Matsuda (1985, fig. 3) identified two conodont faunal provinces in the Early Triassic “Tethys Realm”, namely the PeriGondwana Tethys Province (Kashmir, Salt Range, Spiti Himalayas, Dolpo and Thakkhola area of Nepal, the Mt. Everest area of Chinese side and western Australia) and the Tethys Province s.str. (Southern Alps, Transcaucasia, Iran, Afghanistan, South China, Malaysia, Japan and Sikhote-Alin), respectively. The author stated that the conodont assemblage of the N. timorensis Zone , which is dated as late Olenekian, is quite uniform in composition everywhere it is known, and it is found in Chios, Kashmir, Salt Range, Spiti, Nepal, Western Australia, Timor, South China, Japan and Nevada. Paull (1988, p. 600) noted that the Lower Triassic of the Western United States, with Timorensis zone at its uppermost part, includes representatives from both of Matsuda’s (1985) faunal provinces.

Hirsch & Ishida (2002), when discussing the origin of the pelagic carbonates and chert successions included in the accretionary complexes of the Japanese Islands, placed the oceanic Isanami Plateau at low-latitudes on the Izanagi Plate, having in view the Tethyan low-latitude confinement of the conodont Ch. timorensis occurrences. Kiliç et al. (2015) stated that environmental stress factors, among them thermal and trophic, caused decrease in size and morphological complexity of the conodonts during the Triassic. This may justify also the low-latitude confinement of the condont Ch. timorensis , as already stated by Hirsch & Ishida (2002).

Klets (2008, tab. 4) placed the occurrence of the Chiosella timorensis / gondolelloides group in the Tethys– Panthalassa super-realm, this including the southwestern United States, Greece, Japan, western Pakistan, India, Timor Island and China. With regard to Neospathodus (= Chiosella ) aff. timorensis , subsequently described as Ch. omulyovika Kopylova and Klets, 2008 , which was reported in the Zyryanka River Basin, Kolyma region by Klets & Kopylova (2008) and Konstatinov & Klets (2009), and placed in the Panboreal super-realm by Klets (2008), this is occurring in an allochthonous terrane that originated from low-latitudes in western Panthalassa. It must be noted, from Klets (2008) paleogeographic synthesis several occurrences of Chiosella timorensis are missing, such as those from Western Australia, Southeast Asia, or from Europe (Capelluzzo and Sosio, in Italy, Kçira, in Albania, and Deşli Caira, in Romania).

Chen Y-L et al. (2016) discussed Triassic conodont provincialism but without any reference to Chiosella timorensis .

As may be seen from the Fig. 4 , the genuine occurrences of the conodont species timorensis are confined during the Triassic within a region lying between the low-latitudes, eventually mid-latitudes, of the northern and southern hemispheres, starting from East Panthalassa until Western Tethys. Other known occurrences in the present-day high-latitudes of North America and Europe, also in Arctic Siberia and Far East Russia, are either unconfirmed or doubtful, or are in allochthonous terranes that were tectonically transported from low-latitudes to their present-day high-latitudes.

One may conclude, the conodont species timorensis cannot be used for dating and global correlation of the Triassic successions in regions outside the Tethys domain and Panthalassa. The distribution of other associated groups of fossils clearly demonstrates there existed a latitudinal paleoclimatic control in the distribution of the conodont species timorensis . On the other side, even in the Tethyan domain the distribution of the conodont species timorensis was facies controlled, and this may explain the diachronism of its first occurrence.

The GSSP candidates for the base of the Anisian, having the conodont Chiosella timorensis as a defunct primary biotic proxy

Following the recommendation of the International Commission of Stratigraphy to document the GSSP candidates for the standard chronostratigraphic units by significant biotic and physical events (see Gradstein et al., 2004, 2012, 2020; Lucas, 2018a), a plethora of articles has been focused on the biotic and physical events around the Olenekian-Anisian/Early-Middle Triassic boundary.

As for the biotic events, the conodont biostratigraphy received particular attention, with the desire to find suitable conodont taxa to be designated as biotic proxies for the Triassic standard chronostratigraphic boundaries. In the case of the base Aegean /lower Anisian/Middle Triassic boundary, after the early proposal made by Sweet (1970a) to introduce a Timorensis conodont zone although controversial with regard to the dating of the FO of the conodont species timorensis, Nicora (1977) and Assereto et al. (1980) made for the first time the formal proposal that the FAD of the conodont Gondolella timorensis Nogami, 1968 be used for the definition of the lower boundary of the Anisian in the Chios section, in Greece. However, Gaetani et al. (1992) underlined that in the Chios section the FAD of timorensis precedes the Aegean ammonoid FAD, and concluded that if the boundary is drawn on the base of ammonoids, timorensis FAD is latest Spathian in age. On this basis, Jacobshagen et al. (1993) concluded that the conodont argument of Assereto et al. (1980) should not be proposed as a biotic proxy for the base of the Anisian. During the Halle meeting of the STS (1998), it was decided to abandon the proposal made by Muttoni et al. (1994) of the Chios section as a GSSP candidate (cf. Gaetani, 2000).

Subsequently, Deşli Caira (Dobrogea, Romania) and Guandao (Guizhou Province, South China) have been formally nominated as GSSP candidates for the definition of the Early-Middle Triassic boundary by the International Commission on Stratigraphy, 2004, having as primary markers the near lowest occurrences of the ammonite genera Japonites , Paradanubites , and Paracrochordiceras , and of the conodont Chiosella timorensis , as primary markers, the proposed level being slightly below the base of a normal polarity magnetic zone (see Ogg, 2004), Subsequently, the Deşli Caira section became the first-ranked GSSP candidate, to which the Guandao and South Primorye sections are added as significant GSSP sections in the Geological Time Scale of the Triassic System, with the FAD of the conodont Chiosella timorensis or the base of magnetic normal polarity chronozone MT 1n as correlation events (see Gradstein et al., 2012, 2020; Ogg et al., 2014, 2016). It must be noted, nevertheless, that the conodont species timorensis is absent in the South Primorye section (see Zakharov et al., 2005 a-b).

In China, besides the Guandao section, promoted by Lehrmann et al. (2002, 2015a-b) and Orchard et al. (2007b), other localities in Guizhou Province, South China, e.g., Ganheqiao and Qingyan ( Yao et al., 2011), Wantou and Youping ( Ogg, 2019; Chen Y et al., 2020; Ogg et al., 2020 a-b) have been credited as potential GSSPs for the base of the Anisian. However, in the Guandao section the Olenekian-Anisian boundary is not demonstrated by an ammonoid record, as was recently noted once more by Tong et al. (2019). Like the Guandao section, all other Chinese sections recently proposed as potential GSSPs are also devoid of diagnostic ammonoids to fix the Olenekian-Anisian/Early-Middle Triassic boundary (see Yao et al., 2011, and Chen Y et al., 2020). In none of the Chinese sections the conodont biochronology and the FAD of the conodont species timorensis are not confidently tied to the ammonoid biostratigraphy around the Olenekian-Anisian/Early-Middle Triassic boundary, as ammonoid faunas are missing just in the interval boundary. Moreover, it must be underlined that the timorensis definition and the timorensis versus gondolelloides status in the Chinese publications are at odds with the current opinions of Goudemand et al. (2012). Although the data from Nevada clearly document the FAD of timorensis is in the latest Spathian ( Goudemand et al., 2012), the Chinese conodont workers still continue to pay credit to this conodont species as a primary biotic proxy for the OAB, and for this they are questioning even the adequacy of the ammonoid biostratigraphy to define this boundary. Tong et al. (2019, p. 9), amazingly, even questioned if the ammonoid Neopopanoceras haugi zone belongs to the late Spathian or rather to the early Anisian. This is only repeating an old, untenable assertion by Assereto et al. (1980) and Fantini Sestini (1981), as already shown above.

In spite of the undeniable data regarding the latest Spathian FAD of the conodont Chiosella timorensis , as fairly documented by Goudemand et al. (2012) and Ovtcharova et al. (2015), some authors (e.g., Ogg, in Gradstein et al., 2012; Lehrmann et al., 2015 a-b) still obsessively advocate that this conodont could be used as an index for the Olenekian-Anisian/Early-Middle Triassic boundary.

Recently, other authors like Yan et al. (2015), Liang et al. (2016), Bai et al. (2017), Li M et al. (2018b), Muto et al. (2018, 2019, 2020), Muto (2021), Zhang L et al. (2019a), Song et al. (2021) and Ha et al. (2021) continue to give credit to the conodont Ch. timorensis as a primary biotic index for the Olenekian-Anisian/Early-Middle Triassic boundary, in spite of the firm evidence that the FAD of Ch. timorensis is in the latest Spathian, as Goudemand et al. (2012) and Ovtcharova et al. (2015) already demonstrated.

Moreover, Orchard (2016) and Ogg et al. (2016, 2020ab), minimizing that the standard chronostratigraphic units in the Triassic timescale are primarily defined on ammonoid biostratigraphy, and not on conodont biostratigraphy, repetitively recommended that the ammonoid Neopopanoceras haugi Zone should be assigned to the Anisian, and this only with the desire to support furthermore the conodont Chiosella timorensis as a proxy for the Olenekian-Anisian boundary. The mentioned authors ignore that the ammonoid Haugi Zone is followed by the ammonoid Stevensi Zone in the latest Spathian of the western USA ( Monnet et al., 2013), and that both zones are correlatable to the late Spathian ammonoid Subrobustus Zone in the high-latitude Triassic chronostratigraphy in North America, Svalbard and Siberia.

Lastly, Muttoni et al. (2019) claimed the Kçira-A section in Albania has “excellent” potential as a candidate Global Boundary Stratotype Section and Point ( GSSP) for the Olenekian-Anisian boundary ( OAB), once again based on the FO of Chiosella timorensis . As already shown in the present paper, the GSSP candidate of the Albanian Kçira-A section is inadequate with regard to the ammonoid-conodont record around the Olenekian-Anisian boundary. As regards the chronostratigraphic significance of the FAD of Chiosella timorensis (= Gondolella timorensis Nogami, 1968 ), it was shown in the previous sections of the present paper that it has been for a long time influenced by the fact that the stratigraphic record of this conodont was not properly tied to or was misinterpreted with respect to the ammonoid biostratigraphy around the Olenekian-Anisian/Early-Middle Triassic boundary, and also by its disputable taxonomic interpretation.

The new acquired data on the ammonoid biochronology around the Olenekian-Anisian boundary in the low-latitude Triassic regions, such as in western United States ( Bucher, 1989; Guex et al., 2010), North Dobrogea, Romania ( Grădinaru & Gaetani, 2019) and the North Caucasus, Russia ( Shevyrev, 1995, 1996), may help to clarify the yet unresolved problems of the conodont biochronology around this boundary.

The recent refinement of the bed-by-bed ammonoid succession in the Deşli Caira section (Grădinaru, in Grădinaru & Gaetani 2019, fig. 2) clearly documents that the Olenekian-Anisian boundary is higher than was previously indicated by Grădinaru et al. (2002, 2006, 2007) and Grădinaru & Sobolev (2006). Based on the newlyacquired ammonoid data, the base Aegean is characterized by the FADs of the ammonoid genera Paracrochordiceras , Aegeiceras , Japonites , Stenopopanoceras and Grambergia , and other lower Anisian ammonoids. In particular, the new ammonoid record in the Deșli Caira section shows that the cladiscitids, whose chronostratigraphic location in the Chios section was not yet clear to Assereto et al. (1980) and Fantini-Sestini (1981), and on which these authors prompted their untenable assertions on the base of the Anisian, occur well below the Olenekian-Anisian boundary. As a result, the FAD of the conodont Chiosella timorensis in the Deşli Caira section is now well located below the presently ammonoid-documented Olenekian-Anisian boundary ( Fig. 5 ).

Golding (2021a), having in view the new ammonoid data in the Deşli Caira section that relocates the position of the Olenekian-Anisian boundary in this section (Grădinaru, in Grădinaru & Gaetani, 2019), re-examined the conodont taxonomy and biostratigraphy in the Deşli Caira section, Romania, which is the primary-ranked GSSP for OAB. He nominated new conodont taxa as potential biotic tools to be used in the recognition and correlation of the base of the Anisian Stage/Middle Triassic Series and having potential for more refined correlation of the lower Anisian between North America and Tethys.

In conclusion, the Deşli Caira section, which shares a very good potential for an adequate ammonoid-conodont biostratigraphy, preserves its first-ranked position as a GSSP candidate for the Olenekian/Anisian boundary, and thus for the Early Triassic/Middle Triassic boundary. The lowest occurrence ( LO) of the Paracrochordiceras - Aegeiceras ammonoid assemblage deserves to be a primary biotic event to define the base of the Anisian, whilst the LOs of the conodont species Neogondolella curva, Golding, 2012 and N. gradinarui, Golding, 2021 may be auxiliary biotic events to identify the base of the Anisian.

Figures

Fig. 3 - Present-day geographic distribution of the conodont Chiosella timorensis occurrences and basic references. A – Tethys-originating occurrences (1-18, 25-27); B – Panthalassa-originating occurrences (19-24, 28-33; C – Arctic occurrences, uncertain (34-35). Europe: 1 - Chios, Greece (Nicora, 1977; Assereto et al., 1980); 2 - Perşani Mountains, Romania (Mirăuţă & Gheorghian, 1978); 3 - Capelluzzo, Southern Apennines, Italy (Mietto et al., 1991); 4 - Sosio Valley, Sicilia, Italy (Kozur et al.,1995); 5 - Kçira, Albania (Muttoni et al., 1996, 2019); 6 - Deşli Caira, Romania (Grădinaru et al., 2007; Orchard et al., 2007a); Southwest Asia: 7 - Gebze, Turkey (Kiliç, 2021); 8 - Wadi Alwa, Oman (Orchard, 1994a); Himalayas: 9 - Salt Range, Pakistan (Sweet 1970a, 1973); 10 - Dolpo, west Nepal (Kovács & Kozur, 1980); 11 - Spiti, India (Krystyn et al., 2007; Sue et al., 2021); Garzanti et al., 1995); 12 - Kashmir, India (Chhabra, 1981; Matsuda, 1983); Central Asia: 13 - Southeastern Pamirs, Tajikistan (Bragin et al., 2016); Eastern Asia: 14 – Tulong and Dibucuo, Tibet (Tian 1982; Chen A-F et al., 2021; Wu G C. et al., 2007); 15 - South China, Guandao (Orchard et al., 2007b), Ganheqiao and Qingyan (Yao et al., 2011); 16 - South China, Wantou and Youping (Chen Y et al., 2020); Southeast Asia: 17 - Kodiang, Malaysia (Koike, 1973, 1982); 18 - Western Thailand (Kemper et al., 1976); Japanese Islands: 19 - Kamura and Taho attol carbonates, Kyushu Island and Shikoku Island (Hirsch & Ishida, 2002; Zhang L et al., 2019a; Ha et al., 2021); 20 - Honshu Island-pelagic chert (Muto et al., 2018; Muto, 2021); Far East Russia: 21 - Koryak Upland (Bragin, 1991); 22 - Zyryanka, Kolyma river; Klets (1998); 23 – Dalnegorsk, Sikhote-Alin (Buryi, 1989, 1997; Klets, 1995); 24 - Chernaya River, South Primorye (Buryi, 1979); Timor-Leste: 25 - Mount Lilu (Nogami, 1968); West Timor: 26 - Nifukoko (Orchard, 1994a); Western Australia: 27 - Carnarvon, Perth & Canning basins (McTavish, 1973; Nicoll et al., 2007; Gorter et al., 2019); Western United States: 28 - Northwestern Nevada (Collinson & Hasenmueller, 1978; Orchard, 1994a; Paull & Paull, 1998; Goudemand et al., 2012); 29 - Great Valley, California (Wardlaw & Jones, 1980); 30 - Sheep Creek, Idaho (Paull, 1988); Western Canada: 31 - Ursula Creek, British Columbia (Orchard & Tozer, 1997a); Subsurface British Columbia (Golding, 2014, 2021b); 32 - Quesnellia (Orchard & Tozer, 1997a); 33 - Stikinia (Orchard & Tozer, 1997a); Arctic North America: 34 - Brooks Range, Alaska (Wardlaw & Jones, 1980). Arctic Europe: 35 - Svalbard (Nakrem et al., 2008).

Fig. 4 - Paleogeographic distribution of the conodont Chiosella timorensis around the Olenekian-Anisian/Early-Middle Triassic boundary ( based on Map 48 from Scotese , 2014 ) : Numbers of figured occurrences are those from Fig. 3. A – Tethys occurrences; B – Panthalassa occurrences; C – Arctic occurrences, uncertain; D and E – primary location of allochthonous occurrences in Japanese Islands and Far East Russia, and their tectonic transport pathways. 1 - Chios, Greece; 2 - Perşani Mountains; 3 - Capelluzzo, Southern Apennines; 4 - Sosio Valley, Sicilia; 5 - Kçira , Albania ; 6 - Deşli Caira , Romania ; 7 - Gebze , Turkey ; 8 - Wadi Alwa, Oman; 9 - Salt Range, Pakistan; 10 - Dolpo, Nepal; 11- Spiti, India; 12 - Kashmir, India; 13 - Southeastern Pamirs , Tajikistan ; 14 – Tulong and Dibucuo , Tibet ; 15 - South China, Guandao, Ganheqiao, Qingyan; 16 -South China, Wantou and Youping; 17 - Kodiang, Malaysia; 18 - Western Thailand ; 19 - Kamura and Taho-attol carbonates ; 20 - Hon- shu Island-pelagic chert; 21 - Koryak Upland; 22 - Zyryanka, Kolyma river; 23 - Dalnegorsk, Sikhote-Alin; 24 - Chernaya River , South Primorye ; 25 - Mount Lilu , Timor-Leste ; 26 - Nifukoko, West Timor; 27 - Western Australia, Carnarvon, Perth & Canning basins; 28 - Northwestern Nevada ; 29 - Great Valley , California ; 30 - Sheep Creek , Idaho ; 31 - Ursula Creek and Subsurface British Columbia; 32 - Quesnellia; 33 - Stikinia; 34 - Brooks Range, Alaska; 35 - Svalbard .

Fig. 5 - Chronostratigraphic calibration and the Spathian-Aegean/Olenekian-Anisian/Early-Middle Triassic boundary in the Deşli Caira section, Romania. Conodont biochronology - (A) after Orchard et al. (2007a), and (B) after Golding (2021). The boundary is constrained by the ammonoid biochronology – (C) after Grădinaru, in Grădinaru & Gaetani (2019). Legend: 1 - thick-bedded limestone; 2 - ammonoid occurrence.