NATURAL ASSEMBLAGES OF HINDEODUS

CONODONTS FROM A PERMIAN–TRIASSIC

BOUNDARY SEQUENCE, JAPAN

by SACHIKO AGEMATSU1*, HIROYOSHI SANO2 and KATSUO SASHIDA1

1Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, 305-8572, Japan; e-mails: agematsu@geol.tsukuba.ac.jp,

sashida@geol.tsukuba.ac.jp2Department of Earth and Planetary Sciences, Kyusyu University, Fukuoka, 812-8581, Japan; e-mail: sano@geo.kyushu-u.ac.jp

*Corresponding author

Typescript received 11 October 2013; accepted in revised form 26 March 2014

Abstract: Hindeodus parvus and Hindeodus typicalis occur

in a deep-water chert and claystone section in the Mino

Terrane, Japan, which has been identified as a Jurassic

accretionary complex. Conodont fossils are preserved as

natural assemblages of impression fossils on bedding planes

in claystone. In this study, 13 assemblages of Hindeodus

species were recognized, comprising at most 13 elements

which generally maintain the original composition and

structure of an apparatus. We discriminated pairs of

carminiscaphate P1, angulate P2 and makellate M elements,

as well as a single alate S0 element and two digyrate and

four bipennate elements constituting the S array. Although

the digyrate and bipennate elements are preserved in the S2and S3–4 positions, respectively, a pair of S1 elements was

not found due to incompleteness in the natural assemblages.

The conodont biostratigraphy indicates that the lithological

boundary between chert and claystone units in the study

section corresponds exactly to the Permian–Triassic bound-

ary.

Key words: apparatus, conodont, Hindeodus, natural

assemblage, ozarkodinids, Triassic.

THE biotic turnover at the Permian–Triassic boundary

(PTB), the largest in Phanerozoic history, involved the

extinction of many members of Permian marine com-

munities (Sepkoski 1989). Numerous studies on shal-

low-marine sedimentary successions on the Pangaean

shelves of marginal Tethyan seas have clarified that

drastic palaeoenvironmental changes occurred during

this period (Payne et al. 2004; Knoll et al. 2007; Lehr-

mann et al. 2007; Bond and Wignall 2010; Korte and

Kozur 2010). These studies have greatly enhanced our

understanding of the environmental changes occurring

at the PTB. On the other hand, PTB environmental

crises in the Panthalassic Ocean are less well under-

stood than those in other regions, as most Permian

and Triassic sediments deposited on the Panthalassic

ocean floor were subducted, and survive only in accre-

tionary complexes in circum-Pacific regions (Sano et al.

2010). Moreover, although deep-water pelagic PTB

sequences have been reported from several Jurassic

accretionary complexes in Japan and New Zealand, the

base of the Triassic sections in some of these complexes

remains uncertain, mainly on account of poor age con-

trol and the presence of stratigraphic discontinuities.

Precise determinations of ages are necessary for correla-

tion between shallow-marine and deep pelagic succes-

sions.

In this work, we describe natural assemblages of the

conodont Hindeodus Rexroad and Furnish, 1964, pre-

served as moulds in a deep-water pelagic chert–clay-stone sequence. The earliest Triassic species of

Hindeodus have been increasingly studied since the late

1990s on account of their stratigraphic significance.

However, little is known about these species, because

most studies have been based only on their Pa ele-

ments. Our material, which includes the species Hindeo-

dus parvus (Kozur and Pjatakova, 1976), is based on

specimens preserving the original compositions of the

elements of earliest Triassic Hindeodus species. Con-

odonts often cannot be isolated from the enclosing sed-

iment by acid dissolution. In addition, it seems likely

that deep-water pelagic rocks (cherts, siliceous shales,

siliceous claystones, etc.) generally yield fewer discrete

conodont elements than do shallow-marine rocks (e.g.

limestones). However, in recent years, an increasing

number of bedding plane conodont assemblages have

been reported from pelagic siliceous rocks (Tolmacheva

and Purnell 2002; Koike et al. 2004; Agematsu et al.

2008).

© The Palaeontological Association doi: 10.1111/pala.12114 1

[Palaeontology, 2014, pp. 1–13]

GEOLOGICAL SETTING

In this study, conodont specimens were found in rocks of

the Mino Terrane, a Jurassic accretionary complex in

central Japan (Fig. 1). Wakita (1988) classified the accre-

tionary rocks in the Mino Terrane into two tectonostrati-

graphic units: the coherent units are characterized by

Lower Triassic to Upper Jurassic or lowermost Cretaceous

deep-water sequences characteristic of an oceanic plate

stratigraphy, and the m�elange units comprise various-

sized slabs and blocks of Permian to Jurassic oceanic

rocks in a matrix of Jurassic to lowest Cretaceous mud-

stone. The siliceous rocks that we examined correspond

to the upper part of the Hashikadani Formation, a com-

ponent of the Funabuseyama Unit, which has been identi-

fied as a Middle Jurassic m�elange unit in the Mino

Terrane (Wakita 1988). The Hashikadani Formation,

which was first identified by Sano (1988) and was recently

emended by Kuwahara et al. (2010), consists of a basal

unit of basaltic rocks with hotspot affinities (Jones et al.

1993), followed by a thick succession of bedded cherts

containing redeposited shallow-marine carbonates at sev-

eral levels. The bedded cherts yield Early–latest Permian

radiolarians. The uppermost part of the chert succession

consists of uppermost Permian to upper Lower Triassic

cherts, grey siliceous claystones and black claystones. The

PTB section, tagged as the NF1212R section in this study,

exactly corresponds to section NE1212R of Sano et al.

(2010).

The NF1212R section is a stratigraphically continuous

succession divided into lower, middle and upper units

(Fig. 1). The lower unit, which comprises grey bedded

chert, is overlain by a middle unit of dark grey to black

chert and a weathered pyrite-rich layer. The upper unit

consists of intermittent layers of black claystone with thin

dark grey to black chert beds, 1–5 cm thick. The three

units, which are 1.7, 0.9 and 1.2 m thick, respectively, rest

conformably on one another, without any outstanding

stratigraphic disruption. Neither coarse terrigenous grains

nor volcanic materials have been observed in the section.

Microscopic observations reveal that the black claystone

of the upper unit consists of clay minerals, cryptocrystal-

line quartz and extremely fine-grained carbonaceous mat-

ter, with small amounts of flattened radiolarians and

pyrite grains. Thin chert beds in this unit are chiefly com-

prised of radiolarian tests and yield Mesozoic-type radio-

larian fossils (Sano et al. 2010).

MATERIALS AND METHODS

To examine the conodont biostratigraphy, we collected

six black claystone samples from the upper unit of the

study section (Fig. 1). The stratigraphic levels of samples

NF1212R-52 and NF1212R-q were 5 and 15 cm above the

base of the upper unit, respectively. Slightly siliceous lay-

ers accompanying the chert beds, located 65, 80

and 100 cm above the base of the upper unit, were

also sampled (samples NF1212R-53, NF1212R-54 and

NF1212R-55, respectively). Sample NF1212R-56 is a black

claystone collected 110 cm above the base of the upper

unit. The fieldwork required discreet sampling because of

the brittleness and weakness of the claystone. Siliceous

rocks such as chert, shale and mudstone are usually pro-

cessed using hydrofluoric acid; however, the acid extrac-

tion procedure did not yield any microfossils from these

samples. Therefore, we used the ‘classic’ approach of

direct observations of surface exposures.

We aligned the claystones on a desk and split them

into thin slips. We used a binocular microscope to

observe the surfaces of the slips and continued the work

until the slip decreased in size to small chips, 1–3 mm

thick. Conodont elements, present in extremely fine-

grained materials, were observed in the chips. Most of the

specimens were impression fossils, with corresponding

hard parts likely lost due to diagenetic processes. The

chips were mostly black, but some contained white inclu-

sions approximately 5 mm in diameter. Some moulds

A

B

F IG . 1 . Summary of the study section. A, index map. B, litho-

logical column with conodont horizons.

2 PALAEONTOLOGY

retained brown residual material in their depressions,

which appeared to be the remains of elements (Fig. 2).

The impressions were recorded using a scanning electron

microscope (SEM; JEOL JSM 5500) and a digital micro-

scope (Keyence VHX-2000; Figs 2–5). Because the data

obtained from the SEM and digital microscope were two-

dimensional digital images, it is quite likely that any addi-

tional elements hidden under a visible mould would not

be recognized in the images.

Moulds of conodont elements were present in four

samples: sample NF1212R-52 contained eight natural

assemblages, several isolated carminiscaphate, digyrate, bi-

pennate and alate elements that were not associated with

any other elements, and a small number of element frag-

ments; sample NF1212R-q yielded five assemblages; and

samples NF1212R-54 and NF1212R-56 included a few

isolated carminiscaphate elements. Most of the moulds

were deeply pressed into the claystone and were slightly

deformed, but were sufficiently well preserved to enable

identification of two species: two assemblages of H. par-

vus and two of Hindeodus typicalis (Sweet, 1970a). The

other seven assemblages were classified as Hindeodus spp.

The number of elements in each assemblage varied from

6 to 13. As mentioned below, all specimens in the natural

assemblages were preserved in juxtaposition to the origi-

nal elements of the conodonts’ bodies, although they dif-

fered in their completeness of preservation. Furthermore,

none of the assemblages contained elements that were

representative of two or more conodont apparatuses.

Rather, some of the specimens were nearly ideal natural

assemblages, except that they lacked some elements pres-

ent in the well-known Ozarkodinida skeletal plan (Purnell

et al. 2000). The absence of some elements from the

assemblages may be due to element superposition or bur-

ial in the claystone; however, these possibilities cannot be

tested. Another possibility for the absence of some ele-

ments is that the conodont was captured by a predatory

animal and excreted as faecal pellets; in this case, some

apparatuses may have been broken into pieces, while

others were maintained, to some degree, in their original

arrangements.

APPARATUS COMPOSITION

The composition and three-dimensional architecture of

the oral apparatus in conodonts have been demonstrated

in only a few taxa. One of these taxa is represented by

the ozarkodinid skeletal plan (Aldridge et al. 1987; Ald-

ridge et al. 1995; Purnell and Donoghue 1998; Aldridge

et al. 2013). The 15-element apparatus plan proposed by

Purnell and Donoghue (1998) comprises four P, two M

and nine S elements, which is a template common to

several groups with morphologically complex elements,

including the Prioniodontida group (Stouge and Bagnoli

1988; Purnell 1993; Aldridge et al. 1995; Purnell and

Donoghue 1998; Repetski et al. 1998; Tolmacheva and

Purnell 2002; Donoghue et al. 2008). Based on the previ-

ously described natural assemblages of ozarkodinid con-

odonts, it is reasonable to suppose that all taxa belonging

to the ozarkodinids possess the 15-element plan (Aldridge

et al. 1987; Purnell and Donoghue 1998; Orchard and

Rieber 1999; Koike et al. 2004; Goudemand et al. 2012).

Conodonts identified as Hindeodus were present from the

early Carboniferous to the earliest Triassic (Sweet 1977,

1988). Sweet (1977) and Sweet and Clark (1981)

reconstructed the multielement apparatus of Hindeodus as

‘seximembrate’ with anchignathodontiform Pa, ozarko-

diniform Pb, digyrate M, alate Sa, digyrate Sb and

bipenniform Sc positions. Although the Hindeodus appa-

ratus was controversial for many years, the 2P-1M-9S

composition appears to be widely accepted (Sweet 1988;

Donoghue et al. 2008).

Here, we follow Purnell et al. (2000) in the use of

locational notation and terms of orientation of the appa-

ratus. By convention, terms for the directions of ele-

ments are written using quotation marks, to distinguish

these directions from biological orientations (Purnell

et al. 2000). Each assemblage in this study contains 13

elements at most: paired carminiscaphate, angulate and

makellate forms, single alate elements without a ‘poster-

ior’ process, a pair of digyrate elements and two pairs of

bipennate elements. The carminiscaphate element shows

morphological variations that differentiate Hindeodus

species.

Specimen EES-ag0001 comprises 13 elements whose

arrangement exhibits approximately bilateral symmetry.

In Figure 3, two makellate elements lie on the ‘anterior’

side of the assemblage. One pair of digyrate and two

pairs of bipennate elements, located between the makel-

late elements, are juxtaposed, and their ‘outer lateral’

or ‘posterior’ processes are oriented on the ‘posterior’

sides of the assemblage. One digyrate and two bipen-

nate pairs are aligned from the median region out-

wards. A pair of angulate elements facing each ‘oral’

margin is set in the middle of the digyrate and bipen-

nate array. At the ‘posterior’ end of the assemblage,

two carminiscaphate elements are engaged by their

cusps and denticles.

Sample EES-ag0004 is a natural assemblage consisting

of 12 elements (Fig. 4). A mass of ‘ramiform’ elements,

located in the ‘anterior’ part of the assemblage, contains

an alate, two digyrate, three bipennate and two makellate

elements. In the middle and ‘posterior’ parts of the

assemblage, pairs of angulate and carminiscaphate ele-

ments are placed, respectively.

Specimen EES-ag0003 comprises 13 elements (Fig. 2).

Two makellate elements lie on the ‘anterior’ side of the

AGEMATSU ET AL . : NATURAL ASSEMBLAGE OF HINDEODUS FROM JAPAN 3

A

C D

B

4 PALAEONTOLOGY

assemblage. An alate, six digyrate or bipennate and two

angulate elements are assembled in the middle part. Two

carminiscaphate elements are located on the ‘posterior’

side of the assemblage, their cusps and denticles closed

on one another.

Specimen EES-ag0006 is another 13-element assem-

blage (Fig. 5). In the ‘anterior’ portion of the assemblage,

we can recognize a makellate pair, arrays of two digyrate

and four bipennate elements, a single alate element and

two angulate elements. Two carminiscaphate elements

overlap one another at the ‘posterior’ end of the assem-

blage.

In summary, the arrangements of the elements in each

specimen appear to represent natural assemblages; they

maintain a certain orientation along a rostral–caudal axis.The ‘anterior’ and ‘posterior’ sides of each assemblage

(Figs 2–5) generally correspond to the rostral and caudal

directions, respectively. Makellate elements are usually

located on the rostral side in pairs and are thus com-

pared with the M position. Digyrate and bipennate ele-

ments, which gather, overlap and, in some assemblages,

arrange their processes, are correlated with the S1 to S4positions. We distinguished at most two digyrate and

four bipennate elements (Fig. 3), which disagrees with

C

A

D

B

F IG . 3 . Natural assemblages of Hindeodus parvus. Collection number EES-ag0001, sample horizon NF1212R-52. A–B, SEM photo-

graphs of part and counterpart of the specimen. C–D, outline drawing of the specimen. Scale bar represents 0.2 mm.

F IG . 2 . Natural assemblages of Hindeodus parvus. Collection number EES-ag0003, sample horizon NF1212R-q. A–B, digital micro-

scopic photographs of part and counterpart of the specimen. C–D, outline drawing of the specimen. Scale bar represents 0.2 mm.

AGEMATSU ET AL . : NATURAL ASSEMBLAGE OF HINDEODUS FROM JAPAN 5

the ozarkodinid architecture that contains pairs of S1 to

S4 elements. It is likely that this difference is caused by a

superposition or burial of elements, as mentioned above.

Bipennate elements are located on the outermost posi-

tions of the S array in specimen EES-ag0001 (Fig. 3).

Moreover, in some taxa of ozarkodinid, elements in the

A B

C D

F IG . 4 . Natural assemblages of Hindeodus parvus. Collection number EES-ag0004, sample horizon NF1212R-q. A–B, SEM photo-

graphs of part and counterpart of the specimen. C–D, outline drawing of the specimen. Scale bar represents 0.2 mm.

6 PALAEONTOLOGY

S3 and S4 positions are morphologically similar. There-

fore, alignment of one pair of digyrate and two pairs of

bipennate elements can be assigned to the S2 and S3–4sites, respectively. The existence of a fourth element (of

the S-series) occupying the S1 position remains contro-

versial. A single alate element corresponds to the S0 posi-

tion. Both angulate and carminiscaphate elements occupy

the P positions. The fact that the carminiscaphate pair is

located on the most caudal side and that the angulate

pair occurs near the S array in all assemblages supports

C D

A B

F IG . 5 . Natural assemblages of Hindeodus typicalis. Collection number EES-ag0006, sample horizon NF1212R-q. A–B, SEM photo-

graphs of part and counterpart of the specimen. C–D, outline drawing of the specimen. Scale bar represents 0.2 mm.

AGEMATSU ET AL . : NATURAL ASSEMBLAGE OF HINDEODUS FROM JAPAN 7

the conclusion that the former is in the P1 position and

the latter in the P2 position (Fig. 6).

BIOSTRATIGRAPHY ANDPALAEOENVIRONMENT

Hindeodus parvus is the index fossil of the H. parvus

zone, which corresponds to the lowermost Induan (lower

Lower Triassic); moreover, it is widely accepted that the

first appearance of H. parvus defines the PTB (Yin et al.

2001). Thus, the presence of H. parvus in samples

NF1212R-52 and NF1212R-q clearly defines these hori-

zons as Induan in age. Sano et al. (2010) reported radi-

olarians that characterize the uppermost Permian

Neoalbaillella optima zone (Ishiga 1986; Kuwahara et al.

1998) from the lower and middle units of the study sec-

tion. Therefore, we define the stratigraphic position of the

PTB as the base of the black claystone beds of the upper

unit.

As stated above, the Hashikadani Formation is mainly

made up of basalt, chert and claystone and is thought to

have been deposited on the lower slopes of a mid-oceanic

seamount (Sano et al. 1992, 2010). The PTB section in the

study area is considered to have accumulated in a mid-

Panthalassan pelagic setting without inputs of land-derived

or volcanic matter. The black bedded chert of the middle

unit sharply changes into the black claystone of the upper

unit, which is intercalated with several chert layers. These

lithological transitions indicate that a radiolarian popula-

tion was suddenly extinguished at the PTB in the waters in

which the Hashikadani Formation was deposited and that

over a long period of time, the environment briefly and

occasionally recovered (as evidenced by the occasional

chert layers in the claystone). Throughout the interval

when only clay minerals and carbonaceous materials accu-

mulated in this environment, conodonts and a small num-

ber of radiolarians were the only organisms recorded in

the sediments. Other conodont genera, such as Neogondol-

ella Bender and Stoppel, 1965, which are included in many

peri-Pangaean shallow-marine PTB sequences, do not

occur in the study section.

The PTB conodont faunas and palaeoenvironments have

been divided into a hindeodid-dominated shallow-marine

facies and a neogondolellid-dominated deeper-marine

facies (Wang 1996; Mei et al. 1998; Jiang et al. 2007; Chen

F IG . 6 . The apparatus composition of Hindeodus parvus and Hindeodus typicalis.

8 PALAEONTOLOGY

et al. 2009; Metcalfe and Isozaki 2009; Metcalfe 2012). Lai

et al. (2001) investigated the relationship between these

faunas and lithofacies in the Meishan and other PTB sec-

tions in detail and proposed the following palaeoecological

model: the hindeodid conodonts were pelagic taxa and

exhibited a wide facies tolerance, while the neogondolellid

conodonts were deeper-water nektobenthic taxa that were

restricted to oxygenated environments. It is certain that

Hindeodus dwelled in a pelagic ocean, such as the mid-Pan-

thalassic (Sano et al. 2010). If the natural assemblages in

this study are not inclusions of faecal pellets, there is a fair

possibility that Hindeodus was the only animal that would

have lived near a mid-oceanic seafloor and that exhibited a

dynamic behaviour, migrating between epipelagic environ-

ments and meso- or bathypelagic oceans. On the other

hand, if our specimens are in fact inclusions of faecal pel-

lets, it is possible that Hindeodus exhibited a prey–predatorrelationship with a shallower-marine animal that is

unknown from pelagic PTB sections.

CONCLUSION

The earliest Triassic conodonts H. parvus, H. typicalis

and Hindeodus spp. are described in the PTB siliceous

rock sequence in the Hashikadani Formation of the Mino

Terrane, Japan. The natural assemblages of these species

were preserved when the bodies of individual conodonts

were buried directly in seafloor sediments, or were buried

as inclusions in the faeces of a predatory animal. We rec-

ognized pairs of carminiscaphate P1, angulate P2 and

makellate M elements, a single alate S0 element, and S-

series elements consisting of a pair of digyrate and two

pairs of bipennate elements. Digyrate elements occupy

the S2 position, and bipennate elements occupy the S3and S4 positions, but a pair of S1 elements was not

found, most likely due to incompleteness of the assem-

blages. The PTB section in the study section consists of

chert and siliceous claystone beds. Based on these litholo-

gies, the depositional environment of the study section is

interpreted as the lower slope of a seamount in the pela-

gic realm of the Panthalassa Ocean. There is no sign of

life in the lowermost Triassic strata, except for Hindeodus

conodonts and sparse radiolarians. We conclude that

Hindeodus may have been the only animal that dwelt

near the mid-ocean seafloor, or that some shallow-marine

animals, such as other conodonts, preyed on Hindeodus

at that time.

SYSTEMATIC PALAEONTOLOGY

All specimens described here are deposited at the Gradu-

ate School of Life and Environmental Sciences, University

of Tsukuba, with the prefix EES. The original sample

materials are also housed in the University.

Order OZARKODINIDA Dzik, 1976

Genus HINDEODUS Rexroad and Furnish, 1964

Type species. Hindeodus cristulus (Youngquist and Miller, 1949),

from the Carboniferous of south-central Iowa, USA.

Revised diagnosis. The paired P1 positions are occupied

by carminiscaphate forms with a morphological variation

that is distinctive among Hindeodus species. Angulate and

makellate pairs occupy the P2 and M positions, respec-

tively. The alate element without a posterior process is

assigned to the S0 position. Digyrate and bipennate ele-

ments occupy the S1–2 and S3–4 sites, respectively.

Remarks. The apparatus concept of Sweet (1977) and

Sweet and Clark (1981) is confirmed. Sweet (1977) men-

tioned that discrimination of Hindeodus species must

involve consideration of all elements in its skeletal appara-

tus, as well as P positions. According to von Bitter and

Merrill (1985), however, the Hindeodus apparatus is

monotonous, without any outstanding features, and this

monotony makes species distinctions difficult. Conodonts

belonging to this genus rapidly differentiated into more

than 10 species during latest Permian to earliest Triassic

time (Kozur 1996, 2004; Angiolini et al. 1998; Orchard and

Krystyn 1998; Nicoll et al. 2002; Perri and Farabegoli 2003;

Orchard 2007; Chen et al. 2009; Metcalfe 2012). This rapid

evolution has been discussed, based on the morphology of

the P1 elements. On the other hand, description of the

other elements has progressed slowly. Nicoll et al. (2002),

who reported four new species of latest Permian and earli-

est Triassic Hindeodus, noted that identification of S ele-

ments was not possible, although some samples contained

abundant S elements. In this study, we cannot describe and

compare the M and S elements of different Hindeodus spe-

cies in detail, but we agree with the thinking that element

morphology in the M and S positions is quite conservative,

at least during the latest Permian to earliest Triassic.

Hindeodus parvus (Kozur and Pjatakova, 1976)

Figures 2–4

Multielement

1975 Anchignathodus parvus Kozur and Pjatakova; Kozur,

p. 7–9, pl. 1, figs 17, 19, 20, 22 (= P1), 21 (= S3–4),

23(= M).

AGEMATSU ET AL . : NATURAL ASSEMBLAGE OF HINDEODUS FROM JAPAN 9

1976 Anchignathodus parvus Kozur and Pjatakova, p.

123, 124, pl. 1, figs a–e (= P1), g (= M), h (= S3–4).

1995 Hindeodus parvus (Kozur and Pjatakova); Kozur, p.

69, 70, pl. 2, figs 4, 6, 9, 13 (= P1); pl. 3, figs 1–4

(= P1), 5 (= M), 6 (= S1–2), 7 (= P2), 8 (= S3–4).

1995 Hindeodus parvus (Kozur and Pjatakova); Kozur,

Ramov�s, Wang and Zakharov, p. 206, 207, pl. 1,

figs a, b, g (= P1), e (= S1–2).

1996 Hindeodus parvus (Kozur and Pjatakova); Kozur,

p. 94–96, pl. II, figs 5–8 (= P1); pl. III, figs 1–3, 9,

11 (= P1), 4 (= S0), 5 (= M), 6, 10 (= S1–2), 7

(= P2), 8 (= S3–4); pl. IV, figs 5–7 (= P1).

P1 element

1975 Anchignathodus parvus Kozur and Pjatakova; Kozur,

Mostler and Rahimi-Yazd, p. 4, pl. 1,

figs 6, 13–15 (non fig. 12); pl. 7, figs 7, 9.

1981 Hindeodus parvus (Kozur and Pjatakova); Matsuda,

p. 91–93, pl. 5, figs 1–3.

1994 Isarcicella? parva (Kozur and Pjatakova); Orchard,

Nassichuk and Rui, p. 833, pl. 1, fig 2; pl. 2, figs 5–7.

1998 Hindeodus parvus (Kozur and Pjatakova); Orchard

and Krystyn, p. 351, 352, pl. 6, figs 9, 16, 17, 20.

2002 Hindeodus parvus (Kozur and Pjatakova); Nicoll,

Metcalfe and Wang, p. 628, figs 15, 16.

2003 Hindeodus parvus (Kozur and Pjatakova); Perri and

Farabegoli, p. 294–295, pl. 2, figs 4–12.

2004 Hindeodus parvus (Kozur and Pjatakova); Kozur, p.

51, 52, pl. 1, figs 3, 5–9.

2006 Hindeodus parvus (Kozur and Pjatakova); Aljinovic,

Kolar-Jurkov�sek and Jurkov�sek, p. 46, 47, pl. 1, fig. 6.

2009 Hindeodus parvus erectus (Kozur, 1996); Chen,

Beatty, Henderson and Rowe, p. 452, 453,

fig. 10:1–19, fig. 11:1–5.

2009 Hindeodus parvus parvus (Kozur and Pjatakova);

Chen, Beatty, Henderson and Rowe, p. 452, 453,

fig. 10:1–19, fig. 11:1–5.

Material. Four natural assemblages: EES-ag0001–0004.

Description. The carminiscaphate P1 elements in our specimens

are characterized by the largest distal denticle being on an ‘ante-

rior’ process, which is 1.8–2.1 times as high as the other small

denticles (which are of equal size and height, except for one or

two denticles on the ‘posterior’ edge). The basal cavity expands

‘laterally’ at a ‘posterior’ half of the unit and tips towards a

cusp, which is a denticle located just behind the largest terminal

denticle. The P2 element is angulate, with a long robust cusp

and a relatively long ‘posterior’ process carrying short delicate

denticles. The makellate M element has a slender cusp, the den-

ticulate ‘outer lateral’ process and anticusp. The S0 element is a

symmetrical alate element without a ‘posterior’ process. The

digyrate S2 element has relatively long ‘inner lateral’ and ‘outer

lateral’ processes that form a 90 angle in ‘oral’ view. The S3 and

S4 forms are bipennate and have short ‘anterior’ and long ‘pos-

terior’ processes. The S1 form is not recognized in this study.

Occurrence. This species has been reported worldwide in the

lowest Triassic H. parvus zone. In this study, natural assemblages

occur in the lowermost 10 cm of the black claystone beds in the

study section, which is located in the upper part of the Hashika-

dani Formation in the Funabuseyama Unit of the Mino Terrane.

Hindeodus typicalis (Sweet, 1970a)

Figure 5

Multielement

1977 Hindeodus typicalis (Sweet); Sweet, p. 223, 224, pl.

2, figs 1 (= P1), 2 (= M), 3 (= P2), 4 (= S0), 5

(= S3–4), 6 (= S1–2).

P1 element

1970a Anchignathodus typicalis Sweet, p. 7–8, pl. 1,

figs 13, 22.

1970b Anchignathodus typicalis Sweet; Sweet, p. 222–223,

pl. 1, figs 13, 20.

1987 Hindeodus typicalis (Sweet); Perri and Andraghetti,

p. 308, pl. 32, figs 1, 2.

1995 Hindeodus typicalis (Sweet); Kozur, 65, 66, pl. 1,

figs 1, 3, 4.

1998 Hindeodus typicalis (Sweet); Orchard and Krystyn,

p. 354, pl. 6, figs 14, 18, 19, 25, 26.

2003 Hindeodus typicalis (Sweet); Perri and Farabegoli, p.

296.

2004 Hindeodus typicalis (Sweet); Kozur, p. 52, pl. 2, figs

10, 11; pl. 3, figs 20, 22; pl. 5, figs 6, 9–11.

2007 Hindeodus typicalis (Sweet); Kozur, p. 52, pl. 2, figs

10, 11; pl. 3, figs 20, 22; pl. 5, figs 6, 9–11.

2009 Hindeodus typicalis (Sweet); Chen, Beatty, Hender-

son and Rowe, p. 453, 454, text-figs 9:4–9:6.

Material. Two natural assemblages: EES-ag0005 and 0006.

Description. The carminiscaphate form of the P1 element is

characterized by a long blade with a large, but not particularly

high, distal denticle on an ‘anterior’ process and nine or more

smaller denticles, which gradually decline in height towards the

‘posterior’ end. The cusp is located next to the largest anterior

denticle. The other elements in the apparatus are quite similar

in shape to those of H. parvus.

Occurrence. Hindeodus typicalis has been discovered in Middle

Permian to Lower Triassic strata worldwide. In this study, natu-

ral assemblages were observed in the lowermost 10 cm of the

10 PALAEONTOLOGY

black claystone beds in the study section, which are located in

the upper part of the Hashikadani Formation in the Funabusey-

ama Unit of the Mino Terrane.

Acknowledgements. We are much indebted to R. J. Aldridge, M. A.

Purnell and two anonymous reviewers for reading our manuscript

and offering useful suggestions. We also thank A. Yao and K. Ku-

wahara for comments on radiolarians. This work was supported

by Grants-in-Aid for Scientific Research (no. 21740368) to SA.

Editor. Imran Rahman

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