Natural assemblages of Hindeodus conodonts from a Permian-Triassic...
Transcript of Natural assemblages of Hindeodus conodonts from a Permian-Triassic...
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: [email protected],
[email protected] of Earth and Planetary Sciences, Kyusyu University, Fukuoka, 812-8581, Japan; e-mail: [email protected]
*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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