ARTICLE

Memoir of the Fukui Prefectural Dinosaur Museum 18: 1–20 (2019)© by the Fukui Prefectural Dinosaur Museum

ICHNOTAXONOMIC REVISION OF DINOSAUR TRACKS FROM THE
LOWER CRETACEOUS TETORI GROUP, JAPANYuta TSUKIJI , Yusuke SAKAI and Yoichi AZUMA
1

1

2

1, 3

Fukui Prefectural Dinosaur Museum, 51-11 Terao, Muroko, Katsuyama, Fukui 911-8601, Japan
2 Ono City Board of Education, 1-1, Tenjincho, Ono 912-8666, Japan
3
Institute of Dinosaur Research, Fukui Prefectural University, 4-1-1 Kenjojima,Matsuoka, Eiheiji, Fukui 910-1195, Japan

ABSTRACT

Recently, ichnotaxonomic description and comparison of dinosaur tracks were developed by objective andquantitative analyses using three-dimensional digital data. However, many dinosaur tracks from the Tetori Groupdiscovered in the 1990’s were described on the basis of classical methods. We developed ichnotaxonomic
descriptions for 14 dinosaur tracks from the Tetori Group in the Kuzuryu and Shiramine areas from objective andquantitative analyses. Our assessments of the 14 tracks identified five theropods and seven iguanodontids as
trackmakers. Ichnotaxonomic comparisons show that the theropod tracks include the ichnofamilies Grallatoridae andEubrontidae, and the iguanodontid tracks include the ichnogenera Caririchnium and Amblydactylus. The Tetori
Group has yielded dinosaur tracks from at least three different horizons, and we subdivided this ichnoassemblage into
the Itsuki, Akaiwa, and Kitadani dinosaur ichnofauna on the basis of the depositional age. These dinosaur
ichnofaunas are dominated by theropods and iguanodontids; however, the ichnofaunal diversity of the Itsuki dinosaur
ichnofauna is lower than those of the Akaiwa and Kitadani dinosaur ichnofaunas. This difference is probably related
to depositional environments.
Key words: dinosaur track, Tetori Group, Lower Cretaceous, ichnotaxonomy, Kuzuryu area, Shiramine area
築地祐太・酒井佑輔・東洋一（2019）下部白亜系手取層群から産出した恐竜足跡化石の生痕化石分類学的な再検討．福井県立恐竜博物館紀要 18：1‒20.
近年，恐竜足跡化石の生痕化石分類学的な記載や比較は，3 次元デジタルデータを用いた客観的・定量的な手法によって発展してきた．しかし，1990 年代に手取層群から発見された恐竜足跡化石の多くは，古典的な手法のみに基づいて記載されている．本研究では，近年の手法を用いて九頭竜および白峰地域の手取層群から産出した 14 点の恐竜足印化石の生痕化石分類学的な再検討を行った．再検討の結果，5 点の獣脚類 と 7 点 の イ グ ア ノ ド ン 類 の 足 印 化 石 が 再 同 定 さ れ た．ま た，獣 脚 類 の 足 跡 化 石 に は 生 痕 化 石 科
Grallatoridae と Eubrontidae が 含 ま れ，イ グ ア ノ ド ン 類 の 足 跡 化 石 に は 生 痕 化 石 属 Caririchnium とAmblydactylus が含まれることが分かった．手取層群から産出する恐竜足跡化石は，少なくとも 3 つの層準から産出しており，本研究ではそれらを堆積年代に基づいて，伊月・赤岩・北谷恐竜生痕化石動物群に細分した．これらの生痕化石動物群は，獣脚類とイグアノドン類が優勢なことで特徴づけられるが，伊月恐
竜生痕化石動物群は赤岩・北谷恐竜生痕化石動物群に比べ多様性が低い．これは，堆積環境の違いによるものと考えられる．

INTRODUCTION

depiction of dinosaur tracks was done by photos or illustrations
drawn by researchers or professional artists, but there could be
differences on the illustrations of the same specimens (Arakawa
et al., 2002).
Many dinosaur tracks were reported from several localities of
the Lower Cretaceous Tetori Group in the 1990s (Manabe et al.,
1989; Kunimitsu et al., 1990; Azuma and Takeyama, 1991;
Azuma et al., 1992; Kojima et al., 1992). Among them wereseveral dinosaur tracks from the Kuzuryu and Shiramine areas
described and illustrated by different researchers (Azuma and
Takeyama, 1991; Lockley and Matsukawa, 1998). Azuma andDetailed morphological examination of dinosaur tracks is themost basic and important in ichnotaxonomic classification (e.g.,
Thulborn, 1990; Arakawa et al., 2002; Falkingham et al., 2018;
Marchetti et al., 2019). In most cases until the 2000s, theReceived July 22, 2019. Accepted November 12, 2019.
Corresponding author―Yuta TSUKIJI
E-mail: ytsukiji＊dinosaur.pref.fukui.jp
1

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Y. TSUKIJI, Y. SAKAI AND Y. AZUMA

Takeyama (1991) first described seven dinosaur tracks fromthese areas. Using moiré pictures to illustrate the specimens,
they described them as multiple ichnotaxa, whereas Lockley
and Matsukawa (1998) showed different illustrations of thespecimens and argued that these ichnotaxa are nomina dubia.
Because their interpretation lacked objective and quantitative
assessments, ichnotaxonomic classifications of these specimens
are indefinite.
Recent developments in three-dimensional (3D) laser-scanningtechnology have permitted more objective and quantifiableinterpretations of dinosaur tracks (e.g., Arakawa et al., 2002;
Lockley, 2009; Xing et al., 2018; Falkingham et al., 2018). We
therefore reexamined ten dinosaur tracks from the Tetori Groupin the Kuzuryu and Shiramine areas that were originallydescribed or reported in the 1990s (Azuma and Takeyama,
1991; Azuma et al., 1992; Kojima et al., 1992) (Table 1). We
additionally carried out ichnotaxonomic description of
unpublished four dinosaur tracks from same areas.
GEOLOGICAL SETTING
The Tetori Group is a Lower Cretaceous sequence distributedin the Inner Zone of southwestern Japan, on the eastern marginof Asia (Oishi, 1933; Maeda, 1961; Kusuhashi et al., 2002;
Matsukawa et al., 2006a; Sano, 2015; Yamada and Sano, 2018)(Fig. 1A). Abundant terrestrial vertebrate fossils, including
dinosaurs, have been recovered from this group (Fujita, 2003;
Sano, 2015).
The Tetori Group in the Kuzuryu area is composed of the
Yambara, Ashidani, Obuchi, Itsuki, and Nochino Formations inascending order (Sakai et al., in press) (Fig. 1B). The Itsuki
Formation is composed mainly of alternating beds of sandstone
and mudstone. Plant, mollusk, and vertebrate fossils commonlyoccur in the Itsuki Formation (e.g., Oishi, 1933; Maeda, 1952,
1957; Matsukawa and Ido, 1993; Manabe, 1999; Fujita, 2002;
Sakai et al., 2016, in press). Some vertebrate tracks, including
those of dinosaurs and birds, have been recovered from the
Itsuki Formation (Azuma and Takeyama, 1991; Azuma et al.,2002). The Nochino Formation is composed of coarse-grainedsandstone, conglomerate, and alternating beds of sandstone andmudstone. Dinosaur tracks as well as fossil plants have been
recovered from this formation (Azuma et al., 1992; Matsukawa
et al., 2005; Sakai et al., in press).
The Tetori Group in the Shiramine area is composed of theGomijima, Kuwajima, Akaiwa, and Kitadani Formations inascending order (Sakai et al., 2018) (Fig. 1B). The Kuwajima
Formation is composed mainly of alternating beds of sandstone
and mudstone, and plant, mollusk, vertebrate remains, anddinosaur tracks commonly occur in this formation (e. g. Oishi,
1933; Maeda, 1958, Kimura et al., 1978; Manabe and Barrett,2000; Isaji et al., 2005; Sakai et al., 2018). The Akaiwa
Formation is composed of coarse-grained sandstone,
conglomerate, and alternating beds of sandstone and mudstone,
and fossil plants, turtles, and vertebrate tracks have been
recovered from this formation (Azuma and Takeyama, 1991;

FIGURE 1. A, Distribution of the Tetori Group (Maeda, 1961). B, Map
showing the dinosaur track localities in the Kuzuryu and Shiramine
areas. 1, Kaseki-Kabe in the Shiramine area. 2, Byakodan in the
Shiramine area. 3, Nochino in the Kuzuryu area. 4, Itsuki in the Kuzuryu
area. 5, Nagakuradani in the Kuzuryu area. 6, Maesaka in the Kuzuryu
area. 7, Hayashidani in the Kuzuryu area.

Matsuoka et al., 2001; Matsukawa et al., 2005; Hirayama et al.,2012; Sakai et al., 2018).
MATERIALS AND METHODS
The studied 14 specimens were recovered from the Kuzuryu

T2

T1

TABLE 1. List of materials.

Eubrontidae

ICHNOTAXONOMIC REVISION OF DINOSAUR TRACKS FROM THE LOWER CRETACEOUS TETORI GROUP, JAPAN3

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Y. TSUKIJI, Y. SAKAI AND Y. AZUMA

and Shiramine areas (Table 1). Among eight tracks, including
FPDM-F-170 and 173, and OMFJ F-1 to 6, were found in the
Kuzuryu area. Azuma and Takeyama (1991) described
FPDM-F-170, 173, and OMFJ F-5 from the Itsuki Formation,
Kojima et al. (1992) reported OMFJ F-2, 4, and 6 from the
Itsuki and Nochino Formations, among which OMFJ F-4 and 6
were described by Azuma et al. (1992). Recently, three new
tracks, including OMFJ F-3 and 4 (including two tracks), wererecovered from the Itsuki Formation. Another five tracks,
including FPDM-F-164 and ISBEV001 to 004, have been
recovered from the Kuwajima and Akaiwa Formations in the
Shiramine area, and FPDM-F-164 and ISBEV001 to 003 havebeen described by Azuma and Takeyama (1991).
Using a portable 3D-imaging device (Artec Eva, Artec 3D),
we captured 3D digital data of these specimens. However,
ISBEV003 could not be captured because the impression of thisspecimen is filled by sediments. We processed the digital data ofthese materials into topographic images by image-analysis
software (VIVID2Rugle and 3D-Rugle, Medic Engineering
Corporation) and then, using a digital program (Adobe
Illustrator CC, Adobe Systems Incorporated), traced outlines ofthe materials based on macroscopy and the topographic images.
For measurements, we measured the following parameters:
footprint length (FL) and footprint width (FW); total
divarication (TD), divarication between digits II and III (DII-III), and divarication between digits III-IV (D III-IV); anterior
triangle length (ATL) and anterior triangle width (ATW) (Fig.
2). We used standard methods of Leonardi (1987) to measure
FL, FW, TD, D II-III, D III-IV, and PL and modified methodsof Weems (1992) and Lockley (2009) for ATL and ATW. We
also performed bivariate analysis, setting FL/FW against
ATL/ATW ratios for comparison with other dinosaur tracks.
SYSTEMATIC ICHNOLOGY
THEROPOD TRACKS
Ichnofamily GRALLATORIDAE Lull, 1904
Diagnosis.—Small bipedal forms; footprint tridactyl, limbs
very long; no manus nor caudal impression.
GRALLATORIDAE indet. (Fig. 3A; Table 2)
Material.—ISBEV003, Byakodan specimen of Azuma and
Takeyama (1991), a natural mold from the Shiramine area.
Horizon and locality.—Byakodan in the Shiramine area,
Hakusan City, Ishikawa Prefecture, Lower Cretaceous Akaiwa
Formation of Tetori Group, Japan.
Description.—ISBEV003 is an isolated left pes track ofnatural mold. Although the depression of the footprint is closely
packed by sediments, the footprint outline is visually
recognizable (Fig. 3A). This specimen exhibits small size,
comparatively slender digit impressions with sharp distal ends,
and a (narrow) metatarsophalangeal impression. FL is longer

FIGURE 2. Measurement of dinosaur tracks modified from Leonardi(1987) and Lockley (2009). FL, footprint length. FW, footprint width. D
II-III, divarication between digits II and III. D III-IV, divarication
between digits III and IV. TD, total divarication. ATL, anterior triangle
length. ATW, anterior triangle width.

than FW, and its mesaxony is strong. Digit III is longer than thedigit IV, which is longer than the digit II. The proximal part ofdigit IV connects to the metatarsophalangeal impression, which
is approximately situated on the longitudinal axis of the
footprint.
Remarks.—The specimen ISBEV003 was first described as
the ichnospecies Byakudansauropus shiraminensis (Azuma and
Takeyama, 1991). Matsukawa et al. (1995) noted that thedescription is undiagnostic and lacking ichnotaxonomic
comparison. Lockley and Matsukawa (1998) considered that this
ichnotaxon is a nomen dubium.
On the other hand, our ichnotaxonomic revision indicates that
ISBEV003 is comparable to the ichnofamily Grallatoridae.
Generally, the ichnofamily Grallatoridae is characterized by FL< 25 cm, by a pes track longer than its width (FL > FW), and bystrong mesaxony (Lull, 1904; Olsen et al., 1998). These features
are also seen in ISBEV003.
The ichnofamily Grallatoridae or Grallator-like tracks havebeen discovered and described from around the world. In East
Asia, most of them were considered to be the ichnogenera
Grallator and Jialingpus (Lockely and Matsukawa, 2009;
Lockley et al., 2013). Grallator is characterized by FL/FW > 2
and by TD in the range of 10 °–30 ° (Olsen et al., 1998). The TD
of ISBEV003 is much wider than that of Grallator, and its
FL/FW = 1.35, far lower than is characteristic of Grallator.
Jialingpus has distinctively well-preserved phalangeal pad,hallux, and metatarsal impressions (Zhen et al., 1983; Lockley
et al., 2013; Xing et al., 2014). Although the specimen
ISBEV003 has metatarsophalangeal impression, it lacks
well-preserved phalangeal pad and hallux impressions. From theabove, the specimen ISBEV003 lacks distinct features fromother ichnogenera, and we concluded that this specimen is not
assigned to any ichnogenera.
Ichnofamily EUBRONTIDAE Lull, 1904
Diagnosis.—Large bipedal forms, more or less roundedclaws, digits broad with distinct phalangeal pads. Foot
functionally, possibly structurally tridactyl as the hallux claw
never impresses. No caudal trace.

5

ICHNOTAXONOMIC REVISION OF DINOSAUR TRACKS FROM THE LOWER CRETACEOUS TETORI GROUP, JAPANTABLE 2. Metrics of dinosaur footprints from the Kuzuryu and Shiramine areas (in centimeters and degrees).

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7$%/(EUBRONTIDAE indet. (Fig. 3B; Table 2)
Material.—ISBEV001, Shiramine specimen C of Azuma and
Takeyama (1991), a natural cast from the Shiramine area.
Horizon and locality.—The Kaseki-Kabe in the Shiraminearea, Hakusan City, Ishikawa Prefecture, Lower Cretaceous
Kuwajima Formation of Tetori Group, Japan.
Description.—ISBEV001 is an isolated right pes tracknatural cast. This footprint is characterized by large size, and awell-developed metatarsophalangeal impression. FL is notably
longer than FW, and its mesaxony is strong. The digits II and III

6

Y. TSUKIJI, Y. SAKAI AND Y. AZUMAFIGURE 3. Theropod tracks from the Shiramine area. A, ISBEV003. B, ISBEV001. Figure parts include photo, topographic image, and sketch from left toright. Color bar of each topographic image shows a depth of the footprint. II of each sketch means digit II impression.

impressions are well depressed and are deeper than the digit IV
impression. A weak notch is visible between proximal parts ofthe digits II and III impressions. The distal part of digit III iscurved slightly inward.
Remarks.—The specimen ISBEV001 was first described as
the ichnospecies Kuwajimasauropus shiraminensis (Azuma and
Takeyama, 1991). However, this ichnospecies is considered as anomen dubium because the description lacks adequate diagnosis
and comparison with other tracks (Lockley and Matsukawa,
1998).
Our revision suggests that ISBEV001 is comparable to theichnofamilies Eubrontidae, Tyrannosauripodidae, andOrnithomimipodidae, which are formed by large theropods andlarger than 25 cm in FL (Lull, 1904; Thulborn, 1990; Olsen etal., 1998; Lockley et al., 2011; McCrea et al., 2014). The typespecimens of ichnogenus Asianopodus is also larger than 25 cm
in FL (Matsukawa et al., 2005; Li et al., 2011).
Eubrontidae is the most typical ichnofamily of amonglarge-sized theropod footprint, and its diagnostic features arerecognized in ISBEV001 except for distinct phalangeal pad
impressions. On the other hand, the specimen ISBEV001 isdifferent from Tyrannosauripodidae on the basis of tapered
distally digit impressions with claw marks (McCrea et al.,2014). Ornithomimipodidae is characterized by wider TD than
60° and separated proximal part of digit II from other parts oftrack, which are absent in ISBEV001 (Lockley et al., 2011).
Asianopodus is characterized by a well-developed metatarsophalangeal
pad impression on the longitudinal axis (Matsukawa et al.,2005). Although a well-developed metatarsophalangeal
impression is seen in ISBEV001, it does not form pad
impression. Thus, we concluded that ISBEV001 is assigned tothe ichnofamily Eubrontidae.
The ichnofamily Eubrontidae includes the ichnogenera
Eubrontes, Megalosauripus, and Chapus (Hitchcock, 1845; Li etal., 2006; Razzolini et al., 2017). Eubrontes and Chapus have nowell-developed metatarsophalangeal impression, unlike

ICHNOTAXONOMIC REVISION OF DINOSAUR TRACKS FROM THE LOWER CRETACEOUS TETORI GROUP, JAPAN7

FIGURE 4. Theropod tracks from the Kuzuryu and Shiramine areas. A, FPDM-F-170. B, OMFJ F-1. C, ISBEV004. Figure parts include photo,
topographic image, and sketch from left to right.

8

Y. TSUKIJI, Y. SAKAI AND Y. AZUMAFIGURE 5. Caririchnium isp. from the Kuzuryu and Shiramine areas. A, FPDM-F-164. B, FPDM-F-173. C, ISBEV002. Figure parts include photo,
topographic image, and sketch from left to right. Color bar of each topographic image shows a depth of the footprint. II of each sketch means digit II
impression.

ICHNOTAXONOMIC REVISION OF DINOSAUR TRACKS FROM THE LOWER CRETACEOUS TETORI GROUP, JAPAN

Megalosauripus and ISBEV001. Megalosauripus is diagnosed by“Elongate heel (metatarsophalangeal impression), relative tolength of digit impression III” (Lockley et al., 1998). The
specimen ISBEV001 also has an elongate metatarsophalangeal
impression. However, the specimen ISBEV001 is a single
footprint, and the border between digit III andmetatarsophalangeal pad is inadequate. Therefore, we concluded
to assign this footprint to the ichnofamily Eubrontidae.
OTHER THEROPOD TRACKS (Fig. 4A–C)
Materials.—Three isolated pes tracks. FPDM-F-170, Itsuki
specimen A of Azuma and Takeyama (1991), a natural moldfrom the Kuzuryu area. OMFJ F-1, a natural cast from theKuzuryu area. ISBEV004, a natural cast from the Shiramine
area.
Horizons and localities.—FPDM-F-170 and OMFJ F-1 from
Nochino in the Kuzuryu area, Ono City, Fukui Prefecture,
Lower Cretaceous Itsuki Formation of Tetori Group, Japan.
ISBEV004 from the Kaseki-Kabe in the Shiramine area,
Hakusan City, Ishikawa Prefecture, Lower Cretaceous
Kuwajima Formation of Tetori Group, Japan.
Descriptions.—Three isolated pes tracks from the Itsuki andKuwajima Formations are incomplete tracks but represent
typical morphology of theropod tracks such as sharp-ended,
slender digit impressions.
The specimen FPDM-F-170 is probably a right pes track ofnatural mold (Fig. 4A). This footprint is a large size andpreserves digits II and III impressions, whereas the digit IV
impression is lacking. The distal part of the digit III impression
is turned slightly toward the left side. The phalangeal pad andmetatarsophalangeal impressions are not preserved.
The specimen OMFJ F-1 is probably a left pes track of natural
cast (Fig. 4B). This specimen is a large size and shows amesaxonic morphology. The distal parts of the digits III and IV
impressions and proximal part of the metatarsophalangeal
impression are lacking. The proximal part of the digit II
impression is separated from those of digits III and IV
impressions. TD is relatively wide, and the phalangeal pad
impressions of each digit are not preserved.
The specimen ISBEV004 is a right pes track of natural cast(Fig. 4C). This footprint is a small size and shows a mesaxonic
morphology. The digit impressions are slender and preserve thephalangeal pad impressions. The phalangeal formulae are two,
three, and three in digits II, III, and IV, respectively. However,the distal part of the digit IV impression is not present, which
we interpret to mean that the digit IV mark probably consistedof four phalangeal pad impressions. The proximal phalangeal
pad of digit IV forms a metatarsophalangeal impression, whichis slightly outside the longitudinal axis of the footprint. The digit
II impression is deeper than the digit IV impression, and D
II-III is notably narrower than D III-IV.
Remarks.—The specimen FPDM-F-170 was originallydescribed as the ichnospecies Itsukisauropus izumiensis (Azuma
and Takeyama, 1991). This ichnotaxon is now considered as a9nomen dubium because of inadequate preservation and lacking
ichnotaxonomic comparison (Lockley and Matsukawa, 1998).
OMFJ F-1 and ISBEV004 have not been reported so far.
The specimens FPDM-F-170 and OMFJ F-1 are large tracks(FL > 25 cm), but these tracks are not comparable with otherlarge theropod ichnotaxa because the tracks are incomplete. The
specimen ISBEV004 is similar to small theropod ichnotaxa suchas the ichnofamily Grallatoridae and ichnogenus Asianopodus.
The ichnofamily Grallatoridae is characterized by narrow TD
and strong mesaxony, unlike ISBEV004. The ichnogenus
Asianopodus is mesaxonic and sub-symmetrical track.
Asianopodus also has a bulbous metatarsophalangeal pad
impression on the longitudinal axis (Matsukawa et al., 2005).
On the other hand, the specimen ISBEV004 has a slightly
vertically long metatarsophalangeal pad which is slightly outside
the longitudinal axis, and its D III-IV is wider than II-III.
IGUANODONTID TRACKS
Ichnofamily IGUANODONTIPODIDAE Vialov, 1988 sensu
Lockley, Xing, Lockwood and Pond, 2014, emend.
Díaz-Martínez, Pereda-Suberbiola, Pérez-Lorente and Canudo,
2015
Diagnosis.—Mesaxonic, tridactyl, sub-symmetrical pes
tracks that are as wide as or wider than long; one pad impressionin each digit and one in the heel; digit pads longer than wide;
well-developed notches in the proximal part of the digit II and
IV impressions; manus tracks occasionally present and muchsmaller than the pes tracks.
Ichnogenus CARIRICHNIUM Leonardi, 1984, emend.
Díaz-Martínez, Pereda-Suberbiola, Pérez-Lorente and Canudo,
2015
Diagnosis.—Pes tracks belonging to Iguanodontipodidae,
with a large heel impression that is rounded, centered and wide
(wider than the width of the proximal part of the digit III
impression); short, wide digit impressions.
CARIRICHNIUM isp. (Fig. 5)
Materials.—Three isolated tracks. FPDM-F-164 and
ISBEV002, Shiramine specimens A and B of Azuma and
Takeyama (1991), natural casts from the Shiramine area.
FPDM-F-173, Hayashidani specimen of Azuma and Takeyama(1991), a natural cast from the Kuzuryu area.
Horizons and localities.—FPDM-F-164 and ISBEV002 fromthe Kaseki-Kabe in the Shiramine area, Hakusan City, Ishikawa
Prefecture, Lower Cretaceous Kuwajima Formation of Tetori
Group, Japan. FPDM-F-173 from Hayashidani in the Kuzuryu
area, Ono City, Fukui Prefecture, Lower Cretaceous Itsuki
Formation of Tetori Group, Japan.
Descriptions.—The specimen FPDM-F-164 is a relatively
small iguanodontid track that shows mesaxonic and short, wide10

Y. TSUKIJI, Y. SAKAI AND Y. AZUMAFIGURE 6. Amblydactylus isp. and iguanodontid track from the Kuzuryu area. A, OMFJ F-2. B, OMFJ F-3. C, OMFJ F-4. Figure parts include photo,
topographic image, and sketch from left to right. Color bar of each topographic image shows a depth of the footprint. II of each sketch means digit II
impression.

digit impressions with blunt distal ends. The digital pad andmetatarsophalangeal pad impressions are well-preserved. The
digits II and III impressions are slightly deeper than the digit IV
impression. The metatarsophalangeal pad impression, which islarger than the digital pad impressions, is triangular and islonger than it is wide. The specimen FPDM-F-173 is similar but

slightly larger, and its mesaxony is stronger than FPDM-F-164(Table 2).
The specimen ISBEV002 is much larger than FPDM-F-164,
but similar to FPDM-F-164 in morphology. The digits II and IV
impressions are well-preserved, but the digit III impression iseroded. The digit II and metatarsophalangeal impressions are

ICHNOTAXONOMIC REVISION OF DINOSAUR TRACKS FROM THE LOWER CRETACEOUS TETORI GROUP, JAPAN

deeper than other parts of the track. The widths of digits II and
III are almost the same, while that of digit IV is wider than thoseof other digit impressions.
Remarks.—The specimens FPDM-F-164 and 173 wereoriginally described as the ichnospecies Shiraminesauropus
reini and S. hayashidaniensis respectively, and ISBEV002 wasdescribed as the ichnospecies Gigantoshiraminesauropus matsuoi(Azuma and Takeyama, 1991). Matsukawa et al. (1995) pointed
out that these specimens are inadequate and undiagnostic, andichnotaxonomic comparison was not taken into the description.
Lockley and Matsukawa (1998) considered that these ichnotaxa
are nomina dubia. On the other hand, Díaz-Martínez et al.
(2015) noted that these tracks are classified within theichnofamily Iguanodontipodidae.
The ichnofamily Iguanodontipodidae includes several valid
ichnogenera such as Iguanodontipus, Caririchnium,
Amblydactylus, and Hadrosauropodus (Lockley et al., 2014;
Díaz-Martínez et al., 2015). Among them, Caririchnium ischaracterized by pes tracks for which FL > FW, large
metatarsophalangeal impressions, relatively strong mesaxony,
three well-separated digital pads, and one metatarsophalangeal
pad impression (Lockley et al., 2014; Díaz-Martínez et al., 2015;
Xing et al., 2015; Tsukiji et al., 2018). FPDM-F-164,
ISBEV002, and FPDM-F-173 show these morphologies. Thus,
we concluded that these tracks are attributed to the ichnogenus
Caririchnium.
Ichnogenus AMBLYDACTYLUS Sternberg, 1932, emend. Currie
and Sarjeant, 1979
Diagnosis.—Bipedal, with three functional pedal digits. The
outer contours of digits II and IV diverge at low angle from thelongitudinal axis of the ichnite. A distinct posterior impression
is produced by a metatarsal-phalangeal pad. Interdigital webs
link the proximal portions of the fleshy digital pads; the digits
end in blunt claws or pointed hooves. The ichnite is almost as
wide as, or wider than, it is long.
AMBLYDACTYLUS isp. (Fig. 6A, B)
Materials.—Two tracks from the Kuzuryu area. OMFJ F-2,
Hayashidani specimen 2 of Kojima et al. (1992), a natural cast.
OMFJ F-3-T1, a natural cast.
Horizons and localities.—OMFJ F-2 from Hayashidani and
OMFJ F-3-T1 from Itsuki tracksites in the Kuzuryu area, Ono
City, Fukui Prefecture, Lower Cretaceous Itsuki Formation ofTetori Group, Japan.
Descriptions.—The specimen OMFJ F-2 is a large pes trackwith short, wide digit impressions that have blunt distal ends
(Fig. 6A). The proximal width of digit III impression is greaterthan those of other digit impressions. Digits II and III
impressions are deeper than other parts of the footprint. The
proximal margin of the footprint is shallow, and its outline issomewhat indistinct. The outer margins of digits II and IV
impressions are nearly parallel to the longitudinal axis. The

11

digital pad and metatarsophalangeal pad impressions are notpreserved.
The specimen OMFJ F-3 is composed of two pes footprint
natural casts, numbered T1 and T2 (Fig. 6B). T1 is shallower
than T2, and the directions of each track are almost in the same.
Thus, these footprints do not compose a trackway. Because T2
is incomplete, it is described in a separate section below. T1 is awell-preserved footprint that shows tridactyl, mesaxony, andquadripartite morphology. The digit impressions are deeper thanthe metatarsophalangeal pad impression. The proximal parts of each
digit impression are well detached from the metatarsophalangeal
pad impression. The metatarsophalangeal pad is wider thanlong, and its proximal margin is rounded.
Remarks.—The specimen OMFJ F-2 was first reported by
Kojima et al. (1992). However, ichnotaxonomic description anddetailed illustration have not been published. The specimen
OMFJ F-3 have not been reported so far.
The specimens OMFJ F-2 and OMFJ F-3-T1 arecharacterized by wider pes track than its length and by relatively
weak mesaxony. These morphologies are seen in theichnogenera Amblydactylus and Hadrosauropodus (Currie andSarjeant, 1979; Díaz-Martínez et al., 2015; Tsukiji et al., 2018).
Díaz-Martínez et al. (2015) proposed that the type ichnogenus A.
gethingi is a nomen dubium but A. kortmeyeri is valid andremoved to the ichnogenus Caririchnium. Tsukiji et al. (2018)
mentioned that A. gethingi is a nomen dubium; however, A.
kortmeyeri differs from Caririchnium on the basis of following
features: 1) wider pes track than its length with weak mesaxony;2) wider metatarsophalangeal impression than its length. We
therefore concluded that Amblydactylus should be divided from
Caririchnium, and A. kortmeyeri is a new type ichnospecies.
Currie and Sarjeant (1979) diagnosed that Amblydactylus has
interdigital webs, which is absent in OMFJ F-2 and OMFJ
F-3-T1. Because interdigital webs of iguanodontid tracks werereinterpreted as mud structures (Lockley and Hunt, 1995;
Lockley et al., 2003), we rejected this feature as diagnosis.
OMFJ F-2, OMFJ F-3-T1, and the ichnogenus Amblydactylus
show rounded posterior margin of the track. However, theichnogenus Hadrosauropodus is characterized by a bilobed
posterior margin of the track (Lockley et al., 2003). Thus, thespecimens OMFJ F-2 and OMFJ F-3-T1 are attributed to theichnogenus Amblydactylus.
OTHER IGUANODONTID TRACKSIGUANODONTIPODIDAE indet. (Fig. 6B, C)
Material.—Two tracks from the Kuzuryu area. OMFJ
F-3-T2, a natural cast. OMFJ F-4, Nagakuradani specimen of
Azuma et al. (1992), a natural cast.
Horizon and locality.—OMFJ F-3-T2 from the Itsuki in the
Kuzuryu area, Ono city, Fukui Prefecture, Lower Cretaceous
Itsuki Formation of Tetori Group, Japan. OMFJ F-4 from
Nagakuradani in the Kuzuryu area, Ono City, Fukui Prefecture,
Lower Cretaceous Nochino Formation of Tetori Group, Japan.

12

Y. TSUKIJI, Y. SAKAI AND Y. AZUMAFIGURE 7. Possible dinosaur tracks from the Kuzuryu area. A, OMFJ F-5. B, OMFJ F-6. Figure parts include photo, topographic image, and sketch fromleft to right. Color bar of each topographic image shows a depth of the footprint. II of each sketch means digit II impression.

Description.—Although OMFJ F-3-T2 is well-impressed anddeeper than OMFJ F-3-T1, it lacks the digit IV impression andproximal part of the footprint. The digital pad andmetatarsophalangeal pad impressions are not detached, and the
distal ends of digits are rounded.
The specimen OMFJ F-4 shows mesaxony and quadripartite
morphology (Fig. 6C). This footprint lacks a proximal track
margin. The digit II impression is deeper than that of digit III,
which is deeper than that of digit IV. The digit IV impression isshorter than other digit impressions. The width of themetatarsophalangeal pad impression is wider than that of thedigit III impression. D II-III is much narrower than D III-IV.
Remarks.—The specimen OMFJ F-3-T2 is preserved in thesame block of OMFJ F-3-T1. Although this footprint isincomplete, it can be seen that digit impressions are short andwide with rounded distal end. Thus, we attributed that thisfootprint is the ichnofamily Iguanodontipodidae. The specimen

OMFJ F-4 was first reported by Kojima et al. (1992) anddescribed by Azuma et al. (1992) subsequently. They consideredthat this footprint was formed by iguanodontids. We agree with
their interpretation and classified this footprint as theichnofamily Iguanodontipodidae. The specimen OMFJ F-4
shows weak mesaxony, and such morphology is typically seenin the ichnogenera Amblydactylus and Hadrosauropodus.
However, the posterior margin of this track, which is importantfor ichnotaxonomic classification of iguanodontid tracks, was
not preserved (Díaz-Martínez et al., 2015). Thus, we could not
assign this footprint to any iguanodontid ichnogenus.
INDETERMINATE DINOSAUR TRACKS (Fig. 7A, B)
Materials.—Two isolated tracks from the Kuzuryu area.
OMFJ F-5, Itsuki specimen B of Azuma and Takeyama (1991),
a natural cast. OMFJ F-6, Meoto-sugi specimen of Azuma et al.

ICHNOTAXONOMIC REVISION OF DINOSAUR TRACKS FROM THE LOWER CRETACEOUS TETORI GROUP, JAPAN13

FIGURE 8. Bivariate analysis (FL/FW ratio plotted against ATL/ATW ratio) of tridactyl tracks from Tetori Group. A, Theropods. B, Iguanodontids. Plotsof Kitadani dinosaur quarry (KDQ) specimens are modified from Tsukiji et al. (2018, 2019).

(1992), a natural cast.
Horizons and localities.—OMFJ F-5 from Nochino in the
Kuzuryu area, Ono City, Fukui Prefecture, Lower Cretaceous
Itsuki Formation of Tetori Group, Japan. OMFJ F-6 from
Maesaka in the Kuzuryu area, Ono City, Fukui Prefecture,
Lower Cretaceous Nochino Formation of Tetori Group, Japan.
Descriptions.—The specimen OMFJ F-5 is a large pes tracknatural cast, which shows a flattened preservation (Fig. 7A). The
digit impressions exhibit mesaxonic morphology and are
relatively wide. The distal ends of each digit are lacking, and thephalangeal pad impressions are not preserved. The posterior partof the track is somewhat narrow and rounded.

The specimen OMFJ F-6 is a large pes track natural cast thatshows a tridactyl and strongly mesaxonic morphology (Fig. 7B).
The digit impressions are relatively slender with rounded distal
ends. The posterior part of the track is shallow and ill-formed. D
II-III is much narrower than D III-IV (Table 2). The phalangeal
pad and metatarsophalangeal pad impressions lack definition.
Remarks.—The specimen OMFJ F-5 was first reported by
Azuma and Takeyama (1991) and identified as an iguanodontid
footprint. However, this footprint lacks distal ends of digit
impressions, which are important parts to classify a trackmaker
between theropod or iguanodontid (e.g., Thulborn, 1990).
Therefore, we could not determine the trackmaker of this footprint.

14

Y. TSUKIJI, Y. SAKAI AND Y. AZUMAFIGURE 9. Dinosaur ichnofauna from the Tetori Group. Orang, Kitadani dinosaur ichnofauna. Green, Akaiwa dinosaur ichnofauna. Blue, Itsuki dinosaur
ichnofauna.

The specimen OMFJ F-6 was first reported by Kojima et al.
(1992) and assigned to theropod footprint by Azuma et al.
(1992). This footprint has rounded distal ends of digit
impressions, which is typical morphology of iguanodontid
tracks. However, iguanodontid tracks are characterized by alarge well-defined metatarsophalangeal impression, which is notseen in this track (e.g., Díaz-Martínez et al., 2015). Thus, we
could not identify the trackmaker of this footprint.

DISCUSSION
Ichnotaxonomic revision
Azuma and Takeyama (1991) first described following
ichnotaxa: Byakudansauropus shiraminensis (ISBEV003),
Kuwajimasauropus shiraminensis (ISBEV001), Itsukisauropus
izumiensis (FPDM-F-170), Shiraminesauropus reini(FPDM-F-164), S. hayashidaniensis (FPDM-F-173), andGigantoshiraminesauropus matsuoi (ISBEV002). Among them,B. shiraminensis, K. shiraminensis, and I. izumiensis were

ICHNOTAXONOMIC REVISION OF DINOSAUR TRACKS FROM THE LOWER CRETACEOUS TETORI GROUP, JAPANconsidered as theropod tracks, and S. reini, S. hayashidaniensis,
and G. matsuoi were iguanodontid tracks. In addition, they
assigned OMFJ F-5 to an iguanodontid track. Matsukawa et al.
(1995) referred that the trackmakers of these tracks aretheropods and iguanodontids. On the other hand, they noted thatthese ichnotaxa are inadequate preservation, undiagnostic, andlacking ichnotaxonomic comparison with other tracks. Lockley
and Matsukawa (1998) followed their suggestion and consideredthat these ichnotaxa are nomina dubia. However, objective andquantitative analyses have not been taken into consideration.
Our revision of dinosaur tracks using 3D digital data shows
more adequate morphological observation. For example,
phalangeal and metatarsophalangeal pad impressions of
FPDM-F-164 were well-defined and illustrated in our figures,
whereas not in previous studies. In addition, this study carriedout the bivariate analysis plotting the FL/FW and ATL/ATW
ratios, which was not taken into consideration of previous
studies. Three theropod tracks, including ISBEV001, 003, and004, show similar pattern to the ichnofamilies Grallatoridae,
Eubrontidae, and the ichnogenus Asianopodus from the Kitadani
Formation (Fig. 8A). Among the specimen ISBEV003 hasdiagnostic features of the ichnofamily Grallatoridae, and
ISBEV001 has those of the ichnofamily Eubrontidae. Three
iguanodontid tracks, including FPDM-F-164, 173, and ISBEV002,
plot in same patterns of the ichnogenus Caririchnium from the
Kitadani Formation, whereas OMFJ F-2 plots in the lower leftpart of the graph, concordant with the ichnogenus
Amblydactylus from the Kitadani Formation (Fig. 8B). Although
OMFJ F-3-T1 shows the medium value between the
Caririchnium and Amblydactylus, its metatarsophalangeal pad
impression is wider than long, which is same with Amblydactylus.
These results strongly support ichnotaxonomic division of theropod
and iguanodontid tracks from the Kuzuryu and Shiramine areas.
Dinosaur ichnofauna in the Tetori Group
Our ichnotaxonomic division of dinosaur tracks from theKuzuryu and Shiramine areas revealed that their trackmakers aretheropods and iguanodontids. Among the ichnofamilies,
Grallatoridae and Eubrontidae of theropod and the ichnogenera
Caririchnium and Amblydactylus of iguanodontid ichnotaxa
have also been recovered from the Kitadani Formation in the
Takinamigawa area (Tsukiji et al., 2018, 2019). Recently, theichnofamilies Eubrontidae and Iguanodontipodidae(Amblydactylus-type) have been recognized in the Kagidani
Formation in the Oshirakawa area (Tsukiji et al., in press).
Previous studies suggested that the assemblage of dinosaur
ichnofauna from the Tetori Group in the Hakusan region ischaracterized by theropod- and iguanodontid-dominatedcommunity (Matsukawa et al., 2005, 2006b; Tsukiji et al., inpress). The result of this study supports these suggestions.
On the other hand, Matsukawa et al. (2005, 2006b)
interpreted that the dinosaur tracks from the Tetori Group areyielded in the same horizon stratigraphically and are grouped
into the same assemblage. However, on the basis of recent

15

stratigraphic and geochronological studies suggests that there arethree horizons of dinosaur track bearing in the Tetori Group(Sano, 2015; Sano and Yabe, 2016; Sakai et al., 2018; Nagata etal., 2018). Therefore, we propose a new interpretation of thedinosaur track assemblage from the Tetori Group. We
subdivided this assemblage into following three ichnofaunas: 1,
Itsuki dinosaur ichnofauna from the Itsuki, Kuwajima, andKagidani Formations (Barremian); 2, Akaiwa dinosaur
ichnofauna from the Akaiwa, Nochino, and Wasabu Formations(early Aptian); and 3, Kitadani dinosaur ichnofauna from the
Kitadani Formation (Aptian).
The ichnofaunal composition shows that the Itsuki dinosaur
ichnofauna only yields theropod, bird, and iguanodontid tracks;
however, the Akaiwa and Kitadani dinosaur ichnofaunas consistof diverse vertebrate ichnotaxa (Fig. 9). Although the Akaiwa
and Nochino formations are composed of theropod andiguanodontid tracks, the Wasabu Formation in the Jinzu Region
yields theropod, bird, sauropod, iguanodontid, ankylosaur, andpterosaur tracks (Matsukawa et al., 1997, 2002; Toyama
Dinosaur Research Group, 2002; Fujita et al., 2003; Shigeno,
2003; Shigeno et al., 2004; Fujita, 2008). The Kitadani dinosaur
ichnofauna is the most diverse in the Tetori Group and includes
five ichnotypes of theropod, two ichnotypes of bird, sauropod,
small ornithischian, two ichnotypes of iguanodontid,
ankylosaur, and pterosaur tracks (Lee et al., 2010; Imai et al.,2018; Tsukiji et al., 2018, 2019).
Difference between the Itsuki and Akaiwa dinosaur
ichnofaunas is indicated that the ichnofaunal change has
occurred in the Tetori Group during the Barremian–Aptian age.
It is concordant with the suggestion that the climatic change(warmer and dryer) has occurred in the Barremian–Aptian
boundary on the basis of floral and faunal change (Sano andYabe, 2016; Shibata et al., 2017; Sakai et al., 2018). However,sauropod, small ornithischian, and pterosaur remains have beenreported from the Kuwajima Formation (Manabe and Barrett,2000; Unwin and Matsuoka, 2000; Barrett et al., 2002; Ohashi
and Barrett, 2009). The general facies analyses suggested that
the Itsuki and Kuwajima Formations were deposited in estuarinedelta environments (Azuma et al., 1992; Okazaki and Isaji,2008), whereas the Wasabu and Kitadani formations were
deposited in a meandering river system of inland zone (Shigeno,
2003; Shigeno et al., 2004; Yabe and Shibata, 2011; Suzuki etal., 2015). Therefore, the ichnofaunal diversity may have been
influenced by the depositional environments.
There is a large number of discoveries of dinosaur footprints
and tracksites from the Lower Cretaceous of East and Southeast
Asia (e.g., Zhen et al., 1989; Chen et al., 2006; Matsukawa etal., 2006b; Lockley et al., 2013). Matsukawa et al. (2005)
suggested that dinosaur ichno-assemblage from the Tetori Groupis dominated by theropods and gracile-toed ornithopods(iguanodontids) and compared with dinosaur tracksites from thenortheastern part of China. This study shows that the Itsuki
dinosaur ichnofauna is also composed of theropod andiguanodontid footprints. This pattern is similar to dinosaur
ichno-assemblage of the Xiguayuan Formation in Hebei

16

Y. TSUKIJI, Y. SAKAI AND Y. AZUMA

Province (Xing et al., 2019). In contrast, it is clearly different
from those of the Jingchuan Formation in Nei Mongol and
Tianjialou Formation in Shandong Province, which are
dominated by theropod and sauropod footprints (Lockley et al.,2002, 2018; Xing et al., 2018).
However, the Itsuki dinosaur ichnofauna is composed of afew numbers, and most of them lack trackways andco-occurrences with other footprints. Further discoveries ofdinosaur footprints from the Itsuki, Kuwajima, and Kagidani
Formations are needed for our understanding about dinosaur
ichnofaunas from the Tetori Group and comparisons with theother dinosaur ichnofaunas.
Recently, it was revealed that wide-toed iguanodontid
footprints, such as Amblydactylus from the Kitadani and Itsuki
Formations, have been recovered (Tsukiji et al., 2018). In
addition, sauropod, ankylosaur, and pterosaur footprints werereported from the Akaiwa and Kitadani dinosaur ichnofaunas(Fujita, 2008; Tsukiji et al., 2016). Similar assemblage isreported from the Sichuan Basin, southwestern part of China,
where yields various theropod, sauropod, iguanodontid(including wide-toed morphotype), ankylosaur, and pterosaur
footprints (Xing and Lockley, 2016; Xing et al., 2016). Becausea few of dinosaur body fossils were recovered from the Lower
Cretaceous of the Sichuan Basin, this similarity may add new
insights for our understanding of Asian dinosaurs during the
Early Cretaceous age.
CONCLUSION
Morphological identification along with objective andquantitative analyses using 3D digital data revealed that
dinosaur tracks from the Kuzuryu and Shiramine areas belonged
to theropods (including the ichnofamilies Grallatoridae andEubrontidae) and iguanodontids (including the ichnogenera
Caririchnium and Amblydactylus).
Revision of dinosaur tracks in this study supports the previous
suggestion that the dinosaur track assemblage in the Tetori
Group is dominated by theropods and iguanodontids. In
addition, this assemblage can be subdivided into the Itsuki,
Akaiwa, and Kitadani dinosaur ichnofaunas based on thedepositional age. The Itsuki dinosaur ichnofauna includes few
varieties of dinosaur tracks, whereas the Akaiwa and Kitadanidinosaur ichnofaunas show diverse assemblage of dinosaur
ichnotaxa. This difference may have been influenced bydepositional environments; however, discoveries of additional
specimens of the Itsuki dinosaur ichnofauna are needed for more
rigorous discussion.
The 3D digital data, coupled with quantitative analysis of thedata, were essential to identify the trackmakers. We strongly
recommend that other dinosaur tracks from the Tetori Groupshould be described or reanalyzed using 3D digital data tofurther compare the ichnotaxonomy and ichnofauna in thisregion and to provide additional insights into the ecosystems of
the Lower Cretaceous Tetori Group.

ACKNOWLEDGMENT
We gratefully thank reviewers for reviewing our manuscript
and making constructive suggestions. We are grateful to Prof.
Toshihiro Yamada for providing the materials of OMFJ F-1
from the Nochino tracksite and OMFJ F-3 from the Itsuki
tracksite, and Mr. Kento Otsuka for sharing useful information
about materials from the Shiramine area. We also thank staffs
and members of FPDM for providing constructive comments
and supports to this study. We sincerely thank Dr. Fumito
Shiraishi and his laboratory members in Hiroshima University
and Institute of Dinosaur Research's laboratory members in
Fukui Prefectural University for sharing useful discussion. We
would like to thank Enago (www.enago.jp) for English language
review.
SUPPORTING INFORMATIONS
Data DOI of materials are available from the following
repositories:
FPDM-F-164, https://doi.org/10.6084/m9.figshare.8868767.v2
FPDM-F-170, https://doi.org/10.6084/m9.figshare.8868779.v2
FPDM-F-173, https://doi.org/10.6084/m9.figshare.8868788.v1
ISBEV001, https://doi.org/10.6084/m9.figshare.8868791.v1
ISBEV002, https://doi.org/10.6084/m9.figshare.8868797.v1
ISBEV004, https://doi.org/10.6084/m9.figshare.8868800.v1
OMFJ F-1, https://doi.org/10.6084/m9.figshare.8868803.v3
OMFJ F-2, https://doi.org/10.6084/m9.figshare.8868806.v1
OMFJ F-3, https://doi.org/10.6084/m9.figshare.8868809.v1
OMFJ F-4, https://doi.org/10.6084/m9.figshare.8868815.v1
OMFJ F-5, https://doi.org/10.6084/m9.figshare.8868818.v1
OMFJ F-6, https://doi.org/10.6084/m9.figshare.8868821.v1
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