[Palaeontology, Vol. 52, Part 4, 2009, pp. 681–688]
THE AFFINITIES OF THE ENIGMATIC DINOSAUR
ESHANOSAURUS DEGUCHIIANUS FROM THE EARLY
JURASSIC OF YUNNAN PROVINCE, PEOPLE’S
REPUBLIC OF CHINA
by PAUL M. BARRETT
Department of Palaeontology, The Natural History Museum, Cromwell Road, SW7 5BD London, UK; e-mail: p.barrett@nhm.ac.uk
Typescript received 31 July 2008; accepted in revised form 31 October 2008
Abstract: Eshanosaurus deguchiianus is based on a single left
dentary from the Lower Lufeng Formation (Lower Jurassic)
of Yunnan Province, China. It was originally identified as the
earliest known member of Therizinosauroidea (Theropoda:
Coelurosauria), a conclusion that results in a significant
downward range extension for this clade (>65 million
years) and for many other major lineages within Coelurosauria. However, this interpretation has been questioned and
several authors have proposed that the anatomical features
used to refer Eshanosaurus to Therizinosauroidea are more
consistent with attribution to a basal sauropodomorph
dinosaur. Detailed consideration of the holotype specimen
suggests that several features of the dentary and dentition
G host lineages inferred from phylogenetic analyses of
theropod dinosaurs suggest that Coelurosauria, the clade
that includes birds and their closest relatives, appeared
and diversified during the Middle Jurassic (Sereno 1999;
Holtz 2000; Rauhut 2003, 2005; Holtz et al. 2004). Direct
evidence for the timing of this event is also known, as
definitive coelurosaur specimens are now recognised from
this interval (Proceratosaurus from the Bathonian of England; Holtz 2000; Rauhut 2003; Holtz et al. 2004; Rauhut
and Milner 2008). Reports of pre-Middle Jurassic coelurosaurs, including the Late Triassic genera Protoavis
(originally described as the earliest known bird: Chatterjee
1991) and Shuvosaurus (proposed as the earliest known
ornithomimosaur: Chatterjee 1993) have been regarded
with scepticism (e.g. Rauhut 1997; Witmer 2002; Nesbitt
et al. 2007). Recent discoveries and new phylogenetic
analyses have demonstrated that Shuvosaurus is a non-dinosaurian archosaur (e.g. Nesbitt 2007). In addition, it is
generally accepted that most of the material referred to
Protoavis pertains to an indeterminate archosaur; however, there is still a possibility that some of the individual
elements assigned to this species are of coelurosaurian (if
ª The Palaeontological Association
exclude Eshanosaurus from Sauropodomorpha and support
its inclusion within Therizinosauroidea. If accepted as
an Early Jurassic coelurosaur, Eshanosaurus has important
implications for understanding the timing and tempo of
early theropod diversification. Moreover, its provenance also
suggests that substantial portions of the coelurosaur fossil
record may be missing or unsampled. However, the Early
Jurassic age of Eshanosaurus requires confirmation if this
taxon is to be fully incorporated into broader evolutionary
studies.
Key words: Therizinosauroidea, Sauropodomorpha, Coelurosauria, systematics.
not avian) origin and this taxon requires further investigation (Witmer 2002; Nesbitt et al. 2007).
Another potential pre-Middle Jurassic coelurosaur,
Eshanosaurus deguchiianus, was described on the basis of
an almost complete (but damaged) left dentary from the
Lower Lufeng Formation of Yunnan Province, China
(IVPP V11579: Zhao and Xu 1998; Xu et al. 2001). The
Lower Lufeng Formation was formerly regarded as Late
Triassic in age (Young 1951), but subsequent authors
now assign it to the Early Jurassic (e.g. Luo and Wu
1994). Several characters present in Eshanosaurus, including the presence of a broad, flat shelf of bone lateral to
the tooth row, a high tooth count and various details of
the tooth morphology, suggest that this genus may be
referable to Therizinosauroidea (Zhao and Xu 1998; Xu
et al. 2001).
Therizinosauroidea is a clade of unusual, herbivorous
coelurosaurian theropods that is known primarily from
the Late Cretaceous of North America and eastern Asia
(Clark et al. 2004). Although the recent discoveries of
Beipiaosaurus (late Barremian, China: Xu et al. 1999) and
Falcarius (Barremian, USA: Kirkland et al. 2005) extend
doi: 10.1111/j.1475-4983.2009.00887.x
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PALAEONTOLOGY, VOLUME 52
the temporal range of definitive therizinosauroids into the
Early Cretaceous, Eshanosaurus remains the only Jurassic
representative of the group, and therefore implies the
presence of an extensive ghost lineage stretching from the
Sinemurian to the Barremian (over 65 mya: Gradstein
et al. 2004). If correctly identified, Eshanosaurus pulls the
origin of Therizinosauroidea into the earliest Jurassic or
Late Triassic. This would also result in major range extensions to many other coelurosaur and tetanuran lineages,
most of which have first occurrences in the Bajocian or
Bathonian (Weishampel et al. 2004). Consequences of this
would include a reduction in the stratigraphical congruence of all current theropod phylogenies (Wills et al.
2008) and it would also imply that theropod diversification occurred much earlier than would be expected on
the basis of other data.
The early occurrence of Eshanosaurus has led some
authors to question its therizinosauroid affinities, particularly as Eshanosaurus possesses a number of features that
are more derived than those present in some Early Cretaceous representatives of the clade (Kirkland et al. 2005).
In addition, it has been suggested that the morphology of
the type specimen is more consistent with referral to
Sauropodomorpha (Lamanna in Kirkland and Wolfe
2001; Rauhut 2003). Here, I review the evidence that has
been used to support these conflicting opinions in order
to determine if Eshanosaurus is a basal sauropodomorph
or a therizinosauroid and to assess the implications of its
systematic position and provenance.
Institutional abbreviations. AMNH, American Museum of
Natural History, New York; BP, Bernard Price Institute for
Palaeontological Research, Johannesburg; IVPP, Institute of
Vertebrate Paleontology and Paleoanthropology, Beijing; NHM,
The Natural History Museum, London; PST, Paleontological and
Stratigraphic Section, Geological Institute, Mongolian Academy
of Sciences, Ulan Bataar; SAM, Iziko South African Museum,
Cape Town.
AFFINITIES OF ESHANOSAURUS
Eshanosaurus was referred to Therizinosauroidea, and
excluded from both Sauropodomorpha and Ornithischia,
following consideration of eleven features (Xu et al.
2001). These features are: (1) rostrally positioned teeth
larger than more caudally positioned teeth; (2) small size
and large number of teeth; (3) recurvature of the dentary
teeth; (4) denticles almost perpendicular to the mesial
and distal margins of the tooth crown; (5) tooth crowns
asymmetrical in mesial or distal view; (6) presence of a
constriction between the tooth root and crown; (7) tooth
root slightly wider than the crown mesiodistally; (8) root
with a sub-circular cross-section; (9) presence of inter-
dental plates; (10) presence of a broad, flat shelf lateral to
the tooth row; and (11) ventrally deflected rostral end of
the dentary. However, Rauhut (2003) noted that several of
these features are present in sauropodomorphs (characters
3, 6 and 8–11), one is a dinosaur symplesiomorphy (character 4), two might be under ontogenetic control (characters 1 and 2) and the remaining dental characters might
depend on the position in the tooth row that was sampled (characters 5 and 7). Xu et al. (2001) also noted that
some of these features were shared by other dinosaur
clades, but considered that the combination of characters
in Eshanosaurus was characteristic of therizinosauroids
and differed from those present in other dinosaurs. Each
of these characters is discussed in turn, below. As there
is general agreement that Eshanosaurus is not an
ornithischian, those features used to distinguish sauropodomorphs from therizinosauroids are emphasised.
1. Therizinosaurs can be distinguished from all other
theropods by the reduction in tooth size (both tooth
length and width) that occurs from the rostral to the
middle part of the dentary tooth row (Russell and Dong
1993; Clark et al. 1994, 2004; Xu et al. 2001). Rauhut
(2003) suggested that this character was unreliable, stating
that a similar condition may be present in juvenile basal
sauropodomorphs. However, although a continuous
caudad reduction in dentary tooth size does occur in
adult eusauropod sauropodomorphs (Upchurch et al.
2004) this condition is either absent or cannot be determined in basal sauropodomorph taxa. In Massospondylus
(e.g. SAM-PK-K1314, BP ⁄ 1 ⁄ 4934: Sues et al. 2004; Barrett
and Yates 2006), Plateosaurus (AMNH 6810: see Galton
1984), Pantydraco (NHM P24: Yates 2003) and Jingshanosaurus (Zhang and Yang 1994), the rostralmost dentary
teeth (in the first two or three alveoli) are smaller, rather
than larger, than those in more caudal tooth positions, so
that tooth size initially increases caudally, in contrast to
the condition in therizinosauroids. Unfortunately, this
character cannot be determined in any juvenile specimens
of basal sauropodomorphs as the dentary teeth are often
obscured, as occurs in Mussaurus (Bonaparte and Vince
1979; Pol and Powell 2007) and Massospondylus (e.g.
BP ⁄ 1 ⁄ 4376: Gow et al. 1990; Sues et al. 2004). Consequently, not only is this feature synapomorphic for
Therizinosauroidea within Theropoda, but it can also
be used to differentiate therizinosauroid and sauropodomorph dentary dentitions, at least on the basis of current
data (contra Rauhut 2003).
2. Rauhut (2003) posited that the high number of dentary teeth present in Eshanosaurus was not a useful character, as tooth numbers are generally variable among
reptiles. However, no known sauropodomorph possesses
more than 28 dentary teeth (i.e. Plateosaurus: see Galton
and Upchurch 2004) whereas Eshanosaurus possesses a
BARRETT: THE ENIGMATIC DINOSAUR ESHANOSAURUS
minimum of 34 tooth positions and may have had 37
teeth or more (Xu et al. 2001; Clark et al. 2004; the rostralmost part of the dentary is missing in IVPP V11579).
Sauropodomorphs gain additional tooth positions during
growth (Galton and Upchurch 2004) and the highest
tooth counts occur in the largest individuals of Plateosaurus (which have skull lengths of 25 cm or more: e.g.
AMNH 6810). In contrast, the holotype dentary of Eshanosaurus pertains to a much smaller animal; the high tooth
count in this species is inconsistent with its interpretation
as a juvenile basal sauropodomorph as a similarly-sized
‘prosauropod’ would be expected to have only 15–20 dentary teeth (based on comparisons with Massospondylus:
SAM-PK-K1314, BP ⁄ 1 ⁄ 4779). Primitive therizinosauroids,
such as Beipiaosaurus and Alxasaurus, have similar numbers of dentary teeth to Eshanosaurus (Russell and Dong
1993; Xu et al. 1999; Clark et al. 2004). Several other
theropod clades have members that possess >30 dentary
teeth (e.g. basal ornithomimosaurs, troodontids and
spinosaurids), but in each of these cases the tooth morphology is clearly distinct from that of Eshanosaurus
(Currie 1987; Pérez-Moreno et al. 1994; Charig and
Milner 1997). Thus, the combination of small size and
high tooth count does provide a useful character combination that allows the dentaries of therizinosauroids to be
distinguished from those of basal sauropodomorphs: on
this basis Eshanosaurus should be excluded from the latter
group.
3. Xu et al. (2001) and Rauhut (2003) pointed out that
dentary tooth crowns in both theropods (including therizinosauroids) and basal sauropodomorphs may exhibit slight
recurvature; as a result, this feature is ambiguous and does
not help to determine the relationships of Eshanosaurus.
4. Rauhut (2003) noted that possession of marginal
tooth denticles that extend perpendicular to the crown is
a dinosaur symplesiomorphy, which is an assumption that
is prevalent among dinosaur workers (see character
codings in the following phylogenetic analyses for several
examples: Butler et al. 2008; Upchurch et al. 2007; Yates
2007). However, this may not be the case: no
sauropodomorphs or ornithischians exhibit this character state and basal dinosaurs that lie outside of the
ornithischian ⁄ saurischian dichotomy are currently
unknown (Herrerasaurus and Eoraptor have sometimes
been considered to occupy this position but are now
generally regarded as primitive saurischians: Langer and
Benton 2006). Moreover, the situation in dinosaur
outgroups is unclear, as teeth are not preserved in the
majority of nondinosaurian dinosauromorph specimens
(Lagerpeton and Dromomeron, Sereno and Arcucci 1994;
Irmis et al. 2007) or have very weak denticles whose morphology is difficult to interpret (Silesaurus, Dzik 2003).
The assumption that perpendicular denticles represent the
primitive condition is, therefore, based primarily on the
683
presence of teeth bearing perpendicular serrations in a
referred specimen of the basal dinosauriform Marasuchus
(Bonaparte 1975) and in herrerasaurids (Sereno and
Novas 1994). However, given the lack of information on
many non-dinosaurian dinosauromorphs and the diversity of tooth morphologies present in the taxa close to the
base of Dinosauria, it could be argued that the distribution of this character is ambiguous in basal dinosaurs.
Resolution of this problem will be dependent on the
discovery of additional basal dinosaur and non-dinosaurian dinosauriform cranial material. On the basis of current
data, the possession of tooth serrations oriented perpendicular to the crown should probably be regarded as
either a saurischian or theropod symplesiomorphy. If the
former, this character cannot be used to resolve the
position of Eshanosaurus.
The near-perpendicular marginal denticles present in
Eshanosaurus appear to be autapomorphic for the taxon
whether it is referable to Sauropodomorpha or Therizinosauroidea (Xu et al. 2001), where members of both clades
generally have denticles that are oriented apically (e.g.
Clark et al. 2004; Galton and Upchurch 2004). However,
given the prevalence of perpendicular denticles in theropods, and their absence from all sauropodomorphs, it
could be argued that this feature provides additional support for referral of Eshanosaurus to Theropoda.
5. Ornithischian tooth crowns possess a basal swelling
(‘cingulum’) that is present on the lingual surface of maxillary teeth and the labial surface of maxillary teeth, so
that in mesial ⁄ distal view the crowns are asymmetrical
(Galton 1986). In contrast, the teeth of basal sauropodomorphs lack this structure and have symmetrical
crowns. Eshanosaurus teeth possess a swelling at the base
of the crown on the lingual surface (Xu et al. 2001, fig.
2F) and therefore differ from those of basal sauropodomorphs. However, it should be noted that sauropod teeth are also asymmetrical in mesial ⁄ distal view due
to the development of the ‘labial concavity’ and can also
be considered as similar to therizinosaur teeth in other
respects (e.g. in the retention of marginal denticles in
some non-neosauropods, such as Shunosaurus and Omeisaurus; see Upchurch and Barrett 2000). As a result, this
character cannot be used definitively to exclude Eshanosaurus from Sauropodomorpha. Rauhut (2003) was concerned that assessment of this character would depend on
the tooth position sampled in the dentary tooth row;
however, this is not the case, as the presence ⁄ absence of
the basal swelling is consistent along the entire dentary
tooth row in both sauropodomorph and ornithischian
dinosaurs (Galton 1986; pers. obs.).
6. As originally worded (Xu et al. 2001) this character
cannot be used to distinguish between the competing
referrals of Eshanosaurus: both therizinosauroids and basal
sauropodomorphs possess a constriction of the tooth
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PALAEONTOLOGY, VOLUME 52
crown adjacent to the root (Rauhut 2003). Although Xu
et al. (2001) note that the constriction seen in therizinosauroids differs from that in sauropodomorphs, this difference is actually created by the morphology described
by their character 7 (mesiodistal expansion of the tooth
root). Characters 6 and 7 essentially describe the same
feature and character 6 should be regarded as redundant.
7. In Eshanosaurus the tooth root constricts immediately below the crown and then expands mesiodistally so
that the width of the root equals or exceeds that of the
crown (IVPP V11579: Xu et al. 2001). This combination
of features does not occur in any known ornithischian or
sauropodomorph (pers. obs.), but does occur in some
theropods (e.g. troodontids, basal ornithomimosaurs),
including most therizinosauroids (Clark et al. 1994, 2004;
Xu et al. 1999; Zhang et al. 2001; Kirkland et al. 2005).
Although Rauhut (2003) has suggested that this feature
may vary along the dentary tooth row no evidence was
presented in support of this statement. Indeed, this feature does not appear to vary along the dentary tooth rows
of either sauropodomorphs or ornithischians (pers. obs.).
8. As noted by Xu et al. (2001) and Rauhut (2003),
both sauropodomorphs and therizinosaurs possess tooth
roots with circular cross-sections, so this feature does not
help to distinguish between isolated teeth from these two
clades.
9. Interdental plates are present in the majority of
theropods and basal sauropodomorphs and cannot be
used as a reliable character for distinguishing members of
these two clades (Xu et al. 2001; Rauhut 2003). Inclusion
of this character does indicate that Eshanosaurus cannot
be referred to Ornithischia, however, as all known members of this clade lack interdental plates.
10. Both basal sauropodomorphs and therizinosauroids
possess a ridge on the lateral surface of the dentary that
forms the ventral margin of a buccal emargination (Paul
1984; Barrett and Upchurch 2007; Text-fig. 1). As a result,
it was suggested that this character could not be used to
help determine the affinities of Eshanosaurus (Rauhut
2003). However, the morphology of this ridge (and of the
structures adjacent to it) differs markedly in basal sauropodomorphs and therizinosauroids, allowing the dentar-
ls
A
nf
lr
?emf
d
B
nf
lr
C
lr
ls
emf
Left mandibles of A, Eshanosaurus (IVPP V11579; reproduced and modified from Xu et al. 2001: ª2001 The Society
of Vertebrate Palaeontology. Reprinted with the permission of the Society of Vertebrate Palaeontology); B, the basal sauropodomorph
Massospondylus (SAM-PK-K1314); and C, the therizinosauroid Erlikosaurus (PST 100 ⁄ 111). Note that the lateral ridge of
Massospondylus is so weak that it is difficult to distinguish in lateral view. It is essentially a smooth change in the orientation of the
slope of the lateral surface. In contrast, the lateral ridges of Eshanosaurus and Erlikosaurus are well defined, forming an abrupt, angular
change in slope, and clearly demarcate a lateral shelf. The lateral shelf of Erlikosaurus is only visible rostrally in lateral view. The caudal
part of this structure faces almost directly dorsally and so is not visible laterally. Abbreviations: d, depression; emf, external
mandibular fenestra; lr, lateral ridge; ls, lateral shelf; nf, nutrient foramen. Scale bars equal 20 mm (A, B) and 50 mm (C).
TEXT-FIG. 1.
BARRETT: THE ENIGMATIC DINOSAUR ESHANOSAURUS
ies of these animals to be distinguished from each other.
In basal sauropodomorphs, the ridge is a low, rounded
eminence that merges into the main body of the dentary
ventrally without any distinct break in slope. This ridge
extends rostrally for a short distance, terminating within
the caudal half of the dentary. It delimits a very shallow,
transversely narrow buccal emargination that faces mainly
laterally; the tooth row is not strongly inset with respect to
the lateral margin of the buccal emargination (Barrett and
Upchurch 2007). In contrast, therizinosauroids possess an
exceptionally prominent and clearly defined lateral ridge
that forms the ventral and lateral boundary of a dorsolaterally oriented and transversely expanded shelf of bone
(‘lateral shelf’; Text-fig. 1): there is a clear and sharp
change in angle between the lateral shelf and the remainder of the lateral surface of the dentary. The shelf faces
dorsolaterally in its rostral part and dorsally in its caudal
part, and the tooth row is strongly inset from the lateral
margin of the dentary in dorsal view (e.g. Alxasaurus –
Russell and Dong 1993; Erlikosaurus – Clark et al.
1994; Beipiaosaurus – Xu et al. 1999). Moreover, the
dentary ridge extends into the rostral half of the dentary
in therizinosauroids. The morphology of Eshanosaurus
is almost identical to that of the therizinosauroids
Alxasaurus, Beipiaosaurus and Erlikosaurus and differs considerably from that present in any basal sauropodomorph,
thereby providing strong support for referral of Eshanosaurus to Therizinosauroidea (Xu et al. 2001).
11. Rauhut (2003) correctly points out that a ventrally
deflected rostral end of the dentary is present not only
in therizinosaurs, but also in some basal sauropodomorphs (e.g. Mussaurus: Pol and Powell 2007). Consequently, this feature cannot be used to support the
therizinosauroid affinities of Eshanosaurus to the exclusion of other taxa.
It has also been suggested that Eshanosaurus cannot be
referred to Therizinosauroidea as its dentary teeth bear a
distinct, apicobasally extending ridge on the lingual surface: this feature was stated to be ‘present on at least
some prosauropod teeth, but … unknown in therizinosaurid teeth’ (Lamanna in Kirkland and Wolfe 2001,
p. 412). However, although a lingual ridge is present in
eusauropods, it is completely absent in basal sauropodomorphs (Galton and Upchurch 2004; Upchurch
et al. 2004; Barrett and Upchurch 2007). Moreover, a
similar ridge is present on the dentary teeth of the North
American therizinosauroid Falcarius (Kirkland et al. 2005;
L. E. Zanno, pers. comm. 2008), demonstrating that this
feature is present in at least some members of the clade.
Consequently, the presence of the lingual ridge could be
regarded as evidence for the referral of Eshanosaurus to
Therizinosauroidea and against its assignment to a basal
sauropodomorph (contra Lamanna in Kirkland and Wolfe
2001).
685
Finally, Zhao and Xu (1998) proposed one other character in support of the therizinosauroid affinities of
Eshanosaurus, which was mentioned but not discussed by
Xu et al. (2001): the presence of a small number of large
nutrient foramina on the dorsal surface of the lateral
shelf. However, although such foramina are rare among
theropods, they are common in ornithischians and basal
sauropodomorphs (Galton 1973; Paul 1984). As a result,
this character is equivocal and could be used to support
relationships with either sauropodomorphs or therizinosauroids.
In summary, many of the aforementioned characters
are insufficient to distinguish the dentaries and dentary
dentitions of basal sauropodomorphs and therizinosaurs
(Rauhut 2003). This is perhaps unsurprising as Paul
(1984) noted a large number of similarities between the
skulls of these groups, which he proposed were evidence
of a close phylogenetic relationship. However, subsequent
work has clearly demonstrated that therizinosauroids are
deeply nested within Theropoda and these features
are now regarded as homoplasies (Clark et al. 2004). Nevertheless, at least three features – the caudad reduction in
dentary tooth size, the high dentary tooth count per unit
length of jaw and the detailed morphology of the buccal
emargination and ridge – provide positive evidence for
referral of Eshanosaurus to Therizinosauroidea. Several
other features, such as the morphology of the tooth roots,
are also consistent with this interpretation. In contrast,
Eshanosaurus possesses no unequivocal sauropodomorph
synapomorphies: indeed, several of the character states
present in the specimen argue against referral to this
clade. On the basis of current evidence, referral of Eshanosaurus to Therizinosauroidea is more strongly supported
than the alternative hypothesis of referral to Sauropodomorpha.
DISCUSSION
If accepted as a member of Therizinosauroidea, the provenance of Eshanosaurus implies that coelurosaur diversification occurred much earlier than is generally acknowledged
and also indicates that numerous coelurosaur lineages
should be represented in the Early and early Middle Jurassic (Xu et al. 2001; Rauhut 2003; Wills et al. 2008).
These conclusions conflict with current knowledge of
theropod phylogeny and the remainder of the known
fossil record of coelurosaurs, which otherwise indicates
that Coelurosauria began its radiation sometime in the late
Middle Jurassic (Sereno 1999; Holtz 2000; Rauhut 2003,
2005; Holtz et al. 2004). No other Early Jurassic coelurosaurs are known and Eshanosaurus implies that a significant portion of the history of this clade may still remain
to be discovered. However, the purported Early Jurassic
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PALAEONTOLOGY, VOLUME 52
age of the specimen remains a cause for concern. Some of
the features present in Eshanosaurus (e.g. the lateral shelf
and the ventrally deflected rostral end of the dentary)
indicate that this taxon is more derived than the Early
Cretaceous therizinosauroid Falcarius (Kirkland et al.
2005). Although this may simply indicate that other basal
therizinosaur fossils still await discovery in the Jurassic,
the length of time separating Eshanosaurus and Falcarius is
anomalous (Kirkland et al. 2005). It may be noteworthy
that the type area for Eshanosaurus, the Dianzhong Basin,
contains a thick Mesozoic sequence that includes not only
basal Jurassic sediments (referred to as the Lower Lufeng
Formation or the Fengjiahe Formation by different
authors: Ye 1975; Xu et al. 2001) but also Middle Jurassic
and Early Cretaceous deposits (Bureau of Geology and
Mineral Resources of Yunnan Province 1990). As the precise age of Eshanosaurus has profound implications for
understanding the timing of the coelurosaur radiation,
additional collecting and stratigraphical work is needed at
the type locality in order to confirm or refute its Early
Jurassic age. In the meantime, the potential importance of
Eshanosaurus should be assessed critically and its unprecedented stratigraphical position should not be used as a criterion for excluding this taxon from analyses of
coelurosaurian and theropod evolution.
Acknowledgements. Many thanks to Xu Xing for granting access
to material in IVPP and to many other colleagues in China for
their help and hospitality, including Wang Xiao-Lin, Wang
Yuan, Zhang Jiang-Jong and Zhou Zhonghe. Richard Butler,
Lindsay Zanno, Xu Xing and Jim Clark are also thanked for discussion and their careful reviews of the manuscript. Thanks also
to those curators in the other institutions mentioned: Sheena
Kaal (SAM), Michael Raath (BP) and Carl Mehling (AMNH).
Phil Crabb (NHM Image Resources) provided the photograph
in Text-figure 1B; Angela Milner supplied the photograph of
Erlikosaurus in Text-figure 1C, which was taken with the kind
permission of Perle Altangerel. Travel to Beijing was funded by
the Royal Society of London, the Hodson Award of the Palaeontological Association and the Palaeontological Innovation Fund
of the Natural History Museum.
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