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LETTER doi:10.1038/nature14307
An enigmatic plant-eating theropod from the Late
Jurassic period of Chile
Fernando E. Novas
1,2
, Leonardo Salgado
1,3
, Manuel Sua
´rez
4
, Federico L. Agnolı
´n
2,5
, Martı
´n D. Ezcurra
6
, Nicola
´s R. Chimento
2
,
Rita de la Cruz
7
, Marcelo P. Isasi
1,2
, Alexander O. Vargas
8
& David Rubilar-Rogers
8,9
Theropod dinosaurs were the dominant predators in most Mesozoic
era terrestrial ecosystems
1
. Early theropod evolution is currently
interpreted as the diversification of various carnivorous and curs-
orial taxa, whereas the acquisition of herbivorism, together withthe
secondary loss of cursorial adaptations, occurred much later among
advanced coelurosaurian theropods
1,2
. A new, bizarre herbivorous
basal tetanuran from the Upper Jurassic of Chile challenges this
conception. The new dinosaur was discovered at Ayse
´n, a fossil
locality in the Upper Jurassic Toqui Formation of southern Chile
(General Carrera Lake)
3,4
. The site yielded abundantand exquisitely
preserved three-dimensional skeletons of small archosaurs. Several
articulated individuals of
Chilesaurus
at different ontogenetic stages
have been collected, as well as less abundant basal crocodyliforms,
and fragmentary remains of sauropod dinosaurs (diplodocids and
titanosaurians).
Theropoda Marsh, 1881
Tetanurae Gauthier, 1986
Chilesaurus diegosuarezi
gen. et sp. nov.
Etymology. In reference to Chile, and honoring Diego Sua
´rez, who at
the age of 7, discovered the first bone remains in the Toqui Formation.
Holotype. Servicio Nacional de Geologı
´a y Minerı
´a, Chile (SNGM)-
1935 consists of a nearly complete, articulated skeleton, approximately
1.6 m long (Fig. 1, Supplementary Information and Extended Data
Fig. 1). Holotype specimen was skeletally immature at the time of its
death, as evidenced by the incomplete fusion of neurocentral sutures.
This ontogenetic inference agrees with the size of the holotype, which
represents 50% the length of the larger specimen SNGM-1888 (ref. 3).
Paratypes. Postcranial skeletons of four individuals, corresponding to
different ontogenetic stages, ranging approximately from 1.2 to 3.2 m
in total length (Extended Data Table 1). Several specimens referred to
as indeterminate theropods and tetanurans previously
3
are here
referred to as Chilesaurus diegosuarezi.
Locality and horizon. Central Patagonian Cordillera, Ayse
´n (Chile;
approximately 46uS); Toqui Formation
3,4
, Tithonian, latest Jurassic.
Diagnosis. Chilesaurus differs from other dinosaurs in the following
combination of autapomorphies: premaxilla short and deep, with
prominent plate-like postnarial process; teeth leaf-shaped, being finely
denticulate only on the crown apex of erupting teeth; coracoid sub-
quadrangular in side view and with transversely thick margins; manual
digit II with short pre-ungual phalanges; manual digit III atrophied;
iliac blade with posterodorsal prominence; ischiadic peduncle of ilium
robust; supracetabular crest absent; pubis fully retroverted; pubic
shaft rod-like and distally unexpanded; femoral mediodistal crest
absent; tibia without fibular crest. In addition, Chilesaurus shows the
following unique combination of characters: dentary deeper anteriorly
than posteriorly; cervicals with septate and paired pleurocoels; pubic
apron transversely narrow; ischia connected through a proximodis-
tally extended medial lamina (‘ischial apron’); femoral greater trochan-
ter anteroposteriorly expanded, astragalar ascending process lower
than astragalar body; calcaneum subtriangular in distal view; meta-
tarsal I robust, elongate, and proximally compressed transversely;
metatarsal II transversely wider than the other metatarsals; pedal digit
I large.
Isolated skull material (including premaxilla, maxillae, frontals,
postorbital, squamosal, basicranium, ectopterygoid and dentary;
Extended Data Fig. 2), suggests a proportionally small head for
Chilesaurus. The premaxilla is short and deep, with a rugose rostral
margin that suggests a ramphotheca (Fig. 2). Frontals are elongate and
narrow and participate extensively in the orbital margin. The basi-
sphenoidal recess is deep. The dentary is short and deep, with a down-
turned symphyseal region but a straight alveolar margin. Dentary teeth
are tall, leaf-shaped, and procumbent, with small serrations restricted
to the crown apex (Fig. 2).
Cervical vertebrae are long and low, forming a slender neck.
Cervical and anterior dorsal vertebrae possess a pair of septate pleur-
ocoels, which are absent posterior to the pectoral region (Fig. 1g).
‘Pectoral’ vertebrae bear prominent hypapophyses.
The scapular blade (Extended Data Fig. 3) is elongate and slightly
anteroposteriorly expanded distally, as in basal averostrans
5
. The cor-
acoid is subquadrangular and lacks theropod characteristics such as
the posteroventral process and biceps tuberosity
1
. It is notably thick
transversely, contrasting with the delicate anterodorsal and dorsal
margins of most dinosaurs. The limb bones are stout, as in sauropo-
domorphs, and forelimb length is 56% that of hind limbs. The
humerus is proximodistally short and transversely wide (Extended
Data Fig. 3). The single proximal carpal is large, with a transversely
convex proximal articular surface. Metacarpals I–III are present, but
only manual digits I and II are well developed (Fig. 1d–f). Metacarpal I
is stout, and phalanx 1-I is short and strongly twisted along its main
axis, as in basal sauropodomorphs
6
. The ungual of digit I is shorter
than metacarpal II and less curved than most basal tetanurans
5,7
.
Metacarpal II is the longest, and its digit presents strongly shortened
pre-ungual phalanges, as in some ceratosaurians
8
. Metacarpal III is
much more slender than in basal theropods, and its digit comprises
a single minute phalanx.
The ilium is dolichoiliac, typical for Theropoda
1
(Fig. 1b). The pubic
pedicle is elongate (as in sauropods, ornithischians and therizino-
saurs
2,9
), and the ischiadic peduncle is bulbous, as in ornithischians
and alvarezsaurid coelurosaurs
10
. A prominent supratrochanteric pro-
cess is present on the posterodorsalcorner of the ilium, similar to those
of sauropods, therizinosaurs, paravians, and some ornithischians
11–13
.
The acetabular roof is transversely narrow and a supracetabular crest
is absent, as occurs in derived coelurosaurs and ornithopods
1,11,13
.
The pubis (Fig. 1b, c) closely resembles that of basal ornithischians,
1
Conicet.
2
Museo Argentino de Ciencias Naturales ‘‘B. Rivadavia’’, Av. A
´ngel Gallardo 470 (C1405DJR), Buenos Aires, Argentina.
3
Instituto de Investigacio
´n en Paleobiologı
´a y Geologı
´a, Universidad
Nacional de Rı
´o Negro, General Roca 1242, General Roca (8332), Rı
´o Negro, Argentina.
4
Universidad Andres Bello, Geologı
´a, Facultad de Ingenierı
´a, Sazie 2315, Santiago, Chile.
5
Fundacio
´n de Historia
Natural Fe
´lix de Azara, Universidad Maimo
´nides, Hidalgo 775 (C1405BDB), Buenos Aires, Argentina.
6
School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham
B15 2TT, UK.
7
Servicio Nacional de Geologı
´a y Minerı
´a, Avenida Santa Marı
´a 0104, Santiago 8330177, Chile.
8
Red Paleontolo
´gica U-Chile. Laboratorio de Ontogenia y Filogenia, Departamento de Biologı
´a,
Facultad de Ciencias, Universidad de Chile, Santiago 7800003, Chile.
9
A
´rea Paleontologı
´a, Museo Nacional de Historia Natural de Chile, casilla 787, Santiago, Chile.
00 MONTH 2015 | VOL 000 | NATURE | 1
therizinosaurs and dromaeosaurid paravians in being fully retroverted,
with a reduced proximal end bearing a posteriorly open obturator
notch
1,2
. The pubic apron is transversely narrow and the pubis has a
rod-like shaft. It is distally unexpanded with a rounded contour, shar-
ply contrasting with the prominent distal ‘foot’ of other theropods
1
.
The ischium (Fig. 1a, b) is proximally expanded and lacks an obturator
process. Notably, both ischia are connected through a proximodistally
extended medial lamina (ischial apron), a feature reported in some
megalosauroids
14
.
The femur is robust (Extended Data Fig. 4). The greater trochanter
is anteroposteriorly expanded, similar to coelurosaurs. The anterior
trochanter is wing-like and proximally projected, and the fourth tro-
chanter is semicircular. The distal third of the femur resembles saur-
opodomorphs in that it lacks distinctive theropod features, such as an
anteromedial elliptical muscle scar, a mediodistal crest and its assoc-
iated medial adductor fossa. The cnemial crest of tibia (Extended Data
Fig. 4) is rounded in lateral view, as in basal sauropodomorphs and
basal ornithischians, and differs from the subtriangular crest
present in most basal theropods
1,15
. As in sauropodomorphs, and
unlike most theropods, the proximal end of the tibia lacks a fibular
crest
1
. Like theropods, the distal end of the tibia is anteroposteriorly
compressed with a laterally extending malleolus, more transversely
expanded than in coelophysoids, but less than in tetanurans
1
.
The fibula lacks a proximomedial pocket and iliofibular tubercle.
The tarsus (Fig. 1k–m) resembles basal saurischians
16
. The astragalar
ascending process is low and broad, unlike tetanurans, in which
it is laminar, tall, and transversely wide
1,6,17
. The proximal astragalar
surface possesses a deep, well-defined basin posterior to the ascending
process, as in basal dinosaurs. As in early saurischians (for example,
Herrerasaurus, basal sauropodomorphs), the calcaneum of Chilesaurus
is transversely wide and subtriangular in distal view, rather than rect-
angular and disc-shaped as in theropods
1,16,17
. The foot is wide and
proximodistally short (Fig. 1h–j). The proximal half of metatarsal I is
transversely compressed but anteroposteriorly expanded, unlike most
theropods, in which it tapers proximally. Metatarsal I of Chilesaurus
representsmore than 50% of the length of metatarsal II, in contrast with
b
a
jih
k
m
l
edc
gf
ap
b
mt I
mt I
I
II III
IV
mt IV
I
I
I
II
II
III
IV
prz
2 cm
2 cm 0.5 cm
0.5 cm
50 cm
ap
2 cm
2 cm
poz
ppl
ast
calc
c
mtc I
mtc III
mt II
mt III
isa
p
is
ps
Figure 1
|
Skeletal anatomy of
Chilesaurus diegosuarezi
gen. et sp. nov.
a, Reconstructed skeleton (SNGM-1935). b, Fourth cervical vertebra (SNGM-
1935) in right lateral view, with a close-up of tabicated anterior pleurocoel.
c,d, Composite reconstruction of right hand (carpals, metacarpals, and non-
ungual phalanges of digits I and II are from specimen SNGM-1935; ungual
phalanges I and II are from specimen SNGM-1937; metacarpal III is from
specimen SNGM-1887) in dorsal (c) and medial (d) views. e, Pelvic girdle
(SNGM-1936) in right lateral view. f, Articulated ischia (SNGM-1936) in
posterior view. g, Articulated pubes (SNGM-1936) in anterior view.
h, Proximal tarsals (SNGM-1888) in distal view. i,j, Left astragalus (SNGM-
1936) in proximal (l) and anterior (m) views. k–m, Left pes (SNGM-1937) in
dorsal (k), medial (l) and proximal (m) views. ap, ascending process; ast,
astragalus; b, basin; c, carpal; calc, calcaneum; ia, ischiadic apron; is, ischium;
mtc, metacarpal;p, pubis; poz, postzygapophysis; pps,posterior pleurocoel; prz,
prezygapophysis; ps, pubic symphysis; I, II, III, IV, digits first to fourth.
2 | NATURE | VOL 000 | 00 MONTH 2015
RESEARCH LETTER
most other theropods (25–33%)
1,17
. Metatarsal III is the longest, but
metatarsal II is the thickest, as in basal sauropodomorphs. Digit I is
large, only slightly shorter than digit II, approaching the tetradactyl
condition of early sauropodomorphs, ornithischians
18
and derived
therizinosaurs
2
.
The bizarre anatomy of Chilesaurus raises interesting questions
about its phylogenetic relationships. We scored Chilesaurus into four
different integrative archosauriform, theropod and sauropodomorph
data sets
9,19–21
. Remarkably, all these analyses placed Chilesaurus as
a member of Theropoda, near the origin of tetanurans
5
(Fig. 3a),
dismissing conceivable positions near Therizinosauria, Sauropodo-
morpha or Ornithischia. The theropodan position of Chilesaurus is
supported by pleurocoels in cervical and anterior dorsal vertebrae;
hypapophyses on ‘pectoral’ vertebrae; preacetabular process of ilium
ab
c
ed
f
alv
cr
1 cm
0.2 cm 0.05 cm
0.01 cm
ro
Figure 2
|
Selected cranial bones and teeth of
Chilesaurus diegosuarezi
gen.
et sp. nov. (SNGM-1935). a, Partial right (?) maxilla in lateral view. b,Left
premaxilla in medial view. c, Right dentary in lateral view. d, Details of dentary
teeth in lingual view. e, Crownof unerupted dentarytooth. f, Detail of the carina
of an unerupted tooth (arrows indicate denticle positions). alv, alveoli; cr,
crown tooth; ro, root tooth.
4
PCO2PCO2
PCO2
PCO1
2
–2
–4
–6
–5
–4
–5 0 5
–2 0
0510
2
–6
–4
–2
2
4
6
0
–4
–3
–2
–1
0
1
2
0
237
201.3
174.1
163.5
145
100.5
66
Crn
Nor
Rht
Het
Sin
Plb
Toa
Aal
Baj
Bth
Clv
Oxf
Kim
Tth
Ber
Vlg
Hau
Brm
Apt
Alb
Cnm
Tur
Con
Stn
Cmp
Maa
a
Triassic
L
L
L
E
E
M
suoecaterCcissaruJ
Oviraptorosauria
Paraves
Therizinosauria
Ornithomimosauria
Megalosauroidea
Allosauroidea
Tyrannosauroidea
Sauropoda
Ceratosauria
Dinosauria
Saurischia
Theropoda
Neotheropoda
Averostra
Tetanurae
Neotetanurae
Coelurosauria
Maniraptora
Alvarezsauroidea
‘Prosauropods’
Coelophysoidea
Herrerasauridae
Chilesaurus
Ornithischia
b
c
d
Figure 3
|
Phylogenetic relationships of
Chilesaurus diegosuarezi
gen. et sp.
nov. among main dinosaur clades and its plots in the theropod
morphospaces. a, Time-calibrated simplified strict consensus tree, in which
the green bars indicate herbivorous dinosaur lineages
28
. E, Early; L, Late; M,
Middle. Aal, Aalenian; Alb, Albian; Apt, Aptian; Baj, Bajocian; Ber, Berriasian;
Brm, Barremian; Bth, Bathonian; Clv, Callovian; Crn, Carnian; Cmp,
Campanian; Cnm, Cenomanian; Con, Coniacian; Hau, Hauterivian; Het,
Hettangian; Kim, Kimmeridgian; Maa, Maastrichtian; Nor, Norian; Oxf,
Oxfordian; Plb, Pliensbachian; Rh, Rhaetian; Sin, Sinemurian; Stn, Santonian;
Tth, Tithonian; Toa, Toarcian; Tur, Turonian; Vlg, Valanginian. Numbers
indicate millions of years ago. b–d,Chilesaurus diegosuarezi gen. et sp. nov.
plotted in the theropod morphospace (principal coordinate (PCO)1 versus
PCO2) based on axial skeleton (b); scapular girdle and forelimb (c); and pelvic
girdle (d). Red dots in b–d indicate the position of Chilesaurus.
00 MONTH 2015 | VOL 000 | NATURE | 3
LETTER RESEARCH
dorsoventrally expanded; femoral fourth trochanter semicircular; and
tibia distally expanded and with lateral malleolus extending strongly
laterally. Tetanuran affinities are supported by scapular blade elongate
and strap-like; distal carpal semilunate; and manual digit III reduced
(Supplementary Information). For a basal tetanuran, Chilesaurus pos-
sesses a number of surprisingly plesiomorphic traits on the hindlimbs,
especially in the ankle and foot, which resemble basal sauropodo-
morphs
7,9,12
. These features are here considered as secondary reversals
that might be related to a less-cursorial mode of locomotion.
Furthermore, derived features of the dentary and teeth shared by
Chilesaurus, sauropodomorphs and therizinosaurs are interpreted as
homoplasies related to herbivorous habits
22–25
.Inthiscontext,pubic
retroversion of Chilesaurus may be related to an increased gut capacity
for processing plant material
25
.
The discovery of Chilesaurus lends support to the interpretation
22,23
that dietary diversification towards herbivory was more common-
place among basal theropods than previously thought. Independent
evolution of herbivory has been recognized for several major coelur-
osaurian subclades
23
, but for just a single probable example outside
Coelurosauria (that is, the toothless ceratosaurian Limusaurus
26,27
).
Chilesaurus expands the list of non-coelurosaurian theropods that
shifted their diet from carnivore to herbivore.
Chilesaurus represents an extreme case of mosaic evolution among
dinosaurs, owing to the presence of dental, cranial and postcranial fea-
tures that are homoplastic with multiple disparate groups. Using quant-
itative morphospace analysis, we explored morphospace occupation of
different skeletal regions in Chilesaurus with respect to a variety of avian
and non-avian theropods. This shows that Chilesaurus has a ceratosaur-
like axial skeleton, a ‘basal tetanuran’ forelimb and scapular girdle, a
coelurosaur-like pelvis, and a tetanuran-like hindlimb (Fig. 3b–d and
Extended Data Fig. 5). General ankle and foot construction does not
group with any theropod clade, probably as a result of the characters
shared by Chilesaurus, sauropodomorphs and herrerasaurids.
Chilesaurus is the numerically dominant taxon in the Ayse
´n tet-
rapod fossil assemblage, and represents an unusual case of a theropod
having the palaeoecological role of a preeminent small-to-medium
sized herbivore in a Jurassic ecosystem. This is in sharp contrast with
other Late Jurassic dinosaur assemblages (for example, Tendaguru and
Morrison formations
11,27
), in which ornithischian dinosaurs are the
most abundant small-to-medium sized herbivores. Available evidence
indicates that Chilesaurus is a unique dinosaur lineage known only
from southern South America, suggesting an outstanding case of
endemism among otherwise relatively cosmopolitan worldwide
Jurassic dinosaur faunas
28
.
Chilesaurus illustrates how much relevant data on the early diver-
sification of major dinosaur clades remain unknown. It also provides
an important cautionary benchmark in our attempts to gain a reliable
view of the overall evolutionary history of Dinosauria.
Online Content Methods, along with any additional Extended Data display items
and SourceData, are available in theonline version of the paper;references unique
to these sections appear only in the online paper.
Received 19 September 2014; accepted 10 February 2015.
Published online 27 April 2015.
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Supplementary Information is available in the online version of the paper.
Acknowledgements We thankP. Barrett, A. Milner and R. Butler for comments on early
versions of this manuscript. We are grateful to C. Alsina, M. Milani, R. Stoll and
M. Aranciaga for field assistance and technical preparation of Chilesaurus specimens.
G. Lio executed the silhouette of Chilesaurus in Fig. 1. C. Burke offered support to
conduct fieldwork and technical preparation of the specimens. We are indebted to the
AgenciaNacional de Promocio
´n Cientı
´ficay Tecnolo
´gica (PICT 2010-066to F.E.N.) and
the Fondo Nacionalde Desarrollo Cientı
´ficoy Tecnolo
´gico (no. 1121140and 1030162
to M.S.) for continuing financial assistance.
Author Contributions F.E.N., L.S., M.S., F.L.A., M.D.E., N.R.C.,A.O.V. and D.R.-R. designed
the study,collected data, performed the comparative and analytical work, andwrote the
paper. R.d.l.C. and M.P.I. collected data and contributed to the writing and discussion.
Author Information Datahave been deposited in ZooBankunder Life ScienceIdentifier
(LSID) urn:lsid:zoobank.org:act:7B6DE8C7-C78D-48C0-B818-65C454AEFB58.
Reprints and permissions information is available at www.nature.com/reprints. The
authors declare no competing financial interests.Readers are welcome to comment on
the online version of the paper. Correspondence and requests for materials should be
addressed to F.E.N. (fernovas@yahoo.com.ar).
4 | NATURE | VOL 000 | 00 MONTH 2015
RESEARCH LETTER
Extended Data Figure 1
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Holotype of
Chilesaurus diegosuarezi
gen. et sp.
nov. (SNGM-1935) as it was found in the field. Cd, caudal vertebrae; Cv,
cervical vertebrae; Dv, dorsal vertebrae; Lf, left forelimb; Lfem, left femur; Lsc,
left scapulocoracoid; Ltib, left tibia; Rf, right forelimb; Sk, skull.
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Extended Data Figure 2
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Selected skull bones of
Chilesaurus diegosuarezi
gen. et sp. nov. (SNGM-1935; holotype). a, Right frontal in dorsal view;
b, right postorbital in lateral view;c, incomplete right (?) maxilla in lateral view;
d, right dentary in medial view. al, alveolus; ao, antorbital opening; or, orbital
rim; t, teeth; tf, lower temporal fossa rim.
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Extended Data Figure 3
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Scapular girdle and selected forelimb bones of
Chilesaurus diegosuarezi
gen. et sp. nov. a, b, Left scapula and coracoid
(SNGM-1938) in lateral (a) and posterior (b) views. c, Left humerus (SNGM-
1938) in anterior view; d, left radius (SNGM-1935, holotype) in lateral view;
and e, left ulna (SNGM-1935, holotype) in lateral view. cf, coracoid foramen;
dp, deltopectoral crest; gl, glenoid cavity; ol, olecranon process.
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Extended Data Figure 4
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Selected hindlimb elements of
Chilesaurus
diegosuarezi
gen. et sp. nov. a, b, Right femur (SNGM-1935) in anterior
(a) and lateral (b) views. c–e, Articulatedright tibia and fibula (SNGM-1935) in
posterior (c), medial (d) and proximal (e) views. at, anterior trochanter; cn,
cnemial crest; f, fibula; fh, femoral head, 4t, fourth trochanter; gt, greater
trochanter, ic, inner condyle; oc, outer condyle; t, tibia; tfc, tibiofibular crest.
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Extended Data Figure 5
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Bivariate plots showing the results of the
morphospace occupation analysis of
Chilesaurus diegosuarezi
gen. et sp.
nov. based on characters of different regions of the skeleton, taken from the
modified data matrix and the first and second axes of the principal
coordinate analysis. a–d, Bivariate plots using all the characters (a), cranial
characters (b), hindlimb zeugopodium and stylopodium characters (c), and
tarsal and pedal characters (d). The convex hulls represent different
dinosauriform groups rather than statistically distinct clusters. Light grey
polygon, non-neotheropod dinosauriforms; blue polygon, non-averostran
neotheropods; green polygon, ceratosaurs; pink polygon, megalosauroids; dark
grey polygon, allosauroids; light blue polygon, coelurosaurs; red dot,
Chilesaurus.
LETTER RESEARCH
Extended Data Table 1
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Selected postcranial measurements of
three specimens of Chilesaurus diegosuarezi gen. et sp. nov.
Measurements are in mm. All the values represent maximum mea-
surable lengths.
Maximum deviation of the digital calliper equals 0.02 mm but measurements were rounded to the
nearest 0.1 mm.
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