Content uploaded by Federico Agnolin
Author content
All content in this area was uploaded by Federico Agnolin on Dec 13, 2017
Content may be subject to copyright.
FORELIMB POSTURE IN
CHILESAURUS DIEGOSUAREZI
(DINOSAURIA, THEROPODA)
AND ITS BEHAVIORAL AND
PHYLOGENETIC IMPLICATIONS
1Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino de Ciencias Naturales ‘‘Bernardino Rivadavia’’, Av. Ángel Gallardo 470, C1405DJR
Buenos Aires, Argentina.
2Fundación de Historia Natural Félix de Azara, Universidad Maimónides, Hidalgo 775, C1405BDB Buenos Aires, Argentina.
3CONICET, Consejo Nacional de Investigaciones Científicas y Tecnológicas.
4Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales ‘‘Bernardino Rivadavia’’, Av. Ángel Gallardo 470, C1405DJR Buenos Aires, Argentina.
5Instituto de Investigación en Paleobiología y Geología, Universidad Nacional de Río Negro, Av. General Roca 1242, 8332 General Roca, Río Negro, Argentina
6Universidad Andrés Bello, Geología, Facultad de Ingeniería, Sazie 2315, 8370092 Santiago, Chile.
7Servicio Nacional de Geología y Minería, Av. Santa María 0104, 8330177 Santiago, Chile.
8Área Paleontología, Museo Nacional de Historia Natural de Chile, Casilla 787 Santiago, Chile.
9Red Paleontológica U-Chile. Laboratorio de Ontogenia y Filogenia, Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, 7800003
Santiago, Chile.
NICOLÁS R. CHIMENTO1
FEDERICO L. AGNOLIN1,2
FERNANDO E. NOVAS1,3
MARTÍN D. EZCURRA3,4
LEONARDO SALGADO3,5
MARCELO P. ISASI1,3
MANUEL SUAREZ6
RITA DE LA CRUZ7
DAVID RUBILAR-ROGERS8
ALEXANDER O. VARGAS9
Also appearing in this issue:
Two new taxa unveil the
previously unrecognized diversity
of Coelophysidae in the Late Triassic
of South America.
A new ornithomimosaur taxon
from the Early Cretaceous of Niger
and new anatomical data on
Nqwebasaurus from South Africa.
Murusraptor had a brain morphology
similar to tyrannosaurids but
neurosensorial capabilities
resembling that of allosauroids.
Submitted: January 24th, 2017 - Accepted: June 11st, 2017 - Published online: June 13rd , 2017
To cite this article: Nicolás R. Chimento, Federico L. Agnolin, Fernando E. Novas, Martín D. Ezcurra, Leonardo
Salgado, Marcelo P. Isasi, Manuel Suarez, Rita De La Cruz, David Rubilar-Rogers, and Alexander O. Vargas (2017).
Forelimb posture in Chilesaurus diegosuarezi (Dinosauria, Theropoda) and its behavioral and phylogenetic
implications. Ameghiniana 54: 567–575.
To link to this article: http://dx.doi.org/10.5710/AMGH.11.06.2017.3088
PLEASE SCROLL DOWN FOR ARTICLE
567
AMGHB2-0002-7014/12$00.00+.50
FORELIMB POSTURE IN CHILESAURUS DIEGOSUAREZI
(DINOSAURIA, THEROPODA) AND ITS BEHAVIORAL AND
PHYLOGENETIC IMPLICATIONS
NICOLÁS R. CHIMENTO1, FEDERICO L. AGNOLIN1,2, FERNANDO E. NOVAS1,3 , MARTÍN D. EZCURRA3,4, LEONARDO SALGADO3, 5,
MARCELO P. ISASI1, 3, MANUEL SUAREZ6, RITA DE LA CRUZ7, DAVID RUBILAR-ROGERS8, AND ALEXANDER O. VARGAS9
1Laborat orio de Anatomía Comparada y Evolución de los Vertebrados , Museo Argentino de Ciencias Naturales ‘‘Bernard ino Rivadavia’’, Av. Ánge l Gallardo 470,
C1405DJR Bue nos Aires, Argentina.
2Fundación de Historia Natural Félix de Azara, Universidad Maimónides, Hidalgo 775 , C1405BDB Buenos Aires, Argentina.
3CONICET, Consejo Nacional de Invest igaciones Científicas y Tecnológicas.
4Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales ‘‘Bernar dino Rivadavia’’, Av. Ángel Gallardo 470, C1405DJR Buenos Aires, Argentina.
5Instituto de Investigación en Paleo biología y Geología, Universidad Nacional de R ío Negro, Av. General Roca 1242, 8332 General Roca, Río Ne gro, Argentina
6Universidad Andrés Bello, Geología, Facultad de Ingeniería, Sazie 2315, 8370092 Santiago, Chi le.
7Servicio Nacional de Geología y Minería, Av. Sa nta María 0104, 8330177 Santiago, Chile.
8Área Paleonto logía, Museo Nacional de Historia Natural de Chile, Casilla 787 Santiago, Chile.
9Red P aleontológic a U-Chile . Laboratorio de Ontogenia y Filogenia, Departament o de Biología , Faculta d de Ci encias, U niversidad de Chile , Las P almeras 3 425,
7800003 Sant iago, Chile.
Abstract. Many dinosaur skeletons show evidence of behavior, including feeding, predation, nesting, and parental care. The resting posture
of the forelimbs has been studied in some theropod species, in relation to the acquisition of flight in advanced maniraptoran theropods. Chile-
saurus diegosuarezi is a bizarre tetanuran recently described from the Toqui Formation (latest Tithonian) of southern Chile that is represented
by multiple well-preserved and articulated specimens. The aim of the present work is to analyze the forelimb posture of four articulated
specimens of Chilesaurus diegosuarezi, focusing on its anatomical description, and phylogenetic and behavioral implications. All the preserved
specimens show strongly ventrally flexed arms with the hands oriented backwards, an arrangement that closely resembles those in dinosaur
specimens previously described as preserving resting posture, such as Mei long, Sinornithoides youngi and Albinykus baatar. As a result, it seems
that individuals of Chilesaurus diegosuarezi have been in passive activity (e.g. feeding, resting) when they were buried quickly, allowing their
fossilization in life position and preserving the forelimb resting posture. The arrangement of the forelimb bones in Chilesaurus could show the
first evidences of the structures linked to the muscles that flex the forearms, features related with the acquisition of flying control in advanced
maniraptorans.
Key words. Forelimb resting posture, soft tissue, flexion, flight evolution.
Resumen. POSTURA DE LAS EXTREMIDADES ANTERIORES EN CHILESAURUS DIEGOSUAREZI (DINOSAURIA, THEROPODA) Y SUS IMPLICAN-
CIAS FILOGÉNETICAS Y DE COMPORTAMIENTO. Muchos esqueletos de dinosaurios muestran evidencias de comportamiento, incluyendo
alimentación, depredación, anidación y cuidados parentales. La posición de reposo de los miembros anteriores ha sido estudiada en algunos
terópodos, particularmente en relación con la adquisición del vuelo en maniraptores derivados. Chilesaurus diegosuarezi es un extraño teta-
nuro recientemente descrito, proveniente de la Formación Toqui (Titoniano superior) del sur de Chile, el cual se encuentra representado
por varios especímenes bien preservados y articulados. El objetivo de este trabajo es analizar la postura de los miembros anteriores de cua-
tro especímenes articulados de Chilesaurus diegosuarezi, focalizando en su descripción anatómica, y las implicancias filogenéticas y de com-
portamiento. Todos los especímenes conservados muestran brazos fuertemente flexionados ventralmente, con las manos orientadas hacia
atrás, una posición muy similar a la que ha sido reconocida como postura de reposo en ejemplares de dinosaurios descritos previamente, como
Mei long, Sinornithoides youngi y Albinykus baatar. Como resultado, es posible que los individuos de Chilesaurus hayan estado en actividad pa-
siva (por ejemplo, alimentándose o descansando) cuando fueron sepultados rápidamente, permitiendo su fosilización en posición de vida y
preservando una posición de reposo de los miembros anteriores. La disposición de los huesos de los miembros anteriores de Chilesaurus po-
dría mostrar las primeras evidencias sobre la presencia de estructuras vinculadas a los músculos que flexionan los brazos, rasgos relaciona-
dos con la adquisición del control del vuelo en maniraptores derivados.
Palabras clave. Miembros anteriores, postura de reposo, tejido blando, flexión, evolución del vuelo.
GONDWANAN PERSPECTIVES
ISSN 0002-7014
AMEGHINIANA - 2017 - Volume 54 (5): 567 – 575
MANY dinosaur skeletons show evidence of behavior, in-
cluding feeding, predation, nesting, and parental care (Dong
and Currie, 1995; Norell et al., 1995; Varricchio et al., 1997;
Carpenter, 1998; Clark et al., 1999; Zhou and Zhang, 2002;
Grellet-Tinner et al., 2006; Erickson et al., 2007; O’Connor
et al., 2011). A unique kind of resting posture has been
recognized as shared by living birds (Wing, 1956) and some
non-avian theropods and basal dinosaurs (Xu and Norell,
2004; Nesbitt et al., 2011; Agnolín and Martinelli, 2012).
This interpretation was reached after analyses based
mainly on the posture in which some fossil dinosaur skele-
tons have been preserved. Particularly, the resting posture
of the forelimbs has been studied in theropod species, in
relation to the acquisition of flight in advanced manirap-
toran theropods (Sereno and Chenggang, 1992; Carpenter,
2002; Senter and Robins, 2005; Senter, 2006a, b; Fowler
et al., 2011; White et al., 2015) and some of them focused
on the relationship between bones with feathers or soft
tissues (Garner et al., 1999; Xu, 2006; Xu et al., 2014, 2015).
Chilesaurus diegosuarezi Novas et al. (2015) is a bizarre
tetanuran recently described from the Toqui Formation
(latest Tithonian) of southern Chile (De la Cruz and Suarez,
2006; Salgado et al., 2008). This species is represented by
the holotype, which is a nearly complete skeleton, and
several other partial skeletons. All these specimens are
articulated and preserve evidence about the posture of the
limbs. The aim of the present work is to study the posture
of four articulated specimens of Chilesaurus diegosuarezi,
focusing in the anatomical description of the resting pose
of the forelimbs and their phylogenetic and behavioral im-
plications.
MATERIALS AND METHODS
We analyze the resting posture of Chilesaurus diego-
suarezi based on four specimens housed at the Servicio
Nacional de Geología y Minería of Chile (SNGM): SNGM-
1935 (holotype), a nearly complete skeleton only lacking
several skull bones, distal caudal series, and feet; SNGM-
1936, complete and articulated forelimbs, nearly complete
left ilium, incomplete right ilium, both pubes and ischia, right
astragalus, and right metatarsals; SNGM-1937, associated
forelimbs, left himdlimb, and incomplete right distal ends of
tibia and fibula; and SNGM-1938, both forelimbs with in-
complete hands, left and right scapula and coracoids, and
nearly complete dorsal vertebral series and articulated ribs.
All the specimens were collected in the lower beds of
Toqui Formation, which crops out in the mountains flanked
by the Maitenes and Horquetas rivers, south of Lago Gene-
ral Carrera (De la Cruz and Suárez, 2006; Salgado et al.,
2008). The specimens mentioned above were found and
collected in natural articulation in the field. Here we describe
these specimens of Chilesaurus as they were originally pre-
served in the field, before mechanical disarticulation, but
the joint motion could not be analyzed in detail.
The relative position and orientation of the bones is
described with respect to the main anteroposterior axis of
the backbone (see Gatesy and Baier, 2005; Baier et al., 2013),
and is referred along the text as the “main body axis”.
DESCRIPTION
SNGM-1935.The holotype specimen lacks information of
the posterior autopodial elements and some cranial bones.
However, the rest of the skeleton is almost complete (see
Figure 1). The preservation of each bone is affected by
weathering and abrasive preparation techniques, but lacks
any sign of post-mortem transport and taphonomical de-
formation is nearly absent. A slight taphonomical flattening
is seen on the left anterior side, where the shoulder girdle is
attached to the vertebral column. Indeed, the skeleton is
relatively intact, with most of the bones preserved in tight
articulation. The few cranial bones are preserved disarticu-
lated, but associated to each other. The neck is almost
complete, with several cervical vertebrae articulated. The
forelimbs are flexed and laterally located with respect to
the main body axis. The humerus and radius-ulna are in the
same plane forming an angle of 80° between them. The
right humerus is posterolaterally extended and the radius-
ulna is anterolaterally oriented with respect to the main
body axis. The right manus is medioventrally and posteri-
orly oriented. The hand is immediately ventral to the radius-
ulna. The angle of flexion of the wrist with the forearm is
very acute, nearly 20º. The left humerus and radius-ulna are
in very similar position to the right forelimb. The hindlimbs
are slightly flexed, and posteriorly directed, with the femora
located sub-parallel to the pelvic girdle and the tibia-fibula
dorsally flexed.
SNGM-1936.The pelvic girdle and hindlimb bones are asso-
ciated but disarticulated. However, the elements of the left
AMEGHINIANA - 2017 - Volume 54 (5): 567 – 575
568
forelimb are articulated and in life position, preserving their
relationship with the dorsal column and allowing the orien-
tation of the bones (Figure 2). Only the distal end of the
humerus is preserved in articulation with the radius-ulna.
The humerus is posterolaterally oriented in dorsal view,
with respect to the main body axis. The elbow is more flexed
than in the holotype. The radius-ulna is weathered and
forms an angle of 70º with the humerus. These elements
are anteroventrally oriented with respect to the body axis.
As a result, the angle between the humerus and radius-ulna
is observed in lateral view. In lateroventral view, the main
axis of the metacarpus forms an acute angle (approximately
45º) with the radius-ulna. The main axis of the hand is pos-
teriorly oriented relative to the main body axis, and as a
consequence the palmar surface faces dorsally.
SNGM-1937.This specimen has only the coracoids and
forelimbs preserved in articulation (Figure 3), but the right
coracoid and humerus are twisted backwards. The left
coracoid shows a posteriorly oriented scapular facet. The
humerus is lateroventrally and posteriorly oriented with
respect to the main body axis. In anterodorsal view, the
angle between the humerus and radius-ulna is acute, near
40º. The elbow shows a stronger flexion than in the holo-
type and SNGM-1936. The radio-ulna is medioventrally and
anteriorly oriented respect of the main body axis. The major
axis of the hand is ventrally oriented relative to the main
body axis. In this position, the wrist is not as flexed as in
the above-described specimens, showing an angle of 60º.
The palmar surface of the hand is posteriorly oriented, with
respect to the main body axis.
CHIMENTO ET AL.: FORELIMB POSTURE IN CHILESAURUS
569
Figure 1. Cast of SNGM-1935 specimen (holotype) of Chilesaurus diegosuarezi. 1, Skeleton in dorsal view; 2, detail of the right forelimb in dor-
sal view; 3, detail of right hand in posterolateral view; 4, detail of right hand in anteromedial view. Abbreviations: cr, coracoid; hu, humerus; mcI,
first metacarpal; mcII, second metacarpal; phI-1, first phalanx of the first digit; rd, radius; sc, scapula; ul, ulna. Scale bar in 1= 200 mm; scale
bar in 2, 3 and 4 = 20 mm.
SNGM-1938.This specimen preserves part of the dorsal
vertebrae, ribs, shoulder girdle, and forelimbs in articulation.
All elements show less weathering and post-mortem de-
formation than the holotype, and only a slight torsion of the
posterior dorsal vertebrae is observed (Figure 4). The dorsal
vertebral column is parallel to each scapular blade. The left
humerus is posterolaterally oriented respect of the main
body axis and the radius-ulna are perpendicular to it. The
elbow shows the same angle as the right forelimbs of the
holotype. The left and right manus are incomplete, but the
preserved metacarpals are placed parallel and ventral to the
ulna, in the same position as the right manus of the holo-
type. This suggests that the hands would have been under
the trunk and posteromedially oriented with respect to the
main body axis, as in the holotype.
DISCUSSION
All the specimens of Chilesaurus showed a similar posi-
tion and arrangement of the forelimb bones, being notably
flexed. The position of the forelimb elements of Chilesaurus
resembles previous descriptions for resting posture in some
dinosaurs, mainly derived coelurosaur theropods, such as
Mei long, Sinor nithoides youngi, and Albinykus baatar (Xu
and Norell, 2004; Nesbitt et al., 2011). The resting posture
has been described in coelurosaur theropods as the body
resting on its symmetrically folded hindlimbs, the forelimbs
vertically flexed and laterally extended with the elbows
slightly displaced laterally, and the neck curved postero-
laterally to the left side of the body (Xu and Norell, 2004).
This posture was reported by the first time in a non-coelu-
rosaurian dinosaur by Agnolín and Martinelli (2012) for the
early saurischian Guaibasaurus candelariensis, and these
authors also described a similar pattern in the non-di-
nosaurian ornithodirans Saltopus and Scleromochlus. In
concordance with resting posture, the four specimens of
Chilesaurus here described have the forelimbs ventrally
flexed and with the hands oriented backwards, similar to
the resting pattern of Aves (Wing, 1956) and the taxa men-
tioned above (Xu and Norell, 2004; Nesbitt et al., 2011;
Agnolín and Martinelli, 2012). However, the hindlimb posi-
tion of Chilesaurus is inconsistent with this pattern, because
the hindlimbs are posteriorly extended respect of the
main body axis, rather than ventrally flexed. It is possible
that the flexed position of the forelimbs in Chilesaurus not
necessarily implies a sleeping behavior at the moment of
death. Rather, this position seems to show a passive
forelimb activity following previous studies of standard
theropod resting posture (Senter and Robins, 2005; Milner
AMEGHINIANA - 2017 - Volume 54 (5): 567 – 575
570
Figure 2. Cast of SNGM-1936 specimen of Chilesaurus diegosuarezi
and drawings. 1–2, Dorsal view; 3–4, lateral view; 5–6, lateroventral
view; 7–8, medial view; 9–10, anterior view. Abbreviations: ad, ante-
rior dorsal vertebrae; hu, humerus; mcI, first metacarpal; mcII, second
metacarpal; phI-1, first phalanx of the first digit; phII-1, first phalanx
of the second digit; rb, rib; rd, radius; ul, ulna. Scale bar= 20 mm.
et al., 2009). In this aspect, the acute angles between the
humerus and the radio-ulna and between the radio-ulna
and manus could indicate the presence of a strong limita-
tion to anterior extension of the forelimbs, as noted for
other theropods (Senter and Robins, 2005). The specimen
SNGM-1937 shows an angular relation in the wrist that
resembles that in Deinonychus (Gishlick, 2001; Carpenter,
2002). In fact, numerous coelurosaurs have the same
resting position as the forelimbs of Chilesaurus, with the
humerus and radius-ulna in perpendicular relation or elbow
flexed in an acute angle, manus under the radius-ulna, and
palmar surface posterodorsal and dorsomedial oriented
with respect to the main body axis (e.g. Balaur, Hexing, Sinor-
nithosaur us, Sinosauropteryx, Anchiornis, Microraptor and
Xiaotingia, described by Xu et al., 1999; 2000; 2011; Liyong
et al., 2012 and Brusatte et al., 2013).
CHIMENTO ET AL.: FORELIMB POSTURE IN CHILESAURUS
571
Figure 3. Cast of SNGM-1937 specimen of Chilesaurus diegosuarezi. 1, dorsal; 2, lateral; 3, anterolateral view. Abbreviations: cr, coracoid; ha,
hand; hu, humerus; mcIII, third metacarpal; rd, radius; sc, scapula; ul, ulna. Arrows indicate anterior direction. Scale bar= 20 mm.
Figure 4. SNGM-1938 specimen of Chilesaurus diegosuarezi in dorsal view. 1, photograph; 2, drawing. Abbreviations: hu, humerus; lcr, left cora-
coid; lmcIII, left third metacarpal; lsc, left scapula; phII-un?, probable ungual phalanx of the second digit; rcr, right coracoid; rd, radius; rmcIII,
right third metacarpal; rsc, right scapula; ul, ulna. Scale bar= 20 mm.
The position of folded versus extended forelimb is an
interesting topic in theropod evolution. Several authors
have suggested that the presence of many avian traits in
the forelimb bones are related with soft structures, as
patagial skin and muscles, present in several maniraptoran
dinosaurs (Sereno and Chenggang, 1992; Xu et al., 2014).
Hopp and Orsen (2004) suggested that the forelimb folded
structure in advanced theropods could be a consequence
of the need to manage the evolving set of brooding fore-
limb feathers. Chatterjee and Templin (2004) related the
swivel wrist joint with climbing behavior. Maniraptorans and
some other tetanurans possess a relatively large degree
of forearm flexion, though many appear to have been non-
flying species (Novas and Puerta, 1997; White et al., 2015),
resembling the condition described here in Chilesaurus (see
Figure 5). Xu et al. (2014) mentioned that a three-fingered
hand (TFH) with initial laterally folding capability (LFC)
may be a synapomorphy of Tetanurae, while the extended
forelimbs were considered a plesiomorphic condition for
Theropoda (see Sereno, 1993; Xu et al., 2014). However,
presence of partially folded forelimbs in Guaibasaurus may
suggest that such condition may be more widespread than
previously thought (Agnolin and Martinelli, 2012). In this
sense, folded limbs were also presumably present in croco-
dile-line archosaurs, as proposed by Hutson and Hutson
(2014).
The cojoined flexion of wrist and elbow in living birds
was studied in detail by Vazquez (1992, 1994). This au-
thor concludes that this flexion is mainly conducted by the
action of a large number of tendons located within the
propatagium. The existence of propatagium was considered
unique to modern birds (Vazquez, 1994), but recently, Ag-
nolin and Novas (2013) and Feduccia and Czerkas (2015)
found that it was more widespread than previously thought
among coelurosaurs. In this regard, Feduccia and Czerkas
(2015) considered that because a propatagium must be ex-
clusively linked with aerodynamic adaptations, its presence
in non-volant taxa as Caudipteryx may necessarily represent
a secondary derived flightless condition. Because the pro-
patagium controls the flexion of wrist and elbow, the pre-
served flexed forearm in Chilesaurus may be also regarded
as an indirect indication of the presence of propatagium in
AMEGHINIANA - 2017 - Volume 54 (5): 567 – 575
572
Figure 5. Illustration showing the degree of flexion of the left forelimb in Chilesaurus diegosuarezi. 1,dorsal view with the hand exposed in
palmar view; 2, lateral view. The arrows points anteriorly. Abbreviations: hu, humerus; ra, radius; se, semilunar; ul, ulna.
this taxon. This suggests that presence of propatagium
was not only more widespread than previously thought,
but also that it is not uniquely related to flight capabilities.
The propatagium and related structures have also been
described for Pterosauria (Wang et al., 2002; Frey et al., 2003;
Wilkinson, 2007; Bennet, 2008; Kellner et al., 2010). More
recently, Hutson and Hutson (2014) in a detailed analysis
also sustained that crocodiles also exhibit automatic wrist
folding guided mainly by soft tissues (see also Walker,
1972). These authors propose that the capability of auto-
matic wirst folding was probably plesiomorphic for croco-
dile-line archosaurs. This opens interesting questions
regarding the origin of forelimb folding in archosaurs.
Summarazing, on the basis of evidence published by pre-
vious works and the present contribution, it is possible to
infer that the presence of soft structures related to auto-
matic folding of the forelimbs may be more widespread
than suspected (Figure 6).
CHIMENTO ET AL.: FORELIMB POSTURE IN CHILESAURUS
573
Figure 6. Phylogenetic relationships of Chilesaurus diegosuarezi within Avemetatarsalia showing the distribution of an avian-like forelimb
postures and propatagial structures (modified from Martínez et al., 2011; Porfiri et al., 2014; Agnolin and Novas, 2013; Novas et al., 2015).
CONCLUSIONS
All the specimens of Chilesaurus diegosuarezi described
here present the forelimb elements arranged following a
resting posture. Thus, it seems that the specimens of Chi-
lesaurus were buried quickly and fossilized almost in life
position during passive activity (e.g. feeding, resting). The
position of the forelimb bones in Chilesaurus may show the
first evidences of the structures linked to the muscles that
flex the forearms, features related with the acquisition of
flying control (Vazquez, 1994; Agnolín and Novas, 2013).
ACKNOWLEDGMENTS
We are grateful to C. Alsina, M. Milani, R. Stoll, and M. Aranciaga
Rolando for field assistance and technical preparation of Chilesaurus
specimens. Thanks also to A. R. Gentil, J. S. D’Angelo, G. L. Lio, M.
Motta, S. Rozadilla, G. Muñoz, G. Lo Coco, J. García-Marsá, and S.
Lucero for their comments and observations during the develop-
ment of present contribution. C. Burke offered support to conduct
field work and technical preparation of the specimens. We are in-
debted to the Agencia Nacional de Promoción Científica y Tec-
nológica (PICT2010-066 to F.E.N.) and the Fondo Nacional de
Desarrollo Científico y Tecnológico (no.1121140 and 1030162 to
M.S .) for continuing financial assis tance . We thank Matthew
Bonnan and an anonymous reviewer for their enlightening review
of the MS. We also thank the editor Diego Pol for his comments
and advice.
REFERENCES
Agnolin, F.L., and Martinelli, A.G. 2012. Guaibasaurus candelariensis
(Dinosauria, Saurischia) and the early origin of avian-like resting
posture. Alcheringa 36: 263–267.
Agnolín, F.L., and Novas, F.E. 2013. Avian ancestors: a review of the
phylogenetic relationships of the theropods Unenlagiidae, Micro-
raptoria, Anchiornis and Scansoriopterygidae. Springer Briefs in
Earth Systems Sciences, Springer, Dordrecht, Heidelberg,
Springer SBM, 96 p.
Baier, D.B., Gatesy, S.M., and Dial, K.P. 2013. Three-Dimensional,
High-Resolution Skeletal Kinematics of the Avian Wing and
Shoulder during Ascending Flapping Flight and Uphill Flap-
Running. PLoS ONE 8 (5): e63982.
Bennet, S.C. 2008. Morphological evolution of the wing of pterosaurs:
myology and function. Zitteliana, series B 28: 127–141.
Brusatte, S.L., Vremir, M., Csiki-Sava, Z., Turner, A.H., Watanabe, A.,
Erickson, G.M., and Norell, M.A. 2013. The Osteology of Bal-
aur bondoc, an island-dwelling dromaeosaurid (Dinosauria:
Theropoda) from the Late Cretaceous of Romania. Bulletin of
the American Museum of Natural History 374: 1–100.
Carpenter, K. 1998. Evidence of predatory behavior by carnivorous
dinosaur. GAIA 15: 135–144.
Carpenter, K. 2002. Forelimb biomechanics of nonavian theropod
dinosaurs in predation. In: M. Gudo, M. Gutmann, and J. Scholz
(Eds.), Concepts of Functional, Engineering and Constructional
Morphology. Senckenbergiana Lethaea 82: 59–76.
Chatterjee, S., and Templin, R.J. 2004. Feathered coelurosaurs from
China: new light on the arboreal origin of avian flight. In: P.J.
Currie, E.B. Koppelhus, M.A. Shugar, J.L. Wright (Eds.), Feathered
dragons: studies on the transition from dinosaurs to birds. Indiana
Univ Press, Bloomington, p. 251–281.
Clark, J.M., Norell, M.A., and Chiappe, L.M. 1999. An oviraptorid
skeleton from the Late Cretaceous of Ukhaa Tolgod, Mongolia,
preserved in an avian-like brooding position over an oviraptorid
nest. American Museum Novitates 3265: 1–36.
De la Cruz, R., and Suárez, M. 2006. Geología del área de Puerto
Guadal-Puerto Sánchez, región de Aisén del General Carlos
Ibáñez del Campo, escala 1:100.000. Carta Geológica de Chile
95: 1–117.
Dong, Z.-M., and Currie, P.J. 1995 On the discovery of an ovirap-
torid skeleton on a nest of eggs at Bayan Mandahu, Inner Mon-
golia, People’s Republic of China. Canadian Journal of Earth
Sciences 33: 631–636.
Erickson, G.M., Rogers, K.C., Varricchio, D.J., Norell, M.A., and Xu, X.
200 7. Growth pat terns in broodi ng dinosau rs reveals th e
timing of sexual maturity in non-avian dinosaurs and genesis
of the avian condition. Biology Letters 3: 558–561.
Feduccia, A., and Czerkas, S.A. 2015. Testing the neoflightless hy-
pothesis: propatagium reveals flying ancestry of ovirap-
torosaurs. Journal of Ornithology 156: 1067–1074.
Frey, E., Tischlinger, H., Buchy, M.C., and Martill, D.M. 2003. New
specimens of Pterosauria (Reptilia) with soft parts with impli-
cations for pterosaurian anatomy and locomotion. In: E. Buffe-
taut and J.-M. Mazin (Eds.), Evolution and palaeobiology of
pterosaurs. Geological Society, London, UK, p. 233–266.
Fowler, D.W., Freedman, E.A., Scannella, J.B., and Kambic, R.E. 2011
The Predatory Ecology of Deinonychus and the Origin of Flap-
ping in Birds. PLoS ONE 6: e28964.
Garner, J.P., Taylor, G.K., and Thomas, A.L.R. 1999. On the origins of
birds: the sequence of character acquisition in the evolution of
avian flight. Proceedings of the Royal Society of London B 266:
1259–1266.
Gatesy, S.M., and Baier, D.B. 2005. The origin of the avian flight
stroke: a kinematic and kinetic perspective. Paleobiology 31:
382–399.
Gishlick, A.D. 2001. The function of the manus and forelimb of
Deinonychus antirrhopus and its importance for the origin of
avian flight. In: J. Gauthier and L.F. Gall (Eds.), New Perspectives
on the Origin and Early Evolution of Birds. Yale Peabody Museum,
New Haven, p. 301–318.
Grellet-Tinner, G., Chiappe, L., Norell, M., and Bottjer, D. 2006. Di-
nosaur eggs and nesting behaviors: A paleobiological investi-
gation. Palaeogeography, Palaeoclimatology, Palaeoecology 232:
294–321.
Hopp, T.P., and Orsen, M.J. 2004. Dinosaur brooding behavior and
the origin of flight feathers. In: E.J. Currie, E.B. Koppelhus, M.A.
Shugar, and J.L. Wright (Eds.), Feathered Dinosaurs: Studies on the
Transition from Dinosaurs to Birds. University Press, Blooming-
ton, Indiana, p. 234–250.
Hutson, J.D., and Hutson K.N. 2014. A Repeated-Measures Analy-
sis of the Effects of Soft Tissues on Wrist Range of Motion in
the Extant Phylogenetic Bracket of Dinosaurs: Implications for
the Functional Origins of an Automatic Wrist Folding Mecha-
nism in Crocodilia. The Anatomical Record 297: 1249–1228.
Kellner, A.W.A., Wang, X., Tischlinger, H., Campos, D.A., Hone, D.W.E.,
and Meng, X. 2010. The soft tissue of Jeholopterus (Pterosauria,
Anurognathidae, Batrachognathinae) and the structure of the
pterosaur wing membrane. Proceedings of the Royal Society of
London B 277: 321–329.
Liyong, J., Jun, C., and Godefroit, P. 2012. A New Basal Ornithomimo-
saur (Dinosauria: Theropoda) from the Early Cretaceous Yixian
Formation, Northwest China. In: P. Godefroit (Ed.), Bernissart
Dinosaurs and Early Cretaceous Terrestrial Ecosystems. Indiana
University Press, Bloomington and Indianapolis, p. 485–506.
AMEGHINIANA - 2017 - Volume 54 (5): 567 – 575
574
Martínez, R.N., Sereno, P.C., Alcober, O.A., Colombi, C.E., Renne, P.R.,
Montañez, I.P., and Currie, B.S. 2011. A Basal Dinosaur from the
Dawn of the Dinosaur Era in Southwestern Pangaea. Science
331: 206–210.
Milner, A.R.C., Harris, J.D., Lockley, M.G., Kirkland, J.I., and Matthews,
N.A. 2009. Bird-like anatomy, posture, and behavior revealed
by an Early Jurassic Theropod Dinosaur resting trace. PLoS ONE
4: e4591.
Nesbitt, S.J., Clarke, J.A., Turner, A.H., and Norell, M.A. 2011. A small
alvarezsaurid from the Eastern Gobi Desert offers insight into
evolutionary patterns in the Alvarezsauroidea. Journal of Verte-
brate Paleontology 31: 144–153.
Norell, M.A., Clark, J.M., Chiappe, L.M., and Dashzeveg, D. 1995. A
nesting dinosaur. Nature 378: 774–776.
Novas, F.E., and Puerta, P. 1997. New evidence concerning avian
origins from the Late Cretaceous of Patagonia. Nature 387:
390–392.
Novas, F.E., Salgado, L., Suarez, M., Agnolín, F.L., Ezcurra, M.D., Chi-
mento, N.R., de la Cruz, R., Isasi, M.P., Vargas, A.O., and Rubilar-
Rogers, D. 2015. An enigmatic plant-eating theropod from the
Late Jurassic period of Chile. Nature 522: 331–334.
O’Connor, J., Zhou, Z., and Xu, X. 2011. Additional specimen of Mi-
croraptor provides unique evidence of dinosaurs preying on
birds. Proceedings of the National Academy of Sciences 108:
19662–19665.
Porfiri, J.D., Novas, F.E., Calvo, J.O., Agnolín, F.L., Ezcurra, M.D., and
Cerda, I.A. 2014. Juvenile specimen of Megaraptor (Dinosauria,
Theropoda) sheds light about tyrannosauroid radiation. Creta-
ceous Research 51: 35–55.
Salgado, L., De la Cruz, R., Suárez, M., Gasparini, Z., and Fernández,
M. 2008. First Late Jurassic dinosaur bones from Chile. Journal
of Vertebrate Paleontology 28: 529–534.
Senter, P.J. 2006a. Forelimb function in Ornitholestes hermanni Os-
born (Dinosauria, Theropoda). Palaeontology 49: 1029–1034.
Senter, P.J. 2006b. Comparison of forelimb function between
Deinonychus and Bambiraptor (Theropoda: Dromaeosauridae).
Journal of Vertebrate Paleontology 26: 897–906.
Senter, P., and Robins, J.H. 2005. Range of motion in the forelimb of
the theropod dinosaur Acrocanthosaurus atokensis, and implica-
tions for predatory behaviour. Journal of Zoology 266: 307–318.
Sereno, P.C. 1993. The pectoral girdle and forelimb of the basal
theropod Herrerasaurus ischigualastensis. Journal of Vertebrate
Paleontology 13: 425–450.
Sereno, P.C., and Chenggang, R. 1992. Early evolution of avian flight
and perching: New evidence from the Lower Cretaceous of
China. Science 255: 845–848.
Vasquez, R.J. 1992. Functional osteology of the avian wrist and the
evolution of flapping flight. Journal of Morphology 211: 259–268.
Vasquez, R.J. 1994. The automating skeletal and muscular mecha-
nisms of the avian wing (Aves). Zoomorphology 114: 59–71.
Varricchio, D.J., Jackson, F., Borkowski, J., and Horner, J.R. 1997.
Nest and eggs clutches of the dinosaur Troodon formosus and
the evolution of avian reproductive traits. Nature 385: 247–250.
Walker, A.D. 1972. New light on the origin of birds and crocodiles.
Nature 237: 257–263.
Wang, X., Zhou, Z., Zhang, F., and Xu, X. 2002. A nearly completely
articulated rhamphorhynchoid pterosaur with exceptionally
well-preserved wing membranes and “hairs” from Inner Mon-
golia, northeast China. Chinese Science Bulletin 47: 226–230.
White, M.A., Bell, P.R., Cook, A.G., Barnes, D.G., Tischler, T.R., Bassam,
B.J., and Elliott, D.A. 2015. Forearm Range of Motion in Aus-
tralovenator wintonensis (Theropoda, Megaraptoridae). PLoS
ONE 10: e0137709.
Wilkinson, M.T. 2007. Sailing the skies: the improbable aeronauti-
cal success of the pterosaurs. Journal of Experimental Biology
210: 1663–1671.
Wing, L.W. 1956. Natural history of birds. Ronald Press, New York,
527 p.
Xu, X. 2006. Feathered dinosaurs from China and the evolution of
major avian characters. Integrative Zoology 1: 4–11.
Xu, X., and Norell, M.A. 2004. A new troodontid dinosaur from China
with avian-like sleeping posture. Nature 431: 838–841.
Xu, X., Wang, X.L., and Wu, X.C. 1999. A dromaeosaurid dinosaur
with a filamentous integument from the Yixian Formation of
China. Nature 401: 262–266.
Xu, X., Zhou, Z., and Wang, X. 2000. The smallest known nonavian
theropod dinosaur. Nature 408: 705–708.
Xu, X., You, H., Du, K., and Han, F. 2011. An Archaeopteryx-like thero-
pod from China and the origin of Avialae. Nature 475: 465–470.
Xu, X., Zhou, Z., Dudley, R., Mackem, S., Chuong, C.-M., Erickson, G.M.,
and Varricchio, D.J. 2014. An integrative approach to understand-
ing bird origins. Science 346: DOI: 10.1126/science.1253293.
Xu, X., Zheng, X., Sullivan, C., Wang, X., Xing, Y., Zhang, X., O’Connor,
J., Zhang, F., and Pan, Y. 2015. A bizarre Jurassic maniraptoran
theropod with preserved evidence of membranous wings. Na-
ture 521: 70–73.
Zhou, Z., and Zhang, F. 2002. A long-tailed, seed-eating bird from
the Early Cretaceous of China. Nature 418: 405–409.
doi: 10.5710/AMGH.11.06.2017.3088
Submitted: January 24t h, 2017
Accepted: June 11st, 2017
Published online: June 13rd, 2017
CHIMENTO ET AL.: FORELIMB POSTURE IN CHILESAURUS
575
