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Novas, F.E., Aranciaga Rolando, A.M. and Agnolín, F.L. 2016. Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy. Memoirs of Museum Victoria 74: 49–61. General comparisons of the manual elements of megaraptorid theropods are conducted with the aim to enlarge the morphological dataset of phylogenetically useful features within Tetanurae. Distinctive features of Megaraptor are concentrated along the medial side of the manus, with metacarpal I and its corresponding digit being considerably elongated. Manual ungual of digit I is characteristically enlarged in megaraptorids, but it is also transversely compressed resulting in a sharp ventral edge. We recognize two derived characters shared by megaraptorans and coelurosaurs (i.e., proximal end of metacarpal I without a deep and wide groove continuous with the semilunar carpal, and metacarpals I and II long and slender), and one derived trait similar to derived tyrannosauroids (i.e., metacarpal III length <0.75 length of metacarpal II). However, after comparing carpal, metacarpal and phalangeal morphologies, it becomes evident that megaraptorids retained most of the manual features present in Allosaurus. Moreover, Megaraptor and Australovenator are devoid of several manual features that the basal tyrannosauroid Guanlong shares with more derived coelurosaurs (e.g., Deinonychus), thus countering our own previous hypothesis that Megaraptora is well nested within Tyrannosauroidea.
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Memoirs of Museum Victoria 74: 49–61 (2016) Published 2016
ISSN 1447-2546 (Print) 1447-2554 (On-line)
Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor
and Australovenator: the evidence afforded by their manual anatomy
Fernando e. novas1,2,*, alexis M. aranciaga rolando1 and Federico l. agnolín1,3
1 Museo Argentino de Ciencias Naturales, Avenida Ángel Gallardo 470, 1405DJR Buenos Aires, Argentina
2 CONICET, Consejo Nacional de Investigaciones Cientícas y Técnicas, Argentina
3 Fundación de Historia Natural “Félix de Azara”, Universidad Maimónides, Hidalgo 775, 1405BDB, Buenos Aires,
* To whom correspondence should be addressed. E-mail:
Abstract Novas, F.E., Aranciaga Rolando, A.M. and Agnolín, F.L. 2016. Phylogenetic relationships of the Cretaceous Gondwanan
theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy. Memoirs of Museum
Victoria 74: 49–61.
General comparisons of the manual elements of megaraptorid theropods are conducted with the aim to enlarge the
morphological dataset of phylogenetically useful features within Tetanurae. Distinctive features of Megaraptor are
concentrated along the medial side of the manus, with metacarpal I and its corresponding digit being considerably
elongated. Manual ungual of digit I is characteristically enlarged in megaraptorids, but it is also transversely compressed
resulting in a sharp ventral edge. We recognize two derived characters shared by megaraptorans and coelurosaurs (i.e.,
proximal end of metacarpal I without a deep and wide groove continuous with the semilunar carpal, and metacarpals I and
II long and slender), and one der ived trait similar to derived tyrannosauroids (i.e., metacarpal III length <0.75 length of
metacar pal II). However, after comparing carpal, metacarpal and phalangeal morphologies, it becomes evident that
megaraptorids retained most of the manual features present in Allosaurus. Moreover, Megaraptor and Australovenator
are devoid of severa l manual feat ures that the basa l tyran nosauroid Guanlong shares with more derived co elurosaurs (e.g.,
Deinonychus), thus countering our own previous hypothesis that Megaraptora is well nested within Tyrannosauroidea.
Keywords Dinosauria, Theropoda, Megaraptoridae, Cretaceous, Argentina, Australia, morphology.
Megaraptoridae is a Cretaceous theropod family including
several taxa recorded from different regions of Gondwana
(Novas et al., 2013). The best known megaraptorids are
Megaraptor namunhuaiquii (Novas, 1998; Calvo et al., 2004;
Porri et al., 2014), Orkoraptor bukei (Novas et al., 2008),
and Aerosteon riocoloradensis (Sereno et al., 2008), coming
from different formations of Turonian through Santonian age
of Argentina; and Australovenator wintonensis (Hock null et
al., 2009; White et al., 2012, 2013), from Cenomanian rocks
of Australia.
The megaraptorids and their sister taxon Fukuiraptor
kitadaniensis (Azuma and Currie, 2000), from Barremian beds
of Japan, constitutes the clade Megaraptora, originally coined
by Benson et al. (2010a). After a comprehensive phylogenetic
analysis, these authors considered megaraptorans as
allosauroids closely related with carcharodontosaurid
theropods, an interpretation subsequently followed by later
authors (Carrano et al., 2012; Zanno and Makovicky, 2013).
However, recent studies conducted by some of us (e.g., Novas et
al., 2013; Porri et al., 2014) have suggested that megaraptorans
are not representative of archaic allosauroid tetanurans, but
instead argued that megaraptorans are coelurosaurs, and
representatives of a basal tyrannosauroid radiation in particular
(Novas et al., 2013). Recent discovery of cranial remains of a
juvenile specimen of Megaraptor namunhuaiquii (Porri et
al., 2014) offered novel anatomical information that supported
this phylogenetic interpretation.
The fossil record of megaraptorids in Gondwana has
increased over the last few years. Additional evidence of the
presence of megaraptorids in regions of South America other
than Argentina comes from Brazil, from which isolated caudal
vertebrae have been described (Mendez et al., 2013).
Cretaceous formations of Australia have yielded several
isolated elements referred to Megaraptoridae, including
Rapator ornitholestoides (Huene, 1932; Agnolín et al., 2010;
White et al., 2012), an isolated ulna closely similar to that of
Megaraptor and Australovenator (Smith et al., 2008), more
than one hundred isolated teeth (Benson et al., 2012), and
probably an isolated astragalus (Molnar et al., 1981; Fitzgerald
et al., 2012), and paired pubes originally described as
tyrannosauroid (Benson et al., 2010b; Novas et al., 2013).
F.E. Novas, A.M. Aranciaga Rolando & F.L. Agnolín
Available information demonstrates that megaraptorans
were a diverse and relatively abundant clade of large predatory
dinosaurs in the southern landmasses (Novas, 1998, 2008;
Calvo et al., 2004; Benson et al., 2010a; Novas et al., 2013),
sharing with abelisauroids and carcharodontosaurids the role
of top predators.
We offer here a comparative survey of the manual bones of
Megaraptor and Australovenator with the aim to recognize
anatomical features characterizing these theropods. Also, we
briey discuss the distribution of some manual features among
theropods that may inform the phylogenetic relationships of
megaraptorid among Tetanurae.
Institutional abbreviations
AODF, Australian Age of Dinosaurs Fossil, Winton, Australia;
BMNH, British Museum of Natural History, London, England;
IVPP, Institute of Vertebrate Paleontology and
Paleoanthropology, Beijing, China; MUCPv, Museo de la
Universidad Nacional del Comahue, Neuquén, Argentina;
UUVP, University of Utah Vertebrate Paleontology, Utah,
USA; YPM, Yale Peabody Museum, New Haven, USA.
Materials and Methods
Material examined. A comparative study of the holotype and
referred specimens of Megaraptor namunhuaiquii (MUCPv
595, MUCPv 1353, and MUCPv 341), Australovenator
wintonensis (AODF 604), and cast of Rapator ornitholestoides
(cast of BMNH R3718) was conducted. The following
specimens were also studied: Guanlong wucaii (IVPP V14531),
Allosaurus fragilis (cast of UUVP 6000), Deinonychus
antirrhopus (cast of YPM 5205), Xuanhanosaurus qilixiaensis
(cast of IVPP V6729), Coelurus fragilis (cast of YPM 2010),
and Ornitholestes hermanni (cast of AMNH 619).
Comparative Anatomy
Megaraptor and Australovenator are currently the only
megaraptorans in which the forelimb bones are fairly well
documented (Calvo et al., 2004; Hocknull et al., 2009; White
et al., 2012). Specimen MUCPv 341 of Megaraptor
namunhuaiquii preserves articulated forearm bones (i.e., ulna
and radius) and manus, but no humerus (g. 3). However, the
recent discovery of a juvenile specimen of M. namunhuaiquii
(Porri et al., 2014) documents for the rst time the humeral
morphology in this genus. Although the humerus does not
preserve complete proximal and distal ends, it offers reliable
information to calculate humeral proportions in this
Patagonian taxon. The type specimen of Australovenator
preserves most of the forelimb except metacarpal III and some
manual phalanges.
Humerus. The humerus of Megaraptor (Porri et al., 2014) and
Australovenator (White et al., 2012) resembles basal tetanurans
(e.g., Allosaurus, Acrocanthosaurus, Piatnitzkysaurus; Madsen,
1976; Currie and Carpenter, 2000; Bonaparte, 1986) and basal
coelurosaurs (e.g., Coelurus, Ornitholestes, Guanlong; Osborn,
1903; Carpenter, 2005; Xu et al., 2006; g. 1) in being sigmoid-
shaped in anterior and lateral views, with a prominent
deltopectoral crest. These characters are absent in non-
coelurosaurian theropods like Xuanhanosaurus ( Dong, 1984),
Ceratosaurus (Madsen and Welles, 2000), Tor vos a urus (Galt on
and Jensen, 1979), Baryonyx (Charig and Milner, 1997), and
some coelurosaurs including ornithomimids (Kobayashi and Lü,
2003; Nichols and Russel, 1985), and tyrannosaurids (Brochu,
2002) (g. 1). The internal tuberosity also resembles basal
tetanurans in being conical-shaped (e.g., Bonaparte et al., 1990).
However, the humerus of both Megaraptor and Australovenator
exhibits a deep longitudinal furrow that runs on the medial
surface of the shaft, distally to the internal tuberosity, a feature
also present in Fukuiraptor and some coelurosaurs (Deinonychus,
tyrannosaurids; Ostrom, 1969; Brochu, 2002). This character is
absent in other coelurosaurs like Chilantaisaurus, Ornitholestes,
Coelurus, oviraptorosaurs (Benson and Xu, 2008; Osborn, 1903;
Carpenter, 2005; Lu, 2002), and non-coelurosaurian tetanurans
(e.g. Allosaurus, Acrocanthosaurus, Piatnizkysaurus; Madsen,
1976; Currie and Carpenter, 2000; Bonaparte 1986) (g. 1).
Furthermore the entire distal end bends anteriorly, showing a
sigmoid shape in lateral view. Notably, the distal humeral
condyles of Australovenator (White et al., 2012) are wel l-dene d
and much more rounded anteriorly than those of Allosaurus,
Acrocanthosaurus or Xuanhanosaurus (Madsen 1976; Currie
and Carpenter, 2000; Dong 1984) (g. 2), and are separated by
deep extensor and exor grooves not present in non-celurosaurian
tetanurans. In this regards, the distal end of the humerus of
Australovenator (Wh ite et al., 2012) resembles coelurosaurs li ke
Coelurus, Ornitholestes (Car penter, 2005), Guanlong (IVPP
IVPP V14531), Deinonychus (Novas, 1996) (g. 2) and Aves, and
may suggest a more complex folding system than in basal
theropods, a hypothesis that needs to be tested properly. Apart
from the similarity with some coelurosaurs described for the
distal end, the robust construction of the humerus in Megaraptor
and Australovenator is closer to Allosaurus (width:length ratio
approximately 40; Madsen, 1976; Hocknull et al., 2009; Porri
et al., 2014) than the elongate and more gracile humeral
proportions of Guanlong and Deinonychus (width:length ratio
approximately 30; pers. obs.).
Ulna. As already noted by previous authors (e.g., Novas, 1998;
Calvo et al., 2004; Smith et al., 2008; Agnolin et al., 2010;
Benson et al., 2010a; Hocknull et al., 2009; White et al., 2012;
Novas et al., 2013), the megaraptorid ulna exhibits a
transversally compressed blade-like olecranon process, and a
robust and dorsoventrally extended lateral tuberosity. These
two features are absent in the remaining theropods, including
the basal megaraptoran Fukuiraptor, thus they have been
interpreted as unambiguous synapomorphies of Megaraptoridae
(Novas et al., 2013). The megaraptorid ulna narrows distally, a
condition similar to that of Allosaurus (e.g., Madsen, 1976) or
basal coelurosaurs (e.g. Guanlong, Ornitholestes, Coelurus;
Ornithomimids; Nichols and Russel, 1985; Xu et al., 2006;
Osborn, 1903; Carpenter, 2005). But absent in megalosauroids
(Dong, 1984; Charig and Milner, 1997) and derived
coelurosaurs (e.g. Deinonychus; Ostrom, 1969).
Remarkable features characterizing megaraptorids
correspond to the manus, in particular the formidable
development of the manual unguals of digits I and II, and the
Megaraptor manual osteology 51
transverse compression and ventral sharpness of the ungual of
digit I (Calvo et al., 2004; Novas et al., 2013).
Carpus. In Megaraptor (Ca lvo et al., 2004) and Australovenator
(White et al., 2012) two carpal elements are documented: a disk-
shaped radiale, and an enlarged distal carpal described as distal
carpal 1 by White et al. (2012). Because the homology of this
bone among theropods is difcult to interpret (e.g., Xu et al.,
2006, 2009, 2014), we will informally describe it as a “semilunate
carpal”, based on its proximally arched prole in dorsal view.
Semilunate carpals of Megaraptor and Australovenator
resemble Allosaurus (Madsen, 1976) in being gently convex
proximally (gs. 3, 4, 5). As in the latter taxon, the semilunate
carpal is in contact with most of the proximal end of metacarpal
I, and also the medial half of the proximal end of metacarpal
II. The semilunate carpal of megaraptorids bears a pair of
distal projections for articulation with metacarpal bones, also
present in Allosaurus, Acrocanthosaurus and the basal
coelurosaur Guanlong (Madsen, 1976; Currie and Carpenter,
2000; Xu et al., 2006). One of these projections is visible in
ventral view, and wedges between metacarpals I and II. The
other projection is seen in dorsal view, and lodges into a socket
on the proximal end of metacarpal I. Such interlocking among
the semilunate carpal and metacarpals I and II probably
constitutes a tetanuran feature, apomorphically lost among
derived coelurosaurs (e.g., oviraptorosaurs, paravians) in
which the distal surface is at or slightly concave, without
projecting between metacarpals I and II (Rauhut, 2003).
Aside from the genera l similarities noted with Allosaurus,
the semilunate carpal of megaraptorids exhibits a
proximodistally deep prole, mainly due to the bulged
condition of the distal projection that lodges into the proximal
end of metacarpal I. In this regard, the semilunate carpal of
Megaraptor and Australovenator differs from the
Figure 1. Humerus in lateral (C-I) and medial (A-B,J) views of: A, Megaraptor (MUCPv 341), B, Australovenator, C, Allosaurus, D,
Acrocanthosaurus, E, Coelurus, F, Ornitholestes, G, Xuanhanosaurus, H, Tor vo s aur us, and I, Baryonyx. J, Fukuiraptor. B, modied from
White et al. (2012). D, modied from Cur rie and Carpenter (2000). H, modied from Galton and Jensen (1979). I, modied from Charing and
Milner (1997). Scale bar: 5cm. Abbreviations: it, internal tuberosity; lf, longitudinal furrow.
F.E. Novas, A.M. Aranciaga Rolando & F.L. Agnolín
proximodistally shallower semilunate carpal of basal
tetanurans (e.g., Allosaurus, Acrocanthosaurus) and basal
coelurosaurs, such as Tanycolagreus (Carpenter et al., 2005),
Sinosauropteryx (Currie and Chen, 2001), Scipionyx (Dal
Sasso and Maganuco, 2011), Coelurus, and ornithomimosaurs
(Kobayashi and Lü, 2003).
In sum, megaraptorids retained a carpal morphology
di agn ost ic at the level of Teta nu r ae. No der ived feat u res share d
with coelurosaurs are identied. The distally convex condition
of the semilunate carpal probably represents a synapomorphic
feature for Megaraptoridae.
Metacarpus. Comparing the forearms of Megaraptor with
those of Allosaurus and Acrocanthosaurus (equaling the
length of the ulna), permits recognition that the manus of the
rst taxon is much more elongate and slender than in those
basal tetanurans. In particular, metacarpal I of Megaraptor is
less massive than the block-like Metacarpal I of Allosaurus,
Acrocanthosaurus, and Torvo s auru s (gs. 3, 6; Madsen, 1976;
Galton and Jensen, 1979; Currie and Carpenter, 2000). In
Megaraptor the ratio between transverse diameter and total
length of the metacarpal I results in, approximately 40, whereas
in Allosaurus the same ratio is of 50 (Novas, 1998). Digits II
and III of Megaraptor are considerably elongate, in particular
their respective ungual phalanges. The exception is digit III,
which is not proportionally longer with respect to Allosaurus.
In this regard, the shortness of digit III was considered as a
derived feature shared by megaraptorids and tyrannosaurids
(Novas et al., 2013). Moreover, the ungual phalanx of digit III
of Megaraptor is less curved and trenchant than its homologue
in Allosaurus. Australovenator also exhibits slender
metacarpals as in Megaraptor, as well as an enlarged ungual on
digit I. However, proportions of the remaining phalanges are
intermediate between those of Allosaurus and Megaraptor.
Metacarpal I. As pointed out by Rauhut (2003), metacarpal I in
most coelurosaurs is much longer than broad. Rauhut (2003)
proposed that a length:width ratio greater than 2.2 is diagnostic
for derived coelurosaurs (e.g., Ornitholestes, troodontids,
oviraptorids, dromaeosaurids), and that was <2 in other
theropods. Metacarpal I of megaraptorids exhibits slender
proportions resembling those of coelurosaurs, contrasting with
most non-coelurosaurian theropods in which the metacarpal is
approximately as broad as long (e.g., Allosaurus, Torvosaurus,
Acrocanthosaurus; g. 7). In megaraptorids the metacarpal I
has a length:width ratio of 1.85 for Megaraptor, and 2 for
Australovenator. This contrasts with non-coelurosaurian
theropods, such as Allosaurus, Acrocanthosaurus, and
Xuanhanosaurus, in which the relationship between
length:width is 1.52, 1,24 and 1,67 respectively (Madsen, 1976;
Dong, 1984; Currie and Carpenter, 2000). In addition, the
elongation of metacarpal I is also shared by the Australian
Rapator” (see White et al., 2013). On the other hand, in
coelurosaurians like Deinonychus and Guanlong, the ratio is
1,89 and 1,86 respectively (Ostrom, 1076; obs. pers.), resembling
in this aspect the megaraptoran condition.
As already said, the proximal end of metacarpal I bears a
deep embayment to lodge the semilunate carpal. This proximal
concavity of metacarpal I is also present in basal tetanurans (e.g.,
Allosaurus) as well as basal tyrannosauroids (e.g., Guanlong),
but in megaraptorids it is emphasized by the presence of a
prominent proximal projection on the medial corner of the bone.
Huene (1932), in the original description of Rapator
ornitholestoides, pointed out the peculiar proximomedial
process of metacarpal I (gs. 7, 8). This feature was usually
considered as a probable autapomorphic trait diagnostic for this
taxon (e.g., Molnar, 1980, 1990). However, Agnolín et al. (2010)
recognized that a similar process is also present in
Australovenator and Megaraptor, thus suggesting that it may
constitute a synapomorphy of Megaraptoridae (see also White et
al., 2012). The proximal concavity on metacarpal I and its
associated proximomedial process are less well developed in
basal coelurosaurs (e.g., Scipionyx; Dal Sasso and Maganuco,
2011), basal tyrannosauroids (e.g., Tanycolagreus; Car penter,
Miles and Cloward, 2005), and paravians (e.g., Deinonychus;
Ostrom, 1976), in which the proximal margin of metacarpal I is
almost straight and a proximomedial process is lacking. The
only possible exception among basal coelurosaurs is the
compsognathid Sinosauropteryx, which appears to posseses a
metacarpal I that is proximally notched and bears an associated
proximomedial process (Figure 6; Currie and Chen, 2001).
In the Australian megaraptorids Australovenator and
Rapator” the lateral margin of metacarpal I is straight (in
dorsal and ventral views), and the lateral surface for ar ticulation
with metacarpal II is slightly faced dorsally (g. 8). This
morphology resembles metacarpal I of basal tyrannosauroids
(e.g., Guanlong; Xu et al., 2006) and derived coelurosaurs
(e.g., Deinonychus; Ostrom, 1969), and differs from basal
tetanurans (e.g., Tor vosa u rus, Allosaurus, Acrocanthosaurus;
Madsen, 1976; Currie and Carpenter, 2000; Galton and Jensen,
Figure 2. Distal end of humerus in anterior (A,C,E,G,I,K,) and distal
(B,D,F,H,J,L) views of Australovenator (A ,B), Allosaurus (C, D),
Xuanhanosaurus (E ,F ), Chilantaisaurus (G, H), Guanlong (I,J), and
Coelurus (K,L). Not to scale. A,B, modied from White et al. (2012).
G,H, modied from Benson and Xu (2008).
Megaraptor manual osteology 53
1979) in which metacarpal I possesses a well-developed
posterolateral surface (also partially faced proximally) for
articulation with metacarpal II. The latter bone has a
transversely expanded its proximal head, embracing
metacarpal I ventrally. The morphology of the proximolateral
portion of metacarpal I and the way it articulates with
metacarpal II is not uniform among megaraptorids, as shown
by Megaraptor in which the proximolateral corner of
metacarpal I is truncated in a similar condition to that
described for Allosaurus (Madsen, 1976). In other words,
Megaraptor exhibits the ancestral tetanuran condition, but its
close relative Australovenator developed an articulation of
metacarpal I that is morphologically closer to that of
coelurosaurian theropods. This suggests that character
transformation within Megaraptoridae has been more complex
than we expected.
In megaraptorids (i.e., Australovenator, Megaraptor,
“Rapator”) the medial edge of metacarpal I is transversely
rounded and dorsoventrally deep (as seen in proximal view;
g. 8). This prominent medial margin resembles Allosaurus,
being different from the dorsoventrally depressed and sharp
medial margin present in some coelurosaurs, such as Guanlong
and Deinonychus (Ostrom, 1976; Xu et al., 2006).
In megaraptorids (e.g., Megaraptor, Australovenator,
“Rapator”) the medial distal condyle of metacarpal I is more
distally placed than in other theropods (Calvo et al, 2004;
Figure 3. Left manus of Megaraptor namunhuaiquii (MUCPv 341) in dorsal view (A) and schematicrepresentation (B) . Scale bar: 1 cm.
F.E. Novas, A.M. Aranciaga Rolando & F.L. Agnolín
White et al., 2012; g. 8). In addition, the distal end of
metacarpal I in megaraptorids is distally oriented, lacking a
medial tilting (Calvo et al., 2004; Agnolin et al., 2010; White
et al., 2012, 2013). This morphology results in a metacarpal I
that is distally less asymmetrical than in other theropods, with
the exception of derived paravians, including Archaeopteryx,
dromaeosaurids and troodontids, in which the distal end lacks
the medial twisting present in other theropods (Rauhut, 2003).
In most saurischians, including theropods, the distal end of
the rst metacarpal I shows asymmetrically developed
articular condyles, in which the lateral condyle is larger than
the medial condyle (Galton, 1971). This pattern is also present
in all known megaraptorids (Calvo et al., 2004; White et al.,
2012, 2013). However, the distal end of metacarpal I shows
some minor distinctions among megaraptorids: in Megaraptor
metacarpal I differs from Allosaurus and Australovenator in
the presence of a greatly developed lateral distal condyle,
which is ventrally wider than in the above mentioned taxa. In
Australovenator, the medial distal condyle is prominently
projected ventrally (as seen in distal view; see White et al.,
2012, g.13C), constituting a condition hitherto unreported
among theropods, with the exception of of Guanlong in which
the medial condyle projects incipiently ventrally. Differences
between Megaraptor and Australovenator may reveal subtle
variations in the way digit I functioned. Contrasting with
Acrocanthosaurus and Allosaurus (Madsen, 1976; Currie and
Carpenter, 2000), Megaraptor has a metacarpal I that bears
distal articular condyles that are little-developed dorsally and
lack the globe-shaped morphology characteristic of the
aforementioned allosauroids. In the same way, Xuahanosaurus
has a poorly developed distal articular surface in both views
(Dong, 1984). The extensor ligament pit of metacarpal I in
Megaraptor is roughly triangular in outline, unlike the
transversely elongate and elliptical form of this feature
Acrocanthosaurus and Allosaurus (Madsen, 1976; Currie and
Carpenter, 2000; g. 7). Guanlong has a similar condition to
Megaraptor (Xu et al., 2014).
The dorsal surface of metacarpal I in non-coelurosaurian
theropods (e.g., Allosaurus, Acrocanthosaurus, Torvosaurus;
Madsen, 1976; Galton and Jensen, 1979; Currie and Carpenter,
2000) is longitudinally grooved. This groove is contiguous
with a similar trough on the dorsal surface of the semilunate
carpal (g. 5). By contrast, in coelurosaurs (e.g., Scipionyx,
Tyrannosaurus, Falcarius, Gallimimus, Deinonychus;
Ostrom, 1979; Brochu, 2003; Zanno, 2010; Dal Sasso and
Maganuco, 2011) the dorsal surface of metacarpal I and its
Figure 4. Left manus of (A,C), Allosaurus fragilis, and (B,D), Australovenator wintonensis in (A,B) dorsal, and (C,D) ventral views. Not to scale.
B,D, moed from White et al. (2012).
Figure 5. Left “semilunate” carpal in proximal (upper row) and dorsal (lower row) of A, Allosaurus, B, Acrocanthosaurus (modi ed from Cu rrie
and Carpenter, 20 00); C, Megaraptor; D, Guanlong (modied from Xu et al., 2014); E, Ornitholestes (moied from Ca rpenter et al., 2005); F,
Tanycolagreus (modied from Carpenter et al., 2005); G, Alxasaurus (modied from Xu et al., 2014); H, Deinonychus (modied from Ostrom,
1969); and I, Australovenator (modied from White et al., 2012). Not to scale. Abbreviations: ag, anterior groove; dp, distal projections.
Megaraptor manual osteology 55
corresponding carpal is almost at or slightly concave. In
Australovenator the dorsal surfaces of both metacarpal I and
the semilunate carpal are almost at, resembling the condition
described for coelurosaurs. In Megaraptor the metacarpal I is
slightly concave, and although the semilunar carpal is
damaged, its dorsal surface is attened. A similar condition to
Megaraptor is retained in other basals coelurosaurs like
Guanlong, Ornitholestes and Tanycolagreus which possesses
a deep groove in dorsal view (Carpenter et al., 2005; Xu et al.,
2006). In sum, the absence of a continuous proximodistal
groove on metacarpal I and semilunate carpal may constitute
a sinapomorphic trait uniting megaraptorids with coelurosaurs
retained in some basals coelurosaurs.
Metacarpal II. In Megaraptor and Australovenator the
metacarpal II is long and slender, with a distal ginglymoid
transversely narrower than the proximal end of the bone. This
condition differs from that of Syntarsus, Dilophosaurus,
Allosaurus, and Acrocanthosaurus, in which the distal end of
metacarpal II bears a prominent ginglymus that ares on both
sides, with a transverse diameter equals to that of the proximal
end. The just condition described for megaraptorids resembles
that of Compsognathus (Ostrom, 1969) and Sinocalliopteryx
(Ji et al., 2007). An intermediate step between the allosauroid
and the megaraptorid condition is seen in Guanlong (Xu et al.,
2006). Scaled at the same size, the distal ginglymoid of
metacarpal II of Megaraptor is considerably narrower than that
of Allosaurus, representing half the transverse diameter of the
latter taxon´s metacarpal II. Another condition is seen in
derived coelurosaurids (Deinonychus; Ostrom, 1969) which
has a slender metacarpal I with equally developed extremities.
In congruence with the narrow condition of distal ginglymus,
the extensor ligament pit of metacarpal II in Megaraptor has a
proximodistally extended sub-triangular contour, similar to
Sciurumimus (Rauhut et al., 2012), but different from the
proximodistally short and transversely wide ligament pit of
Allosaurus (Madsen, 1976).
As mentioned above, in Megaraptor the proximal head of
metacarpal II is medially expanded, ventrally embracing
metacarpal I. This condition differs from that of most
coelurosaurs, including Compsognathus, tyrannosauroids
(e.g., Guanlong, Tanycolagreus, Tyrannosaurus; Xu et al.,
2009; Carpenter et al., 2005; Brochu, 2003), and more
crownward forms (e.g., Ornitholestes, Deinonychus,
Velociraptor; Carpenter et al., 2005; Ostrom, 1976), in which
Figure 7. Right metacarpals II and I in dorsal view of A, Acrocanthosaurus (modied from Curr ie and Carpenter, 2000); B, Tor vosau r us
(modied from Galton and Jensen, 1979); C, Megaraptor; D, Deinonychus ( modied from Ostrom, 1969); E, Guanlong (modied from Xu et
al., 2009). Not to scale. Abbreviations: ep, extensor pit; pdp, proximomedial process; ps, proximolateral surface.
Figure 6. Left manus in dorsal view of A, Dilophosaurus (modied from Welles, 1980); B, Allosaurus; C, Megaraptor; D, Sinocalliopteryx; E,
Tanycolagreus (modied from Carpenter et al., 2005); F, Deinonychus (modied from Ostrom, 1969); G, Scipionyx (modied from Dal Sasso
and Maganuco, 2011); H, Guanlong (modied from Xu et al., 2009); and I, Sinosauropteryx (modied from Cur rie and Ch en , 20 01). Not to scale.
F.E. Novas, A.M. Aranciaga Rolando & F.L. Agnolín
the lateroventral margin of metacarpal I is laterally projected,
thus embracing the ventral surface of metacarpal II.
Metacarpal III. Among megaraptorans, this bone has been
solely recorded in Megaraptor. Calvo et al. (2004) described
the metacarpal III of Megaraptor as transversally compressed,
its distal end being narrower than its proximal end. This
condition is also present in most tyrannosaurids (e.g.,
Daspletosaurus, Tyrannosaurus, Albertosaurus; Russell,
1970; Lipkin and Carpenter, 2008), in which metacarpal III is
extremely slender. This condition has been interpreted as
diagnostic of advanced tyrannosauroids (Holtz, 2004).
The reduction of metacarpal III is correlated with the
reduction of the entire digit III. In Megaraptor the phalanges
of digit III are proximodistally shortened and transversely
compressed, thus resulting in a digit III shorter and more
slender than in basal tetanurans (e.g., Allosaurus,
Acrocanthosaurus; Madsen, 1976; Currie and Carpenter,
2000). This peculiar morphology may be regarded as
autapomorphic for Megaraptor.
In Megaraptor, the length of metacarpal III represents 71%
of metacarpal II, a ratio that matches that of specialised
tyrannosauroids (Russell, 1970; Barsbold, 1982; Rauhut, 2003;
Holtz, 2004). This proportion, as well as the short length of the
entire digit III may be a condition sha red between both groups.
Megaraptor retained a small and rod-like metacarpal IV,
and no evidence of phalanges of digit IV have been found in the
preserved manus (Calvo et al., 2004), thus it is probable that
digit IV was completely lost. The only available specimen of
Australovenator does not preserve metacarpal IV (Hocknull et
al., 2009; White et al., 2012). Presence of metacarpal IV in
Megaraptor is here interpreted as an apomorphic reversal from
the neotetanuran ancestral state, in which metacarpal IV is
absent (e.g., Sciurumimus, Allosaurus, Acrocanthosaurus;
Rauhut, 2003). This conclusion agrees with Rauhut et al. (2012)
who recognized a high level of homoplasy in this characteristic,
given that the basal allosauroid Sinraptor (Currie and Zhao,
1993) and the basal tyrannosauroid Guanlong (Xu et al., 2006)
retained a rudimentary fourth metacarpal.
Manual phalanges. In Megaraptor and Australovenator,
manual phalanges exhibit shallow and triangular-shaped
extensor ligament pits, which lack well-dened margins and
are not proximally delimited by a transverse ridge (g. 7).
Rauhut (2003) pointed out that coelurosaurs lack well-dened
extensor pits on manual phalanges. In contrast, in non-
coelurosaurian theropods, extensor ligament pits are deep and
transversely extended, as shown for example in Eoraptor,
Dilophosaurus, Syntarsus, Xuanhanosaurus, Torvosaurus,
Allosaurus, Acrocanthosaurus, Sinraptor, and Baryonyx
(Raath, 1969; Madsen, 1976; Galton and Jensen, 1979; Welles,
1984; Dong, 1984; Currie and Zhao, 1993; Sereno et al., 1993;
Charig and Milner, 1997; Currie and Carpenter, 2000; Rauhut,
2003). In contrast most coelurosaurian theropods have shallow
or absent extensor pits (e.g. Deinonychus, Nothronychus,
Tyrannosaurus, Troodon; Ostrom, 1969; Currie and Russel,
1987; Bochu, 2003; Zanno et al., 2009; Zanno, 2010).
Phalanges of digit I. Megaraptor is distinguished from the
remaining theropods, including Australovenator, in the
remarkable elongation of the internal bones of the manus (i.e.,
metacarpal I, phalanx 1.I, and especially the ungual phalanx).
The tip of digit I ungual ends at the level of the mid-length of
the second ungual digit (g. 3).
Phalanx 1 of digit I of Megaraptor exhibits a proximodorsal
lip. In most basal theropods (e.g., coelophysoids, To r vosa u rus,
Spinosaurus, Allosaurus, Acrocanthosaurus; Rauhut, 20 03;
Ibrahim et al., 2014) the phalanx I.1 bears a transversely wide
proximodorsal lip on phalanx 1 of digit I. Such a wide lip appears
to be related with a transversely extended, deep, and well-dened
extensor ligament pit on distal metacarpal I, a condition regarded
as plesiomorphic among theropods (Sereno et al., 1993; Rauhut,
2003). However, among coelurosaurs (e.g., Tanycolagreus,
Guanlong, Tyrannosaurus, Gallimimus, Deinonychus; Ostrom,
1976; Brochu, 2003; Carpenter et al., 2005; Xu et al., 2006) the
proximodorsal lip of phalanx 1 is narrower. In Megaraptor and
Australovenator the proximal surface of the proximal phalanx
presents a pointed proximodorsal lip, which is different from the
condition described for the remaining theropods. This pointed
process appears to be related with a reduction in the distal
extensor pits of the metacarpals, as diagnostic of coelurosaurs
(Rauhut, 2003).
In Megaraptor and Australovenator the proximal end of
phalanx I.1 is sub-quadrangular in outline (g. 9). It shows
robust and thickened lateral, medial, and dorsal margins,
conforming to an expanded articular surface for metacarpal I.
The lateral margin is even more thickened than the medial one
and is strongly proximally expanded. This set of features
Figure 8. A-C, left rst metacarpal in dorsal view of A, Megaraptor,
B, Australovenator, and C, Rapator; D-F, proximal view of left
metacar pus of D, Gua nlong (modied from Xu et al.,20 09), E,
Tanycolagreus (modied from Carpenter et al., 20 05), and F,
Deinonychus (modied from Ostrom, 1969); G-H, proximal view of
right rst metacarpal of G, Rapator, and H, Australovenator. Not to
scale. Abbreviations: pdp, proximomedial process; vpI, ventral
process of metacarpal I; vpII, ventral process of metacar pal II.
Megaraptor manual osteology 57
appears to be unique to megaraptorids: in other theropods, the
proximal end is transversely narrow and dorsoventrally deep,
being sub-rectangular in shape (e.g., Allosaurus,
Acrocanthosaurus, Torvosaurus, Tyrannosaurus; Galton and
Jensen, 1979; Madsen, 1976; Currie and Carpenter, 2000;
Brochu, 2003) or subtriangular in outline (as in Guanlong and
Deinonychus; Ostrom, 1976; Xu et al., 2006). Furthermore, in
Megaraptor the proximal articular surface is transversely
wider dorsally than ventrally (Novas, 1998). This condition is
unknown in other theropods, including Australovenator
(White et al., 2012), in which the proximal end is transversely
wider on its ventral margin than on its dorsal edge.
Phalanx 1 of digit I in Megaraptor shows a deep and wide
furrow along its ventral surface (Novas, 1998). As a result, both
lateral and medial margins of this surface acquired the form of
sharp longitudinal ridges (g. 10). These features are also
documented in Australovenator (White et al., 2012). In other
theropods, phalanx 1.I is ventrally excavated, but the furrow is
restricted on the proximal half of the bone, and it is not as deep
as in megaraptorids. No longitudinal ridges are present. It is
interesting to note that in megaraptorids, the ventral margin of
the proximal articular surface of phalanx 1.I is concave,
reecting the deep furrow present along the ventral surface of
the bone. This is in contrast with other theropods, in which this
margin is straight (e.g., Allosaurus; Madsen, 1976) or convex
(e.g., Guanlong, Deinonychus; Ostrom, 1976; Xu et al., 2006).
The distal ginglymus of phalanx 1.I of Megaraptor is
dorsoventrally deeper and transversely narrower than in other
theropods (including Australovenator), and the dorsoventral
sulcus is much more incised.
Megaraptor is well-known by its extremely large and
elonga te manual ung ual on digit I (Ca lvo et al., 20 04), wh ich is
subequal in length to the ulna. This condition is unusual
among theropods, being absent among basal tetanurans (e.g.,
Allosaurus; Madsen, 1976), basal coelurosaurs (e.g., Scipionyx,
Tanycolagreus, Chilantaisaurus; Dal Sasso and Maganuco,
2011; Carpenter et al., 2005; Benson and Xu, 2008),
ornithomimosaurs (e.g., Gallimimus), oviraptorosaurs, basal
therizinosaurs (e.g., Falcarius, Nothronychus; Zanno, 2010;
Zanno et al., 2009), and paravians (e.g., Deinonychus; Ostrom,
1969). Furthermore, in the megaraptorans Australovenator
and Fukuiraptor, the ungual of digit I is much shorter than the
ulna, representing approximately half of its length. Basal
tetanurans that evolved an enlarged ungual in manual digit I
are the compsognathid Sinosauropteryx (Currie and Chen,
2001), and the megalosauroids Baryonyx and Tor vos a uru s
(Galton and Jensen, 1979; Charig and Milner, 1997).
In the original description of Megaraptor (Novas, 1998), it
was remarked that the ungual phalanx bore a sharp longitudinal
ventral keel. This trait was later considered as a synapomorphy
of Megaraptoridae (Novas et al., 2013). In Megaraptor, towards
the prox i mal en d of th e claw, the ven t ral ke el gra duall y displa c es
laterally, joining the lateral margin of the claw on its most
proximal portion, a condition also reported in Australovenator
(White et al., 2012; g. 11). Other theropods, including
Fukuiraptor (Azuma and Currie, 2000), basal tyrannosauroids
(e.g., Guanlong; Xu et al., 2006), megalosauroids (e.g.,
Baryonyx, Tor v osau r us; Galton and Jensen, 1979; Charig and
Milner, 1997) and the problematic Chilantaisaurus (Benson
and Xu, 2008) have unguals with a transversely rounded
expanded ventral surface, without traces of a ventral keel. In
sum, such a transverse compression of the enlarged ungual
constitutes a distinctive feature of Megaraptoridae.
In addition, the manual ungual I of Megaraptor and
Australovenator share very deep and well-dened exor
facets on the lateral and medial surfaces of the exor tubercle.
These facets are deep, wide, and more well-dened than in
other theropods, including Allosaurus, Baryonyx and
Tor v osau r us (Madsen, 1976; Galton and Jensen, 1979; Charig
and Milner, 1997). Furthermore, in Megaraptor such facets
are delimited by acute ridges of bone (Figure 12). It is worth
nothing that similar facets were described for Fukuiraptor
(Azuma and Currie, 2000).
Digit II. In Megaraptor, phalanx 1.II is shorter than phalanx
2.II, a condition similar to that of some allosauroids, such as
Allosaurus (Gilmore, 1920; Madsen, 1976) and
Acrocanthosaurus (Currie and Carpenter, 2000), and selected
coelurosaurs, as for example Sinocalliopteryx (Ji et al., 2007),
Sinosauropteryx (Currie and Chen, 2001), Scipionyx (Dal Sasso
and Maganuco, 2011), Guanlong and Deinonychus. Distribution
of this feature (i.e., length ratio of pre-ungual phalanges of digit
II) is not uniform among tetanurans. For example, in the
megaraptorid Australovenator and the basal tyrannosauroid
Tanycolagreus (Carpenter et al., 2005), phalanges 1 and 2 of
Figure 9. Proximal end of right phalanx I.1 of A, Megaraptor; B, Australovenator; C, Allosaurus; D, Tyrannosaurus (modied from Brochu,
2003); and E, Deinonychus (modied f rom Ostrom, 1969). Not to scale.
F.E. Novas, A.M. Aranciaga Rolando & F.L. Agnolín
Figure 10. Right manual phalanx 1 of digit I in ventral view and schematic representations of Megaraptor (A, C), Australovenator (B,D). Scale
bar: 2 cm. Note the well-developed longitudinal ventral furrow.
Figure 11. Right manual ungual phalanx of digit I in ventral view and schematic representation of Megaraptor (A,C); an d Australovenator (B, D).
Not to scale.
Megaraptor manual osteology 59
digit II are subequal in length, and the megalosauroid
Sciurumimus (Rauhut et al., 2012) shows coelurosaur-like
proportions, with phalanx 1.II shorter than phalanx 2.II.
In Megaraptor, the proximal articular surface of phalanx
1.II describes a dorsoventrally deep ovoid contour. Its ventral
margin bears a rounded process that projects proximomedially,
a feature shared with Australovenator (White et al., 2012) and
Fukuiraptor (Azuma and Currie, 2000). This results in a
relatively narrow ventral margin of the proximal end of phalanx
1.I. This shape is in contrast with other theropods, such as
Allosaurus and Tyrannosaurus (Madsen, 1976; Brochu, 2003),
in which the ventral margin is straight. Furthermore, in
Megaraptor, and probably also in Australovenator and
Fukuiraptor, the proximal articular surface phalanx 1.II is
obliquely oriented with respect to the distal articular trochlea,
a condition unknown in other theropods, in which the main
axes of both proximal and distal ends are sub-parallel.
In Megaraptor, metacarpal II and its corresponding non-
ungual phalanges have respective distal articular trochleae
with a medial condyle more ventrally projected than the lateral
one. In probable correlation with this shape, it is seen that non-
unguals of digit II exhibit a longitudinal keel that runs along
their ventromedial margins. Such strong asymmetry of distal
condyles and longitudinal ridges appear to be absent in other
theropods, including Australovenator, although in the
available phalanx 1.II of Fukuiraptor (Azuma and Currie,
2000) a similar ventromedial ridge seems to be present.
Digit III. In Megaraptor phalanges of this digit look similar in
proportions to those of Allosaurus (Gilmore, 1920; Madsen,
1976), except for the ungual, which is proportionally shorter
and smaller. The pre-ungual phalanx of digit III of Megaraptor
is longer than phalanges 1 and 2 of the same digit, as generally
occurs among tetanurans, although it does not reach the
elongation that characteristically occurs in coelurosaurs (e.g.,
Sinocalliopteryx, Dilong, Guanlong, Deinonychus; Ostrom,
1976; Xu et al., 2006; Ji et al., 2007).
Shared presence of a longitudinal groove along the medial side
of humeral shaft in megaraptorans and tyrannosaurids
conforms a novel feature supporting close relationships
between these theropod families. Comparison of the manus in
Megaraptor and Australovenator allowed the recognition of
several features that may shed light on the phylogenetic
relationships of megaraptorids. The manus of Megaraptor
exhibits the following unique traits that are not present in
other theropods, and are here interpreted as autapomorphies
of this genus: 1) metacar pal I with an acute medial condyle on
distal gynglimus; 2) phalanges of digit II with ventromedial
ridges; and 3) an extremely elongate manual ungual on digit I,
approximating the length of the ulna.
Manual characters here interpreted as diagnostic of
Megaraptoridae include: symmetrical-shaped metacarpal I,
proximal end of phalanx 1.I transversally expanded, phalanx 1.I
with a longitudinal ventral furrow, and ungual phalanx of digit
I with a laterally displaced sharp ventral margin. Manual
characters diagnostic of Megaraptora are more difcult to
recognize because the manus of the basal megaraptoran
Fukuiraptor is poorly known. Nevertheless, two possible
derived features have been identied: asymmetrical phalanx 1.
II; and rst digit ungual with deep facets on the exor tubercle.
After comparing carpal, metacarpal and phalangeal
morphology, it becomes evident that megaraptorids retained
several of the manual features present in basal tetanurans, such
as Allosaurus. In this regard, Megaraptor and Australovenator
are devoid of several manual features that the basal
tyrannosauroid Guanlong shares with more derived coelurosaurs
(e.g., Deinonychus). However, there are some manual characters
that support Megaraptora as members of Coelurosauria,
including the elongate and slender shaft of metacarpals I and II,
and the presence of separated exor and extensor distal end of
the humerus, and the absence of a longitudinal furrow on the
dorsal surface of metacarpal I, and a semilunar carpal.
Furthermore, megaraptorans are similar to specialised members
of Tyrannosauroidea in having a transversely narrow metacarpal
III that represents 0.75 the length of metacarpal II, a set of
features previously interpreted as synapomorphies uniting both
clades (Novas et al., 2013; Porri et al., 2014).
The senior author wishes to thank deeply Tom and Pat Rich for
their genereous invitation to visit Australia, and for allowing
the study of the valuable Cretaceous theropod materials they
collected in Victoria. Scott Hocknull and his crew kindly
facilitated access to the specimen of Australovenator. Xu
Figure 12. Right manual ungual phalanx of digit I in A,C, ventral, and B,D, lateral views. A-B, Megaraptor; C-D, Australovenator and sch em at ic
representation in E,G, ventral, and F,H, lateral views. E-F, Megaraptor; G-H, Australovenator. Scale bar: 2 cm. Abbreviations: ff, exor facets.
F.E. Novas, A.M. Aranciaga Rolando & F.L. Agnolín
Xing allowed access to several theropod specimens under his
care. Special thanks to Steve Brusatte and an anonymous
reviewer that made clever observations that improved the
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... Megaraptorids are medium to large-sized theropods that lived in the Cretaceous of Gondwana. These theropods were specialised predators with long skulls, serrated and curved teeth, highly pneumatized skeletons, gracile hindlimbs, robust pectoral girdles and stout forearms with enlarged trenchant manual claws (Calvo et al. 2004;Hocknull et al. 2009;Novas et al. 2013Novas et al. , 2016Porfiri et al. 2014Porfiri et al. , 2018Coria and Currie 2016;Aranciaga-Rolando and Novas 2019;Lamanna et al. 2020). The pectoral girdle and forelimbs show several modifications that make them very efficient and powerful tools for prey capture (White et al. 2015;Novas et al. 2016). ...
... These theropods were specialised predators with long skulls, serrated and curved teeth, highly pneumatized skeletons, gracile hindlimbs, robust pectoral girdles and stout forearms with enlarged trenchant manual claws (Calvo et al. 2004;Hocknull et al. 2009;Novas et al. 2013Novas et al. , 2016Porfiri et al. 2014Porfiri et al. , 2018Coria and Currie 2016;Aranciaga-Rolando and Novas 2019;Lamanna et al. 2020). The pectoral girdle and forelimbs show several modifications that make them very efficient and powerful tools for prey capture (White et al. 2015;Novas et al. 2016). Although several megaraptorid taxa has been discovered, the phylogenetic relationships of this clade are still being questioned (Benson et al. 2010;Novas et al. 2013;Porfiri et al. 2014Porfiri et al. , 2018Coria and Currie 2016;Aranciaga-Rolando and Novas 2019). ...
... In contrast, in megaraptorids the necks seem lighter and thinner which is reasonable, when we thought that it shows slender and long skulls. Furthermore, megaraptorids as Australovenator and Megaraptor show strong modifications for predation in their forelimb (e.g., large degree of forearm flexion, distally displacement of the radius during flexion or hyperextension of the manual digits; White et al. 2015;Novas et al. 2016), which shows that the forelimbs have played a very important role during prey capture. ...
Aerosteon riocoloradensis represents one of the most complete megaraptorans yet discovered. This theropod comes from Anacleto Formation (Campanian) of Mendoza Province, Argentina. The aims of this contribution are: to present a detailed, bone by bone description of this specimen with figures of each bone; provide comparisons to other closely related theropods; revise the original assignation and diagnosis of such taxa. Three bones were re-assigned and almost all the autapomorphies of Aerosteon were modified. Features in the vertebral columns, which are shared with other megaraptorans, show that these theropods shared features with basal coelurosaurs. Anatomical Abbreviations ACDL: Anterior centrodiapophyseal lamina; CDF: Centrodiapophyseal fossa; CPAL: Centroparapophyseal lamina; CPRL: Centroprezygapophyseal lamina; CPRF: Centroprezygapophyseal fossa; CPR-CDF: Centroprezygapophyseal-centrodiapophyseal fossa; Hye: Hyposphene; Hym: Hypantrum; ILT: Intervertebral ligament tuberosity; IPOL: Infrapostzygapophysela lamina; IZL: Intrazygapophyseal lamina; PADL: Paradiapophyseal lamina; PAD-CDF: Paradiapophyseal-centrodiapophsyeal fossa; PCDL: Posterior centrodiapophyseal lamina; POEL: Postzygaepipophysela lamina; PODL: Postzygadiapophyseal lamina; POSF: Postspinal fossa; POCDF: Postzygapophsyeal-centrodiapophyseal fossa; Poz: Postzygapophysis; PRDL: Prezygadiapophyseal lamina; PRPAF: Prezygaparapophyseal fossa; PRPAL: Prezygaparapophyseal lamina; PRSF: Prespinal fossa; PRSL: Prespinal lamina; PRD-CDF: Prezygadiapophyseal-centrodiapophyseal fossa; PRD-PADF: Prezygadiapophyseal-paradiapophyseal fossa; PRD-PODF: Prezygadiapophyseal-postzygadiapophyseal fossa; PRCDF: Prezygapophyseal-centrodiapophyseal fossa; Prz: Prezygapophyses; SDF: Supradiapophsyeal fossa; SDL: Supradiapophyseal lamina; SPOF: Spinopostzygapophyseal fossa; SPOL: Spinopostzygapophyseal lamina; SPRF: Spinoprezygapophyseal fossa; SPRL: Spinoprezygapophyseal lamina; SR(number): Sacral rib; STP(number): Sacral transverse process
... Most recently, some authors (e.g., Apesteguía et al. 2016;Aranciaga Rolando et al. 2018;Porfiri et al. 2018) have (in at least some of their respective phylogenetic analyses) recovered Megaraptora as an early branching radiation of non-tyrannosauroid coelurosaurs, whereas others (e.g., Porfiri et al. 2014;Aranciaga Rolando et al. 2019) have continued to find support for proposed tyrannosauroid affinities of the clade. Still others (e.g., Novas et al. 2016) have identified conflicting morphological characters within Megaraptora, some of which support a position with Coelurosauria and others that are more consistent with allosauroid affinities. Even the lower-level taxonomic composition of the clade has proven controversial in recent years, with various authors linking other Laurasian (Chilantaisaurus tashuikouensis, Eotyrannus lengi, Phuwiangvenator yaemniyomi, Siats meekerorum, Vayuraptor nongbualamphuensis, Vectaerovenator inopinatus; e.g., Zanno and Makovicky 2013; Samathi et al. 2019; Barker et al. 2020) and/or Gondwanan (e.g., the mysterious bahariasaurids Aoniraptor libertatem, Bahariasaurus ingens, Deltadromeus agilis, and Gualicho shinyae [Stromer 1934;Sereno et al. 1996;Apesteguía et al. 2016;Motta et al. 2016;Aranciaga Rolando et al. 2020;Ibrahim et al. 2020]) species to the clade as putative nonmegaraptorid megaraptorans. ...
... 7A-C; Table 3). Based on its size, morphology, and comparisons with other large-bodied avetheropods (e.g., Allosaurus fragilis [Gilmore 1920;Madsen 1976 [Calvo et al. 2004;Novas et al. 2016], metriacanthosaurids [Dong 1984;Currie and Zhao 1993;Gao 1993]), it is tentatively identified as phalanx II-2 of the right manus. The proximal half and most of the medial condyle are missing. ...
... The distal end appears less dorsoventrally expanded than that of manual phalanx II-2 of Megaraptor (Calvo et al. 2004: fig. 8b;Novas et al. 2016: fig. 3), appearing more similar to that of Australovenator (White et al. 2012: figs. ...
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We describe two partial postcranial skeletons belonging to the enigmatic theropod dinosaur clade Megaraptoridae from the Upper Cretaceous (lower Cenomanian-upper Turonian) Bajo Barreal Formation of southern Chubut Province, central Patagonia, Argentina. The specimens are assigned to Megaraptoridae due to their possession of multiple anatomical features that are considered synapomorphies of that predatory dinosaur group, such as a greatly enlarged, laterally compressed ungual of manual digit I that possesses asymmetrical lateral and medial vascular grooves. Overlapping elements of the two skeletons are nearly identical in morphology, suggesting that they probably represent the same taxon, a large-bodied theropod that was previously unknown from the early Late Cretaceous of southern South America. The Bajo Barreal specimens constitute the most ancient unquestionable records of Megaraptoridae from that continent, and exhibit particularly strong osteological resemblances to penecontemporaneous megaraptorids from the Winton Formation of Australia. Phylogenetic analysis recovers the unnamed Bajo Barreal taxon as the earliest-diverging South American megaraptorid and the oldest-known representative of this clade that likely attained a body length of at least seven meters and a mass of at least one metric ton. Overall, the balance of the evidence suggests that megaraptorids originated in eastern Gondwana (Australia) during the Early Cretaceous, then subsequently dispersed to western Gondwana (South America) during the mid-Cretaceous, where they attained substantially larger body sizes, ultimately coming to occupy the apex predator niches in their respective habitats.
... The tree topology is very similar with the first analysis but shows a higher resolution within Megaraptora. As in previous works, the more basal forms of this clade are the Asian Phuwiangvenator, Vayuraptor, and Fukuiraptor; which constitute successive sister taxa to Megaraptoridae 2,7,10,12,19 . Among megaraptorids, the Australian LRF 100-106 and Australovenator represent the earliest-branching members of the clade and are more closely related to each other than to South American megaraptorids (See Supplementary Information I). ...
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Megaraptora is a theropod clade known from former Gondwana landmasses and Asia. Most members of the clade are known from the Early to Late Cretaceous (Barremian–Santonian), with Maastrichtian megaraptorans known only from isolated and poorly informative remains. The aim of the present contribution is to describe a partial skeleton of a megaraptorid from Maastrichtian beds in Santa Cruz Province, Argentina. This new specimen is the most informative megaraptoran known from Maastrichtian age, and is herein described as a new taxon. Phylogenetic analysis nested the new taxon together with other South American megaraptorans in a monophyletic clade, whereas Australian and Asian members constitute successive stem groups. South American forms differ from more basal megaraptorans in several anatomical features and in being much larger and more robustly built.
... Simplified cladogram of theropod relationships, showing common relationships between theropod dinosaurs and alternative phylogenetic positions for several problematic taxa (modified fromRauhut 2003) have been supported by several more recent analyses using new material(Porfiri et al. 2014; Aranciaga Rolando et al. 2019), but the exact position of this interesting clade is still uncertain (e.g.Apesteguía et al. 2016;Coria and Currie 2016;Novas et al. 2016). ...
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Research in the late 1900s has established that birds are theropod dinosaurs, with the discovery of feather preservation in non-avian theropods being the last decisive evidence for the dinosaur origin of this group. Partially due to the great interest in the origin of birds, more phylogenetic analyses of non-avian theropod dinosaurs have probably been published than any other group of fossil vertebrates. Despite a lot of uncertainty in the exact placement of many taxa and even some major clades, there is a remarkable consensus about the hierarchical position of birds (here used for the total group, Avialae) within theropod dinosaurs. Thus, birds are part of Paraves, together with such well-known theropod groups as dromaeosaurids and troodontids; Paraves are part of Maniraptora, which furthermore include Oviraptorosauria, Therizinosauria, and Alvarezsauroidea; Maniraptora belong to Maniraptoriformes, which also include Ornithomimosauria; Maniraptoriformes are a subclade of Coelurosauria, to which Tyrannosauroidea and some other basal taxa also belong; Coelurosauria are part of Tetanurae, together with Allosauroidea and Megalosauroidea; finally, Tetanurae are a subclade of Theropoda, which also include Ceratosauria and Coelophysoidea.
Megaraptora is a group of enigmatic, carnivorous non‐avian theropod dinosaurs from the Cretaceous of Asia, Australia, and especially South America. Perhaps the most striking aspect of megaraptoran morphology is the large, robustly constructed forelimb that, in derived members of the clade, terminates in a greatly enlarged manus with hypertrophied, raptorial unguals on the medialmost two digits and a substantially smaller ungual on digit III. The unique forelimb anatomy of megaraptorans was presumably associated with distinctive functional specializations; nevertheless, its paleobiological significance has not been extensively explored. Here we draw from observations of the pectoral girdle and forelimb skeletons of Megaraptora and myological assessments of other archosaurian taxa to provide a comprehensive reconstruction of the musculature of this anatomical region in these singular theropods. Many muscle attachment sites on megaraptoran forelimb bones are remarkably well developed, which in turn suggests that the muscles themselves were functionally significant and important to the paleobiology of these theropods. Furthermore, many of these attachments became increasingly pronounced through megaraptoran evolutionary history, being substantially better developed in derived taxa such as Australovenator wintonensis and especially Megaraptor namunhuaiquii than in early branching forms such as Fukuiraptor kitadaniensis. When considered alongside previous range of motion hypotheses for Australovenator, our results indicate that megaraptorans possessed a morphologically and functionally specialized forelimb that was capable of complex movements. Notable among these were extensive extension and flexion, particularly in the highly derived manus, as well as enhanced humeral protraction, attributes that very probably aided in prey capture.
Dryptosaurus aquilunguis is a tyrannosauroid from the late Maastrichtian of Eastern North America (Brusatte et al., 2011, pp. 2 and 5). This is also known as Appalachia (Brownstein, 2018, p. 1). So far, only one good specimen, the holotype ANSP 9995, has been found for the genus. A few teeth have been assigned to the genus (Brownstein, 2018, p. 5 Table 1), but no relatively complete specimens have been described yet. However, after an exhaustive examination of the controversial “Nanotyrannus”/juvenile Tyrannosaurus rex specimens, a new hypothesis is going to be brought forth: Dryptosaurus lived in Appalachia and Laramidia towards the end of the Maastrichtian. The tyrannosauroid specimens previously labeled as “Nanotyrannus” are actually Dryptosaurus. Both Dryptosaurus and “Nanotyrannus” lived during the same time (Brusatte et al., 2011, p. 5) (Larson, 2013, p. 15). Numerous publications have suggested that Laramidia and Appalachia reconnected when the Western Interior Sea subsided around 70.8-67 Ma (Blakey, 2014) (Bell and Currie, 2014, Figure 4) (Brownstein and Bissel, 2021, Discussion, para. 3-4) (Druckenmiller et al., 2021, Figure 1). Both Laramidia and Appalachia seemed to have had similar fauna: lambeosaurs, ceratopsians, and mosasaurs (Gallagher et al., 2012, p. 147) (Van Vranken and Boyd, 2021, Abstract; p. 5) (Rolleri et al., 2020, pp. 284-285) (Sullivan et al., 2011) (Brownstein and Bissel, 2020, Abstract; Discussion, para. 3-4) (Serrano-Branas and Prieto-Marquez, 2022). Ceratopsids, in particular, were thought to have not existed in Appalachia. However, a ceratopsian tooth has been found in the Maastrichtian-aged Owl Creek Formation, which is in Appalachia (Farke and Phillips, 2017) (Brownstein and Bissel, 2021, Discussion, para. 4). If animals in Laramidia can be found in Appalachia, and vice versa, then hypothetically, Dryptosaurus could migrate into Laramidia. Dryptosaurus and “Nanotyrannus” share many physical characteristics: Both Dryptosaurus and “Nanotyrannus” have a first maxillary tooth that is incisiform (small and similar in morphology to the premaxillary teeth) (Cope, 1869, pp. 100-101) (Brusatte et al., 2011, p. 9) (Larson, 2013, pp. 33-35). This trait is not present in T. rex (Molnar, 1978, p. 77) (Bakker et al., 1988, p. 24) (Larson, 2013, pp. 33-35). Both genera have about 25 or so caudal vertebrae (Cope, 1869, p. 102) (pers. obs. in Pantuso, 2019) (pers. obs. in Mapping, North Carolina Museum of Natural Sciences, North Carolina, United States). T. rex and Tarbosaurus/Tyrannosaurus bataar have 40 or more caudal vertebrae (Brochu, 2003, pp. 49 and 90). This is also seen in the young T. bataar specimen PIN 552-2, so the bone count didn’t increase or decrease during ontogeny (Maleev, 1955b, p. 4) (Maleev, 1974, pp. 13 and 29). Morphology of the arms of both genera are identical ( Brusatte et al., 2011, p. 19) (Pantuso, 2019). The humeri are identical and differ in shape compared to T. rex’s (Brochu, 2003, p. 97 Figure 85) (pers. obs. in Holtz, 2021). The manual phalanx 1-1 of Dryptosaurus and “Nanotyrannus” are extremely elongated, and this is an autapomorphy of Dryptosaurus (Brusatte et al., 2011, pp. 5 and 47; Table 3) and Megaraptor (Novas et al., 2016, p. 53 Figure 3; p. 56). G./A. libratus’ manual phalanx 1-1 is somewhat longer than other tyrannosaurids (9.8 cm) (Brusatte et al., 2011, p. 47 Table 3), but it’s still only half as long as Dryptosaurus’ (16 cm) (Table 3) or “Nanotyrannus’” (Larson, 2020). T. rex’s, and T. bataar’s, manual phalanx 1-1 are shorter than Dryptosaurus’ and “Nanotyrannus’’’ (Maleev, 1974, p. 36 Table 5) (Larson, 2008, pp. 41-42) (Brusatte et al., 2011, p. 47 Table 3) (Larson, 2018) (Persons IV et al., 2019, p. 669 Table 1). The manual unguals of the two genera are large and comparable in morphology and size (Brusatte et al., 2011, p. 20 Table 2) (Pantuso, 2019) (Stein, 2021, p. 43 Figure 8 C) (Larson, 2016), contra to T. rex’s and T. bataar’s short manual unguals (Tsuihiji et al., 2011, p. 2 Figure 1 A) (Larson, 2018) (TD-13-047, PaleoAdventures, South Dakota, United States). Both genera have tibiae that are either longer than their femora, or they are about the same size as each other (Carpenter et al., 1997, p. 568 Table 3) (Persons IV et al., 2016, Tables 1 and 4). This is a trait seen in basal tyrannosauroids. Brusatte et al., (2011) said that Dryptosaurus’ tibia is smaller than the femur (p. 20 Table 2; p. 30), but other sources say the tibia is longer (Carpenter et al., 1997, p. 568 Table 3) (Persons IV and Currie, 2016, Table 1). Brusatte et al., (2011) also stated that the tibia’s “proximal and distal ends are slightly eroded” (p. 30), so the tibia could have been longer. The Dryptosaurus holotype specimen is considered to be an adult, or close to maturity (p. 5). Other examples are Qiazhousaurus/Alioramus sinensis, Appalachiosaurus, Alectrosaurus, Dilong, Guanlong, and Yutyrannus (Lu et al., 2014, Supplementary Materials, p. 9 Table 5) (Persons IV and Currie, 2016, Table 1). These are all basal or derived tyrannosauroids, and most of these specimens are considered to be adults or subadults. As for the basal tyrannosaurids, both Gorgosaurus/Albertosaurus libratus and Albertosaurus sarcophagus have femora and tibiae lengths that fluctuate between the femur being longer than the tibia, or both bones are about the same length (Persons IV and Currie, 2016, Tables 1 and 2). As for the tyrannosaurinae, the 14-year old T. rex specimen LACM 23845 (Erickson et al., 2004, p. 774 Table 1), had a femur and tibia length of 82.5 cm, while the adult specimen CM 9380 has a longer femur (Table 2). Rozhdestvensky (1965) said that the young T. bataar specimen, PIN 552-2, had a femur and a tibia that are “almost the same length,” while an older specimen, PIN 551-2, has a longer femur (p. 10). There are other traits that “Nanotyrannus” had that are seen in other basal and advanced tyrannosauroids, such as the lingual bar on the interior side of the dentary covering the first alveoli instead of the first two as in T. rex or T. bataar (Dalman and Lucas, 2017, pp. 23-24). All of the information listed above indicates that “Nanotyrannus” could be Dryptosaurus. This would also indicate that Dryptosaurus was present in Appalachia and Laramidia, creating a regional barrier that would help separate “Nanotyrannus” from being lumped into T. rex because, as of right now, no Tyrannosaurus specimens have been found in the Eastern United States. This technique helped to separate Torosaurus from Triceratops (Deak and McKenzie, 2016, slide 7). An alternative hypothesis could be that Dryptosaurus was actually a juvenile T. rex. Brusatte et al., (2011) did not perform a histological test to see how many LAGs the Dryptosaurus holotype had in its femur or tibia, which could potentially go against their conclusion that the holotype was actually mature. They just used the closed neurocentral sutures to estimate the age of the specimen (p. 5). The “Nanotyrannus” specimen BMRP 2002.4.1 (“Jane”) had visible neurocentral sutures on caudals 1-11, but caudals 12 and others, along with one dorsal vertebra, show closed sutures and are fused. This was used to suggest an older age for the specimen (Larson, 2013, p. 19). However, a histological analysis on the specimen’s femur showed that “Jane” was just 13 years old, and was still growing when it died (Woodward et al., 2020, Results, para. 4). Since Dryptosaurus lived during the same time as T. rex, and has similar traits that the “Nanotyrannus”/juvenile T. rex specimens have, then perhaps it was a juvenile T. rex? The author of this paper does not believe this to be the case, especially since actual juvenile T. rex specimens are already known and have different traits that are not present in “Nanotyrannus” or Dryptosaurus (Dalman, pers. comm.). This will be elaborated on in the future. In conclusion, the traits that are present in the “Nanotyrannus” specimens are also seen in the holotype specimen of Dryptosaurus. Both genera lived during the same time, and had coexisting taxa that were present in Appalachia and Laramidia. This suggests that the Western Interior Sea began to recede, or it had already. This could have allowed Dryptosaurus to migrate into Laramidia. More publications will be published in the future to explore this hypothesis further.
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Megaraptorans are a theropod clade distributed in former Gondwana landmasses and Asia. Most members of the clade are known from early Cretaceous to Turonian times whereas Maastrichtian megaraptorans are known just from isolated and poorly informative remains. The aim of present contribution is to describe a partial skeleton of a megaraptorid coming from Maastrichtian beds at Santa Cruz province, Argentina. This new taxon constitutes the most informative megaraptoran from post-Turonian beds. Phylogenetic analysis nested the new taxon together with South American megaraptorans in a monophyletic clade, whereas Australian and Asian members constitute successive stem groups. South American forms differ from more basal megaraptorans in several anatomical features and in being much larger and more robustly built. It is possible that the Cenomanian-Turonian extinction of carcharodontosaurids was allowed to megaraptorans to occupy the niche of top predators in South America.
Phuwiangvenator yaemniyomi is a mid-sized, early branching megaraptoran theropod from the Lower Cretaceous Sao Khua Formation of Phu Wiang Mountain, Khon Kaen Province, northeastern Thailand. The holotype includes dorsal and sacral vertebrae, lower legs, hand and foot elements. Here we describe new skeletal material pertaining to the same individual representing the holotype of Phuwiangvenator based on size, shape, and shared phylogenetic affinities. This material was recovered at the same quarry as the holotype and consists of an incomplete fibula, left and right metatarsals. A new autapomorphy observed from the new material is the presence of a long, deep fossa between the lateral and medial distal condyles of the metatarsal II that extends to the distal articular facet is visible in anterior view. The metatarsal III of Phuwiangvenator is relatively short, more similar to the proportion present in basal carcharodontosaur Concavenator than in the derived megaraptorans, but more gracile than other basal allosauroids. Its hindlimb proportions are similar to the basal carcharodontosaur Neovenator than other more derived megaraptorans and coelurosaurs. Phuwiangvenator shows a combination of features shared with allosauroids and basal coelurosaurs and appears to be “intermediate” between non-megaraptorid and megaraptorid theropods. The present work adds anatomical data on this theropod and provides information on the early evolution of the Megaraptora.
The titanosaurian sauropod dinosaur Diamantinasaurus matildae is represented by two individuals from the Cenomanian-lower Turonian 'upper' Winton Formation of central Queensland, northeastern Australia. The type specimen has been described in detail, whereas the referred specimen, which includes several elements not present in the type series (partial skull, atlas, axis and postaxial cervical vertebrae), has only been described briefly. Herein, we provide a comprehensive description of this referred specimen, including a thorough assessment of the external and internal anatomy of the braincase, and identify several new autapomorphies of D. matildae. Via an expanded data matrix consisting of 125 taxa scored for 552 characters, we recover a close, well-supported relationship between Diamantinasaurus and its contemporary, Savannasaurus elliottorum. Unlike previous iterations of this data matrix, under a parsimony framework we consistently recover Diamantinasaurus and Savannasaurus as early-diverging members of Titanosauria using both equal weighting and extended implied weighting, with the overall topology largely consistent between analyses. We erect a new clade, named Diamantinasauria herein, that also includes the contemporaneous Sarmientosaurus musacchioi from southern Argentina, which shares several cranial features with the referred Diamantinasaurus specimen. Thus, Diamantinasauria is represented in the mid-Cretaceous of both South America and Australia, supporting the hypothesis that some titanosaurians, in addition to megaraptoran theropods and possibly some ornithopods, were able to disperse between these two continents via Antarctica. Conversely, there is no evidence for rebbachisaurids in Australia, which might indicate that they were unable to expand into high latitudes before their extinction in the Cenomanian-Turonian. Likewise, there is no evidence for titanosaurs with procoelous caudal vertebrae in the mid-Cretaceous Australian record, despite scarce but compelling evidence for their presence in both Antarctica and New Zealand during the Campanian-Maastrichtian. These later titanosaurs presumably dispersed into these landmasses from South America before the Campanian (~85 Mya), when seafloor spreading between Zealandia and Australia commenced. Although Australian mid-Cretaceous dinosaur faunas appear to be cosmopolitan at higher taxonomic levels, closer affinities with South America at finer scales are becoming better supported for sauropods, theropods and ornithopods.
Evolutionary teratology recognises certain anatomical modifications as developmental anomalies. Within non avian-theropod dinosaurs, the strong forelimb shortening of Tyrannosauridae, Carnotaurinae and Limusaurus – associated with a reduction or loss of autonomy – have been previously diagnosed as evolutionary anterior micromelias. The feature is here examined with Acrocanthosaurus atokensis (Carcharodontosauridae) and Gualicho shinyae (Neovenatoridae). The micromelic diagnosis is confirmed for Acrocanthosaurus, without supplementary malformations. Gualicho is considered as a borderline case, outside of the micromelic spectrum, but shows a total phalangeal loss on digit III. The reduction in the biomechanical range of Acrocanthosaurus’ forelimbs was compensated by the skull and jaws as main predatory organs. The same is assumed for Gualicho, but its robust first digit and raptorial claw are to be underlined. Other gigantic-sized and derived representatives of Carcharodontosauridae probably shared the anterior micromelia condition, potentially due to developmental modifications involving differential forelimbs/hindlimbs embryological growth rates, secondarily associated with post-natal growth rates leading to large and gigantic sizes; a converging state with Tyrannosauridae. Nevertheless, whereas developmental growth rates are also considered in the shortened condition of Gualicho, there is no association with post-natal gigantism. Finally, the digit III reduction likely followed the same evolutionary pathways as Tyrannosauridae, potentially involving BMPs, Fgfs and Shh signalling.
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Many recent studies of theropod relationships have been focused on the phylogeny of coelurosaurs and the question of the origin of birds, but the interrelationships and evolution of basal theropods are still poorly understood. Thus, this paper presents a phylogenetic analysis of all theropods, but focuses on the basal members of this clade. The result supports the inclusion of Eoraptor and herrerasaurids in the Theropoda, but differs from other recent studies in two main aspects: (1) The taxa usually grouped as ceratosaurs form two monophyletic clades that represent successively closer outgroups to tetanurans. The more basal of these clades, the Coelophysoidea, comprise the majority of Late Triassic and Early Jurassic theropods. The other clade of basal theropods that are usually included in the Ceratosauria comprises Ceratosaurus, Elaphrosaurus, and abelisaurids. (2) Two monophyletic groups of basal tetanurans are recognized: the Spinosauroidea and the Allosauroidea. In contrast to other recent phylogenetic hypotheses, both clades are united in a monophyletic Carnosauria. The branching pattern of the present cladogram is in general accordance with the stratigraphic occurrence of theropod taxa. Despite the differences in recent analyses, there is a significant level of consensus in theropod phylogeny. At least four different radiations of non-avian theropods can be recognized. These radiations show different patterns in Laurasia and Gondwana, and there are increasing differences between the theropod faunas of the two hemispheres from the Triassic to the Cretaceous.
A spectacular pair of Sinosauropteryx skeletons from Jurassic-Cretaceous strata of Liaoning in northeastern China attracted worldwide notoriety in 1996 as the first dinosaurs covered with feather-like structures. Sinosauropteryx prima is important not only because of its integument, but also because it is a basal coelurosaur and represents an important stage in theropod evolution that is poorly understood. Coelurosauria, which includes (but is not limited to) dromaeosaurids, ornithomimosaurs, oviraptorosaurs, troodontids, and tyrannosaurids, formed the most important radiation of Cretaceous carnivorous dinosaurs in the Northern Hemisphere. It also includes Aves. Sinosauropteryx prima has a number of characters that were poorly preserved in known specimens of the closely related Compsognathus longipes from Europe. These include the longest tail known for any theropod and a three-fingered hand dominated by the first digit, which is longer and thicker than either of the bones of the forearm. Both specimens have a thick coat of feather-like structures, which seem to be simple branching structures. The claim that one skeleton of Sinosauropteryx has preserved the shape of the liver is unsupportable, if only because the fossil had collapsed into a single plane, which would have distorted any soft, internal organs.
A new compsognathid dinosaur, Sinocalliopteryx gigas gen. et sp. nov., is erected based on a complete skeleton from the Early Cretaceous Yixian Formation of western Liaoning, northeastern China. It shares the features with Huaxiagnathus orientalis in having a manus as long as the humerus plus radius, very large and subequally long manual claws I and II, and reduced olecranon process on the ulna. But it differs from Huaxiagnathus orientalis in having the much large size, a very long maxillary process of premaxilla not extending the vertical level of the maxillary antorbital fossa, and the proportionally longer ulna and so on. Sinocalliopteryx gigas gen. et sp. nov. represents the largest species among the known compsognathid dinosaurs, suggesting the tendency of the body enlargement in compsognathids to some extent. The long filamentous integuments are attached to the whole body of this compsognathid, confirming that such integuments evolved firstly in the basal coelurosaurs. This new giant compsognathid was a fierce carnivorous theropod, as shown further by an incomplete dromaeosaurid leg inside its abdominal cavity.