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Journal of Anatomy. 2023;00:1–37.
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1wileyonlinelibrary.com/journal/joa
Received: 15 June 2023
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Revised: 10 November 2023
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Accepted: 15 November 2023
DOI : 10.1111/joa.1398 3
ORIGINAL ARTICLE
Reconstruction of the pelvic girdle and hindlimb musculature
of the early tetanurans Piatnitzkysauridae (Theropoda,
Megalosauroidea)
Mauro B. S. Lacerda1,2 | Jonathas S. Bittencourt3 | John R. Hutchinson1
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,
provided the original work is properly cited.
© 2023 The Authors. Journal of Anatomy published by John Wiley & Sons Ltd on behalf of Anatomical Society.
1Structure and Motion Laboratory,
Department of Comparative Biomedical
Sciences, The Royal Veterinary College,
Hatfield, UK
2Pós-Graduação em Zoologia, Instituto de
Ciências Biológicas, Universidade Federal
de Minas Gerais, Belo Horizonte, Brazil
3Departamento de Geologia, Instituto
de Geociências, Universidade Federal de
Minas Gerais, Belo Horizonte, Brazil
Correspondence
Mauro B. S. Lacerda and John R.
Hutchinson, Structure and Motion
Laboratory, Department of Comparative
Biomedical Sciences, The Royal Veterinar y
College, Hatfield AL9 7TA, United
Kingdom.
Email: mlacerda22@rvc.ac.uk;
jhutchinson@rvc.ac.uk
Funding information
Conselho Nacional de Desenvolvimento
Científico e Tecnológico, Grant/Award
Number: 200203/2022-3; Coordenação
de Aper feiçoamento de Pessoal de Nível
Superior, Grant/Award Number: 001;
European Research Council Horizon 2020,
Grant/Award Number: 695517; Fundação
de Amparo à Pesquisa do Estado de Minas
Gerais, Grant/Award Number: PPM-
003 0 4 -18
Abstract
Piatnitzkysauridae were Jurassic theropods that represented the earliest diverging
branch of Megalosauroidea, being one of the earliest lineages to have evolved moder-
ate body size. This clade's typical body size and some unusual anatomical features raise
questions about locomotor function and specializations to aid in body support; and
other palaeobiological issues. Biomechanical models and simulations can illuminate
how extinct animals may have moved, but require anatomical data as inputs. With a
phylogenetic context, osteological evidence, and neontological data on anatomy, it is
possible to infer the musculature of extinct taxa. Here, we reconstructed the hindlimb
musculature of Piatnitzkysauridae (Condorraptor, Marshosaurus, and Piatnitzkysaurus).
We chose this clade for future usage in biomechanics, for comparisons with myologi-
cal reconstructions of other theropods, and for the resulting evolutionary implications
of our reconstructions; differential preservation affects these inferences, so we dis-
cuss these issues as well. We considered 32 muscles in total: for Piatnitzkysaurus, the
attachments of 29 muscles could be inferred based on the osteological correlates;
meanwhile, in Condorraptor and Marshosaurus, we respectively inferred 21 and 12
muscles. We found great anatomical similarity within Piatnitzkysauridae, but differ-
ences such as the origin of M. ambiens and size of M. caudofemoralis brevis are ev.
Similarities were evident with Aves, such as the division of the M. iliofemoralis externus
and M. iliotrochantericus caudalis and a broad depression for the M. gastrocnemius pars
medialis origin on the cnemial crest. Nevertheless, we infer plesiomorphic features
such as the origins of M. puboischiofemoralis internus 1 around the “cuppedicus” fossa
and M. ischiotrochantericus medially on the ischium. As the first attempt to reconstruct
muscles in early tetanurans, our study allows a more complete understanding of myo-
logical evolution in theropod pelvic appendages.
KEYWORDS
Dinosauria, extant phylogenetic bracket, functional morphology, Jurassic, soft-tissue
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L ACERDA e t al.
1 | INTRODUC TION
Pi atn itzkysaurid ae is a cl ade of me diu m-s i zed (~4 to 6 m long; ~200 kg
body mass) tetanuran theropods within Megalosauroidea (sensu
Carrano et al., 2012), known from the Jurassic of South America
and North America (Bonaparte, 1979; Madsen, 1976; Rauhut, 2005).
However, in alternative phylogenies (Rauhut & Pol, 2019; Schade
et al., 2023), Piatnitzkysauridae is considered to be an early diver-
gent clade of Allosauroidea. Evolutionary implications related to the
locomotor skeletal system of Tetanur ae based on the alternative po-
sition of Piatnitzkysauridae were discussed by Lacerda et al. (2023).
Currently, at least three taxa constitute Piatnitzkysauridae:
Piatnitzkysaurus floresi Bonaparte, 1979 and Condorraptor curru-
mili Rauhut, 2005, from the late Toarcian to late Bajocian (Middle
Jurassic) assemblages of the Cañadón Asfalto Formation in Patagonia,
Argentina (Cúneo et al., 2013; Olivera et al., 2015); and Marshosaurus
bicentesimus Madsen, 1976 , from the Kimmeridgian (Upper Jurassic)
assemblages of the Morrison Formation in the United States (Utah;
possibly Colorado). A phylogenetic definition of the clade was pre-
sented by Carrano et al. (2012) as all megalosauroid theropods that
are more closely related to Piatnitzkysaurus than to Spinosaurus or
Megalosaurus. However, in some phylogenetic studies/hypotheses
(e.g., Benson, 2010; Dai et al., 2020; Rauhut et al., 2016), the poorly
preserved Middle Jurassic taxon Xuanhanosaurus from China falls
within piatnitzkysaurids as an early diverging species. However,
this taxon also has been recovered as an early tetanuran (Holtz
et al., 2004) or an allosauroid (Carrano et al., 2012); and, therefore, is
considered a “wildcard” taxon (Carrano et al., 2012).
Condorraptor and Piatnitzkysaurus are taxa of great importance,
both geographically and temporally, as they are some of the few
known Middle Jurassic theropods with a relatively well-preserved
skeleton, especially considering the fossil record from South America
(Bonaparte, 1979; Carrano et al., 2012; Rauhut, 2003, 2004, 2005,
2007). They also provide important phylogenetic clues about the
evolution of early theropod dinosaurs (Carrano et al., 2012; Lacerda,
2023; Rauhut, 2003). Concerning the skull, the North American
taxon Marshosaurus is better known than both Condorraptor and
Piatnitzkysaurus (Ca r ra n o et al. , 2012; Chure et al., 1997; Madsen, 1976),
also preserving a rare case of osteopathological evidence (Chure
et al., 1997 ). Additional skeletal elements (e.g., Chure et al., 1997) are
as yet unde scr ibed . The two Argentine an tax a are als o known fr om de -
cent skeletal material: both skeletons of Piatnitzkysaurus are relatively
well-preserved including a sizeable portion of the appendicular skele-
ton and braincase, for example; and Condorraptor, although more frag-
mentary, has numerous postcranial elements (e.g., Bonaparte, 1986;
Novas, 2009; Paulina-Carabajal, 2015; Rauhut, 2004, 2005, 2007 ).
Pi atni t zky sau ridae is a key clad e for un d erstand ing the evol uti on of
tetanuran theropods because they are the earliest and oldest known
members of this clade (Carrano et al., 2012; Rauhut et al., 2016).
The main distinctions between Piatnitzkysaurus, Condorraptor and
Marshosaurus are based on characters present in the dentaries,
axial skeleton, and tibia (Bonaparte, 1986; Carrano et al., 2012;
Madsen, 1976; Rauhut, 2005); however, additional dissimilarities in
pelvic bones and zeugopodial elements are also recognizable (Lacerda
et al., 2023). Furthermore, the Middle Jurassic was an important time
for the diversification of tetanuran theropods, which soon populated
all continents, although these main evolutionary patterns remain
poorly known (e.g., Rauhut, 2004, 2005; Sereno, 1999).
Piatnitzkysaurid species can be diagnosed, for example, by the
following morphological features: (1) short or absent anterior max-
illary ramus, (2) presence of two parallel rows of foramina on the
maxilla, (3) vertically striated paradental plates, and (4) anteriorly
inclined neural spines of the posterior dorsal vertebrae (further
details in Carrano et al., 2012). The first cladistic studies that phy-
logenetically positioned and characterized these species as a clade
were Benson (2010) and Carrano et al. (2012), who included the
piatnitzkysaurids within the clade Megalosauroidea, differing from
other approaches. Historical classifications generally had assigned
Marshosaurus and Piatnitzkysaurus as members of allosaurids or
megalosaurids (e.g., Bonaparte, 1979, 1986; Russell, 198 4; for a sum-
mary see Carrano et al., 2012).
Marshosaurus and Piatnitzkysaurus are known from skeletons
of adult individuals (Bonaparte, 1986; Madsen, 1976), whereas
Condorraptor is known from a probably subadult specimen
(Rauhut, 2005). The estimated typical body length of the three spe-
cies is 4.5 m, with a body mass of about 200 kg for Marshosaurus and
Condorraptor; whereas the body mass of Piatnitzkysaurus was esti-
mated as 275 kg (Paul, 198 8, 2016). Hendrickx et al. (2015) estimated
longer body lengths, between 5 and 6 m, and Foster (2020) estimated
a slightly greater body mass for Marshosaurus (250 kg). Nevertheless,
one estimate of body mass, which differs from the others, as it is
based on femoral morphometrics, suggests that the Argentinean
taxa Condorraptor and Piatnitzkysaurus could have reached ~360 and
750 kg in mass, respectively; exemplifying the origin of medium-sized
tetanurans during the Jurassic and thus suggesting an increase in
theropod macropredatory habits (Benson et al., 2014).
2 | MUSCLE RECONSTRUCTION IN
EXTINCT VERTEBRATES
Reconstruction of muscles and estimation of their architecture and
functions is an important approach in palaeobiology (e.g., Bates &
Falkingham, 2018; Bishop et al., 2021; Cuff, Demuth et al., 2023;
Witmer, 1995). Even with intrinsic limitations to these reconstruc-
tions for fossil organisms, biomechanical models and simulations;
and other useful methods; have been developed with the aid of com-
putational techniques (e.g., Hutchinson, 2012). Advances in mor-
phofunctional and ecomorphological studies in extinct vertebrates,
together with advances in evolutionary biomechanics applied to lo-
comotion, for example, are essential for understanding broader mac-
roevolutionary aspects such as paleoecology and potential selective
pressures (e.g., Jones et al., 2021).
Over a century of studies has focused on the variations in pel-
vic and hindlimb functional morphology in extinct and extant ar-
chosaur species and its implications for muscle architecture and
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LACERDA et al.
locomotor biomechanics. These studies have provided broad data-
sets, a solid background, and general inferences that have led to a
greater understanding of comparative myology and biomechanical
evolution of locomotion at different levels (e.g., Allen et al., 2021;
Bates, Benson, & Falkingham, 2012; Bates, Maidment, et al., 2012;
Bishop, Hocknull, Clemente, Hutchinson, Barret, et al., 2018; Bishop,
Hocknull, Clemente, Hutchinson, Farke, et al., 2018; Bishop, Cuff, &
Hutchinson, 2021; Carrano & Hutchinson, 2002; Cerroni et al., 2022;
Costa et al., 2014; Cuff, Demuth, et al., 2023; Cuff, Wiseman,
et al., 2023; Farlow et al., 1995, 2000; Gatesy, 1990; Gatesy &
Middleton, 1997; Gregory & Camp, 1918; Grillo & Azevedo, 2011;
Hutchinson, 2001a, 2004a, 2004b, 2012; Hutchinson et al., 2005;
Hutchinson & Allen, 2009; Hutchinson & Garcia, 2002; Langer, 2003;
Liparini & Schultz, 2013; Maidment & Barrett, 2011; Mallison, 2010;
Piechowski & Tałanda, 2020; Romer, 1923a, 1923b , 1923c , 1927;
Rowe, 1986; Russell, 1972; Schachner et al., 2011; Smith, 2021,
2023; Tarsitano, 198 3; Zinoviev, 2011).
However, how can these reconstructions be accurately performed
for extinct vertebrates? In general, soft tissues (e.g., muscles/tendons)
are not normally preserved in fossils. Yet there are rare exceptions
where favourable geochemical conditions occurred during fossil dia-
genesis, providing rare preservation. These exceptions include mus-
cle fibres or tendons, partial musculature and internal organs (e.g.,
Dal Sasso & Signore, 1998; Kellner, 1996; Surmik et al., 2023), as well
as integumentary structures (e.g., Barbi et al., 2 019; Bell et al., 2022)
in dinosaurs. With few exceptions, almost all vertebrate fossils con-
sist of some degree of biomineralization (e.g., bones, teeth, ossified
ligaments/tendons). Nonetheless, some bony structures (e.g., muscle
origins/insertions) leave discernible anatomical traces on fossils; thus,
this muscle–bone interface allows reconstruction of unpreserved lo-
comotor musculature based on a reliable osteological set of features
(e.g., Bishop et al., 2021; Carrano & Hutchinson, 2002; Dilkes, 2000;
Gatesy, 199 0; Grillo & Azevedo, 2011; Hutchinson, 2001a, 2001b;
Maidment & Barrett, 2011; Rhodes et al., 2021; Romer, 1923 b,
1923 c, 1927; Smith, 2021).
A methodology that has been widely used in recent decades is
the Extant Phylogenetic Bracket (EPB), formalized by Witmer (1995).
The EPB is based on the phylogenetic relationships of the extinct
clade under study, with at least two evolutionarily outgroups having
extant representatives. The EPB method represents a rigorously ex-
plicit method that aims to minimize speculations in muscle reconstruc-
tion, allowing tissue reconstruction to be performed and then judged
through inference levels (see Section 4 below). Additionally, the inclu-
sion of fossil taxa facilitates interpretations about muscular homology
and evolution, because extinct relatives of the study taxon may present
evidence for transitional character states or even novel states; either
of these being absent in extant taxa (Bishop et al., 2021; Dilkes, 2000;
Hutchinson, 2001a, 20 01b, 2002; Maidment & Barrett, 2011).
The EPB has been particularly popular for studying locomotor
form and function in archosaurs (e.g., Bates, Maidment, et al., 2012;
Bishop, Hocknull, Clemente, Hutchinson, Barret, et al., 2018; Bishop,
Hocknull, Clemente, Hutchinson, Farke, et al., 2018; Carrano &
Hutchinson, 2002; Grillo & Azevedo, 20 11; Hutchinson, 2001a,
2001b; Langer, 2003; Liparini & Schultz, 2013; Otero, 2018; Otero
et al., 2017; Rhodes et al., 2021; Smith, 2021). Because many extinct
organisms do not have analogous extant taxa (Bishop et al., 2021;
Costa et al., 2014), muscle reconstructions can provide different a
posteriori interpretations and revisions of previously raised hypoth-
eses (e.g., for Tyrannosaurus rex, pelvic muscle reconstructions by
Romer, 1923b vs. Carrano & Hutchinson, 2002; and running abilities
by Paul, 1988 vs. Hutchinson & Garcia, 2002).
3 | WHY STUDY MUSCULATURE IN
NON-AVIAN THEROPODS?
Hutchinson and Allen (2009) listed at least four questions considered
fundamental for the understanding of macroevolution and morpho-
functional adaptations that support and motivate researchers to
reconstruct the musculature and locomotor aspects in theropod
dinosaurs: (1) how did the bipedal stance and gait of birds evolve?
(2) what myological/locomotor traits are novel for birds? (3) how far
down the phylogenetic tree is it possible to trace ancestral traits in
theropods (or other archosaurs), and what are the plesiomorphic
traits? and (4) how did novelties such as bipedalism and flight arise
and/or were modified, or even how did the performance of terres-
trial/aerial locomotion change over evolutionary time?
To answer some of these questions, there are growing efforts in
the study of musculature, especially the locomotor apparatus in di-
nosaurs (e.g., Dilkes, 2000; Langer, 2003; Maidment & Barrett, 2011;
Mallison, 2010). Considering Theropoda, among the myological
reconstructions and modelling carried out so far, in addition to
pioneering work (e.g., Farlow et al., 2000; Gatesy, 1990; Gatesy
& Middleton, 1997; Romer, 1923a, 1923b, 1927; Russell, 1972;
Tarsitano, 1983), the results presented for one of the earliest thero-
pods, the herrerasaurid Staurikosaurus (Grillo & Azevedo, 2 011), are
worth highlighting, in addition to the reconstruction of the coelo-
physoid Coelophysis (Bishop et al., 2021). Regarding ceratosaurs,
Persons IV and Currie (20 11) did not fully reconstruct the locomotor
musculature, but explored the caudal musculature in the abelisau-
roid Carnotaurus. Cerroni et al. (2022) explored the pelvic and hind-
limb musculature of the abelisaurid Skorpiovenator. Concerning early
tetanuran theropods, the only efforts to date relate to the allosau-
roids Allosaurus and Acrocanthosaurus, not only on the basis of mus-
culature (e.g., Cau & Serventi, 2017), but also body mass estimation
and biomechanical analysis (Bates, Benson, & Falkingham, 2012).
Other muscle reconstructions generally have been carried out for
lineages that are more closely related to Aves, with great effort spent
on Coelurosauria; for example, the tyrannosauroid Tyrannosaurus
(Carrano & Hutchinson, 2002), Ornithomimidae (Russell, 1972),
Megaraptoridae (White et al., 2016), unenlagiids (Motta et al., 2018),
alvarezsaurids (Meso et al., 2021), and maniraptoran species
(Hutchinson et al., 2008; Rhodes et al., 2021; Smith, 2021, 2023).
In addition to the studies cited above, there is an ongoing ef-
fort to understand the main evolutionary features related to bi-
pedalism in theropod dinosaurs (e.g., Allen et al., 2021; Bishop,
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L ACERDA e t al.
Hocknull, Clemente, Hutchinson, Barret, et al., 2018; Bishop,
Hocknull, Clemente, Hutchinson, Farke, et al., 2018; Cuff, Demuth,
et al., 2023). However, the earliest tetanuran clades studied gener-
ally include only allosauroids; whereas there have not been detailed
studies of Megalosauroidea, the earliest-diverging branch of tetanu-
ran evolution. Recently, Lacerda et al. (2023) mapped the evolution
and reconstructed the ancestral states of the morphological charac-
ters of the pelvic appendage in Megalosauroidea, characterizing po-
tential variations related to muscle attachments; and tested whether
different homoplastic signals in different regions of the locomotor
system are present in theropods. That study provides a stronger
basis for the muscle reconstruction performed here (see below).
Although piatnitzkysaurids are important representatives for un-
derstanding theropod evolution (Carrano et al., 2012; Rauhut, 2003),
as we ll as te tanur an diversity and the acquisit ion of larger bod y size in
terms of locomotor function and body support, little is known about
these paleobiological issues (Lacerda et al., 2023). Our aim here is to
begin addressing these deficiencies by reconstructing the hindlimb
muscles (origins and insertions) of the three piatnitzkysaurid species
(Condorraptor, Marshosaurus, and Piatnitzkysaurus), and to compare
our findings with the myological reconstructions of other extinct and
extant archosaurs. We chose these taxa not only for: (1) future usage
in biomechanical models, and (2) comparisons with existing myologi-
cal reconst ructions of other theropods and resulting evolutionar y im-
plications, but also (3) addressing how similar their musculature might
have been, (4) determining if any show unusual apomorphies, and (5)
assessing how differential taphonomic preservation affects these in-
ferences. We considered a total of 32 muscles, focusing on the major
muscles (not the many, small, complex pedal muscles).
Institutional abbreviations. MACN, Museo Argentino de Ciencias
Naturales “Bernardino Rivadavia,” Buenos Aires, Argentina. MPEF,
Museo Paleontológico Egidio Feruglio, Trelew, Argentina. PVL,
Fundación “Miguel Lillo,” San Miguel de Tucumán, Argentina. UMNH,
Natural History Museum of Utah, Utah, United States.
4 | MATERIALS AND METHODS
4.1 | Species and specimens
For Piatnitzkysaurus, we pe rsonall y examine d the holot ype PV L 4073 ,
housed at Fundación Miguel Lillo (Universidad Nacional de Tucumán,
Argentina), and the partial skeleton (hypodigm MACN-Pv-CH 895),
housed at Museo Argentino de Ciencias Naturales “Bernardino
Rivadavia” (Argentina). For Condorraptor, we directly inspected
the holotype MPEF-PV 1672, as well as the hypodigm specimens
(MPEF-PV 1676–1683, MPEF-PV 1686–1688, MPEF-PV 1690–1693,
MPEF-PV 1696–1697, MPEF-PV 1700–1702, MPEF-PV 1704–1705),
deposited in the Museo Paleontológico Egidio Feruglio (Argentina).
For Marshosaurus, although one of us (JRH) personally examined
known specimens (UMNH VP 6372 [=UUVP 1845], UMNH VP 6374
[=UUVP 2742], UMNH VP 6380 [=UUVP 2878], UMNH VP 6384
[=UUVP 40–295], UMNH VP 6387 [=UUVP 4736]) deposited in
the Natural History Museum of Utah (United States), the myologi-
cal inferences presented here are based upon photographs and notes
from those examinations, and the original description provided by
Madsen (1976). More detailed information is focused only on the
South American taxa, for which we have the best image quality and
which have been studied recently by one of us (MBSL).
4.2 | Myological reconstruction, homology and
character mapping
We used the EPB method (Witmer, 1995) for our reconstructions
(Figure 1a). Three levels of inference are established by EPB to
characterize the confidence in reconstructing a particular soft tis-
sue for an extinct species: (I) represents an unequivocal structure
of a particular feature, that is, when the two (or more) extant taxa
have the homologous soft tissue and its osteological correlate; (II)
FIGURE 1 (a) Simplified example of the Extant Phylogenetic Bracket (EPB) application in Theropoda. (b), Theropod phylogeny (up to
Coelurosauria on the right side of the phylogeny) highlighting the phylogenetic position of Piatnitzkysauridae. (a), adapted from Grillo
& Azevedo, 2 011; (b), adapted from Carrano et al., 2012. M, muscle; O, osteological correlate. Silhouettes are from phylo pic. org; see
Acknowledgements.
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LACERDA et al.
represents an equivocal reconstruction, when the ancestral condi-
tion for two or more taxa is ambiguous, such as the presence of
a particular soft tissue and the osteological correlate only in one
of the extant taxa; (III) represents an unequivocal absence of a
particular feature, that is, when the ancestral condition favoured
by the EPB involves not having the soft tissue and its osteologi-
cal evidence (i.e., inferring an absent feature; with no or contrary
evidence). In addition, if soft tissue inferences lack conclusive
data from their osteological correlates, they are qualified as level
I′, II', and III' inferences (Witmer, 19 95). Using the EPB, our com-
parisons mainly were based on Crocodylia and Aves, but not re-
stricted to these groups; Lepidosauria and Testudines were also
considered (Bishop et al., 2021; Hutchinson, 2002). The pelvic and
thigh musculature of extant taxa was evaluated from the follow-
ing literature on Crocodylia (e.g., Hattori & Tsuihiji, 2021; Otero
et al., 2010; Romer, 1923a; Suzuki et al., 2011; Wilhite, 2023),
Avialae (e.g., Clifton et al., 2018; Hattori & Tsuihiji, 2021;
Hudson et al., 1959; Meso et al., 2021; Patak & Baldwin, 1998;
Picasso, 2010; Romer, 1923c ; Rowe, 1986; Suzuki et al., 2014), an d
other Tetrapoda/Reptilia (e.g., Dick & Clemente, 2016; Gregory &
Camp, 1918 ; Hattori & Tsuihiji, 2021; Romer, 1942). Dissection of
one Crocodylus niloticus and one Numida meleagris specimen dur-
ing this study further enhanced our musculoskeletal comparisons
and delineations of the locomotory muscle positioning.
The phylogenetic framework adopted here was provided
by Carrano et al. (2012), where Piatnitzkysauridae is an early
Megalosauroidea clade composed of Marshosaurus as the earliest
piatnitzkysaurid taxon to diverge, being sister taxon of a subclade
composed of Piatnitzkysaurus a nd Condorraptor (Figure 1b). However,
see Rauhut and Pol (2019) and Schade et al. (2023) for an alternative
hypothesis; as discussed above (see also Lacerda et al., 2023).
The nomenclature and homology of the musculoskeletal sys-
tem here follow the propositions of Hutchinson and Gatesy (2000),
Hutchinson (2001a, 20 01b, 2002), Carrano and Hutchinson (2002),
and Hattori & Tsuihiji, 2021 (adaptations summarized in Table 1),
which bu ilt on earlier work by Rom er (1923a, 1942) and Rowe (1986).
The nomenclature of Baumel and Witmer (199 3) is followed in the
descriptions of osteological correlates and muscle scars.
Piatnitzkysaurus was scored for character states of 86 characters
related to the pelvic musculature (character ranges 1–71, 78–88, and
97–100; see Appendix A), to replace the “basal Tetanurae” lineage
(which previously was a rough composite of transitional character
states from this and other lineages) from Hutchinson (2001a, 20 01b,
2002) and Bishop et al. (2021) in a new taxon-character matrix. As
usual for the EPB, we used the maximum parsimony criterion for our
reconstructions, similar to previous studies (e.g., Bishop et al., 2021;
Molnar et al., 2018; Witmer, 19 95). By doing so, we refine character
scoring for early Tetanurae in general, which will be useful for future
studies. We only scored Piatnitzkysaurus, as it has more osteologi-
cal correlates preserved than the other taxa do, and consequently,
a greater number of muscles could be inferred for this species (see
Section 5). However, we sought to test if any muscles reconstructed
differed in any details across the three taxa. To score and trace
evolutionary changes in locomotor muscles, as well as to assess the
most parsimonious states in our reconstructions, we used Mesquite
software version 3.6 (Maddison & Maddison, 2015), using an informal
composite “consensus” tree of Reptilia based on the recent phyloge-
netic framework used by Bishop et al. (2021) and references therein.
5 | RESULTS AND DISCUSSION
5.1 | Myological reconstruction
5.1.1 | Triceps femoris
Mm. iliotibiales (IT1, IT2, and IT3): In Aves and Crocodylia, the Mm.
iliotibiales is a large and superficial sheet that generally is composed
of three heads over the dorsal and anteroposterior rim of the ilium,
superficially positioned in relation to the other pelvic and thigh mus-
cles (Clifton et al., 2018; Hudson et al., 1959; Hutchinson, 20 01b,
2002; Otero et al., 2010; Patak & Baldwin, 1998; Picasso, 2010;
Romer, 1923a). In other Reptilia, the homologous muscle pre-
sents one or two weakly separated heads (Dick & Clemente, 2016;
Hutchinson, 2002; Romer, 1942). The IT1–3 muscles attach to the
dorsal rim of the ilium and are dorsally delimited by the crista dorso-
lateralis ilii, marking the border between the dorsal and lateral sur-
faces of the supraacetabular iliac blade (Baumel & Witmer, 1993).
In the Piatnitzkysaurus ilium MACN-Pv-CH 895, the anterior-
most margin of the preacetabular process is not preserved, so
the anterior limits/extension of the IT1 are not possible to infer;
however, a great part of the supraacetabular rim is preserved. On
the anteriormost part of the preacetabular blade, an expanded
area is evident. This area is posteriorly delimited by an invagina-
tion present over the dorsalmost part of the supraacetabular rim
(Figure 2a,b). Furthermore, immediately ventral to the dorsal rim
of the ilium, there is a rough osteological delimitation, which pos-
teriorly becomes more dorsally positioned (Figure 3a). Because
these osteological correlates are topologically compatible with the
positions (and similar osteological correlates) noted in extant ar-
chosaurs (e.g., Carrano & Hutchinson, 2002; Hudson et al., 1959;
Otero et al., 2010; Picasso, 2010 ; Romer, 1923a), the rough delim-
itation and the dorsal invagination seem to be the posterior edge
of the IT1 (level I), as well as the anterior demarcation of the IT2
(Figures 2a and 3a). Concerning th e IT2, we infer the anterior limit s
to be at the same position as the main axis of the pubic pedun-
cle, on a dorsal invagination of the dorsal rim of the preacetab-
ular blade (level I) (Figure 2a), as aforementioned. Although not
clearly preserved, the posterior limits of this muscle head seem
to be demarcated by a small protuberance on the dorsal postace-
tabular blade (Figure 2a), which is posterior to the posterior facet
of the ischial peduncle. This protuberance also probably delimited
the anterior origin of the IT3; the attachment area of the IT3 is on
the posterior dorsal rim of the postacetabular blade of the ilium.
A rough scar which becomes posteriorly large is on the ilium of
MACN-Pv-CH 895, seeming to be dorsally delimited by the crista
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6
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L ACERDA e t al.
dorsolateralis ilii. This area of the IT3 is delimited by a faint oste-
ological protuberance (level I). Most of the origination region of
the IT1–3 muscles is not preserved in Condorraptor—the supraac-
etabular crest is highly damaged anterior and dorsal to the ace-
tabulum in the only preserved ilium MPEF-PV 1687 of this taxon
(Figure 2c,d). Al tho ugh frag mentar y, this regi on ha s an os teol ogical
correlate indicating that the anterior boundaries of the IT2 origin
were from an invagination preserved at the same axis of the pubic
peduncle (level I). However, as a consequence of this poor preser-
vation of the Condorraptor ilium, our reconstructions of the origins
of IT1 and IT3, as well as the extent of IT2, are uncertain, although
these origins should have been similar to those reconstructed for
Piatnitzkysaurus. In the studied ilia of Marshosaurus (UMNH VP
6372 and UMNH VP 6374) and the holotype UMNH VP 6373
[=UUVP 2826] specimen (Madsen, 1976), the best-preserved part
is the postacetabular process of the ilium. Although the subdivi-
sions of the IT heads are not as discernible as in Piatnitzkysaurus,
the origin of the IT3 in both UMNH VP 6372 and UMNH VP 6373
is clear ly discer nible by seve ral scars on the dorsa l edge of the pos-
tacetabular blade and the presence of the crista dorsolateralis ilii
(level I) (Figures 2e,f and 3b).
In Crocodylia, Aves and other Reptilia, those three heads of Mm.
iliotibiales converge with M. ambiens and Mm. femorotibiales into at
leas t one exte nso r tendon and fascial sheet, which ins erts on the tib-
ial cnemial crest or crista cnemialis cranialis (Baumel & Witmer, 1993)
of the proximal metaphysis of the tibia (Dick & Clemente, 2016;
TAB LE 1 Muscular homologies in extant archosaurs, considering
the musculature of the pelvic girdle and hindlimb (modified from
Carrano & Hutchinson, 2002). The EPB uses the state in each
most recent common ancestor of Crocodylia and of Aves as its
bracket, informed by further data from outgroups Lepidosauria and
Testudines (not shown here; see Hutchinson, 2002).
Muscles (Crocodylia) Muscles (Aves)
Dorsal group
Triceps femoris
M. iliotibialis 1 (IT1) M. iliotibialis cranialis (IC)
Mm. iliotibialis 2, 3 (IT2, IT3) M. iliotibialis lateralis (2 main
parts) (IL)
M. ambiens (AMB) M. ambiens (AMB)
M. femorotibialis externus
(FMTE)
M. femorotibialis lateralis
(FMTL)
M. femorotibialis internus (FMTI) M. femorotibialis intermedius
(FMTIM) & M.
femorotibialis medialis
(FMTM)
M. iliofibularis (ILFB) M. iliofibularis (ILFB)
Deep dorsal
M. iliofemoralis (IF) M. iliofemoralis externus (IFE)
& M. iliotrochantericus
caudalis (ITC)
M. puboischiofemoralis 1 (PIFI1) M. iliofemoralis internus (IFI)
M. puboischiofemoralis internus
2 (PIFI2)
M. iliotrochantericus
cranialis (ITCR) & M.
iliotrochantericus medius
(ITM)
Ventral group
Flexor cruris
M. puboischiotibialis (PIT) [absent]
M. flexor tibialis internus 1 (FTI1) [absent]
M. flexor tibialis internus 2 (FTI2) [absent]
M. flexor tibialis internus 3 (FTI3) M. flexor cruris medialis
(FCM)
M. flexor tibialis internus 4 (FTI4) [absent]
M. flexor tibialis externus (FTE) M. flexor cruris lateralis
pars pelvica (FCLP and
accessoria FCLA)
Mm. adductores femores
M. adductor femoris 1 (ADD1) M. puboischiofemoralis pars
medialis (PIFM)
M. adductor femoris 2 (ADD2) M. puboischiofemoralis pars
lateralis (PIFL)
Mm. puboischiofemorales externi
M. puboischiofemoralis ex ternus
1 (PIFE1)
M. obturatorius lateralis (OL)
M. puboischiofemoralis ex ternus
2 (PIFE2)
M. obturatorius medialis
(OM)
M. puboischiofemoralis ex ternus
3 (PIFE3)
[absent]
M. ischiotrochantericus (ISTR) M. ischiofemoralis (ISF)
Muscles (Crocodylia) Muscles (Aves)
Mm. caudofemorales
M. caudofemoralis brevis (CFB) M. caudofemoralis pars
pelvica (CFP)
M. caudofemoralis longus (CFL) M. caudofemoralis pars
caudalis (CFC)
Digital extensor group
M. extensor digitorum longus (EDL) M. extensor digitorum longus
(EDL)
M. extensor digitorum brevis (EDB) [absent]
M. extensor hallucis longus (EHL) M. extensor hallucis longus
(EHL)
M. tibialis anterior (TA ) M. tibialis cranialis (TC)
Mm. gastrocnemii
M. gastrocnemius externus (GE) M. gastrocnemius pars
lateralis (GL) et
intermedia (GIM)
M. gastrocnemius internus (GI) M. gastrocnemius pars
medialis (GM)
Lower leg muscles
M. fibularis longus (FL) M. fibularis longus (FL)
M. fibularis brevis (FB) M. fibularis brevis (FB)
TAB LE 1 (Continued)
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LACERDA et al.
Gregory & Camp, 1918; Hutchinson, 2002; Otero et al., 2010; Patak
& Baldwin, 1998 ; Romer, 1923a , 1923b, 1942).
The tibiae of both Piatnitzk ysaurus specimens, MACN-Pv-CH
895 and PVL 4073 (Figure 4a,b), have an expanded and rough area
on the tibial cnemial crest with an anterior protuberance, in lat-
eral view, that is distal to the cnemial crest. On this basis, we infer
the same condition that is observed in extant archosaurs, with the
cnemial crest as the osteological correlate for the insertion of IT1–3
(and the remainder of the triceps femoris: AMB and FMTE, FMTI)
(level I) (Figure 4a,b). In the Condorraptor holotype MPEF-PV 1672,
the cnemial crest is rounded and presents a small ridge (Figure 4c,d)
when compared with Piatnitzkysaurus, and similar to other archo-
saurs, this was probably the same attachment area for the main ten-
don(s) of IT1–3 and other triceps femoris mus cles (l eve l I) (Figure 4c,d).
No tibia associated with Marshosaurus has been formally described
so far, to our knowledge.
M. ambiens (AMB): The AMB in extant Reptilia typically takes
its origin from the pubic tubercle or tuberculum preacetabulare
(Hutchinson, 2001b, 2002; Picasso, 2010; Romer, 1923a, 1923b,
1942), also termed the pectineal process (Hudson et al., 1959; Suzuki
et al., 2014), preacetabular tubercle (Hutchinson, 2002), or ambiens
process (Langer, 2003). In general, this muscle is wider at its origin,
becoming more tapered distally. As noted by Hutchinson (2001b),
the pubic tubercle is small or even absent in Crocodylia which
have a derived feature, relative to other Reptilia, related to hav-
ing mobile pubes and two heads of AMB (Gregory & Camp, 1918;
Hutchinson, 20 01b; Romer, 1923 a, 1923b; Suzuki et al., 2011). In
most Aves, as is ancestral for other non-archosaurian Reptilia, the
AMB has a single head (Hutchinson, 2001b; Picasso, 2010).
The pubes of both Piatnitzkysaurus individuals (left and right
in MACN-Pv-CH 895 and left in PVL 4073) have a pubic tubercle
that is well-developed (Figure 5a–d), as in Aves and other thero-
pods (Carrano & Hutchinson, 2002; Gregory & Camp, 1918 ;
Grillo & Azevedo, 2011; Hudson et al., 1959; Hutchinson, 2001b;
Romer, 1923 b). However, this tubercle slightly differs from other
piatnitzkysaurid species in position—being more laterally and dis-
tally positioned instead of anterior as in Condorraptor, and more dis-
tally positioned than the condition in Marshosaurus (Madsen, 1976)
(Figure 5). Nonetheless, the pubic tubercle is an osteological cor-
relate of the presence and origin of the single head of the AMB in
Piatnitzkysaurus (level I), as previously noted by Bonaparte (1986).
The pubic tubercle in Condorraptor is remarkably large (Figure 5e–
h); this strongly pronounced tubercle generally is not seen in other
tetanuran theropods (Rauhut, 2005). It thus is plausible, based on
the osteological correlate of the right pubis MPEF-PV 1696 and a
small fragment of the left pubis MPEF-PV 1688, that the AMB had a
robust attachment to the pelvic girdle of Condorraptor (level I). The
best-preserved pubis of Marshosaurus (right pubis UMNH VP 6387)
also osteologically concurs with the single head of the AMB; as pre-
viously noted, the anterolateral part of the proximal portion of the
pubis presents a visibly rough area (Madsen, 1976) topographically
equivalent to the AMB origin (level I) (Figure 5i,j).
FIGURE 2 Osteological correlates observed in the ilia of Piatnitzkysauridae (left ilia, lateral view). (a, b) Piatnitzkysaurus (MACN-Pv-CH
895). (c, d) Condorraptor (MPEF-PV 1687). (e, f) Marshosaurus (UMNH VP 6372). The M. flexor tibialis externus is not marked in the line drawings.
Anatomical/muscular abbreviations: bf, brevis fossa; cf, “cuppedicus” fossa; CFBf, M. caudofemoralis brevis origin fossa; IFEf, M. iliofemoralis
externus origin fossa; ILFBf, M. iliofibularis origin fossa; ip, ischiadic peduncle; IT1–3, Mm. iliotibiales 1–3 origin scars; PIFI1, M. puboischiofemoralis
internus 1 origin fossa; poap, postacetabular process; pp, pubic peduncle; prap, preacetabular process; sac, supraacetabular crest; vr, vertical
ridge. Arrows indicate potential subdivision of IT heads. Dark grey represents broken areas of bones. Scale bar = 100 mm.
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8
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L ACERDA e t al.
The AMB insertion converges onto the tibial cnemial crest with
the rest of the triceps femoris muscle group (Hutchinson, 2001b,
2002; Romer, 1923 a, 1923 b; Suzuki et al., 2014). Furthermore,
as noted by Romer (1923a, 1923b), McKitrick (1991), and
Hutchinson (2002), the AMB muscle has a secondary tendon which
perforates the extensor tendon and merges with the origin of M.
gastrocnemius externuslateralis near the proximal fibula. Although
this shared tendon might have been present in early tetanurans such
as piatnitzkysaurids, as is ancestral for Archosauria, there is no evi-
dence of it (Level I′).
Thus, as previously described, the insertion of the AMB in
Piatnitzkysaurus and Condorraptor occurred via a shared tendon at-
tached to the cnemial crest (level I) (Figure 4). As there is no formally
described tibia for Marshosaurus, the insertion of this muscle is not
reconstructed here.
Mm. femorotibiales (FMTE and FMTI): The Mm. femorotibiales of
Crocodylia has two heads (i.e. M. femorotibialis externus—FMTE and M.
femorotibialis internus—FMTI), whereas in Aves, the re are three heads
(i.e. M. femorotibialis medialis—FMTM, M. femorotibialis intermedius—
FMTIM, and M. femorotibialis lateralis—FMTL) (Clifton et al., 2018;
Hudson et al., 1959; Hutchinson, 2001a, 20 02; Mckitrick, 1991;
Otero et al., 2010; Picasso, 2010; Romer, 1923a; Suzuki et al., 2011;
Zinov iev, 2011); here we use the names from Crocodylia as per
other studies of non-avian theropods (e.g., Bishop et al., 2021;
Carrano & Hutchinson, 2002; Grillo & Azevedo, 2011). The origins
of FMTE and FMTI are located between the trochanteric (proxi-
mal) and the condylar (distal) regions across a great portion of the
femoral shaft by a fleshy attachment (Carrano & Hutchinson, 2002;
Grillo & Azevedo, 2011 ; Hutchinson, 2001a, 2002; Mckitrick, 19 91;
Picasso, 2010; Romer, 1923a, 1923b; also see Cuff, Wiseman,
et al., 2023). On the femoral shaft, the FMTE and FMTI origins are
delimited by three ridges, namely: linea intermuscularis cranialis (lia),
linea intermuscularis caudalis (lip) and linea aspera (=adductor ridge, la)
(Baumel & Witmer, 1993; Hutchinson, 2001a). However, these struc-
tures are variable throughout ontogeny in both extant and extinct
archosaurs (Griffin, 2018). The FMTE origin has boun daries delimited
by the lia and lip (on the lateral femoral shaft), whereas the FMTI or-
igin is delimited by the lia and la (on the anteromedial femoral shaft)
(Griffin, 2018; Hutchinson, 2001a, 2002), also there seems to have
been the participation of the craniomedial distal crest (cdc) in those
subdivisions in some extinct archosaurs (Hutchinson, 2001a).
The three femora of the two Piatnitzk ysaurus skeletons lack
well-preserved shaft surfaces. Regardless, the left femur of PVL
4073 preserves the most distal parts of both la and lip on the pos-
terior shaft of the femur, and lia on the distal femur, arising medially
and becoming anteriorly positioned along the proximal shaft of the
femur (Figure 6c,d). Furthermore, the right femur of PVL 4073 pre-
serves the distal base of the la (Figure 6g,h). Although not entirely
preserved, the presence of the la, lia and lip allows inference of the
FMTE and FMTI origins without precise boundaries (Figure 6). The
FMTE and FMTI in Piatnitzkysaurus, as well as in other theropods
(e.g., Staurikosaurus—Grillo & Azevedo, 2011; Coelophysis—Bishop
et al., 2021; allosauroids—Bates, Benson, & Falkingham, 2012;
Tyrannosaurus—Carrano & Hutchinson, 2002; Nothronychus—
Smith, 2021; and Skorpiovenator—Cerroni et al., 2022) seem to have
had the same origins from the lateral and the anteromedial surfaces
of the femoral shaft, respectively (level I). In Condorraptor, both fem-
ora are quite fragmentary, lacking the proximal portions. The right
femur MPEF-PV 1690 is better preserved, with a great portion of
the femoral shaft (Figure 7); however, the three longitudinal ridges/
lineae (lia, lip and la) are not completely preserved. It remains pos-
sible to reconstruct the FMTE and FMTI origins in positions similar
to our Piatnitzkysaurus reconstruction (level I), but their proximal
extent remains indeterminate. Rauhut (2005) noted the presence
of the cdc in both Condorraptor femora (Figure 7e–h); this being a
structure related to the distal divisions between the FMTE and FMTI
origins (Hutchinson, 2001a). Marshosaurus has no preserved femur,
preventing any inferences about these muscles.
FIGURE 3 Osteological correlates of M. iliotibiales 1–3
observed on the ilia of Piatnitzkysauridae (left ilia, lateral view). (a),
Piatnitzkysaurus (MACN-Pv-CH 895). (b), Marshosaurus (UMNH VP
6372). Anatomical/muscular abbreviations: cdi, crista dorsolateralis
ilii; IT1–3s, Mm. iliotibiales scars; IT1–2l, M. iliotibialis 1 and 2 limits.
Arrows indicate muscle scars. Scale bar = 20 mm.
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LACERDA et al.
The FMTE and FMTI heads converge into a main tendon and fas-
cia inserting onto the tibial cnemial crest deep to IT1–3 and AMB
(level I) (Figure 4), as noted above.
M. iliofibularis (ILFB): In extant Reptilia, the ILFB originates from
the lateral surface of the ilium in the postacetabular blade, posi-
tioned posterior to the IFE (IF in Crocodylia), anterior to the FTE
(FCLA and FCLP in Aves), and ventral to the IT. ILFB is a large, fu-
siform and superficial muscle of the thigh (Clifton et al., 2018; Dick
& Clemente, 2016; Gregory & Camp, 1918; Hutchinson, 2001a,
2001b, 20 02; Mckitrick, 1991; Picasso, 2010; Romer, 1923a , 1923b,
1942; Suzuki et al., 2011), more expanded in the ilium of dinosaurs
(Hutchinson, 2002).
As previously noted by Bonaparte (1986), the lateral surface of
the iliac blade in Piatnitzkysaurus has a large and deep depression.
This lateral depression is subdivided by a swollen vertical ridge, po-
sitioned just above the acetabulum (Carrano et al., 2012; Lacerda
et al., 2023). This ridge has been suggested as the anterior limit of the
ILFB (Carrano & Hutchinson, 2002; Hutchinson, 2001b). Anterior to
the vertical ridge and anterodorsal to the acetabulum, the lateral
depression is large and deep; whereas the posterior depression is
shallow and positioned just above the ischial peduncle (Figure 2a,b).
Topographically, this posterior concavity is equivalent to the ILFB
origin, as in other extinct theropods and extant archosaurs (Carrano
& Hutchinson, 2002; Grillo & Azevedo, 2011; Hutchinson, 2001a;
Otero et al., 2010 ; Picasso, 2010). The ventral limit of the ILFB origin
is indicated by the brevis shelf, and its anterior limits seem to be
related to the vertical iliac ridge (Hutchinson, 2001a), whereas the
posterodorsal limits appear to have been demarcated by a semi-cir-
cular scar just below the IT3 origin (level I). In Condorraptor, although
the supraacetabular crest is fragmentary, the left ilium MPEF-PV
1687 bears a small and shallow concavity dorsal to the ischiadic
peduncle and posterior to the supraacetabular vertical ridge, on
the postacetabular blade (Figure 2c,d), which may be the osteolog-
ical correlate for the anterior limits of the ILFB origin. As noted by
Carrano and Hutchinson (2002), the scars made by ILFB are difficult
to discern; however, a well-developed iliac ridge lies just above the
acetabulum in most megalosauroids (Carrano et al., 2012; Lacerda
et al., 2023) and abelisaurids (Cerroni et al., 2022), indicating the
anterior edge of the ILFB origin and the posterior edge of the M.
iliofemoralis externus. Ventrally, the concavity related to the ILFB or-
igin is delimited by the brevis shelf. Although the anterior, posterior
and ventral limits of the ILFB origin are discernible (level I), the dorsal
limit of this muscle origin is unclear, because the supraacetabular rim
is not preserved in the only known ilium of Condorraptor. The ilia of
Marshosaurus seem to lack the supraacetabular vertical ridge, or at
least taphonomic issues preclude scoring this character in this taxon
(Carrano et al., 2012; Lacerda et al., 2023); however, the dorsal, ven-
tral and posterior boundaries of the ILFB origin can be inferred in
this species based on the presence of a concavity and its posterior,
dorsal and ventral delimitations (level I) (Figure 2e,f).
The insertion of the ILFB in Reptilia is located on the fibular
tubercle; a scarred or rounded and prominent structure on the
FIGURE 4 Osteological correlates of the triceps femoris insertion and origins of lower leg muscles from the tibiae of Piatnitzkysauridae
(left tibiae, lateral view). (a, b) Piatnitzkysaurus (PVL 4073). (c, d) Condorraptor (MPEF-PV 1672). Anatomical/muscular abbreviations:
cc, cnemial crest; EDLs, M. extensor digitorum longus scar; fc, fibular crest; it1–3 + amb + fmt, insertion of the tendon from the
iliotibiales + ambiens + femorotibiales muscles; lc, lateral condyle; mc, medial condyle; pas, proximal articular surface; si, sulcus intercnemialis;
TAd , M. tibialis anterior depression. Scale bar = 50 mm.
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10
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L ACERDA e t al.
proximal region of the fibular shaft; typically most prominent in
archosaurs. Furthermore, a secondary tendon is present in extant
taxa (in Aves, constrained by a loop termed ansa m. iliofibularis—
Baumel & Witmer, 1993; also see Hutchinson, 2001a), which in-
serts onto M. gastrocnemius externus/lateralis near its origin (Dick &
Clemente, 2016; Carrano & Hutchinson, 2002; Clifton et al., 2018;
Hutchinson, 20 01a, 2002; Otero et al., 2010; Picasso, 2010;
Romer, 1923a).
The right fibula of Piatnitzkysaurus PVL 4073 preserves the
fibular tubercle (Lacerda et al., 2023), which also presents a small
scar (Figure 8), as sometimes seen in other archosaurs. As in other
theropods (e.g., Tyrannosaurus—Carrano & Hutchinson, 2002),
there is no osteological evidence for a secondary tendon in early
tetanurans based on Piatnitzkysaurus, although this structure is pre-
dicted to have been present (level I′). The fibula is not preserved in
Condorraptor and Marshosaurus.
5.1.2 | Deep dorsal group
M. iliofemoralis or M. iliofemoralis externus (IFE) and M. iliotrochanteri-
cus caudalis (ITC): The M. iliofemoralis in Crocodylia is a single muscle,
FIGURE 5 Osteological correlates observed on the pubes of Piatnitzkysauridae (right pubes, lateral and anterior views). (a–d)
Piatnitzkysaurus (MACN-Pv-CH 895). (e–h) Condorraptor (MPEF-PV 1696). (i, j) Marshosaurus (UMNH VP 6387). Anatomical/muscular
abbreviations: ac, acetabulum; AMBt, M. ambiens tubercle; ap, apron; ilc, iliac peduncle; ip, ischial peduncle; of, obturator foramen; pb, pubic
boot; PIFE1s, M. puboischiofemoralis externus 1 scar; PIFE2s, M. puboischiofemoralis externus 2 scar; pt, pubic tubercle. (a, b, e, f, i, j) in lateral
view; (c, d, g, h) in anterior view. Scale bar = 50 mm.
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LACERDA et al.
FIGURE 6 Osteological correlates observed on the femur of Piatnitzkysaurus (right femur, PVL 4073). (a, b) lateral view; (c, d) anterior
view; (e, f) medial view; (g, h) posterior view. Anatomical/muscular abbreviations: add1 + 2 s, Mm. adductores femores insertion scar; at,
acessory trochanter; cdc, craniomedial distal crest; cfbs, M. caudofemoralis brevis insertion scar; cfls, M. caudofemoralis longus insertion scar;
eg, extensor groove; fh, femoral head; fg, flexor groove; fmtes, M. femorotibialis externus scar; fmtis, M. femorotibialis internus scar; fn, femoral
neck; ft, fourth trochanter; GLd, M. gastrocnemius pars lateralis depression; gt, greater trochanter; ifes, M. iliofemoralis externus insertion
scar; istrs, M. ischiotrochantericus insertion scar; itcs, M. iliotrochantericus caudalis insertion scar; la, linea aspera; lc, lateral condyle; lia, linea
intermuscularis cranialis; lip, linea intermuscularis caudalis; lt, lesser trochanter; mc, medial condyle; pifes, Mm. puboischiofemorales externi
insertion scar; pifi1s, M. puboischiofemoralis internus 1 insertion scar; pifi2s, M. puboischiofemoralis internus 2 insertion scar; TA?, M. tibialis
anterior?, origin?; tfc, tibiofibular crest; ts, trochanteric shelf. Scale bar = 100 mm.
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L ACERDA e t al.
not divided, with an origin located just above the acetabular aper-
ture and deep to IT2, on the lateral surface of the ilium (Gregory &
Camp, 1918; Hutchinson, 2002; Otero et al., 2010; Romer, 1923a,
1923b). In Aves, the “M. iliofemoralis” is split into two muscles (i.e.
M. iliofemoralis externus—IFE and M. iliotrochantericus caudalis—
ITC; Clifton et al., 2018; Hudson et al., 1959; Hutchinson, 2001a,
2002; Picasso, 2010 ; Rowe, 1986) which are located above the
acetabular aperture (IFE) and on the anteriormost surface of the
FIGURE 7 Osteological correlates observed on the femur of Condorraptor (left femur, MPEF-PV 1690). (a, b) lateral view; (c, d) anterior
view; (e, f) medial view; (g, h) posterior view. Anatomical/muscular abbreviations: add1 + 2 s, Mm. adductores femores insertion scar; cdc,
craniomedial distal crest; cfb + cfls, Mm. caudofemorales insertion scar; cfbs, M. caudofemoralis brevis insertion scar; eg, extensor groove;
fg, flexor groove; fmtes, M. femorotibialis externus scar; fmtis, M. femorotibialis internus scar; ft, fourth trochanter; GLd, M. gastrocnemius
pars lateralis depression; ifes?, M. iliofemoralis externus insertion scar?; itcs?, M. iliotrochantericus caudalis insertion scar?; la, linea aspera; lc,
lateral condyle; lia, linea intermuscularis cranialis; lip, linea intermuscularis caudalis; lt, lesser trochanter; TA?, M. tibialis anterior?, origin?; tfc,
tibiofibular crest; ts?, trochanteric shelf? Scale bar = 100 mm.
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LACERDA et al.
preacetabular blade (ITC) (Hutchinson, 2002; Rowe, 1986; Suzuki
et al., 2014). The subdivision of the M. iliofemoralis in extant Aves
might be evidenced by two insertion areas on the proximal femur
(Hutchinson, 2001a). Dinosauromorpha, in general, have a protuber-
ance (lesser/anterior trochanter) on the proximolateral femur (e.g.,
Müller & Garcia, 2023), homologous with the ITC insertion area in
Aves; Dinosauriformes also have a more posterodistal scarred ridge
or lump (trochanteric shelf; Novas, 1996) that might correspond to
the IFE insertion, suggesting that the M. iliofemoralis was subdivided
in ancestral Dinosauriformes (Carrano & Hutchinson, 20 02; Grillo &
Azevedo, 2011; Hutchinson, 2001a; Hutchinson & Gatesy, 2000). As
per below, Piatnitzkysaurus and Condorraptor show evidence of this
subdivision, too.
Nonetheless, the area of origin of M. iliofemoralis does not
present scars indicating these subdivisions between the IFE and
ITC (Carrano & Hutchinson, 2002; Hutchinson, 2001a). We con-
sider the semi-circular concavity of the Piatnitzkysaurus preace-
tabular ilium (MACN-Pv-CH 895; Bonaparte, 1986) anterior to the
iliac ridge as the origin of both of these muscular divisions (level
I) (Figure 2a,b). The dorsal limits of both muscle origins are quite
visible, indicated by striations located just ventral to the origins of
the IT1–3 (Figures 2 and 3). The anterior limits of the ITC are unde-
fined in this specimen due to the lack of the anteriormost and an-
teroventralmost preacetabular blade (Bonaparte, 1986). Following
avian myology (e.g., Hutchinson, 2002; Picasso, 2010; Rowe, 1986),
the ITC origin presumably would be anterior to the IFE head (level
II'). Even though the dorsal rim of the iliac blade is not preserved
in Condorraptor, a large, deep, almost circular concavity is antero-
dorsal to the acetabulum (Figure 2c,d); again suggesting the origins
of the IFE and ITC (level I). Otherwise, due to the fragmentary na-
ture of the specimen, it is not possible to delimit the boundaries of
these muscle origins in this taxon; only to suggest relative general
positions. Although the ITC and IFE origins in Marshosaurus must
have been in a similar pattern, it is not possible to reconstruct this
musculature because the anterior par t of the ilium is not preserved
and the figured ilium (Figure 2e,f) represents a plaster reconstruc-
tion of the preacetabular process.
As commented by Bonaparte (1986), the femur of
Piatnitzkysaurus has a well-developed lesser trochanter in the
shape of a proximodorsally positioned blade (Figures 6a–d a nd
9); as in other megalosauroids, it rises past the ventral margin of
the femoral head (Carrano et al., 2012; Lacerda et al., 2023). A
rough area on the trochanteric shelf is not discernible; however,
this structure is quite elevated and distinct (Figure 9), being pos-
terodistal to the lesser trochanter and anterodistal to the greater
trochanter of the femur. It is thus possible to infer the subdivi-
sion of M. iliofemoralis in this taxon; IFE should have inserted onto
the femoral trochanteric shelf (level II) and ITC onto the lesser/
anterior trochanter (level II) (Figures 6 and 9). The left femur of
Condorraptor MPEF-PV 1690 has the base of the lesser trochan-
ter anterolaterally located, also indicating a quite well-developed
lesser trochanter in Condorraptor (and perhaps a fragment of the
trochanteric shelf) and IFE and ITC muscle subdivisions (level II)
(Figure 7). The femur of Marshosaurus is not preserved.
M. pubo-ischio-femoralis internus 1 (PIFI1): The PIFI1 in Crocodylia
(or M. iliofemoralis internus—IFI or M. “cuppedicus” in Aves;
Rowe, 1986) is considered to be homologous to the muscles PIFI1
and PIFI2 in Reptilia (Romer, 1923 b; Rowe, 1986; Patak & Baldwin,
1999; Hutchinson, 2002; Suzuki et al., 20 11) and represents a short,
thick muscle. The PIFI1 origin in Crocodylia is located on the me-
dioventral surface of the ilium, as well as on the proximal ischium
(Hutchinson, 2001a, 2002; Otero et al., 2010; Romer, 1923a, 1923b).
The IFI origin in Aves is on the lateral surface of the ilium, between
the anterodorsal region of the pubic peduncle and the postero-
ventral extremity of the preacetabular blade (Hudson et al., 1959;
Hutchinson, 2002; Picasso, 2010; Romer, 192 3a; Rowe, 1986;
Suzuki et al., 2014). In many extinct theropods, there is evidence
of the muscle origin (in a state intermediate between the ancestral
reptilian and derived avian condition) from a preacetabular “cup-
pedicus” fossa (Hutchinson, 2002 [or preacetabular notch—Carrano
et al., 2012; Lacerda et al., 2023]) in that same region, suggesting a
shift of the muscle origin from the medial to lateral pelvis (Carrano &
Hutchinson, 20 02; Hutchinson, 2002; Romer, 1923a; Rowe, 1986).
This inference is complicated by the fact that homologs of the PIFI2
in Crocodylia also originate from a similar area in Aves, so there
is some ambiguity about which PIFI1 or PIFI2 muscle(s) may have
shifted into this fossa and when (Carrano & Hutchinson, 2002;
Hutchinson, 2001b, 20 02).
In Piatnitzkysaurus, even though the anterior margin of the
preacetabular iliac blade is not entirely preserved on the specimen
MACN-Pv-CH 895, the “cuppedicus” fossa is evident in the ventro-
medial surface of the iliac blade (Figure 2a,b), being dorsally delim-
ited by the preacetabular ridge, suggesting the PIFI1 origin (level
I). In Condorraptor and Marshosaurus (Madsen, 1976), despite the
fragmentary nature of the ilium of MPEF-PV 1687 (Figure 2c,d) and
UMNH VP 6372 (Figure 2e,f), respectively, the same “cuppedicus”
fossa is evident and inferred as the PIFI1 origin (level I).
FIGURE 8 Osteological correlate observed on the left fibula of
Piatnitzkysaurus (PVL 4073). (a, b) lateral view. Anatomical/muscular
abbreviations: ift, iliofibularis (fibular) tubercle; ilfbs, M. iliofibularis
insertion scar. Scale bar = 50 mm.
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L ACERDA e t al.
The PIFI1/IFI inser tion in extant archosaurs is located on the an-
teromedial surface of the femoral shaft. In Crocodylia, the insertion
is on a keel that separates the site of insertion of PIFI2 laterally; and
the origin of FMTI; medially, anteromedial to the fourth trochanter
(Hutchinson, 2001b, 2002; Otero et al., 2010; Romer, 1923a). In
Aves, IFI inserts onto a rounded mark on the proximomedial portion
of the femur (Hudson et al., 1959; Hutchinson, 2001b, 20 02; Suzuki
et al., 2014).
The femoral surface in Piatnitzkysaurus is not well-preserved,
however, a rounded and small tubercle is positioned distal to the an-
terior trochanter in both femora PVL 4073, which corresponds to
the PIFI1 insertion (level II) (Figure 6d,f). This bump is not discernible
on the Condorraptor femora MPEF-PV 1690–1691 (level I′).
M. pubo-ischio-femoralis internus 2 (PIFI2) or M. iliotrochan-
tericus cranialis (ITCR) and M. iliotrochantericus medius (ITM): The
PIFI2 muscle in Crocodylia is considered to be the homologous
to the PIFI3 in non-archosaurian Reptilia instead of the hom-
onymous muscle; however, it is uncertain whether, in the avian
lineage, PIFI2 was completely lost (in this hypothesis IF split
into four muscles: IFE, ITC, ITCR, and ITM) or whether PIFI2
split into ITCR and ITM in Aves (Carrano & Hutchinson, 2002;
Hutchinson, 2002; Romer, 1923a; Rowe, 1986). Even with these
uncertainties, the second hypothesis (PIFI2 = ITCR + ITM) is con-
sidered better supported, as it requires fewer transformations
(Grillo & Azevedo, 2011; Rowe, 1986). Although with variations,
most recent theropod reconstructions (e.g., Bishop et al., 2021;
Grillo & Azevedo, 2011; Rhodes et al., 2021; Smith, 2023) have
adopted the second hypothesis, which is also followed here.
In Crocodylia, the PIFI2 is a triangular and broad “fan-shaped”
muscle that originates from the centra of the last 6–7 dorsal ver-
tebrae and the ventral surfaces of their transverse processes
(Otero et al., 2010; Romer, 1923a; Suzuki et al., 2011). In Aves,
the homologous ITCR and ITM are small muscles that originate
from the anteroventralmost part of the lateral portion of the
preacetabular iliac blade (Rowe, 1986; Patak & Baldwin, 1998 ;
Picasso, 2010). As ab ove , this evi d ent ev olut ionary shif t of mus cle
origins is related to the expansion of the preacetabular blade and
the origination of the preacetabular notch (Hutchinson, 2001b,
2002; Romer, 1923a).
The last dorsal vertebrae in Piatnitzkysaurus possess well-de-
veloped vertebral centra (Bonaparte, 1986) lacking pleurocoels. A
large and shallow concavity located bellow the parapophyseal re-
gion is well-demarcated on some vertebrae (e.g., 19th and 20th;
Figure 10) and could be part of the PIFI2 origin (level II) as in
Crocodylia, which also potentially originated near the PIFI1 on the
ilium (I′). Only two posteriormost presacral vertebra are preserved
in Condorraptor (MPEF-PV 1680 and 1700), with massive vertebral
centra (Rauhut, 2005) similar to those of Piatnitzkysaurus and also
possessing a wide and well-demarcated shallow concavity that could
have been part of the PIFI2 origin (level II). No vertebrae associated
with Marshosaurus were studied, so no inference was made here.
The PIFI2 insertion in Crocodylia occurs via a tendon on the
proximolateral femur near (anterolateral to) the fourth trochan-
ter, on an anteromedial keel at two distinct points separated by
the proximal FMTE origin (Hutchinson, 2001a; Otero et al., 2010 ;
Romer, 1923a; Suzuki et al., 2011). In Aves, the homologous mus-
cles insert onto the distal end of the trochanteric crest, marked
by small scars (Patak & Baldwin, 1998; Hutchinson, 2001a, 2002).
FIGURE 9 Osteological correlates observed on the femur of Piatnitzkysaurus (right femur, PVL 4073). (a, b) lateral view. Anatomical/
muscular abbreviations: at, acessory trochanter; cfbs, M. caudofemoralis brevis insertion scar; ft, fourth trochanter; gt, greater trochanter;
ifes, M. iliofemoralis externus insertion scar; istrs, M. ischiotrochantericus insertion scar; itcs, M. iliotrochantericus caudalis insertion scar; lt,
lesser trochanter; pifes, Mm. puboischiofemorales externi insertion scar; pifi2, M. puboischiofemoralis internus 2 insertion scars; ts, trochanteric
shelf. Scale bar = 20 mm.
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LACERDA et al.
Avetheropoda (Allosauroidea + Coelurosauria; Paul, 1988) evolved a
large accessory trochanter, as a “blade-like” structure that, although
small, is also present in some ceratosaurs as well as early Tetanurae
(Brissón Egli et al., 2016; Carrano et al., 2012; Cerroni et al., 2022;
Hutchinson, 2001a; Lacerda et al., 2023). The accessory trochanter
is topologically equivalent to the PIFI2 insertion (Hutchinson, 2001a,
2002).
The right femur of Piatnitzkysaurus PVL 4073 preserves a
well-developed blade-shaped lesser trochanter (Bonaparte, 1986)
with a clear anterolateral and distal projection (the accessory tro-
chanter) which is inferred as the insertion of the PIFI2 muscle (level
I) (Figures 6a–f and 9). In Condorraptor, although the best-preserved
femur MPEF-PV 1690 has the base of a prominent lesser trochanter
(Rauhut, 2005), the most proximal part of it is not preserved and the
accessory trochanter is not discernible, so the PIFI2 insertion cannot
directly be reconstructed.
5.1.3 | Flexor cruris
M. flexor tibialis internus 1 (FTI1): In Aves, the FTI1 muscle is absent
(Hutchinson, 2002), wh ereas in Croco dyl ia it is a thin and lo ng musc le
originating from the distal portion of the ischium, on the posterodor-
sal surface (Gregory & Camp, 1918; Otero et al., 2010; Romer, 1923a ,
1923b; Suzuki et al., 2011) as a relatively long and thin muscle. Other
non-archosaurs lack an obvious FTI1, so homologies are unclear (e.g.,
PIT in Romer, 1942 or FTI (D) in Dick & Clemente, 2016); originating
from the posterior ischium (Dick & Clemente, 2016). Many theropod
dinosaurs have a distal ischial tubercle on the posterolateral ischial
shaft (e.g., Carrano & Hutchinson, 2002; Hutchinson, 2001b, 2002),
which is topographically equivalent to the approximate FT1 origin
in Crocodylia.
Bonaparte (1986) speculated that the ischial tubercle might be
the origin of the “M. ischiofemoralis” (or homologous M. ischiotro-
chantericus, ISTR). However, we interpret the ischial tubercle on the
distal ischial shaft of the PVL 4073 left ischium as the origin for the
FTI1 in Piatnitzkysaurus, as a level II inference (Figure 11a,b) (see
below for rationale for the ISTR origin). The distalmost portion of
the ischial shaft in the ischium of Condorraptor MPEF-PV 1689 is not
well-preserved, with no sign of the ischial tubercle; thus, we made
no inference of the FTI1 origin in this taxon. In the left ischium of
Marshosaurus UMNH VP 6380, although not as discernible as in
Piatnitzkysaurus, the ischial tubercle appears to be positioned on
the medial shaft of the ischium (Figure 11d,e), similar in position to
Piatnitzkysaurus and topographically equivalent to the FTI1 origin
(level II).
In Crocodylia, the FTI1 insertion is onto the medial (Otero
et al., 2010; Suzuki et al., 2011) or posterior portion of the proximal
tibial metaphysis (Carrano & Hutchinson, 2002), whereas its possi-
ble homologue inserts onto the lateral surface of the tibia in other
non-archosaurs (Dick & Clemente, 2016).
The posteromedial surface of the proximal region of the tibia in
Piatnitzkysaurus has a broad depression below the medial condyle
(Figure 12a–d), mainly visib le in the PVL 4073 specimen (Figure 12a).
We interpret this depression as the FTI1 insertion (level II). In
Condorraptor, a topologically similar depression is also noticeable
(Figure 12e), and here considered the FTI1 insertion (level II).
FIGURE 10 Osteological correlates observed on the
vertebrae of Piatnitzkysaurus (PVL 4073) in lateral view. (a) 19th
dorsal vertebra. (b) 20th dorsal vertebra. Anatomical/muscular
abbreviations: ns, neural spine; poz, postzygapophysis; prz,
prezygapophysis; vb, vertebral body. Arrows indicate the fossa.
Scale bar = 20 mm.
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L ACERDA e t al.
M. flexor tibialis internus 2 (FTI2): In Crocodylia, the FTI2 origi-
nates from the lateral ilium, on the postacetabular iliac process just
ventral to the origin of FTE (see below); it inserts together with
FTI1 and M. puboischiotibialis onto the posteromedial proximal tibia
(Hutchinson, 2002; Otero et al., 2010; Romer, 1923a, 1923b). In Aves,
the FTI2 appears to be absent (Hutchinson, 2002). Similar to other
theropod dinosaurs such as Staurikosaurus (Grillo & Azevedo, 2011),
Coelophysis (Bishop et al., 2021), and Tyrannosaurus (Carrano &
Hutchinson, 2002), there are no scars suggesting the presence of
FTI2 in Piatnitzkysaurus and Marshosaurus, so it is ambiguous if this
FIGURE 11 Osteological correlates obser ved on the ischia of Piatnitzkysauridae. (a, b) Piatnitzkysaurus (right ischium, MACN-Pv-CH 895).
(c, d) Condorraptor (left ischium, MPEF-PV 1696). (d–f) Marshosaurus (left ischium, UMNH VP 6387) in lateral view. Anatomical/muscular
abbreviations: ac, acetabulum; ADD1s, M. adductor femoris 1 scar; ADD2s, M. adductor femoris 2 scars; de, distal expansion; FTI1t, M. flexor
tibialis internus 1 tubercle; FTI3t, M. flexor tibialis internus 3 tubercle; ip, iliac peduncle; it, ischial tuberosity; op, obturator process; pp, pubic
peduncle; PIFE3, M. puboischiofemoralis externus 3; ti, ischiadic tubercle. Scale bar = 50 mm.
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LACERDA et al.
muscle was present or not (Level II'); the postacetabular blade is not
well-preserved in Condorraptor, preventing infer anything about this
muscle. The latter studies generally considered the FTI2 to more
likely be a crocodylian autapomorphy or a trait lost at some early
point in Avemetatarsalia–Dinosauromorpha (e.g., Allen et al., 2021;
Hutchinson, 2002).
M. flexor tibialis internus 3 (FTI3): In Crocodylia, the FTI3 (=M.
flexor cruris medialis, FCM in Aves; Hutchinson, 2001b) has its ori-
gin on the lateral surface of the ischial tuberosity, on the proximo-
lateral portion of the ischium (Otero et al., 2010 ; Romer, 1923a;
Suzuki et al., 2 011), which tends to be a scarred area in most non-
avian archosaurs (Hutchinson, 2001b). In Aves, the homologous
muscle, FCM, originates from a similar position, although more dis-
tally positioned and shifted closer to the ilium via rotation of the
ischia (Patak & Baldwin, 1998; Hutchinson, 2002; Picasso, 2010;
Suzuki et al., 2 014). In other non-archosaurian Reptilia, the FTI
has only two heads, that is, FTI1 and FTI2 (Gregory & Camp, 1918;
Hutchinson, 2002; Romer, 1942; Russel & Bauer, 1988). In non-avian
theropods, the origin of the FTI3 is thought to have been from the
prominent ischial tuberosity (Bonaparte et al., 199 0; Carrano &
Hutchinson, 2002; Grillo & Azevedo, 20 11; Romer, 1923a , 1923b;
Smith, 2021), which gradually shifted its relative position distally to
merge with the ilium within stem-birds (Hutchinson, 2001b).
On the ischium of Piatnitzkysaurus MACN-PV-CH 895, which
is better preserved proximally, a prominent ischial tuberosity that
is triangular in shape is present near the proximoposterior edge of
the ischium, ventral to the iliac peduncle; we infer this location as
the FTI3 origin (level II) (Figure 11a,b). The delimitation of the FTI3
origin in Condorraptor is less evident than in Piatnitzkysaurus, but is
similarly positioned (level II) (Figure 11c,d). In Marshosaurus is not
possible to determine the FTI3 origin due to a lack of osteological
correlates (level II'), so the muscle origin was not reconstructed in
any detail, but it should have been in the same location.
The FTI3 in extant archosaurs inserts onto the posterior surface
of the proximal portion of the tibia together with the FTE and other
FTI head(s), which may form a slightly roughened and rounded
structure made by the “tibiocalcaneal tendon” (or ligament) (Otero
et al., 2010; Romer, 1923a; Suzuki et al., 2011).
A region topologically related to the FTI3 insertion in
Piatnitzkysaurus is positioned on the posteromedial surface of the
proximal tibia, just below the medial and lateral condyles, and some
scarring is proximally located here (level II). Again, in Condorraptor
there is no scar (level II').
M. flexor tibialis internus 4 (FTI4): The M. flexor tibialis internus di-
vision called FTI4 is only present in the Crocodylia clade (though it
may have been lost in Caiman; Otero et al., 2010), being the divi-
sion equivalent to the superficial portion of FTI2 of other non-ar-
chosaurian Reptilia (Romer, 1942). It is a small and thin muscle that
originates from the fascia around the posteroventral ilium and
posterodorsal ischium (Romer, 1923 a, 1923b; Suzuki et al., 20 11).
FIGURE 12 Osteological correlates observed on the tibiae of Piatnitzkysauridae (left tibiae, medial view). (a, b) Piatnitzkysaurus (PVL
4073). (c, d) Piatnitzk ysaurus (MACN-Pv-CH 895). (e, f) Condorraptor (MPEF-PV 1672). Anatomical/muscular abbreviations: cc, cnemial crest;
d, depression; fti1d, M. flexor tibialis internus 1 depression; GMd, M. gastrocnemius pars medialis depression; it1–3 + amb + fmt, insertion of the
tendons of the iliotibiales + ambiens + femorotibiales muscles; mc, medial condyle; r, ridge. Scale bar = 50 mm.
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L ACERDA e t al.
Since this muscle leaves no evident scars and is absent in Aves
(Carrano & Hutchinson, 2002; Hutchinson, 2002), the presence in
Piatnitzkysaurus and Marshosaurus is equivocal (level II')