ArticlePDF Available

The pelvic and hindlimb myology of the basal titanosaur Epachthosaurus sciuttoi (Sauropoda: Titanosauria)

Historical Biology

October 2018
32(6):1-16

DOI:10.1080/08912963.2018.1535598

Authors:

Lucio Manuel Ibiricu

National Scientific and Technical Research Council

Rubén Darío Francisco Martínez

National University of Patagonia San Juan Bosco

Gabriel Andrés Casal

National University of Patagonia San Juan Bosco

Epachthosaurus sciuttoi is a basal titanosaur from the early Late Cretaceous of central Patagonia, Argentina. Here, we present the reconstruction of the pelvic and hindlimb musculature of this titanosaur, based on the soft tissue data of extant archosaurs. The majority of the pelvic, hindlimb and pes muscles are within a decisive and positive level of inference. Comparison with a derived titanosaur such as Neuquensaurus, shows several morphological differences which are directly related with the muscular attachments, supporting differences about the musculature arrangement between these two sauropod dinosaurs. For example, the anterior projection of the preacetabular process of Neuquensaurus extends more laterally, whereas in Epachthosaurus the preacetabular process is laterally less extended. The fibular lateral tuberosity in Neuquensaurus is closer to the fibular head than it is in Epachthosaurus. The femoral fourth trochanter in Neuquensaurus is closer to the femoral head than it is in Epachthosaurus. Likewise, the caudofemoralis longus may have extended more distally in the tail in Epachthosaurus.These differences, among others, may have influenced the muscular arrangement and, therefore, the locomotor function abilities of these titanosaurs. Finally, this myological description of Epachthosaurus, where twenty one muscles were reconstructed, constitutes useful data for researches interested in functional anatomy.

Content uploaded by Gabriel Andrés Casal

Content may be subject to copyright.

ARTICLE

The pelvic and hindlimb myology of the basal titanosaur Epachthosaurus sciuttoi

(Sauropoda: Titanosauria)

Lucio M. Ibiricu

, Rubén D. Martínez

and Gabriel A. Casal

Instituto Patagónico de Geología y Paleontología (IPGP), CCT CENPAT-CONICET, Chubut, Argentina;

Laboratorio de Paleontologia de Vertebrados,

Universidad Nacional de la Patagonia San Juan Bosco, Chubut, Argentina

ABSTRACT

Epachthosaurus sciuttoi is a basal titanosaur from the early Late Cretaceous of central Patagonia,

Argentina. Here, we present the reconstruction of the pelvic and hindlimb musculature of this titano-

saur, based on the soft tissue data of extant archosaurs. The majority of the pelvic, hindlimb and pes

muscles are within a decisive and positive level of inference. Comparison with a derived titanosaur such

as Neuquensaurus, shows several morphological diﬀerences which are directly related with the muscular

attachments, supporting diﬀerences about the musculature arrangement between these two sauropod

dinosaurs. For example, the anterior projection of the preacetabular process of Neuquensaurus extends

more laterally, whereas in Epachthosaurus the preacetabular process is laterally less extended. The

ﬁbular lateral tuberosity in Neuquensaurus is closer to the ﬁbular head than it is in Epachthosaurus. The

femoral fourth trochanter in Neuquensaurus is closer to the femoral head than it is in Epachthosaurus.

Likewise, the caudofemoralis longus may have extended more distally in the tail in Epachthosaurus.

These diﬀerences, among others, may have inﬂuenced the muscular arrangement and, therefore, the

locomotor function abilities of these titanosaurs. Finally, this myological description of Epachthosaurus,

where twenty one muscles were reconstructed, constitutes useful data for researches interested in

functional anatomy.

ARTICLE HISTORY

Received 6 March 2018

Accepted 10 October 2018

KEYWORDS

Epachthosaurus sciuttoi;

pelvis and hindlimb;

myological reconstruction;

Titanosauria

Introduction

The titanosaurians are the most abundant, morphologically

diverse and geographically widespread group of sauropod

dinosaurs. The record of this group is present on all conti-

nents (Cerda et al. 2012), however, in South America the

Titanosauria are by far the most abundant herbivorous dino-

saurs, and include more than 40 genera (González Riga 2011;

Faria et al. 2015). Continental deposits of the Bajo Barreal

Formation (Early Cenomanian - Late Turonian, Casal et al.

2016) exposed in central Patagonia, Argentina preserve a rich

and important fossil record (Martínez et al. 1986;2016;

Martínez & Novas 2006; Ibiricu et al. 2013a, Ibiricu et al.

2015; among others).A well preserved, and articulated skele-

ton of Epachthosaurus sciuttoi was found in this Cretaceous

unit, along with other dinosaur specimens. Epachthosaurus

was brieﬂy described by Martínez et al. (1988,1989) support-

ing its inclusion within Titanosauria. Consequently, Martínez

et al. (2004) provide a detailed description of E. sciuttoi.

The study of soft tissue in extinct taxa is always a diﬃcult

task, particularly in sauropod dinosaurs, because the absence

of proportional extant forms and biomechanics correlatives.

Nevertheless, the ‘Extant Phylogenetic Bracket’(Witmer 1995,

1997) had been an interesting and frequently used methodol-

ogy when reconstructing soft tissue of extinct dinosaurs

(Hutchinson and Gatesy 2000; Hutchinson 2002; Jasinoski

et al. 2006;O’Connor 2006; Schwarz-Wings 2009; Sander

et al. 2011; among others). The musculoskeletall system in

extant crocodylians and birds is well documented (McGowan

1979; Rowe 1986; Meers 2003; Reilly and Blob 2003; Gangl

et al. 2004; Carril et al. 2014).

Although, Romer (1923)wastheﬁrst to analyze the

pelvic musculature in Camarasaurus and all saurischians,

Borsuk-Bialynicka (1977)wastheﬁrst author which

focused in the appendicular musculature in titanosaurs

(i.e. Opisthocoelicaudia). Nevertheless, the only compre-

hensive study of musculature and functional morphology

in a South American titanosaurian to date is that of Otero

and Vizcaino (2008). These authors performed a hindlimb

musculature reconstruction in order to interpret appendi-

cular muscle arrangements and function in Neuquensaurus

australis (Lydekker 1893)anditsimplicationswithinsalt-

asaurines. This titanosaur, is one of the most derived forms

within Titanosauria (Wilson 2002; Salgado and Bonaparte

2007). On the other hand, Epachthosaurus is one of the

basal forms within the group (Salgado et al. 1997;Salgado

and Bonaparte 2007). This situation is particularly inter-

esting, because it establishes an opportunity to evaluate the

musculature within two diﬀerent evolutionary stages. An

interpretative study of the musculature system of

Epachthosaurus constitutes an excellent opportunity to

gain insight into the morphology and function of the

appendicular bones within Titanosauria. Although

Epachthosaurus is a medium-size titanosaur, the increase

in body size observed in sauropods entailed an evolution-

ary change to quadrupedal posture from the early

CONTACT Lucio M. Ibiricu ibiricu@cenpat-conicet.gob.ar

HISTORICAL BIOLOGY

https://doi.org/10.1080/08912963.2018.1535598

Published online 22 Oct 2018

The appendicular myology of Stegoceras validum (Ornithischia: Pachycephalosauridae) and implications for the head-butting hypothesis

Article

Full-text available

Sep 2022
PLOS ONE

In this study, we use an exceptional skeleton of the pachycephalosaur Stegoceras validum (UALVP 2) to inform a comprehensive appendicular muscle reconstruction of the animal, with the goal of better understanding the functional morphology of the pachycephalosaur postcranial skeleton. We find that S . validum possessed a conservative forelimb musculature, particularly in comparison to early saurischian bipeds. By contrast, the pelvic and hind limb musculature are more derived, reflecting peculiarities of the underlying skeletal anatomy. The iliotibialis, ischiocaudalis, and caudofemoralis muscles have enlarged attachment sites and the caudofemoralis has greater leverage owing to the distal displacement of the fourth trochanter along the femur. These larger muscles, in combination with the wide pelvis and stout hind limbs, produced a stronger, more stable pelvic structure that would have proved advantageous during hypothesized intraspecific head-butting contests. The pelvis may have been further stabilized by enlarged sacroiliac ligaments, which stemmed from the unique medial iliac flange of the pachycephalosaurs. Although the pubis of UALVP 2 is not preserved, the pubes of other pachycephalosaurs are highly reduced. The puboischiofemoralis musculature was likely also reduced accordingly, and compensated for by the aforementioned improved pelvic musculature.

Myological reconstruction of the pelvic girdle and hind limb of the giant titanosaurian sauropod dinosaur Dreadnoughtus schrani

Article

Full-text available

Oct 2020

Osteological correlates preserve more readily than their soft tissue counterparts in the fossil record; therefore, they can more often provide insight into the soft tissue anatomy of the organism. These insights can in turn elucidate the biology of these extinct organisms. In this study, we reconstruct the pelvic girdle and hind limb musculature of the giant titanosaurian sauropod Dreadnoughtus schrani based on observations of osteological correlates and Extant Phylogenetic Bracket comparisons. Recovered fossils of Dreadnoughtus exhibit remarkably well‐preserved, well‐developed, and extensive muscle scars. Furthermore, this taxon is significantly larger bodied than any titanosaurian for which a myological reconstruction has previously been performed, rendering this contribution highly informative for the group. All 20 of the muscles investigated in this study are sufficiently well supported to enable reconstruction of at least one division, including reconstruction of the M. ischiocaudalis for the first time in a sauropod dinosaur. In total, 34 osteological correlates were identified on the pelvic girdle and hind limb remains of Dreadnoughtus, allowing the reconstruction of 14 muscles on the basis of Level I or Level II inferences (i.e., not Level I' or Level II' inferences). Comparisons among titanosaurians suggest widespread myological variation, yet potential phylogenetic and other paleobiologic patterns are often obscured by fragmentary preservation, infrequent myological studies, and lack of consensus on the phylogenetic placement of many taxa. However, a ventrolateral accessory process is present on the preacetabular lobe of the ilium in all of the largest titanosauriforms that preserve this skeletal element, suggesting that the presence of this process (representing the origin of the M. puboischiofemoralis internus part II) may be associated with extreme body size. By identifying such myological patterns among titanosauriforms, we can begin to address specific evolutionary and biomechanical questions related to their skeletal anatomy, how they were capable of leaving wide‐gauge trackways, and resulting locomotor attributes unique to this clade.

Appendicular myological reconstruction of the forelimb of the giant titanosaurian sauropod dinosaur Dreadnoughtus schrani

Article

Full-text available

Mar 2020

Soft tissues are variably preserved in the fossil record with external tissues, such as skin and feathers, more frequently preserved than internal tissues (e.g. muscles). More commonly, soft tissues leave traces of their locations on bones and, for muscles, these clues can be used to reconstruct the musculature of extinct vertebrates, thereby enhancing our understanding of how these organisms moved and the evolution of their locomotor patterns. Herein we reconstruct the forelimb and shoulder girdle musculature of the giant titanosaurian sauropod Dreadnoughtus schrani based on observations of osteological correlates and dissections of taxa comprising the Extant Phylogenetic Bracket of non-avian dinosaurs (crocodilians and birds). Fossils of Dreadnoughtus exhibit remarkably well-preserved, well-developed, and extensive muscle scars. Furthermore, this taxon is significantly larger-bodied than any titanosaurian for which a myological reconstruction has previously been attempted, rendering this myological study highly informative for the clade. In total, 28 muscles were investigated in this study, for which 46 osteological correlates were identified; these osteological correlates allowed the reconstruction of 16 muscles on the basis of Level I or Level II inferences (i.e. not Level I' or Level II' inferences). Comparisons with other titanosaurians suggest widespread myological variation in the clade, although potential phylogenetic patterns are often obscured by fragmentary preservation, infrequent myological studies, and lack of consensus on the systematic position of many taxa. By identifying myological variations within the clade, we can begin to address specific evolutionary and biomechanical questions related to the locomotor evolution in these sauropods.

Last Titans: Titanosaurs From the Campanian–Maastrichtian Age

Chapter

Apr 2022

After the extinction of rebbachisaurids during the Cenomanian–Turonian interval, titanosaurs were the only group of sauropods to face the K–Pg event. This same global pattern also holds for the end-Cretaceous (Campanian–Maastrichtian) titanosaur record in South America, where their remains can be found from southern Argentina to Ecuador, with more frequent findings in Argentina and Brazil. In this chapter, we review these fossil findings and the main aspects of the taxonomy, systematics, and paleogeographic implications of this record and briefly discuss the importance of these occurrences for the understanding of titanosaur evolution. The diversity and abundance of end-Cretaceous titanosaur taxa in South America represent about 25% of the known Titanosauria species in the world, which makes them the most common group of large terrestrial herbivores of that time. Cretaceous titanosaurs from South America also vary highly in morphology and size, comprising small to large-sized taxa, for example. Their record mainly consists of appendicular and axial remains, including rare skull material, but also comprises eggs, nests, footprints, and coprolites. In South America, by the end of the Late Cretaceous, titanosaurs were generally represented by more derived titanosaurians that are mainly taxonomically assigned to more derived species within Aeolosaurini and Saltasaurinae.

Walking with early dinosaurs: Appendicular myology of the Late Triassic sauropodomorph Thecodontosaurus antiquus

Article

Full-text available

Jan 2022

Dinosaur evolution is marked by numerous independent shifts from bipedality to quadrupedality. Sauropodomorpha is one of the lineages that transitioned from small bipedal forms to graviportal quadrupeds, with an array of intermediate postural strategies evolving in non-sauropodan sauropodomorphs. This locomotor shift is reflected by multiple modifications of the appendicular skeleton, coupled with a drastic rearrangement of the limb musculature. Here, we describe the osteological correlates of appendicular muscle attachment of the Late Triassic sauropodomorph Thecodontosaurus antiquus from multiple well-preserved specimens and provide the first complete forelimb and hindlimb musculature reconstruction of an early-branching sauropodomorph. Comparisons with other sauropodomorphs and early dinosaurs reveal a unique combination of both plesiomorphic and derived musculoskeletal features. The diversity of appendicular osteological correlates among early dinosaurs and their relevance in muscle reconstruction are discussed. In line with previous evidence, aspects of the limb muscle arrangement, such as conspicuous correlates of lower limb extensors and flexors and low moment arms of hip extensors and flexors, suggest Thecodontosaurus was an agile biped. This reconstruction helps to elucidate the timing of important modifications of the appendicular musculature in the evolution of sauropodomorphs which facilitated the transition to quadrupedalism and contributed to their evolutionary success.

Casal et al. 2022. D.7. VERTEBRADOS CONTINENTALES CRETÁCICOS Relatorio XXI CGA

Chapter

Full-text available

Nov 2021

En la cuenca del Golfo San Jorge se encuentran unidades de origen continental reunidas en el Grupo Chubut (Barreamiano-Maastrichtiano) que son portadoras de un alto contenido fosilífero. Este registro paleontológico de vertebrados continentales cretácicos de la cuenca es una de los más diversos de América del Sur. Es relativamente escaso al momento en la Formación Matasiete (Aptiano), pero mucho más abundante en las formaciones Bajo Barreal (Cenomaniano temprano-Turoniano tardío) y Lago Colhué Huapi (Conianciano-Maastrichtiano). Incluye una importante cantidad de grupos de vertebrados, destacándose los dinosaurios saurópodos, terópodos y ornitópodos. También están bien documentados otros taxones como cocodrilos y tortugas, pero son escasos hasta el momento los restos de reptiles voladores, anuros y peces. Muchos de los hallazgos son de gran importancia y han contribuido al conocimiento de diferentes grupos y de sus relaciones filogenéticas y paleobiogeográficas. Se describe en este trabajo, solo el registro paleontológico más relevante y especies válidas conocidas hasta el momento.

Two Late Cretaceous sauropods reveal titanosaurian dispersal across South America

Article

Full-text available

Oct 2020

South American titanosaurians have been central to the study of the evolution of Cretaceous sauropod dinosaurs. Despite their remarkable diversity, the fragmentary condition of several taxa and the scarcity of records outside Patagonia and southwestern Brazil have hindered the study of continental-scale paleobiogeographic relationships. We describe two new Late Cretaceous titanosaurians from Quebrada de Santo Domingo (La Rioja, Argentina), which help to fill a gap between these main areas of the continent. Our phylogenetic analysis recovers both new species, and several Brazilian taxa, within Rinconsauria. The data suggest that, towards the end of the Cretaceous, this clade spread throughout southern South America. At the same locality, we discovered numerous accumulations of titanosaurian eggs, likely related to the new taxa. With eggs distributed in three levels along three kilometres, the new site is one of the largest ever found and provides further evidence of nesting site philopatry among Titanosauria.

New materials and an overview of Cretaceous vertebrates from the Chubut Group of the Golfo San Jorge Basin, central Patagonia, Argentina

Article

Dec 2019
J S AM EARTH SCI

In this paper, we present an updated revision of fossil vertebrates from the Chubut Group, Golfo San Jorge Basin, while also describing some new remains. Extensive exposures of both Lower and Upper Cretaceous sedimentary sequences are present in central Patagonia. These outcrops have, over the past several decades, yielded a varied vertebrate fauna, including fishes, turtles, crocodyliforms, pterosaurs, and dinosaurs, currently herein characterized and described. Although vertebrate diversity in the Chubut Group in central Patagonia is remarkable, the most abundant vertebrates recovered are dinosaurs. The Matasiete Formation (Hauterivian?–Albian) is markedly less prolific in terms of fossils discoveries than either the Bajo Barreal Formation (Cenomanian–early Turonian) or the recently recognized Lago Colhué Huapi Formation (Coniacian–Maastrichtian). The Bajo Barreal fauna is, at a high level, typical of coeval Gondwanan faunas. However, interestingly, several taxa occupy a basal position within their respective groups. The Lago Colhué Huapi Formation has produced a more derived vertebrate fauna, again similar to those from other Gondwanan regions. Finally, in a broad context, the new materials described augment our understanding of Cretaceous terrestrial vertebrate assemblage of central Patagonia and add to the generally meager record of vertebrate in the Cretaceous of the Southern Hemisphere.

New sauropod appendicular remains from the Upper Cretaceous of Romania: accessing the morphological variability.

Article

Jun 2024
CRETACEOUS RES

Body Size Evolution and Locomotion in Sauropodomorpha: What the South American Record Tells Us

Chapter

Full-text available

Apr 2022

The transition from early sauropodomorphs to sauropods is of special interest given that a shift from obligatory or facultative bipedalism to an obligatory quadrupedalism is evident. In this chapter, we review and discuss the biological mechanisms underpinning such evolutionary transformations. The discovery of the South American sauropodomorph Mussaurus patagonicus has helped elucidate changes in the upper forelimb from bipedality to quadrupedality. Shoulder range of motion studies has shown that Mussaurus could not protract its forelimb past vertical, which suggests that quadrupedal locomotion could not have been possible, although it might have been if the elbow was habitually strongly flexed, as has been hypothesized for ornithischian quadrupeds. Yet muscle moment arm studies indicated that Mussaurus could not straighten its elbow, suggesting it did not have columnar forelimbs like later, fully quadrupedal sauropods. Quadrupedal locomotion first evolved in the adult forms of the sauropodomorphs closest to Sauropoda (e.g., Melanorosaurus). However, it has been suggested that already some early sauropodomorphs (e.g., Massospondylus) were quadrupedal during early ontogenetic stages and adopted a bipedal stance, at least facultatively, as adults. The postural shifting that some sauropodomorphs experienced during their ontogeny has important implications for understanding evolutionary processes that caused those shifts. Available ontogenetic series of Mussaurus provide additional insight into these evolutionary developmental transitions. The body’s center of mass of this species moved from a position in the mid-thorax to a more posterior position close to the pelvis, consistent with a shift from quadrupedalism to bipedalism at a young age. This postural modification could be the product of the relative enlargement of the tail and the reduction of the neck during ontogeny, challenging previous studies, which emphasized that that transformation would have been linked to a relative enlargement of the forelimbs. Viewed in a phylogenetic context, the South American sauropodomorph record provides key information regarding the evolution of body size and limb mechanics in this group. An anterior center of mass shift occurred during the evolution of quadrupedalism in the Late Triassic, followed by a more striking anterior shift in Late Jurassic–Cretaceous titanosauriforms, a phenomenon apparently closely linked with locomotion (e.g., weight distribution; reduced athleticism) and environment. As South American titanosaurs included the largest land animals ever, these also inform us about the constraints on terrestrial gigantism and the surprising diversity of giant forms that can exist despite these biomechanical and other constraints.

Characterizing the Evolution of Wide-Gauge Features in Stylopodial Limb Elements of Titanosauriform Sauropods via Geometric Morphometrics

Article

Full-text available

Apr 2017
Anat Rec

Wide-gauge posture of titanosauriform sauropods remains an enigmatic peculiarity among terrestrial vertebrates. Here, two-dimensional geometric morphometrics and thin plate splines analyses were used to quantitatively analyze shape differences among sauropodomorph humeri and femora to identify how these elements may differ according to body gauge. Results demonstrate that titanosauriforms generally possess proportionately gracile humeri in comparison to other sauropods, with relatively more medially oriented humeral heads and proximally located deltopectoral crests. Myological repercussions of these features demonstrate a relative sacrificing of muscular torque for forelimb abduction/adduction in exchange for minimization of necessary muscle contraction to generate the same degree of limb excursion. Regarding femora, titanosauriforms possess significantly broader femora mediolaterally than other sauropods, with comparatively proximomedially placed fourth trochanters. Canonical variates results also identify a trend for titanosauriform femora to present distal condyles that are more frequently perpendicular to the long axis of the shaft or beveled medially. All of these femoral shape characteristics are expressed to the greatest degree by titanosaurians. Myologically, mediolateral femoral broadening increases relative mechanical advantages for hind limb abductor and adductor musculature. This supports previous hypotheses that suggested titanosauriforms were capable of a greater degree of hind limb abduction and adduction. This capability may have been necessary to maintain dynamic stability during wide-gauge locomotion over uneven terrain. Overall, our results corroborate previous qualitative assessments of wide-gauge attributes, afford new insights into statistically significant but obscure shape patterns, and add new clarity to aspects of the functional morphology of wide-gauge posture. This article is protected by copyright. All rights reserved.

A novel form of postcranial skeletal pneumaticity in a sauropod dinosaur: Implications for the paleobiology of Rebbachisauridae

Article

Full-text available

Apr 2017

In dinosaurs and other archosaurs, the presence of foramina connected with internal chambers in axial and appendic-ular bones is regarded as a robust indicator of postcranial skeletal pneumaticity (PSP). Here we analyze PSP and its paleobiological implications in rebbachisaurid diplodocoid sauropod dinosaurs based primarily on the dorsal vertebrae of Katepensaurus goicoecheai, a rebbachisaurid from the Cenomanian–Turonian (Upper Cretaceous) Bajo Barreal Formation of Patagonia, Argentina. We document a complex of interconnected pneumatic foramina and internal chambers within the dorsal vertebral transverse processes of Katepensaurus. Collectively, these structures constitute a form of PSP that has not previously been observed in sauropods, though it is closely comparable to morphologies seen in selected birds and non-avian theropods. Parts of the skeletons of Katepensaurus and other rebbachisaurid taxa such as Amazonsaurus maranhensis and Tataouinea hannibalis exhibit an elevated degree of pneumaticity relative to the conditions in many other sauropods. We interpret this extensive PSP as an adaptation for lowering the density of the skeleton, and tentatively propose that this reduced skeletal density may also have decreased the muscle energy required to move the body and the heat generated in so doing. Given that several rebbachisaurids inhabited tropical to subtropical paleolatitudes during the extreme warmth of the mid-Cretaceous, increased PSP may have better enabled these sauropods to cope with extraordinarily high temperatures. Extensive skeletal pneumaticity may have been an important innovation in Rebbachisauridae, and perhaps also in saltasaurine titanosaurs, which evolved an even greater degree of PSP. This may in turn have contributed to the evolutionary success of rebbachisaurids, which were the only diplodocoids to survive into the Late Cretaceous.

Digital dissection and three-dimensional interactive models of limb musculature in the Australian estuarine crocodile (Crocodylus porosus)

Article

Full-text available

Apr 2017
PLOS ONE

Digital dissection is a relatively new technique that has enabled scientists to gain a better understanding of vertebrate anatomy. It can be used to rapidly disseminate detailed, three-dimensional information in an easily accessible manner that reduces the need for destructive, traditional dissections. Here we present the results of a digital dissection on the appendicular musculature of the Australian estuarine crocodile (Crocodylus porosus). A better understanding of this until now poorly known system in C. porosus is important, not only because it will expand research into crocodilian locomotion, but because of its potential to inform muscle reconstructions in dinosaur taxa. Muscles of the forelimb and hindlimb are described and three-dimensional interactive models are included based on CT and MRI scans as well as fresh-tissue dissections. Differences in the arrangement of musculature between C. porosus and other groups within the Crocodylia were found. In the forelimb, differences are restricted to a single tendon of origin for triceps longus medialis. For the hindlimb, a reduction in the number of heads of ambiens was noted as well as changes to the location of origin and insertion for iliofibularis and gastrocnemius externus.

Ordenamiento y caracterización faunística del Cretácico Superior del Grupo Chubut, Cuenca del Golfo San Jorge, Argentina

Article

Full-text available

May 2016

The Chubut Group, central Patagonia, Argentina, is characterized by a lacustrine and fluvial-lacustrine system with variable participation of volcanic ash. This group includes the Bajo Barreal Formation (Cenomanian-Turonian) and a recently nested new lithostratigraphic unit, the Lago Colhue Huapi Formation (Coniacian-Maastrichtian). The Lago Colhue Huapi Formation overlies the Bajo Barreal Formation. These sedimentary units preserve a rich and diverse vertebrate fossil record including, among others, representatives of Crocodylomorpha, Testudines, Pterosauria and abundant Dinosauria. Nevertheless, the stratigraphic position of several of its taxa has been historically controversial. The unclear stratigraphic provenance of these taxa difficults the correct interpretation of the relationships with other Patagonian and South American basins. In this context, we present a detailed stratigraphic study to clarify the position of the vertebrate fossils of both Late Cretaceous formations. We also discuss the implications of this faunistic arrangement in terms of vertebrate evolution and paleobiogeography. Finally, this study broadens our knowledge on the fossil fauna of these units and therefore the vertebrate assemblages of central Patagonia.

A Basal Lithostrotian Titanosaur (Dinosauria: Sauropoda) with a Complete Skull: Implications for the Evolution and Paleobiology of Titanosauria

Article

Full-text available

Apr 2016
PLOS ONE

We describe Sarmientosaurus musacchioi gen. et sp. nov., a titanosaurian sauropod dinosaur from the Upper Cretaceous (Cenomanian-Turonian) Lower Member of the Bajo Barreal Formation of southern Chubut Province in central Patagonia, Argentina. The holotypic and only known specimen consists of an articulated, virtually complete skull and part of the cranial and middle cervical series. Sarmientosaurus exhibits the following distinctive features that we interpret as autapomorphies: (1) maximum diameter of orbit nearly 40% rostrocaudal length of cranium; (2) complex maxilla-lacrimal articulation, in which the lacrimal clasps the ascending ramus of the maxilla; (3) medial edge of caudal sector of maxillary ascending ramus bordering bony nasal aperture with low but distinct ridge; (4) 'tongue-like' ventral process of quadratojugal that overlaps quadrate caudally; (5) separate foramina for all three branches of the trigeminal nerve; (6) absence of median venous canal connecting infundibular region to ventral part of brainstem; (7) subvertical premaxillary, procumbent maxillary, and recumbent dentary teeth; (8) cervical vertebrae with 'strut-like' centroprezygapophyseal laminae; (9) extremely elongate and slender ossified tendon positioned ventrolateral to cervical vertebrae and ribs. The cranial endocast of Sarmientosaurus preserves some of the most complete information obtained to date regarding the brain and sensory systems of sauropods. Phylogenetic analysis recovers the new taxon as a basal member of Lithostrotia, as the most plesiomorphic titanosaurian to be preserved with a complete skull. Sarmientosaurus provides a wealth of new cranial evidence that reaffirms the close relationship of titanosaurs to Brachiosauridae. Moreover, the presence of the relatively derived lithostrotian Tapuiasaurus in Aptian deposits indicates that the new Patagonian genus represents a 'ghost lineage' with a comparatively plesiomorphic craniodental form, the evolutionary history of which is missing for at least 13 million years of the Cretaceous. The skull anatomy of Sarmientosaurus suggests that multiple titanosaurian species with dissimilar cranial structures coexisted in the early Late Cretaceous of southern South America. Furthermore, the new taxon possesses a number of distinctive morphologies-such as the ossified cervical tendon, extremely pneumatized cervical vertebrae, and a habitually downward-facing snout-that have rarely, if ever, been documented in other titanosaurs, thus broadening our understanding of the anatomical diversity of this remarkable sauropod clade. The latter two features were convergently acquired by at least one penecontemporaneous diplodocoid, and may represent mutual specializations for consuming low-growing vegetation.

A gigantic new dinosaur from Argentina and the evolution of the sauropod hind foot

Article

Full-text available

Jan 2016

Titanosauria is an exceptionally diverse, globally-distributed clade of sauropod dinosaurs that includes the largest known land animals. Knowledge of titanosaurian pedal structure is critical to understanding the stance and locomotion of these enormous herbivores and, by extension, gigantic terrestrial vertebrates as a whole. However, completely preserved pedes are extremely rare among Titanosauria, especially as regards the truly giant members of the group. Here we describe Notocolossus gonzalezparejasi gen. et sp. nov. from the Upper Cretaceous of Mendoza Province, Argentina. With a powerfully-constructed humerus 1.76 m in length, Notocolossus is one of the largest known dinosaurs. Furthermore, the complete pes of the new taxon exhibits a strikingly compact, homogeneous metatarsus-seemingly adapted for bearing extraordinary weight-and truncated unguals, morphologies that are otherwise unknown in Sauropoda. The pes underwent a near-progressive reduction in the number of phalanges along the line to derived titanosaurs, eventually resulting in the reduced hind foot of these sauropods.

New Material of Katepensaurus goicoecheai (Sauropoda: Diplodocoidea) and Its Significance for the Morphology and Evolution of Rebbachisauridae

Article

Full-text available

Jan 2014

Cretaceous outcrops in southern South America preserve a rich and evolutionarily important record of sauropod dinosaurs. Among Sauropoda, South American titanosaurs have garnered particular interest due to their abundance and taxonomic diversity. Nevertheless, the fossil record of rebbachisaurids has also improved significantly in recent years, and consequently so has knowledge of the group. However, many aspects of the anatomy and phylogenetic relationships of Rebbachisauridae remain unresolved, due in large part to the fragmentary nature of many members of the clade. Within this context, we describe new fossils of Katepensaurus goicoecheai Ibiricu, Casal, Martínez, Lamanna, Luna, and Salgado, a recently-named rebbachisaurid from the Upper Cretaceous (Cenomanian/Turonian) Bajo Barreal Formation of central Patagonia (Argentina). Based on these additional materials, we propose two new autapomorphies of this taxon: (1) ventral portion of posterior articular surface of anterior dorsal vertebral centrum wider than dorsal portion, conferring a ‘teardrop-shaped’ contour; and (2) ovoid fossa on dorsal aspect of anterior to middle dorsal vertebral transverse processes. These features enhance our understanding of morphological diversity within Rebbachisauridae and augment the diagnosis of Katepensaurus. Furthermore, phylogenetic analysis confirms the assignment of this taxon to the rebbachisaurid subclade Limaysaurinae. Katepensaurus is the southernmost record of a rebbachisaurid that is identifiable to the generic level.

A new titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Lo Hueco (Cuenca, Spain)

Article

Aug 2016

The upper Campanian-lower Maastrichtian site of Lo Hueco (Cuenca, Spain) has provided a set of well-preserved partial skeletons in anatomical connection or with a low dispersion of their skeletal elements. One partial skeleton is herein described and a new titanosaurian sauropod is established, Lohuecotitan pandafilandi. This titanosaur is diagnosed by eight autapomorphic features: dorsally and ventrally widened or bifurcated posterior centrodiapophyseal lamina in anterior and middle dorsal vertebrae; short postspinal lamina with a transversely expanded distal end represented by smooth scars in the dorsal vertebrae; anteriormost caudals with the medial spinoprezygapophyseal and medial spinopostzygapophyseal laminae ventrally connected with the prespinal and postspinal laminae, respectively; anterior caudal neural spines with a dorsal projection of the prespinal and postspinal laminae; anterior caudal neural spines bears a “greek-cross”-like cross-section; middle caudal centra having two round and rough structures in the dorsal edge of the posterior articulation, which extends to the dorsal surface of the centrum; the articular ends of the rami of the haemal arches are divided in two articular surfaces; and tuberosity between the anterior and the lateral trochanter of the fibula. The herein performed phylogenetic analysis considered L. pandafilandi as a member of Lithostrotia more derived than Malawisaurus. The known palaeodiversity of the Late Cretaceous Ibero-Armorican titanosaurs is increasing, and further analyses focused on this group will be necessary to better understand the evolutionary history of European titanosaurs and to clarify their relationships within Titanosauria.

A new titanosaur from the Lower Cretaceous of Brazil

Article

Jul 2016

Here we describe a new record of a sauropod dinosaur from the Lower Cretaceous (Hauterivian-Barremian) Rio Piranhas Formation, Sousa Basin, NE Brazil. Dinosaur fossil bones from this deposit were unknown until now. Thus, the discovery of a sauropod fibula from this locality is highly significant. Our discovery represents an indeterminate titanosaur and the earliest stratigraphic occurrence of this group in central Gondwana. When compared to chronocorrelate titanosaur trackmakers of this geological unit, this fossil specimen appears substantially smaller. Histological analysis of the fibula suggests that this is a relatively young individual (approximately 40-50% adult body size) that had passed its most rapid phase of early juvenile growth, but had not yet attained somatic maturity. Thus, the fibula recovered is from a young individual rather than from a small-bodied adult titanosaur.

Convergences and trends in the evolution of the archosaur pelvis

Article

Jun 2014

The pelvic structure in non-avian archosaurs plays a key role in understanding the evolution of terrestrial locomotor patterns because the pelvis contains major attachment sites for proximal hind limb musculature. In order to investigate patterns of pelvic evolution in archosaurs, this study compiled three pelvic indices, as well as femoral head orientation, for 92 archosaur taxa. With the metrics and a reconstructed supertree, we examined the correlated evolution of the pelvis and femur, the correlation among pelvic components, and temporal trends in the evolution of the pelvis. The result shows that archosaurs with medially directed femoral heads have more cranially shifted iliac centroids and more posteriorly rotated pubes than taxa with anteromedially directed femoral heads. The craniad shift of the iliac centroid might be correlated to the posterior rotation of pubis. The pelvic structures of pterosaurs, ornithischians, sauropods, and avetheropods occupy a different morphospace from basal archosaurs, pseudosuchians, basal dinosauromorphs, basal theropods, and basal sauropodomorphs in having more cranially expanded ilia, more posteriorly rotated pubes, and medially deflected femoral heads. This may imply that pterosaurs and those derived dinosaurs independently underwent similar shifts in thigh muscles and locomotion. The evolutionary model fitting supports the early-burst model for iliac and pubic metrics in more inclusive archosaur clades, indicating that larger changes of archosaur pelves occurred in early times of the clade's history

The pelvic and hindlimb myology of the basal titanosaur Epachthosaurus sciuttoi (Sauropoda: Titanosauria)

Abstract

Recommended publications

The Cervical Vertebrae of the Late Cretaceous Abelisaurid Dinosaur Carnotaurus sastrei

Bone microstructure and diagenesis of saurischian dinosaurs from the Upper Cretaceous (Neuquén Group...

A new abelisauroid theropod from northwestern Patagonia

A natural cranial endocast with possible dicraeosaurid (Sauropoda, Diplodocoidea) affinities from th...