Reconstruction of the pectoral girdle and forelimb musculature of Megaraptora (Dinosauria: Theropoda).

Megaraptora is a group of enigmatic, carnivorous non-avian theropod dinosaurs from the Cretaceous of Asia, Australia, and especially South America. Perhaps the most striking aspect of megaraptoran morphology is the large, robustly constructed forelimb that, in derived members of the clade, terminates in a greatly enlarged manus with hypertrophied, raptorial unguals on the medialmost two digits and a substantially smaller ungual on digit III. The unique forelimb anatomy of megaraptorans was presumably associated with distinctive functional specializations; nevertheless, its paleobiological significance has not been extensively explored. Here we draw from observations of the pectoral girdle and forelimb skeletons of Megaraptora and myological assessments of other archosaurian taxa to provide a comprehensive reconstruction of the musculature of this anatomical region in these singular theropods. Many muscle attachment sites on megaraptoran forelimb bones are remarkably well developed, which in turn suggests that the muscles themselves were functionally significant and important to the paleobiology of these theropods. Furthermore, many of these attachments became increasingly pronounced through megaraptoran evolutionary history, being substantially better developed in derived taxa such as Australovenator wintonensis and especially Megaraptor namunhuaiquii than in early branching forms such as Fukuiraptor kitadaniensis. When considered alongside previous range of motion hypotheses for Australovenator, our results indicate that megaraptorans possessed a morphologically and functionally specialized forelimb that was capable of complex movements. Notable among these were extensive extension and flexion, particularly in the highly derived manus, as well as enhanced humeral protraction, attributes that very probably aided in prey capture.

First definitive record of Abelisauridae (Theropoda: Ceratosauria) from the Cretaceous Bahariya Formation, Bahariya Oasis, Western Desert of Egypt.

Numerous non-avian theropod dinosaur fossils have been reported from the Upper Cretaceous (Cenomanian) Bahariya Formation, Bahariya Oasis, Western Desert of Egypt, but unambiguous materials of Abelisauridae have yet to be documented. Here we report Mansoura University Vertebrate Paleontology Center (MUVP) specimen 477, an isolated, well-preserved tenth cervical vertebra of a medium-sized abelisaurid from the Bahariya Formation. The new vertebra shows affinities with those of other Upper Cretaceous abelisaurids from Madagascar and South America, such as Majungasaurus crenatissimus, Carnotaurus sastrei, Viavenator exxoni and a generically indeterminate Patagonian specimen (Museo Padre Molina specimen 99). Phylogenetic analysis recovers the Bahariya form within Abelisauridae, either in a polytomy of all included abelisaurids (strict consensus tree) or as an early branching member of the otherwise South American clade Brachyrostra (50% majority rule consensus tree). MUVP 477, therefore, represents the first confirmed abelisaurid fossil from the Bahariya Formation and the oldest definitive record of the clade from Egypt and northeastern Africa more generally. The new vertebra demonstrates the wide geographical distribution of Abelisauridae across North Africa during the middle Cretaceous and augments the already extraordinarily diverse large-bodied theropod assemblage of the Bahariya Formation, a record that also includes representatives of Spinosauridae, Carcharodontosauridae and Bahariasauridae.

Subaqueous foraging among carnivorous dinosaurs.

Secondary aquatic adaptations evolved independently more than 30 times from terrestrial vertebrate ancestors1,2. For decades, non-avian dinosaurs were believed to be an exception to this pattern. Only a few species have been hypothesized to be partly or predominantly aquatic3-11. However, these hypotheses remain controversial12,13, largely owing to the difficulty of identifying unambiguous anatomical adaptations for aquatic habits in extinct animals. Here we demonstrate that the relationship between bone density and aquatic ecologies across extant amniotes provides a reliable inference of aquatic habits in extinct species. We use this approach to evaluate the distribution of aquatic adaptations among non-avian dinosaurs. We find strong support for aquatic habits in spinosaurids, associated with a marked increase in bone density, which precedes the evolution of more conspicuous anatomical modifications, a pattern also observed in other aquatic reptiles and mammals14-16. Spinosaurids are revealed to be aquatic specialists with surprising ecological disparity, including subaqueous foraging behaviour in Spinosaurus and Baryonyx, and non-diving habits in Suchomimus. Adaptation to aquatic environments appeared in spinosaurids during the Early Cretaceous, following their divergence from other tetanuran theropods during the Early Jurassic17.

An oviraptorid preserved atop an embryo-bearing egg clutch sheds light on the reproductive biology of non-avialan theropod dinosaurs.

Recent studies demonstrate that many avialan features evolved incrementally prior to the origin of the group, but the presence of some of these features, such as bird-like brooding behaviours, remains contentious in non-avialan dinosaurs. Here we report the first non-avialan dinosaur fossil known to preserve an adult skeleton atop an egg clutch that contains embryonic remains. The preserved positional relationship of the adult to the clutch, coupled with the advanced growth stages of the embryos and their high estimated incubation temperatures, provides strong support for the brooding hypothesis. Furthermore, embryos in the clutch are at different developmental stages, suggesting the presence of asynchronous hatching-a derived feature even among crown-group birds-in non-avialan theropods. These findings demonstrate that the evolution of reproductive biology along bird-line archosaurs was a complex rather than a linear and incremental process, and suggest that some aspects of non-avialan theropod reproduction were unique to these dinosaurs.

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

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.

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.

New mammalian and avian records from the late Eocene La Meseta and Submeseta formations of Seymour Island, Antarctica.

The middle-late Eocene of Antarctica was characterized by dramatic change as the continent became isolated from the other southern landmasses and the Antarctic Circumpolar Current formed. These events were crucial to the formation of the permanent Antarctic ice cap, affecting both regional and global climate change. Our best insight into how life in the high latitudes responded to this climatic shift is provided by the fossil record from Seymour Island, near the eastern coast of the Antarctic Peninsula. While extensive collections have been made from the La Meseta and Submeseta formations of this island, few avian taxa other than penguins have been described and mammalian postcranial remains have been scarce. Here, we report new fossils from Seymour Island collected by the Antarctic Peninsula Paleontology Project. These include a mammalian metapodial referred to Xenarthra and avian material including a partial tarsometatarsus referred to Gruiformes (cranes, rails, and allies). Penguin fossils (Sphenisciformes) continue to be most abundant in new collections from these deposits. We report several penguin remains including a large spear-like mandible preserving the symphysis, a nearly complete tarsometatarsus with similarities to the large penguin clade Palaeeudyptes but possibly representing a new species, and two small partial tarsometatarsi belonging to the genus Delphinornis. These findings expand our view of Eocene vertebrate faunas on Antarctica. Specifically, the new remains referred to Gruiformes and Xenarthra provide support for previously proposed, but contentious, earliest occurrence records of these clades on the continent.

An overview of the appendicular skeletal anatomy of South American titanosaurian sauropods, with definition of a newly recognized clade.

In the last two decades, the number of phylogenetically informative anatomical characters recognized in the appendicular skeleton of titanosaurian sauropod dinosaurs has increased dramatically with the discovery of new and comparatively complete specimens. Here we provide an overview of the appendicular skeletal morphology of South American titanosaurs and discuss its significance for phylogenetic reconstruction. The appendicular skeletal diversity of South American titanosaurs is substantially greater than was initially appreciated. Moreover, some regions of the appendicular skeleton, such as the pes, exhibit remarkable variability in form. Multiple synapomorphies of Titanosauria and the less inclusive clades Lithostrotia and Saltasauridae consist of characters of the girdles and limbs. Although the phylogenetic definitions of titanosaurian clades such as Saltasaurinae and Lognkosauria are stable, the taxonomic content of these clades has varied in recent analyses depending on the phylogenetic topology recovered. Within Titanosauria, the results of four recent, largely independent analyses support the existence of a derived titanosaurian lineage distinct from the 'Saltasaurinae line,' which is herein termed Colossosauria. At present, this clade is mainly comprised by taxa within Lognkosauria and Rinconsauria, and is useful in discussions of titanosaurian lower-level relationships.

An avian femur from the Late Cretaceous of Vega Island, Antarctic Peninsula: removing the record of cursorial landbirds from the Mesozoic of Antarctica.

In 2006, a partial avian femur (South Dakota School of Mines and Technology (SDSM) 78247) from the Upper Cretaceous (Maastrichtian) Sandwich Bluff Member of the López de Bertodano Formation of Sandwich Bluff on Vega Island of the northern Antarctic Peninsula was briefly reported as that of a cariamiform-a clade that includes extant and volant South American species and many extinct flightless and cursorial species. Although other authors have since rejected this taxonomic assignment, SDSM 78247 had never been the subject of a detailed description, hindering a definitive assessment of its affinities. Here we provide the first comprehensive description, illustration, and comparative study of this specimen. Comparison of characters that may be assessed in this femur with those of avian taxa scored in published character matrices refutes the inclusion of SDSM 78247 within Cariamiformes, instead supporting its assignment to a new, as-yet unnamed large-bodied species within the genus Vegavis, and therefore its referral to a clade of semiaquatic anseriforms. Important character states diagnostic of Vegavis + Polarornis include strong craniocaudal bowing of the femoral shaft, the presence of a distinct fossa just proximal to the fibular trochlea, and the broad and flat shape of the patellar sulcus. Referral to Vegavis is based on the presence of a distinctive proximocaudal fossa and distolateral scar. This genus was previously known only from Vegavis iaai, a smaller-bodied taxon from the same locality and stratigraphic unit. Our reassignment of SDSM 78247 to Vegavis sp. removes the record of cariamiform landbirds from the Antarctic Cretaceous.

An Early Cretaceous enantiornithine (Aves) preserving an unlaid egg and probable medullary bone.

Understanding non-crown dinosaur reproduction is hindered by a paucity of directly associated adults with reproductive traces. Here we describe a new enantiornithine, Avimaia schweitzerae gen. et sp. nov., from the Lower Cretaceous Xiagou Formation with an unlaid egg two-dimensionally preserved within the abdominothoracic cavity. Ground-sections reveal abnormal eggshell proportions, and multiple eggshell layers best interpreted as a multi-layered egg resulting from prolonged oviductal retention. Fragments of the shell membrane and cuticle are both preserved. SEM reveals that the cuticle consists of nanostructures resembling those found in neornithine eggs adapted for infection-prone environments, which are hypothesized to represent the ancestral avian condition. The femur preserves small amounts of probable medullary bone, a tissue found today only in reproductively active female birds. To our knowledge, no other occurrence of Mesozoic medullary bone is associated with indications of reproductive activity, such as a preserved egg, making our identification unique, and strongly supported.

New Egyptian sauropod reveals Late Cretaceous dinosaur dispersal between Europe and Africa.

Prominent hypotheses advanced over the past two decades have sought to characterize the Late Cretaceous continental vertebrate palaeobiogeography of Gondwanan landmasses, but have proved difficult to test because terrestrial vertebrates from the final ~30 million years of the Mesozoic are extremely rare and fragmentary on continental Africa (including the then-conjoined Arabian Peninsula but excluding the island of Madagascar). Here we describe a new titanosaurian sauropod dinosaur, Mansourasaurus shahinae gen. et sp. nov., from the Upper Cretaceous (Campanian) Quseir Formation of the Dakhla Oasis of the Egyptian Western Desert. Represented by an associated partial skeleton that includes cranial elements, Mansourasaurus is the most completely preserved land-living vertebrate from the post-Cenomanian Cretaceous (~94-66 million years ago) of the African continent. Phylogenetic analyses demonstrate that Mansourasaurus is nested within a clade of penecontemporaneous titanosaurians from southern Europe and eastern Asia, thereby providing the first unambiguous evidence for a post-Cenomanian Cretaceous continental vertebrate clade that inhabited both Africa and Europe. The close relationship of Mansourasaurus to coeval Eurasian titanosaurians indicates that terrestrial vertebrate dispersal occurred between Eurasia and northern Africa after the tectonic separation of the latter from South America ~100 million years ago. These findings counter hypotheses that dinosaur faunas of the African mainland were completely isolated during the post-Cenomanian Cretaceous.

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

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.

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.

A gigantic, exceptionally complete titanosaurian sauropod dinosaur from southern Patagonia, Argentina.

Titanosaurian sauropod dinosaurs were the most diverse and abundant large-bodied herbivores in the southern continents during the final 30 million years of the Mesozoic Era. Several titanosaur species are regarded as the most massive land-living animals yet discovered; nevertheless, nearly all of these giant titanosaurs are known only from very incomplete fossils, hindering a detailed understanding of their anatomy. Here we describe a new and gigantic titanosaur, Dreadnoughtus schrani, from Upper Cretaceous sediments in southern Patagonia, Argentina. Represented by approximately 70% of the postcranial skeleton, plus craniodental remains, Dreadnoughtus is the most complete giant titanosaur yet discovered, and provides new insight into the morphology and evolutionary history of these colossal animals. Furthermore, despite its estimated mass of about 59.3 metric tons, the bone histology of the Dreadnoughtus type specimen reveals that this individual was still growing at the time of death.

Melanosomes or microbes: testing an alternative hypothesis for the origin of microbodies in fossil feathers.

Microbodies associated with fossil feathers, originally attributed to microbial biofilm, have been reinterpreted as melanosomes: pigment-containing, eukaryotic organelles. This interpretation generated hypotheses regarding coloration in non-avian and avian dinosaurs. Because melanosomes and microbes overlap in size, distribution and morphology, we re-evaluate both hypotheses. We compare melanosomes within feathers of extant chickens with patterns induced by microbial overgrowth on the same feathers, using scanning (SEM), field emission (FESEM) and transmission (TEM) electron microscopy. Melanosomes are always internal, embedded in a morphologically distinct keratinous matrix. Conversely, microbes grow across the surface of feathers in continuous layers, more consistent with published images from fossil feathers. We compare our results to both published literature and new data from a fossil feather ascribed to Gansus yumenensis (ANSP 23403). 'Mouldic impressions' were observed in association with both the feather and sediment grains, supporting a microbial origin. We propose criteria for distinguishing between these two microbodies.

A new large-bodied oviraptorosaurian theropod dinosaur from the latest Cretaceous of western North America.

The oviraptorosaurian theropod dinosaur clade Caenagnathidae has long been enigmatic due to the incomplete nature of nearly all described fossils. Here we describe Anzu wyliei gen. et sp. nov., a new taxon of large-bodied caenagnathid based primarily on three well-preserved partial skeletons. The specimens were recovered from the uppermost Cretaceous (upper Maastrichtian) Hell Creek Formation of North and South Dakota, and are therefore among the stratigraphically youngest known oviraptorosaurian remains. Collectively, the fossils include elements from most regions of the skeleton, providing a wealth of information on the osteology and evolutionary relationships of Caenagnathidae. Phylogenetic analysis reaffirms caenagnathid monophyly, and indicates that Anzu is most closely related to Caenagnathus collinsi, a taxon that is definitively known only from a mandible from the Campanian Dinosaur Park Formation of Alberta. The problematic oviraptorosaurs Microvenator and Gigantoraptor are recovered as basal caenagnathids, as has previously been suggested. Anzu and other caenagnathids may have favored well-watered floodplain settings over channel margins, and were probably ecological generalists that fed upon vegetation, small animals, and perhaps eggs.

A nearly modern amphibious bird from the Early Cretaceous of northwestern China.

Three-dimensional specimens of the volant fossil bird Gansus yumenensis from the Early Cretaceous Xiagou Formation of northwestern China demonstrate that this taxon possesses advanced anatomical features previously known only in Late Cretaceous and Cenozoic ornithuran birds. Phylogenetic analysis recovers Gansus within the Ornithurae, making it the oldest known member of the clade. The Xiagou Formation preserves the oldest known ornithuromorph-dominated avian assemblage. The anatomy of Gansus, like that of other non-neornithean (nonmodern) ornithuran birds, indicates specialization for an amphibious life-style, supporting the hypothesis that modern birds originated in aquatic or littoral niches.

An abelisaurid from the Late Cretaceous of Egypt: implications for theropod biogeography.

Recent paleogeographic scenarios postulate the isolation of continental Africa during the Late Cretaceous. The absence of abelisaurid theropods from Upper Cretaceous African strata was offered as support of hypothesized African isolation with the acknowledgement that the paucity of African abelisaurids may be mostly an issue of sampling. Here we report on a shed theropod tooth from the Upper Cretaceous (Maastrichtian, approximately 70 Ma) Duwi Formation of Egypt. The tooth was referred to the Malagasy abelisaurid "Megalosaurus" crenatissimus (=Majungasaurus crenatissimus) in 1921. A discriminant function analysis was run to test for morphological congruence between the Egyptian tooth and the dentitions of 24 theropod taxa. The analysis correctly classified 96.6% of the teeth in the sample and assigned the tooth to Majungasaurus. As current paleogeographic reconstructions posit Madagascar had attained its current position relative to Africa before the Late Cretaceous, it is unlikely that the Egyptian tooth actually pertains to Majungasaurus. Nevertheless, its classification as an abelisaurid supports its referral to the clade. This tooth thus constitutes defensible evidence of an abelisaurid from the post-Cenomanian Cretaceous of mainland Africa. Combined with recent discoveries of abelisaurids in Niger and Morocco, the result indicates that Abelisauridae was a diverse group in Africa during the Cretaceous, existing in multiple places for at least approximately 25 Ma and weakens support for hypotheses of an isolated Africa during the Late Cretaceous.