Body size evolution in Titanosauriformes (Sauropoda, Macronaria).

Titanosauriformes is a conspicuous and diverse group of sauropod dinosaurs that inhabited almost all land masses during Cretaceous times. Besides the diversity of forms, the clade comprises one of the largest land animals found so far, Argentinosaurus, as well as some of the smallest sauropods known to date, Europasaurus and Magyarosaurus. They are therefore good candidates for studies on body size trends such as the Cope's rule, the tendency towards an increase in body size in an evolutionary lineage. We used statistical methods to assess body size changes under both phylogenetic and nonphylogenetic approaches to identify body size trends in Titanosauriformes. Femoral lengths were collected (or estimated from humeral length) from 46 titanosauriform species and used as a proxy for body size. Our findings show that there is no increase or decrease in titanosauriform body size with age along the Cretaceous and that negative changes in body size are more common than positive ones (although not statistically significant) for most of the titanosauriform subclades (e.g. Saltasaridae, Lithostrotia, Titanosauria and Somphospondyli). Therefore, Cope's rule is not supported in titanosauriform evolution. Finally, we also found a trend towards a decrease of titanosauriform mean body size coupled with an increase in body size standard deviation, both supporting an increase in body size variation towards the end of Cretaceous.

New specimens of Baurutitan britoi and a taxonomic reassessment of the titanosaur dinosaur fauna (Sauropoda) from the Serra da Galga Formation (Late Cretaceous) of Brazil.

The description of new titanosaur specimens unearthed from deposits of the Serra da Galga Formation (Bauru Group, Late Cretaceous) at the BR-262 site, near Peirópolis (Uberaba, Minas Gerais State, Brazil), sheds light on the taxonomy of two taxa previously known from the same area and geological unit: Baurutitan britoi and Trigonosaurus pricei. A comparative revision indicates that T. pricei represents a junior synonym of Ba. britoi, and that the BR-262 specimens belong to that latter species. The information provided by the new specimens also revealed that the paratype of T. pricei (MCT 1719-R), a caudal vertebral series, actually represents a new taxon, named here as Caieiria allocaudata gen. et sp. nov.

Comparative Three-Dimensional Moment Arm Analysis of the Sauropod Forelimb: Implications for the Transition to a Wide-Gauge Stance in Titanosaurs.

The evolution of extraordinarily large size among Sauropoda was associated with a number of biomechanical adaptations. Changes in muscle moment arms undoubtedly accompanied these adaptations, but since muscles rarely fossilize, our ability to understand them has been restricted. Here, we use three-dimensional (3D) musculoskeletal modeling to reconstruct and quantitatively assess leverage of forelimb muscles in the transition from the narrow-gauge stance of basal sauropods to a wide-gauge stance in titanosaurs. A comparative analysis is conducted on three neosauropods: the narrow-gauge diplodocid Apatosaurus louisae, the intermediate-gauge titanosariform Giraffatitan brancai, and the wide-gauge titanosaur Diamantinasaurus matildae. In this study, moment arm magnitudes and corresponding morphological evidence indicates multiple changes across the narrow-gauge to wide-gauge transition in sauropods. High shoulder adduction was found in Diamantinasaurus, suggesting functional changes for supporting a wider stance and a limb less aligned with ground reaction force. High leverage in shoulder extension of Diamantinasaurus and Giraffatitan is possibly related to the increased use of the forelimb in forward propulsion with an anterior shift in center of mass. In addition, the prominence of the olecranon process in Diamantinasaurus produced high moment arm leverage in elbow flexion and extension, suggesting titanosaurs might have maintained a more flexed forelimb posture and displayed an increased degree of maneuverability. Other results are more variable between taxa but still indicate smaller scale changes. A sensitivity analysis was also conducted to measure the reliability of our models and test specific uncertainties within the modeling process, as well as other uncertainties uncovered during analysis. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:794-817, 2019. © 2018 Wiley Periodicals, Inc.

What do giant titanosaur dinosaurs and modern Australasian megapodes have in common?

Titanosauria is a globally distributed clade of sometimes extremely large Mesozoic herbivorous sauropod dinosaurs. On the basis of current evidence these giant dinosaurs seem to have reproduced in specific and localized nesting sites. However, no investigations have been performed to understand the possible ecological and geological biases that acted for the selection of these nesting sites worldwide. In this study, observations were performed on the best-known Cretaceous nesting sites around the world. Our observations strongly suggest their eggs were incubated with environmental sources of heat, in burial conditions. Taking into account the clutch composition and geometry, the nature and properties of the sediments, the eggshells' structures and conductance, it would appear that titanosaurs adopted nesting behaviors comparable to the modern Australasian megapodes, using burrow-nesting in diverse media and mound-building strategies.