New giant carnivorous dinosaur reveals convergent evolutionary trends in theropod arm reduction.

Giant carnivorous dinosaurs such as Tyrannosaurus rex and abelisaurids are characterized by highly reduced forelimbs that stand in contrast to their huge dimensions, massive skulls, and obligate bipedalism.1,2 Another group that follows this pattern, yet is still poorly known, is the Carcharodontosauridae: dominant predators that inhabited most continents during the Early Cretaceous3-5 and reached their largest sizes in Aptian-Cenomanian times.6-10 Despite many discoveries over the last three decades, aspects of their anatomy, especially with regard to the skull, forearm, and feet, remain poorly known. Here we report a new carcharodontosaurid, Meraxes gigas, gen. et sp. nov., based on a specimen recovered from the Upper Cretaceous Huincul Formation of northern Patagonia, Argentina. Phylogenetic analysis places Meraxes among derived Carcharodontosauridae, in a clade with other massive South American species. Meraxes preserves novel anatomical information for derived carcharodontosaurids, including an almost complete forelimb that provides evidence for convergent allometric trends in forelimb reduction among three lineages of large-bodied, megapredatory non-avian theropods, including a remarkable degree of parallelism between the latest-diverging tyrannosaurids and carcharodontosaurids. This trend, coupled with a likely lower bound on forelimb reduction, hypothesized to be about 0.4 forelimb/femur length, combined to produce this short-armed pattern in theropods. The almost complete cranium of Meraxes permits new estimates of skull length in Giganotosaurus, which is among the longest for theropods. Meraxes also provides further evidence that carchardontosaurids reached peak diversity shortly before their extinction with high rates of trait evolution in facial ornamentation possibly linked to a social signaling role.

A new long-spined dinosaur from Patagonia sheds light on sauropod defense system.

Dicraeosaurids are a group of sauropod dinosaurs characterized by a distinctive vertebral column with paired, long, neural spines, present in an extreme fashion in the South American form Amargasaurus cazaui. This distinctive morphology has been interpreted as a support structure for a thermoregulatory sail, a padded crest for display, a dorsal hump acting as fat reservoir, and even as inner cores for dorsal horns. Other inferred functions (if any) of this structure were related to sexual display and/or defense strategies. Here we describe a new dicraeosaurid sauropod, Bajadasaurus pronuspinax gen. et sp. nov., from Patagonia which preserves the most complete skull of the group and has extremely elongate bifid cervical neural spines that point permanently forward, irrespective of the neck position. Although much shorter versions of this neural spine configuration were already recorded for other dicraeosaurid taxa, the long, anteriorly bent spines of this new dinosaur support the hypothesis that these elongate spines of dicraeosaurid sauropods served as passive defense structures.

A diplodocid sauropod survivor from the early cretaceous of South America.

Diplodocids are by far the most emblematic sauropod dinosaurs. They are part of Diplodocoidea, a vast clade whose other members are well-known from Jurassic and Cretaceous strata in Africa, Europe, North and South America. However, Diplodocids were never certainly recognized from the Cretaceous or in any other southern land mass besides Africa. Here we report a new sauropod, Leikupal laticauda gen. et sp. nov., from the early Lower Cretaceous (Bajada Colorada Formation) of Neuquén Province, Patagonia, Argentina. This taxon differs from any other sauropod by the presence of anterior caudal transverse process extremely developed with lateroventral expansions reinforced by robust dorsal and ventral bars, very robust centroprezygapophyseal lamina in anterior caudal vertebra and paired pneumatic fossae on the postzygapophyses in anterior-most caudal vertebra. The phylogenetic analyses support its position not only within Diplodocidae but also as a member of Diplodocinae, clustering together with the African form Tornieria, pushing the origin of Diplodocoidea to the Middle Jurassic or even earlier. The new discovery represents the first record of a diplodocid for South America and the stratigraphically youngest record of this clade anywhere.

Tunasniyoj, a dinosaur tracksite from the Jurassic-Cretaceous boundary of Bolivia.

Here we report a superbly preserved and profusely represented five-ichnotaxa dinosaur track assemblage near Icla village, 100 km southeast of Sucre, Bolivia. As preserved in reddish Jurassic-Cretaceous boundary aeolian sandstones, this rich and uncommon assemblage is, additionally, the oldest dinosaur tracksite for Bolivia. Four trackmakers were identified in the area: three quadrupedal and one bipedal, all of them with tracks of around 35 cm in lenght. One of the quadrupedals is represented by no less than five adult individuals (ichnotaxon A), and four purported juveniles (ichnotaxon B) walking in association. The other two quadrupedals (ichnotaxa C and D) involve four trackways, and the last, the bipedal trackmaker (ichnotaxon E), is represented by one trackway. The five ichnotaxa represented in the "Palmar de Tunasniyoj" could be tentatively assigned to the following trackmakers: Ichnotaxa A and B are assigned to basal stegosaurians; ichnotaxon C to a basal tyreophoran, perhaps related to the ankylosaur lineage; ichnotaxon D to the Ankylosauria, and ichnotaxon E to Theropoda. The Tunasniyoj assemblage, the oldest dinosaur tracksite for Bolivia, includes the oldest known evidence assigned to ankylosaurs and stegosaurs for South America.

Notes on the axial skeleton of the titanosaur Bonitasaura salgadoi (Dinosauria-Sauropoda)

Sauropod axial anatomy is particularly important in understanding morphological features and phylogenetic analyses. Spatial arrangement of zygapophyses and rib articulations, as well as their complex laminar development, help to recognize the relative position of isolated vertebral elements. The presence of anterior, mid and posterior elements along the cervical, dorsal and caudal series in Bonitasaura salgadoi allows the analysis of several anatomical characteristics. These include the pattern of neurocentral closure with unfused, partially fused and completely fused elements in a peculiar temporal sequence, as well as several neural spine modifications and the laminar arrangement. The variations in neural spine morphology include a lateral expansion of the distal tip in cervico-dorsal region, different lateral constituents of these lateral expansions, and a marked deviation in spine angulation. The spinal inclination allows the division into three easily recognizable vertebral regions separated by two landmarks, which adds support in the determination of an accurate vertebral position for isolated elements. Finally, an analysis of the vertebral laminae reveals the importance of examining vertebral series in order to recognize laminar homologies and developmental series. Two vertebral laminae are analyzed here.

A anatomia axial dos saurópodes compõe um conjunto dedados fundamentais para a caracterização morfológica dostáxons, bem como para a determinação de suas relações filogenéticas. A disposição espacial das zigapófises e articulações das costelas, assim como de seu complexo de lâminas acessórias, auxiliam no reconhecimento da posição relativa de elementos vertebrais isolados. A preservação de vértebras anteriores, médias e posteriores nas séries cervical, dorsal e caudal de Bonitasaura salgadoi permite a análise de características adicionais diagnósticas observadas ao longo das séries vertebrais. Estas incluem o grau de fusão da sutura neurocentral,havendo elementos livres, parcialmente fundidos a completamente fundidos em uma sequência temporal peculiar, assim como a presença de diversas modificações do espinho neural e a disposição laminar. As variações na morfologia do espinho neural incluem uma expansão lateral em seu ápice distal na região cervico-dorsal, outros componentes laterais distintos destas expansões, e um desvio crânio-caudal marcado pela angulação do espinho neural. A inclinação espinal permite a divisão em três segmentos vertebrais reconhecíveis separados por duas linhas de transição. Finalmente, a análise das lâminas vertebrais revela a importância de examinar a série vertebral a fim de reconhecer homologias nas lâminas e nas séries de desenvolvimento. Neste trabalho são analisadas duas lâminas vertebrais.

Tunasniyoj, a dinosaur tracksite from the Jurassic-Cretaceous boundary of Bolivia

Here we report a superbly preserved and profusely represented five-ichnotaxa dinosaur track assemblage near Icla village, 100 km southeast of Sucre, Bolivia. As preserved in reddish Jurassic-Cretaceous boundary aeolian sandstones, this rich and uncommon assemblage is, additionally, the oldest dinosaur tracksite for Bolivia. Four trackmakers were identified in the area: three quadrupedal and one bipedal, all of them with tracks of around 35 cm in lenght. One of the quadrupedals is represented by no less than five adult individuals (ichnotaxon A), and four purported juveniles (ichnotaxon B) walking in association. The other two quadrupedals (ichnotaxa C and D) involve four trackways, and the last, the bipedal trackmaker (ichnotaxon E), is represented by one trackway. The five ichnotaxa represented in the "Palmar de Tunasniyoj" could be tentatively assigned to the following trackmakers: Ichnotaxa A and B are assigned to basal stegosaurians; ichnotaxon C to a basal tyreophoran, perhaps related to the ankylosaur lineage; ichnotaxon D to the Ankylosauria, and ichnotaxon E to Theropoda. The Tunasniyoj assemblage, the oldest dinosaur tracksite for Bolivia, includes the oldest known evidence assigned to ankylosaurs and stegosaurs for South America.

Neste estudo é relatado um conjunto magnificamente preservado de pistas de dinossauros representados por cinco táxons distintos, situado próximo à Vila de Icla, 100 quilômetros a sudeste do Sucre, Bolívia. Preservados em arenitos eólicos avermelhados do limite Jurássico-Cretáceo. Quatro formas geradoras foram identificadas na área, sendo três quadrúpedes e um bípede, todos com as pegadas com cerca de 35 cm de comprimento. Um dos quadrúpedes (trilhas tipos A e B) é representado por pelo menos seis indivíduos em dois grupos de três, com adultos e juvenis juntos. Os outros dois quadrúpedes (trilhas tipos C e D) são geradores de quatro trilhas, e um gerador bípede (trilha E), é representado por uma trilha. Os quatro icnotáxons representados em "Palmar de Tunasniyoj", podem provisoriamente ser atribuídos aos seguintes geradores: Icnotáxon A e B são atribuídos a estegossauros basais. Icnotáxon C a um tireóforo basal, talvez relacionado à linhagem dos anquilossauros. Icnotáxon D aos Ankylosauria; e icnotáxon E a Theropoda. Este raro e belo conjunto de trilhas de dinossauros de Tunasniyoj, representa ainda a icnocenose mais antiga de dinossauros da Bolívia. Além disso, inclui a mais antiga evidência conhecida atribuída a anquilossauros e estegossauros para América do sul.

Notes on the axial skeleton of the titanosaur Bonitasaura salgadoi (Dinosauria-Sauropoda).

Sauropod axial anatomy is particularly important in understanding morphological features and phylogenetic analyses. Spatial arrangement of zygapophyses and rib articulations, as well as their complex laminar development, help to recognize the relative position of isolated vertebral elements. The presence of anterior, mid and posterior elements along the cervical, dorsal and caudal series in Bonitasaura salgadoi allows the analysis of several anatomical characteristics. These include the pattern of neurocentral closure with unfused, partially fused and completely fused elements in a peculiar temporal sequence, as well as several neural spine modifications and the laminar arrangement. The variations in neural spine morphology include a lateral expansion of the distal tip in cervico-dorsal region, different lateral constituents of these lateral expansions, and a marked deviation in spine angulation. The spinal inclination allows the division into three easily recognizable vertebral regions separated by two landmarks, which adds support in the determination of an accurate vertebral position for isolated elements. Finally, an analysis of the vertebral laminae reveals the importance of examining vertebral series in order to recognize laminar homologies and developmental series. Two vertebral laminae are analyzed here.