The last dinosaurs of Brazil: The Bauru Group and its implications for the end-Cretaceous mass extinction

ABSTRACT The non-avian dinosaurs died out at the end of the Cretaceous, ~66 million years ago, after an asteroid impact. The prevailing hypothesis is that the effects of the impact suddenly killed the dinosaurs, but the poor fossil record of latest Cretaceous (Campanian-Maastrichtian) dinosaurs from outside Laurasia (and even more particularly, North America) makes it difficult to test specific extinction scenarios. Over the past few decades, a wealth of new discoveries from the Bauru Group of Brazil has revealed a unique window into the evolution of terminal Cretaceous dinosaurs from the southern continents. We review this record and demonstrate that there was a diversity of dinosaurs, of varying body sizes, diets, and ecological roles, that survived to the very end of the Cretaceous (Maastrichtian: 72-66 million years ago) in Brazil, including a core fauna of titanosaurian sauropods and abelisaurid and carcharodontosaurid theropods, along with a variety of small-to-mid-sized theropods. We argue that this pattern best fits the hypothesis that southern dinosaurs, like their northern counterparts, were still diversifying and occupying prominent roles in their ecosystems before the asteroid suddenly caused their extinction. However, this hypothesis remains to be tested with more refined paleontological and geochronological data, and we give suggestions for future work.

Plate motions, Gondwana Dinosaurs, Noah's Arks, Beached Viking Funeral Ships, Ghost Ships, and Landspans

Gondwana landmasses have served as large-scale biogeographic Noah's Arks and Beached Viking Funeral Ships, as defined by McKenna. The latitudinal trajectories of selected Gondwana dinosaur localities were traced through time in order to evaluate their movement through climate zones relative to those in which they originally formed. The dispersal of fauna during the breakup of Gondwana may have been facilitated by the presence of offshelf islands forming landspans (sensu Iturralde-Vinent and MacPhee) in the Equatorial Atlantic Gateway and elsewhere.

As massas de terra do Gondwana serviram como Arcas de Noe biogeograficas de grande escala e Navios Funerarios Vikings encalhados, conforme definido por McKenna. As trajetorias latitudinais de areas selecionadas de dinossauros do Gondwana foram tracadas ao longo do tempo a fim de avaliar seu movimento atraves de zonas climaticas relativas aquelas nas quais elas foram originalmente formadas. A dispersao da fauna durante a quebra do Gondwana pode ter sido facilitada pela presenca de ilhas oceanicas formando extensoes de terra (sensu Iturralde-Vinent e MacPhee) na entrada do Atlantico Equatorial e em outros lugares.

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.