Paleogene insects: fossil discoveries illuminating post-extinction terrestrial ecosystems

Dinosaurs were ubiquitous in terrestrial ecosystems through most of the Mesozoic and are still diversely represented in the modern fauna in the form of birds. Recent efforts to better understand the origins of the group have resulted in the discovery of many new species of early dinosaur and their closest relatives (dinosauromorphs). In addition, recent re‐examinations of early dinosaur phylogeny have highlighted uncertainties regarding the interrelationships of the main dinosaur lineages (Sauropodomorpha, Theropoda and Ornithischia), and questioned the traditional hypothesis that the group originated in South Gondwana and gradually dispersed over Pangaea. Here, we use an historical approach to examine the impact of new fossil discoveries and changing phylogenetic hypotheses on biogeographical scenarios for dinosaur origins over 20 years of research time, and analyse the results in the light of different fossil record sampling regimes. Our results consistently optimize South Gondwana as the ancestral area for Dinosauria, as well as for more inclusive clades including Dinosauromorpha, and show that this hypothesis is robust to increased taxonomic and geographic sampling and divergent phylogenetic results. Our results do not find any support for the recently proposed Laurasian origin of dinosaurs and suggest that a southern Gondwanan origin is by far the most plausible given our current knowledge of the diversity of early dinosaurs and non‐dinosaurian dinosauromorphs.

<p indent=0mm>The shift from the Paleogene to the Neogene represents an important timeline in the history of life on Earth: A point when the biotic realm approached that of nature today. The uplift of the Tibetan Plateau in the Cenozoic Era has imposed profound influence on the evolution of the terrestrial ecosystem by creating a sustainable life system in a freezing climate. A reconstruction of this epic scene on the plateau relies on fossil discoveries. Based on a recent study of numerous well-preserved fossils from the Paleogene and Neogene deposits of the Lunpola and Nima basins in the central Tibetan Plateau, we recognized therein, for the first time, the turnover of the Late Oligocene tropical or subtropical ecosystem, and the subsequent transition toward a plateau-type biotic assemblage during the Early Miocene epoch. The fossil biota consisting of fishes, insects and plants from the Upper Oligocene suggests that in 26−24 Ma, the hinterland of the Tibetan Plateau was a warm and humid lowland nourished by tropical moisture from the Indian Ocean, which would have been able to reach northern Tibet then. This biota, represented by climbing perches and palms, shows typical tropical or subtropical climatic patterns and maintained a paleoelevation no higher than <sc>2300 m</sc> in the depositional areas. In the Early Miocene, the Tibetan ecosystem underwent comprehensive transformation into the one we recognize today. Primitive snow carps, which are endemic to the plateau today, emerged and, in an “Ascending with the Modifications” mode, evolved into more and more specialized species all the way up until the Pliocene epoch. The vegetation of the Early Miocene was dominated by temperate broad-leaved forests mixed with abundant coniferous trees and booming herbs, hence showing a cool climatic setting. Some mammals adapted to the temperate forest, e.g., <italic>Plesiaceratherium</italic> (a kind of extinct rhinos), appeared at the center of the plateau during the Early Miocene, and gave way to the ancestors of the Ice Age mammals, e.g., the woolly rhino of the Pliocene epoch. Such a dramatic transformation of the Tibetan ecosystem around the Paleogene and Neogene boundary was due to the cooling-down effect accompanying the rise of the main body of the plateau to ca. <sc>3000 m</sc> and the global climate evolution toward icehouse conditions during the Cenozoic.

Twelve new dinosaur teeth have recently been recovered from three localities in the Upper Cretaceous Nenjiang Formation of the Songliao Basin. Although fragmentary, the material offers enough evidence to identify the following taxa: tyrannosaurids, dromaeosaurines, velociraptorines, hadrosauroids, and titanosaurs. In addition to the previously known dinosaurs from the basin, several new ones have been identified, extending the paleogeographic range of related taxa. The discovery of these new fossil remains provides valuable insights into dinosaur diversity and sheds light on the terrestrial ecosystem during the Late Cretaceous in the Songliao Basin.

Sedimentology and depositional environments of the Red Sandstone Group, Rukwa Rift Basin, southwestern Tanzania: New insight into Cretaceous and Paleogene terrestrial ecosystems and tectonics in sub-equatorial Africa

Amber inclusions from New Zealand

New Caledonia was, until recently, considered an old continental island harbouring a rich biota with outstanding Gondwanan relicts. However, deep marine sedimentation and tectonic evidence suggest complete submergence of the island during the latest Cretaceous to the Paleocene. Molecular phylogenies provide evidence for some deeply-diverging clades that may predate the Eocene and abundant post-Oligocene colonisation events. Extinction and colonization biases, as well as survival of some groups in refuges on neighbouring paleo-islands, may have obscured biogeographic trends over long time scales. Fossil data are therefore crucial for understanding the history of the New Caledonian biota, but occurrences are sparse and have received only limited attention. Here we describe five exceptional fossil assemblages that provide important new insights into New Caledonia’s terrestrial paleobiota from three key time intervals: prior to the submersion of the island, following re-emergence, and prior to Pleistocene climatic shifts. These will be of major importance for elucidating changes in New Caledonia’s floristic composition over time.

In modern terrestrial ecosystems, the population size of large predators is low, and a similar pattern has usually been assumed for dinosaurs. However, fossil finds of monospecific, large theropod accumulations suggest that population dynamics were more complex. Here, we report two Early Cretaceous tracksites dominated by large theropod footprints, in Querulpa Chico (Peru) and Chacarilla (Chile). The two sites correspond to distinct depositional environments—tidal basin/delta (Querulpa Chico) and meandering river (Chacarilla)—with both subject to extensive arid or semiarid palaeoclimatic conditions. Although most trackways show no preferred orientation, a clear relationship between two trackmakers is observed in one instance. This observation, coupled with the high abundance of trackways belonging to distinct large theropods, and the exclusion of tracks of other animals, suggests some degree of grouping behaviour. The presence of freshwater sources in a dry climate and perhaps social behaviour such as pai...

The Early Cretaceous of northwest China has yielded abundant vertebrates, invertebrates, and plant fossils from numerous intermontane basins. Developing a chronostratigraphic context for these important fossil finds is important to understanding the development of modern terrestrial ecosystems, the evolution of dinosaurs, and the Cretaceous greenhouse climate. This study utilizes carbon isotope chemostratigraphy of the fossil-rich Xinminpu Group in the Yujingzi Basin in northwest Gansu Province. Lithostratigraphic descriptions defined three facies. The lowest is a tan, coarse arkosic sandstone, overlain by gray to variegated mudstones, sandstones, and thin limestones, which transition to red sandstones, conglomerates, and mudstones. Depositional environment interpretation of these lithofacies assisted in refining 450 samples of bulk sedimentary organic carbon as well as charcoal samples to develop a composite curve to correlate to existing carbon isotope curves from the region and to better constrained Cretaceous sections globally. The carbon isotope curve is correlated based on the broad positive excursion associated with carbon isotope fluctuations of the Paquier Episode that spans the late Aptian to early Albian. Based on this correlation, the middle gray mudstone facies, which contains a diverse fauna including theropods, sauropods, and ornithopods, as well as turtles and invertebrates, is placed within the upper Aptian. The upper red sandstone facies, which contains therizinosaurs and the ceratopsian dinosaur Auroraceratops, is placed in the lower Albian.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Suarez, M. B., T. Milder, P. Nan, C. A. Suarez, H. You, D. Li, and P. Dodson 2019. Chemostratigraphy of the Lower Cretaceous dinosaur-bearing Xiagou and Zhonggou formations, Yujingzi Basin, northwest China; pp. 12–21 in Hailu You, Peter Dodson, and Eric Morschhauser (eds.), Auroraceratops rugosus (Ornithischia, Ceratopsia) from the Early Cretaceous of northwestern Gansu Province, China. Society of Vertebrate Paleontology Memoir 18. Journal of Vertebrate Paleontology 38(Supplement). DOI: 10.1080/02724634.2017.1510412.