Antoine Bercovici is a Peter Buck postdoctoral fellow in the Department of Paleobiology at the National Museum of Natural History. Here, he reports on a July field expedition to southern France.
In three recent posts I reported on a lengthy field expedition into the Hell Creek Formation of North Dakota and Montana to learn more about the last American dinosaurs and the ecosystem they were part of. The Hell Creek Formation rocks record a very important time in Earth history, representing the last 1.3 million years of the age of the dinosaurs, up to their demise at the Cretaceous–Paleogene (K–Pg) boundary. Triggered by the impact of an asteroid the size of Washington DC in the Yucatan Peninsula, the K–Pg mass extinction was a major, global event. But were Late Cretaceous terrestrial ecosystems outside of North America comparable, and were they affected by the extinction in the same way?
Most of what we know about the end of the Cretaceous and the extinction of the dinosaurs comes from research in North America (USA and Canada). This pie-chart summarizes the amount of scientific data we currently have on terrestrial ecosystems across the K–Pg boundary, worldwide. Click diagram to zoom. From Vajda, V., Bercovici, A. (2014).
Answering this question led me back to my home country to join fellow French colleagues who have been digging in Provence (southern France) for many years, making major paleontological discoveries, including several new dinosaur species. Thierry Tortosa, curator for the Natural Reserve of the Montagne Sainte Victoire (Bouches du Rhône Departmental Council), leads expeditions from the Aix en Provence Natural History Museum. The Natural Reserve is surrounded by outcrops of Late Cretaceous Rocks. Isabelle Cojan, sedimentologist at the Paris School of Mines, helped us with her tremendous knowledge of the geology of the area, and I was also accompanied by sedimentologist David Fastovsky from the University of Rhodes Island, who has worked on the dinosaur extinction in North America for the past thirty years. Our main goal was to better understand the environments in which the Late Cretaceous sediments were deposited, which in turn would allow us to depict the landscape in which the Provence dinosaurs lived in. We also sought to find fossil pollen and spores, which could be used to describe the vegetation present at that time.
The French painter Paul Cézanne, from Aix en Provence, was inspired by the Montagne Sainte Victoire (inset). My colleagues and I are trying to paint a rendition of what this landscape looked like 70 million years ago. Click to zoom. Painting is in the public domain.
During the Late Cretaceous, North America was split in its center by an inland sea, the Western Interior Seaway, surrounded by widespread deltaic floodplains and lowlands that would later form some of the most fossiliferous bone beds on the planet. Meanwhile, Europe was also very different from what it is now, consisting of multiple small islands scattered across a vast, shallow carbonate platform of marine sediments, comparable to today's Bahamas. Southern France was part of the emerged land, where deposits of red claystones represented ancient coastal plains and forest.
This paleogeographic map shows the arrangement of continents and seas 66 million years ago, at the very end of the Cretaceous. Each dot represent a terrestrial K–Pg site, corresponding to the pie chart above.Click map to zoom. From Vajda, V., Bercovici, A. (2014)
Above, left: Behind a vineyard, an outcrop of red claystone show some color variations and banding, representing a sequence of stacked floodplain deposits and paleosols (ancient soils). Right: Isabelle and David are prospecting for fossils in the Cretaceous redbeds that were once coastal plains roamed by dinosaurs. Click photos to zoom.
These red deposits are very fossiliferous. The most common finds are dinosaur egg shells, to the point that some paleontologists refer to the Aix en Provence area as "Eggs en Provence". Little shards of eggs are very common, but Thierry has also found several entire eggs grouped in nests, and he is currently excavating these.
The dinosaur ecosystems of Provence are slightly older than the Hell Creek ones, at roughly ~70 Million years old (Campanian–Maastrichtian). One of the most surprising aspects of the European dinosaurs is dwarfism. While Hadrosaurs (duckbilled dinosaurs) like the North American Edmontosaurus would reach up to 12 meters in length, the European species were miniature versions at roughly 3 meters in length. While sauropods (long-necked dinosaurs) disappeared in western North America well before the K–Pg boundary, small Titanosaurs were present in Provence up to the end of the Cretaceous. Other common dinosaurs from Provence include the small Iguanodontid Rhabdodon, carnivorous dinosaurs Dromaeosaurid ("raptor" dinosaur) Variraptor, and the large Abelisaurid Arcovenator. Abelisaurids are a basal group of large carnivorous dinosaurs common in the Southern Hemisphere, while Tyrannosaurids (the large "tyrant" dinosaurs like Tyrannosaurus rex) dominated North America and Asia.
Left: Thierry showing me several bones of Rhabdodon that were excavated by his team. Right: These three little claws are from a Rhabdodon foot.
Titanosaurs big and small: On the left, David and Thierry are holding the femurs of two animals of very different proportions. On the right, Isabelle, myself, Thierry and David in the collection of the Aix en Provence Museum, each holding a bone of Arcovenator. Click photos to zoom. Drawing by Alain Bénéteau.
Although the redbeds of Provence are a goldmine for vertebrate fossils, they are usually bad news for paleobotanists like myself: the red color is indicative of oxidation, a chemical condition that destroys organic matter, including pollen and spores. But thanks to Isabelle’s excellent knowledge of the geology of the area, we were able to find dark grey rocks, unaffected by oxidation, where I could potentially recover fossil pollen and spores. Indeed, after processing the samples I collected from these grey rocks, I found beautifully preserved pollen and spore assemblages that I will now identify and describe. If you visit FossiLab during the next few months, you may see me at my microscope counting the tiny fossils.
Left: Isabelle knew how to make me happy! During her previous geological prospecting in Provence, she had identified several localities with grey, organic rich mudstones, where I could collect pollen samples. Right: A collage of three Normapolles, a type of pollen grain characteristic from the Late Cretaceous of Europe, that I recovered from our samples collected in Provence.
Photos by Antoine Bercovici, Isabelle Cojan and David Fastovsly.
Open access reference: Vajda, V., Bercovici, A. (2014). The global vegetation pattern across the Cretaceous–Paleogene mass extinction interval; a template for other extinction events. Global and Planetary Change, v. 122, pp. 29-49.