Charente Quarry Yields More Than 70,000 Fossils, a 140-Million-Year-Old Swamp Explains Why

In July 2019, a sauropod femur measuring about two meters in length emerged from the Angeac-Charente fossil site, located between Cognac and Angoulême. This giant bone is only one piece among tens of thousands. A study by the Muséum national d’Histoire naturelle explains how a Cretaceous marsh became such a dense archive of dinosaurs.

Spotting in a sand and gravel quarry, the Angeac site has been excavated every summer since 2010

The deposit lies about 700 meters north of the village, in a commercial aggregate quarry. The first bones were noticed during extraction work in the late 2000s. By 2010, paleontologist Ronan Allain of the MNHN opened a dig there.

This initial season yielded a 2.20-meter femur, cataloged under the number ANG 10-400. Later, the 2019 specimen confirmed the presence of giant sauropods. Its weight, estimated at between 400 and 500 kilograms, remains approximate.

The fossil-bearing layers date to the Berriasian and the early Valanginian, around 140 million years ago. Consequently, Angeac provides a rare window into the Early Cretaceous terrestrial Europe. Previously, only the Spanish site of Las Hoyas offered such a precise view of this period.

Between 2010 and 2017, 724 square meters excavated yielded 68,726 bone remains and 3,123 coprolites

The reference article, authored by Lee Rozada, Ronan Allain and eight coauthors, appeared in the journal Lethaia in 2021. It thus summarizes nine field campaigns of about four weeks each, with around forty people. In total, nearly 724 square meters were cleared, by hand or with a mechanical shovel.

Indeed, the average density reaches nearly 95 vertebrate remains per square meter. Among them, 7,152 pieces could be assigned to a species and a specific bone, while more than 66,000 fragments remain undetermined.

A muddy swamp, scavenging crocodiles and herds trampling bones shaped this cemetery

According to the authors, the fossils come from a single deposition interval, within a marshy environment with an argillaceous bottom. Moreover, the rare earth elements in the bones and sediments confirm contemporaneous burial. The site thus locks in a snapshot of the ecosystem.

The bones also carry traces of their history. Thus, numerous bite marks from crocodiles appear on turtles, fish, and ornithomimosaurs. Additionally, trampling marks betray intense dinoturbation.

The dominant species is an as yet undescribed ornithomimosaur, represented by at least 44 individuals of varying sizes. The team therefore contemplates a mass mortality within a herd. By contrast, most sauropod bones would have undergone only limited transport by the water.

Surveying with a tachymeter and sieving tons of sediment, the excavation method evolved over the campaigns

Initially mapped by hand in 2010, the records were later made with a theodolite, then with a total station from 2015. Subsequently, a geographic information system allowed the study of the distribution of remains.

Meanwhile, several tons of sediment were sieved and washed to recover micro-remains, such as the teeth of small crocodiles. The authors acknowledge biases, since plots were not all excavated to the same depth. Sorting could also artificially multiply fragments.

The material joins the collections of the Angoulême Museum, or passes through the MNHN. Most notably, recent identifications, including a sauropod close to Camarasaurus, show that the inventory is not closed. Each summer, the quarry thus adds to the portrait of a vanished marsh.