The dinosaur tracksite is located less a mile (1 km) west of the village of Plagne in the Department of the Ain, southern French Jura Mountains.
It was discovered by members of the ‘Société des Naturalistes d’Oyonnax,’ a group of amateur geologists specializing in the Jurassic, in 2009.
Paleontologists from the Paléoenvironnements et Paléobiosphère research unit at the Claude Bernard Lyon 1 University then confirmed that the Plagne trackway extends over 508 feet in length, which makes this specimen the longest sauropod trackway currently known in the world, a few feet longer than the Middle Jurassic sauropod trackways from Galinha, Portugal.
The trackway is composed of 110 successive paces, and is generally well-preserved. The prints measure between 3.3 and 10 feet (1-3 m) in diameter.
The footprints reveal five elliptical toe marks, while the handprints are characterized by five circular finger marks arranged in an arc.
They were made by a sauropod, or long-necked dinosaur, approximately 150 million years ago, during the Tithonian, the latest age of the Late Jurassic epoch.
“Paleogeographic reconstructions of Western Europe for this stage indicate an archipelago landscape, where the emergent islands were occasionally connected during periods of relatively low sea level, which presumably allowed faunal expansion or migration,” the researchers said.
Biometric analysis suggests the Plagne sauropod dinosaur was at least 115 feet (35 m) long, weighted between 35 and 40 tons, had an average stride of 9.2 feet (2.8 m), and traveled at a speed of 2.5 mph (4 km/h).
“This new trackway site, alongside other Early Jurassic Swiss and French tracksites yielding thousands of sauropod and theropod tracks, can be considered as being the largest dinosaur megatracksite in Europe,” the paleontologists said.
They detailed their findings in the August 2017 issue of the journal Geobios.
Jean-Michel Mazin et al. The dinosaur tracksite of Plagne (early Tithonian, Late Jurassic; Jura Mountains, France): The longest known sauropod trackway. Geobios 50 (4): 279-301; doi: 10.1016/j.geobios.2017.06.004