The world's largest dinosaur footprints were found in the French village, Plagne, near Lyon in 2009. Since then, this 150-meter big excavation site in the Jura Mountains has been subjected to a series of excavations which has led to spectacular findings.

The longest ever sauropod trackway ever recorded has been found at the site. The findings revealed that these tracks were left 150 million years ago by a dinosaur at least 35 meters long and weighing no less than 35 tones.

The data collected was published in the journal Geobios. The findings were made by scientists from the Laboratoire de Géologie de Lyon (CNRS/ENS de Lyon/Claude Bernard Lyon 1 University), the Laboratoire Magmas et Volcans (CNRS/Université Clermont Auvergne/Université Jean Monnet/IRD), and the Pterosaur Beach Museum.

The new findings at the site discovered in 2009, were made by two members of the Oyonnax Naturalists' Society and scientists from the Paléoenvironnements et Paléobiosphère research unit from Centre Nationnal de la Recherche Scientifique (CNRS) and Claude Bernard Lyon 1 University.

According to a press release on the CNRS University website, "between 2010 and 2012, researchers from the Laboratoire de Géologie de Lyon supervised digs at the site, a meadow covering three hectares. Their work unearthed many more dinosaur footprints and trackways. It turns out the prints found in 2009 are part of a 110-step trackway that extends over 155 m — a world record for sauropods, which were the largest of the dinosaurs."

The team made the discovery by using a limestone dating process. This process revealed the trackway was formed 150 million years ago. This is estimated to be around the Early Tithonian Age of the Jurassic Period.

The landmass was rather divided during this period. The islands that were present then were estimated to be a vast carbonate platform bathed in a warm, shallow sea. The Plagne excavation site lay on these islands.

According to the release, "the presence of large dinosaurs indicates the region must have been studded with many islands that offered enough vegetation to sustain the animals. Land bridges emerged when the sea level lowered, connecting the islands and allowing the giant vertebrates to migrate from dry land in the Rhenish Massif."

The excavations from 2010 continued till 2015. This sustained exploration enabled closer study of the tracks. The sauropod's feet span was measured with the footprint and was estimated to be around 37 to 40 inches wide. Including the mud displaced by the sheer weight of the animal, each footprint measured 3 meters. The species had five elliptical toe marks, while the handprints are characterized by five circular finger marks arranged in an arc.

The release also added that, "biometric analyses suggest the dinosaur was at least 35 m long, weighted between 35 and 40 t, had an average stride of 2.80 m, and traveled at a speed of 4 km/h. It has been assigned to a new ichnospecies: Brontopodus plagnensis."

Several unique dinosaur trackways were found at the same excavation site in Plagne. The findings include a series of 18 tracks extending over 38 meters, left by a carnivore of the ichnogenus Megalosauripus. The researchers have since covered these tracks to protect them from the elements. But many more remain to be found and studied in Plagne.