Discover France and Explore the Fossils and Geodiversity of Plagne in Ain, Jura Mountains
- Wayne Munday
- 14 minutes ago
- 4 min read
Sip back and discover France and explore the fossils and geodiversity of Plagne located in the limestone highlands of the southern French Jura Mountains in the Ain department of Auvergne Rhône-Alpes. At its heart lies Dinoplagne, home to one of the longest known sauropod dinosaur trackways, attributed to Brontopodus plagnensis, a colossal sauropod comparable in size to Diplodocus. Preserved in the Late Jurassic Couches du Chailley Formation, these footprints formed on a tidal flat approximately 150 million years ago, capturing an ecosystem where dinosaurs navigated shorelines and shallow seas during fluctuating sea level changes. Discovered in 2009 by the Société des Naturalistes d’Oyonnax, the trackway stretches over 155 meters, showcasing 110 consecutive steps with distinctive hind and forefoot impressions. This extraordinary site offers insights into sauropod biomechanics, gait, and behaviour, unlike body fossils, which capture only a moment in time. Beyond fossil footprints, Plagne’s surrounding Jura Mountains provide scenic hiking to viewpoints like the Col de la Faucille and Plateau de Chamoise, while local wines such as Bugey Cerdon AOC and Coteaux de l’Ain IGP highlight the influence of limestone upon the regions terroir.
Located in the scenic Jura Mountains of the Ain department, Plagne is a must-visit destination for nature and palaeontology enthusiasts seeking an immersive outdoor experience into deep time. At its heart lies Dinoplagne, a world-renowned fossil site among the longest sauropod dinosaur trackways ever discovered. Visitors can follow a curated trail across eight hectares of rugged terrain, enhanced by interpretive panels detailing Jurassic biodiversity, continental drift and the region’s exceptional geodiversity. Beyond the trackway, the surrounding Jura Mountains offer breathtaking hiking trails, including routes to the Col de la Faucille and viewpoints on the Plateau de Chamoise, making Plagne an ideal base for blending dinosaur deep time heritage with adventure. Wine lovers are also drawn to the area, with vineyards producing Bugey Cerdon AOC a group of sparkling, white, rosé, and red wines that pair beautifully with the local dishes of Raclette and Tartiflette, while Coteaux de l’Ain IGP highlights the department’s limestone-rich vineyards and cool, fresh climate.
The footprints are preserved within the upper levels of the Couches du Chailley Formation a succession of Late Kimmeridgian to Tithonian limestones dated to about 154.8 - 143.1 million years ago.
These limestones were formed in a protected supratidal, or supralittoral environment above the normal high-tide line that is only flooded during storms or exceptionally high tides. It was here where repeated episodes of shoreline emergence that large sauropods called Brontopodus plagnensis, comparable in size to Diplodocus, roamed and left their deep and well-defined footprints.
The shoreline at Plagne once supported a vibrant ecosystem where multiple dinosaur groups moved across the tidal flats in search of food, water or travel. Differences in track morphology and crispness not only reveals the behaviour of the animals.
During the Tithonian Stage of the Late Jurassic Western Europe was an archipelago of islands, shoals and shallow limestone platforms shaped by fluctuating sea levels and was also experiencing a transition to a cooler and drier climate. This period saw major marine regressions that periodically connected emergent landmasses by intermittent land corridors or pathways allowing large dinosaurs, particularly sauropods, to migrate across temporary land corridors linking regions of France, Switzerland and Portugal.
In 2009, members of the Société des Naturalistes d’Oyonnax (SDNO) specialising in Jurassic palaeontology located a series of giant footprints in a locality known as Champs d’Argent or the “Silver Fields,” just west of the village of Plagne. What initially appeared to be isolated depressions soon showed itself as the beginning of a continuous trackway of significant scale stretching over 155 meters with 110 consecutive steps.
The Plagne dinosaur trackway displays sauropod morphology including hind footprints marked by five elongated, elliptical toes and forefoot impressions defined by five circular digits arranged in a gentle arc. Analysis of stride length and footprint size suggests that the sauropod responsible for these immense tracks measured roughly 35 meters in length, weighed up to 40 tons, and moved at a steady walking pace of about 4 Km/hr Unlike body fossils, which capture only the moment of death, this extraordinary trackway records a living animal in motion, offering a rare and invaluable insight into sauropod biomechanics, gait, and social behaviour.
The Plagne tracksite in the French Jura Mountains is part of a broader network of extraordinary Jurassic dinosaur tracksites that span the Jura region, establishing it as one of Europe’s most significant centers for ichnological research. In the Swiss Jura, thousands of sauropod and theropod footprints have been documented, highlighting the area’s dense record of dinosaur activity.
On the French side, discoveries at Coisia and Loulle have further enriched this fossil landscape. Coisia, was explored in the 1980s and revealed short sauropod trackways attributed to Parabrontopodus, while the abandoned quarry at Loulle produced over 1,500 footprints, including sauropod and theropod tracks assigned to ichnogenera such as Carmelopodus, Megalosauripus and Brontopodus.
Collectively, these sites form what palaeontologists describe as one of the largest dinosaur megatracksites in Europe. This network of tracksites not only enhances our understanding of Jurassic ecosystems but also underwrites the Jura Mountains’ global importance as a center for dinosaur ichnology or the study of the traces left by living organisms such as footprints, burrows, nests, and fossilised coprolites..
Visiting the Plagne sauropod trackway is like stepping back 150 million years into the Late Jurassic. As you walk alongside the enormous footprints of one of Earth’s largest dinosaurs, it’s easy to imagine these giants slowly traversing tropical tidal flats, lumbering through a landscape of islands and shallow seas shaped by shifting coastlines and ancient waters. For nature and history enthusiasts alike, Plagne offers a truly immersive journey, connecting you directly to the prehistoric world and the awe-inspiring scale of the creatures that once roamed this extraordinary corner of the Jura Mountains.
