Researchers have identified a new freshwater mosasaur species, named Garamaudo bauciensis, which lived approximately 84 million years ago in a southeastern French lake. The 2.5-meter reptile retained limbs looking adapted for terrestrial locomotion and dense, osteosclerotic bones, challenging long-held assumptions about mosasaur evolution and habitat diversity.
Paleontologists describing the new species constrained the fossil’s age during the Santonian age of the Late Cretaceous. The discovery centers on fossilized remains originally found in 1997 at the Bouc-Bel-Air – Sousquières locality in the city of Bouc-Bel-Air, Provence, southeastern France.
Fossil Discovery at Bouc-Bel-Air and Specimen Breakdown
Researchers determined that the sizes of the bones, the absence of duplicates, and the fact that they have been found in close association during one excavation campaign, undertaken by the Muséum d’Histoire Naturelle of Aix-en-Provence (MHNA) in 1997, are consistent with them being derived from a single individual, although the majority of the material belongs to a single specimen designated as the holotype. The study focuses on new mosasauroid remains discovered in Santonian continental deposits of Provence, southeastern France. Such remains are considered here as the holotype of Garamaudo bauciencis.
Garamaudo Bauciensis Lived in Freshwater Environments
While most mosasauroid remains emerge from marine deposits, the Bouc-Bel-Air locality represents a freshwater environment. Particularly common are freshwater occurrences in the Santonian-Campanian continental deposits of Europe, from Portugal to Hungary and Austria, passing through southern France. Rapid flooding episodes could explain the state of preservation of the holotype specimen of Garamaudo bauciensis, which includes broken bones having however well-preserved surfaces.
Classified as a member of the subfamily Tethysaurinae, Garamaudo bauciensis reveals an unusual evolutionary path. The assignment of this new freshwater mosasaurid to the tethysaurines reveals an additional occurrence of a freshwater species in this clade and the fact that, based on current knowledge, it is only within the Tethysaurinae that freshwater forms evolved among mosasaurids, the scientists said.
Garamaudo Bauciensis Kept Limbs Suited for Terrestrial Locomotion
Growing to approximately 2.5 meters in length, the reptile departed from the streamlined, paddle-bearing anatomy of open-ocean mosasaurs. Most mosasauroids possess a morphology modified for an aquatic lifestyle, with paddles and the loss of connection between the vertebral column and the pelvis — that is, the absence of a true sacrum. More primitive forms display limbs looking adapted for a terrestrial locomotion and a sacrum, illustrating a plesiopedal and plesiopelvic condition. Garamaudo bauciensis was about 2.5 m long and, unlike the better-known mosasaurs, kept limbs that look suited to walking on land, along with a pelvis firmly attached to the spine.
CT scans revealed thick, compact bone in the vertebrae and humerus—a condition known as osteosclerosis. Researchers suggest the animal probably hovered at shallow depth in freshwater ecosystems. Its long, straight ribs point to a deep but narrow, side-to-side flattened body. The study was published in the Peer Community Journal.