Manus-only titanosaurid trackway from Fumanya (Maastrichtian, Pyrenees): further evidence for an underprint origin

The origin of manus-only and manus dominated sauropod trackways has been a matter of intense debate since two hyphothesis exist: (a) manus-only and manus-dominated trackways result from a 'swimming' sauropod, and (b) they result from a selective underprint phenomenon that only leaves the manus recorded. Several new sauropod trackways are reported in the Fumanya tracksite area (Maastrichtian), in SE Pyrenees, where both tracks and undertracks are found on the same stratigraphic bedding surface. In one of the trackways, footprint morphology together with the trackway pattern displays a clear succession of manus-only impressions attributed to a sauropod dinosaur in a walking gait. The ichnological comparison between the manus-only trackway with the other complete trackway (manus-pes) display an identical distribution of the manus pattern. This fact clearly points towards an underprint phenomenon as the origin for manus-only trackways, since it is rather unlikely that the same pattern would completely match different locomotion behaviours such as walking and swimming. Therefore, we suggest an interpretation based on the differential loading between the hindfoot and the forefoot on an upper stratigraphic track-level, for the studied manus-only trackway. □ Fumanya tracksite, manus-only trackways, titanosaurs, trackway pattern, underprint, Upper Cretaceous.