In this work the study surface where the footprints were registered was examined carefully. The study surface may or may be not the tracking surface (the surface where the dinosaur stepped) . All the surfaces with true footprints in Iouaridène syncline have been found in the hard layers (red siliceous levels) with mud cracks . The undertracks and underprints are in resistant layers with ripples. The number of hard layers varies from the northwest area of the syncline, about 20 layers, to the southeast area, where there are places with one hard layer. Currently, in the soft levels (shales) footprints have not been found in the soft levels (shales).

Holotype of Boutakioutichnium atlasicus.
A) outline. B) photograph.

The footprints studied in this work were registered after the formation of mud cracks. The cracks are deformed by the dinosaur feet so that the sides of the tracks were moved upward and outward . Sometimes they were also bent, but usually the deformation is closer to an elastic than plastic type. Under the foot, the cracks are broken in small fragments. In the Iouaridène syncline there are also some theropod footprints crossed by mud cracks produced after the dinosaur steps . In the footprint hole, the small rims and the displacement of the mud cracks are due to the dry layer below (elastic or almost) of the tracking surface, were there was a soft zone (of plastic or fluid) mud.

In general, the footprint depth is less than 5 cm, therefore the feet do not get any deeper into the mud. Only some footprints (7IGR6.6, 8IGR1.24 footprint, for instance) show collapse structures in the proximal part of the digit III. This occurs because the mud is accumulated in the interdigital area among the digits.

Most of the footprint shafts have been interpreted as direct structures . Therefore the footprints are considered true footprints and although not all are not an accurate representation of the foot, there are also some elite tracks or stamps . he footprint outline is not always easy to see because sometimes the physical features of the mud cracks do not allow the foot to print it well. The footprint outline does not fit exactly with the foot shape because the mud cracks move as coarse fragments and their behavior is not completely plastic. Nonetheless, in some footprints the diagnostic features as the digits margins, the digital pads and the claws marks are clearly distinghished.

Jaouad Nouri¹, Ignacio Díaz-Martínez^2,3, Félix Pérez-Lorente^2,3*

1 Faculté des Sciences, Université Mohamed V, Rabat, Morocco, 2 Facultad de Ciencas, Universidad de La Rioja, Logroño, La Rioja, España, 3 Fundación Patrimonio Paleontológico de La Rioja, Enciso, La Rioja, España