Figure 1.
Geographical and geological setting of the El Frontal tracksite (Bretun, Soria).
The location of Bretun locality within the Iberian Peninsula is inside the black square. The tracksite locates in DS-3 of the Huerteles Fm [32]. Geological map modified from Castanera et al. [33].
Figure 2.
Tracksite microlayers organization.
A) The El Frontal tracksite is composed of 5 different centimeter-thick layers that intercalate gray siltstones, limestone and sandy-siltstones. Scale bar equals 8 cm. B) El Frontal track layers 4 (penetrative tracks) and 5 (tracking surface), where all the studied tracks originated. When thin layer 5 is not preserved, tracks are found in level 4. C) Stratigraphical log of the five layers found in the El Frontal tracksite. Theropod tracks are found in layers 5 and 4. Scale bar equals 1 cm.
Figure 3.
Thin sections IPS-82477a-d of layers 4 and 5 of the El Frontal tracksite.
A) Sandstone intercalated by siltstone-mudstone bands in which chlorite minerals are scarce (<5%); B) High quartz concentration (>60%) and scarce presence of clay minerals in mud bands; C)Sandstone-siltstone in which the grain size decreases from the bottom to the top; D) Sandstone intercalated by siltstone, mineral clays are abundant (>60%); E) Deformation structures (mud drapes); F) Deformation structure (symmetrical ripple). Black arrows indicate the top of the laminae, white arrows indicate deformation structures. Scale bars are 2000 μ for A, 500 μ for B, C, D, F and 2000 μ for E.
Figure 4.
Cartography and 3-D model of the El Frontal tracksite resulting from the LiDAR scanning (grey colour), modified from Barco et al. [44] and designed by Paleoymas SL.
In the red rectangles (A and B) are the details of the areas with the highest density of tracks. The studied area is detailed in the rectangle B. Studied trackways F17, F7, F5 and F4 are coloured respectively with black, pink, yellow and green.
Figure 5.
Standards for measuring track length (TL) and depths (black and white stars).
A) TL excludes the elongated metatarsal impression, and the depth is taken approximately were the phalanx 1 of metatarsal IV should be. B) In this case there is no metatarsal impression and the TL is easier to measure. Depth is taken in the same point for every track. Color scale green indicates the track layer, purple is the deepest point recorded and red is the highest point recorded.
Table 1.
Table with measurements taken for all the theropod trackways in the El Frontal.
Figure 6.
Morphological characterization of the El Frontal tracks.
A) Morphotype A is track 17.2, A1) Variation of morphotype A, track 17.17, B) Morphotype B is track 7.3, B1) Variation of morphotype B, track 7.13. Color scale green and yellow indicates the track layer, purple is the deepest point recorded for depth and red is the highest point recorded for displacement rims.
Table 2.
Table with measurements taken for all tracks belonging to trackways F17,F 7,F 5 and F4 of the El Frontal tracksite.
Figure 7.
The linear correlation graphic of depth (D) vs displacement rims (DR) shows a positive correlation among these two values.
Pearson’s correlation matrix results in r = 0.871 and Spearman’s correlation matrix in an r = 0.820. F17 (black colour), F7 (purple colour), F5 (yellow colour) and F4 (green colour). Units are in centimeters.
Figure 8.
Dispersion graph of depth (D) vs track length (TL) shows a wide range distribution among the tracks of trackways F17, F7 and F5 (respectively black, purple and yellow colours) of the El Frontal tracksite.
The most concentrated cluster in that of trackway F4 (green colour), in which values are quite consistent and only weakly vary along the trackway. Units are in centimeters.
Figure 9.
Quantification of the intra-trackway depth and length variations, four graphs for trackways F17, F7, F5 and F4 are built using TL, PL (left Y axis) and depth measurements (right y axis).
Units are in centimeters.
Figure 10.
Morphological continuum of the tracks of the El Frontal tracksite. Color scale bar is based on depth intervals.