Discriminating between medium-sized Tridactyl Trackmakers: tracking Ornithopod tracks in the base of the Cretaceous (Berriasian, Spain)

Abstract

Background: Recent work on the Jurassic-Cretaceous transition of the Iberian Range (Spain) has opened a new window onto the interpretation of the trackmakers of some medium-sized tridactyl tracks. The ichnotaxon Therangospodus oncalensis has been described in the Huérteles Formation (Berriasian) and is one of the classical tracks from the area assigned to medium-sized theropods.

Methodology/principal findings: A review of the type locality of Therangospodus oncalensis (Fuentesalvo tracksite) and other tracksites from the Huérteles Formation (Berriasian) has yielded new information on the morphology, gait and trackmaker identity of the aforementioned ichnospecies. The new data suggest that the trackmaker is an ornithopod rather than a theropod on the basis of the length/width ratio, the anterior triangle length-width ratio, the short steps, the round to quadrangular heel pad impression and the probable manus impressions.

Conclusions/significance: T. oncalensis shows similarities with various tracks from the Berriasian of Europe assigned to Iguanodontipus. The ichnotaxonomical status of this ichnospecies is here considered as Iguanodontipus? oncalensis due to the current state of knowledge of the ichnotaxonomy of medium-sized ornithopod tracks. This reassessment of I? oncalensis also has two significant implications for the palaeoecology of the faunas during the deposition of the Huérteles Formation: 1- the high number and percentage of theropod tracks would be lower than previous papers have suggested. 2- the gregarious behaviour described in the type locality (Fuentesalvo) would be among ornithopods instead of theropods.

Figure 1. Geographical and geological setting.

The tracks show the localities where the tracksites with I?oncalensis are located (modified from [7]).

Figure 2. Measurements taken from the tracks.

A) Measurements taken for the whole trackway. B) Measurements taken for the individual tracks. Abbreviations: see text in Materials and Methods.

Figure 3. Sketch map of the Fuentesalvo tracksite (modified from [16]).

The dotted lines indicate the undescribed part of the tracksite and track 1.3 from the holotype trackway (see figure 4).

Figure 4. I?oncalensis tracks from the Fuentesalvo tracksite.

A) Picture and photogrammetric 3D depth analysis model of the new track (FTS19). Note the three microlayers inside the track. B) Outline drawing of track FTS19. C) Pictures of track FTS1.3 from the holotype trackway without any evidence of the aforementioned microlayers. D) Outline drawing of the FTS1.3 from the holotype trackway. E) Picture of track FTS10.3 showing the microlayers. These tracks have been coloured in black with earthy tones. Note also the differences in the morphology of the heel pad impression (round to quadrangular) between the tracks. Scale depth in the models in mm. Scales: coin = 2.5 cm diameter; scale bar = 5 cm.

Figure 5. Sketch map of the La Peña tracksite (Bretún locality).

Figure 6. I?oncalensis tracks from La Peña tracksite.

Figure 7. I?oncalensis tracks from the Salgar de Sillas tracksite.

A) Sketch of trackway SS26. B) Picture of track SS26.3 (the tracks has been coloured in black with earthy tones). C) Picture of track SS27. D) Outline drawing of track SS26.3. E) Outline drawing of track SS27. Scale bar = 5 cm.

Figure 8. I?oncalensis trackway from the Valloria IV tracksite.

A) Picture of the whole trackway VAIV1. B) Picture and photogrammetric 3D depth analysis model of track VAIV1.3. C) Picture and photogrammetric 3D depth analysis model of track VAIV1.2. D) Picture and photogrammetric 3D depth analysis model of track VAIV1.1. Scale depth in the model in mm. Scale bar = 5 cm.

Figure 9. I?oncalensis tracks in the Los Tormos tracksite.

A) Sketch map of the Los Tormos tracksite. B) Picture and photogrammetric 3D depth analysis model of the best-preserved track LTR0.32. C) Picture of part of trackway LTR5. D-E) Pictures of tracks LTR5.6 and LTR5.7. Note in LTR5.7 the two different layers where the track is impressed. Scale depth in the model in mm. Scale bar = 50 cm (A) and 5 cm (B). Scale (card) = 8 cm.

Figure 10. I?oncalensis tracks in other tracksites

I. A) Sketch map of the Fuente Lacorte (level 10) tracksite. B) Sketch of the I?oncalensis trackway from the Valdelavilla (level VIII) tracksite (redrawn from [37]). Scale bar = 20 cm.

Figure 11. I?oncalensis tracks in other tracksites II.

A) Picture of track MNS-2002-96-2 stored in the Museo Numantino (Soria). B) Outline drawing of track MNS-2002-96-2. C) Picture and photogrammetric 3D depth analysis model of track LLII1.4. Scale bar = 5 cm.

Figure 12. Bivariate analysis of the FL/FW ratio and PL/FL ratio of I?oncalensis, T. pandemicus and other ornithopod ichnotaxa.

Plot showing the bivariate analysis results with FL/FW on the X axis and PL/FL on the Y axis. T. pandemicus (green), I? oncalensis (red), Dineichnus (light blue), Iguanodontipus billsarjeanti (pink), Iguanodontipus burreyi (dark blue), Ornithopodichnus (greenish blue), Neoanomoepus (yellow).

Figure 13. Comparison of I? oncalensis, T. pandemicus and other ornithopod ichnotaxa and ornithopod tracks.

A) I? oncalensis; B) T. pandemicus from USA; C) Dineichnus; D) Iguanodontipus burreyi; E) Iguanodontipus billsarjeanti; F) Neoanomoepus; G-H) Ornithopodichnus; I-J) Iguanodontipus from the Las Cuestas I tracksite; K-M) Iguanodontipus from the Berriasian of Germany; N-P) Iguanodontipus from the Berriasian of the UK; Q-R) Iguanodontipus tracks from the Barremian of the Iberian Range (La Rioja and Burgos province). S) Iguanondontipus tracks from the Barremian of Portugal; T-U) Iguanodontipus tracks from the Barremian of the Iberian Range (Teruel province); V) Morphotype II described by Marty [24], from the Late Jurassic of Switzerland; W-X) ornithopod tracks from the Las Cerradicas tracksite. Redrawn from [8, 12, 13, 15, 24, 47-51, 53-55, 57-59, 61-66]. Scale bar = 10 cm.

Figure 14. Bivariate analysis of the FL/FW ratio vs.

AT (anterior triangle length-width ratio) of I?oncalensis and other tridactyl (theropod and ornithopod) ichnotaxa (after [8]).

Figure 15. Bivariate analysis of the FL/FW ratio and PL/FL ratio of I? oncalensis and other ornithopod ichnotaxa and ornithopod tracks from the Late Jurassic-Early Cretaceous.

Plot showing the bivariate analysis results with FL/FW on the X axis and PL/FL on the Y axis. I?oncalensis (red), Iguanodontipus billsarjeanti (pink), Iguanodontipus burreyi (dark blue), Iguanodontipus from the Huérteles Formation (light green), Dineichnus (light blue), Iguanodontipus from Praia Santa (green), Iguanodontipus sp. from Obernkirchen (yellow), Iguanodontipus from the Purbeck Limestone Group (grey), Iguanodontipus from Regumiel de la Sierra (dark green), Iguanodontipus from Cabezón de Cameros (greyish blue), unnamed tracks from Las Cerradicas (greenish blue).