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. 2018 Apr 2:6:e4579.
doi: 10.7717/peerj.4579. eCollection 2018.

A walk in the maze: variation in Late Jurassic tridactyl dinosaur tracks from the Swiss Jura Mountains (NW Switzerland)

Diego Castanera  1 , Matteo Belvedere  2 , Daniel Marty  2   3 , Géraldine Paratte  2 , Marielle Lapaire-Cattin  2 , Christel Lovis  2 , Christian A Meyer  4
Affiliations

A walk in the maze: variation in Late Jurassic tridactyl dinosaur tracks from the Swiss Jura Mountains (NW Switzerland)

Diego Castanera et al. PeerJ. .

Abstract

Background: Minute to medium-sized (footprint length (FL) less than 30 cm) tridactyl dinosaur tracks are the most abundant in the Late Jurassic tracksites of Highway A16 (Reuchenette Formation, Kimmeridgian) in the Jura Mountains (NW Switzerland). During excavations, two morphotypes, one gracile and one robust, were identified in the field. Furthermore, two large-sized theropod ichnospecies (Megalosauripus transjuranicus and Jurabrontes curtedulensis) and an ornithopod-like morphotype (Morphotype II) have recently been described at these sites.

Methods: The quality of morphological preservation (preservation grade), the depth of the footprint, the shape variation, and the footprint proportions (FL/footprint width (FW) ratio and mesaxony) along the trackways have been analyzed using 3D models and false-color depth maps in order to determine the exact number of small to medium-sized morphotypes present in the tracksites.

Results: The study of footprints (n = 93) recovered during the excavations has made it possible to identify and characterize the two morphotypes distinguished in the field. The gracile morphotype is mainly characterized by a high FL/FW ratio, high mesaxony, low divarication angles and clear, sharp claw marks, and phalangeal pads (2-3-4). By contrast, the robust morphotype is characterized by a lower FL/FW ratio, weaker mesaxony, slightly higher divarication angles and clear, sharp claw marks (when preserved), whereas the phalangeal pads are not clearly preserved although they might be present.

Discussion: The analysis does not allow the two morphotypes to be associated within the same morphological continuum. Thus, they cannot be extramorphological variations of similar tracks produced by a single trackmaker. Comparison of the two morphotypes with the larger morphotypes described in the formation (M. transjuranicus, J. curtedulensis, and Morphotype II) and the spatio-temporal relationships of the trackways suggest that the smaller morphotypes cannot reliably be considered as small individuals of any of the larger morphotypes. The morphometric data of some specimens of the robust morphotype (even lower values for the length/width ratio and mesaxony) suggest that more than one ichnotaxon might be represented within the robust morphotype. The features of the gracile morphotype (cf. Kalohipus isp.) are typical of "grallatorid" ichnotaxa with low mesaxony whereas those of the robust morphotype (cf. Therangospodus isp. and Therangospodus? isp.) are reminiscent of Therangospodus pandemicus. This work sheds new light on combining an analysis of variations in footprint morphology through 3D models and false-color depth maps, with the study of possible ontogenetic variations and the identification of small-sized tridactyl ichnotaxa for the description of new dinosaur tracks.

Keywords: Dinosaur ichnology; Kimmeridgian; Late Jurassic; Reuchenette Formation; Switzerland; Theropods.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. Geographical and geological settings of the Highway 16 tracksites (modified from Razzolini et al., 2017; Marty et al., 2017).
(A) Geographical setting of the Ajoie district (NW Switzerland) with the location of the tracksites (1, Courtedoux—Béchat Bovais; 2, Courtedoux—Bois de Sylleux; 3, Courtedoux—Tchâfouè; 4, Courtedoux—Sur Combe Ronde; 5, Chevenez—Combe Ronde; 6, Chevenez—La Combe) along Highway A16. (B) Chrono-, bio-, and lithostratigraphic setting of the Reuchenette Formation in the Ajoie district, Canton Jura, NW Switzerland (after Comment, Ayer & Becker, 2011; Comment et al., 2015).
Figure 2
Figure 2. Pictures and false-color depth maps of the tracks with a high preservation grade that belong to the gracile morphotype.
(A) BEB500-T16-R3; (B) BEB500-T26-R5; (C) BEB500-T73-L5; (D) BSY1020-E2; (E) CHV1000-E4; (F) CRO500-T10-L10; (G) SCR1055-T2-L2*; (H) SCR1055-T3-L2*; (I) TCH1055-E53; (J) TCH1055-T2-L1; (K) TCH1060-E58; (L) TCH1065-E3; (M) TCH1065-E177; (N) TCH1065-T25-L2; (O) TCH1069-T1-R2. *In these two cases, it is not a picture but a colored mesh obtained from the 3D-model. Scale bar = 5 cm.
Figure 3
Figure 3. Pictures and false-color depth maps of the tracks with a high preservation grade that belong to the robust morphotype.
(A) BEB500-T120-R5; (B) BEB500-T120-R6; (C) TCH1065-T21-R1; (D) TCH1065-E188; (E) TCH1065-E124; (F) TCH1065-T15-R1. Scale bar = 5 cm.
Figure 4
Figure 4. Morphological variation in the footprint shape along the studied trackways from BEB500 tracksite.
(A) BEB500-T16 (gracile morphotype); (B) BEB500-T17 (gracile morphotype); (C) BEB500-T58 (gracile morphotype); (D) BEB500-T73 (gracile morphotype); (E) BEB500-T75 (gracile morphotype); (F) BEB500-T78 (gracile morphotype); (G) BEB500-T82 (gracile morphotype); (H) BEB500-T120 (robust morphotype); (I) BEB500-T93 (gracile morphotype).
Figure 5
Figure 5. Morphological variation in the footprint shape along the studied trackways from the CRO500, TCH1055, TCH1065, and TCH1069 tracksites.
(A) CRO500-T10 (gracile morphotype); (B) CRO500-T30BIS (gracile morphotype); (C) TCH1055-T2 (gracile morphotype); (D) TCH1065-T15 (robust morphotype); (E) TCH1069-T2 (robust morphotype); (F) TCH1065-T25 (gracile morphotype).
Figure 6
Figure 6. Bivariate graph plotting the footprint length/footprint width ratio against the mesaxony (AT) of the studied tracks (gracile and robust morphotype) with the larger tracks described in the Reuchenette Formation.
(A) Gracile and robust morphotype compared with Megalosauripus tracks (including tracks classified as Megalosauripus transjuranicus, Megalosauripus cf. transjuranicus and Megalosauripus isp.), the Morphotype II tracks and Jurabrontes curtedulensis (after Razzolini et al., 2017; Marty et al., 2017). Note that in many cases the points represent tracks from the same trackway, so variation through the trackway is also represented. (B) The studied tracks compared with just the holotype and paratype specimens of Megalosauripus transjuranicus and Jurabrontes curtedulensis, plus the best-preserved tracks of Morphotype II (BEB500-TR7). Outline drawings not to scale. The specimen in red is CRO500-T10-L10 (previously classified as Carmelopodus and herein consider as part of the gracile morphotype, see discussion).
Figure 7
Figure 7. Main small-medium-sized tridactyl dinosaur footprints described in the Late Jurassic of Europe.
(A) Grallator from Spain (S, after Castanera, Piñuela & García-Ramos, 2016); (B) Anomoepus from Spain (S, after Piñuela, 2015); (C) Carmelopodus from France (C, after Mazin, Hantzpergue & Pouech, 2016); (D) Eubrontes from France (C, after Mazin et al., 2000); (E) Wildeichnus from Poland (C, after Gierliński, Niedźwiedzki & Nowacki, 2009); (F) cf. Jialingpus from Poland (C, after Gierliński, Niedźwiedzki & Nowacki, 2009). (G) Dineichnus from Poland (C, after Gierliński, Niedźwiedzki & Nowacki, 2009); (H) Dineichnus from Portugal (S, Lockley et al., 1998a); (I) Therangospodus-like track from Portugal (S, after Lockley, Meyer & Moratalla, 2000); (J) Grallator from Germany (S, after Diedrich, 2011); (K) Therangospodus-like track from Italy (C, after Conti et al., 2005); (L) Carmelopodus-like track from Italy (C, after Conti et al., 2005). Scale bar = 1 cm (E), 5 cm (A, F, G), 10 cm (B, C, D, H, I, J, K, L). S and C refer to siliciclastic and carbonate substrate, respectively.
Figure 8
Figure 8. Small-medium-sized tridactyl dinosaur ichnotaxa with affinities with the described morphotypes.
(A) Outline drawing of the holotype of Carmelopodus untermannorum (S, redrawn after Lockley et al., 1998b); (B) outline drawing of the holotype of Wildeichnus navesi (V, redrawn after Lockley, Mitchell & Odier, 2007); (C) outline drawing of the topotype of Therangospodus pandemicus (S, after Lockley, Meyer & Moratalla, 2000); (D) outline drawing of Anomoepus scambus (S, after Olsen & Rainforth, 2003); (E) outline drawing of the holotype of Dineichnus socialis (S, after Lockley et al., 1998a); (F) composite outline drawing of type trackway of Grallator parallelus (S, redrawn from Olsen, Smith & McDonald, 1998); (G) outline drawing of type specimen of Anchisauripus sillimani (S, redrawn from Olsen, Smith & McDonald, 1998); (H) outline drawing of type specimen of Eubrontes giganteus (S, redrawn from Olsen, Smith & McDonald, 1998); (I) outline drawing of type specimen of Jialingpus yuechiensis (S, redrawn from Lockley et al., 2013); (J) outline drawing of type specimen of Kalohipus bretunensis (S, redrawn from Fuentes Vidarte & Meijide Calvo, 1998); (K) drawing of type specimen of Jurabrontes curtedulensis (redrawn from Marty et al., 2017); (L) outline drawing of type specimen of Megalosauripus transjuranicus (redrawn from Razzolini et al., 2017); (M) outline drawing of specimen BSY1020-E2 (cf. Kalohipus isp.); (N) outline drawing of specimen CRO500-T10-L10 (cf. Kalohipus isp.); (O) outline drawing of specimen TCH-1060-E58 (cf. Kalohipus isp.); (P) outline drawing of specimen TCH-1065-T21-R1 (cf. Therangospodus isp.); (Q) outline drawing of specimen BEB500-T120-R5 (Therangospodus? isp.). S, C, and V refer to siliciclastic, carbonate and volcanoclastic substrate, respectively. Scale bar = 2 cm (B, D), 5 cm (F, G, H, I, J), 10 cm (A, C, E, L, M–Q), 50 cm (K).
Figure 9
Figure 9. Bivariate graph plotting the footprint length/footprint width ratio against Mesaxony of the studied tracks (gracile and robust morphotype) with some of the main dinosaur tridactyl ichnotaxa mentioned in the text.
Outline drawings not to scale.
See this image and copyright information in PMC

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Grants and funding

Excavations, scientific documentation of Highway A16 dinosaur tracksites and related research by the Paléontologie A16 (Section d’archéologie et paléontologie, Office de la culture) are funded by the Swiss Federal Roads Office (FEDRO, 95%) and the Canton Jura (5%). Diego Castanera has been supported by the Alexander von Humboldt Foundation (Europe Research Stay and Humboldt Research Fellowship for Postdoctoral Researchers). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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