Abstract
BackgroundRecent 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 FindingsA 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.
Highlights
When it comes to assigning a tridactyl track to a particular producer, controversy is common in the vertebrate ichnology of the Mesozoic
Comparing the footprint length (FL)/footprint width (FW) ratio and the pace length (PL)/FL ratio in a bivariate analysis (Figure 12) with some of the typical small- to medium-sized ornithopod ichnotaxa (Figure 13 A-H) such as Dineichnus [47], Iguanodontipus burreyi [48], Iguanodontipus billsarjeanti [49], Ornithopodichnus [50,51], Neoanomoepus [10] and with the type ichnospecies of Therangospodus pandemicus [15], it can be observed that the data for I?oncalensis and the other tracksites from the Huérteles Formation are closer to the ornithopod ichnotaxa than to the theropod tracks assigned to T. pandemicus
The only two trackways (FTS5 and FTS8) where the FL/FW ratio is near the cluster of the sample from T. pandemicus are those that are poorly preserved, so we consider that these data probably do not represent the real morphology of the trackmaker
Summary
When it comes to assigning a tridactyl track to a particular producer (theropod vs. ornithopod), controversy is common in the vertebrate ichnology of the Mesozoic (see 1-5). In the Huérteles Formation (Berriasian) there seems to be a notable disproportion between the number of theropod and ornithopod tracks [6,7]. Recent work on the Jurassic-Cretaceous interval has shown the difficulties in identifying the producer of small to medium-sized tridactyl tracks [8,9,10,11,12,13], so this disproportion could be a matter of the misidentification of at least some of the ornithopod tracks. The ichnogenus Therangospodus was first used in the Huérteles Formation by Moratalla [14] in his doctoral thesis It was not until 1998 that it was formally erected by Lockley et al [15]. 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
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