Iguanodontipodidae, Vialov, 1988

Castanera, Diego, Silva, Bruno C., Santos, Vanda F., Malafaia, Elisabete & Belvedere, Matteo, 2020, Tracking Late Jurassic ornithopods in the Lusitanian Basin of Portugal: Ichnotaxonomic implications, Acta Palaeontologica Polonica 65 (2), pp. 399-412 : 402

Iguanodontipodidae indet.

Fig. 2 .

Material. —SHN.(JJS).ICNO.03, 48, 54, 75, 110; from Valmitão Norte, Valmitão Sul, Praia Azul, Foz Do Rio Sizandro; Amoreira-Porto Novo (upper Kimmeridgian) and Sobral (upper Kimmeridgian–lower Tithonian) formations (for details see SOM: table S1).

Description. —Medium to large-sized (pes length 28– 32.5 cm) tridactyl tracks ( Fig. 2 and SOM: table S2), generally slightly wider than long or almost as wide as long (length/width ratio 0.82–1.03) with low mesaxony (AT ratio 0.32–0.42). The tracks are relatively symmetrical, with a lateral and medial notch and a rounded to quadrangular metatarsophalangeal pad impression. The medial notch looks slightly more developed in some specimens (SHN.(JJS).ICNO.03, 75), so these tracks are slightly asymmetric. The digits are considerably robust. Digit III is longer than digits II and IV, digit IV being slightly longer than digit II. The hypices are fairly symmetrical. No discrete phalangeal pad impressions can be discerned, possibly suggesting one pad impression in each digit. The distal end of the digit impressions is rounded, possibly indicating blunt claw marks. Only SHN.(JJS).ICNO.03 shows evidence of blunt but acuminate claw marks. The interdigital angle II–IV is medium (65–85°), interdigital angle II–III being slightly greater than interdigital angle III–IV.

Remarks. —Large ornithopod tracks, i.e., those larger than 25 cm and generally assigned to iguanodontians, are not very common during the Late Jurassic, although they are frequent subsequently during the Cretaceous ( Lockley and Wright 2001; Lockley et al. 2014; Díaz-Martínez et al. 2015). On the basis of the metatarsophalangeal pad and digit impressions, the latter authors identified three main groups of large ornithopod tracks, which belong to the ichnofamily Iguanodontipodidae and are related to the ichnogenera Iguanodontipus , Caririchnium , and Hadrosauropodus . Interestingly, this ichnofamily is so far mainly restricted to the Cretaceous. The authors include some tracks from the literature in their so-called Group 1; these were included in Iguanodontipus . This ichnotaxon has been considered monospecific ( I. burreyi ), being characterized by a small, rounded metatarsophalangeal pad and elongate, narrow digit impressions (see also Castanera et al. 2013a), and its distribution is limited to the Berriasian–Valanginian of Europe. Recently, Piñuela et al. (2016) described medium to large-sized (28–30 cm) ornithopod tracks in the Late Jurassic of Asturias ( Spain) and suggested that the tracks “are quite different from known ichnogenera, but they are not sufficiently well preserved to propose a new one”. Moreover, the authors questioned the validity of Iguanodontipus because of the preservation of the material and even called into question the ornithopod origin of the possible trackmaker. The tracks from the Lusitanian Basin studied here share some features with the tracks from Group 1 defined by Díaz-Martínez et al. (2015). Nonetheless, there are some features described in the diagnosis of I. burreyi ( Sarjeant et al. 1998) that they do not share, such as the similar digit length in the three digits. Given the current status of the type material of Iguanodontipus burreyi , the poor preservation of whose holotype has been pointed out by several authors ( Piñuela et al. 2016 and references therein), its distribution apparently limited to the Berriasian–Valanginian ( Díaz-Martínez et al. 2015) and the possible presence of a different ornithopod ichnotaxon in the Late Jurassic ( Piñuela et al. 2016), the tracks studied here are tentatively assigned to Iguanodontipodidae indet. because they perfectly fit the diagnosis proposed for the ichnofamily by Díaz-Martínez et al. (2015). These new specimens expand the record of the ichnofamily Iguanodontipodidae to the Late Jurassic.

Figures

Fig. 2. Photographs, false-colour depth maps, and outline drawing of the tracks of high morphological quality (MP = 2) that belong to the Iguanodontipodidae indet. morphotype. Portugal, Praia de Amoreira-Porto Novo Formation, upper Kimmeridgian (A, B) and Sobral Formation, upper Kimmeridgian–lower Tithonian (C–E). A. SHN.(JJS).ICNO.03, Valmitão Norte. Note that the track still preserves part of the infill. B. SHN.(JJS).ICNO.54, Valmitão Sul. C. SHN.(JJS).ICNO.48, Praia Azul. D. SHN.(JJS).ICNO.75, Foz Do Rio Sizandro. Note that the track has been painted and the real morphology is not exactly the same as the drawing. E. SHN.(JJS).ICNO.110, Foz Do Rio Sizandro. Scale bars E, 15 cm; A–C, 20 cm; D, 25 cm.