Paleontological analysis of Las Peñas Amarillas section

A paleoenvironmental and paleoichnological analysis of Las Peñas Amarillas section (upper Barremian-lower Aptian, Enciso, La Rioja, Spain)

Javier Rubio-Nieto, Jesús Reolid, Félix Pérez-Lorente, and Angélica Torices

Article number: 29.3.a37
https://doi.org/10.26879/1612
Copyright Society of Vertebrate Paleontology, September 2026

Author biographies
Plain-language and multi-lingual abstracts
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Submission: 11 July 2025. Acceptance: 20 August 2026.

ABSTRACT

This study presents a paleoenvironmental and palaeontological analysis of the new upper Barremian-lower Aptian dinosaur tracksite at Las Peñas Amarillas (Enciso, La Rioja, Spain). We described and sampled the stratigraphic section yielding the footprints for microfacies analysis. The tracks were identified, photographed, catalogued, and measured. Facies and microfacies data suggest deposition in the eulittoral zone of a shallow carbonate lake, subject to periodic terrigenous input from the avulsion belt of a large adjoining alluvial plain. The stratigraphic succession exhibits a shallowing-upward trend. A total of 26 footprints, comprising five trackways and two partial trackways, were identified, along with seven vague traces of uncertain affinity. The footprints range from 12 to 67 cm in length and are primarily attributed to ornithopod dinosaurs. Although traces referable to the nomen dubium “Hadrosaurichnoides igeensis” are present, we provide evidence further challenging the validity of this ichnotaxon. Finally, walking and trotting speeds were calculated, and signs of gregarious behaviour were inferred for some of the trackmakers.

Javier Rubio-Nieto. Departamento de Geodinamica, Estratigrafía y Paleontología, Área de Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, 28040 Madrid, Spain. [email protected]
Jesús Reolid. Departamento de Estratigrafía y Paleontología, Universidad de Granada, Facultad de Ciencias, 18071 Granada, Spain. [email protected]
Félix Pérez-Lorente. Universidad de La Rioja. Madre de Dios, 51-53, 26006 Logroño, La Rioja, Spain. [email protected]
Angélica Torices. Departamento de Geodinamica, Estratigrafía y Paleontología, Área de Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, 28040 Madrid, Spain. [email protected]

Keywords: ichnites, Cretaceous, La Rioja, theropod, ornithopod, Spain

Final citation: Rubio-Nieto, Javier, Reolid, Jesús, Pérez-Lorente, Félix, and Torices, Angélica. 2026. A paleoenvironmental and paleoichnological analysis of Las Peñas Amarillas section (upper Barremian-lower Aptian, Enciso, La Rioja, Spain). Palaeontologia Electronica, 29(3):a37.
https://doi.org/10.26879/1612
palaeo-electronica.org/content/2026/5956-paleontological-analysis-of-las-penas-amarillas-section

Copyright: September 2026 Society of Vertebrate Paleontology.
This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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INTRODUCTION AND OBJECTIVES

The Cameros Basin represents the region with the largest number of dinosaur footprints in the Iberian Peninsula and hosts one of the highest concentrations of dinosaur track sites worldwide (Pérez-Lorente, 2001; 2015). Although hundreds of sites have been identified and studied in the region, many others have been inventoried but remain to be studied in detail (García-Ortiz, 2015). In addition to the palaeoichnological record, numerous dinosaur skeletal remains have been recovered from this region over the years, primarily attributed to ornithopods (Torres and Viera, 1994; García-Palou et al. 2025) and spinosaurid theropods such as Riojavenatrix lacustris Isasmendi et al., 2024.

​​The Las Peñas Amarillas site is one of 18 dinosaur track sites discovered to date within the municipality of Enciso, in southern La Rioja, and one of at least 186 inventoried in this province (García-Ortiz, 2015). The site preserves 26 dinosaur footprints and seven vague traces, distributed across three distinct surfaces found on fallen blocks (Figure 1). Despite being inventoried and mentioned in previous publications (Pérez-Lorente, 2013; García-Ortiz, 2015), as well as being easily visible and accessible, the site has not yet been the subject of a comprehensive study.

This work presents an integrated study of 1) the ichnology, including measurements and definition of the main morphological parameters of the footprints, as well as their palaeoethological interpretation; and 2) the sedimentology of the section, in order to reconstruct the palaeoenvironmental conditions that led to the preservation of dinosaur footprints in this area. This study aims to contribute to the palaeoenvironmental characterization of this important Early Cretaceous palaeontological sector in Spain. Furthermore, it seeks to provide new data on the ethology of the dinosaurs of La Rioja, enhancing our understanding of their role in the Cretaceous ecosystem of Cameros. This research is of significant interest not only for the scientific community but also for outreach activities, which are crucial for the regional economy.

LOCATION AND GEOLOGICAL CONTEXT

The study section, Las Peñas Amarillas (42º08'55.5'' N; 2º16’9’’ W), is located near the town of Enciso (La Rioja, Spain), in the northwesternmost sector of the Iberian Range. The site lies within the geological unit of the Cameros Basin, a WNW-ESE oriented hill range covering an area of 7,500 km ^².

The Cameros Basin is bounded by the Paleozoic outcrops of the Sierra de la Demanda and Neila ranges to the northwest, the mostly Triassic Moncayo Range to the southeast, and the Cenozoic basins of the Ebro to the north and Almazán to the south (Figure 2). Based on its sedimentary and structural characteristics, the Cameros Basin can be divided into two clearly differentiated sectors: Western Cameros and Eastern Cameros (Tischer, 1966a; Salomon, 1980; Guiraud, 1983; Alonso and Mas, 1993; Clemente and Pérez-Arlucea, 1993; Mas et al., 1993), with the study section located within the latter (Figure 2).

The oldest fill of the Cameros Basin is Tithonian in age (Aurell et al., 1994; González-Acebrón, 2010). Approximately 5,000 m of Tithonian-lower Albian sediments accumulated in the Cameros Basin (Mas et al., 1993; 2002). Beuther (1966) and Tischer (1966b) divided the basin fill into five large lithostratigraphic units (Tera, Oncala, Urbión, Enciso, and Oliván groups). Other authors (Mas et al., 1993, 2002; 2004; Salas et al., 2001) have suggested that the upper Jurassic-upper Cretaceous materials of the basin form a megacycle or supersequence, divided into eight depositional sequences (DS 1-8). According to Mas et al. (2002) and Omodeo-Salé (2014), the correspondence between the classical lithostratigraphic groups and the newer depositional sequences is as follows:

• Tera Group = DS 1 + DS 2
• Oncala Group = DS 3
• Urbión Group = DS 4 + DS 5 + DS 6 + part of DS 7
• Enciso Group = part of DS 7
• Oliván Group = DS 8

According to the regional stratigraphy, the Las Peñas Amarillas section is included within the Enciso Group (Beuther, 1966; Tischer, 1966) or Sequence 7 of Omodeo-Salé (2014), which ranges from upper Barremian to upper Aptian in age (Schudack, 1987; Guiraud and Séguret, 1985; Doublet and García, 2004).

The Enciso Group is composed of a sedimentary succession more than 2,000 m thick that unconformably overlies the Oncala and Urbión groups, and the Cabretón Formation (Clemente, 2010). The lower part of this unit consists of fluvial deposits from the Río Mayor (Unit C123sa of Cámara-Rupelo and Durántez-Romero, 1981) and Río Cidacos (Clemente, 2010) formations. The middle and upper parts consist of a wide variety of lacustrine and littoral carbonates, evaporites, and limestone banks of varying thickness, alternating with marls exhibiting desiccation cracks, and fine-grained sandstones and siltstones with ripples and hummocky cross-stratification (Doublet et al., 2003). The Enciso Group is interpreted as a huge semi-enclosed coastal lake complex, open to the sea to the north, towards the Bay of Biscay (Clemente, 2010).

Like other basins within the Iberian Rift System, the Cameros Basin began to develop in the Tithonian (Aurell et al., 1994; González-Acebrón, 2010). During the Early Cretaceous, generalized subsidence of the Cameros Basin commenced, creating a marine landscape dotted with islands and transitional sedimentary environments including marshes, deltas, and estuaries (Meléndez-Hevia, 2004). Doublet (2004) proposed a shallow lake fed from the south by a vast alluvial plain during the Barremian-lower Albian time interval as a palaeogeographic model for the Cameros Basin.

According to Rey-Moral (2001), at the end of the lower Albian, a regressive period with a large influx of terrigenous material from emerged areas began, covering large areas of the basin with continental sediments. From the Cenomanian-Turonian onwards, a major marine transgression occurred, creating an elongated epicontinental sea called the Iberian Strait. This connected the Cantabrian and Tethyan domains, covering the previous basins and homogenising sedimentation, which became mostly marine (Alonso et al., 1991). From the upper Albian onwards, the Cameros Basin, like other basins of the Late Jurassic-Early Cretaceous Iberian rift, lost its identity, giving way to large carbonate platforms that occupied the Iberian Strait during the Upper Cretaceous.

Alonso and Mas (1993) stated that the Enciso Group was deposited on large alluvial plains. These were dominated by river systems flowing from the southern margin, with their attached deltas partitioning the permanently flooded area into smaller coastal lakes and lagoons (Figure 3). This depressed and flooded area was also subject to inflows of seawater from episodic transgressions of the Tethys Sea (Doublet, 2004; Hernán-Martínez, 2018). These transgressions into the depressed palaeolake were driven by the NW Iberian Mesozoic Rift System (Doublet, 2004; Hernán-Martínez, 2018). Lacustrine sedimentation appears to have been continuous in space and time (Hernán-Martínez, 2018).

During the Cretaceous, the Iberian Plate occupied a tropical position between latitudes 20° and 30° N (Rat, 1982). Therefore, the climate was predominantly hot and humid during this period. Throughout the Cretaceous, these conditions were maintained with only minor variations (Bowen, 1966; Pearson, 1978; Barron et al., 1995; Frakes, 1999; Quijada et al., 2020).

METHODS

The study of the Las Peñas Amarillas section was based on detailed facies mapping using panoramic photomosaics of the best-exposed intervals of the succession. The 25 m thick study section was described bed-by-bed and sampled for petrographic analysis. Facies and microfacies analyses were based on field observations and the study of 30 thin sections.

Dinosaur footprints were highlighted with chalk, photographed, and mapped using a 3 × 3 m grid subdivided into 30 × 30 cm squares. A 2D reconstruction of the footprints was created using Adobe Illustrator, based on the photographs and their relative positions within the grid.

Subsequently, morphometric parameters were measured for both footprints and trackways. Footprint measurements included: footprint length (l), footprint width (w), interdigital or divarication angles (II^III, III^IV), and digit lengths (II, III, IV) (Figure 4). Trackway measurements included: pace (P), stride (S), pace angle (Pa), trackway deviation (Td), trackway width (Tw), and footprint rotation relative to the trackway midline (O) (Figure 5).

Hip height (h) was calculated following Alexander (1976) as four times the footprint length (h ≈ 4l). This formula is based on observations of “many bipedal dinosaurs of a wide range of sizes, both Theropoda and Ornithopoda” (Alexander, 1976).

RESULTS

Stratigraphy

Six lithostratigraphic units were defined based on their facies, microfacies, and fossil assemblages (Table 1, Figure 6). These units bear many similarities to some of the lithofacies identified by Hernán-Martínez (2018) for the Enciso Group.

Unit 1. At the base of the succession, the facies consist of a 2.80 m thick dark brown mudstone with ostracods (Figure 7A). This facies occurs in beds ranging in thickness from 10 to 70 cm (Figure 7B). The strata are mostly massive, exhibiting minor horizontal lamination that pinches out laterally. Bioturbation is generally scarce or absent. Poorly developed ferruginous horizons are present (Figure 7C).

Unit 2. The massive mudstone of Unit 1 transitions gradually upward (Figure 7D) into a 4.20 m thick massive grey wackestone with abundant micritic intraclasts and ostracods (Figure 8A). This facies contains terrigenous components, including silt-sized fragments of calcite, quartz, and muscovite. The content of terrigenous material increases towards the top of the unit, contrasting with an upward decrease in ostracod abundance. Unit 2 is arranged in decimetre-thick beds, exhibiting a clear thinning-upward trend (Figure 8B). The uppermost part of the unit consists of well-bedded tabular wackestone (Figure 8C). Some beds display centimetre-scale load deformation structures. Iron-stained horizons are common (Figure 8D). The top of this unit interdigitates with the massive quartz sandstones of the overlying unit.

Unit 3. This unit is 2.5 m thick and consists of massive grey quartz sandstones (Figure 9A). Quartz grains constitute between 40-50% of the rock volume (Figure 9B). Bedding is poorly developed and recognizable only towards the top of the interval. The top surface of this unit is exposed and displays numerous centimetre-scale load deformation structures.

Unit 4. Unit 4 comprises a 10.5 m thick package of massive grey marls. The marls are generally unconsolidated, although discontinuous centimetre-scale intervals of consolidated material occur between metre-scale intervals of softer material (Figure 10A-B). Abundant intraclasts are present, some exhibiting imbrication. Bioturbation is intense, locally giving the rock a mottled appearance. The dominant fossils are ostracods, which occur both scattered and in accumulations ranging from millimetres to centimetres in thickness.

Unit 5. This unit consists of a 3 m thick package of dark grey ostracod mudstone. Ostracods are abundant and locally accumulate within centimetre-wide burrows with a packstone texture (Figure 11A). Centimetre-thick mudstone beds with flat bases and wavy tops are intercalated with millimetre- to centimetre-thick marl beds (Figure 11B). A channelized body is present at the top of this unit. It extends laterally for several metres and reaches a maximum thickness of 1 m (Figure 11C). The channel facies consist of very fine-grained quartz sandstone with minor amounts of calcite, muscovite, and biotite (Figure 11D). The siliciclastic grains are embedded in a micritic or sparitic matrix.

Unit 6. Unit 6 is 2 m thick and comprises massive black mudstone to packstone (yellowish-brown when weathered) with abundant ostracods (Figure 12A-B). The unit consists of tabular beds 20 to 70 cm thick, with millimetre-thick marl intercalations between beds (Figure 12C). Towards the top of these intervals, some beds preserve mud cracks on their upper surfaces (Figure 12D). The top of the unit is marked by the occurrence of abundant dinosaur footprints (Figure 12E) and minor invertebrate traces, mostly Thalassinoides (Figure 12F).

Paleoichnology

A total of 33 footprints were identified across three distinct surfaces at the top of Unit 6. Site 1 preserves 22 footprints; Site 2, nine; and Site 3, two. The dataset comprises 26 complete dinosaur footprints and seven poorly defined traces of uncertain affinity--hereafter referred to as partial traces--which are excluded from the detailed description.

Of these 33 recognized footprints, 18 are associated with five trackways and four with two partial trackways, while 11 occur as isolated footprints. Footprint measurements are presented in Table 2 and Table 3.

Site 1. Site 1 is located on the largest of the three fallen blocks and contains the highest abundance of footprints. A total of 22 footprints are preserved at Site 1 (Figure 13), arranged within four trackways (1.1, 1.2, 1.3, and 1.5) and one partial trackway (1.4), alongside isolated footprints 1LPA6, 1LPA7, 1LPA8, 1LPA9, and 1LPA10 (LPA stands for Las Peñas Amarillas) (Figure 13, Figure 14A; Table 2 and Table 3). The trackways comprise the following number of footprints: 1.1 (four footprints), 1.2 (five footprints), 1.3 (three footprints), 1.4 (two footprints), and 1.5 (three footprints).

Different morphologies, or morphotypes, of dinosaur footprints were recognized at this site:

Morphotype 1. The footprints from trackways 1.1 and 1.2, as well as the isolated footprint 1LPA8, display similar morphology. The best-preserved footprints belong to Trackway 1.1, in contrast to those of trackway 1.2, which are poorly preserved, exhibiting an oval shape (1LPA2.4) (Figure 14B) or incomplete tridactyl morphologies (1LPA2.1). Footprint length ranges from 23 to 32 cm, with 1LPA1.2 being the longest. However, the most complete footprints present values exceeding 27 cm (Table 2). Based on their width, it can be inferred that the less complete footprints, such as 1LPA2.1 and 1LPA2.5, would have reached similar length values. Most footprints are longer than they are wide, although the difference between these dimensions does not exceed 12% in most cases. Digit impressions consist of a single pad with a rounded tip and are in contact with each other. Interdigital angles usually range from 20° to 30° for both II^III and III^IV. The middle digit is usually the longest, ranging from 12 to 17 cm, followed by digits II and IV, both of which range from 9 to 14 cm. The heel, as well as the general outline of the footprint, is usually rounded. The distal part of the footprints is typically better defined than the heel area.

As previously noted, the isolated footprint 1LPA8 exhibits a morphology similar to those in trackway 1.1 (Figure 14C), particularly when compared with 1LPA1.4 (Figure 13). Generally, the footprints lack displacement rims, grooves, or other traces associated with foot movement; only the footprint outline and pad separation traces are preserved (Figure 14D). However, footprints 1LPA1.1 and 1LPA1.4 show mud accumulation at their distal end, especially between the digits.

Morphotype 2. Trackway 1.3 consists of three footprints, of which only 1LPA3.3 is well preserved (Figure 14E). Consequently, this footprint provides the only reliable length measurement for the trackway (30 cm) (Table 2). The footprints are wider than they are long, reaching a width of 34 cm (1LPA3.3). The digits are long, separated from each other, and terminate in an acuminate tip. Interdigital angles in 1LPA3.3 are 22° for II^III and 28° for III^IV. Digit II is the longest measured (nearly 16 cm), followed by digit III (11.45 cm) and digit IV (11.28 cm). The heel protrudes slightly, but the footprint outline remains rounded. This footprint also lacks any other structure associated with foot movement.

The isolated footprint 1LPA6 displays a poorly defined morphology, somewhat similar to footprint 1LPA3.2, and is oriented in the same direction (Figure 14F). However, its position relative to trackway 1.3 is problematic, preventing a definite assignment to this trackway.

Morphotype 3. The footprints associated with trackways 1.4 (two footprints) and 1.5 (three footprints) present similar morphologies. The footprints in trackway 1.5 are slightly larger than those in trackway 1.4. Footprint length ranges from 25 to 33 cm (Table 2). The footprints are generally longer than they are wide, with a difference of up to 14% between the two dimensions. The digits are long, well-defined, and separated from each other (except in 1LPA4.1) (Figure 14G), and their tips are rounded (except in 1LPA5.1) (Figure 13). Interdigital angles range from 14° to 19° in trackway 1.4, and from 22° to 35° in trackway 1.5. Digit III is clearly the longest, reaching double the length of the other two digits in 1LPA4.1 and 1LPA5.2 (15.78 and 23.56 cm, respectively). The heel is V-shaped, narrower, and less rounded than in other trackways. The morphology of these footprints is generally well defined, except for the anterior ends of 1LPA4.2 and 1LPA5.3, and the left side of footprint 1LPA5.1, which are eroded (Figure 13). These footprints lack dynamic traces associated with the contact, support, or lift-off phases.

Undefined traces. These isolated traces present markedly different morphologies, sizes, and preservation states compared to the previously described ichnites (Figure 13, Table 3). The preservation of traces 1LPA7 and 1LPA10 is so poor that their identification as true footprints is ambiguous (Figure 13). 1LPA9 displays a rounded heel and acuminate digit impressions (Figure 14H). It is also one of the largest ichnites at the site, reaching a length of 36 cm (Table 3). These traces exhibit no marks associated with foot movement, except for some small displacement rims around 1LPA10.

Site 2. Only one trackway is preserved at Site 2 (Figure 15), containing three large footprints (Figure 16A). In addition, six other, mostly poorly defined footprints are present. Two additional footprint morphotypes were identified at this site.

Morphotype 4. The footprints belonging to trackway 2.1 are of significant size, with a mean length of 53 cm. Footprint 2LPA1.3 reaches 67 cm in length, making it one of the largest ornithopod footprints found in La Rioja (Figure 16B) (Table 2). In some cases, the width exceeds the length, with values around 55 cm. The digits are not well defined and consist of a single pad. Interdigital angles show mean values of 13° for II^III and 34° for III^IV. Digit III is the longest, ranging from 19 to 35 cm, followed by digit II (15 to 34 cm) and digit IV (12 to 31 cm). The digits are generally joined, and the tips are rounded. The heel impression is the most obscure part of the footprints, although some roundness is observable (Figure 16C).

Morphotype 5. Footprints 2LPA2 and 2LPA3 belong to this morphotype (Figure 15, Figure 16D). Footprint 2LPA2 exhibits a well-defined morphology, allowing for all individual measurements to be taken (Table 3). This is not the case for 2LPA3, which is poorly defined. 2LPA2 is 34 cm long and 23 cm wide. Its digits are represented by a single pad, separated from each other, and are pointed. The interdigital angles are 30° for both II^III and III^IV. Digit III is the longest, reaching 14 cm in length. The values for digits II and IV are approximately 5 cm each. The digits are relatively small compared to the heel area, which is V-shaped and elongated (Figure 16D). Although footprint 2LPA3 is poorly defined, its position relative to 2LPA2 suggests that both were produced by the same trackmaker.

Undefined footprints. This site also contains a set of poorly defined isolated traces that cannot be unequivocally identified as true footprints due to both their morphology and their position within the outcrop (Figure 15, Table 3). These correspond to 2LPA4, 2LPA5, 2LPA6, and 2LPA7. Neither these isolated footprints nor those in trackway 2.1 preserve associated sedimentary deformation structures related to foot movement, apart from the footprint outline and pads.

Site 3. This site contains a single trackway with two footprints, representing a distinct morphotype (Figure 17).

Morphotype 6. The footprints in trackway 3.1 present well-defined digits and heels (Figure 17, Figure 18A-B), particularly 3LPA1.2 (Figure 18B). Footprint length is approximately 12 cm, and footprint width ranges between 9 and 10 cm (Table 2). The digits are separated and have pointed tips, with interdigital angles ranging between 27° and 34°. The longest digit is III, followed by II and IV (Figure 18A-B). Mean digit lengths are 6.45, 4.54, and 2.60 cm, respectively. The heels are V-shaped rather than rounded. No marks associated with locomotion are preserved.

DISCUSSION

Paleoenvironmental Reconstruction: Evolution of the Enciso Paleolake

The mudstone of Unit 1, which lacks current structures, indicates deposition from suspension in a low-energy environment, likely below the wave base. The preservation of ostracods does not allow for the specific characterization of a marine, brackish, or freshwater environment. However, palaeogeographically related outcrops in the Enciso Group have been attributed to the Enciso palaeolake, which occupied parts of a large alluvial plain within the Enciso Basin (Hernán-Martínez, 2018). Deposition of Unit 1 likely occurred in the central and deepest areas of this lacustrine basin (Figure 19A). The black colour of the sediment is probably due to the presence of organic matter, which, together with the scarcity of bioturbation, suggests oxygen-restricted conditions. Such conditions do not necessarily imply great depth, as there are numerous examples of shallow anoxic/dysoxic lakes (Jewell, 1992; Fürsich et al., 2007; Schnyder et al., 2009; Hethke et al., 2013; Rogov et al., 2020; Gil-Delgado et al., 2023).

The wackestone of Unit 2, containing abundant intraclasts, indicates a relatively higher-energy depositional environment compared to Unit 1. The fine-grained matrix is consistent with deposition in a quiet setting within the Enciso palaeolake, but likely shallower or more proximal than Unit 1, given the evidence of episodic sediment reworking and the deposition of micritic intraclasts recorded in Unit 2 (Figure 8A). The increasing amount of siliciclastic material towards the top of Unit 2 suggests sediment supply by a river or ephemeral flows. Hernán-Martínez (2018) interprets this facies type as fine-grained deposits typical of an avulsion belt, formed by subaqueous suspension settling (Figure 19B). This material is interpreted as deriving from channel overflows during avulsions, typical of aggrading floodplains such as the Enciso Basin (Bridge and Leeder, 1979; Mackey and Bridge, 1995; Heller and Paola, 1996; Pérez-Alucea and Smith, 1999; Morozova and Smith, 2000). Such currents may also explain the sediment reworking and the deposition of intraclasts. The increased intensity of bioturbation in this facies compared to Unit 1 can be attributed to the input of well-oxygenated waters into the palaeolake, contrasting with the restricted environment that prevailed during the deposition of Unit 1.

The siliciclastic sandstone of Unit 3, exhibiting subaerial exposure features (Figure 9A), indicates deposition in a shallow environment subject to periodic emersion. The high content of siliciclastic material (Figure 9B) in this unit suggests either periods of intensified terrigenous input or a more proximal position to the source area. This facies is interpreted as having been deposited in marginal shallow lacustrine zones, characterized by high terrigenous input (Glass and Wilkinson, 1980; Arribas, 1986), ultimately leading to emersion. This facies represents the culmination of a shallowing-upward sequence comprising Units 1 to 3. The occurrence of marly intervals towards the top of Unit 3 marks the onset of a deepening-upward sequence (Figure 19C).

The massive marl facies of Unit 4 is characterized by a very fine grain size, a high content of limnic fossils, and the absence of traction structures. This points to deposition from suspension under quiet water conditions, likely below the wave base (Figure 19D). Based on facies analysis, Unit 4 was deposited in a deeper environment than Unit 3, consistent with the transgressive trend that began at the top of Unit 3 (Figure 19). Unit 4 exhibits a massive appearance, which may result either from an original lack of lamination during deposition or from the post-sedimentary destruction of primary structures by bioturbation. The latter interpretation is supported by the mottled appearance observed in some intervals. The intense bioturbation and the absence of dark-coloured intervals suggest deposition in a well-oxygenated environment.

The mudstone facies of Unit 5, characterized by the absence of subaerial exposure features, indicates deposition in shallow waters where carbonate production exceeded terrigenous input. This setting is typical of the open-sublittoral zone of shallow carbonate lakes (Dean, 1981; Gierlowski-Kordesch, 2010) (Figure 19E). The presence of ostracod packstone filling the burrows is indicative of periods of relatively high energy (Figure 11A). The occurrence of higher-energy events is also supported by the presence of a palaeochannel several metres wide at the top of the unit (Figure 11C-D). The lack of significant internal erosive surfaces and lateral accretion surfaces suggests mono-episodic channel filling (Friend et al., 1979; Haszeldine, 1984). Channels such as that of Unit 5 are typical of avulsive fluvial systems, similar to those inferred for the Enciso Basin (Tye and Coleman, 1989; Smith and Pérez-Arlucea, 1994; Pérez-Arlucea and Smith, 1999). Unit 5 marks a turning point in the transgressive trend and the onset of a new shallowing-upward sequence (Figure 19).

Unit 6 comprises silty-clay sediments and mudstone facies with abundant ostracods (Figure 12), suggesting that this unit represents deposits of the open-sublittoral zone of a shallow carbonate lake (Figure 19F). The occurrence of distinctive features of subaerial exposure, such as desiccation cracks and dinosaur footprints (Figure 12D-E), points to episodic exposure. This allows the sedimentary environment to be interpreted more precisely as the shore or marsh of the Enciso palaeolake. Accordingly, this unit can be considered to represent the lowest water level of the lake, marking the end of the shallowing-upward trend that began in Unit 5 (Figure 19F).

Palaeoichnogical Analysis

Site 1. Morphotype 1. The footprints assigned to trackways 1.1 and 1.2, as well as the isolated footprint 1LPA8, exhibit features characteristic of ornithopod dinosaurs: a subcircular outline, rounded or rhomboid digit impressions, closely spaced digits with a single pad each, and a wide, rounded heel (Thulborn, 1990; Pérez-Lorente, 2001: Díaz-Martínez et al., 2015) (Figure 13, Figure 14B-D). The footprints belonging to trackway 1.2 are generally poorly defined or incomplete. This preservation state may be attributed to the overprinting of footprints 1LPA1.2 and 1LPA1.3 upon 1LPA2.2 and 1LPA2.3, respectively. However, certain ornithopod features can still be discerned, such as a subcircular shape and rounded, closely spaced digits (Moratalla et al., 1988; Thulborn, 1990; Lockley, 1991; Pérez-Lorente, 2001; Mateus and Milàn, 2008; Romilio and Salisbury, 2011) (Figure 13). Furthermore, they present measurements very similar to those of trackway 1.1, particularly regarding pace, stride length, and speed (Table 2).

The footprint length-to-width ratio classifies footprints 1LPA1.1, 1LPA1.4, 1LPA2.1, and 1LPA2.5 as wide, and 1LPA1.2, 1LPA1.3, and 1LPA2.4 as narrow. Consequently, the footprints exhibit similar length and width values, resulting in a subcircular outline, which is a typical ornithopod feature. The III/l ratio displays a mean value above 0.5 for trackway 1.1 (Table 2). According to Moratalla et al. (1988), this ratio suggests a theropod affinity.

The S/l ratio suggests that the trackmaker’s limbs were robust for trackway 1.1, and normal for 1.2. According to Pérez-Lorente (2001), the minimum values of this ratio for theropod footprints are above 4.8. Given that footprints 1LPA1.2 and 1LPA1.3 present lower values (Table 2), this criterion supports their classification as ornithopod footprints. However, it must be noted that footprints 1LPA2.1 and 1LPA2.5 exceed a value of 5.5 for the S/l ratio (Table 2), a value regarded by Pérez-Lorente (2001) as the maximum for ornithopod footprints. This discrepancy, however, may be attributed to the incomplete preservation of the footprint length (Figure 13). The Td/w ratio indicates that both trackways are very narrow, which is a feature more typical of theropods (Pérez-Lorente, 2001).

Collectively, these data suggest that the trackmaker of this morphotype was likely an ornithopod. Speeds of approximately 4 and 5 km/h were calculated for trackways 1.1 and 1.2, respectively (Table 2). Based on the S/h ratios, it can be inferred that the animals were moving at a walking pace (Pérez-Lorente, 2001). The estimated mean hip heights are approximately 121 cm for trackway 1.1 and 134 cm for 1.2, following the formula proposed by Alexander (1976). Footprint 1LPA8 yields a hip height of 100 cm (Table 3). These measurements indicate that the trackmaker of this morphotype was most probably a small- to medium-sized ornithopod.

Footprints 1LPA1.2 and 1LPA1.3 bear a strong resemblance to the holotype (1PL11.3) and paratype (1PL38) of “Hadrosaurichnoides igeensis” Casanovas et al., 1993, an ichnotaxon originally described at the La Era del Peladillo site in La Rioja (Figure 20). When the footprints shown in Figure 20 are modified by mirroring and scaling them to match footprint 1LPA1.3, and the outline impressions interpreted as interdigital webbing are excluded, the morphological similarities become even more apparent (Figure 21). If the attribution of footprints 1LPA1.2 and 1LPA1.3 to “Hadrosaurichnoides” is correct, this represents the first occurrence of this ichnotaxon outside the La Era del Peladillo site.

Morphotype 2. The footprints assigned to trackway 1.3 are generally poorly defined (Figure 13), except for 1LPA3.3 (Figure 14E). The latter exhibits distinct ornithopod features, such as a subcircular outline and a rounded heel, but also displays some theropod characteristics, including relatively pointed digit tips and discrete separation between the digits (Moratalla et al., 1988; Thulborn, 1990; Lockley, 1991; Pérez-Lorente, 2001; Mateus and Milàn, 2008; Romilio and Salisbury, 2011). Footprint length and width values are very similar, and the trackway is classified as very narrow (Table 2). The III/l ratio is less than 0.5, while the S/l ratio exceeds the maximum threshold typically established for ornithopod footprints. Based on these observations, we conclude that the footprints were most likely produced by a theropod dinosaur.

The calculated speed for this trackway is 8.2 km/h (Table 2), corresponding to a walking gait. The estimated hip height is approximately 110 cm. Thus, the trackmaker of this morphotype was likely a small- to medium-sized theropod. Although a precise taxonomic assignment to a specific genus is not possible, based on the size and age of the footprints, potential candidates can be proposed from among medium-sized theropods known from the Early Cretaceous of the Iberian Peninsula and neighboring European regions. These include three main groups: spinosaurids such as Vallibonavenatrix cani Malafaia et al., 2019 (Barremian of Morella, Castellón) or Riojavenatrix lacustris Isasmendi et al., 2024 (Aptian of Igea); carcharodontosaurids such as Concavenator corcovatus Ortega et al., 2010 (Barremian of Cuenca); or abelisaurids such as Genusaurus sisteronis Accarie et al., 1995 (Albian of Provence, France). Footprint 1LPA6 is too poorly preserved to be classified, although, as previously noted, it bears some resemblance to the footprints assigned to trackway 1.3 (Figure 13, Figure 14F).

Morphotype 3. The footprints assigned to trackways 1.4 and 1.5 exhibit similar morphologies, which are distinct from other footprints at the site. They present an oval outline and a protruding heel, particularly in footprint 1LPA4.2 (Figure 13). These are typically theropod traits (Moratalla et al., 1988; Thulborn, 1990; Lockley, 1991; Pérez-Lorente, 2001; Mateus and Milàn, 2008; Romilio and Salisbury, 2011). However, they also display some ornithopod features, such as closely spaced digits and rounded digit tips (except for 1LPA5.1). The footprints are notably longer than wide, a characteristic reflected by the higher values of the (l-w)/w ratio (Table 2).

The III/l ratio yields values exceeding 0.5 in footprint 1LPA5.2 (a theropod trait), but lower values in 1LPA4.1 and 1LPA5.1 (an ornithopod trait) (Moratalla et al., 1988). In the latter cases, however, this may be attributed to the incomplete preservation of footprint length. The S/l ratio for trackway 1.5 exceeds the theoretical maximum value for ornithopods, although this may again be due to the incomplete length of some footprints (Figure 13). The Td/w values indicate a very narrow trackway (Pérez-Lorente, 2001). Consequently, the footprints exhibit a predominance of theropod over ornithopod traits.

A speed of 8.7 km/h was calculated for trackway 1.5 (Table 2), inferring a trotting gait. Mean hip height values are approximately 120 cm for trackway 1.4 and 128 cm for 1.5. Therefore, the trackmaker was likely a medium-sized theropod, possibly belonging to one of the groups discussed for Morphotype 2.

Undefined traces. Traces 1LPA7 and 1LPA10 are poorly defined, to the extent that their identification as true footprints remains ambiguous (Figure 13).

Footprint 1LPA9 exhibits some theropod traits, such as long, separated digits with acuminate tips, but also features ornithopod characteristics, such as a rounded heel (Moratalla et al., 1988; Thulborn, 1990; Lockley, 1991; Pérez-Lorente, 2001; Mateus and Milàn, 2008; Romilio and Salisbury, 2011) (Figure 13, Figure 14H). It presents an (l-w)/w ratio characteristic of a slightly narrow footprint and III/l values above 0.5, suggesting a theropod affinity (Table 3). Consequently, we conclude that the trackmaker was most likely a theropod dinosaur. Its estimated hip height is 144 cm, based on the ratio proposed by Alexander (1976). As with previous morphotypes, this footprint was likely produced by a medium-sized theropod belonging to one of the groups previously discussed.

The trackways at Site 1 are generally very narrow (Figure 13) and possess high pace angles (Table 2), features typically characteristic of theropods. However, in trackways 1.3 and 1.5, these characteristics may also be explained because of the animal’s speed and trotting gait (Pérez-Lorente, 2001; 2015).

Site 2. Morphotype 4. Trackway 2.1 comprises footprints 2LPA1.1, 2LPA1.2, and 2LPA1.3 (Figure 15). These footprints are of significant size, particularly 2LPA1.3 (Figure 16B), which reaches 67 cm in length (Table 2). This makes it one of the largest ornithopod footprints recorded in La Rioja, comparable to specimens such as NZ9.1 from the Navalsaz site (75 cm long) and AND1.3 from the La Cuesta de Andorra site (62 cm long). They exhibit clear ornithopod features, including a circular outline, rounded and closely spaced digits, and a single pad per digit (Moratalla et al., 1988; Thulborn, 1990; Lockley, 1991; Pérez-Lorente, 2001; Mateus and Milàn, 2008; Romilio and Salisbury, 2011). This attribution is further supported by the relatively low pace angle, the broad foot shape, and the inferred robustness of the limbs.

The length-to-width ratio indicates a slightly wide footprint, although the values are close to the boundary between wide and narrow categories (Table 2). The mean III/l ratio is consistent with an ornithopod trackmaker, and the S/l ratio remains below the minimum threshold for theropod trackways. The Td/w ratio again indicates a very narrow trackway. The speed calculated for this animal is approximately 2.16 km/h, corresponding to a walking gait (Table 2). The mean hip height is calculated at 214 cm; however, this value is likely an underestimate due to the apparently incomplete length of footprint 2LPA1.1 (Figure 15), suggesting the actual height was somewhat greater.

Thus, these footprints were likely produced by a large-bodied ornithopod. Numerous large ornithopod species are known from the Early Cretaceous of the Iberian Peninsula, providing a long list of potential trackmakers, including Delapparentia turolensis Ruiz-Omeñaca, 2011; Proa valdearinnoensis McDonald et al., 2012; Iguanodon galvensis Verdú et al., 2015; Morelladon beltrani Gasulla et al., 2015; Magnamanus soriaensis Fuentes-Vidarte et al., 2016; and Portellsaurus sosbaynati Santos-Cubedo et al., 2021. The poor definition of the footprints in this trackway makes assignment to a particular ichnogenus difficult. Although their size suggests an association with other large ornithopod ichnogenera present in La Rioja, such as Brachyguanodonipus Moratalla, 1993, Iguanodontipus Sarjeant et al., 1998, and Iguanodonipus Moratalla, 1993, they cannot be definitively assigned to any of them.

Morphotype 5. The other measurable footprint at this site is 2LPA2 (Figure 16D). This footprint is notably longer than it is wide, suggesting that the metatarsus sank deeply into the sediment, creating an elongated impression. The III/l ratio suggests an ornithopod affinity (Table 3). However, its morphological features, such as a V-shaped heel, acuminate digit tips, and a significantly longer digit III, indicate a theropod origin (Moratalla et al., 1988; Thulborn, 1990; Lockley, 1991; Pérez-Lorente, 2001; Mateus and Milàn, 2008; Romilio and Salisbury, 2011). The calculated hip height for 2LPA2 is 137 cm; therefore, this footprint was likely produced by a small- to medium-sized theropod.

The outline of 2LPA2 bears a strong resemblance to various taxa within the ichnofamily Eubrontidae, such as Anchisauripus Lull, 1904, Eubrontes Hitchcock, 1845, and Grallator Hitchcock, 1858 (Figure 22). Footprint 2LPA2 could potentially be assigned to this ichnofamily, assuming that the traces of digit separation have been eroded. However, due to the poor preservation of the track and the erosion of diagnostic features, a definitive assignment is not possible, and this association remains tentative. 2LPA2 is oriented in a similar direction to the footprints of trackway 2.1 (Figure 15). This alignment would be further supported if footprint 2LPA3 were confirmed to belong to the same trackway as 2LPA2, although this relationship remains unclear.

Undefined traces. Some of the undefined traces at this site exhibit a rounded morphology that suggests they may be ornithopod manus impressions. However, this interpretation cannot be confirmed due to their isolated occurrence within the site (Figure 15).

Site 3. Morphotype 6. The third site contains only two footprints, which form trackway 3.1 (Figure 17). These footprints exhibit distinct theropod features, such as a less rounded outline, a protruding heel, and long, separated digits with pointed tips (Moratalla et al., 1988; Thulborn, 1990; Lockley, 1991; Pérez-Lorente, 2001; Mateus and Milàn, 2008; Romilio and Salisbury, 2011). Footprint 3LPA1.1 appears to preserve a distinct pad impression corresponding to the distal phalanx of digit III (Figure 18A). The (l-w)/w ratio indicates narrow footprints (Table 2), and the mean III/l value exceeds 0.5, a trait characteristic of theropods (Moratalla et al., 1988). Speed cannot be calculated based on only two footprints. Finally, the estimated mean hip height for the trackmaker is approximately 50 cm, representing the smallest individual recorded at the site (Table 2).

In terms of morphology and size, these footprints resemble certain tracks recorded at the Barranco de Valdebrajés site (also in La Rioja) (Figure 23). The (l-w)/w ratios calculated for some of these footprints are comparable to those of trackway 3.1, suggesting that the trackways at both sites were produced by a similar trackmaker.

However, the identity of the trackmaker responsible for the small footprints at the Barranco de Valdebrajés site remains a subject of debate. Some authors attribute these footprints to a small ornithopod similar to Hypsilophodon (Aguirrezabala, Torres and Viera, 1985; Viera and Torres, 1992; Lockley et al., 1998; Pérez-Lorente, 2015), whereas others argue for a small theropod trackmaker (Casanovas et al., 1991; Casanovas, Fernández, et al., 1992; Pérez-Lorente, 2015). To date, the taxonomic affinity of these footprints remains unresolved. Unfortunately, the limited data from trackway 3.1 does not provide sufficient evidence to resolve this controversy.

Dinosaur behaviour. An analysis of the spatial distribution of footprints at Site 1 reveals that most trackways follow a similar orientation. Isolated footprints 1LPA9 and 1LPA8 also appear to conform to this trend. In contrast, trackway 1.3 exhibits a divergent angle and an opposing direction of movement. This also appears to be the case for footprint 1LPA6, although its poor preservation precludes definitive confirmation. The concordance of trackway headings may be interpreted as evidence of gregarious behaviour (Currie, 1983, 1995; Lockley and Hunt, 1995; Lockley et al., 2006; Castanera et al., 2013a; Fiorillo et al., 2014; García-Ortiz and Pérez-Lorente, 2014; Heredia et al., 2020; Paik et al., 2020; Yoon et al., 2021), particularly among those trackways sharing similar morphologies, such as 1.1 and 1.2, or 1.4 and 1.5. As previously noted, trackways 1.1 and 1.2 exhibit very similar pace, stride, and speed values, with the latter being relatively low (approximately 4 km/h). Thus, it can be inferred that both trackmakers likely belonged to the same taxon and were moving together, with the trackmaker of 1.2 potentially acting as the leading individual. Conversely, trackways 1.4 and 1.5 are spatially more distant and do not intersect or overlap at any point. The inability to measure stride length--and consequently calculate speed--for trackway 1.4 precludes a direct comparison with trackway 1.5. Regarding pace measurements, the similarity observed between trackways 1.1 and 1.2 is absent here. Consequently, there are insufficient criteria to either confirm or rule out gregarious behaviour between the trackmakers of 1.4 and 1.5.

The similarity in trackway headings could alternatively be explained by the presence of a physical barrier that constrained animal movement to specific directions (García-Ortiz and Pérez-Lorente, 2014; Getty et al., 2017). Such a barrier might correspond, for instance, to a lake margin, an interpretation consistent with the paleoenvironment inferred for the site. The divergent direction exhibited by trackway 1.3 could be viewed as an argument against the physical barrier hypothesis. However, the trajectory of trackway 1.3 displays a low angle of deviation relative to the other trackways; therefore, this divergence does not constitute a strong argument to refute the hypothesis. The orientation of trackway 1.3 can be interpreted in various ways compatible with the existence of a geographical barrier, such as temporal variations in the shoreline or the path of an animal approaching the lake to drink. Although the presence of a physical barrier cannot be ruled out, the similarity in speed between trackways 1.1 and 1.2, combined with the fact that their footprints overlap at two distinct points, provides compelling evidence of gregarious behaviour.

It is also possible to establish a chronological sequence for the passage of the animals. This determination is based on the superimposition of footprints 1LPA1.2 and 1LPA1.3 upon footprints 1LPA2.2 and 1LPA2.3, respectively, and the partial superimposition of footprint 1LPA3.3 upon 1LPA1.1. Based on this evidence, it can be inferred that the trackmaker of trackway 1.2 traversed the area prior to the trackmaker of 1.1, which in turn passed before the trackmaker of trackway 1.3. However, it is not possible to determine the time elapsed between the passage of these three individuals, nor are there criteria to establish a temporal relationship with other footprints at the site.

Sites 2 and 3 do not preserve sufficient footprints or trackways to allow for inferences regarding dinosaur behaviour.

The validity of “Hadrosaurichnoides igeensis”. As previously noted, footprints 1LPA1.2 and 1LPA1.3 of Morphotype 1 bear a strong resemblance to specimens assigned to the ichnotaxon “Hadrosaurichnoides igeensis”, suggesting they were likely produced by a similar trackmaker.

The ichnogenus Hadrosaurichnoides was originally erected by Casanovas et al. (1993), with the presence of apparent interdigital webbing serving as its primary diagnostic characteristic. However, subsequent authors have argued that there is no conclusive evidence supporting the biological reality of this feature (Lockley et al., 2003). This situation parallels that of other ichnogenera, such as Amblydactylus and “Hadrosaurichnus”, where impressions resembling interdigital webbing have been reinterpreted as extramorphological features (Lockley and Hunt, 1995; Díaz-Martínez et al., 2015). The purported webbing likely resulted from the animal trampling on microbial mats developed on the bedding planes. This interpretation has led to the classification of this taxon as a nomen dubium (Lockley and Hunt, 1995; Díaz-Martínez et al., 2015). Furthermore, the external morphology of “Hadrosaurichnoides” closely resembles the ichnogenus “Ornithopodichnus”, which is similarly considered a nomen dubium because it lacks indisputable diagnostic traits and was defined based on extramorphological features (Díaz-Martínez et al., 2015).

“Hadrosaurichnoides” was originally described from calcareous sediments exhibiting planar lamination produced by microbial mats parallel to the bedding (Casanovas et al., 1993). At the Era del Peladillo site, charophyte oogonia occur both isolated and in clusters, alongside indicators of algal mudflats attributed to cyanobacterial growth, which would have generated a cohesive, flexible substrate (Pérez-Lorente, 2015). Díaz-Martínez et al. (2015) proposed that these microbially induced sedimentary structures (MISS) were locally ruptured by the weight of the trackmaker, creating a structural discontinuity. Consequently, they interpreted “Hadrosaurichnoides” as a taphotaxon and, therefore, a nomen dubium.

If the attribution of footprints 1LPA1.2 and 1LPA1.3 (and by extension, all footprints assigned to Morphotype 1) to a trackmaker similar to that of “Hadrosaurichnoides” is correct, it implies the presence of a similar animal traversing a substrate where microfacies analysis reveals no evidence of MISS. Notably, despite their eroded state, the Morphotype 1 footprints exhibit no trace of interdigital webbing. These findings strongly support the hypothesis that the "interdigital webbing" associated with “Hadrosaurichnoides igeensis” is merely an artifact of the animal trampling on microbial mats, as suggested by previous authors.

We argue that, in the absence of this webbing, the other traits used to define the ichnospecies--such as digits with a single diamond-shaped pad or a wide, oval heel pad-oriented perpendicular to the axis of digit III--do not convincingly differentiate it from other ornithopod ichnotaxa, such as Hadrosauropodus or Caririchnium. Therefore, we concur with the argument proposed by Díaz-Martínez et al. (2015) and consider “Hadrosaurichnoides igeensis” to be a taphotaxon and a nomen dubium.

Under this interpretation, the “Hadrosaurichnoides” footprints, much like Morphotype 1 from the Las Peñas Amarillas site, still preserve many general ornithopod characteristics, including a subcircular outline, rounded or rhomboid digit impressions, closely spaced digits with a single pad each, and a wide, rounded heel. While it can still be inferred that these footprints were produced by large-bodied ornithopod dinosaurs--potentially moving as a herd--there are no reliable diagnostic traits to determine the specific type of ornithopod. Consequently, the claim by Casanovas et al. (1993) that the trackmaker represents “a transition species between iguanodontids and hadrosaurs” cannot be substantiated based on the available ichnological evidence.

CONCLUSIONS

The sedimentary sequence exposed at the Las Peñas Amarillas site was deposited during the Late Barremian-Late Aptian within an extensive shallow carbonate lake that occupied most of the Cameros Basin, referred to herein as the Enciso palaeolake. This system was strongly influenced by the Tethys Sea and by the influx of terrigenous material from a vast alluvial plain draining into the basin. The studied sequence records two shallowing-upward cycles (Units 1-3 and Units 4-6), separated by a deepening event marked by the deposition of Unit 4. Unit 6 represents the shallowest deposits of the Enciso palaeolake, interpreted as a eulittoral fringe subject to lake-level oscillations that resulted in periodic subaerial exposure, evidenced by the occurrence of desiccation cracks and dinosaur footprints.

The dominant fauna of the Enciso palaeolake comprised marine invertebrates, primarily ostracods and larger molluscs, as indicated by the presence of Thalassinoides burrows. Towards the top of the sequence, dinosaurs become a significant component of the fossil assemblage, as recorded by numerous footprints. Ornithopods and theropods were the primary dinosaur groups roaming the margins of the Enciso palaeolake. At the Las Peñas Amarillas site, six footprint morphotypes belonging to these major dinosaur groups were identified. The behaviour inferred from these trackways suggests that these animals may have exhibited gregarious behaviour along the lake shore (as indicated by the preferential orientation of the footprints), moving at walking or trotting speeds consistently below 10 km/h.

ACKNOWLEDGEMENTS

We would like to thank the town of Enciso for the help and assistance during this research. J. Reolid’s research was supported by the Ramón y Cajal Project RYC2021-034362-I (Ministerio de Ciencia, Innovación y Universidades). We would also like to thank Ó. Rodríguez Ocete and J. Adrián Sánchez López for their assistance with the initial data collection on the ichnites and their graphical representation.

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