Introduction

Palaeontological sites, in general, and tetrapod tracksites, in particular, form part of the natural and cultural heritage in many of the Spanish autonomous communities through various protection regulations (country level (Spain): “Law 16/1985, of 25 June, on the Spanish Historical Heritage”; autonomous community level (Aragon): “Law 3/1999, of 10 March, on the Aragonese Cultural Heritage”). In Spain, there has been an increased interest in the geological heritage in recent years (Carcavilla et al. 2009). Increasingly, palaeontology and, by extension, palaeoichnology are gathering strength as an important draw for tourism which can lead to socioeconomic benefits for some inland areas of Spain. There are many examples of this: Dinópolis and the “Ruta de las huellas de dinosaurios” in Teruel (Alcalá et al. 2006); the dinosaur tracksites of La Rioja (Pérez-Lorente 2015); the “Ruta de las icnitas de las Tierras Altas de Soria” (Barco et al. 2013; Castanera et al. 2017); or the “Jurassic Museum of Asturias” (MUJA, as per its Spanish acronym) and its tracksites (García-Ramos et al. 2003). All of these receive thousands of visitors each year and have brought great economic benefit to these areas of Spain. Palaeoichnological sites are of particularly significant touristic and educational value as they are true natural museums, allowing people to visit and see the natural phenomena, in this case the trace fossils, in their own geographical and geological context. Therefore, some of the most outstanding tracksites in several autonomous communities have been prepared for tourist visits, complying with the criteria of conservation, protection and accessibility to make these visits not only possible but non-destructive. These activities include the installation of information panels that aid the interpretation of this palaeontological heritage. This work has been carried out especially on dinosaur tracksites in the provinces of La Rioja (Pérez-Lorente 2000; Díaz-Martínez et al. 2010a; García-Ortiz et al. 2014; Fuertes-Gutiérrez et al. 2016), Asturias (García-Ramos et al. 2006; García-Ramos and Piñuela Suárez 2006), Teruel (Cobos 2004; Mampel et al. 2009; Castanera et al. 2011; Alcalá et al. 2016), Burgos (Torcida Fernández-Baldor et al. 2015) and Barcelona (Bates et al. 2008; Vila et al. 2008). Some Spanish authors (Mampel et al. 2009; Alcalá et al. 2016) have developed a specific numerical methodology to estimate the heritage value of the vertebrate tracksites on the basis of certain factors: scientific value, sociocultural value and the risk of deterioration. The sociocultural value is calculated according to a series of indicators that include touristic and educational potential, accessibility and the available infrastructure. Through this methodology, it is possible to assess the possibility of taking further measures to foster the conservation and awareness of certain sites.

In the rest of Europe, there is also an increasing interest in the geoconservation of the dinosaur tracksites of the Jurassic and Cretaceous periods (e.g. Marty et al. 2004; Santos et al. 2008; Díaz-Martínez et al. 2010b; Wings et al. 2012). However, the Cenozoic period lacks the palaeoichnological richness of the Mesozoic (Lockley and Meyer 2000). During the Cenozoic, the great diversification and expansion of mammals occurred worldwide (Novacek 1997), with thousands of fossil localities yielding body fossils. In contrast, the record of their footprints is scarce (McDonald et al. 2007; Costeur et al. 2009). Nonetheless, there is a significant number of Cenozoic mammal and bird tracksites in Spain, mainly located in the outcrops in the northeastern part of the country (Casanovas-Cladellas and Santafé-Llopis 1982; Prats and López 1995; Murelaga et al. 2000; Antón et al. 2004; Astibia et al. 2007). Also noteworthy is the site of Hoya de la Sima in Jumilla, Murcia (in the southeast of Spain), because this too is prepared for visits (Pérez-Lorente et al. 1999; Vilas et al. 2006).

One of the areas with the greatest wealth of mammal and bird ichnites from the Palaeogene and Neogene of Spain is Aragon, specifically the southern margin of the Pyrenees and the northern Ebro Basin. The most important tracksites are located in the municipalities of Peralta de Calasanz, Abiego, Bailo, Santa Cruz de la Serós and Loarre, in the province of Huesca, and Sierra de Luna, in the province of Zaragoza (Canudo 2007; Rabal-Garcés and Díaz-Martínez 2010; Castanera et al. 2016a, b). The area comprising the southern margin of the Pyrenees and the northern Ebro Basin has the necessary resources to design a palaeoichnological itinerary that encompasses the main Cenozoic tracksites, emphasizing their value as a touristic and educational asset. In recent years, geoconservation work has been carried out on some of these sites, and as a result, they have been prepared for public display. The aim of this work is to present a proposal, for the first time, of an itinerary which allows people to visit the Cenozoic tracksites of Huesca prepared for public visits.

Geological Setting

The geological framework of the set of sites discussed in this work comprises the Cenozoic units deposited during the Pyrenean orogeny. The Pyrenean Range follows a WNW–ESE orientation and is divided into several structural units, including two foreland basins. From north to south these are the Aquitaine Basin, North Pyrenean Zone, Axial Zone, South Pyrenean Zone and Ebro Basin. The Jaca Basin is located within the South Pyrenean Zone. It is a synorogenic basin whose sedimentary record spans from the Palaeocene to the Early Oligocene age and consists of marine, transitional and continental materials (Puigdefábregas 1975; Teixell and García-Sansegundo 1995; Montes Santiago 2009). The site of Bailo is located in the Jaca Basin, in a transitional facies of the Late Eocene. The sites of La Playa Fósil, Fondota and Casa de la Tejera are located on the northern edge of the central area of the Ebro Basin, close to the External Ranges to the west and the Marginal Ranges to the east. The site of Sierra de Luna is situated more in the centre of the basin (Fig. 1b). The Ebro Basin is the youngest southern foreland basin of the Pyrenees. From the Late Eocene to the Middle–Late Miocene (Salazar 2003), it was isolated from marine influence, and alluvial fan systems developed from the mountain elevations at the basin’s margins. These became well-developed carbonate or saline lacustrine environments in the basin centre (Cuenca et al. 1992; Arenas and Pardo 1999; Muñoz et al. 2002; Pardo et al. 2004; Luzón 2005).

Fig. 1
figure 1

a Geographical setting of the palaeoichnological points (tracksites) that constitute the palaeoichnological itinerary of the southern margin of the Pyrenees and the northern Ebro Basin. 1: Sierra de Luna, 2: Bailo, 3: Casa de la Tejera, 4: Fondota, 5: La Playa Fósil. b Geological framework of the palaeoichnological itinerary (tracksites). T: Tectosedimentary units of the Cenozoic of the Ebro Basin, Mz: Mesozoic (modified from Alonso-Zarza et al. 2002)

Full size image

Palaeoichnological Itinerary

The proposed palaeoichnological itinerary connects the main Cenozoic tracksites of the southern margin of the Pyrenees and the northern Ebro Basin in Aragon over a distance of about 250 km (Fig. 1a). The itinerary includes five palaeoichnological points. Three of them are prepared for visits, with signposted access, implemented conservation and protection measures, as well as information panels: La Playa Fósil (Peralta de Calasanz, Huesca), Fondota (Abiego, Huesca) and Sierra de Luna (Sierra de Luna, Zaragoza). The palaeoichnological point of Bailo (Bailo, Huesca) has none of the above yet, but it is a point of great importance and should be included in the itinerary. Furthermore, our aim is to include an additional site, Casa de la Tejera (Loarre, Huesca). This is of minor importance from both a scientific and an educational point of view, but it is very close to the itinerary route and is located near the Romanesque castle of Loarre, which is one of the most-visited monuments in Huesca. The tracksites are complementary in their fossil content and geology, so visitors to all the sites can acquire and enjoy a wide knowledge of the palaeogeography and sedimentology of this part of the Iberian Peninsula during part of the Cenozoic, as well as learning about the continental vertebrate fossil record.

Palaeoichnological Point: La Playa Fósil

Location and Measures Adopted for Visitors

The tracksite of La Playa Fósil (UTM coordinates 31T X283023 Y4652716) is located in the municipality of Peralta de Calasanz (Huesca), very close to the village of Peralta de la Sal. To access the site, visitors need to go 400 m NW of the village along the road A-2215 and then take a path to the right for 200 m as far as the rocky outcrop (Fig. 2a).

Fig. 2
figure 2

a General view of La Playa Fósil tracksite. b The tracksite completely surrounded by a protection fence and equipped with an information panel

Full size image

The site is completely surrounded by a protection fence to prevent spoilage. This work was carried out in 1998 thanks to an initiative undertaken by the sociocultural association of the village, called Castell de la Mora, and the municipal council of Peralta de Calasanz, and partially funded by the Provincial Council of Huesca. Subsequently, an information panel on the footprints and geology of the outcrop was installed, funded by the district of La Litera (Fig. 2).

Description and Highlights

This is an exceptional tracksite because it includes many bird footprints in an excellent state of preservation, some of them forming long trackways (Fig. 3d) and others in a chaotic configuration (Fig. 3e). The tracksite has been known since 1929 and constitutes the first citation of Cenozoic vertebrate footprints in Spain (Hernández-Pacheco 1929). The author in question identified two different types of bird footprint (Fig. 3b, c). The tracksite is located at the top of a level of sandstone with a vertical arrangement that presents various sedimentary structures such as ripples or crescents (Fig. 3a). Geologically, these layers are part of the south flank of the Peralta anticline and belong to the Peralta Formation (Early Oligocene) (Fig. 1b). This has been interpreted as deposited in a short, high-gradient alluvial fan passing laterally to the marginal part of a dominantly saline lake, where there were precipitations of evaporites and to a lesser degree carbonates (Senz and Zamorano 1992). The tracksite is located in levels that represent distal areas of the alluvial fan. Current studies point to a similar trackmaker for the two types of footprint (Castanera et al. 2016b). The differences between the two types of trace are understood to be due to the distinct consistency of the sediment, on which the birds walked, and the different degrees of water saturation of the sediment. All the footprints are tridactyl, characterized by a foot with three digits pointing forward. Given the depositional environment and the type of trace, the bird that produced them is thought to be closely linked to watery environments such as rivers and lakes, like today’s groups of shorebirds. In addition, the tracksite shows an interesting sample of invertebrate traces (Fig. 3f), which together with the bird footprints and the sedimentary structures makes it an exceptional site for explaining the connection to the geology of today. The visitor can easily see that the sedimentary structures (ripples) are similar to those formed on present-day beaches, where sometimes different shorebirds peck the sand searching for invertebrates to feed on. Nevertheless, in La Playa Fósil tracksite, the rock material was deposited in a completely continental environment, such as the shore of a lake with detrital input or a lateral backwater area of the main river.

Fig. 3
figure 3

a La Playa Fósil tracksite in a stratum of sandstone with a vertical arrangement, with various sedimentary structures (ripples, crescents). b, c The two different types of bird footprint. d Bird footprints forming a long and turning trackway. e Bird footprints in a chaotic configuration. f Invertebrate trace

Full size image

Palaeoichnological Point: Fondota

Location and Measures Adopted for Visitors

Fondota tracksite (UTM coordinates 30T X742534 Y4667764) is located close to the village of Abiego. To reach it, it is necessary to take the road A-1227, starting from Abiego in a northerly direction. Almost before leaving the village, one takes a turn to the right (east), marked by a sign for “Fossil footprints”, and continues over 400 m to the outcrop. The tracksite has very clearly recognizable footprints, so traditionally it was known as the place where “the goats climbed”.

Due to the spectacular nature of the outcrop, in 2004, the district of Somontano de Barbastro financed a conservation project and prepared the tracksite for visitors. The works included the installation of a protective wall in the upper part of the tracksite to avoid both falling debris from higher areas and water runoff, one of the most important agents of deterioration for ichnites (Fig. 4a). Moreover, the Government of Aragon funded the mapping of all the fossil traces and a preliminary scientific study of them. This allowed information to be gathered to make various information panels about the tracksite, the footprints and the trackmakers (Fig. 4e). In order to enable visitors to identify the footprints, some of them were marked with natural paints (Fig. 4c). The scientific study was carried out by the University of Zaragoza and the preparation for visitors by the company Paleoymás. After the initial preparation of the tracksite, it was included in a program for the maintenance, cleaning and conservation of outdoor palaeontological sites, which ran until 2012 and was funded by the Government of Aragon. The work carried out under this program included cleaning and repainting the footprints, removing vegetation and consolidating the ichnological surface, which minimizes the deterioration of the tracksite and keeps it in good condition for visits. Thanks to all this effort in preparing and preserving the tracksite, recently Fondota was incorporated into the catalogue of Geosites (Places of Geological Interest, LIG as per its Spanish acronym) through “Decree 274/2015, of 29 September, of the Government of Aragon”. This tracksite is the only one categorized as a LIG of all those mentioned in the present article.

Fig. 4
figure 4

a Fondota tracksite, equipped with a protective wall in the upper part of the outcrop to avoid both falling debris from higher areas and water runoff. b–d Three types of artiodactyl footprint. e General view of the tracksite with the information panels

Full size image

Description and Highlights

The tracksite is located in an inclined, southwest-dipping limestone sequence that crops out along a distance of more than 100 m and contains a fairly high amount of footprints of quadrupedal animals, forming multiple trackways (Fig. 4a). Recent studies (Castanera et al. 2016b) have confirmed the presence of three types of ichnite (Canudo et al. 2007), characterized by didactyl tracks and produced by artiodactyl mammals (a group that includes animals such as camels, pigs, hippos, cows, deer, giraffes, goats, etc.) of different sizes (Fig. 4b–d). The outcrop is included in the south flank of the Barbastro anticline, situated stratigraphically in the lower part of the Peraltilla Formation (Crusafont et al. 1966), specifically in a carbonate unit called Peraltilla Limestones. The age of this carbonate unit is traditionally considered to be Late Eocene–Early Oligocene on the basis of its charophyte content (Reille 1967, 1971), although more recent studies suggest an Early Oligocene age based on the micromammal faunal content (Álvarez Sierra et al. 1990) (Fig. 1b). The rock materials of the tracksite were deposited in a shallow carbonate lacustrine system located in the distal parts of alluvial fans from the north (Pyrenees) (Luzón 2005), and the layers of the tracksite correspond with the marginal area of this lake (Fig. 5).

Fig. 5
figure 5

Palaeogeographical reconstruction of Fondota tracksite during the Early Oligocene; this illustration can be seen in one of the information panels (illustration by Paleoymás)

Full size image

Palaeoichnological Point: Sierra de Luna

Location and Measures Adopted for Visitors

Sierra de Luna tracksite (UTM coordinates 30T X669718 Y4656354) is located in the municipality of Sierra de Luna (Zaragoza). To access it, it is necessary to take a path eastwards starting from the village of the same name and go over 3.5 km following the signposts indicating the tracksite. There are two outcrops (strata) with ichnites separated by a few metres (Fig. 6a). Although there are no scientific studies of it, the General Directorate of Cultural Heritage of the Government of Aragon appreciated the need to preserve the tracksite and prepare it for visitors. Thus, in 2004, the Government of Aragon funded the cleaning and mapping of the tracksite, which provided a basis for work on conservation and bringing the site to the public attention (Figs. 6 and 7a). In 2007, the district of Las Cinco Villas and the municipal council of Sierra de Luna funded the installation of perimeter fencing to surround and protect the tracksite and the placement of two information panels (Fig. 7c). In 2010–2011 the ichnological surface was consolidated and the restoration of the tracksite was carried out, using resin and mortar to seal small and medium-sized cracks (Fig. 6b, c). Moreover, following a previous geotechnical study, a wall and canals for draining runoff and a retaining wall for the tracksite were built, and access to the tracksite was improved (Fig. 6e–i), all financed by the Government of Aragon and through SODEMASA (the Society for the Environmental Development of Aragon). All these works were carried out by the company Paleoymás. As with the Fondota tracksite, after the initial preparation, Sierra de Luna tracksite was also included in a program for the maintenance, cleaning and conservation of outdoor palaeontological sites, which ran until 2012 and was funded by the Government of Aragon. Work performed included cleaning and repainting the footprints, removing vegetation and consolidating the ichnological surface, with the purpose of minimizing the deterioration of the tracksite.

Fig. 6
figure 6

a Works carried out in Sierra de Luna tracksite funded by the Government of Aragon and accomplished by Paleoymás. b, c Consolidation of the tracksite, using resin and mortar to seal small- and medium-sized cracks. d Blowing away debris after cleaning, e, f Wall and canals for draining runoff. g Retaining wall for the tracksite. h, i Improving access to the tracksite (all pictures belong to Paleoymás)

Full size image
Fig. 7
figure 7

a General view of Sierra de Luna tracksite. b An isolated large footprint. c The tracksite with one of the information panels, d One of the longest trackways in the tracksite

Full size image

Description and Highlights

The tracksite is located in a horizontal limestone layer of Early Miocene age (Fig. 1b), belonging to the Alcubierre Formation (Quirantes 1978) and deposited in the marginal parts of a lacustrine system situated laterally to the great river system of Luna, flowing from the north (Arenas and Pardo 1999). On the surface of the stratum, a great amount of ichnites can be seen, arranged in various trackways (Fig. 7d). The ichnites have been differentiated into two morphotypes. The trackmakers may have been large quadrupedal mammals, possibly belonging to the group of perissodactyls, although other groups such as artiodactyls or proboscideans cannot be ruled out. Sierra de Luna is the tracksite where visitors can see the largest footprints (Fig. 7b) in the whole itinerary, as well as long trackways. Also, it is located in a horizontal level, which helps visitors to understand the movement of track producers along the edge of a lake close to the shoreline (Fig. 8).

Fig. 8
figure 8

Palaeogeographical reconstruction of Sierra de Luna tracksite during the Early Miocene; this illustration can be seen in one of the information panels (illustration by Paleoymás)

Full size image

Palaeoichnological Point: Bailo

Location and Measures Adopted for Visitors

In the town of Bailo (Huesca) (UTM coordinates 30T X679863 Y4708689), there are many well-preserved footprints in the slabs of the stone pavement in the streets and especially in the main square of the village (Fig. 9a). Despite being known for years by many villagers, it was not until 2012 that a forester, a resident of the village of Bailo, drew the attention of the General Directorate of Cultural Heritage of the Government of Aragon to this finding. This locality is of easy access (the footprints are in the middle of the town) and has a great wealth of fossils. For this reason, although it does not yet have any signposting to facilitate visits to the footprints, our aim is to ensure that several activities are carried out to promote the conservation and public awareness of this important palaeontological discovery.

Fig. 9
figure 9

a Aerial photo of the locality of Bailo, pointing out the location of the footprints in the slabs of the stone pavement of the village. b Carnivore (felid-like) type track. c Large artiodactyl-type track and perissodactyl-type track. d Perissodactyl-type track. e Small artiodactyl-type track

Full size image

Description and Highlights

The stones of the pavement where the footprints are found are taken out of their geological context. In spite of this, thanks to a precise geological study and the information given by former stonemasons, it has been possible to locate the outcrop precisely. The footprints of Bailo come from a rock quarry located in Arrés (a village close to Bailo), where several similar footprints have been found in situ in one of the layers (Fig. 10). These levels are part of a broad syncline fold with an E–W direction and belong to a siliciclastic unit, known as the Yeste-Arrés sandstone unit, of Late Eocene age (Fig. 1b). This unit is interpreted as a transitional marine unit, whose facies can be attributed to a shallow environment of a lagoon or bay (Montes Santiago 2009). One of the most notable features of this tracksite is that it is one of the oldest sets of footprints from the Cenozoic of Spain. Four different types of track have been identified, corresponding to four types of mammal: two artiodactyls (Fig. 9c, e), a perissodactyl (Fig. 9c, d) and a carnivore (felid-like) (Fig. 9b). With this association of footprints, the palaeoichnological point of Bailo is endowed with one of the highest diversities of Eocene footprints worldwide (Castanera et al. 2016b). In particular, one of the strengths of this site is that one can recognize carnivore footprints, this being one of the few examples of carnivore footprints from the Cenozoic of Spain. This type of footprint at Bailo is easily identifiable because they are very similar to current felids, which makes them particularly attractive to visitors. It is definitely advisable that these footprints on the streets of Bailo should in the near future be signposted for the enjoyment of visitors.

Fig. 10
figure 10

a Rock quarry located in Arrés (a village close to Bailo), belonging to the Yeste-Arrés sandstone unit of Late Eocene age. b Footprints in one of the layers of the quarry similar to those in the stone pavement of Bailo (large artiodactyl-type and perissodactyl-type)

Full size image

Palaeoichnological Point: Casa de la Tejera

Even though this tracksite may not be of the same relevance as the rest of the analysed fossil sites, both from a scientific and from an educational point of view, it may be interesting to make a stop on the palaeoichnological route to visit it. It is located in the municipality of Loarre (Huesca) (UTM coordinates X30T X696701 Y4687061). The footprints are in the top part of a sandstone slab (Fig. 11) that forms part of the Uncastillo Formation, of Late Oligocene-Early Miocene age (Fig. 1b). This stratigraphic unit is interpreted as a large fluvial system, known as the Luna fluvial system (Arenas and Pardo 1996; Arenas et al. 2001). The morphology and size of all the footprints are similar, so they were probably produced by the same trackmaker. Although no digit impressions can be discerned, the rounded morphology and the relatively large size of the footprints suggest that the trackmaker was a mammal. A peculiarity is the mud border around each track, produced by the animal as it moved over the substrate, and preserved due to the lithification of the rock.

Fig. 11
figure 11

Casa de la Tejera tracksite; the footprints are in the top part of a sandstone slab

Full size image

Touristic and Educational Attraction of the Itinerary

This palaeoichnological itinerary has been designed to draw attention to the palaeodiversity of the vertebrates that occupied the southern margin of the Pyrenean mountain range and the northern Ebro Basin before the existence of human beings. This palaeontological heritage is a wellspring of knowledge about the natural environment and its history. It has the capacity to transport those who approach it to a different time and place, offering visitors a broader view of the natural world. The special attraction of the tracksites is their ability to evoke the image of extinct animals walking across the very place where the visitor is at that particular moment. The tracks are indicators of the activities carried out by the animals, activities such as walking towards the lake shore or besides the shoreline to drink water or search for food in the mud. In this sense, the itinerary takes visitors on a trip of about 20 million years from the Late Eocene to the Early Miocene. This period reflects a change both in fauna and depositional environments (from coastal to fluvio-lacustrine). Moreover, it should be mentioned that although extinct animals produced the footprints in question, they bear some resemblance to those produced by current species.

The main features of this palaeoichnological heritage are vital for teaching purposes, as they offer a firsthand way for young people to approach the world of palaeontology and geology. However, it is essential to keep in mind that to forge a connection between the visitors and the object visited, it is crucial to relate what is shown with something in the personality or experience of the visitors (Tilden 2015), for instance, by using examples taken from everyday life. This transforms the object visited into something closer to their own human experience and thus makes it more meaningful to them. This makes it possible not only to convey a sense of the object’s scientific value but to raise awareness in the population about its relevance and need for protection (Magagna et al. 2013).

The southern margin of the Pyrenean Range has a great appeal in rural and mountain tourism. Nevertheless, this tourism tends to be concentrated in specific locations that are more attractive to tourists because of their beautiful landscape or rich cultural heritage. The creation of the palaeoichnological itinerary presented here could provide a new attraction for tourists in different municipalities that are not among the classic tourist destinations. Thus, the touristic offer would be extended in the region.

Conclusions

The southern margin of the Pyrenees and the Ebro Basin in Aragon (northeast Spain) has accumulated a great wealth of Cenozoic tracksites of mammals and birds, which are relatively scarce worldwide. Some of these tracksites have been prepared for public display, which has allowed people to visit them. The proposed itinerary described here includes the most important tracksites and offers a general and diverse vision of the palaeoichnological record: La Playa Fósil, Fondota, Sierra de Luna, Bailo and Casa de la Tejera. These tracksites are in geographical locations that make them easily accessible. Altogether, they encompass a wide variety of fossil tracks and different sedimentological and lithological features that comprise a time range of about 20 million years. The promotion of this palaeoichnological itinerary as a touristic and educational asset could prove especially important for the territories where the tracksites are located. The described itinerary and the palaeontological heritage thus constitute a set of extremely relevant points of interest with a high educational potential and a valuable socioeconomic asset.