Lopingian tetrapod footprints from the Venetian Prealps, Italy: New discoveries in a largely incomplete panorama

LORENZO MARCHETTI, MATTEO BELVEDERE, and PAOLO MIETTO

Marchetti, L., Belvedere, M., and Mietto, P. 2017. Lopingian tetrapod footprints from the Venetian Prealps, Italy: New discoveries in a largely incomplete panorama. Acta Palaeontologica Polonica 62 (4): 801–817.

After new studies were carried out in the Lopingian Val Gardena Sandstone of northern Italy, in the Recoaro area (Venetian Prealps, NE Italy), the following tetrapod ichnotaxa are identified: cf. Capitosauroides isp., cf. Merifontichnus isp., Pachypes isp., Paradoxichnium isp., and Rynchosauroides isp., probably corresponding to ?parareptile, captorhinid eureptile, pareiasaurid parareptile, archosauromorph neodiapsid, and lacertoid neodiapsid trackmakers, respectively. An undetermined track shows features consistent with possible therapsid producers. These are the first possible records of Merifontichnus and Capitosauroides in the Lopingian (late Permian) and one of the few records of Paradoxichnium worldwide. The paleoecology of the ichnoassociation highlights a relatively high diversity in the floodplain lithofacies, a monospecific association of Rhynchosauroides in distal floodplain/sabkha environments and the occurrence of Paradoxichnium isp. and cf. Capitosauroides only in the lagoon lithofacies, suggesting different habits of the trackmakers. The tetrapod ichnoassociation is characterized by eureptile and parareptile tracks, and differs from the classic Lopingian tetrapod ichnoassociation of the Dolomites mainly because of the absence of chirotheriid and small parareptile ichnotaxa. A comparison of the Italian tetrapod ichnoassociation with other Lopingian non-eolian ichnofaunas suggests a possible preference for marginal marine settings by the archosauromorph and therapsid trackmakers at low-latitudes of Pangaea.

Key words: Tetrapoda, footprints, paleoecology, Lopingian, Val Gardena Sandstone, Venetian Prealps, Italy.

Lorenzo Marchetti [lorenzo.marchetti85@gmail.com], Urweltmuseum GEOSKOP, Burg Lichtenberg (Pfalz), Burgstrasse 19, D-66871 Thallichtenberg, Germany.

Matteo Belvedere [matteo.belvedere@jura.ch], Office de la culture, Section d’archéologie et paléontologie, Paléontologie A16, Hôtel des Halles, P.O. Box 64, 2900 Porrentruy 2, Switzerland.

Paolo Mietto [paolo.mietto@unipd.it], Dipartimento di Geoscienze, Università degli Studi di Padova, Via Gradenigo 6, 35131, Padova, Italy.

Received 27 May 2017, accepted 27 July 2017, available online 7 November 2017.

Copyright © 2017 L. Marchetti et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Introduction

The Lopingian (late Permian) was a key epoch for the evolution of terrestrial vertebrates, which reached a noteworthy abundance and diversity before the Permian–Triassic mass extinction (PTME). Therapsid synapsids and parareptiles were widespread, and archosauromorph eureptiles appeared for the first time. Neodiapsid eureptiles were common, while captorhinid eureptiles and amphibians were declining.

This is mainly inferred from the skeletal record (e.g., Lucas 2006), because few Lopingian footprints are known in the World. These specifically are located in: Italy, Germany, Scotland, Russia, Morocco, Niger, Brazil, South Africa, and Australia. At present, only the ichnogenera Batrachichnus, Dicynodontipus, Dromopus, Erpetopus, Hyloidichnus, Pachypes and Paradoxichnium, and several unidentified or dubious tracks with amniote affinity are known from all of the sites except Italy (Müller 1959; Schmidt 1959; McKeever and Haubold 1996; Warren 1997; De Klerk 2002; Surkov et al. 2007; Voigt et al. 2010; Hminna et al. 2012; Costa da Silva et al. 2012; Smith et al. 2015). The Italian ichnoassociation is by far more diverse and complete (Kittl 1891; Abel 1929; Leonardi 1951, 1974; Leonardi et al. 1975; Conti et al. 1975, 1977, 1980, 2000; Ceoloni et al. 1988; Wopfner 1999; Nicosia et al. 2001; Avanzini and Tomasoni 2004; Valentini et al. 2007, 2008, 2009; Avanzini et al. 2011; Bernardi et al. 2015; Citton et al. 2016), although a comprehensive revision based on the best-preserved material is still lacking since the 1980s. Specifically, the role of footprint taphonomy and extramorphologies, a relatively recent development in tetrapod ichnology (Haubold et al. 1995; Haubold 1996) was not properly taken into account. Thus, aside from the ichnogenera Pachypes, Rhynchosauroides, Dicynodontipus, and Protochirotherium, the ichnotaxonomy of the other morphotypes is unclear.

The revision with the addition of new material from a different site in the Venetian Prealps (Recoaro area, Veneto, NE Italy), preliminarily studied by Mietto (1975, 1981), gives the opportunity to reconstruct a relatively diverse ichnofauna comparable to that of the classic localities of the Dolomites. The aim of this study is a correct ichnotaxonomy based on the most recent methods and approaches, and the reconstruction of the faunistic and paleoecological meaning of these footprints in one of very few Lopingian sites worldwide, and majority of which in a need of revision.

Institutional abbreviations.—FG, Technische Universität Bergakademie Freiberg, Germany; MCV, Museo Civico D. Dal Lago of Valdagno, Italy; MGP, Museo Geologico delle Dolomiti, Predazzo, Italy; MGP-PD, Museo di Paleontologia e Geologia of the University of Padua, Italy. Specimens with provisional number include an additional “P”.

Geological setting

The Lopingian of the Southern Alps is characterized by the deposition of alluvial red beds in an area extending from Lombardy to Slovenia, interfingering to the east into marginal marine and shallow marine lithofacies, the result of the westward-directed Paleotethys transgression (Massari and Neri 1997). Generally, the alluvial red beds are laterally continuous with an average thickness of about 200–250 m and lie unconformably on Cisuralian volcano-siliciclastic successions and on the pre-Permian metamorphic basement. Two different formations were established in the Southern Alps domain: the Verrucano Lombardo Formation from Lombardy region to the Giudicarie area in Trentino-Alto Adige region and the Val Gardena Sandstone from Trentino-Alto Adige to Friuli-Venezia Giulia regions, separated by a structural high. The latter formation interfingers with the marginal marine lithofacies of the Bellerophon Formation in an overall transgressive trend, including some significant regressive events (Massari et al. 1988, 1994). The Val Gardena Sandstone includes deposits related to alluvial fan, braided and meandering fluvial environments; no clear deltaic sequences were detected. The occurrence of calcisols and rarer vertisols points to a semi-arid environment (Massari and Neri 1997). The lithofacies of the Bellerophon Formation interfingering with the alluvial red beds are generally dolostone and evaporites, the expression of sabkha marginal marine environments, with an invertebrate fauna typical of stressed settings (Neri 2007). The Bellerophon Formation passes upwards to the shallow marine and mostly Triassic Werfen Formation, without unconformities.

The fossil content of the Val Gardena Sandstone includes abundant tetrapod footprints, plant remains and palynomorphs (e.g., Conti et al. 1977, 2000; Ceoloni et al. 1988; Pittau 2005; Avanzini et al. 2011; Kustatscher et al. 2012, 2014, 2017), whereas the Bellerophon Formation includes abundant invertebrate fossils such as nautiloids, bivalves, brachiopods, and gastropods and microfossils such as algae, foraminifera, ostracods, and palynomorphs (e.g., Accordi 1956; Broglio Loriga 1960; Broglio Loriga et al. 1988; Pasini 1985; Posenato 1988, 1998; Posenato and Prinoth 1999; Spina et al. 2015). The biostatigraphic analysis of the palynoflora and invertebrate fossils and microfossils is consistent with a Lopingian age for the Val Gardena Sandstone and Bellerophon Formation (e.g., Massari et al. 1988; Farabegoli and Perri 1998), whereas the youngest underlying volcanic unit, Ora Formation, is radiometrically dated as latest Cisuralian (274.1 ±1.6 Ma; Marocchi et al. 2008) implying a large stratigraphic gap roughly corresponding to the entire Guadalupian (Cassinis et al. 2012). The overlying shallow marine Werfen Formation includes the Permian–Triassic boundary in its basal strata (Neri 2007).

The described fossil tetrapod footprints were found in the Venetian Prealps (Italy) in the localities of Merendaore (GPS coordinates N45°43.101’ E11°11.782’ alt 824 m), Ulbe (GPS coordinates N45°42.906’ E11°12.236’ alt 771 m) and Cortiana (GPS coordinates N45°76.443’ E11°23.943’ alt 560 m), close to the village of Recoaro (Fig. 1). In this area, the Val Gardena Sandstone shows a reduced thickness, of about 20–50 m and the successions lies directly and uncomformably on the metamorphic basement (Barbieri et al. 1980). A synthetic stratigraphic column of the study area is provided in Fig. 1D. The lower half of the formation is characterized by alluvial red beds arranged in upward fining- and thinning-cycles constituted of discontinuous conglomeratic lenses with an erosive base, passing upwards to coarse-grained m-thick sandstone, red to gray in color, with cross stratification and dm-thick fine-grained sandstone and cm-thick laminated mudstone (facies association a; Fig 2A, B). The upper half of the formation is characterized by well-stratified and laterally continuous dm-thick red sandstone passing upwards to cm-thick laminated mudstone red, yellow, or gray in color. The mudstone are characterized by pedogenic horizons (facies association b; Fig. 2C, D). The mudstone are interbedded to dark or light gray dolostone in strata 10–80 cm thick with irregular bedding and arranged in upward-thickening sequence, representing the basal lithofacies of the Bellerophon Formation (facies association c; Fig. 2E, F). The upper transition of the Val Gardena Sandstone with the Bellerophon Formation is transitional; the stratigraphic limit between these two formations corresponds conventionally to the last siliciclastic layer. The tetrapod footprints occur in the mudstone of the lower part of the Val Gardena Sandstone and in the mudstone, and dolostone of the upper part of the Val Gardena Sandstone (Fig. 1).

Material and methods

The studied material includes specimens with tetrapod footprints preserved in convex hyporelief or concave epirelief, coming from the localities Merendaore, Ulbe and Cortiana (Venetian Prealps, Recoaro area; Fig. 1E, F) collected in the second part of the 20th century by the amateaur collectors Ottaviano Violati Tescari, Olivo Gonzo, Antonio Rossi, Franco Slaviero, and one of the authors (PM), who published two preliminary reports (Mietto 1975, 1981). The study comprises standard techniques for tetrapod ichnology such as photos in controlled light conditions, outline drawings on transparent films, digital drawings and measurements. 3D data were acquired with NextEngine 3D Scanner HD laser scanner through the NextEngine ScanStudio HD software and then processed with CloudCompare (v.2.7.0, http://www.cloudcompare.org) to obtain the false-color depth maps. All the models used for this study can be downloaded from https://doi.org/10.6084/m9.figshare.4040205. The taphonomy of footprints was strictly considered, in order to exclude from systematic study all the morphologic features related to deformations from the optimal and anatomically-related morphology of the footprint (extramorphologies sensu Haubold et al. 1995 and Bertling et al. 2006). Measurements mainly follow the conventions of Leonardi (1987). The systematic ichnology is based on morphologic features of the best-preserved footprints. The 3D methods provided additional information about morphology, resolving the problems linked to color and lighting of the specimens and allowing a precise interpretation of the footprint depth related to a reference surface. Due to the lack of trackways and the incompleteness of some specimens, we use open nomenclature, avoiding ichnospecific assignments.

Systematic palaeoichnology

Ichnogenus Capitosauroides Haubold, 1971

Type ichnospecies: Capitosauroides bernburgensis Haubold, 1971; Bernburg (Germany), Anisian.

cf. Capitosauroides isp.

Fig. 3.

Material.—MCV 5, left manus; MCV 6, partial left manus; MCV 7, left pes; MCV 11, right manus; MCV 11/05, right manus; MCV 12, right manus and right pes, possibly of the same step cycle; MGP-PD P3; right pes; all tracks are preserved in convex hyporelief; Ulbe and Cortiana (Italy) Lopingian.

Description.—Pentadactyl footprints showing medial fun­ctio­nality, relatively long, thick and straight digits with rounded terminations; and short concave palm/sole impressions. Ectaxonic pes, long about 90 mm. Smaller manus, longer than wide, showing relatively thicker digits, and less marked ectaxony. All footprints show very short digit I, digit V is proximally-positioned and usually not preserved.

Remarks.—The ectaxonic pentadactyl footprints with straight thick digits ending in rounded terminations, short concave palm/sole and a very short digit I are typical of Capitosauroides Haubold, 1971. The pentadactyl manual tracks and the short palm/sole exclude a possible attribution to typical temnospondyl footprints such as Limnopus Marsh, 1894. The lack of marked impressions of digit I basal pads and the short sole exclude the possible attribution to known reptiliomorph amphibian tracks such as Amphisauropus Haubold, 1970. Digit proportions, termination and arrangement are distinct from captorhinid tracks such as Hyloidichnus Gilmore, 1927 and Merifontichnus Gand, Garric, Demathieu, and Ellenberger, 2000. However, the lack of well-­preserved digit V and of trackways hampers a definitive assignment, thus we tentatively classify these tracks as cf. Capitosauroides isp.

Capitosauroides was attributed to capitosaurid amphibians (Haubold 1971) or non-archosauromorph amniotes (Klein and Lucas 2010). MCV 7 was previously attributed to procolonomorph tracks indet. (Mietto 1995). We think that these tracks are likely of non-archosauromorph amniotes, and possibly of parareptiles. Capitosauroides shows a proximally-positioned digit V not separated from the digit I–IV group, typical of other possible parareptile tracks (Erpetopus, Pachypes, Procolophonichnium). This would be consistent with Mietto (1995), but more studies are needed to confirm the attribution of Capitosauroides to parareptiles.

Ichnogenus Merifontichnus Gand, Garric, Demathieu, and Ellenberger, 2000

Type ichnospecies: Merifontichnus thalerius Gand, Garric, Demathieu, and Ellenberger, 2000; La Lieude (France), Guadalupian.

cf. Merifontichnus isp.

Fig. 4

Material.—MCV 2, left pes-manus couple and right pes of a different step cycle, in convex hyporelief; Ulbe (Italy), Lopingian.

Description.—Left pes-manus couple and right pedal impression preserved as convex hyporelief. The pes is long about 100 mm, pentadactyl, ectaxonic, with medial functionality, markedly wider than long. Digits are straight, relatively long, radially disposed, and show rounded terminations. Digit IV is the longest and similar in length to digit III, digit V is about as long as digit I. Digit I is parallel to the medial proximal margin of the sole. The sole is very short medially and longer in the external part; the sole proximal margin is straight to laterally convex. The manus is smaller, ectaxonic, markedly wider than long and probably pentadactyl. Digits are straight, relatively long, radially disposed, and show rounded terminations. Digit IV is the longest and similar in length to digit III, the palm is relatively short and oval in shape. The manus is inward-oriented compared to the pes.

Remarks.—The short sole/palm, the footprints wider than long, the long straight digits with enlarged terminations increasing in length from I to IV with subequal digits III–IV and relatively short pedal digit V, the disposition of pedal digit I parallel to the sole, the median lateral decrease in relief of the pes and the manus sensibly inward-oriented compared to the pes are typical of Merifontichnus Gand et al. 2000, after the preliminary revision of Marchetti (2016).

The only appreciable difference of this material with the Kungurian–Guadalupian material referable to this ichnogenus is its distinct heteropody (Newell et al. 1976; Gand et al. 2000, Marchetti et al. 2013, Marchetti 2016).

Waiting for a comprehensive ichnotaxonomic revision and because of the incomplete manual track, we tentatively classify these footprints as cf. Merifontichnus isp. A discussion of the differences with morphologically-similar ichnotaxa such as Hyloidichnus and Amphisauropus was recently exposed by Marchetti (2016). The studied material differs significantly from the ichnogenus Limnopus, too, mainly because of disposition/relative proportions of digits and sole length and shape. Moreover, a tetradactyl manus is unlikely, since the digit IV is the longest, whereas in Limnopus digit III is the longest.

Several features are consistent with derived captorhinid producers, such as the long rigid digits terminating in enlarged rounded terminations, the short palm/sole, the median-lateral decrease in relief of the pes, and the ectaxonic tracks with digits III–IV of similar length (Olson 1962; Sumida 1989; Holmes 2003). Additionally, the stout digits, the tracks wider than long and the convex proximal-lateral margin of the sole are consistent with the pedal structure of Moradisaurus. This last feature is probably due to the fusion of the calcaneum with the distal tarsal V, and the probable contact with the ground of part of the tarsus, due to a stronger vertical push on the appendicular skeleton (O’Keefe et al. 2005).

Ichnogenus Pachypes Leonardi, Conti, Leonardi, Mariotti, and Nicosia, 1975

Type ichnospecies: Pachypes dolomiticus Leonardi, Conti, Leonardi, Mariotti, and Nicosia, 1975; Bletterbach Gorge (Italy), Lopingian.

Pachypes isp.

Fig. 5.

Material.—MCV 3, left manual track, preserved in convex hyporelief; Ulbe (Italy), Lopingian.

Description.—Left manual imprint preserved as convex hyporelief long about 150 mm, and wide about 200 mm, with a broad palm showing a convex proximal margin, and short and sturdy digits with rounded terminations, continuously connected with the palm. The digit V is missing, digits III and IV are the longest, digits II–IV are bent inward. Foot­print functionality is on digits I–III and on the medial part of the palm.

Remarks.—The broad rounded palm and the digit morphology, relative length and arrangement are characteristic of Pachypes Leonardi, Conti, Leonardi, Mariotti, and Nicosia, 1975, established from a single pedal imprint from the Val Gardena Sandstone of the Bletterbach locality of the Dolomites (Italy). Although trackways are missing, an abundant record from the type locality, including complete pes and manus, pes-manus couples and incomplete step cycles showing a complete range of preservation and size allows us to thoroughly confirm the validity of this ichnotaxon (Valentini et al. 2008, 2009). Here we confirm the determination of Mietto (1981) for the material of the Venetian Prealps. The material described from the Italian Carnian Alps (Dalla Vecchia 2013) and Russia (Surkov et al. 2007) does not show sufficient morphologic details to allow a determination, and the ichnotaxon Pachypes primus (Gubin et al. 2003) sensu Valentini et al. (2009) has to be considered a nomen dubium. Recently, Pachypes has been described from the Lopingian of Morocco (Voigt et al. 2010) and Niger (Smith et al. 2015). This type of track is confidently referred to pareiasaurian parareptile trackmakers (Leonardi et al. 1975; Valentini et al. 2008).

Ichnogenus Paradoxichnium Müller, 1959

Type ichnospecies: Paradoxichnium problematicum Müller, 1959; Culmitzch (Thuringia, Germany), Lopingian.

Paradoxichnium isp.

Fig. 6.

Material.—MCV 8, possible right pes-manus couple; MCV 9, left manus; MCV 10, right manus; MCV 11/05, right manus; all tracks are preserved in convex hyporelief; Ulbe (Italy), Lopingian.

Description.—Pentadactyl manus, longer than wide and long about 70 mm, with thick and almost parallel digits increasing in length from I to IV. The digit V is relatively short, the bases of digits I and V are proximally positioned, both digits are shorter and thinner than digits II–IV. The digits II–IV terminate in large triangular claws, claws of digits I and V are smaller and acuminate. The palm is wider than long, and relatively short. The manual functionality is on digits II–IV, the palm and digits I and V can be absent. Pedal tracks larger with longer digits, lateral to the manus and usually not impressed.

Remarks.—The very characteristic morphology of the manual tracks allow a confident determination of these footprints as Paradoxichnium Müller, 1959, specifically the well-impressed and grouped digits II–IV terminating in large triangular claws and the smaller and proximally-positioned lateral digits (MCV 9, 10; Figs. 5, 6). Some specimens preserve only the digits II–IV of the manus, appearing as tridactyl impressions (MCV 8, 11, 11/05). This is clearly a taphonomic effect due to the higher functionality of digits II–IV. The rarity of pedal tracks is probably a taphonomic effect, the reason can be observed in the trackway holotype (pedal impressions are less-deeply impressed and more incomplete than manual impressions, FG 20/1; Fig. 6). The footprints classified as ?Paradoxichnium radeinensis Ceoloni, Conti, Mariotti, and Nicosia, 1988 from the same formation do not show the main features of the ichnogenus, thus they have to be assigned to a different ichnotaxon. Paradoxichnium is tentatively attributed to protorosaurid archosauromorphs, mainly because of their eureptilian affinity, the functional prevalence of digits II–IV and the trackway pattern that implies a low coupling value (Voigt 2012).

Ichnogenus Rhynchosauroides Maidwell, 1911

Type ichnospecies: Rhynchosauroides rectipes Maidwell, 1911; Daresbury, Cheshire (UK), Early–Middle Triassic.

Rhynchosauroides isp.

Fig. 7.

Material.—MCV 4, right track; MCV 65, right manus, right track and possible straight tail impression; MGP-PD 25510; left manus and right track of the same step cycle; left pes and other two tracks of other step cycles, possible tail/body impression; all tracks preserved in convex hyporelief; Merendaore (Italy), Lopingian.

Description.—Semiplantigrade, pentadactyl manus with long digits markedly and continuously increasing in length from I to IV, distally bent medially and terminating in sharp, thin, and triangular claws in continuity with the digits. Digit V is thin, about as long as digit II, straight, outward-oriented and its base is separated and more proximal compared to the digit IV base. The palm is short and triangular in shape. Functional prevalence is medial. Incomplete pedal tracks and possible straight tail impressions associated with footprints were observed. All the tracks are preserved in convex hyporelief.

Remarks.—The ectaxonic manus showing long digits with sharp claws, the continuous increase in length between digits I–IV, the short palm, the digit V separated from the digit IV base and outward directed are typical of Rynchosauroides Maidwell, 1911. The lack of associated pedal impressions and the unclear ichnotaxonomic status of several Rynchosauroides species is the reason why we classified these tracks as Rhynchosauroides isp. This typical Lopingian–Mesozoic ichnogenus needs a comprehensive revision, because several ichnospecies were introduced but a few might have a real ichnotaxonomic meaning. The studied material was initially classified as Eumekichnium gampsodactylum (Mietto, 1975); the genus Eumekichnium is presently considered a junior synonym of Dromopus lacertoides (Voigt, 2005). However, the manual track of Dromopus differ significantly from that of Rhynchosauroides because it shows a digit IV much longer than digit III, it is semidigitigrade and is identical in morphology with the pes. Rhynchosauroides is the most abundant tracktype of the Val Gardena Sandstone; and in the type locality is usually referred to Rhynchosauroides pallinii Conti, Leonardi, Mariotti, and Nicosia, 1977. A morphologically-­similar ichnogenus is referred to Ganasauripus ladinus Valentini, Conti, and Mariotti, 2007. The trackmakers were likely lacertoid neodiapsid eureptiles (Valentini et al. 2007).

Undetermined track

Fig. 8.

Material.—MCV 14/30, right track, concave epirelief; Cor­tiana (Italy), Lopingian.

Description.—Right footprint showing digits III–V and a partial impression of the palm/sole, with lateral functionality and expulsion rims. Foot length is about 80 mm. Digit IV is the longest, digit V is slightly shorter than digit III. Digits are relatively short and thick and terminate in rounded pads, and are more deeply impressed in their proximal and distal parts. No claws were observed. The footprint is preserved as concave epirelief.

Remarks.—This specimen, in morphology and digit arrangement, resembles the external part of a relatively large track with rounded and large digit terminations. The deeper impression of metapodial-phalangeal pads and digit tips compared to the medial part of digits is consistent with a specific skeletal feature of synapsids, the “digital arcade” sensu Kümmel and Frey (2012). Thus, these footprints are probably assignable to therapsid synapsids. In the Italian Lopingian track record, two morphotypes only show these characteristics: “Ichniotherium cottae” sensu Conti et al. (1977) and “Ichniotherium” accordi Ceoloni, Conti, Mariotti, and Nicosia, 1988. In particular, it resembles the manual track figured by Conti et al. (1977: pl. 8: 3, MGP 9/22) and attributed to “Ichniotherium cottae” (Fig. 8B). Waiting for a revision of morphologically-similar material from the Dolomites and because of the incompleteness of MCV 14/30, we do not assign it to any ichnotaxon, although it was probably produced by therapsid synapsids.

Discussion

Paleoecology.—The tracks found in the lower half of Val Gardena Sandstone in facies association a (Figs. 1, 9, Table 1) of Ulbe, Merendaore, and Cortiana localities represent the more diverse ichnoassociation recording Pachypes isp., cf. Merifontichnus isp., Rynchosauroides isp., and the large undetermined track. This interval is interpreted as a typical sequence of alluvial red beds, the occurrence of abandoned channels and lateral accretion structures suggests a meandering fluvial environment. Tetrapod footprints are preserved in concave epirelief or convex hyporelief in the laminated mudstone or in convex hyporelief in the fine-grained sandstone covering mudstone intervals. The trampling surfaces are generally interpreted as overbank or abandoned channel deposits.

The ichnoassociation found in the upper half of the Val Gardena Sandstone in facies association b of Merendaore locality (Figs. 1, 9, Table 1) includes Rynchosauroides isp. and small invertebrate burrows. These layers show varicolored and laterally-extensive laminated mudstone with pedogenic horizons and are interpreted as distal floodplain to sabkha environments.

The ichnoassociation found in the upper half of the Val Gardena Sandstone in facies association c of Ulbe and Cortiana localities (Figs. 1, 9, Table 1) includes Para­doxichnium, cf. Capitosauroides, and relatively large invertebrate burrows. The trace fossils are preserved in convex hyporelief in the dolostone strata interbedded to the mudstone and interpreted as transgressive lagoon environments passing upwards to the lagoon and marginal marine lithofacies of Bellerophon Formation.

The overall stratigraphic sequence of the Val Gardena Sandstone in the Recoaro area is characterized by an upwards retrogradation of the alluvial environments and a contemporary marine transgression, passing from meandering fluvial to distal floodplain/sabkha to lagoon environments, prelude to the lagoon and shallow marine environments of the Bellerophon Formation. The most diverse ichnoassociation is recorded in the meandering fluvial environment (Fig. 9), including tracks of large herbivores (pareiasaurid, captorhinids, ?therapsids) and small ominivore forms (neodiapsids). This might suggest the presence of a complex trophic structure, the result of stable water source and food availability. The ichnoassociation of the terminal fan/sabkha environment (Fig. 9) includes the only Rhynchosauroides. This is consistent with a stressed environment (e.g., Neri 2007) with reduced water availability and arid conditions, more adapted to small-sized omnivore and opportunistic animals. The ichnoassociation of the lagoon environments (Fig. 9) is instead characterized by Paradoxichnum isp., probable footprints of medium-sized archosauromorph, and cf. Capitosauroides, footprint of medium-sized non-archosauromorph amniotes (?parareptiles), that are absent in the alluvial lithofacies. This might be interpreted as a paleoecological signal, because basal lagoon lithofacies at the Val Gardena Sandstone–Bellerophon Formation transition represent a brackish environment with a specific paleobiota, thus the trackmakers were probably adapted to these conditions, differently to the other tetrapod forms living in the alluvial to sabkha environments. This facies-related distribution of the ichnoassociation confirms once again the impact of the paleoenvironment on the tetrapod ichnoassociations, in terms of different occurrences and different relative abundances. More studies on Lopingian ichnoassociations are needed to eventually confirm the facies-related distribution of the tetrapod ichnotaxa found in the Recoaro area and re-define the Lopingian tetrapod ichnocoenoses (sensu Hunt and Lucas 2006, 2007) and ultimately the meaning of the tetrapod ichnofacies.

Faunistic significance.—Through the ichnotaxonomic study of the Lopingian Val Gardena Sandstone of the Recoaro area, the following tetrapod ichnogenera are identified: cf. Capitosauroides, cf. Merifontichnus, Pachypes, Paradoxichnium, and Rynchosauroides; corresponding to ?parareptile, captorhinid eureptile, pareiasaurid parareptile, archosauromorph eureptile and lacertoid neodiapsid eureptile trackmakers, respectively. An isolated track is probably attributable to therapsid synapsids, and shares similarities with “Ichniotherium cottae” sensu Conti et al. (1977). This is the first possible record of Merifontichnus in the Lopingian, the first possible occurrence of Capitosauroides in the Paleozoic and one of the very few Lopingian localities with Paradoxichnium (Voigt and Lucas 2016).

A comparison with the ichnoassociation of the Val Gardena Sandstone of the Bletterbach site of the Dolomites is presently difficult, because of the necessity of a comprehensive taxonomic revision of these tracks (Abel 1929; Leonardi 1951; Leonardi et al. 1975; Conti et al. 1975, 1977; Ceoloni et al. 1988; Valentini et al. 2007, 2008, 2009; Bernardi et al. 2015). A list with all the ichnotaxa introduced from the Val Gardena Sandstone of Dolomites and other occurrences from the same formation of the Dolomites and Recoaro, with a provisional trackmaker attribution is provided in Table 2. At present, 5 ichnogenera and 13 ichnospecies are known, but most of them are of unclear ichnotaxonomic status, perhaps exclusive of only some intensively-studied ichnotaxa such as Pachypes dolomiticus Leonardi, Conti, Leonardi, Mariotti, and Nicosia, 1975 and Rhynchosauroides pallinii Conti, Leonardi, Mariotti, and Nicosia, 1977 (Valentini et al. 2007, 2008, 2009). The nomina dubia include: the ichnospecies Nanopus grimmi Leonardi, 1951, Ornithoidipius perwangeri Leonardi, 1951, and Phalangichnus perwangeri Conti , Leonardi, Mariotti, and Nicosia, 1977 and the ichnogenus Tridactylichnium leonardii Conti, Leonardi, Mariotti, and Nicosia, 1977 (Conti et al. 1980, 2000). We consider also the ichnogenus Prochirotherium permicum Leonardi, 1951 as nomen dubium, as it is based on a single imprint and lacks an adequate type series (Table 2). The most recent revision by Avanzini et al. (2011) highlights these ichnospecies: Chelichnus tazelwurmi, Dicynodontipus geinitzi, Ganasauripus ladinus, Hyloidichnus tirolensis, Ichniotherium accordii, Ichnio­therium cottae, Janusichnus bifrons, Pachypes dolomiti­cus, Paradoxichnium radeinensis, Protochirotherium isp., Rhynchosauroides pallinii, Rhynchosauroides isp. 1, Rhynchosauroides isp. 2, and therapsid tracks indet. The material assigned to the Chelichnus, Hyloidichnus, Ichniotherium, and Paradoxichnium is probably not assignable to these ichnogenera, because: (i) the ichnogenus Chelichnus sensu McKeever and Haubold (1996) shows a relatively large and circular palm/sole and subequal and short digits in both the pes and the manus; this is not the case of “Chelichnus” tazelwurmi Ceoloni, Conti, Mariotti, and Nicosia, 1988, it is instead characterized by clearly ectaxonic tracks with relatively long digits and a short palm/sole; (ii) Hyloidichnus is characterized by straight digits with enlarged claws and a relatively short palm/sole and non-proximal pedal digit V, this is not the case of “Hyloidichnus” tirolensis Ceoloni, Conti, Mariotti, and Nicosia, 1988, which shows medially-­bent digits terminating in acuminate claws and proximally-positioned digit V; (iii) Ichniotherium shows a marked increase of relative digit length from digit I–IV and digits more deeply impressed distally in both pes and manus; this is not the case in “Ichniotherium” accordii Ceoloni, Conti, Mariotti, and Nicosia, 1988, which is characterized by sub-equal digit length in the pes and “Ichniotherium cottae” (sensu Conti et al. 1977), characterized by a weak increase in length of digits I–IV. Moreover, both show a deeper impression of both the proximal and distal part of digits in the manual tracks; (iv) Paradoxichnium shows thick, straight and parallel manual digits II–IV with large triangular claws and proximally-positioned manual digits I and V, unlike “Paradoxichnium” radeinensis Ceoloni, Conti, Mariotti, and Nicosia, 1988. Additional occurrences from the Dolomitic area are Paradoxichnium and Hyloidichnus, supposed tracks of archosauromorph neodiapsids and captorhinid eureptiles (Voigt and Lucas 2016).

The main difference of the Val Gardena tetrapod ichnoassociation of the Dolomites with the Recoaro ichnoassociation is the occurrence of medium-sized therapsid synapsid tracks (e.g., part of the material identified as “Ichniotherium” accordii and “Ichniotherium cottae”, Dicynodontipus geinitzi), small-sized parareptile tracks (e.g., part of the mate­rial iden­tified as “Chelichnus” tazelwurmi, Janusichnus bifrons, “Hyloidichnus” tirolensis) and chirotheriid tracks (Proto­chiro­therium); and the non-occurrence of medium-­sized ?parareptile tracks (Capitosauroides). However, a partial track from Recoaro might be tentatively attributed to therapsid producers. Derived captorhinid tracks occur in both sites, although with different genera (Hyloidichnus and Merifon­tichnus). The supposed archosauromorph track Paradoxi­chnium occurs in both sites. Rhynchosauroides and Pachypes occur in both sites and are the most abundant ichnotaxa for number of specimens. Therefore, the ichnoassociation of Val Gardena Sandstone in Dolomites and Recoaro seems rather similar, differing only in the occurrence of some ichnogenera/morphotypes such as Dicynodontipus, Protochirotherium, Hyloidichnus, and small parereptile tracks (Dolomites) or Merifontichnus and Capitosauroides (Recoaro). Both the ichnoassociations cleary belong to the Lopingian Paradoxichnium biochron sensu Voigt and Lucas (2016).

Paleobiogeography.—The low-latitude Lopingian inland ichnoassociations of Morocco and Niger are characterized by small neodiapsid and parareptile tracks, medium-sized captorhinid tracks, large parareptile tracks, and temnospondyl tracks (Dromopus, Erpetopus, Hyloidichnus, Pachypes, Limnopus; Voigt et al. 2010; Hminna et al. 2012; Smith et al. 2015). The low-latitude Lopingian ichnoassociations of eolian environments from Germany and Scotland are dominated by supposed therapsid tracks (e.g., Chelichnus-like morphologies) and by probable small parareptile and lacertoid forms (Palmichnus and Akropus sensu Schmidt 1959) (Schmidt 1959; McKeever and Haubold 1996); whereas Lopingian tracks from low-latitude marginal marine environments of Germany only include archosauromorph tracks and small parereptile tracks to date (Paradoxichnium, Erpetopus; Müller 1959; Voigt 2012; Voigt and Lucas 2016). The mid- to high-latitude inland Lopingian ichnoassociations of South Africa and Australia are characterized by therapsid and small amniote tracks (Dicynodontipus and unidentified tracks; De Klerk 2002; Warren 1997). The preliminary study of the low-latitude marginal marine Lopingian Italian ichnofauna, especially as regards the trackmaker attribution, is provided in Table 2. Results indicate a predominance of possible parareptile (Pachypes, cf. Capitosauroides, and material attributed to “Paradoxichnium” radeinensis, “Hyloidichnus” tirolensis, “Chelichnus” tazelwurmi) and lacertoid neodiapsid tracks (Rhynchosauroides pallinii, Ganasauripus ladinus). Noteworthy the occurrence of archosauromorph tracks (cf. Protochirotherium, Paradoxichnium) and therapsid synapsid tracks (Dicynodontipus geinitzi, “Ichniotherium” accor­dii, “Ichniotherium cottae”, and an undetermined track). Therefore, archosauromorph tracks seem to be restricted to low-latitude marginal marine environments (Italy, Germany), and this could be linked to the trackmaker paleoecology.

Therapsid tracks seem to be reltively common in the low-latitude desert paleoenvironments of northern Pangaea. They are present in low-latitude marginal marine paleoenvironments (Italy). They are lacking in the low-latitude inland palaeoenvironments (Morocco, Niger). They were probably common in the high-latitude palaeoenvironments of southern Pangaea (South Africa). The absence of therapsid tracks in the low-latitude inland environments of Morocco and Niger is consistent with the skeletal record (Sidor et al. 2005). The hypothesis of coastal exchange of therapids between the northern and southern parts of Pangaea inferred from the skeleton record (Sidor et al. 2005), from a preliminary evaluation of the low-latitude marginal marine Val Gardena ichnotaxa/trackmakers, could be confirmed by the track record.

In order to verify and expand the discussion on these hypotheses, a comprehensive revision of the historic Bletterbach site material and a detailed study of the Lopingian tetrapod associations and ichnoassociations strictly considering paleolatitude, paleoenvironment, and paleobiogeography is the most urgent task.

Conclusions

The new study of the Lopingian tetrapod footprints of the Recoaro area of Venetian Prealps highlights a relatively diverse ichnoassociation, including the first possible occurrence of Merifontichnus and Capitosauroides in Lopingian strata and one of the few occurrences of Paradoxichnium. The comparison of the ichnoassociation in terms of different lithofacies highlights a probable paleoecologic control on the tetrapod ichnoassociation, which is relatively diverse in floodplain environments and less diverse with opportunistic/specialized forms in sabkha and lagoon environments. A comparison with other Lopingian ichnosites shows a probable preference of Permian archosauromorphs for marginal marine environments. A comparison with the ichnoassociation of the classic Lopingian site of the Dolomites (Bletterbach gorge) shows several similarities and the necessity of a comprehensive ichnotaxonomic revision of the potentially most important Lopingian site of the World either for quality of preservation, abundance of material and ichnotaxonomic diversity.

Acknowledgments

We would like to thank the late Ottaviano Violati Tescari (Vicenza, Italy), the late Olivo Gonzo (Valdagno, Italy), the late Antonio Rossi (Cornedo Vicentino, Italy), and Franco Slaviero (Valdagno, Italy) for collecting and donating the specimens; Bernardetta Pallozzi (Museo Civico D. Dal Lago, Valdagno, Italy), Mariagabriella Fornasiero (Museo di Paleontologia e Geologia of the University of Padua, Padua, Italy), Massimo Bernardi and Riccardo Tomasoni (both MUSE, Trento, Italy), Elio Dellantonio and Daniele Rossi (both Museo Geologico delle Dolomiti, Predazzo, Italy), Birgit Gaitzsch, Jörg W. Schneider, and Frank Scholze (all Technische Universität Bergakademie Freiberg, Freiberg, Germany), and Sebastian Voigt (Urwelt­museum Geoskop, Thallichtenberg, Germany) for the access to the collections and the useful discussions; the reviewers Massimo Bernardi and Grzegorz Niedźwiedzki (Uppsala University, Uppsala, Sweden). Alexander von Humboldt Foundation gave financial support to this study.

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Acta Palaeontol. Pol. 62 (4): 801–817, 2017

https://doi.org/10.4202/app.00392.2017