48LARGE TRIDACTYL FOOTPRINTS ASSOCIATED WITH

A DIVERSE ICHNOFAUNA FROM THE CARNIAN OF THE SOUTHERN ALPS

MASSIMO BERNARDI1,2, FABIO MASSIMO PETTI1, SIMONE D’ORAZI PORCHETTI3 AND MARCO AVANZINI1

1 Museo delle Scienze, via Calepina 14, 38122 Trento, Italy, e-mail: massimo.bernardi@mtsn.tn.it (MB), fabio.petti@mtsn.tn.it (FMP),marco.avanzini@mtsn.tn.it (MA); 2 School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK;

3 via Centuroni, 27, I-02100 Rieti, Italy, email: simone.dorazi.porchetti@gmail.com

Abstract—We report the discovery of two large tridactyl footprints from the late Carnian (Tuvalian) of theSouthern Alps (NE Italy). The tracks can be confidently attributed to a dinosaur trackmaker with an estimatedbody length of about 5 meters. These specimens are part of a diverse ichnofauna testifying to the coexistence oflarge and small dinosaurs, dinosauriforms and crurotarsans. The track-bearing layers are well time-constrained, andprovide one of the earliest reliable evidence of dinosaurs in northern Pangea.

INTRODUCTION

The early diversification of dinosaurs is a long-standing debate invertebrate paleontology. The osteological record suggests that the dino-saur stem lineage (“Dinosauromorpha”) appeared in the latest Anisian(Nesbitt et al., 2010) and that “true” dinosaurs appeared in the earlyCarnian (Benton, 1983; Sereno and Arcucci, 1994; Sereno, 1999; Irmis etal., 2007; Brusatte et al., 2010; Ezcurra, 2010; Langer et al., 2010). Thetrack record, although known to be of problematic interpretation, hasyielded tracks attributed to dinosauromorph trackmakers from theOlenekian (Haubold, 1999; Haubold and Klein, 2002; Gand and Demathieu,2005; Klein and Haubold, 2007; Brusatte et al., 2010) and tridactyltracks referred to dinosaurs from the Ladinian (Marsicano et al., 2007).

In the past, the Late Triassic was described as the period of thecompetitive replacement of faunas dominated by crurotarsan archosaursby those dominated by dinosaurs (Bakker, 1972; Charig, 1984). New,rigorous analysis of the body fossil record together with new discoverieshave, however, shown that during the Late Triassic, crurotarsans hadtwice the variety of body plans, lifestyles, and diets of dinosaurs duringthe first 25–30 million years of dinosaur history (Brusatte et al., 2008,2010, 2011; see also, Benton, 1983; Sereno, 1999). In addition tocrurotarsans, Triassic dinosaurs lived together with dicynodont synapsids(Dzik et al., 2008) and coexisted with dinosauromorphs for at least 20million years (Irmis et al., 2007) becoming dominant in Mesozoic terres-trial ecosystems only from the Jurassic (Brusatte et al., 2010, 2011).These studies have also shown that Late Triassic terrestrial vertebrateassemblages vary significantly in taxonomic composition, diversity andabundance (Irmis, 2011) thus highlighting the importance of local andregional studies to test current hypothesis on the early diversification ofdinosaurs (Irmis et al., 2007; Dzik et al., 2008; Nesbitt et al., 2009;Ezcurra, 2010).

Here we describe new large tridactyl tracks that increase theichnofaunal diversity recently described by some of us (D’Orazi Porchettiet al., 2008) and document the co-occurrence of large and middle-sizeddinosaurs, dinosauriforms and crurotarsans in the late Carnian (Tuvalian)of the Southern Alps.

GEOLOGICAL AND STRATIGRAPHICAL SETTING

The described tracks were found in two distinct outcrops: MonteRoen (specimen MTSN-TRA1) and Mostizzolo (specimen MDS-TRA2)(Fig. 1). Both outcrops can be referred to the Travenanzes Formation (=upper portion of the “Raibl Beds” Auct.; Neri et al., 2005). This forma-tion consists mainly of interbedded white-gray aphanitic to siltydolostones and reddish or greenish shales, with subordinate sandstone toconglomerate intercalations. This mixed siliciclastic-carbonate succes-sion has been interpreted as representing a marginal marine environment

with supplies of terrigenous or fully marine sediments, albeit shallow.Facies alternations suggest interfingering between alluvial-plain, carbon-ate tidal flat and shallow-lagoon deposits (Avanzini et al., 2010; Bredaand Preto, 2011). The marine portion of the Travenanzes are organizedinto meter-scale, shallowing-upward peritidal cycles, not easily distin-guishable from those of the overlying Dolomia Principale (Breda andPreto, 2011). In the Dolomites, the Travenanzes Formation lies on theHeiligkreuz Formation (lower Carnian) while in other areas (i.e., AdigeValley, Non Valley) it can lie directly on the Sciliar Formation (upperAnisian-upper Ladinian) or on volcanics (upper Ladinian), with a sharpand erosional contact (Fig. 2).

The Mostizzolo outcrop, near the village of Cles, is about 48 kmnorth of Trento (Trentino Alto-Adige), and was previously described byAvanzini et al. (2010; in press) and Bernardi et al. (2010), who reported

FIGURE 1. Location map of the study area, Southern Alps (NE Italy). Starsindicate the three main outcrops discussed in the text. Geographicalcoordinates; San Gottardo: 46°13'12'' N, 11°06'35'' E; Mostizzolo: 46°23'02''N, 11°01'56'' E; Monte Roen: 46°21'37'' N, 11°11'33'' E.

Tanner, L.H., Spielmann, J.A. and Lucas, S.G., eds., 2013, The Triassic System. New Mexico Museum of Natural History and Science, Bulletin 61.

49

the presence of archosaurian (crurotarsan) footprints. The Monte Roenoutcrop is located west of the village of Termeno (Bolzano Province;Trentino Alto-Adige) alongside the Rio di Inferno valley at an altitude of2000 m (Sheet 43 Mezzolombardo of the Geological map of Italy, 1:50.000scale; Avanzini et al., in press). In this sector the Travenanzes Formationis constituted by terrigenous, carbonate and evaporitic units deposited influvial, lagoonal and peritidal environments (Avanzini et al., in press).The Travenanzes Formation lies on carbonate platform deposits (SciliarFormation) and upward it passes transitionally to the Dolomia PrincipaleFormation. The footprints have been found about 6 meters above thebase of the Travenanzes Formation. The track-bearing layer lies withinan interval of 50 cm characterized by whitish aphanitic dolostones sepa-rated by thin levels of red and green shales (Gennaro, 2007). The tracksare preserved as natural casts at the top of the described interval.

From the same stratigraphic interval, about 10 km south to theMonte Roen and Mostizzolo sites (San Gottardo nearby Mezzocorona,Trento), D’Orazi Porchetti et al. (2008) reported a diverseichnoassociation discussed further below. There, palynological analysisof the track-bearing horizons (Roghi, 2004) confidently dated the

Travenanzes Formation of this geographic sector of the Southern Alps,and more specifically the trampled horizons, as Tuvalian (late Carnian)236-230 Ma (Roghi, 2004; D’Orazi Porchetti et al., 2008).

MATERIAL

The newly discovered tracks were labelled with the prefix MDS-TRA (Museo delle Scienze, Travenanzes). Ichnological measurementsfollow Leonardi (1987). Abbreviations for the following discussion areas follows: FL = Footprint length; FW = Footprint width; H = hipheight; L = body length. All described tracks are preserved as convexhypo-reliefs.

MTSN-TRA1 (Fig. 3A) was found in the Monte Roen outcrop.The specimen was left in-situ. It is a badly preserved pedal print,mesaxonic and slightly asymmetric, longer than wide (FL = 27 cm; FW =22 cm). Digits are broad and distally taper in possible claw traces. DigitIII is longer than digits II and IV. Total divarication (II–IV) is circa 75°.Three subcircular digital pad traces occur on one of the lateral digits.Only the proximal pad of digit III is preserved.

MTSN-TRA2 (Fig. 3B) was found in the Mostizzolo site and is

FIGURE 2. Stratigraphic scheme of the Middle-Upper Triassic in the Dolomites and surrounding areas (modified from De Zanche et al., 1993).

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now stored in the Paleontological Collection of the Museo delle Scienze,Trento. It is a badly preserved left pedal print, mesaxonic and slightlyasymmetric, longer than wide (FL = 26 cm; FW = 21 cm). Digits arebroad and distally taper in claw traces. Digit III is longer than digit II andIV. Total divarication (II–IV) is about 40°. No distinct digital pad tracesare visible since they collapsed in large bulges, likely resulting from thecoalescence of two or more pads. The pedal hypex between digits II andIII (15°) is wider than the one between III and IV (25°).

DISCUSSION

Given the previously described characters, MTSN-TRA1 andMTSN-TRA2 can be compared to the ichnogenus Eubrontes sensu Lucaset al. (2006). Triassic tridactyl prints are traditionally assigned toDinosauria (Lucas et al., 2006). However, this morphotype cannot beunambiguously assigned to dinosaurs using apomorphy-based identifi-cations, as at least some dinosauroids (e.g., Ornithosuchus, Silesaurus)possess a functionally tridactyl pes (King and Benton, 1996; Carranoand Wilson, 2001; Dzik, 2003; Marsicano et al., 2007; Nesbitt et al.,2007).

Supposed dinosaur tracks are recognized on the base of fewsynapomorphies: i) the prevalence of the digit II-IV group, ii) mesaxonicpattern of foot structure, iii) digit I reduced and shifted backwards (andthus often not preserved in tracks), and iv) tendency towards digitigrady(see also Thulborn, 1990; Haubold, 1999; Brusatte et al., 2010). Thesecharacters are all present in the tracks described herein.

Olsen et al. (1998) have shown that no synapomorphies of three-toed footprints can discriminate among theropods, basal saurischian and

basal ornithischian groups. In our view, however, MTSN-TRA2, can bedescribed as “theropod-like” on the base of the following characters: i)asymmetry of the track with angle between digit III and II lower thanbetween III and IV, ii) digit III longer than IV>II, iii) sharp claw traces onall digits, iv) tip of digit II turned inwards, and v) possible bipedalism.

If the attribution of the described tracks to dinosaurs is correct,the trackmaker’s hip height (H) can be calculated according to Thulborn’s(1990) equation (h = 3.06 × FL1.14) that gives H=1.25 m. The estimatedbody length is circa 5.0 m (L = 4H, Thulborn, 1990) and the estimatedbody mass value is about 200 kg calculated following the formula devel-oped by Weems (2006). This size is not known from dinosaur skeletalremains of Carnian age (Benton, 2006; Brusatte et al., 2010) and isapproximated only by the Norian theropod dinosaur Liliensternus (Cunyand Galton, 1993; Lucas et al., 2006).

Functionally tridactyl footprints are documented in the MiddleTriassic of France (Demathieu, 1989; Lockley and Meyer, 2000), Ger-many (Haubold and Klein, 2000, 2002), Italy (Avanzini, 2002), Argen-tina (Marsicano et al., 2007 and references therein) and are generallyattributed to Dinosauromorpha, with the possible exception of the LosRastros Formation (Argentina) (Marsicano et al., 2007), where dinosaurtracks are reported. Early and Middle Triassic tracks previously attrib-uted to dinosaurs have been reconsidered as partially or badly preserved“chirotheroids” (King and Benton, 1996).

The earliest skeletal remains of dinosaurs are currently restrictedto late Carnian sites in southern Pangea (Argentina, Brazil; see Brusatteet al., 2010; Martinez et al., 2011), but dinosaur tracks are most fa-mously known from the Middle Triassic Los Rastros Formation, Argen-tina (Marsicano et al., 2004; 2007). Furthermore, Marsicano and Barredo(2004) described a rich tetrapod track assemblage recently re-dated asLadinian (Barredo et al., 2012) from the Corral de Piedra Formation(Argentina) that indicates the presence of non-mammalian therapsids(small cynodonts and large dicynodonts), crurotarsal archosaurs anddinosaurs (sauropodomorphs and theropods).

The earliest dinosaur from northern Pangea has recently beendated to the “middle” Norian of western North America (Nesbitt et al.,2009). This has led to the view that the major dinosaurian clades(Ornithischia, Sauropodomorpha, Theropoda) may have originated insouthern Pangea (Brusatte et al., 2010; Langer et al., 2010). The paleo-geographic importance of this distribution, however, is compromised bythe absence of well-preserved skeletal remains of Carnian age from north-ern locales (northern Africa, Europe, North America) (Langer, 2005;Nesbitt et al., 2007; Martinez et al., 2011).

In the late Carnian of the Southern Italian Alps, tridactyl dino-saur-like footprints were recently discovered at the San Gottardo site(D’Orazi Porchetti et al., 2008; Table 1); small tridactyl footprints as-signed to Grallator and attributed to theropod dinosaurs were dominantand co-occurred with the tridactyl Atreipus, often preserved with clearmanual impression, attributed to dinosauriforms (silesaurids, see D’OraziPorchetti et al., 2008 and references therein), and the tetradactyl Evazoum,possibly attributed either to sauropodomorphs (Nicosia and Loi, 2003)or crurotarsans (Klein et al., 2006; Lucas et al., 2010). Furthermore, thepentadactyl track Brachychirotherium was recently discovered by oneof us (M.A.) in the same site, thus testifying to the presence of crurotarsalarchosaurs, possibly aetosaurs (Heckert and Lucas, 2000; Hunt andLucas, 2007; Lucas and Heckert, 2011) (Fig. 4; Table 1).

Crurotarsal archosaurs (e.g., Brachychirotherium eyermani) alsooccur in the Mostizzolo outcrop, (Avanzini et al., 2010, Bernardi et al.,2010; Table 1), further increasing the diversity of the Travenanzesichnoassemblage in the Southern Alps (Fig. 3). Nicosia and Loi (2003)described a rich Carnian ichnoassociation from Lerici, La Spezia (north-ern Italy) with dinosaurian and crurotarsan tracks, but nodinosauromorphs. Dinosaur footprints are small tridactyl grallatorids,Anomoepus-like tracks (possible ornithischian track), and Evazoum (Table1). This find provides further support to the assertion that the

FIGURE 3. A, MDS-TRA1, Pedal imprint, from the Monte Roen site. B,MDS-TRA2, Left pedal print from the Mostizzolo site. Both tracks werefound in the Travenanzes Formation, Tuvalian (late Carnian, Late Triassic),of the Southern Alps, NE Italy.

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FIGURE 4. Late Carnian ichnoassociation form Northern Italy. A-B, Large tridactyl tracks described in the text. C, Brachychirotherium isp.from San Gottardo (Trento). D, Grallator isp. from San Gottardo (Trento; from D’Orazi Porchetti et al., 2008). E, Atreipus isp. from SanGottardo (Trento; from D’Orazi Porchetti et al., 2008). F, Brachychirotherium eyermani from Mostizzolo (Trento; from Avanzini et al.,2010). G, Crurotarsan track from Mostizzolo (Trento; from Bernardi et al., 2010). H, Evazoum sirigui from Lerici (La Spezia; from Nicosiaand Loi, 2003).

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ichnoassemblage described herein is representative of the Carnian tetra-pod faunas along the southern margins of the spreading Tethys ocean.

A well-diversified tetrapod ichnoassemblage from northern Pangeaconstrained to the early Tuvalian (late Carnian), was described fromNorth Carolina by Olsen and Huber (1998). The authors reported thepresence of cf. Brachychirotherium, Apatopus and small bipedal andtridactyl forms, possibly produced by “dinosaurian” trackmakers (Olsenand Huber, 1998). Furthermore, Cameron and Wood (2003, 2004) syn-thetically describe the co-occurrence of Rhynchosauroides,Brachychirotherium, Atreipus and Grallator in the upper portion of theWolfville Formation of Nova Scotia (Canada), Carnian in age.

The findings described herein, supported by those described byOlsen and Huber (1998), Nicosia and Loi (2003), and D’Orazi Porchettiet al. (2008) might partially fill the gap of late Carnian fossil documenta-tion. Furthermore, while the age of some Triassic terrestrial vertebrateassemblages is debated (Irmis et al., 2010; Irmis, 2011; but see Lucas,2010), and the Triassic time scale is poorly constrained as a whole (seeFurin et al., 2006), the here described Tuvalian ichnoassociation pro-vides a reliable record of the late Carnian archosaur fauna of the SouthernAlps.

The co-occurrence of dinosaurs, dinosauriforms and crurotarsalarchosaurs in the late Carnian documents a prolonged coexistence ofdifferent groups of archosaurs, some even sharing the same environment.This provides support to the view of crurotarsan-dominated faunas

TABLE 1. Carnian (Late Triassic) Southern Alps sites discussed in the text and the ichnoassociations discovered therein.

being neither rapidly outcompeted nor quickly opportunistically re-placed by dinosaurs, but rather substituted by a more gradual processesof ecological replacement (Irmis et al., 2007; Nesbitt et al., 2010; Brusatteet al., 2010; Martinez et al., 2011).

CONCLUSION

The Carnian faunal assemblage reported here, which consisted oflarge and small dinosaurs, dinosauriforms and non-dinosaurian archosaurs,can be considered one of the most diversified for this interval. It docu-ments one of the earliest forms of evidence of dinosaurs in northernPangea, and the co-occurrence with dinosauriforms and crurotarsalarchosaurs provides support to the non-abrupt replacement of the ar-chaic fauna by a dinosaurian one.

ACKNOWLEDGMENTS

We thank M. Gennaro and R. Tomasoni for field work. We aregrateful to the editors of this volume, as well as to S.G. Lucas and C.A.Marsicano for their thorough reviews. This study is part of the project“The Permian-Triassic ecological crisis in the Dolomites: extinction andrecovery dynamics in Terrestrial Ecosystems” financed by the Promo-tion of Educational Policies, University and Research Department of theAutonomous Province of Bolzano - South Tyrol. The research was sup-ported also by the Science Museum, Trento – Accordo di Programma2011.

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