Atreipus-Like Footprints and Their Co-Occurrence with Evazoum from the Upper Carnian (Tuvalian) of Trentino-Alto Adige
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Studi Trent. Sci. Nat., Acta Geol., 83 (2008): 277-287 ISSN 0392-0534 © Museo Tridentino di Scienze Naturali, Trento 2008 Atreipus-like footprints and their co-occurrence with Evazoum from the upper Carnian (Tuvalian) of Trentino-Alto Adige Simone D’ORAZI PORCHETTI1*, Umberto NICOSIA1, Paolo MIETTO2, Fabio Massimo PETTI1,3 & Marco AVANZINI3 1Dipartimento di Scienze della Terra, Sapienza Università di Roma, P.le Aldo Moro 5, 00185 Roma, Italy 2Dipartimento di Geoscienze, Università di Padova, Via Giotto 1, 35122 Padova, Italy 3Museo Tridentino di Scienze Naturali, Via Calepina 14, 38100 Trento, Italy *Corresponding author e-mail: [email protected] SUMMARY - Atreipus-like footprints and their co-occurrence with Evazoum from the upper Carnian (Tuvalian) of Trentino-Alto Adige - A new Tuvalian (Carnian) tetrapod ichnocoenosis is described from Trentino-Alto Adige (Northeastern Italy). The outcrop has yielded Atreipus-like and Evazoum-like footprints along with grallatorids and crurotarsan ichnites. Atreipus appears for the first time in the Italian ichnologic record while Evazoum co-occurs with Atreipus uniquely in this outcrop. The ichnocoenosis gives new insights on the palaeo- geographic distribution and biochronologic significance of Atreipus and Evazoum. Riassunto - Orme Atreipus-like e loro compresenza con Evazoum dal Carnico superiore (Tuvalico) del Trentino-Alto Adige - Viene descritta una nuova icnocenosi a tetrapodi dal Tuvalico del Trentino-Alto Adige (Italia Nordorientale). L’affioramento ha restituito orme tipo Atreipus e tipo Evazoum assieme a impronte grallatoridi e di crurotarsi. Atreipus compare per la prima volta nel record icnologico italiano, mentre Evazoum si trova in associazione con Atreipus esclusivamente in questo affioramento. L’icnocenosi fornisce nuove informazioni sul significato biocronologico e sulla distribuzione paleogeografica di Atreipus e Evazoum. Key words: Atreipus, Evazoum, Tuvalian, Travenanzes Fm., Trentino, Italy Parole chiave: Atreipus, Evazoum, Tuvalico, Formazione di Travenanzes, Trentino, Italia 1. INTRODUCTION Car4 in the late Carnian (Tuvalian). This unconformity cor- responds to the top of the Sciliar Fm., Anisian-Ladinian p.p. On April 2004 several archosaur footprints have been in age (De Zanche & Mietto 1988). discovered by one of the authors (M.A.) near the ruins of the The Anisian-Ladinian unconformity at San Gottar- XII century San Gottardo Castle (formerly known as Coro- do Castle is overlain by white-grey aphanitic to silty dolo- na di Mezo), above the Mezzocorona village, about 18 km stones with beds of reddish or greenish shales (Fig. 2, left), North of Trento (Trentino-Alto Adige) (Fig. 1). The analy- assigned to the Travenanzes Formation (= upper portion of sis revealed at least 50 footprints referred to crurotarsans, the “Raibl Beds” Auct.) (Neri et al. 2005). dinosauriforms and dinosaurs preserved on three main car- This lithofacies might be interpreted as a marginal ma- bonate layers. This paper focuses on the description of the rine environment interested sometimes by input of detritical dinosauriform and dinosaur footprints. sediments, accompanied also by open marine, albeit shal- low, sedimentation. This shallow lagoonal deposition has been affected by periodical subaerial exposure marked by 2. GEOLOGY an increase in birdseyes levels, mudcrack surfaces and ar- chosaur footprints. Higher in the sequence, the disappea- The Adige Valley represents the central sector of the rance of shale beds shows that the clastic input was repla- eastern Southern Alps. Several stratigraphical units are pre- ced definitively by deposition of subtidal and peritidal pri- sent here, referable to the 3rd-order depositional sequences mary dolostones. deposited during the Triassic. A correlation of the upper Carnian deposits along the Near the town of Mezzocorona, in the Middle Adige Adige Valley shows a strong lateral variation typical of tran- Valley, the first three of the four Carnian depositional se- sitional and coastal environment with interfingering betwe- quences (Car1-4 sensu De Zanche et al. 1993) are missing en terminal fan/flood plain and a shallow lagoonal environ- due to the erosion that defines the Sequence Boundary of ment with periodic input of continental detritic sediments 278 D’Orazi Porchetti et al. Atreipus-like footprints part of the Travenanzes Formation have yielded a remarka- ble amount of organic matter, mainly composed of amor- phous material, spores and pollen (Gennaro 2007). The spo- res and pollen taxa identified in the samples are listed in ta- ble 1, in which taxa are grouped into paleotaxa (Playford & Dettmann 1965). According to Roghi (2004), the recorded pollen asso- ciations belong to the Granuloperculatipollis rudis assem- blage, characterized by Circumpolles Partitisporites qua- druplicis and Granuloperculatipollis rudis. This latter spe- cies always occurs with the “long range” (Roghi 2004) ele- ments Enzonalasporites vigens, Pseudoenzonalasporites summus, Camerosporites secatus and Duplicisporites verru- cosus. Except for Partitisporites quadruplicis, all the other five species have been found in the collected samples, of- Fig. 1 - Location of the new outcrop. ten with the bryophyte Ricciisporites tuberculatus (Tab. 1). Fig. 1 - Ubicazione del nuovo affioramento. This association indicates a Tuvalian age. (Gennaro 2007). Later, the continental input ended and the climate became progressively dryer until evaporites were de- 3. MATERIAL posited in the upper part of the southern (Po Plain) sections. At the same time, shallow marine conditions prevailed in to The exposed layers are lower surfaces and occur as the north. Higher up, the Travenanzes Formation gradually overhangs (Fig. 2, right) where footprints are preserved as passes into the Dolomia Principale/Hauptdolomit, and only convex hyporeliefs. The surfaces, from the base to the top, the disappearance of shale beds may be used to define a li- are labelled with letters A, B and C. thostratigraphic boundary between these two formations. On the surface of the lowermost layer (Fig. 3a) a thick mud-cracking is preserved; layer A has yielded at least four 2.1. Age of Travenanzes Formation footprints. Layer B (Fig. 3b) is little exposed and has yiel- ded two tridactyl footprints and few scattered round marks. Samples of black and grey shales from the lowermost This level crops out with a small slab just few meters away Fig. 2 - Log of the section (left) with footprint bearing beds (metric scale on the left side) and close-up (right) of the trampled layers (small pole for scale, bottom left). Fig. 2 - Sezione colonnare (sinistra) con indicazione dei livelli ad impronte (sca- la metrica sul lato sinistro) e particolare dei livelli ad impronte (palina per riferi- mento, in basso a sinistra) Studi Trent. Sci. Nat., Acta Geol., 83 (2008): 277-287 279 Fig. 3 - a. Map of the surfaces A, b. B and c. C. Scale bar 10 cm in a. and b., 20 cm in c. Fig. 3 - a. Rilievo delle superfici A, b. B e c. C. Scala 10 cm in a. e b., 20 cm in c. from the main layer; both the surfaces have a well preser- 3.1.2. Atreipus-like ved mud-crack net. More than 40 footprints have been observed on the up- Other tridactyl footprints have indeed a much more permost bed (Fig. 3c). About 14 footprints are tridactyl in symmetric posterior margin. These tracks are associated to some cases associated with smaller round prints, along with small round marks, lying close to the tip of digit III of the poorly preserved chirotheroid tracks. At least three morphot- pes. These small round prints are here interpreted as manus ypes have been observed at the Mezzocorona locality. prints (Fig. 5). A clear difference in the divarication and re- lative length of digits has been observed in this latter record, 3.1. Tridactyl and tetradactyl footprints where a “slender-” (Fig. 6) (foot length: 14 cm, foot width: 8 cm, manus length: ?4 cm) and a “robust-form” (Fig. 7) (fo- 3.1.1. Grallator isp. ot length: 14 cm, foot width 13.8 cm, manus length: ?7 cm) can be therefore separated. The “robust” form is stouter and A first morph is represented by tridactyl footprints more massive, respect to a slim and lighter “slender-form”; (Fig. 4) that have the posterior end of digit IV pulled back this standing, the presence of a manus print is the most cha- in comparison to digit II (foot length: 16 cm, foot width: 11 racterizing feature. Comparisons of this record with known cm); as a consequence, the posterior margin of these tracks ichnotaxa highlighted its likeness with Atreipus, a tulip-sha- is slightly asymmetric. Digit III is dominant respect to digit ped, symmetric footmark, associated to a tri- or, in some ca- II and IV and the footprint is clearly mesaxonic. This set of ses, tetradactyl handprint. Although some author have que- characters suggests an attribution to Grallator isp. stioned the ichnotaxonomic validity of Atreipus (see Weems 280 D’Orazi Porchetti et al. Atreipus-like footprints Fig. 4 - Photograph and in- terpretative drawing of the most representative speci- men referred to Grallator isp. Scale bar 10 cm. Fig. 4 - Fotografia e disegno interpretativo dell’esem- plare più rappresentativo attribuito a Grallator isp. Scala 10 cm. Fig. 5 - Photograph and interpretative drawing of an Atreipus-like specimen. Scale bar 10 cm. Fig. 5 - Fotografia e dise- gno interpretativo di un esemplare tipo Atreipus. Scala 10 cm. 1992; Weems & Kimmel 1993), this taxon is here conside- 1981a, 1981b; Courel & Demathieu 2000; Gand & Dema- red to be defined by a peculiar and constant set of charac- thieu 2005). The Mezzocorona material shows close affini- ters and according to Safran & Rainforth (2004) is clearly ties with the early Tuvalian tridactyl tracks from the Deep distinct from Grallator. Some minor variations are related River Basin succession (Pekin Formation; North Carolina, to the overall dimension of the specimens (see Lockley & USA; Olsen & Huber 1998: fig. 10), characterized by simi- Hunt 1995) and to digit divarication. Although the compo- lar size, proportions and digit divarication. site type specimens as drawn by Olsen & Baird (1986) show little digit divarication, some material from the Newark Su- 3.1.3.