Updating the Dinosaur Tracksites from the Lower Jurassic Calcari Grigi Group (Southern Alps, Northern Italy)

Studi Trent. Sci. Nat., Acta Geol., 83 (2008): 289-301 ISSN 0392-0534 © Museo Tridentino di Scienze Naturali, Trento 2008 Updating the dinosaur tracksites from the Lower Jurassic Calcari Grigi Group (Southern Alps, Northern Italy) Marco AVANZINI1* & Fabio Massimo PETTI1,2 1Museo Tridentino di Scienze Naturali, Via Calepina 14, 38100 Trento, Italy 2Dipartimento di Scienze della Terra, Sapienza Università di Roma, P.le Aldo Moro 5, 00185 Roma, Italy *Corresponding author e-mail: [email protected] SUMMARY - Updating the dinosaur tracksites from the Lower Jurassic Calcari Grigi Group (Southern Alps, Northern Italy) - The discovery in 1989 of the Lavini di Marco tracksite (Lower Jurassic) gave rise to the search of other dinosaur footprint-bearing outcrops in the whole Southern Alps sector. As a result ten new Lower Jurassic ichnosites have been found since then in Trentino Alto-Adige and Veneto (North- eastern Italy), including two new sites described in this volume for the first time. The aim of this paper is to provide an updated summary of the Lower Jurassic dinosaur tracksites discovered to date in the Southern Alps. All the outcrops are lithostratigraphically referred to the Calcari Grigi Group (Hettangian-upper Pliensbachian). Information about the geographic and geological setting, the age, the main features of the footprints, the most likely track makers and the relative bibliographic references are herein provided for each ichnosite. RIASSUNTO - Aggiornamento dei siti con orme dinosauriane attribuiti al Gruppo dei Calcari Grigi, Giurassico inferiore (Alpi Meridio nali, Italia settentrionale) - La scoperta nel 1989 del sito dei Lavini di Marco (Giurassico Inferiore) ha dato il via alla ricerca di nuovi affioramenti con orme dinosauriane in tutto il settore delle Alpi Meridionali. Da allora dieci nuovi icnositi, anch’essi attribuibili al Giuras- sico inferiore, sono stati rinvenuti in Trentino Alto-Adige e in Veneto (Italia nord-orientale), inclusi due siti inediti descritti per la prima volta in questo volume. Lo scopo di questo articolo è di fornire un quadro sintetico e aggiornato dei siti con orme dinosauriane attribuiti al Giurassico inferiore, scoperti sino ad ora nelle Alpi Meridionali. Tutti gli affioramenti presi in esame sono litostratigraficamente riferibili al Gruppo dei Calcari Grigi (Hettangiano-Pliensbachiano superiore). Per ogni icnosito sono forniti l’inquadramento geografico e geologico, l’attribuzione cronologica, i principali caratteri delle orme, i probabili trackmakers ed i relativi riferimenti bibliografici. Key words: dinosaur tracks, Lower Jurassic, Calcari Grigi Group, Trento carbonate Platform, Southern Alps Parole chiave: orme di dinosauro, Giurassico inferiore, Gruppo dei Calcari Grigi, Piattaforma carbonatica di Trento, Alpi meridionali 1. INTRODUCTION 2), namely from bottom to top: the Monte Zugna Forma- tion (Hettangian-Sinemurian), the Loppio Oolitic Limesto- Dinosaur tracks and trackways are widespread in ne (Middle to Late Sinemurian), the Rotzo Formation (Si- the Lower Jurassic of Southern Alps (Northern Italy, Fig. nemurian p.p. -Pliensbachian), locally partially heteropic 1) and up to date eleven dinotracksites were discovered in with the Tovel Member (Sinemurian-Pliensbachian), and this area (Lanzinger & Leonardi 1992; Leonardi & Avan- the Massone Oolitic Limestone (Late Pliensbachian). Re- zini 1994; Mietto & Roghi 1994; Avanzini 1997; Avan- cently the Monte Zugna Formation has been further sub- zini et al. 1997; Leonardi & Mietto 2000; Mietto et al. divided by Avanzini et al. (2006) into three informal units: 2000; Avanzini 2001, 2002; Avanzini et al. 2001a, 2001b, a “Lower Subtidal Cyclic Unit”, a “Middle Peritidal Unit” 2001c, 2003, 2006, 2007a; Piubelli et al. 2005; Avanzini et and an “Upper Subtidal Unit” (respectively LSCU, MPU al. 2008; Petti et al. 2008). All the outcrops belong to the and USU in Fig. 2). Calcari Grigi Group that is a Lower Jurassic shallow wa- From a palaeogeographic point of view, the Calca- ter carbonate succession well-exposed through the eastern ri Grigi Group pertains to the Trento carbonate Platform, sector of the Southern Alps (see Avanzini et al. 2007b for now extending north-south from Verona to Bolzano (NE a review). In this region the Calcari Grigi Group reaches a Italy) and that during the Mesozoic covered an area of ap- thickness of several hundred meters (more than 400 m in proximately 20.000 km2. This domain was characterized the central-western Trento Platform) and is composed of by shallow-water carbonate sedimentation through all the alternating subtidal, peritidal and supratidal deposits. The Early Jurassic and was bounded on the east by the Bellu- Calcari Grigi Group is currently subdivided into four for- no pelagic basin and on the west by the Lombard pelagic mations and one member (CARG project - Geological Map basin through the so-called “Garda escarpment” (Fig. 3), of Italy at the scale 1:50.000; Avanzini et al. 2007b; Fig. a normal fault system active during the Jurassic and the 290 Avanzini & Petti Updtating dinosaur tracksites from the Lower Jurassic of Southern Alps Cretaceous (Castellarin et al. 1993, 2005). As suggested by the palynological analysis of some track-bearing horizons (Avanzini et al. 2006), the climate of the Trento Pla- tform area during the Early Jurassic varied from arid to hu- mid conditions. 2. DINOSAUR TRACKS LOCALITIES Lavini di Marco (Pl. I a; Pl. II a; Pl. III a, e, f; h; Pl. IV 110; Pl. V 1, 2, 3) Discovered by Luciano Chemini in 1989 45°50′37.06″N, 11°02′04.79″E 707 m a.s.l. The Lavini di Marco tracksite is located few kilom- eters south of Rovereto (Trentino-Alto Adige) and repre- sents one of the most important European dinosaur footprint-bearing outcrops. It has been studied thoroughly by Fig. 1 - Location map of the Lower Jurassic dinosaur tracksites several authors since 1990 that carried out extensive ich- from Southern Alps. nological, sedimentological and palynological researches Fig. 1 Ubicazione geografica dei siti con orme dinosauriane delle (Lanzinger & Leonardi 1992; Leonardi & Avanzini 1994; Alpi Meridionali attribuiti al Giurassico Inferiore. Avanzini et al. 1997; Leonardi & Mietto 2000; Avanzini et Fig. 2 - Lithostratigraphic succession of the Lower Jurassic Calcari Grigi Group showing the stratigraphic positions of the different dinosaur tracksites. Fig. 2 Successione litostrati grafica del Gruppo dei Calcari Grigi (Giurassico Inferiore) con la posizione stratigrafica dei siti con orme di dinosauro. Studi Trent. Sci. Nat., Acta Geol., 83 (2008): 289-301 291 al. 2001b; Avanzini 2002; Avanzini et al. 2003; Piubelli et al. 2005; Avanzini et al. 2006). Lithostratigraphy and age The Lavini di Marco trampled horizons have been as- cribed to the middle-upper part of the Monte Zugna Forma- tion (“Middle Peritidal Unit” sensu Avanzini et al. 2006; Fig. 2) and cover approximately 300.000 m2 of monoclinal sur- faces (Piubelli et al. 2005). Seven dinoturbated levels have been recognized in a 7 meter-thick section. The richest level is made of alternating stromatolitic laminae and light gray, pel- oidal mudstones, dark gray bioclastic wackestones and red- dish mudstones (Avanzini et al. 1997). The top of the stromatolitic layer is often pervasively dolomitized and typically white in color. All the track-bearing layers are Hettangian in age (Avanzini et al. 2006). Fig. 3 - Palaeogeographic restoration of the central-eastern sector of Southern Alps during the Early Jurassic. Description of the tracks Fig. 3 Ricostruzione paleogeografica del settore centroorientale delle Alpi Merdionali durante il Giurassico Inferiore. The ichnoassemblage is very rich and diverse. It com- prises predominantly tridactyl footprints of small to medium- sized theropod dinosaurs that fall within the ichnogenera Kay Lithostratigraphy and age entapus isp. Welles 1971, Grallator isp. Hitchcock 1858 and Eubrontes isp. Hitchcock 1845. Kayentapus isp. is the most Dinosaur tracks at Chizzola were discovered in a road common. Some of the tridactyl footprints are considered to be- cut along the SP 22. The trampled horizon has been assig- long to primitive ornithischians that had functionally tridactyl ned to the middle-upper part of the Monte Zugna Formation and clawed, theropod-like feet. Among them, Anomoepus isp. (“Middle Peritidal Unit” sensu Avanzini et al. 2006; Fig. 2) Hitchcock 1848 has also been recognized (Pl. III h; Avanzini and is Hettangian in age. It consists of a light-gray stroma- et al. 2001b; Olsen & Rainforth 2003). Furthermore some of tolitic interval, dolomitized at the top (Avanzini et al. 1997). the tridactyl tracks are elongate, displaying the whole or par- The footprints were destroyed due to the recent works of ro- tial impressions of the metatarsus and indicating a crouching ad widening in the area. posture of the dinosaur (Pl. IV 10; Avanzini et al. 2001b). In addition to tridactyl tracks there are many narrow-gauge Description of the tracks trackways of medium-sized quadrupeds that may likely rep- resent sauropodomorphs. Most of these trackways close re- The Chizzola tracksite yielded three tridactyl foot- semble those of Parabrontopodus Lockley, Farlow & Meyer prints related to medium-sized theropods (ALCH 1, ALCH 2 1994 from the Upper Jurassic of Colorado (USA) and Bre- e ALCH 3). The best preserved footprint (ALCH 1; Pl. III l; viparopus Dutuit & Ouazzou 1980 from the Upper Jurassic- Pl. IV 18), partially eroded, is a left tridactyl track (33 cm in Lower Cretaceous of Morocco

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