Studi Trent. Sci. Nat., 88 (2011): 187-190 ISSN 2035-7699187 © Museo Tridentino di Scienze Naturali, Trento 2011

Asteriacites lumbricalis from the Anisian (Middle ) of Vallarsa (Southern Trentino, NE Italy)

Massimo BERNARDI* & Marco AVANZINI

Sezione di Geologia, Museo Tridentino di Scienze Naturali, Via Calepina 14, 38122 Trento, Italia * Corresponding author e-mail: [email protected]

SUMMARY - Asteriacites lumbricalis from the Anisian (Middle Triassic) of Vallarsa (Southern Trentino, NE Italy) - A single, well pre- served fossil trace Asteriacites lumbricalis is here described. The trace, preserved as convex hyporelief, occurs in the Voltago Conglomer- ate (Voltzia Beds Auct.) and records the burrowing activity of ophiuroids on the substrate. The frequent finding of A. lumbriclis within marginal marine-to-brackish facies is consistent with the palaeoenvironment interpretation for this geographical sector during the Middle Triassic of a shallow marginal marine area influenced by terrigenous supplies, lifted by the Recoaro ridge. This discovery represents the first report ofAsteriacites lumbricalis in the Middle Triassic of the Southern Alps.

RIASSUNTO - Asteriacites lumbricalis dall’Anisico (Triassico Medio) della Vallarsa (Trentino meridionale, NE Italia) – Si riporta del rinvenimento di un esemplare della traccia fossile Asteriacites lumbricalis nei livelli superiori del Conglomerato di Voltago (Strati a Voltzia Auct.) affioranti in Val Scalini, Vallarsa (Trentino meridionale). La traccia, che registra l’attività di infossamento di ofiuroidi, è conservata come iporilievo concavo e mostra buona qualità di preservazione. Il frequente rinvenimento di A. lumbricalis in facies da marino marginali a salmastre è in buon accordo con le ricostruzioni paleoambientali per il settore considerato che, nel Triassico Medio, era occupato da un basso fondale costiero influenzato da apporti terrigeni legati alla presenza dell’alto strutturale di Recoaro. La presente rappresenta la prima segnalazione di Asteriacites lumbricalis nel Triassico Medio delle Alpi meridionali.

Key words: Asteriacites lumbricalis, Ophiuroids, Strati a Voltzia, Conglomerato di Voltago, Vallarsa Parole chiave: Asteriacites lumbricalis, Ofiuroidi, Strati a Voltzia, Conglomerato di Voltago, Vallarsa

1. INTRODUCTION & Stephenson 1972; Dam 1990; Karaszewski 1973; Mun- dlos 1966; Bernardi et al. 2010a,b), the Lower Asteriacites von Schlotheim, 1820 is a star-shaped of Chile (Bell 2004), the upper Cretaceous of France (Bre- resting trace (cubichnia) that belongs to the Cruziana ton et al. 1995), the Eocene of Perù (Olsson 1930), up to ichnofacies (Seilacher 1964, 1967). Although the sci- present-day sediments (Gingras et al. 2008). entific history of this genus is thus already remarkably Asteriacites lumbricalis has been commonly inter- long (nearly two centuries), the earliest known report of preted as the result of the burrowing activity of , this trace dates back to the mid XVIII century when the i.e. sea stars (Asteroidea) and brittle stars (Ophiuroidea) German naturalists Georg Wolfgang Knorr and Johann (e.g., Santos & Campanha 1970; Brito 1977; Crimes & Ernst Immanuel Walch figured a specimen in their fa- Jiang 1986). Mángano et al. (1999), have however con- mous ‘paper museum’ of fossils and other mineral objects vincingly shown that A. lumbricalis is most probably (Knorr & Walch 1755). Asteriacites has since then been produced by ophiuroids hiding in the sediment (see also documented from numerous localities and from a wide Seilacher 1953). stratigraphic range; well known reports are from the Or- In the Southern Alps A. lumbricalis has been classi- dovician of Scotland (Goldring & Stephenson 1972) and cally documented form the Werfen Formation (Dolomites): Czechoslovakia (Mikuláš 1990), of Brazil (Da It occurs sporadically in the shallow subtidal Gastropod Costa 1979; Melo 1988) from the of Okla- Oolite and Val Badia Members, but is widespread in the homa, Kansas and Missouri (Chamberlain 1971; West & Campil Member (Early Olenekian) where has been known Ward 1990; Mángano et al. 1999) and Ireland (Lewarne for more than a hundred years (e.g., Wittenburg 1908). The 1964), the Lower Triassic of Germany (Seilacher 1953), only other report of this trace in the Southern Alps is from Utah (Wilson & Rigby 2000), Italy and Nevada (Ma- the Lower of the Trento carbonate Platform (Ber- laroda 1952; Twitchett & Wignall 1996; Twitchett 1999; nardi et al. 2010a,b) where it has been recently documented Twitchett et al. 2005), the Middle Triassic of Germany in the strata that directly underlay the dinosaurian Coste (Müller 1976) and western Canada (Zonneveld 1999, dell’Anglone ichnosite (see Petti et al. in press) located on 2001; Zonneveld & Gingras 2001), the Lower Jurassic of the Eastern side of the Monte Brento (Dro, Trentino Alto- England, Greenland, Poland Germany and Italy (Goldring Adige, NE Italy). 188 Bernardi & Avanzini Middle Triassic Asteriacites

bearing dasycladaceans, crinoids, gastropods and carbon- ate intraclasts, are interbedded with predominant reddish and yellow grained sandstones. Plant debris are abundant throughout the unit. Owing the presence of the Binodosus Subzone am- monites in the overlaying Recoaro Limestone and a com- parison with marine etheropic sediments in Dolomites and Carnia, this unit can be referred to the early Pelsonian (Cuc- cense Subzone). This unit probably reflects a transitional continental to marine environment characterised by coastal delta mouth bars deposited under relatively arid conditions.

3. ASTERIACITES LUMBRICALIS

The here described specimen is preserved on a fine- ly laminated siltstone yellow/brown in colour. The trace is preserved as convex hyporelief (i.e., positive structure on a lower bedding plane) and shows good morphological details. The typical morphology of the Asteriacites lumbri- calis ichnospecies can be identified: 5 distinct rays (arms) originate from a wide central structure having a diameter of ~ 12 mm. Whole trace diameter (arm tip to arm tip) is ~ 51 mm. Arm impressions are quite straight, slender, and mod- erately long (13÷25 mm) in relation to the central structure. Arm thickness ranges from 1 to 4 mm slightly tapering to- Fig. 1 - Location of the “Val Scalini” ichnosite (Val Gerlano, Val- ward the tip. The trace shows fine morphological details larsa, Southern Trentino, NE Italy). such as delicate V-shaped striations on the rays. Although Fig. 1 - Localizzazione del sito di “Val Scalini” (Val Gerlano, arm impressions are always represented by a ‘main’, con- Vallarsa, Trentino meridionale). tinuous, proximal-to-distal trace, a second or third impres- sion can be sometimes seen on its sides. This horizontal repetition of arm traces is a common phenomena that often results in multiple-rayed partially superimposed structures (Mángano et al. 1999). Sinuous, undulate traces can be 2. GEOLOGICAL SETTING sometimes seen within the broader, main ray impression. This is characteristic of ophiuroid arm movements that The here described specimen has been discovered are typically undulatory, in contrast to asteroids where ray in “Val Scalini”, a narrow valley located in the orographic movements are mainly due to the cyclic action of the tube right side of Val Gerlano, near the Speccheri village (Val- feet (Heddle 1967; Woodley 1967). The polygonal, circa larsa, Southern Trentino, NE Italy; Fig. 1). Here the erosive pentagonal, well-differentiated central disc shows slight action of a small creek has well exposed the Middle Trias- displacement and, on its right side, a series of striae that are sic succession. From the bottom of the valley 23 meters here tentatively linked to the deepening on the ophiuroid in of grey sanstones and silty-limestones belonging to the the substrate (see Fig. 2). Notably, within the central disc, “Voltzia Beds” (Voltago cgm.) are followed by 18 meters of a series of sub-parallel ridge-hollows alternation is present white-grey limestones belonging to the Calcare di Recoaro and here interpreted as the trace of both the proximal arm Fm. and by 30 meters of sandstones, marls and poligenic shields, and of the interambulacral plates (i.e., between the conglometates complexively known as “Conglomerato di arm bases) of the ophiuroid. Tretto” (Richthofen Cgm.) (see Barbieri et al. 1980). Geo- Asteriacites lumbricalis is generally recorded in palaeontological investigation of these outcrops led to the marginal-marine, tidal-flat facies and is considered as in- discovery of several fragmentary marine reptiles remains dicative of fully oxygenated (Muller 1980; Mikuláš 1992; within the Calcare di Recoaro Fm. (Dalla Vecchia & Avan- Twitchett & Wignall 1996), shallow waters (Mángano et zini 2002), and, recently, a diverse ichnoassociation domi- al. 1999; see also Mikuláš 1990, 1992). Facies analysis, nated by lepidosauromorphs and archosaurs (Todesco & indicating high terrigenous influence is consistent with Bernardi 2010, this volume) within the “Conglomerato di these suggestion. Asteriacites has been also shown to Tretto”. be common in brackish-water conditions (Mángano et The here described Asteriacites was found in the al. 1999) giving further support to the palaeoenviron- “Strati a Voltzia” (formerly Voltago Cgm). This unit is ment interpretation for this geographical sector during made up of siltstones and claystones mostly grey or yellow the Middle Triassic of a shallow marginal marine area in colour. The lower part of the Voltago Conglomerate con- influenced by a not too far emerged area, lifted by the sists locally of grey silty-micaceous, nodular, bioturbated Recoaro ridge. wackestones and green and grey quartzy micaceous fine The discovery of Asteriacites lumbricalis in the Ani- grained sandstones. In the upper part of the unit, grey cen- sian Voltago Cgm. of “Val Scalini”, Vallarsa, represents the timetre/decimetre-thick, wavy to nodular, silty grainstones first report of this fossil trace in the Triassic of the Trentino Studi Trent. Sci. Nat., 88 (2011): 187-190 189

Fig. 2 - Asteriacites lumbricalis preserved at the “Val Scalini” ichnosite. Fig. 2 - Asteriacites lumbricalis presso il sito di “Val Scalini”.

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