Rend. Online Soc. Geol. It., Vol. 48 (2019), pp. 106-111, 3 figs. (https://doi.org/10.3301/ROL.2019.43) © Società Geologica Italiana, Roma 2019 First report of Sclerobiont Bryozoans in the Maiolica Fm. of the Umbria-Marche Basin (Northern Apennines, Italy) Simone Fabbi (1), Angelo Cipriani (1), Paolo Citton (2) & Marco Romano (3) (1) Dipartimento di Scienze della Terra, Sapienza Università di Roma, P.le Aldo Moro, 5, 00185, Rome, Italy. (2) CONICET-Consejo Nacional de Investigaciones Científicas y Técnicas. IIPG-Instituto de Investigación en Paleobiología y Geología, Av. Roca 1242 (8332), General Roca, p.cia. de Río Negro, Argentina. (3) Evolutionary Studies Institute (ESI), School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa. Corresponding author e-mail: simone.fabbi@uniroma1.it Document type: Short note. Manuscript submitted 13 March 2019; accepted 13 May 2019; editorial responsibility and handling by C. D'Ambrogi. ABSTRACT We describe the first evidence of sclerobiont bryozoans found loose in the pelagic Maiolica Fm. of the Umbria-Marche Basin (Monte Acuto Massif, Northern Apennines, Italy). The material is represented by three small sub-circular colonies with tube-shaped zooecia radially developing from the centre. These characters are not enough for generic or specific classification, consequently, these cyclostomes have been only identified as belonging to the Suborder Tubuliporina. Calpionellid assemblages allow to constrain the bryozoan-bearing rock sample to the early Berriasian. The occurrence of isolated bryozoans in the Maiolica Fm. enriches the knowledge about the fauna of this unit in pure basinal settings, composed by radiolarians, calpionellids, dinoflagellate cysts and rare macrofossils (ammonites and aptychi), including very rare benthic organisms (gastropods, brachiopods and bivalves). Up to date, no sclerobiont organisms in ‘normal’ pelagic Maiolica facies were known, due to the lack of suitable substrates to be colonised. Encrustation of a planktonic or nektonic hard-shelled organism seems the most parsimonious hypothesis based on our material. KEYWORDS: Cretaceous; Umbria-Marche Succession; Maiolica Fm.; Monte Catria-Monte Nerone Ridge. INTRODUCTION AND GEOLOGICAL SETTING Three small bryozoan colonies and few fragments have been recently found in the pelagic Maiolica Fm. of Monte Acuto Massif, in Northern Apennines (Italy) (Fig. 1). The specimens here discussed represent the first occurrence of such organisms in the Maiolica Fm., a lithostratigraphic unit which commonly lacks benthic biota. The Monte Acuto area belongs to the Umbria- Marche-Sabina (UMS) Domain in Central and Northern Apennines, where a well-known Upper Triassic-to- Neogene stratigraphic succession (Fig. 2) is exposed (e.g.: Centamore et al., 1971). A well-documented Early Jurassic extensional phase produced a particular palaeotopographic setting that controlled the Jurassic sedimentation of the area (Santantonio & Carminati, 2011; Fabbi, 2015; Cipriani & Bottini 2019; Citton et al., 2019; Romano et al., 2019). Starting in the Hettangian, the main result of such extensional phase was the fragmentation of the vast “Calcare Massiccio” carbonate platform in structural highs and lows (Fig. 1b, Fig. 2), which diachronically experienced drowning and the consequent onset of pelagic sedimentation. The last carbonate platforms drowned in the early Pliensbachian (Fabbi & Santantonio, 2012 and references therein), and the UMS palaeogeographic domain was dominated by pelagic sedimentation during the rest of the Mesozoic. While a hundred meters-thick stratigraphic succession filled the structural lows, thin (some meters) condensed successions were deposited during the same time span (Fig. 2) on the structural highs, known as “Pelagic Carbonate Platforms” (PCPs – sensu Santantonio, 1994). The palaeotopographic gaps were generally blanketed by the Maiolica Fm. in the earliest Cretaceous, with local exceptions (Fabbi, 2015; Fabbi et al., 2016; Cipriani & Bottini, 2019). Monte Acuto represents a peculiar type of PCP, being interpreted as a pelagic cusp (Fig. 1b), thus lacking any flat top and related successions (Santantonio & Carminati, 2011). The area where the study material was found belonged to the Bosso-Burano basin (Fig. 1), which separated the Monte Acuto high from the Monte Nerone PCP (Santantonio & Carminati, 2011). Significantly, the Bosso-Burano Basin is characterised by a pure pelagic succession deposited after the drowning of the carbonate platforms on structural highs (i.e. after the early Pliensbachian). It follows that this area should had been far away from shallow-water carbonate platforms, as confirmed by the lack of any re-sedimented neritic material. This fact marks a strong difference with the coeval successions located closer to benthic carbonate production areas (e.g.: Fabbi et al., 2016). For all the above, the first finding of bryozoans in the Maiolica Fm. of the Bosso-Burano basin is something intriguing, deserving further considerations. SCLEROBIONT BRYOZOANS Most bryozoans are sessile organisms colonizing hard substrates (e.g.: Brood, 1998), and forming colonies that can vary greatly in terms of shape and organization (Moissette, 2000; Taylor & James, 2013). Bryozoans can live in a wide range of bathymetric depths, from shallow