Permian tetrapod localities in the Nurra region (NW Sardinia, Italy): The State of the Art

PAOLO CITTON; UMBERTO NICOSIA; MARCO ROMANO; AUSONIO RONCHI

Permophiles

IUGS - International Commission on Stratigraphy

Lugar: Beijing; Año: 2018 vol. 66 p. 9 - 18

1684-5927

The Nurra area in NW Sardinia is quite well known for theoutcropping of a thick succession of more than 600 m of post‐Variscan continental deposits (Fig. 1), with several dedicatedstudies and contribution already starting from the first half of thetwentieth century (e.g. Lotti, 1931; Oosterbaan, 1936; Pecorini,1962; Vardabasso, 1966; Gasperi and Gelmini, 1980). An intensive research program in the last 20 years has led to a better understandingand definition of the sedimentology and stratigraphy ofthe area, with the 600‐m‐thick Permian and Triassic continentalsuccession subdivided in the following six formations (from baseto top): Punta Lu Caparon., Pedru Siligu, Porto Ferro, and Caladel Vino formations for the Permian, and the Conglomerato delPorticciolo and Arenarie di Cala Viola for the Triassic (Gasperiand Gelmini, 1980; Cassinis et al., 2002a, 2003). The careful sedimentologicalanalysis of the Permian-Triassic succession of theNurra area allowed lithostratigraphic correlation with the depositsoutcropping around Toulon in Provence (Cassinis et al., 2002a,2003; Durand, 2006, 2008), with the Cala del Vino Fm. showingquite superimposable lithofacies and fluvial architecture to theone characterizing the Saint‐Mandrier Fm. (Durand, 2008).Despite intensive study of the area especially in the last twentyyears, the fossiliferous content of the outcropping deposits in theNurra is historically rare, and for a long time was essentially representedby macrofloral and microfloral remains from the basalportion of the Punta Lu Caparoni Fm (Gasperi and Gelmini, 1980;Pecorini, 1962; Ronchi et al., 1998) providing a middle Autunianage, and in the upper portion of Arenarie di Cala Viola, indicatingan Early Triassic age (Pecorini, 1962). This situation changeddramatically and unexpectedly when, in 2008, a student from theUniversity of Pavia found accidentally eight articulated vertebrae,still partially embedded in the red Permian sediments of the Caladel Vino Formation, outcropping in the Torre del Porticciolo promontory(Fig. 2). Since that day, more than fifteen field works havebeen conducted in the area, headed by a team of the Departmentof Earth Sciences of Sapienza of Rome in collaboration with theUniversity of Pavia, to collect a truly unique material for bothItalian and European Permian panorama. Overall, about eightybones were recovered, both complete and fragmentary, all referableto the post-cranial skeleton of a very huge animal (Fig. 2).The preparation and study of the material allowed the descriptionand formalization of a new taxon of the Family Caseidae,Alierasaurus ronchii (Romano and Nicosia, 2014) from ?Aliera?or ?Alighera?, the old traditional name of the city of Alghero inSardinia, and Ronchi in honor of Prof. Ausonio Ronchi fromPavia who reported us the new discovery.In 2015, during a field work to collect additional materialreferable to the huge caseids, a second productive site (Torre delPorticciolo 2, TdP2) was discovered about hundred metres fromthe original Alierasaurus site (TdP1) (Fig. 1, bottom). Field worksconducted in the new site in 2016 and 2017 led to the recovery ofseveral bones and bone fragments both still embedded in the originaldeposits, and isolated elements in the deposit deriving fromthe erosion of the productive sedimentary body (see Romano et al.,2018) (Fig. 3). Despite a system of normal alpine fault displacingthe meandering river deposits, the productive sedimentary bodiesof TdP1 and TdP2 can be referred essentially to the same stratigraphiclevel (see Romano, 2018, fig. 4). A detailed taphonomicanalysis allowed to refer all the recovered material to the sameand single individual; in addition, a preliminary study of the mostdiagnostic elements among the already prepared bones allowedto refer the new specimen to a member of the Sphenacodontidae(Romano et al., 2018). Sphenacodontids are a crucial clade ofhighly predaceous non-therapsids synapsids (traditionally knownas ?pelycosaurs?), essentially known from the Permian beds outcroppingextensively in the south‐western United States. The newfinding represents the first record of the group in Italy, throwingnew light on the occurrence and dispersal of the clade in theEuropean continent.In the summer of 2017, during the excavation of skeletalremains at TdP2 locality, palaeontological survey was conductedalong the sedimentary succession outcropping towards SSW anda reddish sandstone slab bearing an isolated tetrapod track wasfound as loose material. The prospecting was then focused in thearea of the discovery and yielded two joined slabs preserving twocouples of footprints (Fig. 4), coming from a very close horizonto the bone-bearing ones (TdP3), about one kilometre from TdP1and TdP2 localities.The new material constitutes the first ichnological evidencefrom the Permian of Sardinia and provides a more comprehensive understanding of the faunal composition of the Cala del Vino Fm.As a matter of facts, the Torre del Porticciolo site turned out tobe one of the few, rare, sites in Europe where both body fossilsand ichnofossils are jointly preserved, enhancing our knowledgeabout the Permian faunal diversity and ecosystem structure in thisarea of Pangea.