Rivista Italiana di Paleontologia e Stratigrafia (Research in Paleontology and Stratigraphy) vol. 126(3): 833-846. November 2020 THE OCCURRENCE OF EOCENOCHELUS (TESTUDINES, PLEURODIRA) FROM SARDINIA SUPPORTS PALAEOGEOGRAPHIC RECONSTRUCTION OF THE PROXIMITY OF THE ISLAND TO CONTINENTAL WESTERN EUROPE DURING THE EOCENE GEORGIOS L. GEORGALIS1,2,*, DANIEL ZOBOLI3, ADÁN PÉREZ-GARCÍA4, GIAN LUIGI PILLOLA3 & MASSIMO DELFINO2,5,* 1 Palaeontological Institute and Museum, University of Zurich, Karl Schmid-Strasse 4, 8006 Zurich, Switzerland 2 Dipartimento di Scienze della Terra, Università di Torino, 35, via Valperga Caluso, 10125 Torino, Italy 3 Dipartimento di Scienze Chimiche e Geologiche, Università di Cagliari, Cittadella Universitaria (Blocco A), 09042 Monserrato, Italy 4 Grupo de Biología Evolutiva, Facultad de Ciencias, Universidad Nacional de Educación a Distancia, Paseo Senda del Rey 9, 28040 Madrid, Spain 5 Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Edifici ICTA -ICP, Carrer de les Columnes s/n, Campus de la UAB, 08193 Cerdanyola del Vallès, Barcelona, Spain * Corresponding authors: dimetrodon82@gmail.com; massimo.delfino@unito.it To cite this article: Georgalis G.L., Zoboli D., Pérez-García A., Pillola G.L. & Delfino M. (2020) - The occurrence of Eocenochelus (Testudines, Pleurodira) from Sardinia supports palaeogeographic reconstruction of the proximity of the island to continental Western Europe during the Eocene. Riv. It. Paleontol. Strat., 126(3): 833-846. Keywords: Pleurodira; Testudines; Paleogene; biogeography; palaeogeography. Abstract. In this paper, we describe pleurodire turtle material from the island of Sardinia, Italy, originating from two Eocene localities of the Cixerri Formation. The more complete among the two specimens bears strong re- semblance with the continental Western European Eocenochelus eremberti and is tentatively referred to the same species, while the second, less complete specimen is only provisionally referred to the genus Eocenochelus. The new Sardinian turtles add to the so far scarcely documented fossil record of pleurodires in Italy, while it ranks as among the very few Paleogene vertebrates known from the island. The identification of the widespread Eocene Western European genus Eocenochelus in the fossil record of Sardinia supports recent palaeogeographic reconstructions of the island, according to which the Sardinia-Corsica Massif was located rather close to mainland Europe and was subjected to a significant, counterclockwise rotation during the Paleogene. Introduction Bandyopadhyay 2020), encompassing a diverse array of extinct taxa, also including Stupendemys geographi- Pleurodires are currently confined solely to cus Wood, 1976, one among the largest turtles of all the southern continents (Rhodin et al. 2017); how- time (Scheyer and Sánchez-Villagra 2007; Cadena et ever, this turtle clade achieved a significantly broader al. 2020). In Europe, pleurodires were one of the distribution during its Mesozoic and Cenozoic past dominant and widespread turtle groups during the (see Gaffney et al. 2006, 2011; Cadena 2015; Pérez- Late Cretaceous, but were also abundant and diverse García et al. 2017b; Ferreira et al. 2018; Joyce & during the Eocene (Owen & Bell 1849; Zigno 1889; Bergounioux 1954; Broin 1977; Kotsakis 1978; Lapparent de Broin 2003; Pérez-García et al. 2012, Received: July 8, 2020; accepted: September 10, 2020 2017a, 2017b, 2019; Rabi et al. 2012; Pérez-García & 834 Georgalis G.L., Zoboli D., Pérez-García A., Pillola G.L. & Delfino M. Lapparent de Broin 2013, 2015; Cadena 2015; Pérez- chelys bolcensis was initially introduced as Platyarkia bol- García 2016; Pérez-García & Chapman 2017; Pérez- censis by Bergounioux (1953); however, he provided García & Smith 2017). Their most recent records in no description, definition, indication to a previous this continent are from the early Neogene (Ristori description, or figure of the material and as such, 1895; Georgalis et al. 2013; Georgalis & Kear 2013). this 1953 binomen has to be considered a nomen A number of Paleogene taxa from Western Europe nudum. Neochelys bolcensis was formally described by have been identified as pertaining to the lineage of the same author the following year (Bergounioux Erymnochelyinae, which is now represented by the 1954), but nevertheless, currently this taxon is con- extant taxon Erymnochelys madagascariensis (Grandidi- sidered to be a junior synonym of N. capellinii (e.g., er, 1867), which is exclusive to Madagascar (Ferrei- Broin 1977). The validity of Emys nicolisii is at flux ra et al. 2018); nevertheless, Erymnochelyinae were with the taxon likely representing a nomen dubium once much more widespread during their Cenozoic or at least a junior synonym of N. capellinii, though it past, distributed over Europe and Africa (Ferreira et has also been recently considered as a valid species al. 2018). Erymnochelyines were widespread in the as well, Neochelys nicolisii (Lapparent de Broin 2003; Eocene of Central and Western Europe, achieving Pérez-García & Lapparent de Broin 2015; Lappar- a diverse radiation comprising multiple species, per- ent de Broin 2018). taining to two genera, the freshwater Neochelys Ber- In a broader frame of a revision of the fos- gounioux, 1954, and the littoral Eocenochelus Pérez- sil turtles of Italy (Abbazzi et al. 2008; Chesi 2009; García, Lapparent de Broin & Murelaga, 2017b Chesi et al. 2007a, 2007b, 2009; Colombero et al. (Bergounioux 1954; Broin 1977; Pérez-García et al. 2014, 2017; Cirilli et al. 2016; Georgalis et al. 2020), 2017b). Despite their abundance and high levels of here we describe two shells of Eocene age from Sar- species diversity, European erymnochelyines became dinia, which are assigned to the genus Eocenochelus. ultimately extinct at the end of the Eocene (Pérez- We address their taxonomic affinities and compare García et al. 2017b). Among European erymnoche- them with other finds of the genus from continen- lyines, the genus Eocenochelus, species of which have tal Europe. Biogeographic implications of the new been found across the Eocene of France, Spain, Bel- pleurodire remains are discussed, along with their gium, and the United Kingdom, is the most phyloge- impact on the palaeogeographic reconstruction of netically proximate genus to the extant Erymnochelys the Western Mediterranean during the Eocene. Baur, 1888 (Pérez-García & Chapman 2017; Pérez- García & Smith 2017; Pérez-García et al. 2017b). Material And Methods In Italy, the fossil record of pleurodire turtles has been so far limited to continental remains com- The fossil material described herein is curated at the collec- ing from the province of Veneto, in the northeastern tions of the MDLCA. The first of the two specimens (the most com- part of the country. The remains from Veneto are plete, MDLCA 14006) was briefly mentioned in abstracts and papers during the past two decades (Righi & Delfino 2003; Delfino & Rook represented by several specimens, including com- 2008; Pérez-García & Chapman 2017; Pérez-García et al. 2017b); plete, articulated skeletons, and are already known however, it has never been formally described or figured. The second since the late nineteenth century (Zigno 1889, 1890). one (MDLCA 3018) is presented here for the first time. Taxonomy They originate from two middle Eocene localities follows Joyce et al. (2004) and Pérez-García et al. (2017b). and have been originally referred to their own spe- Institutional abbreviation. MDLCA, Museo Sardo di Ge- cies: Emys capellinii Zigno, 1889 and Neochelys bolcen- ologia e Paleontologia “Domenico Lovisato”, University of Cagliari, sis Bergounioux, 1954 from the famous Lagerstätte Italy. of Monte Bolca, and Emys nicolisii Zigno, 1890 from Avesa (Zigno 1889, 1890). All of them seem to per- Geological Settings tain to the podocnemidid erymnochelyine genus Neochelys (Bergounioux 1954; Broin 1977; Kotsakis The turtle remains described herein originate 1978; Pérez-García & Lapparent de Broin 2015). Ne- from the Cixerri Formation, a continental succes- ochelys capellinii is in fact the type species of Neochelys sion cropping out discontinuously in southwestern and is currently almost universally considered a valid Sardinia (Pecorini & Pomesano Cherchi 1969). The species (Lapparent de Broin 2003; Pérez-García & most complete specimen (MDLCA 14006) was Lapparent de Broin 2013, 2015; Cadena 2015). Neo- collected in a sand quarry in the locality Medau is The occurrence of Eocenochelus (Testudines, Pleurodira) from the Eocene of Sardinia 835 Fig. 1 - Schematic geological map of the NW Sulcis Basin, Sardinia, showing also the position of the fossil locali- ties which have provided the remains of turtles studied in this paper. 1) Undifferenti- ated Aquitanian–Holocene deposits; 2) Cixerri Forma- tion (middle Lutetian–early Oligocene); 3) Lignitifero Formation (late Ypresian– early Lutetian); 4) Miliolitico Formation (early Ypresian); 5) Variscan metamorphic basement and Carbonifer- ous–Mesozoic deposits. Fenus, near Flumentepido (Municipality of Car- phase sedimentation in Sardinia (Cherchi 1979; bonia). The other specimen (MDLCA 3018) was Barca & Costamagna 2010) and deposed in the collected in the locality of Murecci (Municipality middle to lower, distal part of a foreland alluvi- of Gonnesa, Fig. 1). The geographic distance be- al plain fed by Iberian relieves (Costamagna & tween these outcrops is around 7 km in straight Schäfer 2013). Presently, only a portion of this line. alluvial plain is preserved, because a great part of The Cixerri Formation is a terrigenous for- this was cut in half by the following detachment mation mainly represented by sandstones, sub- of the Sardinia-Corsica Massif from the south- ordinated siltites, and conglomerates with very ern European margin (Costamagna & Schäfer rare intercalations of lignitiferous clays and lacus- 2013). Furthermore, Barca & Costamagna (2010) trine limestones (Pecorini & Pomesano Cherchi reported fluvial facies alternated with siliciclastic 1969; Barca & Costamagna 2010; Costamagna deposits containing marine ichnofacies and tidal & Schäfer 2013). The conglomeratic levels are stratal pattern in the Monastir area (Campidano di more frequent in the upper part of the succes- Cagliari subregion) suggesting at least temporary sion. Generally, these are represented by rounded, coastal/river mouth area. Marine influences are polygenic and heterometric clasts originated from documented in eastern and southeastern Sardinia Paleozoic, Mesozoic and early Eocene lithotypes since the Thanetian (Matteucci 1985). However, cropping out currently in the Sulcis-Iglesiente the general trend in facies distribution during the subregion. Furthermore, several authors report- Cixerri Formation time indicates a provenance of ed the presence of pebbles with ?Aptian–Albian the sediments from the west to the east and sug- microfaunas originated from lithotypes of the gests that the previous “short living” marine to Pyrenean domain, totally absent in the Sardinian lagoonal basin identified in the Sulcis area (start- area (Cherchi & Schroeder 1976; Cherchi 1979; ing with the ?late Thanetian, middle–late Ypresian Barca & Cherchi 2002). The Formation crops out “Calcari a macroforaminiferi” Auct.), showing a extensively in southwestern Sardinia (Sulcis sub- clear transgression, running from the southwest region) and in the Cixerri valley, with a maximum to the east in the present day position, was bound- thickness of about 300 m (Pecorini & Pomesa- ed by emerged land towards the east and filled by no Cherchi 1969; Funedda et al. 2009; Barca & continental deposits during the early Lutetian Lig- Costamagna 2010). The nature of the sediments nitifero Auct Formation and Cixerri Formation indicates a continental depositional context with molasse times. It is difficult to give more detailed a prevalence of fluvial facies (Pecorini & Pome- palaeogeographical information, but the charac- sano Cherchi 1969). More precisely, the Cixerri ters of the transgressive-regressive cycle and the Formation represents the molassic post-Pyrenean tectono-sedimentary setting play in favor of a rel- 836 Georgalis G.L., Zoboli D., Pérez-García A., Pillola G.L. & Delfino M. atively short time for the deposition of the Cixer- Systematic Palaeontology ri Formation. According to Barca & Costamagna (2010) and Costamagna & Schäfer (2013), the Ci- Testudines Batsch, 1788 xerri Formation is settled in a more limited time Pleurodira Cope, 1864 span (middle Lutetian–early Rupelian). These au- Pelomedusoides Cope, 1868 thors used the presence of volcanoclastic pebbles Podocnemididae Cope, 1868 at the top of the continental succession to dis- Erymnochelyinae Broin, 1988 (sensu Pérez-García criminate another Formation (Flumentepido For- et al. 2017b) mation; Barca & Costamagna 2010). Erymnochelyini Pérez-García, Díaz-Berenguer, The Cixerri Formation rests conformably Badiola & Canudo, 2019 to unconformably over the late Ypresian–ear- Eocenochelus Pérez-García, Lapparent de Broin & ly Lutetian Lignitifero Formation or it is posed Murelaga, 2017b unconformably over the Variscan metamorphic Eocenochelus eremberti (Broin, 1977) basement (Costamagna & Schäfer 2013, and references therein). Upwards, it passes sharply Eocenochelus cf. eremberti through an unconformity to the calcalkaline vol- Figs. 2-3 canics of the Oligocene–Miocene cycle (about 22.8±1.3 Ma) in the Sulcis area (Lecca et al. 1997) Material: MDLCA 14006, an almost complete carapace and plastron, missing only tiny fragments of the anteriormost and poste- or to the terrigenous of the late Oligocene to riormost portions of the carapace (Fig. 2-3). Aquitanian Ussana Formation in the Campidano Locality: Medau is Fenus, near Flumentepido (Municipality area (Pecorini & Pomesano Cherchi 1969). In ad- of Carbonia), Sardinia; Cixerri Formation, probably middle Eocene. dition, in the Cixerri Valley, the Cixerri Formation is clearly intruded by the Cenozoic volcanic rocks Description. MDLCA 14006 is an almost dated at 29.9–27.5 Ma (Savelli 1975; Savelli et al. complete shell, preserving most parts of the cara- 1979); more recently these rocks were recently pace and plastron (Figs. 2-3). The carapace misses dated to be 29.30±1.2 to 26 Ma (Funedda et al. only tiny fragments of the anteriormost and poste- 2009). riormost portions, especially at the posterior right The fossiliferous content of the Cixer- portion, near the marginals, as well as near the level ri Formation is rather poor; in addition to the of the first pleurals. Three prominent breakages are herein described turtle remains, only scarce plant apparent on the carapace. Also, certain portions of remains (in particular palms), freshwater gastro- the carapace are slightly deformed. pods (Lymnaea cf. orelongo), and isolated bone frag- The carapace is oval, being 372 mm long and ments from lacustrine levels were reported from 306 mm wide (at mid-length and mid-width respec- the Villamassargia, Gonnesa, and Perdaxius areas tively). Its posterior part is relatively flattened dor- (Taricco 1924; Maxia 1959). sally; there are no signs of a medial or lateral keels. Summarizing, the age of the Cixerri For- The posterior margin of the carapace is dorsally mation is bracketed between the early Lutetian directed. It is not possible to determine whether (which is the age at the top of the Lignitifero a cervical scute was present (in the case of being Formation) and the local first occurrence of in- present it should be extremely narrow, which is un- truded mid-late Rupelian volcanic products. Ac- likely). cording to these data, the turtle remains from the The limits between several plates are not Cixerri Formation (sensu Barca & Costamagna clearly visible and these often coincide with the frac- 2010) can be referred to the middle Lutetian–ear- tures. The plates of the carapace, which has been ly Rupelian; this time range slightly encompass- possible to identify, are represented by: a nuchal, six es the so far known chronologic distribution of neurals, a suprapygal, a pygal, eight right and eight Eocenochelus, that is known exclusively up to the left costals, and at least nine right and nine or ten late Eocene. But, the reasons exposed above (tec- left peripherals. The nuchal is located immediate- tono-sedimentary setting) suggest that the age of ly anterior to the neural series. It is covered by the the Sardinian pleurodire remains is, in all likeli- vertebral I and the first pair of marginals. There are hood, middle Eocene. six neurals. The dimensions of all the neurals are The occurrence of Eocenochelus (Testudines, Pleurodira) from the Eocene of Sardinia 837 Fig. 2 - Eocenochelus cf. eremberti from Sardinia. MDLCA 14006, al- most complete carapace and plastron. Photographs in dorsal (A), ventral (B), and left lateral (C) views. Fig. 3 - Eocenochelus cf. eremberti from Sardinia. MDLCA 14006, almost complete carapace and plastron. Interpretative drawings in dorsal (A), ven- tral (B), and left lateral (C) views. more or less similar between them, with the excep- nal, with their smaller sides situated in their anterior tion of the last one, which has significantly smaller positions and their formula is: 4-6a-6a-6a-6a-5. The dimensions than the others. Their shape is hexago- last neural does not contact with the suprapygal, 838 Georgalis G.L., Zoboli D., Pérez-García A., Pillola G.L. & Delfino M. due to the medial contact of the last three pairs of Scutes are represented by a single gular and costals. The costals at the central area of the cara- a pair of extragulars (sensu Hutchison & Bramble pace are larger than laterally and they are decreasing 1981), humerals, pectorals, abdominals, femorals, both in width and height, towards both the anterior and anals. The element size formula of medial sur- and posterior position in the series. Peripherals I-IX face of the plastron is as follows: abdominals > can be distinguished in the right series; the sutures pectorals > femorals > anals > gular ≥ humerals of peripherals X and XI are hidden by fractures and > extragulars. The gular has small dimensions. The areas in which shell portions are missing. From the femorals have a trapezoidal shape and the sulcus left series, peripherals VII and VIII are not recog- with the anals is slightly posteriorly arched. The nizable. anals are rhomboid. Their posterior extremity is The remains of the scutes on the carapace af- semioval and its margins form an angle of 107o. ford some information about all the elements that originally constituted its external appearance. The cf. Eocenochelus sp. scutes are represented by two series, each arranged Fig. 4 on one side, of 12 marginals and four pleurals and by a single series of five vertebrals. The medial re- Material: MDLCA 3018, an incomplete carapace and plas- gion of both first marginals is not preserved. The tron, missing the most of its anterior halves of both carapace and marginals II-VII have a rather similar shape and size plastron (Fig. 4). Locality: Murecci, (Municipality of Gonnesa), Sardinia; between them, and are longer than wide. Among Cixerri Formation, probably middle Eocene. pleurals, pleural II is the largest, followed by pleu- rals I, III, and IV. The vertebrals II and III are the Description. MDLCA 3018 is a partial shell, largest, both showing a similar size; they are fol- lacking the anterior portion of both carapace and lowed in size by vertebrals I, IV, and V. plastron (Fig. 4). The preserved portion of the shell The plastron is 34.6 cm long and 26.4 cm is filled with matrix and is locally heavily fractured wide (at the level of the mesoplastra). Its central part and incomplete. The surface is partly covered by is slightly concave (it is unclear whether it a prod- a hard concretion. Therefore, most of the skeletal uct of deformation or if it was also the case of the elements are not visible, though their presence can specimen when in life). The anterior plastral lobe, be supposed on the basis of the general shape of 10.9 cm long, is rounded at the front and widens the shell. However, its morphology does not signif- towards a posterior direction. Its outer edge folds icantly differ from that of MDLCA 14006 and thus slightly upwards. The posterior plastral lobe, 11.7 it will be only briefly commented here. cm long, has an anal notch with an angle of 107o; its The carapace has a preserved midline length distal margin folds slightly upwards. The left bridge of 33.6 cm, while its maximum preserved width is is 12.7 cm long. It is damaged by displaced fractures, 28.8 cm. The carapace preserves the neurals from in which the posterior area was collapsed. The right the second (maybe a little portion of the second) side bridge is well preserved, being 12.0 cm long. to the last, but only the third, fourth and fifth can Several variably pronounced (and sometimes dislo- be seen with relative confidence (a posterolateral cated) fractures are visible, mainly with a transversal suture of the sixth could be present); the costals or oblique direction. In the plastron, the sulci that from the second to the last; the peripherals from delimit the scutes are relatively evident, while sever- the fourth to the last one. Pygal and suprapygal al areas corresponding to the sutures between some could be also present but this cannot be deciphered plates are not clearly visible. with certainty. The plates in the plastron are represented by The plastron has a preserved midline length the entoplastron, the epiplastra, hyoplastra, mes- of 26.5 cm, while its maximum preserved width is oplastra, hypoplastra, and xiphiplastra. The ento- 23.2 cm. The plastron preserves partial hyoplastra, plastron is of rhomboid shape and is located in the the hypoplastra, and the xiphiplastra. The entire anterior portion of the plastron. The epiplastra are left mesoplastron and possibly part of the right trapezoidal. The hyoplastra are longer than the hypo- mesoplastron are present but their sutures cannot plastra. The mesoplastra are situated laterally, placed be seen due to the presence of concretion and frac- at the lateral limits of hyoplastra and hypoplastra. tures. The occurrence of Eocenochelus (Testudines, Pleurodira) from the Eocene of Sardinia 839 Fig. 4 - cf. Eocenochelus sp. from Sar- dinia. MDLCA 3018, incom- plete carapace and plastron; photographs and interpre- tative drawings in dorsal (A, B), and ventral (C, D) views. Discussion vertebral II approximately as wide as vertebral III, both scutes lacking wide lateral protrusions anteri- Taxonomic allocation or to the limit between the pleural sulci; first pair MDLCA 14006 can be identified as a mem- of marginals overlapping no more than half of the ber of Pleurodira considering characters as the length of the lateral nuchal margins; posterior plas- present of a pair of laterally located mesoplastra, tral lobe narrower than the anterior one; absence and that of a single gular. The absence of a trape- of clear extragular protrusions; relatively long gu- zoidal anterior plastral margin allows to exclude its lar scute, reaching the anterior margin of the ento- attribution to Neochelys (Pérez-García & Lapparent plastron or overlying its most anterior region; very de Broin 2015), the only genus of Pleurodira that short dorsal expansion of the plastral scute borders was hitherto identified in the fossil record of Ita- (see characters in Pérez-García et al. 2017b, 2019; ly (see Introduction above). The development of a Pérez-García & Smith 2017). Among Eocenochelus long medial contact of the extragulars, due to the spp., this Sardinian specimen shares several charac- presence of a reduced gular, has been recognized ters with the type species of the genus, Eocenochelus as exclusive of Erymnochelyini (Pérez-García et eremberti, which constitute an exclusive combination al. 2017b, 2019). This specimen can be referred to for this form: sinuous lateral margins of the ver- the genus Eocenochelus on the basis of the identifica- tebral scutes; relatively long epiplastral symphysis, tion of an exclusive character combination within less than half the entoplastral length; relatively wide this clade including: absence of a medial keel on posterior plastral lobe; subrounded lateral margins the carapace; vertebral I heptagonal, with short lat- of the posterior plastral lobe; relatively wide anal ero-anterior margins, and wider than the nuchal; notch, its length being equivalent to half this width 840 Georgalis G.L., Zoboli D., Pérez-García A., Pillola G.L. & Delfino M. or less (see Pérez-García et al. 2017b, 2019). It is as compatible with the intraspecific variability ob- worth noting that in terms of size, the Sardinian served in various members of Pleurodira, including material approaches mostly the smallest species of Eocenochelus eremberti (Pérez-García & Smith 2017; the genus (i.e., Eocenochelus lacombianus Pérez-García, Pérez-García et al. 2019). Despite the relative low Lapparent de Broin & Murelaga, 2017b), which has a number of characters provided by MDLCA 3018, plastron length of around 30 cm and not respective it is attributed to cf. Eocenochelus sp. considering its elements of the largest species, E. eremberti, which potential compatibility with the same taxon repre- reaches even around 50 cm in plastron length (see sented by the almost complete Sardinian shell de- Pérez-García et al. 2017b, 2019). The presence of scribed above, as well as the fact that their remains six neurals instead of seven differs from the known are found in the same Formation and, in particular, condition for the middle Eocene E. eremberti, being in two localities that are situated relatively close to compatible with the one that characterizes the late each other. Eocene Eocenochelus farresi Pérez-García, Lapparent The well-preserved specimen (MDLCA de Broin & Murelaga, 2017b (Pérez-García et al. 14006), comprising both carapace and plastron, 2017b). However, other characters allow to exclude ranks as one of the most complete shells of Eoceno- its attribution to this form (e.g., the combination chelus known to date, being surpassed in complete- of characters indicated as shared with E. eremberti ness only by a recently described shell of E. eremberti as well as exclusive characters for E. farresi, such as from Spain (Pérez-García et al. 2019). the presence of a very short epiplastral symphysis, long lateral overlap of the humeral scutes onto hy- Palaeobiogeographic and palaeogeographic oplastra, and an almost as long as wide U-shaped implications anal notch), as well as to the early Eocene E. lacom- The present identification of Eocenochelus in bianus (e.g., the combination of characters indicat- the Eocene of Sardinia provides interesting bio- ed as shared with E. eremberti as well as the devel- geographic implications. So far, Eocene tetrapods opment of concave lateral margins of its notably from Sardinia were represented by pan-trionychids, narrow posterior plastral lobe, which represents an crocodylians, the marsupial Amphiperatherium Filhol, exclusive condition for E. lacombianus) (see Pérez- 1879, and the perissodactyls Atalonodon monterini Dal García et al. 2017b). The differences between the Piaz, 1929, and “Lophiodon” sardus Bosco, 1902 (Bo- shell MDLCA 14006 and those hitherto known for sco 1902; Dal Piaz 1929; Kotsakis 1985; Kotsakis et E. eremberti cannot be ruled out as due different on- al. 1997; Zoboli et al. 2019). With the exception of togenetic stages (e.g., the smaller size of the Sardin- Atalonodon monterini, the crocodylians, and the pleu- ian specimen), and to an intraspecific variability for rodire turtle material described herein, all tetrapod this species greater than that until now known (e.g., fossils come from the late Ypresian–early Lutetian the difference in the number of neurals). Since oth- Lignitifero Formation. The Eocene pan-trionychids er shell characters used for the characterization of from Sardinia are represented by indeterminate E. eremberti (Pérez-García et al. 2017b, 2019; Pérez- remains (Kotsakis 1985) that cannot be identified García & Smith 2017) are unknown in MDLCA beyond the family level (Georgalis & Joyce 2017). 14006, and also considering that the age of MDL- The crocodylians are represented by a single small CA 14006 cannot be confirmed as compatible with tooth from the Ypresian of Escalaplano (southeast- the known stratigraphic range of distribution for ern Sardinia) that cannot be taxonomically more that species (Lutetian), we attribute MDLCA 14006 precisely referred (Zoboli et al. 2019). The marsu- to Eocenochelus cf. eremberti. pial remains have not been yet formally described Most of the characters available in the par- and were only provisionally referred to the genus tial shell MDLCA 3018 are compatible with those Amphiperatherium (Kotsakis et al. 1997), a genus that observed in MDLCA 14006 (e.g., the morphology is widespread in the Paleogene of continental Eu- of the preserved neural plates and vertebral scutes; rope. “Lophiodon” sardus has been either referred to the width/length ratio of the anal notch and the the lophiodontid genera Lophiodon Cuvier, 1822, morphology of its lateral margins), and the differ- and Paralophiodon Dedieu, 1977 (Bosco 1902; Esu & ences observed between them (e.g., the morphol- Kotsakis 1983; Palombo 2009), both genera that are ogy of the posterior plastral lobe) are recognized widespread in the Paleogene of Europe, including The occurrence of Eocenochelus (Testudines, Pleurodira) from the Eocene of Sardinia 841 Fig. 5 - Palaeogeographic recon- struction of the Western Mediterranean during the Eocene, showing the posi- tion of the Sardinia-Corsica Massif. Silhouettes represent the shared continental tetra- pod lineages that occurred in both areas during the late Ypresian–Lutetian. Abbrevi- ations: Ba, Balearic Islands; Be, Betic; Ib, Iberia; Ka, Ka- bylias; CPA, Calabrian-Pelo- ritan Arc; Sa, Sardinia; Co, Corsica; Aq, Aquitania. Map modified after Omodeo and Rota (2008) and Advokaat et al. (2014). the Iberian Peninsula (Holbrook 2009). Anyway, a subsequently taking place during the Eocene (Ad- revision of the type material of “L.” sardus should vokaat et al. 2014). Nevertheless, faunal distinction, be necessary to confirm the taxonomic position and at least to the species or even genus level, is the case validity of the taxon. However, the described fossil for certain vertebrate taxa that occurred in the early material of this perissodactyl is currently lost (Kot- Eocene of continental Western Europe and Sardin- sakis et al. 2008). The other large mammal, Atalono- ia, therefore implying the existence of some sort of don monterini, was collected in the lithotypes of the temporary geographical or palaeoecological barriers Miliolitico Formation (early Ypresian) cropping out between the Sardinia-Corsica Massif and the Iberi- near the Terras de Collu coal mine (Gonnesa). Ata- an-Occitanic area that allowed endemic radiations lonodon is also currently considered a lophiodontid flourishing in these nearby different landmasses (e.g., Prothero & Schoch 1989; Holbrook 2009), during the late Paleocene–early Eocene time span whereas alternative relationships within perisso- (Matteucci et al. 2000; Palombo 2009). The rotation dactyls have also been suggested (Palombo 2009); of the Sardinia-Corsica Massif continued also in however, whether it indeed represents a Sardinian post-Eocene times, as an even more prominent and insular endemic genus or is instead referred to a well documented rotation (counter-clockwise of mainland European one remains yet to be demon- about 50°) took place, mostly during the early Mi- strated. ocene (Gattacceca et al. 2007); that being said, the The presence of related faunal elements total rotation of the Sardinia-Corsica Massif was of among Sardinia and continental Western Europe about 95° counterclock-wise and was completed by should not appear at strange. Rather than that, cur- around 15 Ma (Gattacceca et al. 2007). It is further rent geodynamic reconstructions suggest that, dur- worth noting that during the late Oligocene the Sar- ing the early Paleogene, the Sardinia-Corsica Massif dinia-Corsica Massif was still connected with the was rather close to continental Western Europe, with European mainland as documented by the presence an important, about 45°, counter-clockwise rotation of the continental ruminant “Amphitragulus” quercyi 842 Georgalis G.L., Zoboli D., Pérez-García A., Pillola G.L. & Delfino M. (Mennecart et al. 2017) and early Miocene insular been repeatedly suggested for Cenozoic European taxa with clear mainland affinities (de Bruijn & taxa (Georgalis et al. 2013; Georgalis & Kear 2013; Rümke 1974; Van der Made 2008; Zoboli & Pillola Pérez-García & Chapman 2017; Pérez-García et al. 2017; Mennecart et al. 2019). 2017b, 2019). The 95° counterclock-wise rotation The new material described herein adds the of the Sardinia-Corsica Massif significantly shifted pleurodire turtle Eocenochelus as another shared fau- the position of the fossils of Eocenochelus, that have nal element between Sardinia and continental West- never lived in the central Tyrrhenian area, and there- ern Europe. Rather interestingly, in this case, such fore provides an interesting biogeographic case of shared faunal resemblance reaches almost the spe- “Viking funerary ship” (Mckenna 1973) in a Medi- cies level, as the Sardinian material is identified as terranean setting. Finally, the occurrence of Eoceno- very close to Eocenochelus eremberti, if not conspecif- chelus in the Sardinian fossil record further adds to ic. That species was originally established from the the growing evidence of the rich and diverse extinct middle Eocene of northern France on the basis of reptilian fauna of the island that once comprised both cranial and postcranial remains (Broin 1977), many different lineages that are currently global- while additional, more or less coeval, material from ly extinct or extirpated from Europe (Portis 1901; Belgium (Pérez-García & Smith 2017) and Spain Abbazzi et al. 2004, 2008; Venczel & Sanchíz 2006; (Pérez-García et al. 2019) has recently been referred Chesi et al. 2007a; Delfino et al. 2008, 2011; Geor- to it, demonstrating a rather broad geographic dis- galis et al. 2017, 2019; Tschopp et al. 2018; Zoboli tribution during the middle Eocene. The other two et al. 2019). named species of Eocenochelus are known from only from shell material from southern Europe and have much more confined geographic distributions, as Conclusions only one specimen has been attributed to each of them so far: Eocenochelus lacombianus from the early The first pleurodire material from the island Eocene of southwestern France, and Eocenochelus of Sardinia is described herein, comprising of two farresi from the late Eocene of northeastern Spain shells from two different, probably middle to late (Pérez-García et al. 2017b). Eocene, localities. The most complete shell is re- The new shell material from Sardinia allows ferred to the erymnochelyine podocnemidid Eoceno- the recognition of a form rather close to Eoceno- chelus cf. eremberti, while the incomplete specimen is chelus eremberti. The depositional environment of the only tentatively referred to as cf. Eocenochelus sp. Fur- two Sardinian localities that yielded the new pleu- thermore, the most complete Sardinian specimen rodire remains indicates a freshwater environment represents one of the most complete known shells (in which, Eocenochelus, adapted for life in littoral of the genus Eocenochelus, bearing more resemblance environments, would have arrived), demonstrating with the type species, Eocenochelus eremberti, fossils of the non-marine nature of the sediments. Such close which have also been found in Spain, France, and or even conspecific affinities between continen- Belgium. The biogeographic importance of the new tal Western European coastal areas and Sardinian Eocenochelus remains is discussed, as these represent Eocenochelus do not necessitate direct land connec- another shared related faunal element between Sar- tion between these land masses in order to be ex- dinia and continental Western Europe. Taking into plained. Instead, Eocenochelus has been suggested be consideration the former proximity of Sardinia with a taxon adapted for coastal habitats (Pérez-García continental Western Europe and the rotation of the et al. 2017b) and thus, even short marine distances Sardinia-Corsica Massif from the Eocene onward, between Western Europe and Sardinia during the we envisage that Eocenochelus directly dispersed to Eocene would certainly not be a significant bar- Sardinia somewhen during the Eocene. rier for these pleurodires (see also Pérez-García Acknowledgments. The shell MDLCA 14006 was prepared by & Chapman 2017). After all, pleurodires appear F. Landucci (Department of Earth Sciences, University of Florence); to have been rather capable of marine dispersals, D. Righi (University of Modena and Reggio Emilia) prepared its pre- liminary interpretative drawing and description in the frame of her with many taxa also inhabiting near shore envi- master thesis. MD thanks H. Tong for her comments on MDLCA ronments (Sánchez-Villagra et al. 2000; Gaffney et 14006 and for having suggested its erymnochelyine affinities. Project al. 2006, 2011), with such dispersal events having supported by Fondi di Ateneo dell’Università di Torino (2018-2019), The occurrence of Eocenochelus (Testudines, Pleurodira) from the Eocene of Sardinia 843 Generalitat de Catalunya (CERCA Program) and Spanish Agencia Bergounioux F.M. (1954) - Les Chéloniens fossiles des terrains Estatal de Investigación (CGL2016-76431-P, AEI/FEDER, EU) to tertiaires de la Vénétie. Memorie degli Istituti di Geologia e MD. GLG acknowledges support from a postdoctoral grant from Mineralogia dell'Università di Padova, 18: 1-115. the University of Torino and Forschungskredit of the University of Bosco C. (1902) - Il Lophiodon sardus (n. sp.) delle Lignite di Zurich, grant no. [FK-20-110]. DZ was supported by grants P.O.R. Terras de Collu (Sardegna). Rendiconti dell'Accademia dei Sardegna F.S.E. 2014-2020 - Asse III “Istruzione e Formazione, Obi- ettivo Tematico: 10, Obiettivo Specifico: 10.5, Azione dell’accordo Lincei, 5: 178-182. di Partenariato: 10.5.12 “Avviso di chiamata per il finanziamento di Broin F. de. (1977) - Contribution à l’étude des Chéloniens. Progetti di ricerca - Anno 2017”. APG acknowledges funding by Chéloniens continentaux du Crétacé et du Tertiaire de the Ministerio de Ciencia e Innovación (PID2019-111488RB-I00). France. Mémoires du Muséum national d'histoire naturelle, 38: GLP research is supported by Fondi di Ateneo Cagliari University. 1-366. GLP and DZ work was also supported by grants from Fondazione Broin F. de. (1988) - Les tortues et le Gondwana. Examen des di Sardegna (grant number: F71/17000190002). 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