Echinoidea Astriclypeidae) in the Oligo-Miocene of Sardinia (Italy)
Total Page:16
File Type:pdf, Size:1020Kb
Biodiversity Journal, 2014, 5 (1): 245–268 MONOGRAPH The echinoid genus Amphiope L. Agassiz, 1840 (Echinoidea Astriclypeidae) in the Oligo-Miocene of Sardinia (Italy) Paolo Stara1* & Enrico Borghi2 1Centro Studi di Storia Naturale del Mediterraneo - Museo di Storia Naturale Aquilegia, Via Italia 63, Pirri-Cagliari and Geomuseo Monte Arci, Masullas, Oristano, Sardinia, Italy; e-mail: [email protected] 2Società Reggiana di Scienze Naturali, Via Tosti 1, 42100 Reggio Emilia, Italy; e-mail: [email protected] *Corresponding author ABSTRACT The records of the genus Amphiope Agassiz, 1840 (Astriclypeidae) from Sardinia are revised on the basis of 110 specimens, collected from 15 localities of Oligo-Miocene age. Since the morphological characters stated in the literature to distinguish the species of Amphiope de- scribed in this region cannot provide a clear separation between them, analyses of the plate patterns and of the internal test structure are introduced as taxonomic tools useful for species-level taxonomy in this genus. Five different species of Amphiope are identified. Three of the six species erected on the basis of fossil material from Sardinia are confirmed as valid: Amphiope lovisatoi Cotteau, 1895, A. montezemoloi Lovisato, 1911 and A. nuragica (Comaschi Caria, 1955). Two additional species are left in open nomenclature. The morpho- logical descriptions and the stratigraphical distributions are updated and improved. KEY WORDS Echinoidea; Amphiope; Oligo-Miocene; Sardinia; Mediterranean. Received 25.06.2013; accepted 30.05.2014; printed 30.06.2014 Paolo Stara (ed.). Studies on some astriclypeids (Echinoidea Clypeasteroida), pp. 225–358 INTRODUCTION subsequently placed into synonymy with A. biocu- lata (des Moulins, 1837), the type-species of the The genus Amphiope L. Agassiz, 1840 (Echinoi- genus, by Comaschi Caria (1955), Philippe (1998) dea Astriclypeidae) is known from the Oligocene and Kroh (2005); the last author considered also A. and Miocene of Central and Southern Europe, North- lovisatoi as synonymous with A. bioculata. Since ern Africa, Angola, Middle East, India (Smith & the type-specimens belonging to Lovisato’s collec- Kroh, 2011). tion, at that time housed at the “Regio Museo Mine- It is well represented also in the Oligo-Miocene ralogico e Geologico di Cagliari”, were lost in 1943 of Sardinia (Fig. 1) since ten species of Amphiope (Comaschi Caria, 1955), this work is based mainly were recorded in the literature (Table 1), six of on new material collected from the respective type- which were erected as new taxa on the basis of localities and on the holotype of A. nuragica, still Oligo-Miocene fossils from this region: A. lovisatoi available to study at the “Dipartimento di Scienze Cotteau, 1895, A. dessii Lovisato in Cotteau, 1895, Chimiche e Geologiche, Università di Cagliari”. A. montezemoloi Lovisato, 1911, A. pallavicinoi Lo- The genus Amphiope accounts for more than 40 visato, 1914, A. calvii Lovisato, 1914 and A. nurag- species, most of which are nominal species in need ica (Comaschi Caria, 1955). A. montezemoloi was of revision, due to high intraspecific variation and 246 PAOLO STARA & ENRICO BORGHI particular difficulty was found in the use of the ex- ternal characters alone, because comparison with taxa whose structural characters are unknown re- mained uncertain. This paper presents the results of further studies based on a large and well preserved fossil sample, to bring light into the problem of classification of Amphiope. The main purpose is a modern revision of Sardinian occurrences of Am- phiope, using morphological and morphometric analyses, with emphasis on the plate patterns and the internal test support system. Geological setting The geology and palaeoecology of the Sardinian Amphiope-bearing localities cited in this study were described by Stara et al. (2012) and Mancosu & Nebelsick (2013). In the following a brief summary Figure 1. Regions of Italy in which Amphiope has been is given of the type localities of the three species recorded in the literature (dark grey). Enlarged area (Sardinia): revised from this region. finding localities examined in this study (black circlets), or recorded in the literature (grey squares). Province of Sassari: Central Sardinia (Marmilla). Three main ma- 1 = Porto Torres; 2 = La Crucca; 3 = Bancali; 4 = San Giorgio; rine sedimentary cycles have been recognized in 5 = Sedini; 6 = Monte Oria Pizzinnu; 7 = Billiu and Monte Sa Loca, near Chiaramonti; 8 = San Matteo, near Ploaghe; 9 the Sardinian Basin, from late Oligocene to early = Ardara; 10 = Bessude; 11 = Bonnanaro; 12 = Monte Zarau, Messinian (Assorgia et al., 1997; Funedda et al., near Torralba; 13 = Bonorva. Province of Oristano: 14 = 2000; Carmignani et al., 2001). The Amphiope- Nuraghe Caiu, near Villa Sant’Antonio; 15 = Laconi; 16 = bearing deposits in Central Sardinia belong to the Bruncu Muntravigu and Tanca Sierra, near Senis; 17 = Duid- first cycle, extending from the late Oligocene to duru and Genoni (Nuoro); 18 = Monte Is Casteddus, near Isili; 21 = Santadi and Sa Lisporra, at Capo Frasca. Province of Ca- the late Burdigalian. The Cenozoic sequence gliari: 19 = Cuccuru Tuvullao; 20 = Strintu ‘e Melonis and starts with the late Oligocene-early Aquitanian Nurri; 23 = Monte S. Michele; 24 = Capo S. Elia and Bonaria. Ussana Formation (Pecorini & Cherchi, 1969), Medio Campidano province: 22 = Monte Arcuentu. consisting mainly of sediments of continental ori- gin. The Ussana Formation is partly heteropic with and is followed by the Nurallao formation, poor species definition (Smith & Kroh, 2011). The late Chattian-early Burdigalian (Serrano et al., complex taxonomy of this genus has been tradition- 1997), which consists of the “Conglomerato di ally based on the external morphological features, Duidduru” member, made of coarse clastics from mainly test outline, size and shape of lunules and transitional (deltaic) environments (Sowerbutts & petals. Structural characters, largely used in the ta- Underhill, 1998) and the littoral marine deposits xonomy of other clypeastroids ( Durham, 1955; of the Arenarie di Serralonga member, late Oligocene- Lohavanijaya, 1965; Mooi, 1989; Kroh, 2005; Jansen early Aquitanian (Assorgia et al., 1997; Barca et & Mooi, 2011), were almost overlooked in earlier al., 2005), which yielded the Amphiope specimens studies dealing with Amphiope and, although sev- examined from this area. The Nurallao Formation eral species of Amphiope have been described in the is partially heteropic with and followed by the literature, important features for species-level tax- Calcari di Villagreca, dated to the late Oligocene- onomy, such as oral plating, were poorly illustrated early Burdigalian, and by the Marmilla Forma- or omitted completely. tion, dated to the Aquitanian (Cherchi et al., During a preliminary investigation we attempted 2008). The material studied from this area was to find out whether the specimens from Sardinia collected from eight localities: Villa Sant’Anto- might be attributed to already known species, but a nio, Bruncu Muntravigu, Tanca Sierra, Duidduru, The echinoid genus Amphiope L. Agassiz, 1840 (Echinoidea Astriclypeidae) in the Oligo-Miocene of Sardinia (Italy) 247 Table 1. Records of Amphiope from Sardinia reported in the literature. An asterisk marks the species firstly described on the basis of material collected from this region. Genoni, Isili, Cuccuru Tuvullao and Capo Frasca side down, their long axes being more or less paral- (see Fig. 1). lel to the stratal surfaces. This sand dollar deposit - Cuccuru Tuvullao (n. 19 in Fig. 1). The type- is assigned to a shoreface environment and repre- locality of A. nuragica (Comaschi Caria, 1955) is sents a multiple in situ reworking accumulation located 1.5 km NE of Nuragus (Cagliari). Amphiope (Mancosu & Nebelsick, 2013). occur in high numbers in a medium to coarse- Fragments and rare complete specimens of Am- grained volcanoclastic sandstone (herein named C. phiope occur also at the base of the overlying richly Tuvullao I), 2-2.5 m thick, corresponding to the fossiliferous fine mudstone (herein named C. “Facies B” of Mancosu & Nebelsick, 2013; Fig. 2). Tuvullao II), corresponding to the “Facies C” of Amphiope is the most abundant taxon, followed by Mancosu & Nebelsick (2013); Fig. 2). The fossil Parascutella sp., reworked balanids and bivalves. content is dominated by gastropods, belonging to Seven species of Amphiope were cited by Comaschi the genus Turritella Lamarck, 1799, and by the bi- Caria (1955) in this layer, including A. nuragica. valve Panopea Ménard, 1807. The echinoids are denuded, commonly fragmented in the shape of pie-slices. Loosely packed or dis- Northern Sardinia. Seven Amphiope-bearing lo- persed specimens are both in life position and up- calities were sampled in the Sassari province: Porto 248 PAOLO STARA & ENRICO BORGHI Torres, La Crucca, Bancali, San Giorgio, Chiara- the outcrop. The dense accumulation of well-preser- monti, Ardara and Bonnanaro. These deposits be- ved echinoids of Facies C is considered to represent long to the second Cenozoic sedimentary cycle, late an autochthonous assemblage in a shoreface envi- Burdigalian-early Langhian (Mancosu & Nebel- ronment (Mancosu & Nebelsick, 2013). Amphiope sick, 2013). At the base, the lacustrine and fluvio- prevails by far, followed in abundance by Agassizia deltaic sediments of the Oppia Nuova formation Yoshiyasu, 1987, Parascutella Durham, 1953, Echi- (Funedda et al., 2000) are overlain by the Calcari nolampas Gray, 1825 and small