◄ Carnets Geol. 21 (3) ►
Outline:
[1. Introduction]
[2. Taxonomic history]
[3. Methods]
[4. Systematics]
[5. Provenance of P. oligoplana in Rovereto's collection]
[6. Conclusions] and ... [Bibliographic references]
DISTAV - Università degli Studi di Genova, Corso Europa, 26 - I - 16132 Genova (Italy)
DISTAV - Università degli Studi di Genova, Corso Europa, 26 - I - 16132 Genova (Italy)
DISTAV - Università degli Studi di Genova, Corso Europa, 26 - I - 16132 Genova (Italy)
via Prolungo, 6 - I - 17020 Magliolo (SV) (Italy)
DISTAV - Università degli Studi di Genova, Corso Europa, 26 - I - 16132 Genova (Italy)
Published online in final form (pdf) on February 24, 2021
DOI 10.2110/carnets.2021.2103
[Editor: Bruno R.C. Granier; language editor:
Stephen Carey]
The aim of this paper is the revision and redocumentation of Ostrea (Gigantostrea) gigantica Solander var. oligoplana Sacco, 1897, Ostrea (Ostrea) isseli n. denom. Rovereto, 1897, and Ostrea (Ostrea) isseli n. denom. var. elongata Rovereto, 1897. These taxa are from the Oligocene strata of the Molare Formation (Tertiary Piedmont Basin, southern Piedmont - central Liguria, NW Italy). The syntypes of O. (G.) gigantica var. oligoplana are in the "Collezione Bellardi e Sacco", at the Museo Regionale di Scienze Naturali di Torino; the syntypes of O. (O.) isseli and O. (O.) isseli var. elongata are in the "Collezione BTP" (BTP Collection, at the Dipartimento di Scienze della Terra, dell'Ambiente e della Vita - DISTAV - of the Università di Genova). The var. oligoplana is here moved to the species rank and allocated to the genus Pycnodonte Fischer von Waldheim, 1835. O. (O.) isseli and O. (O.) isseli var. elongata are recognized as junior synonyms of the Sacco's taxon. Rovereto (1897) compared his new species with Ostrea subgigantea Raulin & Delbos, 1855, a poorly known taxon, that is here figured for the first time and shown to represent a species different from P. oligoplana (Sacco, 1897).
• Rovereto;
• Sacco;
•
bivalve type-material;
• Oligocene;
• NW Italy
Bonci M.C., Dagnino D., Mandarino A., Mazzini A. & Piazza M. (2021).- Revision of Ostrea (Gigantostrea) gigantica Solander var. oligoplana Sacco and Ostrea (Ostrea) isseli Rovereto (Oligocene, Tertiary Piedmont Basin, NW Italy).- Carnets Geol., Madrid, vol. 21, no. 3, p. 55-66.
Révision d'Ostrea (Gigantostrea) gigantica Solander var. oligoplana Sacco et d'Ostrea (Ostrea) isseli Rovereto (Oligocène, Bassin tertiaire du Piémont, NO Italie).- L'objectif du présent travail est la révision et la nouvelle illustration d' Ostrea(Gigantostrea) gigantica Solander var. oligoplana Sacco, 1897, d'Ostrea (Ostrea) isseli n. denom. Rovereto, 1897, et d'Ostrea (Ostrea) isseli n. denom. var. elongata Rovereto, 1897. Ces taxons proviennent des couches oligocènes de la Formation de Molare (bassin tertiaire du Piémont, Piémont méridional - Ligurie centrale, Italie du nord-ouest). Les syntypes d'O. (G.) gigantica var. oligoplana figurent dans la collection Bellardi et Sacco du Musée Régional de Sciences Naturelles de Turin ; les syntypes d'O. (O.) isseli et d'O. (O.) isseli var. elongata font partie de la collection BTP (Département de Sciences de la Terre, de l'Environnement et de la Vie - DISTAV - Université de Gènes). La variété oligoplana est ici élevée au rang d'espèce et attribuée au genre Pycnodonte Fischer von Waldheim, 1835. O. (O.) isseli et O. (O.) isseli var. elongata sont ici considérées des synonymes juniors du taxon de Sacco. Rovereto a comparé sa nouvelle espèce à Ostrea subgigantea Raulin & Delbos, 1855, un taxon peu connu qui est figuré ici pour la première fois et considéré comme représentant une espèce distincte de P. oligoplana (Sacco, 1897).
• Rovereto ;
• Sacco ;
•
matériel-type
de bivalves ;
• Oligocène ;
• Italie du nord-ouest
This
paper focuses on the revision and re-documentation of Ostrea
(Gigantostrea)
gigantica Solander var. oligoplana
Sacco, 1897, Ostrea
(Ostrea) isseli n. denom. Rovereto, 1897 and Ostrea (Ostrea) isseli n.
denom. var. elongata
Rovereto, 1897. It is part of a project of
revision of new Oligocene mollusc taxa erected by Gaetano Rovereto
(geologist
and paleontologist of the Genoa University) in the years 1897-1914. The Sacco's
type material is from the Sassello and Carcare (Savona Province, NW Italy, Fig. 1 
) and it is preserved in the "Collezione Bellardi e Sacco"
housed at the Museo Regionale di Scienze Naturali di Torino; the Rovereto's
type material is from Mioglia, Sassello (Rio Zunini), Tagliolo (Rio Chiappino), Casaleggio
Boiro, Case Morera, and
Bandita (Savona and Alessandria Province, NW Italy, Fig. 1 ) and it is preserved
in the "BTP Collection" (BTP is an abbreviation of "Bacino Terziario del
Piemonte", i.e., Tertiary Piedmont Basin - TPB, the geological unit from which
the specimens were collected) housed at the Museo
di Paleontologia, Dipartimento di Scienze della Terra, dell'Ambiente e della
Vita (DISTAV), Università di Genova. Information on the history and composition
of the BTP Collection and on the molluscan taxa described by Rovereto
(1897-1914) was provided by Bonci et
al. (2014).
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Figure 1: Geological sketch map of the central part of the TPB showing the location
of collecting sites. 1) Quaternary deposits; 2) lower Miocene deposits; 3)
Molare Formation, Oligocene; 4) Costa di Cravara Breccia, upper Eocene-lower
Oligocene; 5) Ligurian Alps Units. |
The species Ostrea subgigantea Raulin & Delbos, 1855, is also examined, because Rovereto compared his new species with this taxon, which is very poorly known. We reproduce the photographs of the syntype of this taxon which are kindly provided by Laurent Charles, Muséum d'Histoire naturelle de Bordeaux (MHNB).
For information about the geology of the TPB and the localities from which Rovereto's types come, refer to Lorenz (1969), Gelati and Gnaccolini (1988), Capponi and Crispini (2008), Quaranta et al. (2009a), Gelati et al. (2010), Bonci et al. (2011, 2014, 2017, 2018), Capponi et al. (2013), Ghibaudo et al. (2014), Federico et al. (2016), and references therein.
The taxonomic status of Ostrea (Gigantostrea) gigantica var. oligoplana Sacco, 1897, Ostrea (Ostrea) isseli Rovereto, 1897, and O. (O.) isseli var. elongata Rovereto, 1897, is ambiguous for the following reasons:
a) Sacco (June 1897, p. 14) erected Ostrea (Gigantostrea) gigantica var. oligoplana (characterized by a small cardinal area) and included in the synonymy list the Oligocene specimens attributed to Ostrea (Gigantostrea) gigantica Solander in Brander, 1776, by Sismonda (1855) and Pareto (1855), and to Ostrea pyrenaica Orbigny by Bronn (1856);
b) Rovereto (July 1897, p. 311-312, 318) erected Ostrea (Ostrea) isseli n. denom. on the basis of the specimens erroneously identified as Ostrea delbosi Mayer, 1879 by Michelotti (1861) and Ostrea gigantica Solander in Brander, 1776, by Sismonda (in Pareto, 1855), but he neither defined nor figured the type;
c) Rovereto (July 1897, p. 311-312) stated that O. isseli is identical to Ostrea subgigantea Raulin & Delbos, 1855, and he affirmed that this species is not validly published;
d) Rovereto (July 1897, p. 318) attributed to his new species the specimens collected by him and Arturo Issel in the Oligocene rocks of Sassello, Mioglia and Casaleggio Boiro (Savona and Alessandria Province, NW Italy, TPB);
e) Rovereto (July 1897, p. 318) identified two varieties of O. isseli, i.e., var. lamellata and var. elongata;
f) Rovereto (1900) reviewed O. (O.) isseli (re-proposed as n. mut.) including as a synonym Gigantostrea gigantica Solander var. oligoplana Sacco and removing from the synonymic list Ostrea delbosi of Michelotti (1861);
g) Rovereto (1900) confirmed the validity of O. (O.) isseli var. elongata;
h) Rovereto (1900) added Ostrea delbosi of Michelotti (1861) and O. (O.) isseli var. lamellata to Ostrea oligappenninica (Sacco, 1897); it should be noted that O. oligappenninica is considered a junior synonym of Pycnodonte rarilamella (Deshayes, 1864) by Boschele et al. (2016);
i) Sacco (1904) reassessed G. gigantica (Solander) var. oligoplana Sacco suggesting that it may be a new species ("an species distinguenda", p. 136) and including O. isseli Rovereto (1897) in the synonymic list;
j) Sacco (1904) reassessed G. gigantica var. elongata (Rovereto) suggesting that it may be a variety of G. oligoplana ("an G. oligoplana var.", p. 136);
k) Lorenz (1967, p. A28-A30) uncritically gathered O. isseli, O. isseli var. elongata and O. (G.) gigantica var. oligoplana in Ostrea (Gigantostrea) gigantica Solander;
l) Abad García (2002, p. 560) included the var. oligoplana in Pycnodonte gigantica (Solander) but ignored Rovereto's taxa.
Finally, it should be noted that Ostrea subgigantea was validly erected and described, but not figured, by Raulin & Delbos (1855, p. 1154, lower Oligocene, Bordeaux, SW France). Subsequently, this species was recorded, but neither described nor figured by Delbos and Koechlin-Schlumberger (1867, p. 43, Oligocene, Département de l'Haut-Rhin, E France) and Fallot (1894, p. 366, Oligocene, Département de la Gironde, SW France).
The classification scheme here adopted is that proposed by Bouchet et al. (2010). Additional sources were Stenzel (1971), Harry (1985), Fossilworks, and WoRMS Editorial Board (2018) that also provide useful taxonomic and nomenclatural information. Measurement abbreviations are: L= length of valve, H= height of valve, EE= elongation extent (H/L), LLA= length of ligamental area, HLA= height of ligamental area, WR= width of resilifer.
Class Bivalvia Linnaeus, 1758
Subclass Autobranchia Grobben, 1864
Superorder Pteriomorphia Beurlen, 1944
Order Ostreida Férussac, 1822
Superfamily Ostreoidea Rafinesque, 1815
Family Gryphaeidae Vialov, 1936
Subfamily Pycnodonteinae Stenzel, 1959
Genus Pycnodonte Fischer von Waldheim, 1835
Type species: Pycnodonte radiata Fischer von Waldheim, 1835, type by original designation, Upper Cretaceous, Crimea.
Pycnodonte oligoplana (Sacco, 1897)
1897 Ostrea (Gigantostrea) gigantica Solander var. oligoplana Sacco, p. 14-15, Pl. IV, figs. 6-7b.
1897 Ostrea (Ostrea) isseli n. denom. Rovereto, p. 318.
1897 Ostrea (Ostrea) isseli n. denom. var. elongata Rovereto, p. 318.
1900 Ostrea (Ostrea) isseli n. mut. Rovereto, p. 46.
1900 Ostrea (Ostrea) isseli n. mut. var. elongata Rovereto, p. 46, Pl. I, fig. 2.
1904 Gigantostrea gigantica (Sol.) var. oligoplana Sacc. (an species distinguenda), Sacco, p. 136.
1904 G. gigantica var. elongata (Rovr.) (an G. oligoplana var.), Sacco, p. 136, Pl. XXVII, fig. 9.
1921 Ostrea gigantica Sol. var. oligoplana Sacco, Stefanini, p. 128.
1967 Ostrea (Gigantostrea) gigantica Solander, Lorenz, p. A28-A30, Pl. XXVII, fig. 3. [non Solander in Brander, 1776]
1969 Ostrea gigantica Solander, Lorenz, Pl. II, fig. 2. [non Solander in Brander, 1776]
2007 Gigantostrea gigantica (Solander in Brander) var. oligoplana Sacco, Aimassi, p. 24, Pl. 1, fig. 2.
Diagnosis: Large shell; thin, concave lower valve; thin, flat upper valve; long, straight dorsal margin; small and pointed umbo; small ligamental area and shallow resilifer; short branching vermiculate chomata; growth squamae nonappressed; alternation of foliated and vesicular layers. The subcircular to vertical-oval outline (EE range= 1.05 – 1.51) and the small to relatively large attachment area represent the only intraspecific variation.
Detailed descriptions and measurements of the type material are provided separately in the text below.
Remarks: Pycnodonte gigantica (Solander in Brander, 1776) is the type species of Gigantostrea Sacco, 1897, which is in turn attributed to Pycnodonte in a revision by Stenzel (1970) based on the similar growth patterns of the respective type species. Pycnodonte oligoplana, attributed originally to Gigantostrea, differs from P. gigantica in having a thin shell, small cardinal area, and shallow ligamental groove.
Rovereto (1900) has previously stated that the typical forms of P. gigantica have a thick shell, large cardinal area, and very deep ligamental groove, and are restricted to the Eocene. In contrast, he considered all Oligocene specimens previously referred to P. gigantica to be a different species, i.e., Ostrea (Ostrea) isseli Rovereto, 1897. In our opinion the characters used by Rovereto (1897, 1900) for the erection of this species (i.e., thin shell, small cardinal area, and shallow ligamental groove) are sufficient to separate it from Solander's species. In contrast, Ostrea (Ostrea) isseli var. elongata Rovereto, 1897, differs from O. (O.) isseli only in having a more elongated outline (Rovereto, 1897, 1900), a character that is within the morphological variability of the species.
The type material of O. (O.) isseli and O. (O.) isseli var. elongata exhibits the general morphology, muscle scar, chomata, and shell microstructure that clearly suggest allocation to the genus Pycnodonte Fischer von Waldheim, 1835. Furthermore, comparison with the type material of P. oligoplana confirms their attribution to the same species, as already suggested by Rovereto (1900) and by Sacco (1904). While P. isseli and P. elongata were both published in July 1897, P. oligoplana was published in June 1897 and is the valid name of the species, based on the principle of priority.
Rovereto (1897, p. 311-312) suggested that O. isseli
is identical to Ostrea subgigantea Raulin
& Delbos,
1855, but the similarity is restricted to general
morphological characters. The former species can be easily distinguished because
of a smaller ligamental area, as enlightened by data reported in Figure
6
of the present study.
Finally, the general morphology of the lower valve allows the separation of P. oligoplana from the thick, gryphaeiform P. brongniarti (Bronn, 1831) (Europe, southern Asia, northern and eastern Africa; Eocene – early Miocene), the strongly uniformly convex P. clypeata (Rovereto, 1897) (northern Italy; Oligocene), the crescentic P. callifera (Lamarck, 1819) (northern and central Europe; Eocene - Oligocene), and the winged, antero-posteriorly elongated P. rarilamella (Deshayes, 1864) (Europe and southern Asia; Eocene - Oligocene).
Distribution: Oligocene: Sassello, Carcare, Casaleggio Boiro, Mioglia, Case Morera (Ponzone), Bandita - Molare Formation, TPB, NW Italy; Sidi el Homri and Sidi Jaja (Cyrenaica, NE Libya); Algeria.
Pycnodonte oligoplana (Sacco, 1897) type series
Type material: Lectotype (here designated, Fig. 2.A-H ): one double-valved, relatively
well-preserved shell (outer surface of valves eroded and encrusted, lower valve
ventral margin damaged) with internal mould from Sassello;
catalog
number BS.107.03.003, illustrated by Sacco (1897, Pl.
IV, figs. 7a-b) and Aimassi (2007, Pl. 1, fig. 2).
Paralectotype (Fig. 3.A-J ): one double-valved, damaged shell (outer surface
of valves eroded and encrusted, upper valve dorsal and posterior margins, lower
valve margins are damaged) from Carcare;
catalog number BS.107.03.002, illustrated by Sacco (1897,
Pl.
IV, fig. 6).
Type locality: Sassello, Molare Formation (Oligocene), TPB.
Measurements: Lectotype - lower valve: H= 180.00 mm, L 172.00 mm, EE= 1.05, LLA= 56.40 mm, HLA= 15.14 mm, WR= 14.86 mm; upper valve: H= 190.00 mm, L= 173.00 mm, LLA= 57.04 mm, HLA= 19.98, WR= 14.54 mm. Paralectotype - lower valve: H= 192.00 mm, L= 172.00 mm, EE= 1.12, LLA= 55.34 mm, HLA= 27.69 mm, WR= 16.67 mm; upper valve: H= 182.00 mm, L= 158.00 mm, LLA= 47.07 mm, HLA= 20.07, WR= 16.85 mm.
Description: Lectotype: lower valve (umbo lacking, sculpture not observable): thin, concave, subcircular in outline; long, straight dorsal margin; relatively small attachment area; small ligamental area; shallow resilifer; short, branching, vermiculate chomata; shell structure with an alternation of foliated and vesicular layers. Upper valve: thin, flat, subcircular in outline; nonappressed growth squamae.
Paralectotype: lower valve (margins damaged, sculpture not observable): thin, slightly concave, subcircular in outline; small and pointed umbo; relatively large attachment area; small ligamental area; shallow resilifer; short, branching, vermiculate chomata. Upper valve (sculpture not observable): thin, flat, subcircular in outline.
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Figure 2: Pycnodonte oligoplana (Sacco,
1897), lectotype
BS.107.03.003. Scale bar = 1 cm. A-C:
lower valve. D-F: upper valve. G-H: original labels. |
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Figure 3: Pycnodonte oligoplana (Sacco,
1897), paralectotype BS.107.03.002. Scale
bar = 1 cm. A-C: lower valve. D, G, I-J: original labels. E-F, H:
upper valve. |
Pycnodonte isseli (Rovereto, 1897) type series
Type material: Lectotype: (here designated, Fig.
4.A-D ): articulated, damaged shell
(upper
valve dorsal margin, lower valve anterior and part of ventral margins lacking); catalog
number 2848/M-III-M 87; this specimen is part of the
Collezione Perrando, that was available to Rovereto in 1897, and was
probably taken into consideration
by Rovereto for the identification of the species.
Type locality: Mioglia, Molare Formation (Oligocene), TPB.
Measurements:
Lectotype (Fig. 4.A-D ; 2848/M-III-M 87): lower valve size: H= 160.00 mm, L not less
than 140.00 mm, EE= 1.14, LLA= 26.47 mm, HLA= 21.14 mm, WR= 15.69 mm; upper
valve size: H not less than 140.00 mm, L not less than 130.00 mm.
Description: Lower valve: thin, concave, subcircular in outline; long, straight dorsal margin; small and pointed umbo; small attachment area; small ligamental area; shallow resilifer; short, branching, vermiculate chomata; growth squamae nonappressed; concentric, irregular, gentle puckers; shell structure with an alternation of foliated and vesicular layers. Upper valve: thin, flat, subcircular in outline; nonappressed growth squamae.
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Figure 4:
Pycnodonte oligoplana
(Sacco, 1897). Scale bar
= 1 cm. A-D: lectotype of P. isseli (Rovereto, 1897),
2848/M-III-M 87.
A-B: lower valve. C-D: upper valve. E, H:
lectotype of P.
elongata
(Rovereto, 1897), 1904/M-III-M 18, lower valve. F-G:
paralectotype
of P. elongata
(Rovereto, 1897), 2061/Sa-II-S 157, upper valve. |
Pycnodonte elongata (Rovereto, 1897) type series
Type material: Lectotype (here designated, Fig.
4.E, .H ):
one lower valve from Mioglia, catalog number 1904/M-III-M 18), figured by Rovereto (1900,
Pl. I, fig. 2) as Ostrea isseli var. elongata;
Sacco (1904) reported the same images of Rovereto (1900).
Paralectotypes: a) one lower valve from Mioglia, catalog
number 2846/M-III-M 85 (Fig. 5.C-D ); b) one lower valve from Tagliolo, catalog
number 3163/OV-III-C 2 (Fig. 5.A-B ); c) one damaged upper valve (posterior
and part of the ventral margins lacking, umbo broken) from Sassello, catalog
number 2061/Sa-II-S 157 (Fig. 4.F-G ).
Type locality: Mioglia, Molare Formation (Oligocene), TPB.
Measurements:
Lectotype (Fig.
4.E, .H ; 1904/M-III-M 18): H= 175.00 mm, L= 115.64 mm, EE= 1.51, LLA= 29.73
mm, HLA= 13.96 mm, WR= 11.29 mm. Paralectotypes: lower
valve (Fig. 5.C-D ; 2846/M-III-M 85): H= 163.00 mm, L= 134.58 mm, EE= 1.21, LLA= 20.97
mm (partially preserved), HLA= 16.57 mm, WR= 11.55 mm; lower
valve (Fig. 5.A-B ;
3163/OV-III-C 2): H= 154.00 mm, L= 140.00 mm, EE= 1.10, LLA= 27.12
mm, HLA= 14.20 mm, WR= 12.02 mm; lower valve (Fig. 4.F-G ; 2061/Sa-II-S 157): H= 120.00 mm, L= 100.00 mm, EE= 1.20, LLA= 21.86 mm (partially preserved),
HLA= 5.39 mm, WR= 11.11 mm.
Description: Lower valve: thin, concave, subcircular to vertical-oval in outline; long, straight dorsal margin; small and pointed umbo; small attachment area; small ligamental area; shallow resilifer; short, branching, vermiculate chomata; growth squamae nonappressed; concentric, irregular, gentle puckers; broad, moderately deep radial posterior sulcus (more or less evident); layered shell structure with alternating foliated and vesicular layers. Upper valve: thin, flat, subcircular in outline; nonappressed growth squamae.
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Figure 5: Pycnodonte oligoplana (Sacco, 1897). Scale bar = 1 cm. A-B: paralectotype of P. isseli (Rovereto, 1897), 3163/OV-III-C 2, lower valve. C-D: paralectotype of P. isseli (Rovereto, 1897), 2846/M-III-M 85, lower valve. |
According to Rovereto's papers (1897, 1898, 1900, 1914) and labels, the specimens are from Mioglia (Mioglia cemetery), Sassello (Rio Zunini), Tagliolo (Rio Chiappino), Casaleggio Boiro, Case Morera, and Bandita (Savona and Alessandria Province, NW Italy, TPB). Stratigraphic information on the most probable collecting sites, obtained from surveys performed by the present authors, is recorded below.
Mioglia - The fossiliferous locality at the cemetery at Mioglia (Lat. 44.490605, Long. 8.416042, 364 m a.s.l.) was recently described in brief by Bonci et al. (2017) as a 17 m-thick stratigraphic section composed of thinly bedded, burrowed, very fine sandstones and claystones followed by irregularly bedded, matrix-supported, very poorly to poorly sorted conglomerates alternating with grain-supported, very coarse to fine sandstones overlain by burrowed, richly fossiliferous, poorly sorted sandstones. Mollusc shells and moulds, solitary corals, worm tubes and foraminifers (including Amphistegina sp., Neorotalia sp., Nummulites fichteli Michelotti, 1841 and Operculina complanata [Defrance, 1822]) largely occur at the top of the section. According to Bonci et al. (2017), the section is early-middle Rupelian in age and part of the Molare Formation (Oligocene, TPB).
Sassello - Rio Zunini (Lat. 44.498518, Long. 8.497626, 370 m a.s.l.), also known as Ponte Prina, is an historic fossiliferous site, previously described by Lorenz (1969), Fravega et al. (1987), Quaranta et al. (2009a, 2009b), and Bonci et al. (2018). The stratigraphic section (total thickness of about 13 m) unconformably overlies the serpentinites of the Voltri Unit and is composed of coarse conglomerates with intercalated sandy lenses and coral buildups, followed by coarse sandstones and fine conglomerates with scattered coral colonies, grading up to alternating thin- to medium-bedded calcarenites/hybrid arenites and coral/coralline algal limestones. Corals, molluscan shells and moulds, bryozoans, larger foraminifers (including Nummulites fichteli and Eulepidina), and coralline algae are unevenly distributed throughout the section. According to the authors referred to above, this section is late Rupelian - early Chattian in age and is part of the Molare Formation (Oligocene, TPB).
Tagliolo, Casaleggio Boiro, Case Morera, Bandita - These sites are no longer accessible because they are completely covered by vegetation or built over. Outcrops exposed nearby exhibit lithological features exactly matching those of the Molare Formation (Oligocene, TPB).
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Figure 6: Ostrea subgigantea Raulin & Delbos, 1855. Syntype, Muséum d'Histoire naturelle de Bordeaux, MHNBx 2007.9451. A: original labels. B: internal view with measures. C: external view. D: internal view. For the dimensions refer to B. Photographs and measures kindly provided by Laurent Charles (MHNB). |
The revision of Ostrea (Gigantostrea) gigantica Solander var. oligoplana Sacco, 1897, Ostrea (Ostrea) isseli n. denom. Rovereto, 1897, and Ostrea (Ostrea) isseli n. denom. var. elongata Rovereto, 1897, derived from Oligocene rocks of the Molare Formation (TPB, southern Piedmont - central Liguria, NW Italy) leads to the conclusion that Sacco's species belongs to the genus Pycnodonte (i.e., Pycnodonte oligoplana) and that Rovereto's taxa are junior synonyms of Sacco's species. Pycnodonte oligoplana is restricted to the Oligocene and exhibits a relatively large geographic distribution, occurring in NW Italy, Cyrenaica and Algeria.
Antique references were consulted via https://archive.org, http://jubilotheque.upmc.fr, and http://gallica.bnf.fr. This paper has greatly profited from critical reading by O. Mandic (Wien) and P. Lozouet (Paris). Many thanks are due to L. Charles (Muséum d'Histoire naturelle de Bordeaux) for the photographs and measurements of O. subgigantea and to D. Ormezzano (Museo Regionale di Scienze Naturali di Torino) for help provided during the revision of P. oligoplana. This study has been supported by research funds MIUR - FFABR (100022-2018-MP-FFABR_002 - Piazza).
Abad García A. (2002).- Paleotaxodonta y pteriomorphia del eoceno del margen sur de la depresión central catalana.- Tesi doctoral, Universitat Autònoma de Barcelona, Departament de Geologia, http://ddd.uab.cat/record/37045, http://hdl.handle.net/10803/3432.
Aimassi G. (2007).- Bivalvia Famiglia Ostreidae - 107. In: Merlino B. (ed.), Catalogo dei tipi e degli esemplari figurati della collezione Bellardi e Sacco Parte III.– Museo Regionale di Scienze Naturali di Torino, p. 21-29.
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