Plagiodontes Doering, 1876

Salvador, Rodrigo Brincalepe & Simone, Luiz Ricardo Lopes De, 2013, Taxonomic Revision Of The Fossil Pulmonate Mollusks Of Itaboraí Basin (Paleocene), Brazil, Papéis Avulsos de Zoologia 53 (2), pp. 5-46 : 5-46

Genus Plagiodontes Doering, 1876 Plagiodontes aff. dentatus (Wood, 1828)

( Figs. 62-65 )

Plagiodontes aff. dentatus : Salvador & Simone, 2012: 4 (figs. 9-10).

Locality: Limestones of Parque Paleontológico de São José de Itaboraí, Rio de Janeiro, Brazil. Park’s center coordinates: 22°50’20”S, 42°52’30”W .

Geographic and stratigraphic occurrence: With this record, the species is also known from the limestones of Itaboraí Basin. The precise stratigraphic occurrence can’t be assessed; probably Sequence S1, the same sequence of occurrence of the other orthalicids ( Medeiros & Bergqvist, 1999; Bergqvist et al. 2006).

Age : Tertiary, Middle Paleocene.

Diagnostic features: Shell multispiral, about 1.4 times longer than wide. Spire angle ~45°. Fine ribs (about 77 on penultimate whorl), oblique to suture. Suture well-marked, oblique (diagonal) to columellar axis. First three to four whorls unsculptured (but may be an artifact of preservation). First whorls less convex; middle to last whorls more convex. Greatest width on (apparently) penultimate whorl.

Measures (in mm): 7 whorls, H = 9.6, D = 7.1 (greatest diameter on penultimate whorl). The specimen is partially broken (lacking the aperture and protoconch), so the shell’s real measures would be greater.

Examined material: MCT 6944-I.

Discussion: Plagiodontes is a Recent genus, occurring in tropical and subtropical regions of Brazil and southern South America, sometimes considered a subgenus of Cyclodontina ( Pizá & Cazzaniga, 2003, 2009; Simone, 2006). Plagiodontes dentatus (Wood, 1828) is a Recent species found in the vicinities of La Plata River, Entre Ríos province, Argentina, and in Montevideo, Uruguay ( Pizá & Cazzaniga, 2003, 2009; Morton & Herbst, 2007). However, there is a possible fossil record of this species: Cyclodontina cf. ( Plagiodontes ) dentata (Wood, 1828) from the Miocene of Uruguay and the Miocene and Pleistocene of Argentina ( Caorsi & Goñi, 1958; Parodiz, 1969; Morton & Herbst, 2007).

The only specimen of Itaboraí was found among other orthalicids in the collection of the MCT and the presence of ribs on it has readily set it apart from the others. However, its preservation is far from good: the aperture and part of the protoconch are broken ( Plagiodontes show striae on the protoconch; Pizá & Cazzaniga, 2003). Knowing only the middle portion of the shell, this specimen could fit in many Recent genera of Odontostominae ; the rib pattern, however, narrows the possibilities to Plagiodontes , Cyclodontina and Clessinia Doering, 1875 . The most marked difference between these genera is the apertural dentition: Plagiodontes and Cyclodontina have many teeth while Clessinia has none. Despite not knowing the aperture of the specimen, the placement in the genus Plagiodontes was preferred due to the shape of the whorls (middle to last whorls more convex and not much larger than the less convex preceding ones) and also for its known South American fossil record. Moreover, due to lack of information regarding the aperture, it was preferred to place the specimen provisionally under open classification, showing affinity to the recent species Plagiodontes dentatus . The fossils from this species also have a tentative classification, since not even a single well-preserved specimen was found. Both geographical and temporal distances could indicate that the Itaborahian Plagiodontes belongs to a new species. However, rather than describing it as a new species, the present classification as Plagiodontes aff. dentatus was considered safer (as in Salvador & Simone, 2012), at least until more (and better preserved) material has been found.

Family Strophocheilidae

Subfamily Megalobuliminae

Genus Eoborus Klappenbach & Olazarri, 1970 Eoborus rotundus Salvador & Simone, 2012

( Figs. 66-74 )

Eoborus rotundus Salvador & Simone, 2012: 4 (figs. 11-15).

Holotype: MCT 6941-I (examined; Figs. 70-74 ).

Paratypes: MCT 6942 -I (1 specimen, examined; Figs. 66-67 ) , MCT 6943 -I (1 specimen, examined; Figs. 68-69 ) .

Type Locality: Limestones of Parque Paleontológico de São José de Itaboraí, Rio de Janeiro, Brazil. Park’s center coordinates: 22°50’20”S, 42°52’30”W .

Geographic and stratigraphic occurrence: Known only from the type locality. The precise stratigraphic occurrence can’t be assessed; probably Sequences S1 and S2, the same sequences of occurrence of Eoborus sanctijosephi ( Medeiros & Bergqvist, 1999; Bergqvist et al. 2006).

Age : Tertiary, Middle Paleocene.

Etymology: The name refers to the rounded shell shape of the species.

Diagnosis: Size relatively small (~ 25 mm), shape ovoid, almost as large as high. Aperture rounded (instead of elliptical), with upper palatal region of outer lip meeting obliquely with preceding whorl. Peristome ample and highly reflexed. Large umbilicus.

Description: See Salvador & Simone (2012).

Measures (in mm): Holotype: 5 whorls, H = 23.7, D = 16.8, S = 10.5, h = 12.4, d = 9.9. Paratypes: MCT 6942 -I: 5 whorls, H = 25.5, D = 16.6, S = 10.5, h = 12.5 . MCT 6943 -I: 5 whorls, H = 25.5, D = 16.6; S = 10.4 .

Examined material: Types. Discussion: The genus Eoborus was created to house two species of Paleocene Strophocheilidae : E. sanctijosephi ( Maury, 1935) from Itaboraí and E. charruanus (Frenguelli, 1930) from Uruguay. Both species were previously classified in the genus Strophocheilus Spix, 1827 . Klappenbach & Olazarri (1970) decided to describe this new genus mainly due to a very striking feature of these two species: their wide umbilicus. Besides the type species, E. charruanus , and the now three Itaborahian species, there is only one more species described: E. berroi Klappenbach & Olazarri, 1986 . There are still two other species that could also belong to Eoborus : Strophocheilus chubutensis Ihering, 1904 and S. hauthali (Ihering, 1904) , but the preservation state of their fossils do not allow a precise diagnosis ( Klappenbach & Olazarri, 1970; Martínez et al., 1997). All the species are from the Tertiary of Brazil (the three species from Itaboraí), Uruguay ( E. charruanus and E. berroi ) and Argentina ( E. charruanus ) ( Maury, 1935; Parodiz, 1969; Klappenbach & Olazarri, 1970, 1986; Martínez et al., 1997; Simone & Mezzalira, 1994; Bergqvist et al., 2006; Salvador & Simone, 2012).

E. rotundus shows many of the genus’ characteristic features, such as the smooth protoconch, the teleoconch sculptured by well-marked growth lines and, obviously, the ample umbilicus ( Klappenbach & Olazarri, 1970). It differs from E. sanctijosephi and E. charruanus in being smaller, having fewer whorls (the others have six), an ovoid shell, a more rounded aperture, a larger umbilicus, and a larger and slightly more reflexed peristome. It differs from E. fusiforme by its larger size, less acuminated spire, more convex whorls and orthocline aperture. Moreover, E. rotundus differs from all other species in the genus by the oblique way the upper palatal region of the lip meets the preceding whorl.

Strophocheilidae is a diverse South-American family and its species generally are very large. The fossils (i.e., the genus Eoborus ) are rather small when compared to their living relatives and it is likely that the first branches of the family were smaller and that the Strophocheilidae only achieved larger sizes more recently in their history. Moreover, the wide umbilicus was considered a primitive feature in the family ( Klappenbach & Olazarri, 1970), since the recent species of the family show a tendency towards reducing and eliminating the umbilicus ( Schileyko, 1999b). It should also be noted here that the wide umbilicus is indeed a diagnostic character of the genus Eoborus , as stated by Klappenbach & Olazarri (1970), and it is valid and practical in its utilization, despite Palma & Brito (1974) having defied its utility.

Figures

FIGURES 59-69: 59-60. Cyclodontina coelhoi (MN 5187-I; paratype); shell length 11.5 mm. 61. C. coelhoi (DGM 5410-I; holotype); shell length 15.5 mm. 62-65. Plagiodontes aff. dentatus (MCT 6944-I); shell length 9.5 mm. 66-67. Eoborus rotundus (MCT 6942-I; paratype); shell length 25.5 mm. 68-69. Eoborus rotundus (MCT 6943-I; paratype): shell length 25.5 mm.

FIGURES 70-77: 70-74. Eoborus rotundus (MCT 6941-I; holotype); shell length 23.5 mm. 70-72. Overview. 73. Umbilicus. 74. Smooth protoconch. 75-77. Eoborus sanctijosephi (DGM 4992); shell length 44.5 mm.