Rewriting the fossil history of Cerionidae (Gastropoda: Pulmonata): new family assignment of the Brazilian Palaeocene genus Brasilennea Maury, 1935

Abstract

The limestone formation of the Itaborai Basin at Sao Jose de Itaborai, Rio de Janeiro, Brazil, harbours a rich fauna of wellpreserved terrestrial pulmonates: 18 species have been described to date, mainly in Bulimulidae/Orthalicidae (Simone & Mezzalira, 1994). Following mammal correlations, the Itaborai limestones are now agreed to be of Palaeocene age (e.g. Paula Couto, 1952; Medeiros & Bergqvist, 1999) and, more precisely, the pulmonate fauna to be of Middle to Late Palaeocene age, although influential past malacological works have listed its pulmonate taxa as Miocene or Pliocene (e.g. Zilch, 1959–1960; Parodiz, 1969). Itaborai’s fossils are a valuable tool for studying the evolution of South American taxa due to their early Cenozoic age and the basin location. The genus Brasilennea Maury, 1935 is known only from the Itaborai basin. The type species (by original designation) is B. arethusae Maury, 1935, with B. minor Trindade, 1956 at first considered a variation, now considered a second sympatric species (Brito, 1967). A third Brasilennea species was recently found in museum collections (Salvador & Simone, unpubl.). Brasilennea was assigned to Streptaxidae subfamily Enneinae (1⁄4Ptychotrematinae) of the mainly Old World Streptaxoidea (Maury, 1935) on the basis of similarities with the African genus Ptychotrema Pfeiffer, 1853, in particular its subgenus Ennea Adams & Adams, 1855. This streptaxid allocation has been followed by all subsequent workers on the Itaborai fauna. Brasilennea remains the only fossil New World Enneinae streptaxid and there are no known Recent New World Enneinae (Rowson, 2010). The phylogenetic analysis of Rowson, Tattersfield & Symondson (2010) found that extant South American streptaxids belong to Streptaxinae, unrelated to genera in Enneinae, a result also supported by morphology (Rowson, 2010). They considered Brasilennea to be a Miocene genus (following Parodiz, 1969) that may have dispersed from Africa, but noted that several Cretaceous and early Cenozoic ‘streptaxid’ fossils have been shown to belong to other families (Nordsieck, 1986). As Brasilennea is distant in space and time from other Enneinae streptaxids its family assignment should be carefully examined. To do so we reviewed all existing literature on Brasilennea and examined type and abundant material from Itaborai of both species in the following museums: American Museum of Natural History, New York, USA (AMNH); Museu de Ciencias da Terra, Rio de Janeiro, Brazil (DGM); Museu Nacional, Rio de Janeiro, Brazil (MNRJ); Museu de Zoologia, Sao Paulo, Brazil (MZSP). Comparisons were made with material of extant Cerionidae and Streptaxidae taxa at MZSP and the National Museum of Wales, Cardiff, UK (NMW). The material of Brasilennea examined included: B. arethusae: AMNH 24237–24239 (holotype and 2 paratypes); DGM 4222, 4998, 5002, unregistered (18 specimens); MNRJ 3346, 3348, 4338 (9 specimens); MZSP 86321, 86322, 86324 (25 specimens). B. minor: DGM 4224 (holotype), 4999, unregistered (12 specimens); MNRJ 3346, 4338 (3 specimens); MZSP 86323 (2 specimens). The genus Brasilennea (Fig. 1A–L) is characterized as follows. Shell dextral, pupiform (cylindrical, multispiral, narrowing in both extremities, with acuminate apex), greatest width near central portion; triphasic (sensu Gould, 1989). Whorls slightly convex. Columella hollow in early whorls at least. Sutures well marked and linear, nearly perpendicular to columellar axis. Sculptured by regularly distributed, fine, raised ribs, becoming less oblique towards aperture; first two to three whorls unsculptured. Body whorl with two well-marked spiral furrows. Large ovate aperture, with rounded outer lip and straight inner lip. Peristome complete, upper lip virtually straight, doubled. Nearly median, single, strong parietal tooth/lamella reaching peristome. Columellar spiral lamella present. The genus remains known only from the type locality and stratum: Itaborai Basin, facies of grey limestone: Facies B in sequence S1 (Middle to Late Paleocene) sensu Medeiros & Bergqvist (1999). Our study leads us to argue that Brasilennea should be transferred to Cerionidae in Urocoptoidea, a revision with biogeographic and evolutionary implications [Streptaxoidea and Urocoptoidea (represented by Cerion) are very distantly related; Wade,Mordan,&Naggs, 2006]. AlthoughBrasilennea is not identical to any fossil or Recent taxon, it shows several features common inCerionidae but not Streptaxidae (we restrict ourselves to Enneinae and other pupiform streptaxids). The considerable shell thickness, sculpture, triphasic shape, acuminate apex and large number of whorls are features common among cerionids (Fig. 1M, N) and larger urocoptids, but uncommon or rare among streptaxids. The doubled peristome is very common among cerionids, but almost unknown in streptaxids (apparently present only in the tiny Gulella kimbozae Verdcourt, 2004 from Tanzania). The virtually straight parietal edge of the peristome