First fossil occurrence of the genus Platychelyna Hayward and Thorpe (Bryozoa: Cheilostomata)

LÓPEZ-GAPPA, JUAN; PÉREZ, LEANDRO; GRIFFIN, MIGUEL

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Año: 2018 vol. 55 p. 607 - 612

0002-7014

THE first contribution to the knowledge of the early Miocene Bryozoaof Argentina was a monograph published by Ferdinand Canu (1908). This author described the abundant material collected by Carlos Ameghino mainly from the Chenque Formation at Punta Borja, presently corresponding to Comodoro Rivadavia harbor and abrasion platform (see Bellosi, 1990; Paredes and Colombo, 2001; Cuitiño et al., 2015; among others). Several articles on the bryozoan fauna of the Monte León Formation (Cabeza de León, early Miocene, ArgentinePatagonia) have been published over the last years (Pérez et al., 2015, 2018; Casadío et al., 2010; López-Gappa et al., 2017). The presence of species in common between the Chenque and Monte León formations suggests that the upper levels of the latter might correlate with the lower levels of the former (Pérez et al., 2018). The bryozoan collection assembled by the research vessel 'Scotia' was described taxonomically almost eight decades after the Scottish National Antarctic Expedition 1902-1904 (Hayward, 1980). Station 346 in Burdwood Bank (54° 25? S; 57° 32? W, Fig. 1), at a depth of 102 m, included a small encrusting colony and several erect bilaminar fragments of an unknown cheilostome originally described as Cellarinella planulata Hayward, 1980. In a subsequent study (Hayward and Thorpe, 1990),Scanning Electron Microscope (SEM) images obtained from additional material collected by the research vessel 'William Scoresby' on the northwestern slope of this bank (depth range 368?463 m, Fig. 1), showed that C. planulatabelonged in factto the Smittinidae. The new genus Platychelyna Hayward and Thorpe, 1990 was erected for this species, which resulted in the new combination Platychelyna planulata (Hayward, 1980). The genus was introduced to accommodate smittinids with lyrula, without condyles or oral spines, and with one or two latero-oral adventitious avicularia on either or both of the corners of a prominent peristome developed as distal and proximal flaps. Further material of P. planulata collected by the research vessel 'Polarstern' at a depth of 430 m near Cape Horn (Fig. 1) was listed by Moyano (1997, 2000). No other species of Platychelyna has been described after that. The aim of this article is to describe the first fossil species of Platychelyna found in early Miocene rocks exposed in Santa Cruz Province, Argentina.