A new South American Miocene species of 'one-holed' sand dollar (Echinoidea: Clypeasteroida: Monophorasteridae)

Abstract

A new species of monophorasterid sand dollar, Monophoraster telfordi n. sp., is described from the Early Miocene basal horizons of the Chenque Formation of Patagonia, Santa Cruz Province, in southern Argentina. The new taxon raises the number of known species in the family to six, and represents first unequivocal record of the genus for the Early Miocene of South America. It is therefore also the oldest member of the genus. M. telfordi is characterized by its test width to length ratio, which is much higher than for the other two described species in the genus, but less than that known for the extremely wide members of the sister taxon, Amplaster. M. telfordi is also unusual among monophorasterids in lacking broad continuity between basicoronal and post-basicoronal plates in the oral interambulacra. A key is provided to all the known species of Monophorasteridae.

Late Oligocene–Miocene non-lunulate sand dollars of South America: Revision of abertellid taxa and descriptions of two new families, two new genera, and a new species

“…Although Camachoaster maquedensis n. sp. is found in the same strata as Monophoraster telfordi Mooi et al, 2016, the former is immediately recognizable as a different species, as well as representing a different major scutelliform clade, by its complete lack of an anal lunule. Camachoaster resembles the Abertellidae only in the possession of a shallow notch, and in the discontinuity of the posterior interambulacrum.…”

“…Studied material of the new species was collected from shoreline deposits in southern Argentina, about 2 km south of Punta Maqueda, Santa Cruz Province (Mooi et al, 2016). Specimens of all other taxa considered in this revision were studied at the indicated institutions.…”

“…Geologic setting. The shallow marine deposits in which the new species was found have been described in Mooi et al (2016). In summary, the rocks of the Chenque Formation in the Golfo San Jorge Basin (Chubut and Santa Cruz Provinces, Argentina) exposed near Punta Maqueda have been described as early Miocene (del Río 2004).…”

“…In summary, the rocks of the Chenque Formation in the Golfo San Jorge Basin (Chubut and Santa Cruz Provinces, Argentina) exposed near Punta Maqueda have been described as early Miocene (del Río 2004). The type specimens of Monophoraster telfordi Mooi et al, 2016 were collected from the same thin bed (up to 15 cm thick) of fine-grained sandstones from which the new species of non-lunulate was recovered.…”

“…We were able to confirm the original suggestion, indicated by the figures of Marchesini Santos (1958) and Brito (1979), that all interambulacra are discontinuous. This alone suggests that the attempts to place A. pirabensis in the Monophorasteridae Lahille, 1896 are misguided because all the interambulacra of all species in that family are broadly continuous, both postbasicoronal plates being in contact with the basicoronal, with a minor exception in a specimen of M. telfordi (see Mooi et al 2016). Martínez and Mooi (1997) and Mooi et al (2000) compared A. pirabensis with what was then known as Abertella complanata (here placed in the new genus Placatenella), and became convinced that A. complanata was a junior synonym of A. pirabensis.…”