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Cerro la Bruja, south (Miocene of Peru)

Where: Ica, Peru (14.6° S, 75.7° W: paleocoordinates 15.2° S, 72.7° W)

• coordinate estimated from map

• local area-level geographic resolution

When: Pisco Formation, Serravallian (13.7 - 11.6 Ma)

• Lower levels of the Pisco Formation, Serravallian to early Tortonian. The lowest levels of the Pisco Formation are dated with diatoms, foraminifers and radiolarians to the Serravallian (late middle Miocene; Dunbar, Marty & Baker, 1990 and references therein; DeVries, 1998). Based on recent field observations in Cerro la Bruja and satellite images, the outline of marker bed M3, first mapped by Brand et al. (2011: fig. 2c), was corrected; the southern exposure of this bed is actually much higher along the section than illustrated in figure 2c of Brand et al. (2011) (Fig. 2; C. Di Celma, pers. comm., 2015). The layer containing MUSM 1400 is thus positioned 60m below marker bed M3, distinctly lower than the Cerro la Bruja level (CLB; Muizon, 1988a). The latter was dated with molluscs and marine mammal fauna from the late middle to

•early late Miocene (13–11 Ma) (Muizon & DeVries, 1985; Muizon, 1988a). Furthermore, Ar/Ar dating of biotite from a volcanic tuff about 50 m higher than the CLB layers provided an age of 9.2 Ma (Brand et al., 2011). Interestingly, a specimen of the ziphiid Messapicetus gregarius Bianucci et al., 2010 was discovered a few hundred metres south-east of the holotype of B. ankylorostris, also considerably lower than marker bed M3 (Bianucci et al., 2010). The same ziphiid species is abundant in Cerro Colorado, a locality about 30 km north-west of the type locality of B. ankylorostris, where the lower portion of the Pisco Formation crops out (Bianucci et al., 2010, 2016). The age of these strata was recently constrained to the late Miocene (Di Celma et al., 2016) based on the presence of the diatom Lithodesmium reynoldsii Barron, 1976; the latter has a range spanning between 9.9 and 8.9 Ma (Barron, 2003). This dating suggests a younger age than previously reported, not only for Cerro Colorado (Bianucci et al., 2010; Lambert et al., 2010a, 2015b), but possibly more generally for the earliest fossiliferous deposits of the Pisco Formation. Regardless, the radiometric age of 9.2 Ma reported by Brand et al. (2011) provides an upper limit for the age of the CLB layers, and therefore for the stratigraphically much lower type horizon of B. ankylorostris, whereas the lower limit is for now not constrained with radiometric data. The CLB marine mammal fauna includes the pontoporiid Brachydelphis mazeasi Muizon, 1988, the ‘kentriodontids’ Atocetus iquensis Muizon, 1988 and Belonodelphis peruanus Muizon, 1988, a new species of the stem physeteroid Acrophyseter Lambert et al., 2008, an undetermined ziphiid, one small cetotheriid, one large balaenopteroid-like mysticete and at least one monachine phocid (Muizon & DeVries, 1985; Muizon, 1988a; Lambert, Bianucci & Beatty, 2014a; Lambert, Bianucci & Muizon, 2016; C. de Muizon, pers. comm., 2014).

• bed-level stratigraphic resolution

Environment/lithology: marine; diatomaceous siltstone

Size class: macrofossils

Preservation: original phosphate

Collection methods: surface (in situ),

• Natural History Museum of Lima, Peru (Studied in Pimiento and Balk)

Primary reference: O. Lambert, G. Bianucci, M. Urbina and J. H. Geisler. 2017. A new inioid (Cetacea, Odontoceti, Delphinida) from the Miocene of Peru and the origin of modern dolphin and porpoise families. Zoological Journal of the Linnean Society 179:919-946 [M. Uhen/M. Uhen] more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 184773: authorized by Mark Uhen, entered by Mark Uhen on 22.03.2017

Creative Commons license: CC BY (attribution)