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Cerro del Castillo, Trelew (Miocene to of Argentina)

Where: Chubut, Argentina (43.3° S, 65.3° W: paleocoordinates 44.0° S, 59.2° W)

• coordinate estimated from map

When: Gaiman Formation, Aquitanian to Aquitanian (23.0 - 16.0 Ma)

• formacion patagonica marina; early Miocene date form Fordyce (2002); In the area of the type locality of M. parvus, the lower part of Gaiman Formation overlies the continental Sarmiento Formation, which contains a mammal fauna correlating with the Colhuehuapian South American Land Mammal Age [51,52]. The latter was dated to 19.8-20.9 Ma, based on 40Ar/39Ar dating [53], thus providing a maximum age of ca. 20 Ma (earliest Burdigalian) for the lower part of the Gaiman Formation in this area. Since virtually all vertebrate material recovered so far originated from the lowermost levels of the Gaiman Formation, close to its contact with the Sarmiento Formation (Cozzuol 2010, pers. comm.), the age of Morenocetus is here assumed to be early Burdigalian. (Fordyce & Marx, 2013)

•Both MLP 5-11 and 5-11 were originally reported to have come from the Patagonian Marine Formation [40]. The latter corresponds to the partially correlated Monte León and Gaiman formations, exposed in Santa Cruz (e.g. Garn Bajo de San Juan) and the lower Chubut river valley near Trelew (e.g. at Bryn Gwyn/ Loma Blanca), respectively [42]. In the area around Trelew, the lower part of Gaiman Formation overlies the continental Sarmiento Formation, which contains a mammal fauna correlating with the Colhuehuapian South American Land Mammal Age [43, 45]. The latter has been 40Ar/39Ar dated to 20.9– 19.8 Ma [46], thus providing a maximum age of 19.8 Ma (earliest Burdigalian) for the lower part of the Gaiman Formation in this area. Since virtually all vertebrate material recovered so far originated from the lowermost levels of the Gaiman Formation, close to its contact with the Sarmiento Formation [Cozzuol 2010, pers. comm.], an early Burdigalian age (19.8–18.2 Ma) is here assumed for M. parvus. (Marx & Fordyce, 2015)

• formation-level stratigraphic resolution

Environment/lithology: shallow subtidal; argillaceous sandstone

• The holotype of A. moreni was found in “a mixture of sand and clay, including a stratum of sand capped by volcanic sand.” ([39]:1). The original description further explained that ”an apparently contemporaneous bed in Santa Cruz, also containing cetacean bones, has yielded oysters of an extinct species (Ostrea patagonica), and one skull from Chubut has one of the same oysters attached” [39: 1-2]. MLP 5-14 was later discovered at the same locality, described as “Castillo, frente a Trelew, Chubut” [40: 369], and reported to have come from the Patagonian Marine Formation (“formación patagónica marina”, [40: 364]).

•The Patagonian Marine Formation corresponds to the partially correlated Monte León and Gaiman formations, exposed in Santa Cruz (e.g. Garn Bajo de San Juan) and the lower Chubut river valley near Trelew (e.g. at Bryn Gwyn/ Loma Blanca), respectively [42]. The Gaiman Formation consists of layers of marine sandstones and mudstones, as well as tuffs and tuffaceous sandstones. In addition, the lower part also contains occasional thin layers of Ostrea and bones of marine vertebrates [43]. Thus, the portion of the Gaiman Formation exposed near Trelew provides a likely match for the unit that yielded A. moreni [39, 40, 44].

•11

•In the area around Trelew, the lower part of Gaiman Formation overlies the continental Sarmiento Formation, which contains a mammal fauna correlating with the Colhuehuapian South American Land Mammal Age [43, 45]. The latter has been 40Ar/39Ar dated to 20.9– 19.8 Ma [46], thus providing a maximum age of 19.8 Ma (earliest Burdigalian) for the lower part of the Gaiman Formation in this area. Since virtually all vertebrate material recovered so far originated from the lowermost levels of the Gaiman Formation, close to its contact with the Sarmiento Formation [Cozzuol 2010, pers. comm.], an early Burdigalian age (19.8–18.2 Ma) is here assumed for A. moreni. (Marx & Fordyce, 2015)

•Shows a shallow, storm-dominated marine environment with significant sea level oscillations.

• a mixture of sand and clay, including a stratum of sand capped by volcanic sand

Size class: macrofossils

Preservation: original phosphate

Primary reference: A. Cabrera. 1926. Cetaceos fossiles del Museo de La Plata. Revista del Museo de La Plata 29:363-411 [M. Uhen/M. Uhen/M. Uhen] more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 47303: authorized by Mark Uhen, entered by Mark Uhen on 22.02.2005

Creative Commons license: CC BY (attribution)