No abstract

Exceptionally preserved delicate baleen microstructures have been found in association\ud with the skeleton of a late Miocene balaenopteroid whale in a dolomite concretion of the\ud Pisco Formation, Peru. Microanalytical data (scanning electron microscopy, electron probe\ud microanalysis, X-ray diffraction) on fossil baleen are provided and the results are discussed\ud in terms of their taphonomic and paleoecological implications. Baleen fossilization modes\ud at this site include molding of plates and tubules, and phosphatization. A rapid formation of\ud the concretion was fundamental for fossilization. We suggest that the whale foundered in a\ud soft sediment chemically favorable to rapid dolomite precipitation, allowing the preservation\ud of delicate structures. Morphometric considerations on the baleen plates and bristles\ud coupled with the reconstructed calcification of the latter permit speculation on the trophic\ud preferences of this balaenopteroid whale: the densely spaced plates and the fine and calcified\ud bristles provide evidence for feeding on small-sized plankton, as does the modern sei whale

One hundred and ninety-two fossil marine vertebrate specimens, preserved as bone elements cropping out at Cerro Los Quesos (Pisco Basin, Peru), are identified and reported in a 1:4,000 scale geological map and in the corresponding stratigraphic section. All the fossils originate from the Pisco Formation, which is dated in this area to the late Miocene (from 7.55 Ma to ≥ 6.71 Ma, based on 40Ar/39Ar analyses of three volcanic ash layers along the section). Specimens are particularly concentrated near the top of the two main hills, where the geologically youngest portion of the examined section crops out. The impressive fossil assemblage includes cetaceans (91.6%), represented by mysticetes (balaenopteroids and cetotheriids) and odontocetes (phocoenids, physeteroids, and ziphiids, including the holotype of Nazcacetus urbinai). Seals, a crocodile, a seabird, bony fish, and sharks are also reported. Isolated large teeth of Carcharocles and Cosmopolitodus are common and, in several instances, associated to mysticete skeletons. Together with a similar work recently published for the other late Miocene locality of Cerro Colorado, this work represents a case study for the detailed inventory of the extraordinary paleontological heritage of the Pisco Basin. As such, it constitutes the basis for future taphonomic, paleoecological, and systematic studies, as well as for a much needed conservation effort

Hundreds of fossil marine vertebrates cropping out at Cerro Colorado (Pisco Basin, Peru) are identified and reported on a 1:6500 scale geological map and in a joined stratigraphic section. All the fossils are from the lower strata of the Pisco Formation, dated in this area to the late middle or early late Miocene. They are particularly concentrated (88%) in the stratigraphic interval from 40 to 75 m above the unconformity with the underlying Chilcatay Formation. The impressive fossil assemblage includes more than 300 specimens preserved as bone elements belonging mostly to cetaceans (81%), represented by mysticetes (cetotheriids and\ud balaenopteroids) and odontocetes (kentriodontid-like delphinidans, pontoporiids, ziphiids, and physeteroids, including the giant raptorial sperm whale Livyatan melvillei). Seals, crocodiles, sea turtles, seabirds, bony fish, and sharks are also reported. Isolated large teeth of Carcharocles and Cosmopolitodus are common throughout the investigated stratigraphical interval, whereas other shark teeth, mostly of carcharinids, are concentrated in one sandy interval. This work represents a first detailed census of the extraordinary paleontological heritage of the Pisco Basin and the basis for future taphonomic, paleoecological, and systematic studies, as well as a much needed conservation effort for this extremely rich paleontological site