Pisco Formation
The Pisco Formation is a geologic formation located in Peru, on the southern coastal desert of Ica and Arequipa. The approximately thick formation was deposited in the Pisco Basin, spanning an age from the Late Miocene up to the Early Pliocene, roughly from 9.6 to 4.5 Ma. The tuffaceous sandstones, diatomaceous siltstones, conglomerates and dolomites were deposited in a lagoonal to near-shore environment, in bays similar to other Pacific South American formations as the Bahía Inglesa and Coquimbo Formations of Chile.
The Pisco Formation is considered one of the most important Lagerstätten sites, based on the large amount of exceptionally preserved marine fossils, including sharks, birds including penguins, whales and dolphins, marine crocodiles, and Thalassocnus, a marine giant sloths.
Other famous fossils from this site include the giant raptorial sperm whale Livyatan, the sperm whale relative Acrophyseter, and the walrus-like dolphin Odobenocetops.
Description
The Pisco Formation of the Pisco Basin consists of tuffaceous sandstones, diatomaceous yellow to gray siltstones and a basal conglomerate. The formation is deposited from Pisco in the north to Yauca in the south. The northern portion is known as the Ocucaje Area and the southern part as the Sacaco Area. The total thickness of the formation is estimated at. The formation unconformably overlies the Chilcatay and Caballas Formations.Paleobiota of the Pisco Formation
The Pisco Formation has provided a rich resource of marine fauna, including marine mammals like cetaceans and seals, large fishes, reptiles, and penguins. It is also one of the richest sites in the world for fossil cetaceans, with close to 500 examples being found in the formation.The oldest fossils of the aquatic sloth Thalassocnus come from the Aguada de Lomas horizon of the Pisco Formation and were dated at roughly 7 Ma. The youngest specimen was found in the Sacaco horizon and dated to approximately 3 Ma. Thalassocnus was preyed upon by the probable apex predators of the environment, Livyatan and megalodon. The youngest strata belonging to the formation have been dated at 2 Ma, corresponding to the Early Pleistocene. Fossils of the modern Humboldt penguin were found in these deposits at the Yauca locality.
Birds
Fish
Bony fish
Rays
Sharks
Mammals
Cetaceans
Pinnipeds
;Seals| Taxa | Species | Locality | Material | Description | Images | Notes |
| Acrophoca | A. longirostirus | Sub-Sacaco | A partial skull. | Archaic southern seal | ||
| Australophoca | A. changorum | Aguada de Lomas | A partial skeleton consists of incomplete right ulna, right radius, right and left humeri, and other unidentified remains. | A phocidae seal. | ||
| Hadrokirus | H. martini | Sub-Sacaco | A partial skull | Archaic southern seal | ||
| Hydrarctos | H. lomasiensis | Sub-Sacaco | A skull. | A sea lion and fur seal relative | ||
| Icaphoca | I. choristodon | Cerro La Bruja | A subcomplete skull with associated left and right mandibles, atlas, axis, third, fourth, and fifth cervical vertebrae. | Archaic southern seal | ||
| Magophoca | M. brevirostris | Cerro la Bruja | A partial skeleton of a male. | Archaic southern seal | ||
| Piscophoca | P. pacifica | Sub-Sacaco | A partial skull | Archaic southern seal |
Xenarthrans
;Sloths| Taxa | Species | Locality | Materials | Description | Images | Notes |
| Thalassocnus | T. antiquus | Aguada de Lomas | A partial skeleton including the skull, mandible, and most of the postcranial skeleton. | a semi-aquatic giant sloth inhabiting marine environments | ||
| Thalassocnus | T. carolomartini | Sacaco | An associated skull and mandible and two articulated hands, probably belonging to the same individual. | a semi-aquatic giant sloth inhabiting marine environments | ||
| Thalassocnus | T. littoralis | Sud-Sacaco | A skull with missing jugals. | a semi-aquatic giant sloth inhabiting marine environments | ||
| Thalassocnus | T. natans | Sud-Sacaco | A skull, mandible, and partial skeleton. | a semi-aquatic giant sloth inhabiting marine environments |