High concentration of long-snouted beaked whales (genus Messapicetus) from the Miocene of Peru

Abstract

Eight skulls of beaked whales (Cetacea, Odontoceti, Ziphiidae), in six cases associated with elements of the mandible, were collected from a limited area (about 1.5 km 2 )and roughly from the same stratigraphic horizon at Cerro Colorado, 35 km south-south-west of the city of Ica (Peru), where the late Middle Miocene basal strata of the Pisco Formation crop out. They represent the highest concentration reported of fossil Ziphiidae. These finely preserved Cerro Colorado fossils are described and assigned to a new species Messapicetus gregarius, together with another specimen collected from sediments of the same age at Cerro la Bruja (33 km south-east to Cerro Colorado). Messapicetus gregarius shares with M. longirostris Bianucci, Landini and Varola, 1992 (Tortonian of Italy), an extremely elongated rostrum, but is clearly different from the Italian species in the more distinct maxillary tubercle and prominential notch, the more robust premaxillary crest, and the abrupt ventrolateral descent of the medial margin of the maxilla from the vertex. A parsimony analysis reveals that Messapicetus belongs to a basal clade, which includes other ziphiids with a dorsally closed mesorostral groove and prenarial basin. The high concentration of specimens belonging to the same species (some of them tentatively identified as adult males and females), combined with the presence of a calf, supports the hypothesis of site fidelity; these cetaceans might have lived in a limited region for a long period for both breeding and feeding. Besides the eight specimens of M. gregarius, strata at Cerro Colorado include many other cetacean remains (with several specimens of the pontoporiid Brachydelphis including a foetus), pinnipeds, turtles, fishes, and birds.

No deep diving: evidence of predation on epipelagic fish for a stem beaked whale from the Late Miocene of Peru

“…Available dimensions for the skull (width across occipital condyles 11.4 cm; maximum width of hamular processes in ventral view 10.5 cm; condylobasal length 107 cm) and for the mandible (maximum width of apex 3.4 cm; diameter of the alveolar tusk 2.3 Â 1.2 cm) fitted in the range of the species Messapicetus gregarius [9,22]. The general morphology of the outcropping elements perfectly matches the skull morphology in the latter, by far the most commonly found ziphiid in Cerro Colorado (more than 10 specimens, including several skull-mandible sets, among which five specimens originate from a stratigraphic interval 4 m thick, also containing the specimen described here [17]).…”

“…the holotype of Livyatan melvillei), beaked whales, several delphinidans (Pontoporiidae and kentriodontid-like delphinidans), cetotheriid and balaenopteroid baleen whales, sea turtles, crocodiles, seabirds, sharks and bony fish [9,17,18]. These fossiliferous deposits were first tentatively dated from the late Middle to early Late Miocene (Serravallian to early Tortonian, ca 13 -11 Ma [9,18]). The recent record of Lithodesmium reynoldsii, a diatom species with a range between 9.9 and 8.9 Ma [19], points to a Late Miocene (Tortonian) age [16].…”

“…The ziphiid skeleton with associated fish remains examined here originates in the lower allomember, where a large number of other fossil vertebrate remains were found, including sperm whales (e.g. the holotype of Livyatan melvillei), beaked whales, several delphinidans (Pontoporiidae and kentriodontid-like delphinidans), cetotheriid and balaenopteroid baleen whales, sea turtles, crocodiles, seabirds, sharks and bony fish [9,17,18]. These fossiliferous deposits were first tentatively dated from the late Middle to early Late Miocene (Serravallian to early Tortonian, ca 13 -11 Ma [9,18]).…”

“…Furthermore, computed tomography (with both hospital CT and microCT) of fragments of the concretion did not yield usable data. Complete skulls of the same species available at the MUSM [9] were used for part of the interpretation and discussion.…”

“…[2,4,7]) indicate that it is more parsimonious to characterize the last common ancestor of all modern ziphiids as adapted to deep dives. Second, most stem ziphiids were found in platform deposits, contrasting with the discovery of many fossil crown ziphiid remains in deep-sea deposits [6,[8][9][10][11]. Finally, a few morphological characters provide clues about the feeding technique and habitat of extinct ziphiids [6].…”