Acrophyseter robustus, Lambert & Bianucci & De Muizon, 2017

ACROPHYSETER ROBUSTUS SP. NOV.

Acrophyseter sp. Lambert et al., 2014: figs 1, 2 Holotype: MUSM 1399, a skull with both mandibles and teeth in situ, lacking the anterior part of the rostrum and mandibles, the right part of the rostrum base and the right supraorbital region. The atlas, a fragment of the axis and several hyoid bones (basihyal, partial right and left thyrohyals and stylohyals) are still attached to the skull with hardened sediment.

Referred specimen: MNHN PPI 239, a symphyseal fragment of the right mandible, found in Cerro la Bruja by C. Muizon and previously identified as Physteridae indet ( Muizon, 1988: fig. 111).

Etymology: From Latin robustus , in relation to the thick bone making the margins of the supracranial basin and the rostrum base.

Type locality. Cerro la Bruja, Pisco-Ica desert, 52 km SSE of Ica ( Fig. 1A View Figure 1 ). Geographical coordinates 14 ° 31 0 27.9 ″ S, 75 ° 40 0 13.0 ″ W, altitude 380 m. The holotype was discovered and collected by Mario Urbina. GoogleMaps

Type horizon: Pisco Formation, Cerro la Bruja level (CLB) as defined by Muizon & DeVries (1985). CLB corresponds to some of the lowest levels of the Pisco Formation, dated to late middle to early late Miocene (c. 13 – 11 Ma; Muizon & DeVries, 1985; Muizon, 1988). Ar/Ar dating of biotite from a volcanic ash layer approximately 50 m higher than the CLB layers yielded an age of 9.2 Ma ( Brand et al., 2011), providing a minimum age for the fossil-bearing layers. Many marine vertebrates were described or mentioned from this locality and level: among odontocetes, the pontoporiid Brachydelphis mazeasi Muizon, 1988 , the ‘pithanodelphinine’ Atocetus iquensis Muizon, 1988 , the ‘kentriodontid’ Belonodelphis peruanus Muizon, 1988 , and an undetermined ziphiid, but also undetermined mysticetes, an undescribed monachine phocid, the penguin Spheniscus muizoni Gohlich, 2007 , sea turtles, crocodiles, and the sharks Carcharocles megalodon , Cosmopolitodus hastalis and Carcharhinus sp. ( Muizon & DeVries, 1985; Muizon, 1988; Gohlich, 2007). In addition, a new inioid and the stem ziphiid Messapicetus gregarius Bianucci et al., 2010 were identified from layers somewhat lower than CLB, in a locality about 4 km south of the main Cerro la Bruja locality ( Bianucci et al., 2010; Lambert et al., in press).

Diagnosis. Differs from A. deinodon in: rostrum not as attenuate in dorsal view and lacking abrupt anterior decrease of height of maxilla in lateral view; absence of left anterior and posterior premaxillary foramina; absence of a lateral groove on the right side of the rostrum; proportionally narrower right infraorbital canal, probably dividing into two foramina, one dorsal in the supracranial basin and one anterior; deep sulcus anterior to the main left dorsal infraorbital foramen; dorsal margin of supracranial basin thick and rounded; dorsal margin of coronoid process of mandible smoothly rounded.