New Paleogene records of cartilaginous fishes (Chondrichthyes) from central Chile, including the oldest lamnid diversity from the southeastern Pacific

Background The Paleogene chondrichthyan diversity of the southern hemisphere is mostly known in Antarctica, southernmost South America and New Zealand, but records from the southeastern Pacific remain sparse to date. Among these, lamnid sharks (the lineage of the great white shark) are one of the scarcer groups in the southern hemisphere prior to the Eocene; moreover, their occurrences prior to the Neogene remained unreported in the southeastern Pacific. This contribution presents new Paleogene chondrichthyans recovered from two different horizons at Loanco, central Chile, including the first local records of lamnids, with the description of a new species of the genus Lethenia . Methods Sections of two geologic units were studied. These provided new teeth of chondrichthyans, as well as a single associated tooth set plus fragments of jaw cartilage and vertebrae. The material was taxonomically identified and compared with other local occurrences and other coeval assemblages from the southern hemisphere. Results This research recognizes a lower Paleocene-lower Eocene assemblage including material referable to Palaeohypotodus sp., Megasqualus sp. and Hexanchidae indet., the latter being the oldest known record in the southwestern Pacific. In addition, material from upper Eocene-lower Oligocene levels include dental pieces referable to the lamnids Macrorhizodus praecursor Leriche, and to a new species, Lethenia carranzaensis sp. nov., the latter represented by an exceptional specimen preserving a dental set, mandibular cartilage and vertebrae. Although discrete, this fauna shows the presence of Paleocene- lower Eocene elements commonly present in Antarctica and the Austral Basin, suggesting a typical Weddellian distribution during that timespan. On the contrary, the presence of the genus Lethenia reinforces the evidence of vertebrate interchange with the north Atlantic between the upper Eocene—lower Oligocene, previously suspected by the shared presence of blochiid billfishes. Evidence of such marine interchange is also present during the late Paleocene, based on the previous reports of Palaeogaleus , Physogaleus , and Premontreia , genera with similar known geographic occurrences. The new records of Macrorhizodus and Lethenia also represent the oldest known record of Lamnidae in the southwestern Pacific, proving its early presence previous to its widespread and abundant occurrence during the Neogene.