Abstract
This contribution describes the skull remains of a swordfish (Perciformes, Xiphioidei), recovered from Middle Eocene beds of central Chile. Comparison with known fossil and extant xiphioids reveals derived traits only present in the Neogene swordfish Xiphias gladius (Xiphiidae, Xiphiinae), these being a elongated rostrum composed of premaxillaries and possible prenasals, a dorsoventrally high and slender hyomandibular-metapterygoid complex, and a rounded, convex operculum. Also, strong ridges and sulci are present in the dorsal part of the rostrum, a feature only present in the billfish genera Aglyptorhynchus and Xiphiorhynchus, and in the swordfish genus Blochius. In addition, the specimen also has villiform teeth in the rostrum and lower jaw, a feature previously documented only in the Paleocene genus Hemingwaya. Such a unique combination of characters in the specimen allows classifying it as a new genus and species, Loancorhynchus catrillancai. Phylogenetic analyses obtained Xiphiorhynchus outside the Xiphiidae, suggesting instead narrow relationships to the Paleocene-Eocene genera Hemingwaya + Palaeorhynchus + Homorhynchus. Loancorhynchus is obtained as an intermediate form between Xiphias and Blochius. The specimen represents the first Paleogene swordfish described in the southeastern Pacific.