https://orcid.org/0000-0003-0637-3302
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Abstract
Extant istiophorids are open ocean apex predators that are extensively studied due to their ecological importance and high values for fisheries. Nevertheless, little is known about their evolution because of a fragmentary fossil record and extremely difficult taxonomy of fossil species. Here, we present a new phylogenetic hypothesis covering fossil and living istiophorids. Our results demonstrate that istiophorid richness is larger than previously assumed, comprising eight genera with 20 species. The phylogenetic analysis shows that istiophorids are grouped into four clades: the Istiophorus clade, which includes the sailfish; the Machairostra clade, which comprises Makaira spp., including two new species from the late Miocene (†Makaira colonense sp. nov. and †Makaira fierstini sp. nov.); the Gracilorostra clade, which comprise all remaining istiophorids with exception of spearfishes and includes two new genera and one new species (†Morgula donosochagrense gen. et sp. nov. and †Spathochoira calvertense gen. et. comb. nov.); and the Tetrapturomorpha clade is composed of the spearfishes and the extinct †Prototetrapturus courcelli gen. et. comb. nov. The family Istiophoridae shows an evolutionary trend toward reduction of the premaxillary thickness and increasing the extension of narial cavities. This reduction is related to an increase of adipose tissues in the rostrum base probably driven by the presence of the oleofera gland, an organ involved in feeding, healing, endothermy and hydrophobic functions. Our phylogeny shows a direct relationship between the rostral and cranial shape explained by body size and feeding behaviour. The larger istiophorids have lateral apophysis and the larger spines of the vertebral column. The spearfishes represent the smaller species of the family, with the extant Tetrapturus spp. first appearing in the late Pliocene. The clade Tetrapturomorpha shows an extreme size reduction over time when compared with species of their sister clade Gracilorostra, demonstrating an evolutionary trend towards size reduction.
http://zoobank.org/urn:lsid:zoobank.org:pub:D3D3B15B-36FA-42EB-98AD-FAF369D989EB
Acknowledgements
This project was made possible by various grants to CD: SENACYT APY-NI10-016A grant (National Secretary of Science and Technology of Panama), Ricardo Perez S.A, Smithsonian Tropical Research Institute – Tupper Paleontological Fund, International Travel Grant for Vertebrate Palaeontology of the University of Florida, Travel Program of the Charles University in Prague and the Doctoral and Postdoctoral Scholarships Program from SENACYT BIP-2018-004. TP is grateful for financial support by the Institute of Geology of the Czech Academy of Sciences (RVO67985831). We thank the Dirección de Recursos Minerales of Panama for collecting permits. Thanks also go to Jeffrey Clayton, Jeffrey Williams and Michael Brett-Surman (from the Smithsonian National Museum of Natural History, Washington, DC, USA) for help with osteological and palaeontological collections. Thanks to Phillipe Béarez from the Muséum national d’Histoire naturelle of France and Richard Cooke from STRI for his help with osteological material of I. platypterus. Also to Annelise Folie (Royal Belgian Institute of Natural Sciences, Brussel, Belgium) for access to collections; to Gustavo Ballen and Irvy Quitmyer for their support by providing the specimens FLMNH-EA 210017 and 208089 from collections of the Florida Museum of Natural History, Gainesville, USA for this study; to the CTPA – STRI palaeontological crew (STRI – Panama) and Abraham Osorio for their support during fieldwork. And to Jorge Aleman (STRI – Panama) for preparing photographs of all new described specimens and Angel Aguirre (STRI – Panama) for his valuable help by obtaining rare literature. We extend our gratitude to W. Gelnaw (OC Parks) for providing photos of OCPC 31001. Special thanks go to Félix Rodriguez (STRI, Panama) for his support during the early stages of this project, to Eduardo Villalobos for discussions and to the reviewers who improved our manuscript with their comments and suggestions. We dedicate this work to the late Harry Fierstine (1932–2021), who generously shared unpublished data as well his experience and knowledge about istiophorid morphology during the earliest years of the academic formation of CD, which made this study possible. He will be missed.
Supplemental material
Supplemental material for this article can be accessed here: https://doi.org/10.1080/14772019.2022.2091959.
Associate Editor: Martin Brazeau
