Morphology and phylogenetic relationships of fossil snake mackerels and cutlassfishes (Trichiuroidea) from the Eocene (Ypresian) London Clay Formation

Abstract

Gempylids' (snake mackerels) and trichiurids (cutlassfishes) are pelagic fishes characterized by slender to eel-like bodies, deep-sea predatory ecologies, and large fanglike teeth. Several hypotheses of relationships between these groups have been proposed, but a consensus remains elusive. Fossils attributed to 'gempylids' and trichiurids consist almost exclusively of highly compressed body fossils and isolated teeth and otoliths. We use micro-computed tomography to redescribe two three-dimensional crania, historically assigned to †Eutrichiurides winkleri and †Progempylus edwardsi, as well as an isolated braincase (NHMUK PV OR 41318). All from the London Clay Formation (Eocene, Ypresian), these specimens represent some of the oldest fossils identified as trichiuroids. We find that †Eutrichiurides winkleri does not show diagnostic characters of †Eutrichiurides, and it is assigned to a new genus. To investigate the placement of these fossils relative to extant lineages, we combine existing morphological character sets for 'gempylids' and trichiurids along with published mitogenomic data. Our analyses recover a monophyletic Trichiuridae nested within a paraphyletic 'Gempylidae'. The taxon formerly known as †Eutrichiurides winkleri is considered Trichiuroidea incertae sedis, while †Progempylus edwardsi and NHMUK PV OR 41318 are recovered within the 'gempylid' grade. Using previously published descriptions and character optimizations from our phylogenetic analyses we suggest possible placements for laterally compressed body fossils assigned to Trichiuroidea ( †Argestichthys, †Abadzekhia, †Chelifichthys, †Anenchelum, †Eutrichiurides, †Musculopedunculus).

The complete mitochondrial genome of the South African snoek Thyrsites atun (Euphrasén, 1791) (Perciformes, Gempylidae)

“…Despite having a striking resemblance, Thyrsites atun , also known as snoek, and Thyrsitoides marleyi , commonly known as black snoek, are not closely related according to morphology-based phylogenies of Russo ( 1983 ) and Beckett et al. ( 2018 ). On the other hand, Gempylus and Thyrsites are the only Gempylidae species to share a carangiform swimming mode and a high number of dorsal and anal finlets, making them evolutionary close relatives (Monsch 2000 ).…”

Offshore marine actinopterygian assemblages from the Maastrichtian–Paleogene of the Pindos Unit in Eurytania, Greece

“…The global Paleocene fossil record is even poorer than that of the Maastrichtian, both in terms of number of known sites, but also in terms of recorded biodiversity and, in most cases, quality of preservation ( Patterson, 1964 ; Thomas et al, 1999 ; Cavin, 2002 ; Friedman & Johnson, 2005 ; Parris, Smith-Grandstaff & Gallagher, 2007 ; Schwarzhans & Milàn, 2017 ; Capobianco, Foreman & Friedman, 2019 ). The Danian neritic sites near Palenque, Mexico, constitute notable exceptions from this rule ( Alvarado-Ortega et al, 2015 ; Cantalice & Alvarado-Ortega, 2016 ; Cantalice, Alvarado-Ortega & Bellwood, 2020 ), yielding well-preserved and diverse shallow water actinopterygian assemblages comprising typical Paleogene (e.g., marine osteoglossomorphs) as well as derived faunal elements (including aulostomoids, pomacentrids and other percomorphs), which foreshadow the more modern-like, acanthomorph-dominated assemblages from the early Eocene of Turkmenistan and the Kabardino-Balkaria ( Bannikov & Parin, 1997 ; Bannikov & Carnevale, 2012 ; Bannikov et al, 2017 ), Bolca, the London Clay and other localities ( Arambourg, 1967 ; Daniltshenko, 1962 ; Eastman & Grande, 1991 ; Bannikov, 1993 ; Bonde, 1997 ; Afsari et al, 2014 ; Davesne, 2017 ; Beckett et al, 2018 ; Friedman & Carnevale, 2018 ).…”

Tooth development and replacement in the Atlantic Cutlassfish, Trichiurus lepturus, with comparisons to other Scombroidei

“…In their strict consensus tree of morphological data (Beckett et al, 2018: fig. 13B), P. saltatrix and S. heterolepis are placed in a polytomy with Scombridae (represented by Gasterochisma melampus) and "Gempylidae" including Trichiuridae.…”