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| Rhamphoichthys taxidiotis El Hossny, Cavin, Kaplan, Schwermann, Samankassou & Friedman. 2023 Artwork by Sky Jung. |
Abstract
Only few candidates of Mesozoic fishes with a similar body plan and ecological niche to the modern billfishes are suggested as their analogues. Several specimens were recovered from Cenomanian deposits in Germany and Lebanon and display a billfish-like fusiform body with elongated premaxillae. They are found close to the plethodids and show a unique combination of characters (rostrum pointed and extremely elongated, double articular head of the quadrate, anteroposteriorly elongated abdominal centra indicating a slender body and different types of scales on the body) allowing their inclusion in a new genus. Two ‘Protosphyraena’ species are also assigned to this new genus. This fish can be considered as an ecological analogue to the extant xiphioids sharing their feeding habits. This fish was abundant and roamed, as an apex predator, the Central Tethys and the Boreal realms during the Cenomanian.
Keywords: ecological analogue, Cenomanian, billfishes, Protosphyraena, Plethodidae, Rhamphoichthys taxidiotis
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| Cranial anatomy of Rhamphoichthys taxidiotis gen. et sp. nov., holotype WMNM P 48342. (a) Photograph of the skull in left lateral view. (b) Interpretive line drawing of (a). Ang-rart, angulo-retroarticular; Ao, antorbital; Art, articular; Asp, autosphenotic; Br.r, branchiostegal rays; Ce.a, anterior ceratohyal; Cl, cleithrum; Cor, coracoid; Den, dentary; d.f, dilatator fossa; Dsp, dermosphenotic; Ecp, ectopterygoid; Enp, endopterygoid; Fr, frontal; Hm, hyomandibular; Io, infraorbitals; Mes, mesethmoid; Mpt, metapterygoid; Mx, maxillary; Na, nasal; Op, operculum; Ors, orbitosphenoid; Pa, parietal; Par, parasphenoid; Pmx, premaxillary; Pop, preoperculum; Psp, pterosphenoid; Qu, quadrate; Sc.r, sclerotic ring; Sca, scapula; So, supraorbital; Soc, supraoccipital; Sop, suboperclum; Stt, supratemporal; V, vertebrae. |
Tselfatiiformes Nelson, 1994
Plethodidae Loomis, 1900
Genus: Rhamphoichthys gen. nov.
Diagnosis. Elongate plethotid that differs from all others by the combination of the following characters: fusiform body with a slender rostrum making up half the length of the skull; presence of sclerotic ring; a broad and double-headed articular head of quadrate; hyomandibula hourglass shaped; seven broad branchiostegal rays; vertebral column with at least 100 vertebrae (55 abdominal + 40 caudal); abdominal vertebral centra elongate anteroposteriorly; dorsal fin rays very long with some rays exceeding depth of the body; hypural plate large made of fusion of hypurals 1–4 and an autogenous dorsal hypural 5; scales of different types: weakly mineralized ovoid scales, more robustly mineralized rhombic scales, bilaterally symmetrical scales with midline ridge and notch and at least one scale with a serrated posterior margin.
Etymology. From the Greek: rámfos (rhamphos) meaning beak with the suffix ichthys for fish.
Rhamphoichthys taxidiotis sp. nov.
Holotype. WMNM P 48342, articulated skull and highly disrupted postcranium.
Horizon. Lowermost horizon of upper Cenomanian of the Hesseltal Formation, Halle, Westphalia, Germany.
Etymology. From the Greek taxidiotis, meaning traveller. The combination makes it ‘the traveller fish with a beak’, reflecting the long rostrum and wide geographical distribution of this presumably pelagic taxon.
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| Reconstruction of Rhamphoichthys taxidiotis gen. et sp. nov. Artwork by Sky Jung. |
Tamara El Hossny, Lionel Cavin, Ulrich Kaplan, Achim H. Schwermann, Elias Samankassou and Matt Friedman. 2023. The First articulated Skeletons of enigmatic Late Cretaceous Billfish-like Actinopterygians. R. Soc. Open Sci.10; 231296 DOI:10.1098/rsos.231296
