[PaleoIchthyology • 2023] Rhamphoichthys taxidiotis • The First articulated Skeletons of enigmatic Late Cretaceous Billfish-like Actinopterygians (Tselfatiiformes: Plethodidae)

 Rhamphoichthys taxidiotis

El Hossny, Cavin, Kaplan, Schwermann, Samankassou & Friedman. 2023

 

 DOI:10.1098/rsos.231296 

 twitter.com/Lionel_Cavin

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

 

 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.

 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

  twitter.com/Lionel_Cavin/status/1732676420197880011

[Paleontology • 2022] Taphonomy of Drought afflicted Tetrapods in the Early Triassic Karoo Basin, South Africa

Mummified skin on spreadeagled Lystrosaurus 

in Smith, Botha & Viglietti, 2022. 

DOI: 10.1016/j.palaeo.2022.111207

Highlights: 

• Outcrop containing hundreds of Early Triassic tetrapod fossils interpreted as evidence of drought.

• Clusters of articulated skeletons interpreted as drought-induced aggregations.

• Mummified skin on spreadeagled Lystrosaurus suggest rapid desiccation after death by starvation.

• Bone histology confirms that all the Lystrosaurus were juveniles or early sub-adult.

• Bonebeds of juvenile Lystrosaurus are interpreted as sheet-washed behavioural aggregations.

Abstract

The sedimentology and taphonomy of in-situ fossils from earliest Triassic strata (Induan) in the southern Karoo Basin of South Africa is presented as evidence for episodes of drought-induced mass death of the resident tetrapods. Abundant skeletons are preserved in a 2 m-thick tabular silty-sandstone capping a multi-storeyed low-sinuosity channel sandstone interpreted as a wide shallow channel that became progressively abandoned, with more ephemeral flow regime than in the underlying channels and subjected to intermittent flows of low-density sediment-laden floodwaters. Stratigraphic and planimetric distribution of 170 in-situ tetrapod fossils shows several clusters of up to eight closely-spaced articulated Lystrosaurus skeletons preserved in prone and spread-eagled body position. These are interpreted as drought-stricken carcasses that collapsed and died of starvation in and alongside dried-up water sources. Two of the specimens display an unusual micritic envelope with a distinctive pustular texture interpreted as permineralised mummified skin indicative of rapid desiccation after death. Bonebeds of disarticulated bones of multiple juvenile Lystrosaurus occur in shallow depressions within the rubified mudstones. Layering of different skeletal elements suggests some hydraulic sorting but the initial aggregation was likely a behavioural response to drought. Osteohistology of spread-eagled Lystrosaurus (L. declivis and L. murrayi species) skeletons show that they represent early juvenile stage which is in accordance with previous findings that throughout Pangaea Early Triassic Lystrosaurus died relatively young due to environmental stressors. Our results support the hyperthermal hypothesis that ~252 Mya increased continental aridity, already a consequence of the coalescence of Pangaea, was critically intensified by volcanogenic greenhouse gasses from the Siberian traps. We propose that in the aftermath of the End-Permian mass extinction event, a succession of climatic drying episodes orchestrated a series of fully-functioning terrestrial ecosystems that were markedly different to those of the pre-extinction, and likely had a profound and lasting influence on the evolution of tetrapods.

Keywords: Early Triassic, Katberg Formation, Lystrosaurus, Drought accumulations, Bonebeds, Mummified skin

Roger M.H. Smith, Jennifer Botha and Pia A. Viglietti. 2022. Taphonomy of Drought afflicted Tetrapods in the Early Triassic Karoo Basin, South Africa. Palaeogeography, Palaeoclimatology, Palaeoecology. In Press, 111207. DOI: 10.1016/j.palaeo.2022.111207