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| Dysopodus gezei Schädel, Azar, El Hajj, Maksoud & Robin, 2025 Artwork by Aldrich Hezekiah |
Abstract
Here, we report fossil isopods preserved in laminated oil-shale mudstone (dysodile) from the Lower Cretaceous of Lebanon (Lower Barremian, 125 Ma, Grès du Liban Alloformation, Jezzine District). Based on a variety of proxies, their palaeoenvironments are determined to have been a shallow freshwater lake. The fossil isopods were studied using modern imaging techniques, such as multispectral imaging and photometric stereo, allowing for a detailed comparison of these specimens with comparable extant and fossil taxa. The conspecific fossils are herein recognized as remains of a new species—†Dysopodus gezei gen. et sp. nov.—of uncertain affinity within Cymothoida and bearing a strong resemblance to its non-parasitic lineages (Cirolanidae). A conspicuous pleotelson and uropod morphology set it apart from most species, with the notable exception of †Pseudoplakolana chiapaneca gen. nov. et comb. nov. from the Cretaceous of Mexico, originally attributed to an Australasian lineage (herein disputed). So far, the biogeographical distribution of the peri-Mediterranean underground fauna has predominantly been explained through a passive isolation process of former marine species, driven by regressing coastlines. Stemming from a freshwater lake environment, the 125 million-year-old fossils from Lebanon provide an unconventional perspective on the evolutionary origin of extant cave- and groundwater-dwelling cymothoidans.
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| †Dysopodus gezei gen. et sp. nov., holotype CRU 63124/1, micro-photographic images. (a) coaxial white light, cross-polarized. (b) visible light-induced luminescence, excitation maximum 435 nm (violet), collected light 835 nm ± 70 nm (infrared). (c) false-colour image derived from multispectral imaging, blue channel: excitation maximum 385 nm (UV), collected light 360 nm ± 23 nm (UV), green channel: excitation maximum 490 nm (cyan), collected light 571 nm ± 72 nm (yellow), red channel: excitation maximum 435 nm (violet), collected light 835 nm ± 70 nm. Scale bar: 3 mm. at, antenna; atl, antennula; c, carpus; plt, pleotelson; pp, propodus; pr1−2, pereonites 1−2; un, uropodal endopod; ux, uropodal exopod; ?, unknown structure, likely not part of the isopod. |
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| Palaeoenvironmental habitat reconstruction for †Dysopodus gezei gen. et sp. nov. (foreground) - a Barremian freshwater lake in the region of present-day Bkassine (Lebanon). Artwork by Aldrich Hezekiah. |
Mario Schädel, Dany Azar, Layla El Hajj, Sibelle Maksoud and Ninon Robin. 2025. A 125 Million-year-old freshwater Isopod shines new light on the Origin of Subterranean Freshwater Species. R. Soc. Open Sci. 12; 241512. DOI: doi.org/10.1098/rsos.241512 [02 April 2025]
