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| Cretophengodes azari Li, Kundrata, Tihelka & Cai, in Li, Kundrata, Tihelka, Liu, Huang et Cai, 2021. |
Abstract
Bioluminescent beetles of the superfamily Elateroidea (fireflies, fire beetles, glow-worms) are the most speciose group of terrestrial light-producing animals. The evolution of bioluminescence in elateroids is associated with unusual morphological modifications, such as soft-bodiedness and neoteny, but the fragmentary nature of the fossil record discloses little about the origin of these adaptations. We report the discovery of a new bioluminescent elateroid beetle family from the mid-Cretaceous of northern Myanmar (ca 99 Ma), Cretophengodidae fam. nov. Cretophengodes azari gen. et sp. nov. belongs to the bioluminescent lampyroid clade, and would appear to represent a transitional fossil linking the soft-bodied Phengodidae + Rhagophthalmidae clade and hard-bodied elateroids. The fossil male possesses a light organ on the abdomen which presumably served a defensive function, documenting a Cretaceous radiation of bioluminescent beetles coinciding with the diversification of major insectivore groups such as frogs and stem-group birds. The discovery adds a key branch to the elateroid tree of life and sheds light on the evolution of soft-bodiedness and the historical biogeography of elateroid beetles.
Order Coleoptera Linnaeus, 1758
Suborder Polyphaga Emery, 1886
Superfamily Elateroidea Leach, 1815
Cretophengodidae Li, Kundrata, Tihelka and Cai fam. nov.
Type genus. Cretophengodes gen. nov.
Diagnosis (male). Mandibles slender, sickle-shaped. Frontoclypeal region moderately declined anteriorly. Eyes large, strongly protruding. Antennae 12-segmented; antennomere 1 stout, expanding apically; antennomeres 2 and 3 short; antennomeres 4–11 elongate, bipectinate. Prosternum in front of coxae longer than diameter of procoxal cavity. Prosternal process narrow and elongate, acute apically, reaching posterior edge of procoxae. Elytra oblong, sub-parallel sided, nearly completely covering abdomen, leaving at most only apex of ultimate tergite exposed. Tarsal formula 5-5-5; tarsomeres 2–4 each with membranous lobe. Abdomen with six apparently immovable ventrites; photic organ present on median portions of the basal three abdominal ventrites.
Composition and distribution. Monogeneric, with Cretophengodes gen. nov. known only from mid-Cretaceous Burmese amber.
Cretophengodes Li, Kundrata, Tihelka and Cai gen. nov.
Etymology. The generic name is derived partly from ‘Cretaceous’, in reference to the age of the fossil, and the genus Phengodes, the type genus of the morphologically similar and presumably closely related Phengodidae. The gender is masculine.
Diagnosis. As for the family with additional characters: body moderate (approx. 7.3 mm long); pronotum sub-pentagonal, wider than long; elytra irregularly punctate, with several raised interstrial intervals forming indistinct carinae; claws simple.
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| General habitus of Cretophengodidae and representatives of the closely related Phengodidae and Rhagophthalmidae, under incident light. (a, b) Cretophengodes azari gen. et sp. nov., dorsal and ventral views, respectively, with arrowhead showing the photic organ. (c, d) Zarhipis sp. (Phengodidae), dorsal and ventral views, respectively. (e, f) Rhagophthalmus sp. (Rhagophthalmidae), dorsal and ventral views, respectively. Scale bars: (a,b,e,f) 2 mm; (c,d) 4 mm. (Online version in colour.) |
Cretophengodes azari Li, Kundrata, Tihelka and Cai sp. nov.
Etymology. After Prof. Dany Azar, palaeoentomologist extraordinaire.
Type material. Holotype, NIGP173775, male, mid-Cretaceous (upper Albian to lower Cenomanian [26,27]), from amber mine near Noije Bum Village, Hukawng Valley, Tanai Township, Myitkyina District, Kachin State, northern Myanmar.
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| Geographical distribution of Cretophengodidae (genus Cretophengodes), Phengodidae (subfamilies Cydistinae, Mastinocerinae and Phengodinae) and Rhagophthalmidae. World map adapted from Natural Earth (NaturalEarthData.com). |
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| Artistic reconstruction of Cretophengodes azari gen. et sp. nov. The larviform female in the background is reconstructed based on extant Phengodidae and Rhagophthalmidae. |
Yan-Da Li, Robin Kundrata, Erik Tihelka, Zhenhua Liu, Diying Huang and Chenyang Cai. 2024. Cretophengodidae, A New Cretaceous Beetle Family, sheds light on the Evolution of Bioluminescence. Proc. R. Soc. B. 288: 20202730