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| [A-B] Amplectister terapoides n. sp. [lower] Terapus sp. (probably undescribed) from Cerrado habitats. Colonides beetle with Eciton burchellii army ants in Peru. Yamamoto & Caterino, 2022 Terapus sp. with Eciton ants photo by Taku Shimada (AntRoom, Tokyo). |
Abstract
Myrmecophily is a phenomenon of the symbiosis of organisms that depend on various ant (Formicidae) societies. Such interspecies associations are found in several unrelated lineages within the clown beetle family Histeridae. Recent studies have suggested that the origin of myrmecophily can be traced back to mid-Cretaceous based on a few fossil records from Kachin amber from northern Myanmar. Here, we describe a remarkable new species, Amplectister terapoides n. sp., from Kachin amber. This is the second species of the extinct genus Amplectister Caterino and Maddison, which has been found from the same amber deposit and has also been considered to be myrmecophilous. The new species here described has the most heavily modified hindlegs in any fossil histerids or even beetles discovered until now, indicating further evidence for ant colony association. Our discovery demonstrates that significant and diverse morphological adaptations to myrmecophily had already occurred during the Cretaceous.
Keywords: Histeridae, Mid-Cretaceous, Palaeodiversity, Inquiline, Kachin amber, Southeast Asia
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| Amplectister terapoides n. sp., holotype, SEHU-0000121201. (A) General habitus, dorsal view. (B) General habitus, ventral view. Scale bars = 0.5 mm. |
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| Amplectister terapoides n. sp., holotype, SEHU-0000121201. (A) General habitus, dorsolateral view. (B) General habitus, ventrolateral view. Scale bars = 0.5 mm. |
Systematic palaeontology
Superfamily Histeroidea Gyllenhaal, 1808
Family Histeridae Gyllenhal, 1808
Genus Amplectister Caterino and Maddison, 2018
Amplectister terapoides n. sp.
Stratigraphic position and age: Kachin amber, unnamed horizon, mid-Cretaceous (near Albian–Cenomanian boundary).
Type locality: The Noije Bum hill mines, Hukawng Valley, Kachin State, northern Myanmar.
Etymology: The species name refers to the marked similarity in modifications of the posterior legs to those in the haeteriine genus Terapus Marseul, 1863 (see Fig. 6A). That name, in turn, translates to ‘mutant foot’.
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| Extant Haeteriinae associated with Neotropical army ants (Ecitonini). (A) Terapus sp. (probably undescribed) from Cerrado habitats, with a pronotal-elytral length of 4.8 mm. (B) Colonides beetle with Eciton burchellii army ants in Peru. Photo credit for (B): ©Taku Shimada (AntRoom, Tokyo). |
Conclusions
A remarkable new fossil species of clown beetles, Amplectister terapoides n. sp., is described from mid-Cretaceous Kachin amber from northern Myanmar. Based on the well-preserved adult specimen, we could observe many morphological characters from various angles. The overall morphological characters found in the hindlegs are exceptional; they are markedly expanded and enlarged, also possessing dramatic features such as the presence of numerous peculiar, honeycomb-like large punctures on the metafemora and metatibiae, together with stiff long setae along the inner marginal surface on the metatibiae. We hypothesise that these specialised anatomical features strongly suggest the Mesozoic beetle was a true myrmecophile, a symbiont in some Cretaceous ant’s nest. Along with previous studies (Caterino and Maddison, 2018, Zhou et al., 2019), our discovery further reinforces an ancient origin of obligate behavioral symbioses between clown beetles and ants, and that these associates had diversified considerably by mid-Cretaceous.
Shûhei Yamamoto and Michael S. Caterino. 2022. A Remarkable New Fossil Species of Amplectister with Peculiar Hindleg Modifications (Coleoptera: Histeridae): Further Evidence for Myrmecophily in Cretaceous Clown Beetles. Palaeoworld. In Press. DOI: 10.1016/j.palwor.2022.09.010
