Pseudacritus extinctus, Jan & ºimon-Pražák & Yamamoto & Lackner & Fikáček & Prokop & Michael & Caterino, 2024

Simon-Pražák, Jan, Yamamoto, Shûhei, Lackner, Tomáš, Fikáček, Martin, Prokop, Jakub & Caterino, Michael S, 2024, A bonanza of Cretaceous fossils provides insights into the evolution of antennal protection in clown beetles (Coleoptera: Histeridae), Zoological Journal of the Linnean Society (zlae 137) 202 (3), pp. 1-28 : 13-16

Pseudacritus extinctus sp. nov.

( Fig. 9 )

Material: Kachin amber (c. 99 Mya). Amber piece dimensions: 16 × 5 × 2 mm. Amber clear with a large Hymenoptera fragment, a single specimen of Trogossitidae and large pieces of debris. Deposited at MEBHK ( P1423/E ) .

Measurements: Head width: 0.3 mm; width between anterior pronotal angles: 0.34 mm; width between posterior pronotal angles: 0.68 mm; pronotal length: 0.4 mm; sutural elytral length: 0.48 mm; elytral width (in pair, across widest point): 0.7 mm.— Body: Round and dorsoventrally convex, brown in colour.— Head: Without frontal stria. Frons smooth, slightly convex. Clypeus basally constricted, widening anteriorly. Labial as well as maxillary palpi exposed, the latter rather short, wide. Labrum with a transverse carinate median ridge, with a pair of prominent setae and several shorter setae. Terminal maxillary palpomere oval and pointed. Terminal labial palpomere short, pointed. Eyes large, convex. Antennal scape thickened, as long as antennomeres 2–7 combined. Pedicel approximately third scape’s length, wider basally. Club large, oval, flattened, with two distinct annuli.— Thorax: Pronotal disc almost smooth, with widely isolated small punctures and with a complete, punctuate antescutellar stria. Anterior corners acute. Marginal stria present. Lateral pronotal stria carinate, slightly expanding over pronotal margin medially and gradually distanced from pronotal margin basally. Scutellar shield small, triangular. Elytra dorsally with four weak costae. Elytral epipleuron concave, epipleural stria obscured. Elytral humeri with four short distinct costate striae. Prosternal keel short and wide, largely unobservable, laterally incised for the antennal passage. Round and relatively well-developed antennal cavities located at the anteriormost part of the prosternal hypomeron. Hypomeron excavate, creating a depression shaped to receive the profemur and protibia. When retracted the protibial would probably conceal the antennal club. Mesoventrite obscured by legs and fracturing. Metaventrite very finely punctuated, with a median depression, which may be an artefact. Postmesocoxal stria complete, recurved along mesocoxa. Lateral metaventral stria complete, continuous on to metepisternum. Metepisternum exposed.— Legs: All femora and tibiae thin, laterally flattened. Tarsal formula 5-5-5, ultimate tarsomeres as long as the preceding two.— Abdomen: First abdominal ventrite wide, with thin and complete postmetacoxal striae. Pygidium triangular, laterobasally with depressions, apex with a single short groove medially. Propygidium short and broad, with irregular depressions.

Taxonomic assignment: This species can be tentatively placed in the Abraeinae subfamily, based on the absence of a distinct pronotal lobe, small body size of round shape, and strongly convex eyes ( Fig. 9A ). This position was also supported by all phylogenetic analyses. The species bears characters strikingly similar to the extant Acritini : position of the antennal cavity at the frontmost part of prosternal hypomeron ( Fig. 9C ) and the presence of an antescutellar stria on the pronotal disc ( Fig. 9A, D ). However, it lacks the key defining feature of Acritini , the four-segmented metatarsi. Moreover, the species exhibits a plesiomorphic annulate antennal club ( Fig. 9C ), as opposed to most recent Abraeinae , except Acritomorphini ( Wenzel 1944, Mazur 1997). Recent Acritomorphini , however, have an oblong, elongated body shape. Hence, the placement within a tribe is uncertain.

Diagnosis: Pronotum with antescutellar stria and small widely separated punctures.Elytra with four low costae and without an epipleural stria. Postmesocoxal stria complete, recurved along mesocoxa. Lateral metaventral stria complete, continuous onto metepisternum. The species can be distinguished from Palaeabraeus glabrus (the only similar abraeine reported from Burmese ambers) by the presence of antescutellar stria, the anterior position of antennal cavities, presence of elytral costae, and absence of elytral epipleural stria.

Etymology: The specific name signifies the species’ extinct status.

Figures

Figure 9. Pseudacritus extinctus gen.et sp. nov.. A, dorsal view.B, ventral view. C, lateroventral view.D, antenna. E, frontal view. F, pronotal base. Abbreviations:aca, antennal cavity; acl, antennal club; as, antennal scape; ass, antescutellar stria; lab, labrum; mp, maxillary palpus; sd, scutellar disc.