Cnopus twentyonepilotorum Ferreira & Nel 2026, sp. nov.
Year: 2026
Type: article
Abstract: †Cnopus twentyonepilotorumFerreira & Nel sp. nov. Figs 1, 2 Type material. Holotype C 05038, deposited in the Centre de Recherche en Paléontologie (CR 2 P), Museum National d'Histoire Naturelle (MNHN), Paris, France; lowermost Eocene, Oise amber, Le Quesnoy, France. Differential diagnosis. The new species can be confidently assigned to Aderidae based on the combination of characters typical of the family, including: tenebrionoid tarsal formula 5-5 - 4, but appearing as 4-4 - 3 due to the reduced penultimate tarsomere; antepenultimate tarsomere lobed beneath (Fig. 2 G, H); and the first two abdominal ventrites being partly connate (Fig. 2 C) (Grzymala 2016). It is further characterised by the following combination of characters: (i) minute body size (Fig. 2 A – C), (ii) antennomeres II and III longer than antennomere IV, (iii) antennomeres V – VII subequal in length and width, (iv) antennomere VIII approx. as long as wide, (v) antennomeres IX – X longer than wide, (vi) antennomere XI almost as long as antennomeres IX – X together (Fig. 2 D – F), (vii) pronotum with distinct paired basal foveal depressions (Fig. 2 D), (viii) pronotum with two distinct, deep, circular dimples antero-laterally to basal margin (Fig. 2 D), (ix) two shallow lateral triangular impressions at anterior pronotal angles (Fig. 2 D), (x) elytra with uniseriate pubescence (Fig. 1 B), (xi) metafemora without any excavation or modified setal comb or brush (Fig. 2 H, I), and (xii) metatarsomeres I shorter than combined lengths of the three other ones (Fig. 2 H). In her key to Aderidae genera, Grzymala (2016) characterised Cnopus by the following combination of characters: ‘ Pronotum with distinct subbasal transverse sulcus; eyes strongly protuberant, without or with slight anterior emargination (Scraptogetus, “ Xyloconstrictus ” [= Cedraderus], Cnopus) ’; ‘ Without subapical transverse sulcus; ventrites I and II connate, with suture indicated only laterally; Small size for family (1.0– 1.4 mm) ’. But Gompel (2024) indicated that the ‘ Pronotum […] with a distinct and deep subbasal transverse sulcus extending to the lateral sides’ characterises the genus Cedraderus while the other Nearctic Aderidae (including Cnopus) have the ‘ Pronotum devoid of subbasal transverse sulcus, at most with dimples on both sides of dorsal midline sometimes connected by a shallow groove’. This apparent discrepancy probably reflects a difference in what is considered a sulcus; the paired basal dimples of Cnopus, which may be connected by a shallow groove (Gompel 2024), may have been interpreted as a subbasal transverse sulcus by Grzymala (2016). That being said, Grzymala considered Cnopus on a worldwide scale, whereas Gompel only treated the Nearctic fauna. The discrepancy may therefore reflect differences in the geographic scope of the two studies rather than a true conflict in character interpretation. The new fossil cannot be attributed to Cedraderus because the pronotum is narrower than head, instead of as wide as the head in the latter genus. Gompel and Barrau (2002) indicated that Cnopus has a ‘ head with a neck’, instead of a ‘ head without neck, sunken in thorax’ in the other extant Aderidae from France. The presence of a distinct margin of the head, posterior to the compound eyes, further suggests an attribution to Cnopus. Gompel and Barrau (2002) added that Cnopus can be differentiated from the other French Aderidae by the compound eyes without anterior emargination. It is the case in the new fossil. Following the key to Nearctic aderid genera of Gompel (2024), the new fossil would fall in Cnopus because of the following characters: (i) underside of abdomen without an elevated plate; (ii) metafemur devoid of ventral brush, at most with an inconspicuous, elongate, seta-filled pit (this area could not be seen directly due to the poor preservation of ventral side of the body of the specimen, but no trace of specialised pit or setae was discernible on the synchrotron 2 D scan slices and renderings); (iii) sides of pronotum without tooth; (iv) eyes not separated by a narrow space in frontal view (less than one eye diameter); (v) antennomeres II and III longer than antennomere IV; (vi) pronotum without sharply marked anterior angles; (vii) elytra with uniseriate pubescence; (viii) transverse pronotum; (ix) pronotum with two distinct, deep, circular dimples antero-laterally to basal margin; (x) metatarsomere I shorter than tarsomeres II – IV combined. Grzymala (2016) proposed the following genus diagnosis for Cnopus: (i) the minute body size, with a total body length from 1.1 to 1.4 mm, (ii) uniseriate elytral pubescence, (iii) deep basal pronotal fovea, (iv) metafemora lacking any modified setae, and (v) the metatarsomere I shorter than metatarsomeres II – III combined. All but character (v) fit with the new fossil. The latter character proposed by Grzymala does not fit with the diagnostic character proposed for the genus by Gompel (2024) who indicated that tarsomere I is shorter than II – IV, which agrees with the discussed fossil. Beyond this difference in the exact proportions, both authors agree that in Cnopus the metatarsomere I is short relative to the following metatarsomeres combined. Based on these arguments, the new fossil is recognised within the genus Cnopus. The main character supporting this assignment is the first metatarsomere, shorter than metatarsomeres II – IV combined, a feature unique to the genus (Gompel 2024), together with its overall habitus, minute size, bulging eyes and transverse pronotum. However, extant species of Cnopus are distinguished by characters of the terminalia (Gompel et al. 2022), which are not preserved in the fossil (as confirmed during the 3 D imaging investigation conducted at the synchrotron ALBA). The external characters preserved in the fossil do not allow it to be distinguished with certainty from all extant congeners. However, given the age of the specimen, it is highly unlikely that it belongs to an extant species. Furthermore, the new species is notably characterised by the antennomeres V – VII subequal in length and width, antennomere VIII approximately as long as wide, antennomeres IX – X longer than wide, and antennomere XI nearly as long as antennomeres IX – X combined. These proportions are described here as part of the overall morphology of the species, but they should not be regarded as diagnostic. In extant Cnopus, antennomeres IV – VII are generally subequal in length and width, antennomeres VIII – X are slightly shorter and broader, and antennomere XI is nearly as long as antennomeres IX – X combined (Gompel et al. 2022). However, the relative size and shape of the antennomeres vary between species, within species, and often even between the two antennae of a single specimen. Similar proportions also occur in some extant species, notably C. minor (Baudi di Selve, 1877) (Gompel et al. 2022). Given this variability, and the fact that the description is based on a single fossil specimen, antennal proportions seem to be of limited taxonomic value in this genus. The new species was compared with C. minor, the only extant species of the genus known from the western Palaearctic. Both species have a head strongly transverse and wider than the pronotum, large, convex and protruding eyes, paired basal pronotal foveae and anterior pronotal impressions (Alekseev and Grzymala 2015; Gompel et al. 2022). The new species differs from C. minor in its more elongate body, ~ 2.5 × as long as wide. In C. minor the body is “ stocky and depressed ” (Gompel et al. 2022), and it is 1.9–2.4 × as long as wide in the generic description (Grzymala 2016). The new species is also slightly smaller (SBL ≈ 1.09 mm vs 1.12–1.45 mm in C. minor). However, Gompel et al. (2022) showed that the external morphology of C. minor varies in size, colouration, pronotal shape, and antennal slenderness. In the absence of genitalic characters, these differences should therefore be considered with caution. Nonetheless, the new species also has a proportionally longer pronotum relative to the elytra than indicated in the generic description of Cnopus. Its elytra are ~ 3.7 × as long as the pronotum, compared with ~ 4.1 × according to Grzymala (2016). Finally, the new species differs from the fossil species † C. kraxtepellenensis Alekseev & Grzymala, 2015, described from the Bitterfeld and Baltic ambers, by the presence of shallow anterior pronotal impressions (lacking in † C. kraxtepellenensis); the pronotum with distinct paired basal foveal depressions and with two distinct, deep, circular dimples antero-laterally to basal margin (one arcuate well-defined and deep sub-basal transverse impression and no deep circular punctures antero-laterally to basal margin in † C. kraxtepellenensis) (Alekseev and Grzymala 2015). Note. If the suprageneric classifications proposed for the family by Grzymala (2016) were adopted, the new species would be placed in the subfamily Cnopinae (sensu Grzymala 2016), which comprises Cnopus, Scraptogetus, and Cedraderus. This placement follows from its assignment to Cnopus. It shows all the characters that set Cnopus apart from other aderid genera, including the minute body size, uniseriate elytral pubescence (Fig. 1 B), deep basal pronotal foveae (Fig. 2 D), simple legs (Fig. 2 H, I), and first metatarsomere shorter than tarsomeres II – IV combined (Grzymala 2016; Gompel 2024). However, the placement within Werner’s (1990) groups cannot be assessed, because they are defined by male genitalic characters, which are not preserved in the fossil. Since neither of these classifications has been formally adopted (see Introduction), we refrain from using these names formally. Description. Measurements. EL ≈ 0.67 mm; EW ≈ 0.43 mm; HL ≈ 0.24 mm; HW ≈ 0.34 mm (including the eyes); MTIL ≈ 0.028 mm; MTII – IVL ≈ 0.043 mm; PL ≈ 0.18 mm; PW ≈ 0.27 mm; SBL ≈ 1.09 mm. Habitus. Very small size (SBL ≈ 1.09 mm). Body length ~ 2.5 × width (Fig. 2 A
Language: English
Topic: Fossil Insects in Amber
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7225636482
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