Cretomalus tibiodentatus, 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 : 6-8

Cretomalus tibiodentatus sp. nov.

( Fig. 5 )

Material: Kachin amber (c. 99 Mya). Amber piece dimensions: 13 × 8 × 1.5 mm. Amber clear with several insect fragments and air bubbles. Deposited at HUM ( SEHU-0000121215 ) .

Measurements: Head width: 0.32 mm; width between anterior pronotal angles: 0.35 mm; width between posterior pronotal angles: 0.55 mm; pronotal length: 0.5 mm; sutural elytral length: 0.73 mm; elytral width (in pair, across widest point): 0.53 mm.— Body elongate, rectangular, parallel-sided, and flattened. Cuticle sparsely punctuate dorsally, smooth ventrally. Colour black to chestnut brown.— Head: Frons weakly convex, finely punctuate, punctures separated by three times their diameter. Frontoclypeal suture not evident; frontal stria thin, complete.Labrum short, trapezoidal, with several pairs of prominent setae.Mouthparts retracted. Eyes not visible from above.Scape short, expanded apically, pedicel simple, as long as antennomeres 3–4 combined. Antennomeres 3–8 wide and short (width: length ratio 1.5: 1), almost rectangular. Antennal club round, dorsoventrally flattened, annuli well visible.— Thorax: Pronotum as wide as long (width: length ratio 1: 1), median portion of disk flat, sides curved ventrad. Anterior emarginationdeep,anterioranglesacute,convergentanteriad.Basal pronotal margin rounded. Marginal pronotal stria complete along lateral and anterior margins. Pronotum punctuate, punctures separated by two to three times their diameter.Scutellum not visible (obscured by bubbles). Elytra long and narrow, punctuation density as in pronotum. Sutural area slightly depressed (possibly deformed postmortem), then elevated medially forming a keel. Dorsal elytral striation absent; elytral epipleuron obscured. Prosternal lobe deflexed, long, wide, rounded anteriorly. Prosternal keel with fine punctuation.Prosternalstriationindeterminableduetoairbubbles. Basal prosternal margin rounded, projecting posteriorly. Antennal cavities vaguely defined and widely open, located posterolaterally (covered by the front leg when retracted). Mesoventrite very short and wide (1: 3 ratio). Anterior margin curved posteriorly to fit the basal prosternal margin. Punctuation not apparent. Marginal mesoventral stria complete, continuous with lateral metaventral stria. Transverse mesoventral stria not visible. Metaventrite large, weakly concave, slightly elevated anterad metacoxae, without apparent punctuation. Lateral metaventral striae present and extending posterolaterad on at least anterior half. Postmesocoxal striae present and extending posteriorly. Sides of meso- and metaventrites (and abdominal ventrites) ascending laterad coxae, oblique.— Legs: Profemur flattened and broad. Protibia broad and strongly curved, withsix to seven small, symmetrical teeth along the outer margin. Protarsal groove weakly developed. Small inner and curved median protibial spurs present. Protarsomere 5 as long as protarsomeres 1–4 combined. Protarsal claws short. Mesofemur narrower than profemur, mesotibia smooth, spur present. Terminal mesotarsomere as long as mesotarsomeres 3–4 combined. Hindleg equivalent to middle leg.— Abdomen: First visible abdominal sternite large, intercoxal disc almost square-shaped, with very fine, sparse punctuation (punctures separated by at least 10 times their diameter). Lateral striae strongly impressed, complete, running posterolaterad. Postmetacoxal striae present, curved along metacoxae. Other sternites with identical punctuation pattern. Pygidium strongly convex, apex subtruncate, rugose.

Taxonomic assignment: We place this species in the Paromalini tribe based on the combination of the following characters ( Ôhara 1994): broad, weakly convex frons ( Fig. 5A ), short and wide labrum with several pairs of prominent setae, short and wide prosternal lobe, vaguely defined antennal cavities located at prosternal hypomeron, basal prosternal margin rounded and projecting posteriorly, wide, curving protibia with a laterally directed median apical spur. The position of this genus in Paromalini is also supported by all phylogenetic analyses performed in this study. Within extant Paromalini , possession of dorsal elytral striae in several genera (e.g. Carcinops Marseul and Diplostix Bickhardt ) is probably plesiomorphic, while their absence is apomorphic in others ( Paromalus Erichson , Platylomalus Cooman ) ( Zhou et al. 2020). Cretomalus tibiodentatus would appear to be more closely related to the latter, particularly to Paromalus , with which it shares several characters: absence of prosternal striation and complete frontal stria ( Fig. 6A ) ( Zhang and Zhou 2007). Cretomalus tibiodentatus is significantly smaller than all Paromalus species. The serrated protibial margin ( Fig. 5E ) is unique among the entire tribe.

Diagnosis: Frons weakly convex and finely punctuate, punctures separated by three times their diameter. Pronotum relatively long, punctuated with punctures separated by two to three times their diameter. Elytra without striation, punctuation with the same pattern as in pronotum. Prosternal keel with fine punctuation. Marginal mesoventral stria complete, continuous with lateral metaventral stria. Transverse mesoventral stria not visible. Lateral metaventral striae present, extending posterolaterad on at least anterior half. Postmesocoxal striae present, running posteriorly. Protibia wide and strongly curved, with six to seven small, symmetrical teeth along the outer margin. Protarsal groove weakly developed. Small inner and curved median protibial spurs present. Similarly shaped Histeridae found in Burmese amber are Platycretus muscularis Simon-Pražák and Lackner, 2023, Olexum complanatum Simon-Pražák and Lackner, 2023, and Druantia aeterna Caterino, 2021 . Cretomalus tibiodentatus can be distinguished from all of them by combination of following characters: long and narrow body (length: width 5: 2), shape of the prosterno-mesoventral suture (with a curved anteriorly pointed projection) and the state of regularly toothed protibia.

Etymology: The specific name refers to the unique protibial dentation.

Figures

Figure 5. Cretomalus tibiodentatus gen. et sp. nov. A, dorsal view.B, ventral view; C, postmetacoxal area. D, postmesocoxal area. E, front leg and antenna. Abbreviations: fs, frontal stria; las, lateral stria on first abdominal ventrite; lms, lateral metaventral stria; pl, prosternal lobe; pms, prosternomesoventral stria; pmss, postmesocoxal stria; pmts, postmetacoxal stria.

Figure 6. Anapleus punctulatus sp.nov.. A, dorsal view.B, elytral epipleuron. C, ventral view.D, frontal view.Abbreviations:ees, elytral epipleural striae; lps, lateral pronotal stria; mes, marginal elytral stria; mps, marginal prosternal stria; ms, metaventral stria.