Proteinus undetermined
Creators: name: Jenkins Shaw, Josh
name: Bai, Ming
name: Solodovnikov, Alexey
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Proteinus
Proteinus undetermined

description: Proteinus sp.
(Figure 1 (A–F))
Material. 1 female, NHMD-36909, Baltic amber (Figure 1 (G)). Apparently previously glued to a piece of card with the number 83 written below. With the following labels ′Dr. J. Ipsen, Esbjerg /: STAPHYLINIDAE PROTEININAE det. R.A. Crowson: Proteininae? A. Solodovnikov det. 2007: Proteinini: Proteinus sp. ♀ det. A.Newton 2007̍.
Origin and horizon. The piece of Baltic amber was collected from Esbjerg, Denmark. Baltic amber is dated as 45.0–38.0 Ma (Bartonian to Priabonian, mid-late Eocene).
Description. Measurements (all in millimetres): TL: 1.4; HW: 0.39; PW: 0.5; PL: 0.27; EL: 0.64. Head. Antennae with first two antennomeres distinctly larger than following antennomeres before distinct club(Figure 1 (A,AC)).Eyes occupying almost entire side of head (Figure 1 (B, C)); mentum trapezoidal (Figure 1 (C, Mn)); gular sutures apparently separated (Figure 1 (C, Gs)). Prothorax: widest posteriorly; posterior portion of right hypomeron visible in ventral view (Figure (1D, Hyp)); prosternal process acutely pointed (Figure (1D, Pr)). Procoxae and profemora approximately equal in length; protibiae weakly expanded towards middle, parallelsided from middle to apex. Mesothorax: mesosternal process acutely pointed with distinct ridge along its length (Figure (1E, Ms)). Mesocoxae rather circular;mesofemora and mesotibae with weakly curved outer edge. Metasternum with weak and sparse punctation (Figure 1 (C, Mt)). Elytra rather long but not covering entire abdomen; apical three abdominal segments exposed (Figure 1 (B, C)). Metacoxae wide, anterior portion occupying almost entire posterior edge of metathorax (Figure 1 (C)), slightly expanded into lateral lobe (Figure (1C, MtCx)). Abdomen consisting of clearly visible sternites III to VIII (Figure 1 (C)). Apical segment of abdomen with prong-shaped sternite X and long styli on either side (Figure 1 (F)). Gonocoxal plate as in Figure 1 (F), consisting of forked median lobe (Figure 1 (F, FML)) and the lateral lobes (Figure 1 (F, LL)). The styli are not visible.
Remarks. Placement of the fossil in the subfamily Proteininae is supported by the clubbed antennae; rather widely separated gular sutures; broadly transverse pronotum; and moderately long elytra leaving abdominal segments VII, VIII and genital segments exposed. Other characters that support placement in Proteininae are unfortunately not visible – for example, absence of ocelli on the dorsal side of the head. The specimen can be assigned to the tribe Proteinini based on the simple pro-tibiae (excised internally before apex in Anepiini) and distinctive morphology of the apical abdominal segment in females (see fig. 40 in Steel 1966). It is placed in the genus Proteinus based on the clubbed antennae; trapezoidal mentum; smooth sides of pronotum (often crenulate in Megarthrus and Metopsia); short prosternum with acutely pointed prosternal process; mesosternal process with ridge; wide metacoxae occupying almost entire posterior edge of metathorax; and shortened elytra exposing abdominal segments VI to X. The specimen can be identified as a female based on the lack of any emargination on sternite VIII, which occurs in males of Proteinus, and the structure of the gonocoxal plate (Figure 1 (F)), which is very similar to females of extant Proteinus (Figure 2 (F, FML, Styli, LL)) and is characteristic of the tribe Proteinini (Proteinus, Metopsia, Megarthrus) (Steel 1966). The gonocoxal plate consists of a distinctly forked median lobe (Figure 1 (F, FML)) and lateral lobes (Figure 1 (F, LL)). In the fossil, the styli are either not visible (Figure 1 (F)) despite µ-CT scanning or absent, most likely the former. In extant species the styli can be observed between the forked median lobe and lateral lobes (Figure 2 (F)).
Since the taxonomy of the genus Proteinus is poorly known and many species are very similar to each other (Figure 2 (A, B)), a sound species identification of this fossil would require a through dissection and comparison of all extant congeners. Since species delimitation within Proteinus is largely aided by examination of the male genitalia, attempting such work based on females only was not feasible. It is likely that this fossil is an extinct species to be described as new to science if more material and thus characters become available. From the common and widespread West Palaearctic species Proteinus laevigatus (Figure 2 (C–F)), the amber fossil differs in the shorter mesothorax, much more pointed apex of the weakly notched mesosternal process, and longer styli. Such characters may be informative at the species level and worth further consideration in future works.
description: Published as part of Jenkins Shaw, Josh, Bai, Ming & Solodovnikov, Alexey, 2023, Evolutionary assessment of the rove beetle subfamily Proteininae Erichson, 1839 (Coleoptera: Staphylinidae) triggered by the X-ray based description of its first fossil in Baltic amber from Denmark, pp. 1138-1151 in Journal of Natural History 57 (17 - 20) on pages 1143-1146, DOI: 10.1080/00222933.2023.2231569, http://zenodo.org/record/8273599