Two new species of the family Rhynchitidae (Coleoptera: Curculionoidea) from Eocene Baltic amber, with key to species and assumed trophic relationships

Two new fossil species of Baltocar Kuschel, 1992 and Pseudomesauletes Legalov, 2001 (Curculionoidea: Rhynchitidae) are described from Eocene Baltic amber. Baltocar sontagae sp. nov. is similar to B. groehni Riedel, 2012 but differs in the shorter rostrum, tarsomere 1 shorter than tarsomere 5 and 1.4× as long as tarsomere 2, longer elytra, and shorter body. Pseudomesauletes lobanovi sp. nov. is similar to P. culex (Scudder, 1893) and P. ibis (Wickham, 1912): the new species differs from P. culex in the larger eyes, longer pronotum, being 0.44× shorter than elytra, and slightly smaller body size; from P. ibis it differs in the smaller body size, rostrum shorter than elytra, and weakly convex pronotum. This is the first record of Pseudomesauletes from Baltic amber and the sixth species of Baltocar. Keys to species of the genus Baltocar and to the Eocene species of the genus Pseudomesauletes are given. Assumed trophic relationships of these fossil taxa are discussed (urn:lsid:zoobank.org:pub:260EBE6E-DA6C-4D6DA1D2-2C258224622F).


Introduction
Beetles of the family Rhynchitidae have more than 2000 described species in the Holocene fauna (Legalov, 2015a). Representatives of this family are distributed almost everywhere, with the centre of diversity in the tropics and subtropics (Legalov, 2007). The rhynchitid larvae develop in the dead parts of the plant, usually gnawed by the female (Legalov, 2004). Thirty-five species were found in the fossil record (Legalov, 2015b;Bukejs and Legalov, 2019;Kania and Legalov, 2019). The earliest Rhynchitidae are known from the Cenomanian of Botswana and the Turonian New Jersey amber (Gratshev and Zherikhin, 2000;Legalov, 2015b). They are found in the Paleocene of France (Legalov, 2020b), the Eocene of the USA and Europe (Legalov, 2015b(Legalov, , 2020b, the Oligocene of Europe (Legalov, 2020b), the Miocene of Germany (Heer, 1847), and also Dominican and Mexican amber (Poinar and Brown, 2007;Poinar and Legalov, 2015). Nine rhynchitid species are described from Eocene Baltic amber (Voss, 1953;Legalov, 2012Legalov, , 2013Legalov, , 2015bLegalov, , 2020aKania and Legalov, 2019). The extinct genus Baltocar Kuschel, 1992 includes five species Legalov, 2015bLegalov, , 2020a. A new species of this genus is discovered in examined Baltic amber material. The fossil species of the genus Pseudomesauletes Legalov, 2001 were known from Rovno amber (Bukejs and Legalov, 2019) and Florissant (Legalov, 2015b). A newly described species is the first record of this genus from the Baltic amber.

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A. Bukejs and A. A. Legalov: Two new species of the family Rhynchitidae (Coleoptera: Curculionoidea) allowing improved views of the included specimens and were not subjected to any supplementary fixation.
The photographs of specimens were taken using a Canon 70D camera with a macro lens (Canon MP-E 65 mm). Extended depth of field at high magnifications was achieved by combining multiple images from a range of focal planes using Helicon Focus v. 6.0.18 software, and the resulting images were edited to create figures using Adobe Photoshop CS5.
The X-ray micro-CT observations of specimen 6703 (MAIG) were conducted at Daugavpils University, Daugavpils, Latvia (DU), using a Zeiss Xradia 510 Versa system. Scans were performed with a polychromatic X-ray beam at an energy of 40 kV and power of 3 W. Sample-to-detector distance was set to 17.5 mm, and source-to-sample distance was 47.7 mm. Tomographic slices were generated from 3001 rotational steps through a 360 • rotation, using a 4× objective. The exposure time during each projection was set to 5 s. Acquired images were binned (2 × 2 × 2), giving a voxel size of 4.87 µm. Images were imported into the Dragonfly PRO (ver. 4.1) software platform for interactive segmentation and 3D visualization.

Etymology
Patronymic. This new species is named in honour of our colleague Elżbieta Sontag (Gdańsk, Poland), who provided us the opportunity to study this interesting fossil specimen.

Type stratum
A predominantly Bartonian age (41.3-37.9 Ma) is interpreted for the extinct central European resin-producing forests, which produced the amber that has eroded out of Eocene Blue Earth layers . However, the vast majority of Baltic amber derives from the geological amber-bearing strata of the certainly Priabonian age (37.8-33.9 Ma) (Sadowski et al., 2017(Sadowski et al., , 2020.
Head. Forehead flat, with middle furrow; vertex convex, covered with sparse and fine punctation; temples 0.6× as long as horizontal diameter of one eye, with sparse and fine punctation. Rostrum rather long, 1.1 times as long as pronotum, slightly curved (in lateral view), widened apically (in dorsal view), about 5.1× as long as wide basally, 6.8× as long as wide medially, and 4.1× as long as wide apically; covered with very fine and sparse punctures. Compound eyes large, oval, strongly convex, vertical diameter about 0.7× as horizontal diameter. Maxillary palpi with four palpomeres.
Pronotum. Bell-shaped, elongate, 1.6× as long as wide at apex, 1.4× as long as wide in middle and at base, widest in posterior one-fifth, gradually narrowed anteriad; moderately densely covered with small punctuation; irregularly rugose; disc flat; lateral margins straight, posterior margin distinctly convex, anterior margin convex in dorsal view. Scutellum. Minute, subtriangular, poorly visible in studied specimen.
Elytra. Widely oval, elongate, convex, 2.3× as long as wide combined at anterior margin, 1.5× as long as wide combined medially, 2.0× as long as wide combined in posterior one-quarter, widest behind middle, 2.4× as long as pronotum; elytral base concave, distinctly wider than poste-rior pronotal margin; humeral callus weak; elytral punctation small and rather dense (punctures at lateral sides distinctly sparser), forming regular rows, distance between punctures in rows equal to 0.7-2.0× diameter of puncture, intervals slightly convex, distance between rows about 2.0-3.5× diameter of puncture.
Thorax. Prohypomera with fine and rather sparse punctation. Pre-and postcoxal parts of prosternum short, subequal in length. Epipleuron narrow, with fine punctures. Metaventrite with small punctation at lateral sides; disc convex. Metepisternum narrow, about 6.3× as long as wide medially; with fine punctation.

Note
Sex of examined specimen determined based on micro-CT results. There is no sclerotized structure resembling aedeagus inside the abdominal cavity; therefore, the specimen appears to be female.

Comparison
Baltocar sontagae sp. nov. is similar to B. groehni Riedel, 2012 but differs in the shorter rostrum; tarsomere 1 shorter than tarsomere 5 and 1.4 times as long as tarsomere 2; longer elytra and shorter body.

Remarks
The studied amber specimen possesses the combination of characters corresponding to the family Rhynchitidae: antennae not geniculate, quite long ventrites 3 and 4, narrow epipleuron, tarsal claws free at base, not extended tarsomere 1. Strongly divergent tarsal claws suggest placement in the subfamily Sayrevilleinae and tarsal claws lacking teeth assignments of the specimen to the tribe Sayrevilleini. The new species belongs to the genus Baltocar based on the short precoxal portion of the prosternum and forehead with middle furrow.

Type stratum
A predominantly Bartonian age (41.3-37.9 Ma) is interpreted for the extinct central European resin-producing forests, which produced the amber that has eroded out of Eocene Blue Earth layers . However, the vast majority of Baltic amber derives from the geological amber-bearing strata of the certainly Priabonian age (37.8-33.9 Ma) (Sadowski et al., 2017(Sadowski et al., , 2020.
Head. Dorsally covered with small, sparse punctation, distance between punctures about 0.5-1.5 × diameter of one puncture, ventrally with sharp transverse wrinkles and very sparse punctation; forehead wide, convex; vertex slightly impressed. Rostrum very long, about 1.9× as long as pronotal length, almost straight (in lateral view), widened to apex (in dorsal view), about 6× as long as wide basally, 9.5× as long as wide medially, and 6× as long as wide apically; sparsely covered with fine punctures, punctation denser in basal portion; with longitudinal carina in basal one-third of rostral length. Rostral pleurostomal sinus deep and membranous. Mandibles externally dentated. Maxillary palpi four-articled. Gular suture single. Compound eyes rather large, subspherical, strongly convex.
Pronotum. Nearly as long as wide, widest medially, narrowed posteriad and anteriad; densely covered with small punctation (punctures distinctly larger than punctures of head), distance between punctures about 0.3-1.1× diameter of one puncture (punctation on disc sparser); disc evenly convex; lateral margins convex medially and subparallel anteriorly and posteriorly, posterior margin straight, anterior margin convex in dorsal view.
Scutellum. Subpentagonal with widely rounded apex, transverse, about 1.25× as wide as long, rather large, densely covered with fine punctation.
Elytra. Almost rectangular, elongated, widest behind middle, convex, not ribbed, in anterior one-third slightly impressed medially; elytral base distinctly wider than posterior pronotal margin; humeral callus weak; elytral punctation small and dense, forming regular rows (distinct in basal half), intervals flat; elytral apices rounded together, without large depressed spots and hair stains.

Note
The specimen is a female: elytral apex lacks hair stains, and abdominal ventrites 1-3 are fussed.

Comparison
Pseudomesauletes lobanovi sp. nov. is similar to the North American Eocene species P. culex (Scudder, 1893) and P. ibis (Wickham, 1912), in the long rostrum, almost equal to the length of the elytra. The new species differs from P. culex in the large eyes; longer pronotum, 0.44× shorter than elytra (0.25× shorter than elytra in P. culex); and slightly smaller body size. It differs from P. ibis in the small body size, rostrum shorter than elytra, and weakly convex pronotum. Additionally, the new species differs from P. groehni Bukejs et Legalov, 2019 from Rovno amber in the long rostrum and narrower antennae club.

Remarks
The studied amber specimen belongs to the family Rhynchitidae based on the not geniculate antennae, single gular suture, narrow epipleuron, four-articled maxillary palpi, ventrites 2 and 3 subequal in length, not extended tarsomere 1, tarsal claws free at base, and deep and membranous rostral pleurostomal sinus. Slightly divergent tarsal claws suggest its placement in the subfamily Rhynchitinae and externally dentated mandibles -in the supertribe Rhynchititae. Rounded apex of the elytra when both together confirm the assignment of the species to the tribe Auletini. The new species belongs to the subtribe Pseudomesauletina based on the tarsal claws with a spine, tibia lacking costate dorsal margin and antennae being inserted before middle of the rostrum. The body is covered with short sparse recumbent setae, elytra are not ribbed, elytral apices are without large depressed spots, antennomere 3 is longer than antennomere 2, antennae are inserted before the middle of the rostrum, and eyes are strongly convex, which suggest placement in the genus Pseudomesauletes. The specimen was assigned to the subgenus Pseudomesauletes s. str. on the basis of the almost rectangular elytra and the brown body colouration.

Discussion
The fauna of the Eocene Rhynchitidae is rather diverse and tribes Sayrevilleini, Auletini, Rhynchitini, and Eugnamptini are found in its deposits (Legalov, 2020b). The subfamily Sayrevilleinae is represented by three tribes (Legalov, 2015a(Legalov, , 2018. Recent Minurini Legalov, 2003 andVossicartini Legalov, 2003 are distributed in Chile, Argentina, and Africa (Legalov, 2007(Legalov, , 2018. The Sayrevilleini is an extinct tribe and known from fossils only (Fig. 4). The genus Baltocar is found in Eocene Baltic amber but not found in other Paleogene deposits (Legalov, 2020b (Legalov, 2002). Juniperus are recorded in New Jersey and Baltic amber (Czeczott, 1961;Grimaldi and Nascimbene, 2010). Cupressus is found in Baltic amber (Czeczott, 1961;Alekseev, 2018). Six rather similar species of Baltocar inhabiting the same area were probably associated with different plants. Fourteen species of Cupressaceae are known from Baltic amber (Sadowski et al.,  2017; Alekseev, 2018). It can be assumed that extinct representatives of the genus Baltocar were associated with them. The genus Pseudomesauletes (Rhynchitinae, Auletini) is distributed in East and South Asia, the Zonda Islands, Africa, Madagascar, North America, and Colombia (Legalov, 2007(Legalov, , 2018, but it is absent in Western Palearctic (Fig. 5). Fossil records are known from the Florissant Formation, Colorado, USA (Scudder, 1893;Wickham, 1912), and Rovno amber (Bukejs and Legalov, 2019). The newly described extinct species from Eocene Baltic amber, P. lobanovi sp. nov., belongs to the species group with the long rostrum almost equal to or longer than the elytra. In the Holocene fauna, such species are absent but are recorded in the Eocene deposit of North America (Legalov, 2015b(Legalov, , 2020b. The trophic relationships of most recent Pseudomesauletes species are unknown (Legalov, 2003). Pseudomesauletes uniformis (Roelofs, 1874) develops in flower buds of Rosa (Lee and Morimoto, 1988), and P. formosanus (Voss, 1921) was recorded on Rubus and Rosaceae (Voss, 1934). Fossil species of Pseudomesauletes were probably related to the family Rosaceae as well, as they quickly differentiated in the Eocene (DeVore and Pigg, 2007) and are found in Baltic (Czeczott, 1961;Weitschat and Wichard, 2002) and Rovno amber (Sokoloff et al., 2018) and in the deposits of Florissant (Manchester, 2001).
Data availability. All material included in this paper is deposited in the Museum of Amber Inclusions, University of Gdańsk, Poland, and all data are included in the description. X-ray microtomography volume renderings of the habitus, habitus of Baltocar sontagae sp. nov., holotype, 6703 (MAIG) an available as a Video Supplement.