The holotype of Dignomus regiomontanus Alekseev, 2014, from the Eocene Baltic amber
(Tertiary, Paleogene), is re-examined and re-described. Dignoptinus gen. nov. is
proposed to place this species. Bruchoptinus Reitter, 1884, and Pseudoptinus Reitter, 1884, described
as subgenera of Ptinus Linnaeus, 1767, are the closest relatives of the new fossil
genus. These two subgenera are proposed as independent genera:
Bruchoptinus Reitter, 1884 stat. nov. and Pseudoptinus Reitter, 1884 stat. nov. Forty-four new
combinations for the species of these genera are proposed.
Introduction
The Baltic amber beetle assemblage seems to mark the starting point of the
documented evolution for many extant coleopteran genera, providing
substantial evidence of a general generic stability throughout the Cenozoic.
The family Ptinidae sensu lato, i.e. including the spider beetles and the wood-boring
Anobiinae and allied genera (previously recognized as the Anobiidae), is
abundant and diverse in the Baltic amber beetle assemblage. The family
Ptinidae is represented by 29 described species and numerous still
undescribed taxa from Baltic amber inclusions (Bukejs and Alekseev, 2015;
Bukejs et al., 2017, 2018a, b; Háva and Zahradník, 2019).
Dignomus regiomontanus Alekseev, 2014, recently described from Eocene Baltic amber (Alekseev,
2014), was the first fossil species identified as belonging to the genus
Dignomus Wollaston, 1862. The comparison with additional extant spider beetles
during the descriptive work of the Baltic amber species Dignomus francescovitalii Bukejs, Bellés
et Alekseev, 2018, led to the conclusion that the generic placement of D. regiomontanus
should be revised (Bukejs et al., 2018a). A re-examination of the holotype
of D. regiomontanus, focusing on the detailed structure of the thorax, tarsi and ventral
part of the abdomen, led us to consider that the species belongs to a new
genus that shares a number of morphological similarities with the extant
representatives of the western Palaearctic Bruchoptinus Reitter, 1884 and Pseudoptinus Reitter, 1884.
In the present paper, a new extinct genus Dignoptinus gen. nov. is described, with
Dignoptinus regiomontanus (Alekseev, 2014) comb. nov. as the type species. Moreover, in the context
of the present study, Bruchoptinus Reitter, 1884 stat. nov. and Pseudoptinus Reitter, 1884 stat. nov. are proposed as the independent genera.
Material and methods
The holotype of Dignomus regiomontanus is currently housed in the private collection of Christel
and Hans Werner Hoffeins (Hamburg, Germany) (CCHH) and will subsequently be
deposited at the Senckenberg Deutsches Entomologisches Institut in
Müncheberg, Germany (SDEI). The amber piece containing the insect was
cut, ground, polished, and subsequently embedded in a block of artificial
resin by Christel and Hans Werner Hoffeins, in order to facilitate
stereoscopic examinations (Hoffeins, 2001).
Observations were made with a Nikon SMZ 745T stereomicroscope. Photographs
were taken with a Nikon SMZ 745T stereomicroscope with Nikon DSFi1 digital
camera. Extended depth of field at high magnifications was achieved by
combining multiple images from a range of focal planes using Helicon Focus 6.0.1 software, and the resulting images were edited using Adobe Photoshop CS5. Measurements were taken using an ocular micrometer and are expressed
in millimetres.
Type species Dignomus regiomontanus Alekseev, 2014: 247–248, figs. 17–20, 32.8; by present
designation.
Diagnosis
Dignoptinus gen. nov. is characterized by the following combination of
characters: (1) interantennal space flat and narrow, about 0.3 times as wide
as long scape; (2) thorax simple, with a posterior constriction typical in
Ptininae, without any special structure on the constriction; pronotum with
very prominent discal semi-cylindrical protuberance, with parallel sides and
smooth at the top; (3) tarsi with five tarsomeres in all legs, with
tarsomere 4 notched; (4) abdominal ventrite 4 quite long, more than half as
long as ventrite 3.
The long abdominal ventrite 4 (about 0.7× as long as ventrite 3 in
the holotype of D. regiomontanus) and the notched tarsomere 4, approaches Dignoptinus gen. nov. to
Pseudoptinus Reitter, 1884 and Bruchoptinus Reitter, 1884 (Reitter, 1884a; Freude, 1969; Bellés, 1978;
Iablokoff-Khnzorian and Karapetian, 1991). However, the structure of the
pronotum, with the prominent discal protuberance, as well as the flat
interantennal space, clearly separates Dignoptinus gen. nov. from Pseudoptinus and Bruchoptinus. The species of
Pseudoptinus show a pronounced sexual dimorphism: body shape is elongated and
subparallel in males but oval in females (Reitter, 1884a). The species of
Bruchoptinus also show a similar sexual dimorphism (Reitter, 1884a), with the exception
of Bruchoptinus palliatus, in which both sexes are elongated and subparallel (Iablokoff-Khnzorian
and Karapetian, 1991). This suggests that the type specimen of D. regiomotanus would be a
male, and that the still unknown female might have a general oval shape.
The conspicuous pronotal discal protuberance can appear similar to
structures found in extant species of the genus Dignomus Wollaston, 1862
(Bellés, 1996). However, the posterior thoracic constriction of
Dignomus presents an oval structure on each side, which protrudes from the
constriction (while D. regiomontanus lacks any structure on the constriction). Moreover, the
pronotum of Dignomus, in addition to a discal protuberance, shows two additional
lateral projections, one on each side that have a complex structure that is
pointed and, in some cases, horn-shaped and curved backwards. D. regiomontanus also
possesses lateral protuberances, but they are simple and slightly prominent,
like in some Ptinus species (Bellés, 1996).
The interantennal space narrow and flat of D. regiomontanus appears similar to the extant genus
Trymolophus Bellés, 1990, from the Mascarene Islands, which has a similar feature
and also generally shows a prominent protuberance on the pronotal disc
(Bellés, 1990, 1991a). Nevertheless, the species of Trymolophus are much more
robust in general shape, have the tarsomere 4 simple, and the abdominal
ventrite 4 very short (about 0.3–0.4 times as long as ventrite 3, as in
most Ptinini). The species of the genus Singularivultus Bellés, 1991, also show the
interantennal space narrow and flat. However, the unique morphology of the
clypeus with a broad frontal concavity above the labrum separates
Singularivultus from all the remaining Ptininae (Bellés, 1991b). Arguably, the
characters shared by Dignoptinus gen. nov., Trymolophus and Singularivultus seem rather derived from independent
evolutionary processes than from phylogenetic closeness. Thus they may be
considered features that emerged independently in these groups.
Etymology
The name of the new genus is a compound word composed of the
generic names “Dignomus” (the name of the genus in which the type species was
originally placed) and “Ptinus” (the name of the type genus of the tribe to
which the genus belongs). Gender masculine.
Remarks
The new genus is monotypic, represented by the type species only.
Therefore the generic description considerably overlaps that of the species.
Dignoptinus regiomontanus (Alekseev, 2014) gen. et comb. nov., holotype, No. 883-3[CCHH]:
(a) details of forebody, dorsal view; (b) elytra, dorsal view; (c) details
of metathorax and abdomen, lateral view, the arrow indicate notched
tarsomere 4. Scale bars =0.5mm.
Holotype
Holotype. No. 883-3[CCHH], complete specimen, adult, possibly male. The
beetle inclusion is preserved in a polished piece of transparent amber with
a yellowish shade. The small amber piece is embedded in a block of polyester
resin (total measurements are
15 mm × 9 mm × 7 mm).
Syninclusion. stellate Fagaceae trichomes.
Type strata and locality
Baltic amber, upper Eocene to mid-Eocene; southern
coast of the Baltic Sea (Alekseev, 2014).
Re-description
Size. Medium-sized (body length 3.7 mm, maximum width 1.8 mm);
body shape elongate, subparallel and slender, slightly convex; integument
uniformly dark brown.
Head. hypognathous. Compound eyes large, hemispherical, strongly prominent,
finely facetted, with erect setae inserted between ommatidia. Antennae with
11 antennomeres, filiform and long, slightly shorter than length of body
(approximately 3.5 mm); finely and densely pubescent, antennomeres 1–9 with
additional sparse, moderately long semirecumbent setae; relative length
ratios of antennomeres 1–11 equal to 12:6:10:12:13:14:15:15:15:14:19.
Terminal segment of maxillary and labial palpi elongate and fusiform.
Antennae insertion very close, interantennal space flat and about 0.3 times
as wide as long scape. Forehead and vertex densely pubescent, except
glabrous medio-posterior area.
Thorax. with posterior constriction morphologically simple, without any special
structure on constriction. Pronotum longitudinal (about 1.3 times as long as
wide), distinctly narrower than elytral base; surface coarsely
granulate-punctate, densely pubescent; pronotal disc with very prominent
protuberance, semi-cylindrical in shape, with parallel sides and without any
medial groove at top; two additional medio-lateral protuberances, one at
each side of discal one, also present, being inconspicuous and simple in
structure. Prosternal process narrow, slightly convex, about 0.3 times as
wide as procoxal diameter. Metasternum smooth, covered with fine pubescence.
Scutellum conspicuous, rounded in shape, covered with dense pubescence.
Elytra. subparallel and long, about 1.5 times as long as wide, and about 2.6 times
as long as pronotum; humeri well developed; with round-shaped, moderately
large and deep punctures, arranged in regular rows, scutellar striola
present; covered with sparse long erect setae, and shorter, dense
semirecumbent setae. Metathoracic wings present.
Metaventrite. strongly convex medio-posteriorly, with fine, sparse punctures and fine,
dense recumbent pubescence; metepisternum wide, gradually narrowing
posteriorly, punctuation and pubescence as on metaventrite.
Legs. slender and long, with fine pubescence; pro- and mesocoxae globose,
metacoxae narrow, transverse, all coxae separated; trochanter short, its
apex not reaching elytral margin; tarsal formula 5-5-5, tarsomere 4 notched
in all legs.
Abdomen. with five visible ventrites; moderately densely covered with fine, short
recumbent pubescence; ventrites 2 and 3 equal in length, ventrite 4 about
0.7 times as wide as ventrite 3; abdominal sutures concave, well visible,
sutures between ventrites 1–2 and 2–3 more deeply marked laterally.
Discussion
Dignoptinus gen. nov. should be placed close to Bruchoptinus stat. nov. and Pseudoptinus stat. nov., whose
species also have a Palaearctic distribution, predominating in Europe and the
Mediterranean region (Reitter, 1884a; Iablokoff-Khnzorian and Karapetian,
1991). Bruchoptinus and Pseudoptinus were described as subgenera of Ptinus Linnaeus, 1767 (Reitter, 1884a)
and thus have continued to be considered at this taxonomic level in
subsequent papers (e.g. Freude, 1969; Bellés, 1978; Iablokoff-Khnzorian
and Karapetian, 1991). However, the characters that separate Bruchoptinus and
Pseudoptinus from Ptinus (Reitter, 1884a; Iablokoff-Khnzorian amd Karapetian, 1991) are so
stable and relevant that they deserve to be considered as independent
genera, Bruchoptinus Reitter, 1884 stat. nov. and Pseudoptinus Reitter, 1884 stat. nov. As for the
remaining Ptinus subgenera, Cyphoderes Mulsant and Rey, 1868 could still be considered a
subgenus of Ptinus, Gynopterus Mulsant and Rey, 1868 would fit better as an independent
genus, and Tectoptinus Iablokoff-Khnzorian and Karapetyan, 1986 as a subgenus of
Gynopterus. However, to reach clear conclusions about these additional subgenera, a
further thorough phylogenetic analysis would be required. New combinations
resulting from the new status formally proposed for Bruchoptinus and Pseudoptinus are listed below.
Genus Bruchoptinus Reitter, 1884: 303 stat. nov.
Type species Ptinus rufipes A. G. Olivier (1790) (Zahradník and Háva, 2014)
Diagnosis
Bruchoptinus is characterized by the following combination of characters: (1) in general, males slender, elongate and with subparallel elytra; females
robust, with the sides of the elytra rounded (the only exception is
Bruchoptinus palliatus Perris, 1847, in which both sexes are elongated and have subparallel
elytra); (2) interantennal space narrow and acute; (3) thorax with a
posterior constriction simple; pronotum with the anterior part uniformly
rounded, without any marked longitudinal groove, and with more or less
numerous whitish scales inserted on the disc; (4) tarsi with five tarsomeres
in all legs, with tarsomere 4 excavated, showing the upper edge very
slightly notched, especially in the males; (5) abdominal ventrite 4 quite
long, more than half as long as ventrite 3; and (6) aedeagus with the median
lobe simple, and the parameres symmetrical.
Distribution of the extant genera, close to Dignoptinus gen. nov. (vivid areas
mark centres of diversity with more than five occurring species): (a)Bruchoptinus Reitter, 1884 stat. nov.; (b)Pseudoptinus Reitter, 1884 stat. nov.
Western Palaearctic with the species diversity concentration
in the eastern Mediterranean area (Fig. 3a).
Genus Pseudoptinus Reitter, 1884: 303 stat. nov.
Type species Ptinus coarcticollis Sturm, 1837 (Zahradník and Háva, 2014)
Diagnosis
Pseudoptinus is characterized by the following combination of characters: (1) males slender, elongated and with subparallel elytra; females robust, with
the sides of the elytra rounded; (2) interantennal space narrow and acute;
(3) thorax with a posterior constriction simple; pronotum with the anterior
part showing a marked longitudinal groove, and with the pubescence formed by
isolated setae more or less long and erect; (4) tarsi with five tarsomeres
in all legs, with tarsomere 4 deeply excavated, showing the upper edge
clearly notched in males and females; (5) abdominal ventrite 4 quite long,
more than half as long as ventrite 3; and (6) aedeagus with the median lobe
simple, and the parameres symmetrical.
Western Palaearctic with most diversity concentrated in the
western Mediterranean area (Fig. 3b).
Data availability
No data sets were used in this article.
Author contributions
VIA, AB and XB prepared the paper and contributed to the editing.
Competing interests
The authors declare that they have no conflict of interest.
Acknowledgements
The authors are sincerely grateful to Christel Hoffeins and Hans Werner Hoffeins (Hamburg, Germany) for the loan of the interesting fossil
material. The study of VIA was financially supported by the Russian
Foundation for Basic Research and Kaliningrad Region (research project no. 19-45-390001).
Financial support
The study of Vitalii I. Alekseev was financially supported by the Russian
Foundation for Basic Research and Kaliningrad Region (research project no. 19-45-390001).
Review statement
This paper was edited by Johannes Müller and reviewed by Andrei Legalov and Shuhei Yamamoto.
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