Only in recent years have new genera and species of the subfamily
Silinae Mulsant, 1862 been described as inclusions in amber. However,
no representative of the genus Silis Charpentier, 1825 had been described from
Baltic amber, even if few specimens were already known at the generic level.
Silis lombardii sp. nov. is entirely dark brown and shows (as usual for the genus) the
two characteristic lobes in the sides of pronotum, elongated elytra, and a
basal small tooth only on the anterior claws. The Eocene findings show that
the subfamily is of ancient origin and that at least in the Eocene it was
much more abundant than today in the same territories, where only two
species are known. (urn:lsid:zoobank.org:act:76887127-3D24-41DA-86CC-7DCAB40DC3B7)
Introduction
The subfamily Silinae Mulsant, 1862 is widespread with a very high number of
species in the eastern Palaearctic, Africa, South America and South-East
Asia (Delkeskamp, 1939, 1977; Kazantsev and Brancucci, 2007; Constantin,
2010), but it is very poor in genera and species diversity in the western Palaearctic
and Europe. Biodiversity hotspots appear to be former Indo-China, Indonesia and
South America, even if the systematic knowledge at the generic level is
still to be studied in depth (Ramsdale, 2002) for many regions and in
particular for the Oriental region and North America. Also noteworthy is the
fact that no species of the subfamily has reached southern Australia, Tasmania
and New Zealand (Delkeskamp, 1977; Ramsdale, 2002). Recently, three extinct
genera probably related to Silis and a species of the genus Autosilis Kazantsev, 2011 have
been described from Baltic amber (Kazantsev, 2013; Alekseev and
Kazantsev, 2014; Fanti and Damgaard, 2018; Fanti and Pankowski, 2018).
Concerning the genus Silis Charpentier, 1825 in fossil records, the species Silis chiapasensis has
been described from Miocene Mexican amber (Wittmer, 1963), and few
specimens are known at the generic level for Eocene Baltic amber (Klebs,
1910; Bachofen-Echt, 1949; Fanti, 2017). These findings denote and suggest
an ancient presence in Europe (Fanti and Damgaard, 2018) starting at least
from the Eocene (no representative of the Silinae subfamily is currently
known from the Cretaceous), and with a strong current rarefaction due to causes
unknown to date. With the exception of S. mingrelica (Kazantsev, 1994) from Georgia, only
another species, i.e. S. ruficollis (Fabricius, 1775), is currently present and widespread in
Europe including the Baltic region (Kazantsev and Brancucci, 2007).
Material and methods
The amber piece was cleaned, polished and comes from a Yantarny mine in the
Sambian Peninsula, Russia. The inclusion was photographed with a Zeiss
AxioCam ICc 3 digital camera mounted on a Zeiss Stemi 2000c-stereomicroscope,
with the addition of focus stacking software Helicon Focus, and with a Nikon
D3100 digital camera equipped with AF-S DX Micro-Nikkor lens (40 mm f/2.8G).
Figures were then processed and produced using PhotoImpact Viewer SE.
Measurements were taken with an ocular micrometer mounted on a Leica S8APO
microscope. The material is deposited in the University of Molise (Unimol),
Italy, under accession code Unimol AAA003FP (AAA denotes Department of
Agricoltura (agriculture), Ambiente (environment) and Alimenti
(foods); 003 denotes the sequential number; FP denotes the Francesco Parisi collection).
Systematic paleontology
Family Cantharidae Imhoff, 1856
Subfamily Silinae Mulsant, 1862
Tribe Silini Mulsant, 1862
Genus Silis Charpentier, 1825
Subgenus Silis Charpentier, 1825
Silis (Silis) lombardii sp. nov.
(Figs. 1–3)
Silis (Silis) lombardii sp. nov. in Baltic amber, holotype. (a) Dorsal view, scale bar = 1.0 mm. (b) Ventral view, scale bar = 1.0 mm.
Silis (Silis) lombardii sp. nov. in Baltic amber, holotype. (a) Detail of pronotum
(arrow), scale bar = 0.4 mm. (b) Detail of right antenna, scale bar = 0.4 mm.
Silis (Silis) lombardii sp. nov. in Baltic amber, holotype. (a) Detail of pronotum
(ventral view), elytra, legs and antennae with numbered antennomeres, scale
bar = 0.5 mm. (b) Detail of last abdominal segments (lateral view), scale
bar = 0.5 mm.
Description
Adult, winged, male-defined on the basis of the long antennae and elongate
lateral lobes of the pronotum. Body length: 5.2 mm, elytra: 3.9 mm,
antennae: around 3.2 mm. Entirely dark brown.
Head large, as wide as pronotum, slightly rugose, little exposed being
partially covered by pronotum. Eyes elliptical and protruded, inserted in
the upper and lateral part of the head. Maxillary palpi 4-segmented, unequal
in length with the last palpomere very elongate and securiform. Labial palps
3-segmented with the last palpomere securiform. Antennae inserted near the
eyes, just reaching the metafemora, 11-segmented, filiform, all antennomeres
covered with small setae; scape elongate and enlarged, club-shaped;
antennomere II (pedicel) extremely short and globular; antennomeres III–IV
longer than antennomere II, robust; antennomere V slightly longer than
antennomeres III–IV; antennomeres VI–IX slender and longer than
antennomere V; antennomere X slightly shorter than antennomeres VI–IX;
antennomere XI filiform, oblong with rounded apex. Pronotum slightly
elongate, surface undulating with concavities and small setae and
punctuation; apical margin convex; sides posteriorly expanding, with two
elongated and apically pointed long processes: the posterior processes are
sinuous and with a small basal acute tooth and the anterior ones are slender
and straight. Scutellum triangular. Elytra wider than pronotum with slightly
rugose microsculpture and some setae; elongate and covering the last
abdominal segments; enlarged at humeri and narrow in the middle; apex
strongly rounded. Posterior wings almost completely covered by elytra.
Metasternum very elongate with rounded posterior margin, abdominal segments
transverse and rugose. Legs long, slender and pubescent; coxae short and
robust; trochanters elongate and triangular-shaped with rounded apex; femora
enlarged and slightly curved; tibiae cylindrical, shorter than femora, with
an apical spur. Tarsal formula 5-5-5; first tarsomere elongate and slightly
enlarged apically; second shorter than first; third tarsomere triangular and
shorter than tarsomere II; fourth tarsomere deeply bilobed at sides; fifth
tarsomere very elongate, slender, flat and curved; proclaws with an obtuse
basal tooth, meso- and metaclaws simple without basal tooth. Female unknown,
sexual dimorphism is supposed.
Etymology
Named in honour of Fabio Lombardi (Department of Agricultural Science,
Mediterranea University of Reggio Calabria, Italy), dear friend and
colleague of the first author.
Holotype
Male, in Baltic amber, deposited at the University of Molise (Unimol) with
accession no. Unimol AAA003FP.
Middle Eocene (Lutetian) (47.8–41.2 Myr) to Late Eocene (Priabonian)
(37.8–33.9 Myr).
Syninclusions
Air bubbles and debris (botanical remains).
Remarks
The amber piece is flat and elongate and measures approximately 18 mm × 6–8 mm. The inclusion is complete and well visible. The specimen is crumpled but
not damaged.
Systematic placement
Maxillary palpi sub-equal in length with last palpomere securiform, elytra
elongated, abdomen with only eight visible urites, protarsal claws with
small tooth, meso- and metatarsal claws simple, and pronotum laterally with
two long lobes in each part clearly make this new species belonging to the
subfamily Silinae and to the genus Silis (Brancucci, 1980; Constantin, 2010,
2017).
Differential diagnosis
Silis lombardii sp. nov. differs from S. chiapasensis Wittmer, 1963 (Mexican Chiapas amber) in a slightly
larger size, darker colour, and different shape of pronotum and lateral
processes (Wittmer, 1963). Silis lombardii sp. nov. differs from the extant S. ruficollis in the body
colour (S. ruficollis is black with red pronotum), the smaller size (5.2 instead of 6–7.5 mm in S. ruficollis) and in the more elongate lateral lobes of the pronotum.
Discussion
In temperate and northern Europe the genus Silis composes species of plains,
rarely of higher altitudes, particularly present on shores of lakes or on
marshy meadows (Moscardini, 1972). These habitats were typical in the Baltic
Eocene, where no evident orogenetic events were reported (Sadowski, 2017).
Thus, Silis is considered herein a hygrophilous genus and of temperate climate.
Elsewhere, the genus Silis appears more thermophilic, since it is very frequent
in the tropics (Constantin, 2010, 2017) suggesting that Silis can be paraphyletic.
The elevated temperatures and the extreme environmental variety evidently
favour the diversification and the evolution of the Silinae; for this reason,
in Eocene amber many more species could be found again in the future.
The thermal gradient and the subtropical environment present during the
Eocene (Weitschat and Wichard, 2010; Sadowski et al., 2017) may, however,
have played an important role in their spread in the Baltic area. The
decrease in temperatures and annual precipitation at the end of the Eocene
and continued in the Oligocene (Weitschat and Wichard, 2010) reduced the
number of taxa in northern temperate zones of Europe.
However, for example in the temperate zones of North America there is a
higher number of species than in Europe (Arnett Jr., 1963; Green, 1966;
Ramsdale, 2002). In contrast with Europe the biodiversity centre is in
montane regions, particularly in California (Ramsdale, 2002). This fact
suggests, rather, a Trans-Beringian Pliocene spread of temperate-cold
species, as for example the fossil Opsimini (Coleoptera Cerambycidae) from
Baltic amber (Vitali and Damgaard, 2016). The oldest finds of the Silinae
subfamily are the species included in Baltic amber to which an
Eocene species, as adpression, from fossiliferous deposits of Florissant,
Colorado, USA (Wickham, 1914; Fanti, 2017), and an undescribed specimen from
the argillaceous limestone of the Tertiary strata (Eocene or Oligocene) of
Aix-en-Provence, France (de Serres, 1843; Pictet, 1854; Fanti, 2017), are added.
However, a much older evolution of the subfamily, referable to the
Cretaceous as it is for the subfamily Cantharinae (Fanti, 2017), is
hypothesised.
Data availability
The material included in the paper is accessible in the Department of
Agricultural, Environmental and Food Sciences of the University of Molise
(Unimol), Italy, and all data are included in the description.
Author contributions
Both authors contributed equally to the article.
Competing interests
The authors declare that they have no conflict of interest.
Acknowledgements
We are grateful to Fabio Lombardi (Department of Agricultural
Science, Mediterranea University of Reggio Calabria, Italy) for the constant
scientific support.
Review statement
This paper was edited by Torsten Scheyer and reviewed by Francesco Vitali and one anonymous referee.
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