A new fossil species of the silvanid flat bark beetle genus
Silvanid flat bark beetles have only rarely been reported as inclusions from
Eocene Baltic amber. Up to now, only four species have been described,
namely
The geological backgrounds of the Baltic and Bitterfeld amber deposits have
recently been reviewed (Standke, 2008; Weitschat and Wichard, 2010), and the
interconnectedness of these deposits has been assessed on the basis of
arthropod inclusions (e.g., Hoffeins and Hoffeins, 2003; Szwedo and Sontag,
2013; Dunlop et al., 2018) and geochemistry (Wolfe et al., 2016). Amber from
the former Palmnicken mine (Yatarny settlement, Kaliningrad, Russia) is
part of a commercially mined deposit of Baltic amber. In the present paper,
we provide a description of a new species of the genus
The material examined is deposited in the palaeontology collection of the Royal Saskatchewan Museum (Regina, Saskatchewan, Canada) (RSM).
Observations of this specimen were made using a Nikon SMZ745T
stereomicroscope. Photographs were taken using a Visionary Digital imaging
system, consisting of a Canon EOS 5D camera with a Canon MP-E 65
The following sources were used for the comparison with recent genera: Halstead (1973), Thomas (1993), and Friedman (2015).
Superfamily Family Subfamily Genus
The studied amber specimen shows the combination of characters unequivocally corresponding to the subfamily Silvaninae: subparallel body shape, pentamerous tarsi with tarsomere 4 smallest; closed procoxal cavities; 11-segmented antennae with distinct antennal club; antennal scape comparatively short, about as long as wide; frons laterally without longitudinal sulcus; and frontoclypeal suture absent.
The beetle under consideration is assigned to Figs. 1–3 ZooBank: urn:lsid:zoobank.org:act:E1CAFC19-
2BFA-4DC1-B828-BF098F2D87F8
Baltic amber from Eocene amber-bearing blue Earth layers (mostly Bartonian age is interpreted for the extinct central European resin-producing forests according to Bukejs et al., 2019).
Yantarny settlement (formerly Palmnicken), Sambia (Samland) Peninsula, Kaliningrad region, Russia.
The specific epithet is derived from
The new species from Baltic amber has the anterior edge of the pronotum
almost straight and possesses a single, distinct, sharp denticle at posterior
pronotal angle. In all extant species of
Body length about 2.3
Head nearly as long as wide, impunctate; forehead almost flat, vertex
slightly convex. Labrum with anterior margin widely rounded. Fronto-clypeal
suture absent. Compound eyes relatively small and prominent, hemispherical,
with coarse facets; eyes widely separated, with distance between eyes about
Maxillary palpi short; terminal palpomere elongate, spindle-shaped,
truncate, about
Pronotum slightly elongate,
Scutellar shield distinct, suboval, transverse. Elytra elongate,
Relative length ratios of mesoventrite to metaventrite to abdomen are
Legs short and robust. Procoxa nearly round, mesocoxa oval, metacoxa oval,
not extending laterally to meet elytron. All coxae separated from each
other: procoxae separated by distance approximately half of procoxal
diameter; mesocoxae separated by distance slightly smaller than mesocoxal
diameter; metacoxae widely separated. Trochanters apparently without spines.
Femora widened medially, simple (without denticles or teeth), but with deep,
longitudinal groove apicoventrally. Tibiae curved, dilated apically, shorter
than femora; with minute apical spine. Tarsal formula 5-5-5; tarsomeres 1–3
dilated apically, tarsomere 4 very small; tarsomere 5 longest, about as long
as tarsomeres 1–3 combined. Tarsal claws simple, equal in size, long, about
Abdomen with five visible, similarly articulated ventrites; ventrite 1 with
open femoral line (diverging posteriorly from margin of metacoxal cavities);
ventrite 5 rounded apically; ventrites 1–4 sparsely covered with fine
punctures, and ventrite 5 with much denser punctation, distance between
punctures smaller than diameter of one puncture. Intercoxal process of
abdominal ventrite 1 triangular and acute. Relative lengths (medially) of
ventrites 1–5 equal to
The preservation state and completeness of the Baltic amber inclusions can
differ significantly from one specimen to the next. Damage that results in
the distortion and loss of body parts is the most relevant for the current
study, and this form of damage can have important implications for
descriptions of fossil species based on amber inclusions. This type of
damage can occur at different points in the taphonomic history of each
specimen, and it has three main causes that could be loosely grouped into
the following categories.
Pre- or perimortem damages (during or prior to entrapment in natural
resin) damages include a loss of appendages during life, or a fall
into fresh resin of a dead or damaged specimen. Sometimes, appendage losses
can occur during entrapment of a living insect in resin, due to its struggle
for release. Postmortem damages (after entrapping, during the polymerization of resin
and subsequent transformation of resin to copal) include distortions
of external 3-D morphology and changes of body proportions. This type of
damage is less typical among Baltic amber inclusions and can usually be
found in insects with a soft body cuticle only. The dehydration of the insect
body entrapped in resin leads to decrease in the volume of liquid within
body and, in the case of a pliable cuticle, to compression of the body. In
specimens where the sclerites are loosely bound to one another (e.g., cast
exuviae and dried bodies), resin flows prior to polymerization may also
scatter some of the body parts. Post-extraction damages (breakage, deterioration, and alteration of amber
outside of its original anoxic sediments) are usually slow weathering
or oxidation processes in natural settings, or extremely rapid anthropogenic
changes during extraction, treatment, and processing of amber. Extraction
damage of inclusions can be especially evident after mechanical treatments
(e.g., loss of body parts during amber cutting and polishing); autoclave
processing of samples can have equally deleterious effects – according to
Hoffeins (2012), this processing can lead to fragmentation of cuticle,
disconnection of body segments, compression and shrinking of body parts,
thermal degradation of cuticle, and black discoloration.
The specimen under study represents the comparatively rare (especially among
well-sclerotized imago of Coleoptera) postmortem distortion. The specimen is
complete but almost disconnected along its head-prothorax and
pro-mesothorax articulations. The integument is dorsoventrally compressed
and partially translucent but at the same time not black or artificially
darkened. We interpret this combination of preservational features as the
result of resin trapping the beetle within its imaginal stage, just after
the final pupal ecdysis. The exoskeleton was not completely hardened but
was somewhat soft and pliable. A single occurrence of such a juvenile imago
in amber should be considered a rare occurrence, but future collections of
similar material should be examined to see if this form of preservation
occurs repeatedly. If it is a repetitive occurrence, the phenomenon might
suggest a close ecological association between the resin-producing trees and
a particular beetle species, or it may provide evidence of fresh resin
attracting this species.
No data sets were used in this article.
VIA, AB, and RCM prepared the paper and contributed to the editing.
The authors declare that they have no conflict of interest.
The study was carried out with the support of the state assignment of IO RAS (theme no. 0149-2019-0013) to Vitalii I. Alekseev and a Natural Sciences and Engineering Research Council of Canada Discovery Grant (2015-00681) to Ryan C. McKellar.
This research has been supported by the IO RAS (grant no. 0149-2019-0013) and the Natural Sciences and Engineering Research Council of Canada Discovery Grant (grant no. 2015-00681).
This paper was edited by Florian Witzmann and reviewed by Andrei Legalov and one anonymous referee.