A new genus of cylindrical bark beetle (Coleoptera: Zopheridae: Colydiinae) in mid-Cretaceous Burmese amber

Abstract

A bizarre cylindrical bark beetle from mid-Cretaceous Burmese amber is described as Stegastochlidus saraemcheana, a new genus and species in the subfamily Colydiinae of the family Zopheridae. The male beetle is characterized by elongate protuberances covering its entire dorsal surface, a tarsal formula of 4-4-4 and ten-segmented antennae with the terminal segment expanded into a small club. The fossil is considered to have been a possible predator that lived among moss, lichens and fungi either attached to trees trunks or on the forest floor. A close association with fungi is indicated by strands of conidia attached to the cuticle of the beetle.

Full text

Biosis: Biological Systems (2020) 1(4): 134-140
https://doi.org/10.37819/biosis.001.04.0087
134
A New Genus of Cylindrical Bark Beetle (Coleoptera: Zopheridae:
Colydiinae) in mid-Cretaceous Burmese Amber
George Poinar Jr.a; Fernando E. Vegab, *
aDepartment of Integrative Biology, Oregon State University, Corvallis, OR, 97331 USA. Email:
poinarg@science.oregonstate.edu
bSustainable Perennial Crops Laboratory, United States Department of Agriculture, Agricultural Research
Service, Beltsville, MD, 20705, USA. Tel.: +1 301 504 5101; Fax: +1 301 504 6491.
* Corresponding author. E-mail address: Fernando.Vega@usda.gov (F. E. Vega).
© The Author 2020
ABSTRACT
A bizarre cylindrical bark beetle from mid-Cretaceous Burmese amber is
described as Stegastochlidus saraemcheana, a new genus and species in the
subfamily Colydiinae of the family Zopheridae. The male beetle is
characterized by elongate protuberances covering its entire dorsal surface,
a tarsal formula of 4-4-4 and ten-segmented antennae with the terminal
segment expanded into a small club. The fossil is considered to have been a
possible predator that lived among moss, lichens and fungi either attached
to trees trunks or on the forest floor. A close association with fungi is
indicated by strands of conidia attached to the cuticle of the beetle.
ARTICLE HISTORY
Received 27 October 2020
Revised 18 November 2020
Accepted 11 December 2020
KEYWORDS
Fossils
Myanmar
Stegastochlidus
saraemcheana
Taxonomy
Tenebrionoidea
Introduction
Cylindrical bark beetles in the subfamily
Colydiinae of the family Zopheridae are small
beetles that are rarely collected and little studied.
They are associated with moss and lichens and
also found in fugal fruiting bodies, decaying
vegetation, leaf litter, rotting wood and under
bark. Their diet can be either herbivorous or
carnivorous by preying on other wood boring
invertebrates, such as the larvae of Platypodinae
(Coleoptera: Curculionidae) (Dillon & Dillon,
1961; Lawrence & Britton, 1991). They have had
a complex systematic history, which has been
well documented by lipiski and Lawrence
(1999). Their fossil record is based almost
completely on species recovered from Baltic and
Burmese amber dating back to the mid-
Cretaceous. These records have been updated by
Bullis (2020). The present paper describes a very
unusual cylindrical bark beetle in Burmese amber
with its dorsal surface covered with elongate
protuberances.
Materials and methods
The amber specimen was collected at the Noije
Bum Summit Site mine in the Hukawng Valley,
located southwest of Maingkhwan in Kachin State
(26º20´N, 96º36´E) in northern Myanmar. Based
on paleontological evidence the site was dated to
the late Albian of the Early Cretaceous
(Cruickshank & Ko, 2003), placing the age at 97–
110 million years ago (Mya). A zircon U–Pb and
trace element analyses of amber from different
locations in Myanmar confirmed an age of around
100 Mya for amber from the Hukawng Valley as
well as an age range of 72–110 Mya for amber
from other sites in northern Myanmar (Xing &
Qui, 2020).
ORIGINAL RESEARCH

Poinar Jr. & Vega (2020) Biosis: Biological Systems (2020) 1(4): 134-140
135
The amber was polished close enough to the fossil
to observe specific details, such as spines on the
everted internal sac of the reproductive system,
using a Nikon Optiphot compound microscope.
Helicon Focus Pro X64 was used to stack photos
for improved overall clarity and depth of field.
Images of some characters in amber were difficult
to photograph due to the position of the fossil and
fractures in the amber, which explains why the
resulting images are not as clear as corresponding
photos of extant beetles.
Results
Order: Coleoptera Linnaeus, 1758
Suborder: Polyphaga Emery, 1886
Superfamily: Tenebrionoidea Latreille, 1802
Family: Zopheridae Solier, 1834
Subfamily: Colydiinae Billberg, 1820
Genus: Stegastochlidus gen. nov.
LSID: urn:lsid:zoobank.org:act:36CBCA00-
545C-4A62-ABB3-CBC658160315
Diagnosis: Dorsum of head, pronotum and elytra
of adult male specimen covered with long, erect
protuberances. Twenty protuberances, most
pointing forward, arise from the head and
pronotum. Four longitudinal rows, each
containing 10 protuberances, are on each elytron;
head prognathous, with incised compound eyes
protruding laterally; ommatidia large, with
whitish microsetae between ommatidia; antennae
gradual, smooth, 10-segmented with enlarged
terminal segment serving as club; tarsal formula
4-4-4; claws simple, divergent; abdomen with 5
visible sternites; aedeagus, paired parameres and
everted internal sac bearing an armature of spines
protruding from tip of abdomen.
Species included: Type species only.
Remarks: Based on its 4-4-4 tarsal formula and
10- segmented antennae, the fossil is considered
to be a highly modified member of the Colydiinae
in the Zopheridae.
Type species. Stegastochlidus saraemcheana
gen. et sp. nov. (Figs. 1–12)
Derivation of generic name. From the Greek
“stegastos” = covered and the Greek “chlidos” =
ornament.
Derivation of species name: Named in honor of
Dr. Sarah Emche, a U. S. Department of
Agriculture, Agricultural Research Service
scientist and friend of the second author.
LSID: urn:lsid:zoobank.org:act:D92284E1-
889B-45F7-BC9D-5AA5F3D907CC
Holotype: Male no. B-C-55 deposited in the
Poinar amber collection maintained at Oregon
State University. The tibia and tarsus of the left
hind leg are missing, and the right hind leg is
partially torn from its socket. The head and
abdomen are somewhat distorted from the
fossilization process and the left labial palp is
detached. The right hind leg is torn out of its
socket. Two mites are attached to the body.
Type locality: Kachin (Hukawng Valley) of
northern Myanmar.
Stratigaphic horizon: The lowermost
Cenomanian (98.79 ± 0.62 Mya) mid-Cretaceous.
Diagnosis: As for genus (monotypic).
Description: Body uniformly brown, elongate,
parallel-sided, 4.2 mm in length; 3.9 times longer
than wide; entire dorsal surface covered with erect
protuberances. Head prognathous, hidden from
above by forward directed protuberances; width,
460 µm, length 400 µm (in face view); widest at
level of moderately protruding, coarsely faceted
eyes notched on inner surface, greatest eye
diameter, 170 µm; ommatidia relatively large,
each ommatidium bordered by a ring of white
microsetae; antennal grooves lacking; labial and
maxillary palps short, wide, labial palps 3-
segmented; mandibles long and curved, with
swollen basal portion and pointed tip; labrum
small, border rounded, protruding from head;
antennal insertions adjacent, positioned in center
of head: antennal grooves or cavities absent.
Figure 1. Dorsal view of Stegastochlidus
saraemcheana gen. et sp. nov. in Burmese amber.
Left arrow shows head and pronotum. Right
arrow shows elytra. Scale bar = 0.8 mm.

Biosis: Biological Systems (2020) 1(4): 134-140 Poinar Jr. & Vega (2020)
136
Figure 2. Lateral view of Stegastochlidus
saraemcheana gen. et sp. nov. in Burmese amber.
H = head; M = middle leg; L = hind leg; P =
pronotum; U = everted internal sac. Scale bar =
1.0 mm.
Figure 3. Sub-ventral view of Stegastochlidus
saraemcheana gen. et sp. nov. in Burmese amber.
A = abdomen (somewhat flattened); Ac =
attached mite; E = elytrum; F = foreleg; H = hind
leg; M = middle leg; P = pronotum; U = everted
internal sac. Scale bar = 0.8 mm.
Figure 4. Frontal view of head of Stegastochlidus
saraemcheana gen. et sp. nov. in Burmese amber.
D = detached labial palp; E = eyes; L = flattened
labial palp; M = mandibles; Mp = maxillary palp;
arrowheads show antennal insertions. Scale bar =
0.2 mm.
Figure 5. Reconstruction of face of
Stegastochlidus saraemcheana gen. et sp. nov. in
Burmese amber.
Figure 6. Terminal antennomeres of
Stegastochlidus saraemcheana gen. et sp. nov. in
Burmese amber. Arrowhead shows attached mite.
Scale bar = 0.8 mm.
Figure 7. Subventral view of thorax of
Stegastochlidus saraemcheana gen. et sp. nov. in
Burmese amber showing leg insertions. Scale bar
= 0.4 mm.

Poinar Jr. & Vega (2020) Biosis: Biological Systems (2020) 1(4): 134-140
137
Figure 8. Hind leg of Stegastochlidus
saraemcheana gen. et sp. nov. in Burmese amber
showing femur, tibia and 4-segmented tarsus.
Note apex of mesotarsus with claws in lower right
corner. Scale bar = 0.2 mm. Insert shows detail of
4-segmented tarsus. Scale bar = 0.8 mm.
Figure 9. Lateral view of 4-segmented protarsus
of Stegastochlidus saraemcheana gen. et sp. nov.
in Burmese amber. Note short spine on apex of
tibia. Scale bar = 0.8 mm.
Figure 10. Dorsal view of apex of elytra of
Stegastochlidus saraemcheana gen. et sp. nov. in
Burmese amber showing apparently fused elytral
suture (arrow). Scale bar = 0.2 mm.
Figure 11. Tip of abdomen of Stegastochlidus
saraemcheana gen. et sp. nov. in Burmese amber
showing the extended tubular aedeagus bearing
sclerites (A), two subtending parameres (P) and
the everted internal sac with membranous walls
bearing spines (S). Scale bar = 0.2 mm.
Figure 12. Apparent fungal conidia (arrows)
between the elytra and abdomen of
Stegastochlidus saraemcheana gen. et sp. nov. in
Burmese amber. Scale bar = 0.1 mm.
Antenna 10-segmented, gradual, glabrous, with
weak 1-segmented club; all antennomeres similar
in size except for first antennomere, which is
slightly longer, and the terminal antennomere,
which is slightly wider than the others.
Pronotum longitudinal, covered with
protuberances that mask additional details.
Twenty protuberances, most pointing forward,
arise from the combined head and pronotum.
Procoxal and mesocoxal cavities oval, well
separated; metacoxal cavities somewhat
transverse, separated.

Biosis: Biological Systems (2020) 1(4): 134-140 Poinar Jr. & Vega (2020)
138
Elytra narrow and long, entire dorsal surface
covered with erect protuberances ranging from
105-327 µm in length and 28-107 µm in width;
some 80 protuberances cover the elytra with four
longitudinal rows, each containing 10
protuberances, on each elytron; longest
protuberances occur in the basal to mid-region of
the elytra and the shortest at the tip of the elytra.
Abdomen with 5 freely articulated ventrites; tip of
abdomen with everted internal sac (length, 790
µm), the membranous walls of which have an
armature of spines. Also present is the aedeagus
(length, 510 µm) bearing sclerites and two
subtending parameres (length, 430 µm).
Legs relatively short, with profemur 630 µm long,
protibia 660 µm long and protarsus 263 µm long.
The mesofemur is 630 µm long, mesotibia 400
µm long and the mesotarsus 355 µm long; the
metatibia is 644 µm long, metatarsus 360 µm
long; the lengths of the metatarsomeres are (from
first to fourth) 84 µm, 84 µm, 70 µm, 231 µm. On
all legs, the terminal tarsomere is subequal to the
combined first three.
Remarks: There are no extant or extinct genera
of beetles in the current classification of the
Zopheridae that have the type of dorsal
protuberances found on S. saraemcheana gen. et
sp. nov. (Crowson, 1956; Dillon & Dillon, 1961;
Hatch, 1971; White, 1983; Borror et al., 1989;
Lawrence & Britton, 1991; Alekseev & Lord,
2014; Alekseev, 2015; Alekseev & Bukeja, 2016;
Ivie et al., 2016; Lord & Ivie, 2016; Alekseev &
Alekseev, 2019; Bullis, 2020). The elongate body
of S. saraemcheana gen. et sp. nov. resembles that
of the Australian Pseudendestes australis
(Lawrence & Britton, 1991).
Discussion
Several species of Zopheridae have been
described from Burmese amber, including
Paleoendeitoma antennata Deng, lipiski, Ren
and Pang (2017), P. minuta Deng, lipiski, Ren
and Pang (2017), P. buryi Hva (2019), P.
tuberculata Bullis (2020) and Cretomysteria
burmanica Deng, lipiski, Ren and Pang (2017).
None of the species in the genus Paleoendeitoma
or C. burmanica possess a covering of dorsal
protuberances as occurs in the present fossil. In
addition, the body of S. saraemcheana gen. et sp.
nov. is quite narrow, with the pronotum shaped
longitudinal, while it is transverse in P. antennata,
P. minuta, P. buryi, P. tuberculata and C.
burmanica (Deng et al., 2017; Hva, 2019; Bullis,
2020). In addition, there are no antennal grooves
or cavities on S. saraemcheana and the antennal
club is one-segmented.
An inverted (or everted) type of male genitalia is
one of the features of the Colydiinae (Deng et al.,
2017). While it is not a unique apomorphy of
colydiines, it is present on S. saraemcheana.
Within the spiny everted internal sac is a portion
of the aedeagus as well as the two parameres (Fig.
11), a condition described by Tuxen (1956) for
members of this family.
Lodged between the abdomen and elytra are
chains of one-celled conidia that are exposed at
the posterior end of the beetle (Fig. 12). There is
no mycelium protruding between the body
segments of S. saraemcheana. Since colydiines
are known to live in rotten wood, leaf litter and
decaying vegetation (Dillon & Dillon, 1961;
Lawrence & Britton, 1991) the conidia may
represent a species detached from its habitat.
There also is a possibility that this fungal-beetle
association is natural. Various fungi are known to
grow on the cuticle of species in the colydiine
genus Dryptops Bround, 1882 in Papua-New
Guinea (Samuelson, 1966).
The two mites (Figs. 3,6) are attached to S.
saraemcheana gen. et sp. nov. by their mouthparts
and are considered to have a parasitic, rather than
a phoretic, relationship with the beetle.
The narrow body associated fungal conidia and
presence of attached mites suggests that S.
saraemcheana gen. et sp. nov. could have
inhabited confined spaces, such as the galleries of
bark or other beetles. The pointed mouthparts of
S. saraemcheana gen. et sp. nov. indicates that it
was carnivorous and could have preyed on stages
of other invertebrates.
This discovery is interesting in several ways, not
only because it presents a new morphological
variation of this family of beetles, but that it also
provides information about the male reproductive
system of colydiines, the morphology of which
was considered a valuable character for
classification of Coleoptera (Crowson, 1956). The
discovery of fungi attached to the body of the
fossil beetle provides important information on
the possible habitats (tropical moist) visited by
Cretaceous cylindrical bark beetles.

Poinar Jr. & Vega (2020) Biosis: Biological Systems (2020) 1(4): 134-140
139
Acknowledgements
The authors thank John T. Doyen for suggesting
the Zopheridae as a possible family for the fossil.
Disclosure statement
No potential conflict of interest was reported by
the authors.
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