Dtsch. Entomol. Z. 68 (2) 2021, 341-348 | DOI 10.3897/dez.68.74174

> PENSUFT.

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BERLIN

New species of Omma Newman from mid-Cretaceous Burmese amber
(Coleoptera, Archostemata, Ommatidae)

Yan-Da Li!, Di- Ying Huang!, Chen-Yang Cai!

1 State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, and Centre for Excellence in Life and

Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
2 School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK

http://zoobank. org/F'535A41F-8DC2-420D-8 1B0-94EBEE461B30

Corresponding author: Chen-Yang Cai (cycai@nigpas.ac.cn)

Academic editor: Sonja Wedmann @ Received 8 September 2021 Accepted 18 November 2021 @ Published 30 November

2021

Abstract

A new fossil species of the extant archostematan genus Omma Newman, O. forte sp. nov., is reported from mid-Cretaceous amber

from northern Myanmar. The extinct ommatid genus, Cionocups Kirejtshuk from the same deposit, is considered as a junior synonym

of Omma, and C. manukyani 1s transferred to Omma, as O. manukyani comb. nov. A key to species of Omma from Burmese amber

is also provided.

Key Words

Archostemata, Burmese amber, Cretaceous, Omma, Ommatidae

Introduction

Ommatidae is a small family in the beetle suborder
Archostemata (Hoérnschemeyer and Beutel 2016). In
a recent phylotranscriptomic study, this family has
been recovered as the sister group of Micromalthidae,
rather than the — superficially similar-looking
Cupedidae (McKenna et al. 2019), so it cannot be
included in Cupedidae as a subfamily (for alternative
interpretations, see Kirejtshuk 2021). Traditionally,
two extant genera were recognized in Ommatidae,
i.e., Omma Newman from Australia and TJetraphalerus
Waterhouse from South America (Lawrence 1999).
Recently, the comparatively diverse genus Omma was
split into Omma sensu stricto and Beutelius Escalona
et al. (Escalona et al. 2020), partly based on the
cladistic analysis in Hornschemeyer (2009). Omma
has relatively short maxillary and labial palps, and
the gulamentum is not depressed, while Beutelius has

longer maxillary and labial palps, and the gulamentum
is depressed anteriorly.

The fossil record of Omma is relatively abundant (as list-
ed by Kirejtshuk 2020). The earliest putative Omma fossils
date back to the Late Triassic (Crowson 1962; Fig. 1). Juras-
sic and Cretaceous Omma fossils have been reported from
numerous localities across the continents of Europe and
Asia (e.g., Ponomarenko 1966, 1969; Tan et al. 2012; Cai
and Huang 2017). Recently, well-preserved Omma fossils
have also been reported from the mid-Cretaceous Burmese
amber. Based on our observation, Omma represents a rela-
tively common genus in Burmese amber (compared with
other ommatid genera). To date, three Omma species have
been established based on fossil material from Burmese am-
ber (Jarzembowski et al. 2017, 2020; Kirejtshuk 2020).

In this study, we describe a new species of Omma in
mid-Cretaceous Burmese amber. The placement of some
other previously published Omma and Omma-related fos-
sils are also reviewed based on our new observations.

Copyright Yan-Da Li et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

342

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Yan-Da Li et al.: Omma from Burmese amber

aS a EP ba

Figure 1. General habitus of Omma liassicum Crowson deposited at British Museum of Natural History, under incident light. A. Holo-

type, 1.11095a; B. Holotype, I.11095b; C. Paratype, I.11070a; D. Paratype, I.11070b; The body length is about 15 mm in both specimens.

Materials and methods

The Burmese amber specimens studied herein (Figs 2-6)
originated from amber mines near Nowe Bum (26°20'N,
96°36'E), Hukawng Valley, Kachin State, northern Myanmar.
The specimens are deposited in the Nanjing Institute of Ge-
ology and Palaeontology (NIGP), Chinese Academy of Sci-
ences, Nanjing, China. The amber pieces were trimmed with
a small table saw, ground with emery paper of different grit
sizes, and finally, polished with polishing powder.

Photographs under incident light were mainly taken
with a Zeiss Discovery V20 stereo microscope. Wide-
field fluorescence images were mainly captured with a
Zeiss Axio Imager 2 light microscope combined with a
fluorescence imaging system. Confocal images were ob-
tained with a Zeiss LSM710 confocal laser scanning mi-
croscope, using the 488 nm Argon laser excitation line
(Fu et al. 2021). Images under incident light and wide-
field fluorescence were stacked in Helicon Focus 7.0.2
or Zerene Stacker 1.04. Confocal images were stacked
with Helicon Focus 7.0.2 and Adobe Photoshop CC. Im-
ages were further processed in Adobe Photoshop CC to
enhance contrast.

Systematic palaeontology

Order Coleoptera Linnaeus, 1758
Suborder Archostemata Kolbe, 1908
Family Ommatidae Sharp & Muir, 1912

Genus Omma Newman, 1839
(= Cionocups Kirejtshuk, 2020 syn. nov.)

Type species. Omma stanleyi Newman, 1839.

Congeners in Burmese amber. Omma davidbatteni
Jarzembowski et al., 2020, Omma forte Li & Cai sp. nov.,
Omma Iii Jarzembowski et al., 2016, Omma janetae Kire-
jtshuk, 2020, and Omma manukyani (Kirejtshuk, 2020)
comb. nov.

Diagnosis. Head without prominent posterior protu-
berances. Labrum with dentate anterior margin. Separate
mentum absent. Anterior third of gulamentum not de-
pressed. Pronotal disc with rounded lateral edges; dorsal
surface without ridges or protuberances. Sternopleural
suture absent. Prosternal process short. Punctured expla-
nate elytral epipleura absent. CuA of hind wings forked;
wedge cell present. Abdominal ventrites abutting.

Key to Omma species in mid-Cretaceous amber from northern Myanmar

1 Margins of pronotal disc and elytra without distinct tooth-like tubercles................cccccecscceceeeceeeececeeeeseeesseeeseseeceseeaeeees 2

— Mareinsteis promotalsdisc andielyiraewith, tothe liKestubenCless. 01/2. ecsks sx i5 ceo wseeresccestamasgcees te aesc Masa den ocean ete cce eases 4
2 Body slender; mandibles comparatively elongate, projecting more anteriorly..... Omma davidbatteni Jarzembowski et al.

- Body wider; mandibles curved more pronouncedly..........

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Dtsch. Entomol. Z. 68 (2) 2021, 341-348 343

3 Pronotal disc with convex anterior margin; elytra with narrow subexplanate epipleura ............. Omma janetae Kirejtshuk
_ Pronotal disc with relatively straight anterior margin; elytra with distinct subexplanate epipleura .............ccccceceee cece eeees
ia i ch a aN SE A a A A Omma !ii Jarzembowski et al.
4 Body smaller; elytral window punctures in the second outermost row not distinctly transverse ............ccccceceec cence seen eeees
56 RST ce ees SAY 2 neta Race, emer AS Peale Capris Ne «cali ASR Ys RR ro pr corel a Ete Omma manukyani (Kirejtshuk)
— Body larger; elytral window punctures in the second outermost row distinctly transverse... Omma forte Li & Cai, sp. nov.

Omma forte Li & Cai, sp. nov.
http://zoobank.org/SECF739A-7BF6-4114-A95C-4B151973BFD1
Figures 2—4

Material examined. Holotype, NIGP176634.

Etymology. The specific name is from the Latin ‘for-
tis’, meaning strong, referring to the robust appearance of
the species.

Locality and horizon. Amber mine located near Noi-
je Bum Village, Tanai Township, Myitkyina District,
Kachin State, Myanmar; unnamed horizon, mid-Creta-
ceous, Upper Albian to Lower Cenomanian.

Description. Body comparatively wide, about 9.3
mm long and 3.8 mm wide, tuberculate, with thin setae
and scales.

Head (Fig. 3A, C) prognathous, seemingly wider than
long. Neck region constricted, broad. Compound eyes
comparatively large, protuberant. Antennal insertions lo-
cated at anterior corners of head, separated by more than
three diameters of antennomere 1. Subantennal grooves
absent. Frontoclypeal suture absent. Labrum (Fig. 4A)
transverse, with dentate anterior margin. Antenna (Fig. 3A)
long, extending beyond base of prothorax when posterior-

f

F,

ly directed, 11-segmented and filiform. Mandibles (Fig.
4B) tridentate with vertically aligned teeth. Maxillary and
labial palps short, not reaching the level of the eyes when
extending posteriorly (Figs 3C, 4C); apical maxillary and
labial palpomeres probably expanded and securiform.

Pronotal disc (Fig. 3B) widest in the anterior third,
slight narrowing posteriorly; anterior corners rounded;
lateral edges with distinct tooth-like tubercles (dentate)
(Fig. 4D).

Scutellar shield (Fig. 4E) subtrapozoidal, wider pos-
teriorly. Elytra (Figs 2, 3E, F) with ten rows of window
punctures; lateral edges with distinct tooth-like tubercles
(dentate); surface with ribbed slender scales (Fig. 4G);
punctures in the ninth row distinctly transverse; inter-
space between eighth and ninth puncture rows thickened
(Fig. 2). Metaventrite narrowed anteriorly; discrimen
present; metakatepisternal suture well developed
(Fig. 4H). Metacoxae (Fig. 4H) strongly transverse with
subconical mesal projections, contiguous, extending lat-
erally to meet elytra, with weak coxal plates.

Hind wings (Fig. 3G, H) well developed. CuA forked;
CuA, fused with MP,,; CuA,,, fused with CuP+AA,;
wedge cell present.

B | a

at

Figure 2. General habitus of Omma forte sp. nov., holotype, NIGP176634, under incident light. A. Dorsal view; B. Ventral view;

Scale bars: 2 mm.

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344

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Yan-Da Li et al.: Omma from Burmese amber

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Figure 3. Details of Omma forte sp. nov., holotype, NIGP176634, under widefield fluorescence. A. Head, dorsal view; B. Prothorax,
dorsal view; C. Head, ventral view; D. Hind leg, ventral view; E. Elytral base, dorsal view; F. Elytral apex, dorsal view; G. Hind
wing, dorsal view; H. Hind wing, ventral view. Abbreviations: anl—3, antennomeres 1-3; el, elytron; ey, compound eye; md, man-
dible; mtf, metafemur; mttb, metatibia; mttsl, metatarsomere 1; pc, procoxa; pf, profemur; pn, pronotum; wc, wedge cell. Scale

bars: 500 um.

Legs long and slender. Tibiae with at least one well-de-
veloped spur. Tarsi long and slender; metatarsus especial-
ly long; metatarsomere | about as long as metatibia (Fig.
3D). Pretarsal claws simple.

Abdomen with five coplanar ventrites, separated by
distinct grooves (Fig. 41).

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Remarks. The new species can be confidently as-
signed to Omma. The length of maxillary and labial palps
is a key diagnostic character separating Beutelius from
Omma (Escalona et al. 2020). Omma forte sp. nov. has
short maxillary and labial palps, not reaching the level of
the eyes, which is in accordance with Omma. The hind

Dtsch. Entomol. Z. 68 (2) 2021, 341-348

345

images labeled in Suppl. material 1. A. Mouthparts, posterodorsal view; B. Mouthparts, anterior view; C. Mouthparts, ventral view;

D. Prothorax, dorsal view, showing the gradual change from rounded tubercles to teeth (arrowheads); E. Scutellum, dorsal view;

F. Elytron, dorsal view; G. Scales, tubercles, and window punctures on elytron, dorsal view; H. Metacoxa, ventral view; I. Abdo-

men, ventral view. Abbreviations: el, elytron; lb, labrum; lbp, labial palp; md, mandible; mtc, metacoxa; mxp, maxillary palp; pn,

pronotum; sc, scutellum; v4,5, ventrites 4,5. Scale bars: 300 um.

wing venation (especially the branching pattern of CuA)
is another important character differentiating the two gen-
era. In most beetle fossils preserved in amber, the hind
wings are hidden by the elytra, and are thus not available
for taxonomic purpose. Fortunately, the hind wings are
partly exposed in the holotype of O. forte. In O. forte, the
posterior branch of CuA (CuA,,) is fused with CuP+AA,,
closing the wedge cell, and the anterior branch of CuA
(CuA, ) is fused with MP, (Fig. 3G), which matches per-
fectly with the venation of Omma stanleyi (fig. 64 in Es-
calona et al. 2020; fig. 4B in Lawrence et al. 2021), while

the CuA of Beutelius is unforked (figs 67—68 in Escalona
et al. 2020) or with an incomplete anterior branch only
(fig. 4A in Lawrence et al. 2021).

Discussion
Extant Omma stanleyi and Omma fossils from Burmese
amber are characterized by the dentate anterior margin of

labrum (Escalona et al. 2020; Figs 4A, 6C). Such a char-
acter is not detected in any other ommatids in Burmese

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346

Yan-Da Li et al.: Omma from Burmese amber

Figure 5. General habitus of Omma cf. manukyani, NIGP176635, under incident light. A. Dorsal view; B. Ventral view. Scale bars:

1.5 mm.

amber we examined (though it would be hard to con-
firm the state in other compression fossils). Thus, this
character could possibly be an autapomorphy of Omma
and the closely related Beutelius. The presence of scales
(ribbed scale-like setae) has been suggested as a diag-
nostic feature separating Beutelius from Omma (Escalo-
na et al. 2020). In the newly discovered fossil O. forte,
the setae on elytra are relatively slender, which is kind
of similar to that of extant O. stanleyi. However, under
confocal microscopy, the ribs could be clearly seen on
the flat setae of O. forte (Fig. 4G), suggesting the interre-
lationships among Omma and Omma-like species might
be more complicated.

Numerous Mesozoic fossils have been assigned to the
genus Omma. Unfortunately, as noted by Escalona et al.
(2020), some key diagnostic characters (e.g., anterior de-

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pression in the gulamentum) are not easily available for
many compression/impression fossils, making it hard to
validate their generic attribution. Escalona et al. (2020),
nevertheless, confirmed the placement of several fossil
Omma species, including the Late Triassic O. liassicum
Crowson. However, the key characters such as mouth-
parts and gulamentum are not well-preserved in O. lias-
sicum as well. Besides, in its holotype, the propleuron 1s
likely to be separated from the prosternum by a distinct
suture (Fig. 1B). As such, we think O. /iassicum cannot be
confidently differentiated from Beutelius (and even some
more distantly related genera, e.g., Bukhkalius Kirejtshuk
& Jarzembowski; Li et al. 2021).

Kirejtshuk (2020) created the genus Cionocups to
accommodate a new species from Burmese amber, C7-
onocups manukyani. He noted that Cionocups is similar

Dtsch. Entomol. Z. 68 (2) 2021, 341-348

347

E F
pn
H
al

Figure 6. Details of Omma cf. manukyani, NIGP176635, under widefield fluorescence (A, D, G) or confocal microscopy (B, C, E,
F, H, D, with the relative positions of the confocal images labeled in Suppl. material 1. A—-C. Head, dorsal view (A, B) or ventral

view (C); D-F. Prothorax, dorsal view (D, E) or ventral view (F); G—I. Elytra, dorsal view. Abbreviations: anl, antennomere 1; el,
elytron; ey, compound eye; lb, labrum; lbp, labial palp; md, mandible; mxp, maxillary palp; pc, procoxa; pn, pronotum; ps, proster-

num; v4,5, ventrites 4,5. Scale bars: 600 um (A, D, G); 300 um (B, C, E, F, H, I).

to Cionocoleus, an extinct genus found in the Cretaceous
of Eurasia. Cionocoleus shares a similar morphology with
extant Omma, except for the lack of window punctures on
the elytra (Tan et al. 2007). Cionocups, however, is clear-
ly different from Cionocoleus in having clear window
punctures on the elytra, though somewhat smaller than
that of Omma. Thus, Cionocups is more similar to extant
Omma, rather than Cionocoleus. Cionocups manukyani
differs from extant O. stanleyi in antennae longer and with
serration (teeth) along the lateral sides of pronotum and
elytra (Kirejtshuk 2020). However, in some fossil Omma
species, the antennae can also be elongated. For example,
the antennae of O. /ii and O. forte also reach the elytral
base when posteriorly directed (Fig. 2). Besides, our new-
ly reported O. forte also possesses teeth along the sides of

pronotum and elytra (Fig. 3B, E, F). Detailed observations
under confocal microscopy suggest that the difference be-
tween teeth and rounded tubercles is not always distinct,
with a set of transitional states between the two extremes
(Figs 4B, 6E). Therefore, we suggest that the character
combination of C. manukyani is not unique enough for a
separate genus. Here Cionocups is considered as a junior
synonym of Omma and C. manukyani is transferred to the
genus Omma, as Omma manukyani comb. nov.

Data availability

The original confocal data are available in the Zenodo
repository (https://doi.org/10.5281/zenodo.5693059).

dez.pensoft.net

348

Acknowledgements

We are grateful to Rong Huang for technical help in con-
focal imaging. We also thank Thomas Hornschemeyer
and André Nel for their valuable comments on an earli-
er version of this paper. Financial support was provid-
ed by the Second Tibetan Plateau Scientific Expedition
and Research project (2019QZKK0706), the Strate-
gic Priority Research Program of the Chinese Acade-
my of Sciences (XDB26000000 and XDB18000000),
and the National Natural Science Foundation of China
(41688103).

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Supplementary material 1

Habitus of Omma forte and O. manukyani,
with the relative positions of confocal images
in Figs 4 and 6 labeled

Authors: Yan-Da Li, Di-Ying Huang, Chen- Yang Cai

Data type: PDF file

Explanation note: Figure S1. General habitus of Omma
forte sp. nov., holotype, NIGP176634, under widefield
fluorescence. Whiterectangles indicate the regions
magnified in Figure 4. Figure S2. General habitus of
Omma cf. manukyani, NIGP176635, under widefield
fluorescence. White rectangles indicate the regions
magnified in Figure 6.

Copyright notice: This dataset is made available under
the Open Database License (http://opendatacommons.
org/licenses/odbl/1.0). The Open Database License
(ODbL) is a license agreement intended to allow us-
ers to freely share, modify, and use this Dataset while
maintaining this same freedom for others, provided
that the original source and author(s) are credited.

Link: https://doi.org/10.3897/dez.68.74174.suppll