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Fossil e idence o ely a educ ion
in ship- imbe bee les
shûhei Yamamo o
Bee les (Coleop e a) comp ise abou one qua e o all desc ibed animal species. one o he main
con ibu o s o hei e olu iona y success is he ely a, o ha dened o ewings, which ha e p o ec i e
unc ions while main aining hei abili y o ly. Unlike o he bee les, some ship- imbe bee les
(Lymexylidae) ha e ex emely small ely a and la gely exposed unc ional hindwings. he e is li le
ossil e idence illumina ing he e olu iona y his o y o sho ely a in lymexylids. He e, I epo i e
well-p ese ed lymexylid ossils in mid-C e aceous and Cenozoic ambe s om Myanma (ca. 99 million
yea s ago [Mya]), Russia (ca. 44 Mya), and he Dominican Republic (ca. 16 Mya). Th ee C e aceous ossils
ha e s ongly educed, sho ened ely a, wi h unexpec ed a ia ion in ely al size and shape, whe eas
e y small, modi ied ely a a e ound only in much younge Dominican ambe . These mo phologically
di e se ex inc lymexylids shed new ligh on he ea ly o igin and e olu iona y his o y o ely a educ ion
and i s di e se a ia ion in he ship- imbe bee les. Based on he s iking mo phological simila i ies wi h
ex an lymexylids, hese ex inc axa migh ha e had he same, o simila , ecological, beha iou al, and
ligh modes as he ex an ship- imbe bee les.
Wi h nea ly 400,000 named li ing species, bee les (Coleop e a) comp ise he la ges monophyle ic o de in he
T ee o Li e, showing as onishing mo phological, ecological, and beha iou al di e si y in nea ly all e es ial
and eshwa e ecosys ems1–3. Ely a, which a e hea ily scle o ised o ewings, cha ac e ise bee les and co e he
do sal su ace o he abdomen. These shield-like s uc u es ha e a ious inno a i e unc ions in bee les. They
p o ec he hindwings and do sal abdomen om p eda o s o ha sh en i onmen al condi ions. Ely a also sup-
po desicca ion ole ance, minimise he e ec o apid empe a u e shi s, and e en play oles in mimic y o
camou lage4–7. The s ong scle o isa ion enabled ea ly bee les o pene a e and adap o li e unde ba k, like he
adul s o ex an a chos ema an bee les (Cupedidae and Omma idae)8. The e o e, he p esence o ely a makes a
majo con ibu ion o adap a ions o a a ie y o habi a s o mic o-en i onmen s. Despi e hese ad an ages, some
bee les possess sho ened o educed ely a. The pa ial educ ion o he ely a, i.e. b achely y, is widely sca e ed
ac oss Coleop e a. Fo example, he o e bee le amily S aphylinidae alone con ains o e 64,000 species and mos
a e b achely ous. Howe e , he hindwings o o e bee les a e hidden unde sho ened ely a. Al hough he e a e
some excep ions (see Discussion), his condi ion o ely a, i.e. b achely y wi h hidden hindwings, a e almos
uni e sal o he en i e Coleop e a. Female ilobi e bee les (Lycidae, Pla e od ilus spp.) a e excep ional because
hey lack ace o ely a9. Excluding Pla e od ilus, he deg ee o ely al educ ion anges om mode a e o almos
comple ely educed, as seen in he ship- imbe bee le sub amily A ac oce inae (Lymexylidae)7; he la e ha e
exposed hei abdomens and unc ional hindwings (Fig.1i,j and Supplemen a y Fig.1b).
Lymexylidae is a small, monophyle ic bee le amily, wi h only 72 species in 12 gene a dis ibu ed globally
(excluding ossils)10,11. Based on se e al dis inc mo phological cha ac e s (e.g. highly modi ied maxilla y palpus),
lymexylids cons i u e he sole membe o he supe amily Lymexyloidea. This g oup is so specialised ha e en a
di e en insec o de , S epsip e a (S ylopidae), was once placed in his supe amily1, al hough his was based on
an in alid a gumen . In some ecen s udies, Lymexylidae was ully nes ed wi hin Teneb ionoidea12–14 o o med
a clade wi h Teneb ionoidea and Cle oidea15. Howe e , he la es , mos comp ehensi e genomic s udy s ill eco -
e ed i as a dis inc supe amily16. Lymexylids cu en ly comp ise ou sub amilies: A ac oce inae (se en gene a,
one ex inc ), Hylecoe inae (one genus), Lymexylinae (one genus), and Meli omma inae ( i e gene a, one ex inc ).
A ac oce inae is cha ac e ised by exceedingly educed ely a and is sis e o Lymexylinae10,11. Di ec ossil e i-
dence o he educed, sho ely a in lymexylids has ne e been p o ided.
He e, I epo i e a ac oce ine bee les in mid-C e aceous Bu mese, mid-Eocene Bal ic, and Middle Miocene
Dominican ambe s. All o he specimens epo ed he e ha e ex emely educed ely a. The h ee Bu mese ambe
a ac oce ines clea ly show he educed ely a, bu hey also demons a e some a ia ion in he shape and size o
In eg a i e Resea ch Cen e , Field Museum o Na u al His o y, 1400S Lake Sho e D i e, Chicago, IL, 60605-2496,
USA. co espondence and eques s o ma e ials should be add essed o S.Y. (email: s.[email p o ec ed])
Recei ed: 18 Janua y 2019
Accep ed: 4 Ma ch 2019
Published: xx xx xxxx
opeN
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Figu e 1. Di e se Lymexylidae bee les, do sal iews. (a–c) A ac oce inae om mid-C e aceous Bu mese
ambe , d A ac oce inae om mid-Eocene Bal ic ambe , e A ac oce inae om ea ly Middle Miocene
Dominican ambe , ( –k) ex an ep esen a i es o Lymexylidae, aken om each sub amily. (a) Ve a ac oce us
bu mi icus gen. e sp. no ., holo ype, FMNHINS-3965988. (b) Ra ac oce us ex inc us sp. no ., holo ype,
FMNHINS-3965989. (c) R. ossilis sp. no ., holo ype, FMNHINS-3965990. (d) R. bal icus sp. no ., holo ype,
FMNHINS-3965991. (e) A ac oce us sp., FMNHINS-3965992. ( ) Meli omma se iceum (Ha is),
Meli omma inae, om Indiana, U.S.A., showing ully de eloped, comple e ely a. (g) Hylecoe us de mes oides
(L.), Hylecoe inae, om De byshi e, U.K., showing well de eloped, bu sligh ly educed ely a. (h) Lymexylon
na ale (L.), Lymexylinae, om Su olk, U.K., showing well de eloped, bu mode a ely educed ely a. (i–k)
A. b asiliensis Lepele ie & Audine -Se ille, A ac oce inae, om Blue ields, Nica agua, showing dis inc ly
educed, minu e ely a; (i) do sal habi us, (j) enla gemen o ely on om (i), (k) ely on. Pho os c edi s: (g,h)
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he ely a, anging om much longe ely a han in he ex an axa o e y simila ones. Sho e ely a a e also
seen in he Bal ic ambe ossil. Exceedingly minu e, sh unken, de o med ely a a e ep esen ed by only a single
occu ence in he much younge Dominican ambe . This se ies o new lymexylid ossils indica es he an iqui y o
he ely a educ ion in he ship- imbe bee les and demons a es a ious pa e ns o ely a du ing he C e aceous.
The ex emely educed lymexylid ely a as in he ex an A ac oce us a e hough o ha e a pos -C e aceous
o igin. Al hough ely a educ ion exposing he hindwings and abdomen is seen only in a iny ac ion o he
mega-di e se bee les, my disco e y b oadens ou knowledge o he e olu ion o ely a in Coleop e a.
Resul s
sys ema ic palaeon ology. O de Coleop e a Linnaeus, 1758
Supe amily Lymexyloidea Fleming, 1821
Family Lymexylidae Fleming, 1821
Sub amily A ac oce inae Lapo e, 1840
Ve a ac oce us gen. no .
LSID (Li e Science Iden i ie ): u n:lsid:zoobank.o g:ac :EF9F7C08-DA9E-4D63-81D8-D674B74E18EC.
ype species. Ve a ac oce us bu mi icus sp. no .
e ymology. The gene ic name is a combina ion o he La in adjec i e e us (meaning, ancien ) and he genus
A ac oce us.
Diagnosis. Ve a ac oce us is dis inguished om all o he a ac oce ines by he ollowing combina ion o
cha ac e s: body small (ca. 8.5 mm)and na ow, uni o mly pale yellowish b own; head la ge, a he e ical,
sligh ly wide han p ono um; eyes la ge, occupying almos he en i e ons, eyes nea ly con iguous an e io ly;
an enna ili o m, as long as he head and p ono um combined, each an ennome e dis inc ly elonga e; p ono um
subpa allel sided, mode a ely p oduced an e io ly; mesoscu ellum small and na ow, occupying abou hal he
wid h o he ely al base; each ely on educed, bu ela i ely long and slende , app oxima ely 8.7 imes longe
han wide, exposing la ge pa s o he abdomen, do sum lacking ma king; and me acoxae ema kably modi ied,
s ongly p ojec ing pos e io ly.
Rema ks. Among all ex an a ac oce ines, Ve a ac oce us gen. no . is mo phologically simila o he ex an
genus U ea Paulus om G eece in ha ing dis inc ly modi ied me acoxae, la ge, con iguous eyes, and an e io ly
p oduced p ono um, bu i is easily sepa a ed om U ea as ollows11: body much smalle (16 mm in U ea); eyes
smalle , occupying less o he pos e io ons; and an ennae slende e and longe . In addi ion, Ve a ac oce us
gen. no . can be dis inguished om all o he A ac oce inae gene a as ollows17: om A ac oce us, Fusico nis,
and Hymaloxylon in ha ing la ge, con iguous eyes; om A ac oce us and Ra ac oce us in ha ing slende e an en-
nae and ma kedly modi ied me acoxae; om C a oa ac oce us in he absence o M+ Cu olk o hindwing,
bu al e na i ely ha ing much smalle body (28 mm in C a oa ac oce us) and elonga e p ono um. In addi ion,
Ve a ac oce us gen. no . di e s om all ex an gene a in he p esence o longe , slende e ely a.
Ve a ac oce us bu mi icus sp. no .
(Figu es1a and 2a, and Supplemen a y Figs2a,3)
LSID (Li e Science Iden i ie ): u n:lsid:zoobank.o g:ac :BC26AB2F-E7B3-4A19-B033-5E0574602A17.
e ymology. The speci ic epi he is de i ed om he occu ence o he ossil in Bu mese ambe known as
‘bu mi e’.
Ma e ial. Holo ype: FMNHINS-3965988 (Supplemen a y Fig.2a), a comple ely p ese ed emale adul .
Mid-C e aceous (ea lies Cenomanian) ambe [ca. 99 million yea s ago (Mya)18], om he Hukawng Valley,
Kachin S a e, no he n Myanma .
Diagnosis. As o he genus (see abo e), wi h he ollowing mino addi ions: p ono al disc wi h blackish and
longi udinal comple e lines along midline and la e al ma gins; mesoscu ellum wi h comple e, hick, longi udinal
blackish line along midline.
Desc ip ion. Re e o online Supplemen al No e o a comple e desc ip ion.
Genus Ra ac oce us Ku osawa, 1985
Rema ks. This genus was once synonymised10, bu i was la e esu ec ed11. Wi h only wo ex an species,
Ra ac oce us is a small genus in Lymexylidae. The dis ibu ion is es ic ed mainly o he O ien al egion, bu i is
also ound in sou he nmos Aus alia11. The C e aceous ossils desc ibed below a e biogeog aphically consis en
by Udo Schmid , licensed unde he C ea i e Commons A ibu ion-Sha e Alike 2.0 Gene ic license (CC BY-SA
2.0, h ps://c ea i ecommons.o g/licenses/by-sa/2.0/), de i ed om Wikimedia Commons, (h) modi ied. Scale
ba s: 3 mm (a,c,j), 5 mm (b,d,e–h), 1 cm (i), 1.5 mm (k).
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wi h he mode n species. By con as , he occu ence o a Ra ac oce us ossil om Bal ic ambe is in iguing. The
cu en dis ibu ion o A ac oce inae is ela i ely cosmopoli an, and only a single species o he sub amily is
ound in Eu ope, namely U ea g acea Paulus om G eece11. The e o e, he disco e y o Ra ac oce us in no h-
e n Eu ope is su p ising and no ewo hy, al hough his dis ibu ion pa e n has been known o se e al bee le
g oups19–21.
Ra ac oce us ex inc us sp. no .
(Figu es1b and 2b,g and Supplemen a y Figs2b,4,5).
LSID (Li e Science Iden i ie ): u n:lsid:zoobanko g:ac : u n:lsid:zoobank.o g:ac :94130B93-6FFE-4C43-
89E6-8B0987C7FEAD.
e ymology. The speci ic epi he e e s o he La in adjec i e ex inc , highligh ing i as a C e aceous ossil.
Ma e ial. Holo ype, FMNHINS-3965989 (Supplemen a y Fig.2b), a comple ely p ese ed emale adul .
Mid-C e aceous (ea lies Cenomanian) ambe (ca. 99 Mya18), om he Hukawng Valley, Kachin S a e, no he n
Myanma .
Figu e 2. Di e si y o educed ely a in ex inc A ac oce inae bee les, do sal iews. (a–c) A ac oce inae
om mid-C e aceous Bu mese ambe , showing sho o ma kedly sho ely a, (d) A ac oce inae om mid-
Eocene Bal ic ambe , showing e y sho ely a, e A ac oce inae om ea ly Middle Miocene Dominican
ambe , showing dis inc ly sho and minu e ely a. (a, ) Ve a ac oce us bu mi icus gen. e sp. no .,
holo ype, FMNHINS-3965988; ( ) enla gemen o ely on. (b,g) Ra ac oce us ex inc us sp. no ., holo ype,
FMNHINS-3965989; (g) enla gemen o ely on. (c,h) R. ossilis sp. no ., holo ype, FMNHINS-3965990; (h)
enla gemen o ely on. (d,i) R. bal icus sp. no ., holo ype, FMNHINS-3965991; (i) enla gemen o ely on. (e,j)
A ac oce us sp., FMNHINS-3965992; (j) enla gemen o ely on. Scale ba s: 3 mm (a,c), 5 mm (b,d,e), 1 mm
( ,g,i), 0.5 mm (h,j).
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Diagnosis. This new species o A ac oce inae can be assigned o he ex an genus Ra ac oce us based on he
ollowing combina ion o cha ac e s17: head a he e ical, mode a ely wide han p ono um; eyes la ge, con ig-
uous, occupying almos he en i e ons; an enna slende , somewha usi o m; mesoscu ellum ela i ely na ow,
occupying abou wo hi ds he wid h o he ely al base. Ra ac oce us ex inc us sp. no . can be dis inguished om
o he Ra ac oce us species by he ollowing combina ion o cha ac e s: an ennae a he usi o m, hicke ; head
wide, mode a ely wide han p ono um; p ono um weakly elonga e, an e io ma gin weakly ounded, p ono al
disc wi h hick deep longi udinal blackish line/g oo e along he midline; mesoscu ellum sligh ly wide han long,
occupying abou wo hi ds he wid h o he ely al base, do sum wi h conspicuous blackish ma king along mid-
line; each ely on sho , na owly elonga e, app oxima ely 3.2 imes longe han wide, g adually na owing pos e-
io ly, wi hou ma king; meso en i e ca ina e along midline; and me acoxae a he s ongly modi ied, ela i ely
s ongly p ojec ing pos e io ly.
Desc ip ion. Re e o online Supplemen al No e o a comple e desc ip ion.
Ra ac oce us ossilis sp. no .
(Figu es1c and 2c,h and Supplemen a y Figs2c,6,7)
LSID (Li e Science Iden i ie ): u n:lsid:zoobank.o g:ac :ACB32243-DDD8-461B-9D31-FE006252913E.
e ymology. The speci ic epi he is de i ed om he ac ha i is a ossil species.
Ma e ial. FMNHINS-3965990 (Supplemen a y Fig.2c), a nea ly comple e adul , bu pa ially damaged, sex
unde e mined. Mid-C e aceous (ea lies Cenomanian) ambe (ca. 99 Mya18), om he Hukawng Valley, Kachin
S a e, no he n Myanma .
Diagnosis. This new species o A ac oce inae can be assigned o he ex an genus Ra ac oce us based on he
ollowing combina ion o cha ac e s17: head a he e ical, sligh ly wide han p ono um; eyes la ge, con iguous,
occupying almos he en i e ons; mesoscu ellum ela i ely small and na ow, occupying abou wo hi ds he
wid h o he ely al base. Ra ac oce us ossilis sp. no . can be dis inguished om o he Ra ac oce us species by
he ollowing combina ion o cha ac e s: an ennae ela i ely s ongly usi o m, slende ; head wide, da k b own,
sligh ly wide han p ono um; p ono um subquad a e, e y weakly elonga e, g adually widened apically, wid-
es and nea ly unca e a an e io ma gin, p ono al disc wi h hin comple e da ke line/g oo e along midline;
mesoscu ellum as long as wide, occupying abou wo hi ds he wid h o he ely al base, do sum wi h blackish
conspicuous ma king on base; each ely on slende , app oxima ely 3.9 imes longe han wide, na owes a ound
middle, an e io hal wi h elonga e-o al, whi ish ma king, o ming ela i ely clea pa e n; and me acoxae mod-
e a ely modi ied, ela i ely s ongly p ojec ing pos e io ly.
Desc ip ion. Re e o online Supplemen al No e o a comple e desc ip ion.
Ra ac oce us bal icus sp. no .
(Figu es1d and 2d,i and Supplemen a y Figs2d,8,9).
LSID (Li e Science Iden i ie ): u n:lsid:zoobank.o g:ac :F77CB344-EF73-4EC0-8E6B-AEFDD3AB2D5C.
e ymology. The speci ic epi he is de i ed om he English adjec i e bal ic in e e ence o Bal ic ambe .
Ma e ial. FMNHINS-3965991 (Supplemen a y Fig.2d), a comple ely p ese ed emale adul . Mid-Eocene
Bal ic ambe (ca. 44 Mya22), om Yan a ny, Kalining ad Oblas , Russia.
Diagnosis. This new species o A ac oce inae can be assigned o he ex an genus Ra ac oce us based on he ol-
lowing combina ion o cha ac e s17: head a he e ical, sligh ly wide han p ono um; eyes la ge, con iguous, occu-
pying almos he en i e ons; an enna slende , ela i ely s ongly usi o m; mesoscu ellum ela i ely wide, occupying
li le mo e han wo hi ds he wid h o he ely al base. Ra ac oce us bal icus sp. no . can be dis inguished om o he
congene s by he ollowing combina ion o cha ac e s: an ennae a he s ongly usi o m, bu slende ; head wide,
sligh ly wide han p ono um; p ono um subquad a e, nea ly as long as wide, an e io ma gin weakly ounded,
la e al ma gins gen ly a cua e, p ono al disc wi h deep, comple e, longi udinal g oo e along midline (while lacking
blackish line); mesoscu ellum ans e se, occupying li le mo e han wo hi ds he wid h o he ely al base, do sum
wi hou ma kings o macula ion; ely on slende , app oxima ely 3.5 imes longe han wide, nea ly subpa allel sided,
lacking pa e n; and me acoxae mode a ely modi ied, ela i ely s ongly p ojec ing pos e io ly.
Desc ip ion. Re e o online Supplemen al No e o a comple e desc ip ion.
Rema ks. Ra ac oce us bal icus sp. no . is he i s a ac oce ine desc ibed om Bal ic ambe .
Genus A ac oce us Paliso de Beau ois, 1802
A ac oce us sp.
(Figu es1e and 2e,j and Supplemen a y Figs2e,10)
Ma e ial. FMNHINS-3965992 (Supplemen a y Fig.2e), a comple e, ela i ely well, p ese ed emale adul .
Ven al side is la gely no isible. Ea ly Middle Miocene ambe (ca. 16 Mya23), om he Dominican Republic, no
u he de ails a e a ailable.
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Diagnosis. The ossil can be placed in he ex an genus A ac oce us using he ollowing diagnos ic cha ac-
e s17: head clea ly na owe han p ono um; la ge, con iguous eyes; sho usi o m an enna; b oadened mesoscu-
ellum ha occupies mo e han wo hi ds he wid h o he ely al base; and ex emely sho ened, small ely a.
This ossil axon may be dis inguished om o he congene s by he ollowing cha ac e s: smalle body; s ongly
usi o m, bu dis ally slende , an ennae; minu e, modi ied and ele a ed ely a; and he s uc u es o he emale
geni alia. The en al side is no ully isible. Fu he compa ison wi h he mode n congene s is di icul because
o a poo isibili y o he en al side and he ambigui y o he species limi o he ex an A ac oce us.
Desc ip ion. Re e o online Supplemen al No e o a comple e desc ip ion.
Rema ks. The dis ibu ion o A ac oce us in Cen al and Sou h Ame ica (including he Dominican Republic),
A ica, Madagasca , India, Suma a, and no he n Aus alia sugges s Gondwanan elic ualism11. The e o e, he
Figu e 3. Phylogene ic amewo k o Lymexylidae and A ac oce inae, based on Wheele 10, Paulus11, and
Wol -Schwenninge 28. (a) Time-da ed cladog am o Lymexylidae, (b) hypo hesised gene ic cladog am o
A ac oce inae. (a) 1: Oldes A ac oce inae om Lowe C e aceous (~113 Mya) C a o Fo ma ion, B azil28;
2: A ac oce inae om mid-C e aceous (ca. 99 Mya) Bu mese ambe ; 3: A ac oce inae om mid-Eocene
(ca. 44 Mya) Bal ic ambe ; 4: A ac oce inae om ea ly Middle Miocene (ca. 16 Mya) Dominican ambe ;
5: oldes Meli omma inae om mid-Eocene Bal ic ambe 33. Two olde eco ds o Hylecoe inae29 and
Meli omma inae31,32 we e omi ed due o unce ain y in hei sys ema ic posi ions. Red lines show lineages
suppo ed by ossil eco ds. Squa e, comp ession ossil. Ci cles, ambe inclusions. (b) The ely a o i e ossil
species epo ed he e a e mapped on o he cladog am. Ve a ac oce us gen. no . is en a i ely placed as a sis e
axon o U ea based on he dis inc ly modi ied me acoxae, la ge, con iguous eyes, and an e io ly p oduced
p ono um. C a oa ac oce us was conside ed he mos basal membe o A ac oce inae based on i s hindwing
ena ion, al hough he gene al cha ac e s esemble hose o Ra ac oce us28. Since he e is signi ican lack o
mo phological in o ma ion on his ossil genus, I en a i ely ollowed he iew o Wol -Schwenninge 28.
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occu ence o A ac oce us in Dominican ambe is cong uen wi h he mode n congene s. G imaldi & Engel2 men-
ioned a much la ge (ca. 29 mm) unnamed A ac oce us in Dominican ambe , bu he ely a we e no illus a ed.
Discussion
Th ee C e aceous and wo Cenozoic bee les unambiguously belong o Lymexylidae, based on hei na owly elon-
ga e bodies, cylind ical p ojec ing p ocoxae, ili o m o usi o m, ai ly sho an ennae, highly modi ied maxilla y
palp o gan, and emale geni al s uc u es10,24. They can be u he assigned o A ac oce inae based on he ma k-
edly educed ely a wi h he exposed hindwings, la ge bulging eyes, and dis inc ly modi ied maxilla y palp o gan
in he emale10. The di e se a ac oce ines om Bu mese, Bal ic, and Dominican ambe s epo ed he e ep esen
he i s desc ibed and named ambe inclusions in he sub amily.
The oldes membe s o he ship- imbe bee les we e ound in Lowe C e aceous Lebanese ambe (~125 Mya)25.
They a e no o mally desc ibed and he e o e no de ailed mo phological in o ma ion is a ailable, al hough hey
ha e long, nea ly comple e ely a25. I hese ossils a e uly lymexylids, his is consis en wi h he Ju assic-Ea ly
C e aceous o igin o he c own g oup o he amily, sugges ed by p e ious molecula s udies16,26. Cu en ly, he
ea lies de ini i e ossil o he amily is C a oa ac oce us g imaldii Wol -Schwenninge desc ibed based on a
comp ession ossil om he Lowe C e aceous C a o Fo ma ion (~113 Mya27) in B azil28 (Fig.3a). This ossil
species was assigned o he sub amily A ac oce inae based on se e al cha ac e s, including gene al body shape,
la ge con iguous eyes, wo longi udinal idges on he mesoscu ellum, and hea ily scle o ised emale geni alia28.
This assignmen appea s co ec , al hough, un o una ely, he ely a o his ossil axon we e o iginally missing28.
Un il now, his unce ain y p e en ed us om elucida ing he o igin and e olu iona y his o y o ely a educ-
ion in A ac oce inae, since no o he ossil lymexylid has been desc ibed om he Mesozoic. An undesc ibed
A ac oce inae ossil om Bu mese ambe has been epo ed, he au ho s did no include a igu e o he ely a o
his ossil2. All o he amily eco ds a e con ined o Eocene–Miocene (~16 Mya) comp ession and ambe ossils
wi h ei he long ely a o wi hou su icien in o ma ion abou hem2,29–33. My s udy p o ides he i s documen ed
e idence o he ely al educ ion in Lymexylidae, which can now be eliably aced back o he mid-C e aceous
(~ea lies Cenomanian, ca. 99 Mya18).
In compa ison wi h he mega-di e si y o bee les, only a small mino i y o bee les ha e educed ely a wi h
exposed hindwings. None heless, his phenomenon is ound epea edly ac oss he o de , indica ing mul iple inde-
penden o igins. Because he condi ion and deg ee o de elopmen o he ely a a ies g ea ly among bee les, a
p e ious s udy classi ied he educed ely a in o h ee mo pho- ypes7: 1) ely a educed along wi h a educ ion in
he hindwings, e.g. Lycidae34 and Lampy idae35; 2) ely a unca ed bu comple ely co e ing he olded unc ional
hindwings, e.g. he hype -di e se S aphylinidae36; and 3) educed ely a exposing (o pa ially exposing) unc-
ional hindwings, e.g. some Ce ambycidae (i.e. Necydalinae37), Ripipho idae38, o Lymexylidae10. The hi d o m
is he a es and mos in e es ing ely al ype because i appa en ly does no ha e a p o ec i e unc ion and o he
me i s. Despi e hese disad an ages, his ely al o m is ound in un ela ed bee le lineages7. The o igin and ole o
his ype o b achely y ha e s ill no been adequa ely explo ed. Howe e , i was sugges ed ha ely a educ ion
a ec s he e olu ion o bee le hindwings by op imising he ae odynamic e iciency o changes in ligh mechanics
induced by ely a loss7. In a ac oce ine species, ex eme cases o educed ely a a e known. Indeed, he ely a a e
so minu e ha mos o he hindwings and abdomen a e exposed do sally. A ema kable dip e an hal e e-like ole
o minu e ely a was e ealed by su gically emo ing he ely a o A ac oce us b e ico nis (L.)39,40. These sho -
ened ely a ib a e du ing ligh and may pe o m a senso y unc ion essen ial o s abilising ligh , p oducing
he unique ligh mode o a ac oce ines39,40. In ac , A. b e ico nis was incapable o s eady ligh a e emo ing
he ely a39,40. Based on he minu e ely a, my disco e y o wo new species o Ra ac oce us om Bu mese ambe
sugges s ha hey had a ligh mode simila o ha o A. b e ico nis du ing he mid-C e aceous, as his seems o
be a common ligh mechanism o he sub amily as a whole.
The ossils desc ibed he e show a ema kable a ia ion in shape and leng h o ely a. Fo example,
Ve a ac oce us gen. no . di e s g ea ly om he emaining ex an and ex inc A ac oce inae. Wi h a e y
slende , unusually long (8.7 imes longe han wide) ely on, his new genus is dis inc among he a ac oce -
ines. Mo e signi ican ly, he leng h o he ely a and hei co e age on he abdomen seems o be in e media e
be ween he sub amily Lymexylinae (Fig.1h), which is a sis e axon o A ac oce inae, and he o he membe s
o A ac oce inae. None heless, he ely a o Ve a ac oce us gen. no . a e s ill much sho e han in Lymexylinae,
wi h mo e han ou abdominal e gi es exposed do sally. The p esence o a highly modi ied maxilla y palp
o gan in he emale p e en s he sys ema ic placemen o Ve a ac oce us gen. no . wi hin Lymexylinae, bu i
is de ini ely placed in A ac oce inae. This new genus migh o m a sis e g oup wi h U ea based on he dis-
inc ly modi ied me acoxae, la ge, con iguous eyes, and an e io ly p oduced p ono um. These wo gene a may
be nes ed oge he a he basal posi ion o A ac oce inae (Fig.3b), al hough u u e s udies need o assess he
de ailed sys ema ic posi ion o Ve a ac oce us gen. no . The wo C e aceous Ra ac oce us species ha e a pai
o sho , bu weakly pos e io ly na owing ely on (Fig.2b,c,g,h), while one Eocene Ra ac oce us species has a
nea ly pa allel-sided ely on (Fig.2d,i). Compa ed wi h hese axa, one Miocene A ac oce us has a sho e (2.1
imes longe han wide), dis inc ly poin ed, modi ied ely on, wi h an i egula ly do sally aised su ace (Fig.2e,j).
Consequen ly, he modi ied ely on as seen in ex an axa is conside ed a de i ed condi ion ha may ha e o igi-
na ed by he Middle Miocene, based on my ossil in Dominican ambe (ca. 16 Mya).
O no e, he e a e al eady some C e aceous examples o b achely ous bee les wi h exposed hindwings. The
mos no able cases a e se e al wedge-shaped bee les (Ripipho idae) om mid-C e aceous F ench and Bu mese
ambe s38,41,42. They clea ly exhibi he ypical o m o educed ely a wi h exposed hindwings, al hough hey a e
much less educed han he examples p esen ed he e. Ano he example is ound in soldie bee les (Can ha idae)
om Bu mese ambe ; o example, he gene a O na omal hinus43 and Sanaungulus44 ha e sho ened ely a expos-
ing he hindwings do sally. These disco e ies indica e ha educ ion in ely al leng h wi h exposed hindwings,
occu ed be o e he mid-C e aceous independen ly in dis an ly ela ed bee le g oups.
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Ely a educ ion may a ec he e olu ion o hindwing s uc u es7. A cha ac e is ic ea u e o ecen
A ac oce inae is he ex emely educed hindwing ena ion wi h a comple e lack o ans e se olds28,45,46.
Hindwing shape di e s ma kedly be ween ela ed b achely ous and mac oely ous bee les, wi h he excep ion
o A ac oce us, ha ing a wide hindwing han in mac oely ous congene s and ha ing an elonga ed anal ield28.
Al hough I could no adequa ely obse e he hindwing shape in he ossils desc ibed he e, he wing ena ion pa -
e ns we e simple and he wings olded leng hwise, as in all ex an a ac oce ine gene a; hey lack a M + Cu o k
basad o he le el o he -m c oss ein, clea ly di e en ia ed om he Lowe C e aceous C a oa ac oce us, and
also lack a adial cell along he cos al ma gin o he C + Sc + R ein. The gene al leng h o he hindwings is he
same as in he ex an a ac oce ines, wi h a leas wo ee abdominal e gi es unco e ed by he hindwings. This
demons a es he mid-C e aceous o igin o he mode n a ac oce ine hindwings. Because hese a ac oce ines
a e unlike examples o bee le axa inhabi ing mesic mic o-en i onmen s47–50, he close mo phological simila i ies
wi h he ex an axa a e in e es ing.
The ossil e idence epo ed he e sheds ligh on he mac oe olu ion o ship- imbe bee les, especially he
sub amily A ac oce inae. These mo phologically di e se ex inc lymexylids highligh he ea ly di e si ica ion
o ely a educ ion in his sub amily. The di e se se ies o a ia ion in ely al o ms epo ed he e also sugges
much g ea e mo phological di e si y o he ely al shape in he pas han seen a p esen . In e es ingly, al hough
only sugges i e, he e y minu e, modi ied ely a seen in ex an A ac oce us we e ound only om younge
Dominican ambe . The epo ed ossils he e also clea ly show se e al synapomo phic cha ac e s o lymexylids,
including he modi ied maxilla y palp o gan unc ions as chemo ecep o s51,52, which ep esen an au apomo phy
o he amily (Supplemen a y Fig.1c,d)10. Ano he insigh is he possible b igh colou a ion o Ve a ac oce us
bu mi icus gen. e sp. no ., Ra ac oce us ex inc us sp. no ., and R. ossilis sp. no . when hey we e ali e, based on
hei macula ion and pa e ns o he head, p ono um, mesoscu ellum, and ely a. I has been hypo hesised ha
he pale species o A ac oce inae, e.g. A ac oce us and Ra ac oce us, wi h la ge eyes appea o mimic ce ain noc-
u nal wasps (Vespidae and Ichneumonidae)17,52. Hence, hey may e en be conside ed po en ial mimics, al hough
mo e e idence is needed o suppo his hypo hesis. All known lymexylid la ae a e wood bo e s and a e belie ed
o o m symbio ic associa ions wi h amb osia ungi, Ascoidea spp. (Ascomyce es: Saccha omyce ales) ha g ow
on he walls o hei unnels24,52,53. Conside ing his, i is possible ha hese ossil axa had he same, o simila ,
ecological li es yles as he mode n ship- imbe bee les. Indeed, he Ra ac oce us ossils show s iking gene al
mo phological simila i ies o he ecen congene s, sugges ing hey had he same ecological, beha iou al, and
e en ligh modes in he mid-C e aceous.
Me hods
Ma e ials. The h ee C e aceous ossils desc ibed he ein we e ob ained om ambe om he Hukawng
Valley, Kachin S a e, no he n Myanma (26°21′33.41″N, 96°43′11.88″E). Bu mese ambe , o bu mi e, da es
o he mid-C e aceous, cu en ly ecognised as he ea lies Cenomanian (98.79 ± 0.62 Mya) age based on U–
Pb da ing o zi con c ys als om he olcaniclas ic ma ix o he ambe ou c ops18. The Bal ic ambe specimen
desc ibed he e was om Yan a ny, Kalining ad Oblas , wes e nmos Russia. Al hough he age o Bal ic ambe has
been he subjec o much deba e, I ollow he mid-Eocene (44.1 ± 1.1 Mya) age om he mos ecen es ima es
o he ambe -bea ing ‘Blue Ea h’ o ma ion based on he absolu e da ing analyses22. The Dominican ambe
ossil comes om he Dominican Republic and u he de ails a e unknown. The age o Dominican ambe is
also somewha con o e sial, bu I ollow he ea ly Middle Miocene (ca. 16 Mya) age23. All o he ossil spec-
imens used in his pape a e deposi ed in he insec collec ion o he Gan z Family Collec ions Cen e , Field
Museum o Na u al His o y (FMNH), Chicago, IL, USA, wi h consecu i e numbe s om FMNHINS-3965988
o FMNHINS-3965992.
Imaging. Specimens we e pho og aphed using a Canon 80D digi al came a wi h a Canon MP-E 65 mm
mac o lens (F2.8, 1–5 × ) and a Canon MT-24EX mac o win li e as he ligh sou ce (Figs1a–e, 2a–e,g–j and
Supplemen a y Figs3,4,5a–e,g,6a,b,d,7h,8,9). Al e na i ely, a Dun Ink BK PLUS Lab Sys em moun ed on a
Canon 6D digi al came a, a ached wi h ei he CF4 o 5 × lens, was used (Fig.2 and Supplemen a y Figs5 ,
6c,e, ,7a–g,10). All images we e la e s acked using he au o-mon age so wa e Combine ZM o Helicon Focus
5.3. Figu es we e edi ed and assembled wi h Adobe Pho oshop® Elemen s 15. Specimens we e s udied unde a
Leica MZ16 s e eomic oscope.
Classi ica ion. I ollow he classi ica ions o Ku osawa17 and Paulus11.
Mo phological e minology. The mo phological e minology gene ally ollows Ku osawa17 and Wheele 10
o gene al body pa s, and Wol -Schwenninge 28 o wing ena ion. Abb e ia ions o he hindwing ena ion
a e as ollows: C, cos a; Cu, cubi us; M, median ein; R, adius; -m, a c oss ein ha connec s M and Cu; Sc,
subcos a.
Nomencla u al ac s. This published wo k and he nomencla u al ac s i con ains ha e been egis e ed
in ZooBank, he p oposed online egis a ion sys em o he In e na ional Code o Zoological Nomencla u e
(ICZN). The ZooBank LSIDs (Li e Science Iden i ie s) can be esol ed and he associa ed in o ma ion iewed
h ough any s anda d web b owse by appending he LSID o he p e ix ‘h p://zoobank.o g/’. The LSIDs o
his publica ion a e: u n:lsid:zoobank.o g:pub:256304D4-479E-44B5-A14D-893D9E898479; u n:lsid:zoobank.
o g:ac :EF9F7C08-DA9E-4D63-81D8-D674B74E18EC; u n:lsid:zoobank.o g:ac :BC26AB2F-E7B3-4A19-B033-
5E0574602A17; u n:lsid:zoobank.o g:ac :94130B93-6FFE-4C43-89E6-8B0987C7FEAD; u n:lsid:zoobank.
o g:ac :ACB32243-DDD8-461B-9D31-FE006252913E;
u n:lsid:zoobank.o g:ac :F77CB344-EF73-4EC0-8E6B-AEFDD3AB2D5C.
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Da a A ailabili y
All ossil ma e ials a e deposi ed in he FMNH. The da a suppo ing he s udy indings a e p o ided in bo h he
pape and Supplemen a y In o ma ion. Highe - esolu ion igu es ha e been deposi ed in he igsha e da abase
(h ps://doi.o g/10.6084/m9. igsha e.7800830).
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