The oldest osoriine rove beetle from Cretaceous Burmese amber (Coleoptera: Staphylinidae)

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Cretaceous Research xxx (2014) 1e6

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Cretaceous Research

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The oldest osoriine rove beetle from Cretaceous Burmese amber(Coleoptera: Staphylinidae)

Chenyang Cai a,b,*, Diying Huang a

a State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East BeijingRoad, Nanjing 210008, ChinabGraduate School, University of Chinese Academy of Sciences, 19A Yuquanlu, Beijing 100049, China

a r t i c l e i n f o

Article history:Received 4 December 2013Accepted in revised form 17 March 2014Available online xxx

Keywords:StaphylinidaeOsoriinaeThoracophoriniCretaceousBurmese amber

* Corresponding author. State Key Laboratory of PaNanjing Institute of Geology and Palaeontology, ChinEast Beijing Road, Nanjing 210008, China.

E-mail address: [email protected] (C. Ca

http://dx.doi.org/10.1016/j.cretres.2014.03.0200195-6671/� 2014 Elsevier Ltd. All rights reserved.

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a b s t r a c t

A remarkable new genus and species, Mesallotrochus longiantennatus n. gen. n. sp., is described andfigured based on a well-preserved individual in the lowermost Upper Cretaceous (Cenomanian) amberfrom Myanmar. Mesallotrochus is placed in the extant tribe Thoracophorini based on its general habitus,including the protibia with inner edge straight, without ctenidium, exposed protrochantins, open pro-coxal cavities, and more or less flatted body. Mesallotrochus is separated from other allied genera by thelong antennae, very long maxillary palpomere 4, contiguous procoxae, and well-developed anterolateralpronotal angles. The new discovery of the oldest Osoriinae from about 99 million years not only suggeststhe antiquity of the subfamily, but also bears significant biogeographic implications.

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1. Introduction

With more than 2083 described species and 103 genera, therove beetle subfamily Osoriinae is the most diverse group of theOxyteline group of subfamilies (Grebennikov and Newton, 2012;Thayer, 2005). Modern osoriine rove beetles are widely distrib-uted in all biogeographic regions except the Antarctic (Herman,2001; Thayer, 2005). The subfamily Osoriinae is a very distinctivegroup among Staphylinidae, which lacks paratergites on eachabdominal segment (Newton et al., 2000). Although a few otherstaphylinids, including certain genera of Euaesthetinae, Paederinae,Tachyporinae and some Stenus species, have unmargined abdomen,they can be easily separated from Osoriinae by having slender,more or less falcate mandibles lacking molar lobes and concealedantennal insertions (Newton et al., 2000).

Fossil osoriines are relatively rare, and all of them are limited tothe Tertiary (Hope, 1837; Irmler, 2003; Ortega-Blanco et al., 2013;Zhang, 1989). Zhang (1989) described a fossil oxyteline species,Sinolispinodes torosus Zhang, from the Miocene in Shanwang ofShandong Province, China. Sinolispinodeswas then transferred fromOxytelinae to Osoriinae as supported by the absence of paratergiteson abdominal segments (Herman, 2001; Yue et al., 2010). Irmler

laeobiology and Stratigraphy,ese Academy of Sciences, 39

i).

ng, D., The oldest osoriine rovg/10.1016/j.cretres.2014.03.02

(2003) described an extinct genus Lispinomimus Irmler, twoextinct species (Thoracophorus palaeobrevicristatus Irmler andNacaeus dominicanensis Irmler), and five unnamed species ofgenera Liberiana Blackwelder, Osoriellus Fagel, and Neosorius Fagelfrom the Early Miocene Dominican amber. Recently, Ortega-Blancoet al. (2013) described a new genus and species, Paleosorius cam-bayensis Ortega-Blanco, Chatzimanolis and Engel, from the EarlyEocene amber of India, which is regarded as the oldest known fossilof Osoriinae. Until now, no fossil osoriines of Mesozoic age havebeen reported. The origin and early evolutionary history of Osor-iinae thus remain unclear.

Herein, we report a discovery of a much older osoriine rovebeetle (ca. 99 million years old; see details in Shi et al., 2012) as anew genus from the Cretaceous Burmese amber. Based on UePbdating of zircons, an earliest Cenomanian age (ca. 99 Ma) for thefossilized inclusions in Burmese amber is established (Shi et al.,2012). The new fossil, about twice the age of the previouslyknown Eocene fossil from India, represents the oldest record for thesubfamily Osoriinae.

2. Material and methods

The material described here derives from amber deposits inthe Hukawng Valley of northern Myanmar. The mining is done ata hill named Noije Bum near Tanai Village (26�21033.4100N,96�43011.8800E) (e.g., Cruickshank and Ko, 2003; Grimaldi et al.,2002). Observations and photographs were taken using a Zeiss

e beetle from Cretaceous Burmese amber (Coleoptera: Staphylinidae),0

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C. Cai, D. Huang / Cretaceous Research xxx (2014) 1e62

Discovery V20 stereo microscope and a Zeiss Axio Imager 2 lightmicroscope with a digital camera attached. Photomicrographs withgreen background (Fig. 3) are taken using green fluorescence aslight source attached to a Zeiss Axio Imager 2 light microscope. Thematerial has been prepared, including cut with a razor bladeand polished with sand papers with different grain sizes andwith diatomite mud. A polished slab of amber measuring3.5 mm � 2.8 mm contains the beetle specimen, which (in dorsalview) is oriented at approximately a 40� angle to the surface.

3. Systematic palaeontology

Order: Coleoptera Linnaeus, 1758Family: Staphylinidae Latreille, 1802Subfamily: Osoriinae Erichson, 1839Tribe: Thoracophorini Reitter, 1909Subtribe: Clavilispinina Newton and Thayer, 1992

Genus: Mesallotrochus gen. nov.

Type speciesMesallotrochus longiantennatus sp. nov., here designated.

EtymologyThe genus name is a combination of Meso-, meaning Mesozoic,

and the supposed related genus Allotrochus; it is masculine ingender.

DiagnosisSmall, slightly flattened Staphylinidae with: eyes moderate,

distinctly protruding, coarsely faceted; antennal insertions con-cealed; antennae densely setose, not clubbed, long, extendingbeyond posterior margin of pronotum; maxillary palpi long, withreduced palpomere 3 and elongate article 4; pronotum transverse,

Fig. 1. General habitus of Mesallotrochus longiantennatus n. gen. n. sp., holotype, NIG

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widest nearly at middle, with lateral carinae, anterolateral pronotalangles well-developed; elytra longer than pronotum, covering partof abdominal tergite III, with epipleural keels; protrochantinsexposed; pro- and metacoxae contiguous; mesocoxae narrowlyseparated; femoraweakly dilated, somewhat flatted, with relativelydeep concave groove in ventral side to conceive tibia; tibiae veryslender, without strong spins; all tarsi 5-segmented; abdominalsegments IIIeVIII well-developed, without paratergites, tergiteswithout basolateral ridges.

Mesallotrochus longiantennatus sp. nov. (Figs. 1e4).

EtymologyDerived from the combination of the Latin adjectives longus and

antennatus, meaning with (or having) long antennae.

MaterialHolotype, NIGP157737. The fossil beetle is a completely pre-

served adult. The type specimen is housed in the Nanjing Instituteof Geology and Palaeontology, CAS, Nanjing, China.

OccurrenceLowermost Upper Cretaceous (ca. 99Ma) amber from the village

of Tanai, Hukawng Valley, northern Myanmar.

DiagnosisAs for the genus (vide supra).

DescriptionBody: 2.86 mm long; sub-parallel, deep brown throughout.Head: relatively small, 0.43 mm long and 0.51 mm wide

(including eyes), without lateral or dorsal neck constriction; withfour long setae at apical margin of frons; antennal insertions con-cealed under shelf-like corner of frons, located before a line drawn

P157737. A. dorsal view; B. ventral view. Under normal light. Scale bars: 1 mm.


Fig. 2. Enlargements of Mesallotrochus longiantennatus n. gen. n. sp., under normal light. A. Enlargement of right maxillary palpus and left protarsus, showing the elongatepalpomere; B. details of right antenna with maxillary palpus partly shown; C. enlargement of protibia and protarsus, note the lobed tarsomeres 2e4; D. enlargement of mesotibiaand mesotarsus, note the single long seta on tarsomeres 1e4; E. enlargement of metatarsus and partial metatibia. Scale bars: 500 mm in B, 200 mm in others.

C. Cai, D. Huang / Cretaceous Research xxx (2014) 1e6 3

before anterior margin of eye. Eye positioned laterally. Antennaelong (Fig. 2B; 3A), 11-segmented, moniliform; antennomeres 1broad and elongate, antennomere 2 elongate, slightly narrowerthan antennomere 1, antennomere 3 gradually dilated to apex,nearly as long as antennomere 2, antennomeres 4e7 graduallywidened, antennomere 8 slightly smaller than 7 and 9, anten-nomere 10 almost in the same size and shape as 9, antennomere 11conical, 1.6 times as long as antennomere 10. Labrum and labialpalpus not observable. Mandibles with sharp apex visible. Maxil-lary palpus (Fig. 2A) relatively long, apparently 4-segmented, pal-pomere 2 longer than wide, palpomere 3 as wide as 2, but shorterthan 2, palpomere 4 elongate, about 2.8 times as long as palpomere3, glabrous.

Thorax: Pronotum wider than head. 0.69 mm wide, 0.54 mmlong. Pronotum in dorsal view slightly narrowed from middle tobase; anterior margin concave, posterior margin nearly straight.Anterolateral angels distinctly pronounced, posterolateral angelsrectangular. Pronotum with well-developed lateral carina. Pros-ternum transverse, procoxae contiguous (Fig. 3B), with a smallprosternal process; procoxal cavities open. Pronotal hypomerondeveloped, subtriangularly produced inwards. Mesocoxae narrowlyseparated by smaller mesoventral and larger metaventral processes(Fig. 3B); metacoxae contiguous. Mesoscutellum sub-triangular,longer than wide, distinctly narrowed at anterior third. Elytraelongate, sub-parallel, 0.75 mm long and each 0.44 mm wide,


partly covering abdominal tergite III; surfacewithout striae, carinaeor microsetae; hind margin truncate. Epipleural keel present. Hindwings fully developed, with setae forming fringe alongmargin. Legsrelatively long; protrochantins exposed; procoxae small, rounded,protrochanters small, profemora clavate and flatted, protibiaeelongate, slightly narrowed to apex, protarsi 5-segmented (Fig. 2A,C; 3B), protarsomeres 1e4 short, almost in same shape and size,each with long setae in ventral side, tarsomere 5 elongate; meso-tibiae slender, longer than protibiae, mesotarsi 5-segmented(Fig. 2D; 3A), mesotarsomere 1 longer than wide, tarsomeres 2e4shorter, almost in same shape and size, each with long setae inventral side; metacoxae sub-triangular, without metacoxal plate,metafemora robust, larger than mesofemora, metatibiae slender,metatarsi 5-segmented (Fig. 2E). All tarsomeres 2e4 lobed in dorsalview. Pretarsal claws simple; empodium bisetose.

Abdomen: narrow, sub-parallel, with long setae at lateralmargin. Abdominal tergite III partly covered by elytra. All segmentswithout paratergites. Basolateral ridges absent. Wing-foldingpatches absent. Abdominal segment VII long, segment VIII retrac-ted to segment VII; tergite and sternite VIII sub-triangular.

4. Discussion

Among the 32 extant and one extinct subfamilies of Staph-ylinidae (Newton et al., 2000), the newgenus and species described


Fig. 3. Enlargements of Mesallotrochus longiantennatus n. gen. n. sp., under green fluorescence. A. Enlargement of left antenna (dorsal view) with maxillary palpus partly shown; B.enlargement of pro- and mesothorax, showing contiguous procoxae and separated mesocoxae. Abbreviations: mc: mesocoxa; pc: procoxa; pcp: procoxal process. Scale bars:200 mm.


here is easily placed in the Osoriinae based on its general habitus,including parallel and elongate body shape, antenna inserted infront of eyes and under shelf-like corner of frons, 5-segmented tarsiwith elongate tarsomere 5,11-segmented non-clavate antenna, andmore importantly, on the presence of unmargined abdominalsegments, i.e., entirely without paratergites (Newton et al., 2000).The subfamily Osoriinae currently comprises four tribes, viz. Eleu-sinini Sharp, Leptochirini Sharp, Osoriini Erichson, and Thor-acophorini Reitter (Bouchard et al., 2011). The new genusMesallotrochus is easily separated frommembers of the remarkabletribe Leptochirini by its general habitus, especially the absence ofmodifications in cephalic characters and posteriorly open procoxalcavities. Mesallotrochus cannot be confused with the genera of thetribe Eleusinini based on the slightly (not extremely) flattenedbody, very slightly (not greatly) basally narrowed pronotum, small(not larger than pronotum) head, relatively large procoxae, andsmall (not greatly enlarged) protrochantins. Mesallotrochus differsfrom members of Osoriini by lacking deep groove and carina onmesal surface of procoxae, protibia with concave and ctenidium-bearing inner edge, or convex body. The new genus is confidentlyattributed to the modern tribe Thoracophorini as supported by theabsence of ctenidium on inner edge of protibia and the more or less


flatted body (e.g., Irmler, 2010; Newton et al., 2000). The tribeThoracophorini includes four extant subtribes: ClavilispininaNewton and Thayer, Glyptomina Newton and Thayer, LispininaBernhauer and Schubert, and Thoracophorina Reitter (Newtonet al., 2000). Mesallotrochus is easily separated from members ofthe subtribe Glyptomina by having exposed protrochantins; fromThoracophorina by having exposed protrochantins and the absenceof any carinae on head, pronotum or elytra. Mesallotrochus super-ficially resembles certain genera belonging to the extant subtribesClavilispinina and Lispinina. However, it can be ruled out fromLispinina by its contiguous procoxae, which are not well separatedby a distinct prosternal process as in Lispinina. Therefore, Mesal-lotrochus is readily placed in the recent subtribe Clavilispinina onthe basis of the general adult morphology, including the contiguousprocoxae. There are nine extant genera included in the Clav-ilispinina (Herman, 2001). Among the nine genera, Mesallotrochusclosely resembles Allotrochus Fagel and Myrmelibia Newton inhaving small head and transverse pronotum (Newton, 1990). Spe-cifically, it shares with the Australia-endemic myrmecophilousMyrmelibia the elongate antennae (extending beyond the posteriormargin of pronotum) and transverse pronotum with pronouncedanterolateral angels, but it differs from the later by longer


Fig. 4. Line drawings of Mesallotrochus longiantennatus n. gen. n. sp., holotype, NIGP157737. A. Dorsal view; B. Ventral view. Scale bars: 1 mm.

C. Cai, D. Huang / Cretaceous Research xxx (2014) 1e6 5

tarsomeres 1e4, much longer maxillary palpomere 4, and theabsence of carinae on head, pronotum and elytra. It shares withAllotrochus the general body shape, transverse pronotum, anddorsally lobed tarsomeres 1e4. The new genus is separated fromAllotrochus by having much longer antennae and pronounced andsharp anterolateral pronotal angels (e.g., Irmler, 2000; Naomi andIrmler, 2012).

Ortega-Blanco et al. (2013) described a new genus PaleosoriusOrtega-Blanco, Chatzimanolis and Engel, from the Early Eocene ofIndia, and it is tentatively placed in the tribe Thoracophorini basedon the absence of ctenidium from the protibia and the globoseprocoxae. However, due to the relatively poor preservationalcondition of the holotype of Paleosorius cambayensis, a compre-hensive comparison between the new genus Mesallotrochus andPaleosorius cannot be made. The new genus is separated fromPaleosorius by its small head (narrower than pronotum), trans-verse pronotum, the absence of striae on femora, and distinctlylobed tarsomeres 1e4. Unfortunately, a key character for subtribalplacement (procoxae contiguous or not) is obviously not wellshown or described in Paleosorius. Thus, it makes further com-parison between Paleosorius and specific genera of certain subtribeof Thoracophorini impossible.

5. Conclusions

Our new discovery of a definitive member belonging to theOsoriinae from the Cenomanian represents the first Mesozoic andaccordingly the oldest fossil record for the subfamily Osoriinae. Theosoriine rove beetle from the Cretaceous Burmese amber provides


direct evidence that Osoriinae and its sister group have minimumages of about 99 million years. In addition, the new finding bearssignificant biogeographic implications. The closely related moderngenus Allotrochus is known from the subtropics and tropics inAustralian, Ethiopian and Madagascan Regions (Herman, 2001;Newton, 1990). Recently, Naomi and Irmler (2012) recorded thefirst representative of the genus Allotrochus from the Oriental Re-gion. It is possible that the disjunctive distribution pattern ofAllotrochus suggest very ancient origins of Allotrochus-relatedgenera, which is consistent with the finding of the new genus fromthe Cretaceous. The subfamily Osoriinae had likely shown its firstappearance on the Pangaea in the Jurassic.

Acknowledgements

We are grateful to two anonymous reviewers for providingconstructive suggestions. This research was supported by NationalBasic Research Program of China (2012CB821903), OutstandingYouth Foundation of Jiangsu Province (BK 2012049), and theNational Natural Science Foundation of China (91114201 andJ1210006).

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The oldest osoriine rove beetle from Cretaceous Burmese amber (Coleoptera: Staphylinidae)