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Cretaceous Research 34 (2012) 334e339

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Cretaceous Research

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Prosinodendron krelli from the Yixian Formation, China: A missing link amongLucanidae, Diphyllostomatidae and Passalidae (Coleoptera: Scarabaeoidea)

Ming Bai a, Dong Ren b,*, Xingke Yang a,*aKey Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Box 92, Datun Road, Chaoyang District, Beijing 100101, ChinabCollege of Life Sciences, Capital Normal University, Beijing 100048, China

a r t i c l e i n f o

Article history:Received 16 September 2010Accepted in revised form 25 November 2011Available online 2 December 2011

Keywords:LucanidaeYixian FormationChinaProsinodendronNew species

* Corresponding authors.E-mail addresses: baim@ioz.ac.cn (M. Bai), rendo

yangxk@ioz.ac.cn (X. Yang).

0195-6671/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.cretres.2011.11.017

a b s t r a c t

Prosinodendron krelli Bai, Ren and Yang gen. et sp. nov. (Scarabaeoidea: Lucanidae), an exceptionally well-preserved, new lucanid fossil, is described and illustrated from the Yixian Formation of western LiaoningProvince, northeastern China. Based on its unique combination of characters, it is considered to bea missing link among Lucanidae, Diphyllostomatidae and Passalidae. A key to known fossil species ofLucanidae and adjacent families from Mesozoic is given. The close phylogenetic relationship of thesethree families of the Scarabaeoidea is supported by the fossil evidence.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

The scarab beetles (Scarabaeoidea or Lamellicornia) area cosmopolitan monophyletic group of Coleoptera: Polyphaga,comprising about 28,000 described extant species, which are wellknown for their exceptionally large mandibles (Browne andScholtz, 1995; Lawrence et al., 2011). The family Lucanidae haslong been considered to be one of the most primitive groups in theScarabaeoidea (Ritcher, 1966; Crowson, 1967; Howden, 1982), andscarabaeoid classifications and evolutionary hypotheses havegenerally regarded the Lucanidae as basal to all scarabaeoids(Iablokov-Khnzorian, 1977; Howden, 1982; Lawrence and Newton,1995). However, based on comparison of “primitive” scarabaeoidgroups, Scholtz et al. (1994) hypothesized that the family Glar-esidae, rather than the Lucanidae, is the most primitive. Accordingto this hypothesis, the Lucanidae is a member of a clade thatincludes the Passalidae and Diphyllostomatidae.

Prior to the taxonomic elevation of the genus Diphyllostoma tothe family Diphyllostomatidae (Holloway, 1972), the Lucanidae wasconsidered as most closely related to the Passalidae (Howden,1982). Based on shared characters, it is now thought that theLucanidae is most closely related to the Diphyllostomatidae(Caveney, 1986; Browne and Scholtz, 1995). However thesehypotheses have not been supported by the fossil evidence.

ng@mail.cnu.edu.cn (D. Ren),

All rights reserved.

So far, 266 fossil scarabaeoid species have been described, ofwhich 231 probably or reliably belong to Scarabaeoidea, 31 areconsidered doubtful owing to a lack of key characters, and ninebelong to other taxa (Krell, 2000, 2007; Nikolajev, 2007; Bai et al.,2010, 2011). The earliest lucanid species, Juraesalus atavusNikolajev et al., 2011, was found in Middle Jurassic deposits inDaohugou Village, Chifeng City, Inner Mongolia, China. Hitherto, 20fossil lucanid species and four passalids have been reported, but nofossil diphyllostomatids have been found and none has been claimedas the missing link of these three families. Prosinodendron krelli Bai,Ren and Yang, gen. et sp. nov., an exceptionally well-preservedscarabaeoid fossil, which is described here, was collected from theYixian Formation, near Chaomidian Village, Beipiao City, LiaoningProvince, China. Based on its unique combination of characters, it isregarded as a missing link among Lucanidae, Diphyllostomatidaeand Passalidae. A key to known fossil species from Lucanidae andadjacent families from Mesozoic is given herein.

2. Geological background

Numerous researchers have discussed the age of the YixianFormation in light of the biostratigraphical correlations and theradiometric dates (Chen,1988;Renet al.,1997; Chenet al.,1998;Wang,1998; Swisher et al., 1999; Zhou et al., 2003). However it is nowgenerally accepted that it is the Early Cretaceous in age andmost likelyto be restricted to 129.7e122.1 Ma: Barremianeearly Aptian (Yanget al., 2007; Zhu et al., 2007; Chang et al., 2009; Zhou andWang, 2010).

mailto:baim@ioz.ac.cnmailto:rendong@mail.cnu.edu.cnmailto:yangxk@ioz.ac.cnwww.sciencedirect.com/science/journal/01956671http://www.elsevier.com/locate/CretReshttp://dx.doi.org/10.1016/j.cretres.2011.11.017http://dx.doi.org/10.1016/j.cretres.2011.11.017http://dx.doi.org/10.1016/j.cretres.2011.11.017

M. Bai et al. / Cretaceous Research 34 (2012) 334e339 335

The strata of Yixian Formation are mainly of lacustrine sedi-ments intercalated with volcaniclastics (Ren et al., 1995). Thestratigraphy and depositional environments of this area have beendiscussed in detail by Jiang and Sha (2007) and Jiang et al. (2011).The palaeoclimate of this area was recently interpreted as cooltemperate with mean air temperatures of 10 � 4 �C. (Amiot et al.,2011). It contains a large number of fossils of the Jehol Biota,including the feathered dinosaur Sinosauropteryx prima, the birdConfuciusornis sanctus, angiosperms such as Archaefructus liao-ningensis (Hou et al., 1999; Ding et al., 2001), and numerous insectfossils (Zhang et al., 2006, 2010; Chang and Ren, 2008; Liu et al.,2008; Yao et al., 2008; Bai et al., 2010, 2011; Ren et al., 2010).

3. Material and methods

This study is based on one specimen, registration no. CNU-COL-LB2010607, housed in the fossil insect collection of the KeyLab of Insect Evolution and Environmental Changes, College of LifeSciences, Capital Normal University, Beijing (CNUB). It was exam-ined using a LEICA MZ 12.5 dissecting microscope and illustratedwith the aid of a drawing tube attachment.

Systematic Paleontology

Order Coleoptera Linnaeus, 1758Superfamily Scarabaeoidea Latreille, 1802Family Lucanidae Latreille, 1804Genus Prosinodendron gen. nov.

Type species. Prosinodendron krelli sp. nov.

Derivation of name. Latin “pro”, meaning ancient or primitive, withreference to its age, and affinity with genus Sinodendron inmorphology.

Diagnosis. Elongate, antennae lamellate, club loose, incisor edge ofmandible with two or three teeth, mandibular apex bidentate,anterior or mesal edge of eye not emarginated, metacoxaeextending laterally tomeet sides of body, scutellumwell developed.

Description. Elongate, compact. Head: antennae with three-segmented lamellate club, club loose; eyes not protuberant,

Table 1Comparison of Prosinodendron gen. nov., Lucanidae (Sinodendron), Diphyllostomatidae an

Prosinodendron (Lucanidae) Sinodendron (Lucanidae)

Metacoxae extendinglaterally to meet sides ofbody (Fig. 3A, B)

Yes (Fig. 3B, white arrow) Yes (Fig. 3B, white arrow)

Scutellum (Fig. 3CeE) Well developed(Fig. 3C, white arrow)

Well developed(Fig. 3C, white arrow)

Anterior or mesal edgeof eye (Fig. 3FeH)

Not emarginated(Fig. 3H, black arrow)

Not or only barely emargi(Fig. 3G, H, black arrow)

Eyes (Fig. 3G, H) Not protuberant(Fig. 3G, white arrow)

Strongly protuberant(Fig. 3H, white arrow)

Incisor edge ofmandible (Fig. 3IeL)

With two or threeteeth (Fig. 3K)

Simple (Fig. 3I, L)

Mandibular apex (Fig. 3IeL) Bidentate(Fig. 2E, black arrows)(not illustrated in Fig. 1 orFig. 3K of fossil)

Unidentate, truncate orrounded (Fig. 3I)

anterior or mesal edge of eye not emarginated; mandibular apexbidentate, incisor edge of mandible with two or three teeth.Pronotum: Obviously wider than head, sides of prothorax more orless straight. Scutellum: well developed, triangular. Legs: procoxalcavity strongly transverse; protibia dilated apically and with fourteeth on outer margin; mesocoxal cavities, circular, at middlenarrowly separated, not or only slightly oblique; metacoxae extend-ing laterally to meet sides of body; meso- and metatibia slender, notstronglywidened. Abdomen: five-segmented, apex slightly rounded.

Comparison. The comparison of key characters of Prosinodendron(Lucanidae), Sinodendron (Lucanidae), Diphyllostomatidae and Pas-salidae is given in Table 1 and Fig. 3. A key to known fossil species ofLucanidae andadjacent families fromtheMesozoic is given inTable2.

Prosinodendron krelli sp. nov.Figs. 1, 2 and 3K

Derivation of name. This species is named in honor of Dr. Frank Krell,a curator of entomology at the Denver Museum of Nature andScience, Denver, Colorado, USA. He has made great contributions toresearch on scarab fossils.

Material examined. Holotype: a well-preserved almost completebody with elytra collected from the Yixian Formation, near thevillage of Chaomidian, Liaoning Province and now housed in theKey Lab of Insect Evolution and Environmental Changes, College ofLife Sciences, CNUB, as noted above.

Diagnosis. As for genus.

Description. The fossil is an adult with body length 11.3 mm andwidth: 4.6 mm (base of pronotum). Shape elongate-cylindrical andcompact. Head: slightly wider than long, ovate, broadest at base;clypeus front margin straight; antennae with three-segmentedlamellate club, club loose (Fig. 2B); eyes not protuberant, anterioror mesal edge of eye not emarginated; mandibular apex bidentate(Fig. 2E, black arrows), incisor edge of mandible with two or threeteeth (Figs. 1A, B and 3K). Pronotum: shape parabolic: 2.1 timeswider than long, obviously wider than head, widest at base; ante-rior margin of pronotum slightly concave, lateral sides straight toround. Scutellum: triangular, 2.0 times wider than long. Elytron:shape parabolic: elytron 2.8 times longer than wide, elytron 3.1

d Passalidae.

Diphyllostomatidae Passalidae

Yes (Fig. 3B, white arrow) No (Fig. 3A, white arrow)

Well developed(Fig. 3C, white arrow)

Highly reduced (Fig. 3D, white arrow);or absent or not visible(Fig. 3E, white arrow)

nated Not or only barely emarginated(Fig. 3G, H, black arrow)

Deeply emarginated or stronglydivided by canthus(Fig. 3F, black arrow)

Not or slightlyprotuberant(Fig. 3G, white arrow)

Strongly protuberant(Fig. 3H, white arrow)

Simple (Fig. 3I, L) With single tooth; or with twoor more teeth (Fig. 3J)

Unidentate, truncate orrounded (Fig. 3I); orbidentate or bilobed (Fig. 3L)

Bidentate or multidentate (Fig. 3L)

Fig. 1. Line drawings of Prosinodendron krelli gen. and sp. nov., holotype specimen. A, dorsal view. B, ventral view (reconstruction).

Table 2Key to known fossil species of Lucanidae and adjacent families from Mesozoic.

1 Small, body length normally shorter than 10 mm, elongate; mesofemur wide, first metatarsomere approximately as long as the secondtarsomere.......................................................................2

10 Large, body length normally over 10 mm, ovoid; mesofemur slender, first metatarsomere longer than the second tarsomere..................42(1) Eye without canthus...................................................................320 Eye deeply divided by canthus...........................................Paralucanus mesozoicus Nikolajev, 20003(2) First four ventries sub-equal in length.................................Juraesalus atavus Nikolajev, Wang, Liu et Zhang, 201130 First four ventries not sub-equal in length......................................Protolucanus jurassicus Nikolajev, 20074(1) Eye partially or deeply divided by canthus, first metatarsomere shorter than combined length of the second and third tarsomeres.................540 Eye without canthus, first metatarsomere longer than combined length of the second and third tarsomeres.........................85(4) Eye deeply divided by canthus..........................................Cretaesalus ponomarenkoi Nikolajev, 199350 Eye partially divided by canthus.............................................................66(5) Narrow pronotum (ratio of width to length smaller than 1.8)...............................Cretolucanus longus Nikolajev, 200760 Broad pronotum (ratio of width to length over 1.8)...................................................77(6) Body width about 4.3 mm.............................................Cretolucanus ordinarius Nikolajev, 200770 Body width about 3.0 mm...............................................Cretolucanus sibericus Nikolajev, 20078(4) Protibia with five denticles on the outer margin............................Sinaesalus curvipes Nikolajev, Wang, Liu et Zhang, 201180 Protibia with four denticles on the outer margin....................................................99(8) Preapical surfaces of metatibia without transverse ridges or denticles......................Prosinodendron krelli Bai, Ren et Yang sp. nov.90 Preapical surfaces of metatibia with denticles.....................................................1010(9) Metatibia with several small denticles on outer margin and one large denticle at outer distal end.....Sinaesalus longipes Nikolajev, Wang, Liu et Zhang, 2011100 Metatibia with one large denticle at outer distal end and without small denticles on outer margin......Sinaesalus tenuipes Nikolajev, Wang, Liu, Zhang, 2011

Penichrolucanus kabakovi Nikolajev, 2011 is excluded from the key because too few characters are available.

M. Bai et al. / Cretaceous Research 34 (2012) 334e339336

Fig. 2. A, Prosinodendron krelli gen. and sp. nov., holotype specimen. B, antennae. C, protibia. D, mesocoxal cavities. E, mandible. F, mesotibia. G, metatibia. Scale bars represent l mm.

M. Bai et al. / Cretaceous Research 34 (2012) 334e339 337

times longer than pronotum; striae strongly and rather widelygrooved, strial punctures distinct. Legs: procoxal cavity stronglytransverse; protibia dilated apically and with four teeth on outermargin, protarsi present (Fig. 2C); mesocoxal cavities circular,narrowly separated at middle, 1.1 times longer than wide (Fig. 2D);meso- and metatibia with spur on the end; meso- and metatibiaslender, not strongly widened; preapical surfaces of meso- andmetatibia without transverse ridges, meso- and metatibia outermargin with longitudinal row of teeth (Fig. 2F, G); mesotarsusrelative length of each segment (base to apex) 6: 3: 5: 7: 15;mesotarsus relative length of each segment (base to apex, exceptfor the last segment) 11: 5: 4: 6. Abdomen: five-segmented, firstventrite not completely divided by metacoxae, apex rounded.

4. Discussion

Key characters among Prosinodendron (Lucanidae), Sinodendron(Lucanidae), Diphyllostomatidae and Passalidae are compared inTable 1 and Fig. 3 and supports the interpretation that Prosinoden-dron krelli is a missing link among Lucanidae, Diphyllostomatidaeand Passalidae, the close phylogenetic relationship of these threescarabaeoid families being supported by this fossil evidence.

Most species of Lucanidae are characterized by pronouncedsexual dimorphism owing to the increased development of themandibles in the males, which are used as weapons in contests foraccess to mates. A preliminary exploration based onmolecular datasuggests that strong sexual dimorphism with the well-developed

Fig. 3. A, Peploglyptus belfragei. B, Pelidnota lugubris. C, Pleocoma behrensii. D, Hister remotus. E, Heliocopris dominus. F, Nigidius passaliformis. G, Lissotes lacroixi. H, Hydrophilusstriolatus. I, Phyllostoma fimbriata. J, Lucanus maculifemoratus. K, Prosinodendron krelli. L, Lissotes lacroixi.

M. Bai et al. / Cretaceous Research 34 (2012) 334e339338

mandibles in males evolved independently at least twice, or hasundergone secondary loss in stag beetles (Hosoya and Araya, 2005).In some tropical species, the mandibles can easily exceed half of thebody length, and in a few species they are longer than the body. Themandibles of the specimen of Prosinodendron described in thispaper are small within Lucanidae, but similar in size to those ofPassalidae. The growth of the mandibles of lucanids is allometric.Within a species, those males with greatly developed mandiblesare customarily referred to as male majors whereas those withsmall mandibles are called male minors. The holotype specimen ofProsinodendron krelli could presumably be classified as a maleminor because of its incisor edge of the mandible with two or threeteeth and rounded apex of the abdomen. Since we have only found

a single specimen, it is not possible to draw any conclusion aboutmandible variation. Pending the recovery of more specimens,Prosinodendron may provide important evidence from Mesozoic ofhorn evolution in the Lucanidae lineage, which has received wideattention from entomologists.

Acknowledgments

We are grateful to Dr. Shih Chungkun (College of Life Sciences,CNUB) for improvement of our manuscript. This research wassupported by the National Basic Research Program of China (973Program) (Nos. 2011CB302102, 2012CB821906), the NationalNatural Science Foundation of China (Nos. 30900144, 31010103913,

M. Bai et al. / Cretaceous Research 34 (2012) 334e339 339

31172143, 40872022, 31071964), the Knowledge InnovationProgram of Chinese Academy of Sciences (Nos. KSCX2-EW-G-4 andKSCX2-EW-Z-8) and the China Geological Survey (1212011120116).

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Prosinodendron krelli from the Yixian Formation, China: A missing link among Lucanidae, Diphyllostomatidae and Passalidae ( ...IntroductionGeological backgroundMaterial and methodsDiscussionAcknowledgmentsReferences