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Corresponding author: Jiří Kolibáč ( jkolibac@mzm.cz ) Academic editor: André Nel
© 2023 Jiří Kolibáč, Kateřina Rosová, Jan Simon Pražák, Jörg U. Hammel, Jakub Prokop.
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A larva of Cleroidea in Burmese amber is described, which is the first record of an immature beetle of the basal cucujiform superfamily for the Mesozoic. Well-preserved unique specimen is described and illustrated using traditional methods as well as synchrotron-radiation-based micro-computed tomography (SRµCT) to reconstruct the specimen and discern integumental details of cephalic structures, especially the mouthparts. Cretorhadalus constantini gen. et sp. nov. is unambiguously assigned to the melyrid lineage of Cleroidea and tentatively classified within the basal family Rhadalidae. Within this family, this fossil larva has the ancestral cleroid pattern of the stemmata (2+3) and well-developed hooked urogomphi. Based on a comparison with extant rhadalids, as well as most members of the melyrid lineage, the larvae and adults of this new species were probably carnivorous, living on the trunks and branches of trees or in galleries where they foraged for soft xylophagous insects.
Coleoptera, Cleroidea, larva, Cenomanian, burmite
The “melyrid lineage” of Cleroidea is the most species-rich clade of cleroid beetles (
The Cleroidea is considered to belong among the ancestral superfamilies of Cucujiformia, the largest group of beetles, and sister group to Tenebrionoidea (
Here we describe the oldest larva of the melyrid lineage and first representative of the lineage in Burmese amber and the Mesozoic. We also discuss its implications for phylogeny and palaeoecology and compare it with other extinct and extant taxa in this part of Cleroidea.
The material examined is deposited in the following collections:
· The type specimen of the newly described fossil species: Charles University, Faculty of Science, Department of Zoology, Prague, Czechia; registration number PřFUK20.
· All recent species used for morphological study: Moravian Museum, Department of Entomology, Brno, Czechia.
Details above the fossil material record are given under holotype description.
The amber piece was polished, allowing improved views of the included specimen, and was not subjected to any supplementary fixation.
Detailed photographs of small, semi-transparent parts of the body of the specimen were taken using an Olympus BX41 fitted with a Canon EOS 1200D digital camera or Leica S9D fitted with a Canon EOS 90D. Photographs of the fossil specimen were taken using a Leica Z16Apo. Body parts were measured using LAS 3.6.0 software. QuickPhoto Camera 2.3 with DeepFocus 3.1 module, LAS 3.6.0 and Helicon Focus (Helicon Soft) programs were used to stack certain images. Adobe CS6 software (Illustrator 16.0.3 and Photoshop 13.0.) was used to assemble the plates and adjust particular images.
Along with traditional optical devices we used synchrotron-radiation-based micro-computed tomography (SRµCT) to reconstruct the specimen and discern otherwise hardly accessible integumental details on cephalic structures. Imaging of amber specimens was done at the Imaging Beamline P05 (IBL) (
The reconstructed 32 bit TIFF image stacks were cropped, converted into 8 bit TIFF files, inverted and exported using the Dragonfly software (Object Research Systems (ORS) Inc, Montreal, Canada). Amira 6.0 software (Visage Imaging GmbH, Berlin, Germany) was used for segmentation of the structures in every 40th slice. The segmentation process was finalised using Biomedisa (
The raw scan data will be made available at Zenodo repository at https://doi.org/10.5281/zenodo.7701916.
We follow the classification of the melyrid lineage of
The publication and the included nomenclatural acts have been registered in ZooBank (www.zoobank.org), the online registration system for the ICZN. The LSID for this publication is: urn:lsid:zoobank.org:pub:8EE85535-FA17-418B-B1BA-6929C4EC7F34.
Order Coleoptera Linnaeus, 1758
Suborder Polyphaga Emery, 1886
Superfamily Cleroidea Latreille, 1802
Melyrid lineage (sensu
Family ?Rhadalidae LeConte, 1862
A classification of the fossil larva within Cleroidea is unambiguously based on the shape of its body, sparse but long pubescence, mouthparts, characteristic pattern of thoracic terga (protergal plate + 2 pairs of tergites) and hooked urogomphi (
Character | Clerid lineage | Trogossitidae Lophocateridae | Peltidae | Melyrid lineage |
Median endocarina | Present/absent | Present | Absent | Absent |
Frontal sutures | V/Y/U-shaped, stalk of Y shorter than 1/3 of head | V/Y-shaped, stalk of Y shorter than 1/3 of head | Weakly Y-shaped, reduced in size | Y-shaped, stalk of Y at least 1/3 of head (Figs |
Head capsule ventrally | Capsule open but mouthparts shortened | Capsule closed along anterior margin | Capsule closed along anterior margin | Capsule open or inconspicuously closed |
Gula | Gula nearly as long as cranium, sutures subparallel | Gula not exceeding half of cranium, without protrusions; sutures convergent | Gula not exceeding half of cranium, with 2 protrusions; sutures convergent | Gula not exceeding half of cranium, without protrusions; sutures subparallel |
Mandible | Unidentate | Bidentate/rarely unidentate | Bidentate | Bidentate |
Mandibular mola | Absent | Absent (rudiment rarely present) | Present | Absent |
Colour | Pink/red/whitish | Whitish | Whitish | Red/whitish |
An assignment to a particular family of the melyrid lineage is based on limited set of known larvae. The families Prionoceridae (
Character | Phycosecidae | Rhadalidae | Prionoceridae | Melyrinae | Dasytinae | Malachiinae | Fossil larva |
Antennomere 3 | Longer than 2, weakly longer with sensory appendix | As long as 2 or longer than 2, with 1 long seta | As long as 2 | Shorter than 2 | As long as 2 | As long as 2 | Longer than 2, with 1 long seta |
Stemmata | 6 (2+3+eye spot) | 2 (1+1) | 5 (2+3) | 4 (1+3) or 5 (2+3) | 5 (2+3) | 4 (1+3) | 5 (2+3) |
Pronotal tergites | Divided tergal plate | Divided tergal plate | Split into several fragments | Reduced in size/absent | Split into 2 or more tergites/reduced in size | Split into 3–4 sclerites | Divided tergal plate |
Meso- + metathoracic tergites | 0+0 | 2+2 | Split into several fragments | 2+2 | 4+4 | 2+2 | 2+2 |
Urogomphi | Present | Present: well-developed, shortened or absent | Present | Present | Present: well-developed or shortened | Present | Present: well-developed |
Urogomphi shape | Straight, weakly upturned | Hooked/absent | Straight, divergent | Hooked (Fig. |
Hooked | Hooked (Fig. |
Hooked |
Body vestiture | Sparse, short | Sparse, long/dense and short | Dense, short | Dense, long | Sparse/dense and short/long | Sparse, short | Sparse, long |
We tentatively propose attribution of this fossil to Rhadalidae. Such a classification is based on i) the structure of the antenna with 3rd antennomere longer than antennomere 1 or 2, ii) the trapezoidal cranium (Fig.
It is important to note that no larva of the basal melyrid lineage family Mauroniscidae has been found for comparison, but its presumptive adult is recorded in Callovian deposits in Inner Mongolia (
Cretorhadalus constantini Kolibáč & Prokop gen. et sp. nov.
Cranium weakly trapezoidal, approximately as wide as long, its anterior margin wider than base (Figs
The generic name is composed of the prefix creto- (derived from Cretaceous period) and the root rhadalus that denotes the supposed affiliation of the new genus with the family Rhadalidae, not a relationship with the nominate genus. Gender of name is masculine.
Holotype PřFUK20 preserved in a polished, transparent yellow piece of amber (18.1 × 9.9 × 3.6 mm); deposited in the collection of Charles University, Faculty of Science, Department of Zoology, Prague.
Lowermost Cenomanian (Upper Cretaceous); age based on U-Pb dating of zircon crystals from the volcaniclastic matrix (
Hukawng Valley, Kachin State, northern Myanmar.
Body length from clypeus to the last abdominal segment (excluding urogomphi) 2.41 mm. For other measurements see Table
Measurements of some body parts of Cretorhadalus constantini gen. et sp. nov. (in millimetres).
Body part | Measurements |
Body length from clypeus, excl. urogomphi | 2.41 |
Body length from clypeus, incl. urogomphi | 2.59 |
Head capsule anterior, max. width | 0.36 |
Head capsule base, width | 0.28 |
Head capsule, max. length | 0.34 |
Antenna, length incl. connecting membrane | 0.22 |
Antennomeres 1+2+3, length | 0.03+0.04+0.05 |
Prothorax, width | 0.42 |
Prothorax, length | 0.31 |
Mesothorax, width | 0.47 |
Mesothorax, length | 0.22 |
Metathorax, width | 0.52 |
Metathorax, length | 0.24 |
Metafemur, length | 0.16 |
Metatibia, length | 0.14 |
Urogomphi, approx. circumference | 0.21 |
Body habitus and pubescence (Fig.
The specific epithet honours Robert Constantin (Saint Lô, France), the eminent specialist of beetles in the melyrid lineage and leading authority on their larvae.
Although the larva of Cretorhadalus constantini gen. et sp. nov. has distinct features of the melyrid lineage, they are mostly limited to structures of the head. Other parts of the body including the general habitus, morphological structures of the thorax and abdomen, body colour, sculpture and vestiture are shared with basal representatives of other cleroid families including Cleridae, Trogossitidae, Metaxinidae/Chaetosomatidae and Acanthocnemidae, which is why they can be considered symplesiomorphic. In fact, the larva without its cranium could be easily identified within Cleroidea, but not indisputably assigned to the melyrid lineage, however, this may also be the case for larvae of Phycosecis (Phycosecidae) or Aplocnemus (Rhadalidae). Both of the latter families share with the fossil the single large longitudinally divided protergal plate, which is also present in all the major cleroid families mentioned above outside the melyrid lineage. The prothoracic tergite is always split into several sclerites in Prionoceridae and the former Melyridae sensu lato and the structure and/or number of the meso- and metathoracic tergites also differ in the mentioned groups in comparison with Cretorhadalus constantini gen. et sp. nov., Phycosecidae and Rhadalidae. Both of the latter families are considered to be basal within the lineage in the molecular phylogenies of
Maxillolabial complex of Cretorhadalus constantini gen. et sp. nov. Dotted lines indicate indistinct margins. Cranium apparently compressed and its ventral side artificially wide open; that is why gular sutures seem divergent and widely separated. The length of the gular sutures is not clear.
Extant species of the family Rhadalidae are today distributed worldwide except for the Australasian zoogeographical realm and Pacific islands (
Phylogenetic tree of the melyrid lineage based on the molecular analysis of
The fossil genus Aploceble with three species described from Baltic amber is considered to be related to the extant Palaearctic Trichoceble while other undescribed but studied rhadalid Eocene fossils (nine specimens) was placed in the extant genera Xamerpus (currently distributed from East Africa to India, incl. Madagascar and Seychelles) and Aplocnemus (Palaearctic) (
Palaearctic adults of Rhadalidae, in particular in terms of their habitus, are similar to Melyridae: Dasytinae and it is for this the reason they were classified within the former Dasytidae (
Cretorhadalus constantini gen. et sp. nov. tentatively assigned to Rhadalidae is the earliest described larva of Cleroidea (the only one for the Mesozoic) and the first representative of the melyrid lineage (sensu
This contribution demonstrates the potential of studying Cretaceous beetle larvae preserved in amber. These studies are frequently overlooked in recent taxonomic studies mainly due to the lack of diagnostic characters. By using various classical and modern microscopy tools like inverted light microscopy or SRµCT it is possible to see details of their morphology and surface microstructures that reveal larval specializations and lifestyles that can be compared with those of extant species (e.g., Batelka et al. 2018,
J.K. was supported by the long-term conceptual development program for research institutions provided to the Moravian Museum by the Ministry of Culture of the Czech Republic (ref. MK000094862). The work of K.R, J.S.P. and J.P. was supported by the Grant Agency of the Czech Republic (No. 21-05216S). Scanning of the holotype specimen was supported by the DESY Block Allocation Group project “Scanning the past – Reconstructing the diversity in million years old fossil amber specimens using SRµCT“ at PETRA III (Hamburg, Germany).
The authors are grateful to Anthony F. G. Dixon (University of East Anglia, Norwich, United Kingdom) for improving the English and to an anonymous reviewer for insightful comments and suggestions.