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Two new earwigs (Dermaptera) recently discovered in mid-Cretaceous (latest Albian) amber from Myanmar are described and figured. Astreptolabis ethirosomatia gen. et sp. n. is represented by a peculiar pygidicranoid female, assigned to a new subfamily, Astreptolabidinae subfam. n., and differs from other protodermapterans in the structure of the head, pronotum, tegmina, and cercal forceps. Tytthodiplatys mecynocercus gen. et sp. n. is a distinctive form of first-instar nymph of the Diplatyidae, the earliest record for this basal earwig family. The taxon can be distinguished from other Early Cretaceous nymphs by the structure of the head, antennae, legs, and most notably its filamentous and annulate cerci. The character affinities of these taxa among Neodermaptera are generally discussed as is the identity of an enigmatic ‘earwig-like’ species from the Jurassic of China.
Albian, Amber, Mesozoic, Earwigs, Polyneoptera, Pygidicranidae, Diplatyidae
It is with great pleasure that I dedicate this brief contribution to my friend and colleague, Dr. Alexandr P. Rasnitsyn, one of the great statesmen of paleoentomology. For the last 52 years Alex has produced some of the most influential works in the field, fueling the interests and investigations of generations of subsequent students of both Hymenoptera and fossil insects in general. On the same day Alex marks his 75th year, I shall mark my 40th. If in the coming 35 years I can undertake merely a similar fraction of what he has achieved, then I shall consider myself pleased. It is with considerable pride that Alex may look back on a career of tremendous accomplishment, and we all look forward to many more years of such successful endeavors from him.
IntroductionEarwigs are certainly one of the lesser-studied lineages of insects, with comparatively few current investigations underway into their diversity, behavior, biology, and general natural history. This is unfortunate given the remarkable diversity of form for these often subsocial insects, with their prominent and immediately recognizeable cercal forceps which are used in aggressive/defensive interactions, courtship, and prey capture (e.g.,
Herein I provide the description of two newly recognized earwigs in mid-Cretaceous amber from Myanmar. The morphology and possible affinities of these taxa are discussed as is the attribution to Dermaptera of some recently described enigmatic insects from the Jurassic of China (
The material discussed herein originates from the latest Albian amber deposits of northern Myanmar in the State of Kachin. The general paleobiota, dating, and origin of this amber have been overviewed by
Suborder Neodermaptera Engel
Family Pygidicranidae Verhoeff
urn:lsid:zoobank.org:act:FF43BCB1-914D-48DC-9EE6-BA1331525633
Astreptolabis Engel, gen. n.
Female: Minute earwigs (ca. 3.5 mm in length); somewhat dorsoventrally compressed; densely setose, but not chaetulose; integument dull and matt. Head prognathous, broad, slightly broader than anterior border of pronotum (Fig. 1), apparently tumid, posterolateral corners gently curved, posterior border straight; compound eyes well developed, prominent, separated from posterior border of head by slightly less than compound eye length, setose; ocelli absent; antenna with at least 14 antennomeres (an unusually small number for basal Neodermaptera and likely autapomorphic for this subfamily), scape stout, pedicel longer than wide, flagellomeres longer than wide, progressively more elongate from flagellomere II–X, with X–IV subequal in size. Pronotum exceptionally large (Fig. 1), anterior margin relatively straight, posterior border gently convex, lateral borders slightly divergent in anterior half, flared and convex in posterior half, posteriorly broader than head, all borders ecarinate. Tegmina present, without venation, symmetrical, elongate, outer margins convex, apex gently curved and tapering to midline (not truncate), covering first four abdominal segments (Fig. 1); hind wings present, with squama slightly exposed from under tegmina. Femora apparently not carinulate; tarsi trimerous, second tarsomere shortest, not extending beneath base of third tarsomere; pretarsal ungues simple; arolium absent. Abdomen slender, elongate (eight visible segments, typical for females), lateral margins parallel-sided, most segments only slightly wider than long, apicalmost segment with straight apical margin, without tubercles. Cerci symmetrical, slightly longer than apicalmost three abdominal segments, straight, tubular, gently tapering to acute apex, densely covered in microtrichia, without tubercles, dentition, or serrations, broadly separated at base (Fig. 1); pygidium not evident; valvulae not exposed at abdominal apex.
Male: Unknown.
Dorsal aspect photomicrograph of holotype female of Astreptolabis ethirosomatia gen. et sp. n. (AMNH Bu-FB20). In this orientation the head is slightly dipped forward making the postocular area appear minutely foreshortened relative to the compound eyes.
urn:lsid:zoobank.org:act:D1E57007-13A3-45BD-B732-D77235E57FF8
Astreptolabis ethirosomatia Engel, sp. n.
As for the subfamily (vide supra).
The new genus-group name is a combination of the Greek words astreptos (meaning, “not curved”) and labis (meaning, “forceps”). The name is feminine.
urn:lsid:zoobank.org:act:EEF799CF-0A18-420D-B228-58E3CC0851E0
http://species-id.net/wiki/Astreptolabis_ethirosomatia
Fig. 1AMNH Bu-FB20; adult female; amber, mid-Cretaceous, Myanmar: Kachin State (nr. Myitkyina), ex coll. Federico Berlöcher; deposited in the Division of Invertebrate Zoology (Entomology), American Museum of Natural History, New York.
As for the genus (vide supra).
As for the subfamily and genus, with the following additions: Female: Total length as preserved (including cerci) ca. 3.5 mm; head medial length from clypeal apex to posterior border 0.38 mm, maximum width (across level of compound eyes) 0.56 mm; compound eye length 0.13 mm; length of head behind compound eye 0.11 mm. Pronotum medial length 0.45 mm, anterior width 0.47 mm, posterior width 0.70 mm; tegmen length 1.21 mm, maximum width 0.49 mm. Abdominal length as preserved (excluding cerci) 1.65 mm, maximum width 0.44 mm; cercal forceps length 0.65 mm, basal width 0.05 mm, separation between bases 0.12 mm. Integument as preserved apparently brown to dark brown, impunctate, dull, matt throughout. Legs without spines or bristle-like setae. Setae of body short and dense except more elongate setae posterolaterally on abdominal terga (Fig. 1).
Male: Unknown.
The specific epithet is a combination of the Greek words etheira (meaning, “hairy”) and somation (diminutive form of the word for, “body”).
urn:lsid:zoobank.org:act:F81ABA76-CE78-4616-BE31-01FB81CE0DDE
Tytthodiplatys mecynocercus Engel, sp. n.
Minute earwigs (ca. 1.9 mm in length excluding cerci), with eight antennomeres (groundplan condition for first instars of Neodermaptera). Body dorsoventrally compressed (Fig. 2), with sparsely scattered setae, not chaetulose; integument dull and matt. Head prognathous, slightly broader than long (estimated as direct dorsal view of specimen not possible: Fig. 2), somewhat tumid, posterior angles rounded, posterior border relatively straight, rounded (not truncate or concave); compound eyes well developed, somewhat prominent, separated from posterior border of head by slightly more than compound eye diameter; ocelli absent; antenna with eight articles, scape relatively slender, pedicel short, subquadrate, very slightly wider than long, meriston longer than other flagellomeres; mouthparts typical for Dermaptera (e.g.,
Photomicrograph of holotype nymph of Tytthodiplatys mecynocercus gen. et sp. n. (AMNH Bu-FB75) (arrows indicate most easily discernible cercomere joints).
The new genus-group name is a combination of the Greek word tytthos, meaning “small” or “young”, and Diplatys, type genus of the family (itself a combination of the Greek words di and platys, meaning “two” and “broad”, respectively). The name is masculine.
urn:lsid:zoobank.org:act:C49383C4-8C91-49BE-ADDA-06B45D854AAE
http://species-id.net/wiki/Tytthodiplatys_mecynocercus
Fig. 2AMNH Bu-FB75; female nymph (first instar); amber, mid-Cretaceous, Myanmar: Kachin State (nr. Myitkyina), ex coll. Federico Berlöcher; deposited in the Division of Invertebrate Zoology (Entomology), American Museum of Natural History, New York.
As for the genus (vide supra).
As for the genus with the following minor additions: First-instar nymph: Total length as preserved (including cerci) ca. 1.9 mm; head medial length from clypeal apex to posterior border 0.46 mm; compound eye length 0.08 mm; length of head behind compound eye 0.10 mm. Pronotum medial length 0.25 mm; mesonotum medial length 0.22 mm; metanotum medial length 0.12 mm. Abdominal length as preserved (excluding cerci) 0.83 mm; cerci length 1.58 mm. Integument as preserved apparently brown, impunctate, strongly imbricate, dull, matt throughout. Legs without spines or bristle-like setae except for a few stiff setae on dorsal surface of profemora. Cerci separated at base by about cercal basal width. Setae of body sparse, where present setae stiff and erect to suberect, particularly those apicolaterally on abdominal terga; cerci with numerous, elongate, stiff, erect setae scattered along cercomeres.
The specific epithet is a combination of the Greek words mekyno (meaning, “prolong”) and kerkos (meaning, “tail”).
Discovery of these two specimens brings the diversity of earwigs in Burmese amber to four species – Myrrholabia electrina (
Astreptolabis is easily placed among the Neodermaptera owing to the absence of ocelli, the trimerous tarsi, unsegmented cerci, vestigial ovipositor, and absence of venation in the tegmina (
Astreptolabidinae can be readily differentiated from other pygidicranid subfamilies by the peculiar form of the female cercal forceps, as well as the combination of a broad, somewhat truncate head, large pronotum, and densely and finely setose body. From Burmapygiinae, also in Burmese amber, the new subfamily further differs in the stout scape, the absence of the arolium, and the shorter valvulae which do not apparently extend beyond the apex of the subgenital plate. In some respects, the head and pronotal structure of Astreptolabis are reminiscent of Echinosomatinae (head broad, transverse, somewhat truncate posteriorly; pronotum large, subquadrate or transverse; scape stout), but the absence of chaetae on the integument (instead dense, fine setae), particularly the head, pronotum, and tegmina, excludes inclusion therein. Echinosomatines are also rather large, broad, and stout (ca. 8–30 mm in length), never as minute as Astreptolabidinae, and although the cercal forceps are simple (i.e., lacking dentition or serrations) and generally widely separated as in the latter, they are distinctly arcuate and more stout in the former. In addition, the female valvulae of echinosomatines typically extend slightly beyond the apex of the subgenital plate. Astreptolabidinae may represent an early ally of the Echinosomatinae.
It is interesting to note that the tegminal form and minute body size are reminiscent of the recently described Atopderma ellipta
1. Head shape: The assertion that in Staphyliniformia the head is much narrower than the pronotum is incorrect, and triangular heads are very common in Staphylinidae (as well as numerous other beetle families). Yes, there are many staphylinids in which the pronotum is narrower than the head, but there are similarly many in which the head is as broad as or broader than the pronotum (e.g., many Oxytelinae, Staphylininae, Scydmaeninae, &c.), not to mention this similar condition among other families such as Hydraenidae, Hydrophilidae, &c. The head shape of Astreptolabis ellipta certainly does not exclude placement in Coleoptera. Moreover, the total antennal number (unknown for the holotype and unreported for the paratypes which have more completely preserved antennae), seems to be approximately 11 in some specimens (momentarily overlooking the concern that some of the paratypes do not appear to be conspecific with the holotype; some of the paratypes look more dermapteran-like while the holotype looks awfully coleopteran), a distinctly polyphagan, if not also staphyliniform, groundplan condition. What is known of the head and antenna in Astreptolabis ellipta neither supports nor refutes a placement in Coleoptera or Dermaptera.
2. Prothorax without pleural sulcus separating pronotum and propleuron: This is an enigmatic character for ‘distinguishing’ between these orders, and it is not entirely clear what difference the authors are really referring to as both Staphyliniformia and Dermaptera have a sulcal separation between the pronotum and propleuron (e.g.,
3. ‘Tegmina’ purportedly long and thin, and with curved outer (costal) margins: Certainly most staphylinids do have short, more rectangular elytra, but many Staphyliniformia may also have more elongate elytra, and definitely of the form appearing in Astreptolabis ellipta. For example, some Scydmaeninae, Omaliinae, and Scaphidiinae have more fully-developed elytra, particularly of the latter subfamily. Lastly, the assertion that Coleoptera should have more heavily sclerotized elytra than the condition observed in Astreptolabis ellipta is both ad hoc and erroneous. No one could argue that the reduced elytra of many Ripiphoridae, or those of Meloidae, Melyridae, Phengodidae, Pyrochroidae, or even some Coccinellidae are more heavily sclerotized than those of Astreptolabis ellipta. There is certainly a considerable range of cuticle thickness and development across beetle elytra (e.g.,
4. Carinated and spined femora: Although the authors of Astreptolabis ellipta state that it has carinulate femora, this is not the case in any of their figures. Some primitive earwigs have femora with visible lamelliform edges dorsally but the presumed carina referred to by
5. Abdominal shape: That the abdominal terga in Dermaptera are always transverse and the implicit assumption from the account of
The purpose here is not to assert that Astreptolabis ellipta is a beetle, and more precisely a staphyliniform beetle, but to demonstrate instead that a coleopteran attribution cannot be so readily dismissed by the stated characters. Naturally, dramatically autapomorphic taxa can appear in any period of time and such may be the case with Astreptolabis ellipta should more complete material reveal definitive dermapteran synapomorphies. Thorough redescriptions of the type series are needed but more critical will be the discovery of more complete and finely-preserved specimens. Only then will accurate conclusions on the phylogenetic affinities of these wonderful animals be permitted. For the time being, however, I conservatively consider Astreptolabis ellipta to be of uncertain ordinal assignment.
On the surface the phylogenetic affinities of Tytthodiplatys mecynocercus would appear more challenging than those of Astreptolabis given that the morphology and systematics of immature Dermaptera has not received as much attention as that of the adults. Indeed, many challenges remain for making conclusive statements about fossil earwig nymphs (e.g.,
The Cretaceous amber record of Dermaptera is steadily growing and it is only a matter of time before informative new specimens are discovered in the deposits of Spain, Canada, and elsewhere (e.g.,
Dr. Ismael A. Hinojosa-Díaz is gratefully acknowledged for producing the excellent photomicrographs presented herein, Dr. Stylianos Chatzimanolis for constructive comments and discussion, Dr. Dmitry E. Shcherbakov and two anonymous reviewers for informative critiques, and Dr. David A. Grimaldi for bringing these specimens to my attention. This is a contribution of the Division of Entomology, University of Kansas Natural History Museum.