Research Article |
Corresponding author: György Makranczy ( makranczy.gyorgy@nhmus.hu ) Academic editor: Adam Brunke
© 2018 György Makranczy, Shûhei Yamamoto, Michael S. Engel.
This is an open access article distributed under the terms of the CC0 Public Domain Dedication.
Citation:
Makranczy Gy, Yamamoto S, Engel MS (2018) Description of a Cretaceous amber fossil putatively of the tribe Coprophilini (Coleoptera, Staphylinidae, Oxytelinae). ZooKeys 782: 81-94. https://doi.org/10.3897/zookeys.782.27733
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An unusual and well-preserved fossil staphylinid is described and figured from a single specimen in Upper Cretaceous Burmese amber. Gollandia planata gen. et sp. n. is tentatively placed in the extant oxyteline tribe Coprophilini, although it lacks a few characteristic features of present-day members of the group, likely indicating it to be either a stem group of the tribe or prove to be distinct pending future discoveries. The discovery of this genus suggests that early oxytelines were more morphologically diverse during the Cretaceous and their evolutionary history was more complicated than previously documented. Tribal placement as regards fossil oxyteline taxa is discussed.
Burmese amber, Cenomanian, Mesozoic, Myanmar, new genus, new species
The staphylinid subfamily Oxytelinae Fleming, 1821 is a relatively large group with over 2049 valid extant species placed in 40 genera (
Despite
The tribe Coprophilini is currently without identified synapomorphies, and is instead defined by a lack of features of the more derived lineages (i.e., it is presently circumscribed by putative plesiomorphies, may be paraphyletic, and is in need of considerable revisionary and phylogenetic exploration). The extant coprophilines are characterised by the following combination of traits: mesocoxae narrowly separated by mesosternal process or contiguous, tarsal formula 5-5-5, abdominal segments with two pairs of laterosclerites, and with only six sternites visible. According to
The various records of fossil Oxytelinae and its related subfamilies were summarized by
This new taxon represents the second fossil occurrence of Oxytelinae documented from Mesozoic amber, and is also the oldest amber inclusion presently recorded for the subfamily along with Prajna tianmiaoae Lü et al., 2017, a species of Thinobiini (a more derived tribe) described from the same deposit.
Specimen photography was done with the amber piece mounted on a small plastic plate surface with a drop of viscous glycerine covered with a glass cover slip to eliminate distortions from the otherwise rounded amber surface. The habitus photographs were made with a Canon 5D Mark III camera and C Canon MP-E 65mm f/2.8 1–5× macro lens with two Canon Macro Twin Lite MT-24EX flash units and a Canon Speedlite 430EX III-RT flash unit standing on the shoe foot directly in front of the specimen (shooting directly into the head of the specimen). The light was diffused by a single ring of mylar. Raw photograph files were imported to Adobe Lightroom 5.7.1, and layers stacked with ZereneStacker (Richland, Washington, USA). Details of the specimen were photographed with a Canon EOS 6D camera attached to a Leica M205 C stereomicroscope with the help of a Canon EOS Utility 3.4.30.0 software, before being stacked using the same software as previously mentioned. Abbreviations for measurements are defined as follows:
HW head width with compound eyes;
TW head width at temples;
PW maximum width of pronotum;
SW approximate width of shoulders;
MW maximum width of elytra;
AW maximum width of abdomen;
HL head length at the middle-line from front margin of clypeus to the beginning of neck;
EL compound eye length;
TL length of temple;
PL length of pronotum at the middle-line;
SL length of elytra from shoulder;
SC length of elytra from hind apex of mesoscutellum;
FB fore-body length (combined length of head, pronotum, and elytra);
BL approximate body length.
The specimen is exceptionally well preserved but in a rather unfortunate position within the amber piece. Under UV-light examination it can be seen that the specimen is sitting within a dip in the internal flow of the amber (the amber flowed in layers when it was originally exuded from the tree and the beetle is in a dip within these flows). The result of its placement within the dip in the flow means ideal, clear images cannot be produced at high magnification unless some of the flows can be polished away. Whoever made the original preparation (probably local workers in Myanmar) polished the specimen too close to the amber surface and cut the piece poorly. The result is that it is now impossible to cut and polish the piece closer to minimize the optical impact of the flow lines.
The recent commercial amber mines are located in the Hukawng Valley (26°16.5’N, 96°34.0’E), Kachin, northern Myanmar. The minimum age of the amber is estimated to be 98.79 ± 0.62 Mya (by radioisotope dating of zircon crystals obtained from the volcanoclastic matrix,
Gollandia planata sp. n., (described below).
Head. Head somewhat retracted under large pronotum; head capsule rather short. Epistomal sulcus not well visible, but presence suggested by a tranvserse ‘run’ of air between amber and cuticle. Supraantennal prominences weak. Antennomeres with long tactile setae near apices (prominent on articles 3–11). Labial palp trimerous, basal two palpomeres rather stout, last palpomere thin. Labrum with two thick, forward-directed setae. Mandibles not prominent, apices acute. Maxillary palp tetramerous, basal three palpomeres moderately elongate, last palpomere much wider and long, not reduced, apex pointed. Gular sulci seemingly widely separated at base but confluent anteriorly (this area is not well visible as preserved). Neck separated by gentle constriction and (at least laterally) a groove. Thorax. Pronotum strongly explanate, margin slightly reflexed, marginal bead present, lateral edge finely serrate/sinuous. Laterally with a strong seta at each of ‘anteroangularis’ and ‘lateralis’ positions, plus strong seta on both sides well inside lateral margin at about 1/3 length, posterior edge appearing slightly concave (might be artefact of preservation). Pronotal disc with shallow impressions, with fine and dense punctation and setation. Procoxae contiguous, projecting; procoxal fissure present and open (Figure
All extant Coprophilini have a 5-5-5 tarsal formula, and even the fossil genus Mesocoprophilus has five tarsomeres, so the 4-4-4 condition in Gollandia is significant. The new genus differs greatly from Mesocoprophilus in the antennal structure, stout and short in Mesocoprophilus, slender and elongate with well-developed tactile setae on all antennomeres in the present fossil. The neck (lateral constriction, postoccipital groove) also differentiates this genus from Mesocoprophilus where these features are absent. The lack of striae or puncture rows on the elytra makes this genus distinct from all extant Coprophilini, while a distinction from Mesocoprophilus cannot be made as that fossil lacks its dorsal portion (
The only feature that clearly unites the fossil with extant Coprophilini is the lack of the well-developed second sternite. Beyond that, the head shape is reminiscent of Homalotrichus, while the pronotum bears some similarity to that of some Coprophilus (e.g., Coprophilus striatulus (Fabricius, 1793) plus its close relatives) and to a lesser extent some Homalotrichus (e.g., Homalotrichus impressicollis Solier, 1849), but none of these are as explanate as in the fossil.
The new genus is named after Susan Golland, exhibition developer at the Field Museum of Natural History, Chicago, whom the first author met at 10:32am on 14 March 2018 in front of Crystal Maier’s office. The fossil specimen described here was shown to him by the second author later on the same day. The gender of the name is considered feminine.
Sex unknown, probably male, in a flattened drop shaped, light yellow amber piece (20.0 × 9.9 × 4.5 mm, 0.98g): “FMNHINS 3729858 ex S. Yamamoto collection (SYAC0482)” deposited in Field Museum of Natural History (Chicago, USA).
Noije Bum hill near Tanai Village, SW part of Hukawng Valley (SW of Maingkhwan), Kachin State, northern Myanmar; lowermost Cenomanian, Upper Cretaceous.
As for the genus (vide supra).
Measurements: HW = 0.45; TW = 0.41; PW = 0.64; SW = 0.59; MW = 0.68; AW = 0.70; HL = 0.29; EL = 0.10; TL = 0.04; PL = 0.50; SL = 0.66; SC = 0.55; FB = 1.47; BL = 3.29 mm (all measured from dorsal view). Habitus: General habitus as in figures 1–6. Colour reddish dark brown. Body moderately lustrous, covered with fine microsculpture and forebody finely, not very densely setose. Abdomen with longer and stronger lateral setae posteriorly. Head. Head rather short. Antennae rather elongate, scape almost twice as wide as pedicel and not much longer, second antennomere (pedicel) more than 3.5× as long as wide, third antennomere (first flagellomere) slender at base and almost as long as previous. Further antennomeres spindle-shaped and each with rudimentary basal dish, gently constricted above them. Antennomeres 4–7 at least 2.5× as long as wide, from antennomere 8 becoming wider, gently clubbed, last three antennomeres only about 1.5× as long as wide. Compound eyes more than 2× as long as weakly formed temples. Neck not constricting strongly. Thorax. Pronotum rather large, widest point slightly before middle with both anterior and posterior corners rather narrowly rounded, lateral margin slightly concave before quite acute posterior angles. Surface finely microsculptured, thereby punctation partly obscured. Disc transversally impressed before base (in a curved fashion), also with a semi-triangular mid-longitudinal impression anteriad; rather large but shallow paralateral depressions on sides. Elytra. Elytra together just slightly broader than pronotum, trapezoidal, shoulders well developed, narrowly rounded, even slightly projecting forward in relation to anterior edge at mesoscutellar area. Dorsal surface finely punctate and setose, no major lateral setae, epipleural ridge with moderately long setae at regular intervals. Abdomen. Sides of abdomen gently curved, almost parallel. Surface of tergites with moderately fine, longitudinally elongate punctures, apical edges of tergites (up to tergite VI) with row of equal-sized setae at regular intervals. Specimen is without any feature suggesting strong sexual dimorphism. No genital traits observable.
The specific epithet is a Greek adjective derived from platys (= wide) and refers to the pronotum of the species being unusually explanate.
The specimen is exceedingly well preserved, with the hind wings unfolded over part of the abdomen, minor air bubbles under segmental edges, a thin air layer over some sculptured dorsal parts, and the ventral side exceptionally clearly visible. As explained before, the specimen is sitting within a layer of resin covered by another layer, and this creates an effect similar to the specimen being glued to a glass, evident in the photos of the ventral side. The legs are somewhat distorted (but each pair is almost perfect on one side). Primitive oxytelines often have distinctive coxites and styli in females (if not exposed, then setation gives them away), and in their absence the specimen is presumed to be a male.
Gollandia planata gen. et sp. n. 7 head, pro- and mesothorax, ventral view 8 fore-body, dorsal view 9 meso- and metacoxae, ventral view 10 mid leg, dorsal view 11 protarsus, ventral view. t 1–4 = tarsomeres, em = empodial seta, ts = mesotibial spur, sc = mesoscutellar impression, ec = elytral posterior corner, gs = gular sulcus, pf = procoxal fissure, ms = mesosternal, and mt = metasternal process. Scale bars: 0.15 mm.
There can be a great debate on how to place fossil species in higher taxa when the classification is otherwise based entirely on present-day species. Naturally, fossil species placed cladistically within the crown group are not difficult, but when potential stem groups are discovered some difficulties and strong differences of opinion arise. Does one include them within the formal group, necessitating a new circumscription of the taxon boundaries in order to accommodate the fossil, or, at another extreme, more radically establish a new group for the fossil as a potential sister to its extant relatives? The latter will inevitably lead to a proliferation of meaningless and often monobasic groups based on limited characters (e.g., often lacking critical data on genital traits) and collectively forming a pectinate stem to any lineage circumscribed solely on the basis of its extant constituents, the end result becoming a classification of little explanatory power. Ideally, there one desires a balance between maintenance of a good diagnostic power and keeping the classification simple while simultaneously reflecting the hierarchical relationships supported among the various taxa being classified and granting the system maximal explanatory and predictive significance. These goals are sometimes simultaneously achieved, but more often than not the former objective becomes muddied while attempting to adequately reflect the latter. This challenge is particularly great for ancient groups, such as the Oxytelinae whose history goes back at least 150 Mya, where there has been inevitably considerable extinction over the intervening epochs between the first divergence of a given clade and its modern fauna. Cretaceous deposits will undoubtedly supply for generations to come a continuous stream of unusual fossil species that will force us to rethink our estimates of relationship and concomitantly the classifications from which they are built. Descriptive science (
In the case of the presently known fossil oxytelines or putative oxytelines this challenge is acute as there are limited character data available. The four fossil species presently placed in Sinoxytelus possess a mixture of ancient and relatively modern traits. The basolateral ridges on the abdominal tergites are a trait of the tribe Oxytelini, while the somewhat reduced second abdominal sternite suggests placement in more primitive tribes. A solid age estimate is available for part (Lujiatun Bed) of the Yixian Formation and at approximately 126 Mya, or Aptian (
The current Burmese amber fossil species has a similarly conflicting combination of traits, on the one hand it can be placed in Coprophilini because of the plesiomorphic condition of the basal abdominal segments (although the tribe is presently defined on putative plesiomorphies and so this feature alone indicates nothing more than the potential for the fossil to belong therein or to belong to stem-group coprophilines, assuming the tribe is truly monophyletic). On the other hand, the apomorphically reduced number of tarsomeres, is a derived feature, but currently cannot be considered anything more than autapomorphic for the genus. Thus, given the lack of abundant evidence definitively demonstrating its phylogenetic placement relative to modern oxyteline genera, we prefer to tentatively consider the genus as a member (a stem group member) of Coprophilini. Hopefully, in time further material and other fossil species will be discovered that will ultimately permit a clarification of its relationships along with its broader implications toward affinities among lineages of Oxytelinae, and at which time a redefinition of oxyteline tribes may be attempted.
We are grateful to Al Newton (Field Museum of Natural History, Chicago) for providing an initial set of notes and comments on the specimen, and to Aslak Kappel Hansen and Janina Lisa Kypke (University of Copenhagen, Denmark) who aided the first two authors with taking photographs and experience with photographing amber specimens. A Visiting Scholarship from the Field Museum supported the first author (GyM) (12 March–5 April 2018) for portions of this research. The second author (SY) was supported by a Japan Society for the Promotion of Science (Tokyo, Japan) Overseas Research Fellowship (29-212).