The Mecoptera are currently a small, relict order of insects consisting of little more than 600 species (Cai et al. Reference Cai, Huang and Hua2008; Bicha Reference Bicha2010). Living Mecoptera are divided into nine families among which only two, Panorpidae and Bittacidae, are comparatively abundant and widely distributed. Since the Cretaceous biotic changes which affected the insect fauna (Szwedo & Nel Reference Szwedo and Nel2015), mecopteran abundance has significantly decreased (e.g. Kopeć et al. Reference Kopeć, Soszyńska-Maj, Krzemiński and Coram2016), and the order has gradually evolved into its modern composition. The family Orthophlebiidae is considered to be the ancestral stock of Eocene panorpoid scorpionflies (Krzemiński et al. Reference Krzemiński, Soszyńska-Maj, Kopeć and Sukatsheva2017 (this volume)) which reached their peak of diversity during the Palaeogene (Archibald et al. Reference Archibald, Mathewes and Greenwood2013). The oldest Orthophlebiidae are known from the Middle Triassic (e.g., Hong et al. Reference Hong, Hen and Liu2002) and the last known are from the Early Cretaceous of China (Ren et al. Reference Ren, Ren, Lu, Guo and Ji1995; Ren Reference Ren1997).
To date, Mecoptera from the Early Cretaceous Wealden Supergroup of southern England have been little studied (Table 1). They are uncommon as fossils in the Wealden and only a few taxa have been documented. The family Orthophlebiidae, without species descriptions, was reported as present by Crowson (Reference Crowson and Given1946), Jarzembowski (Reference Jarzembowski1984, Reference Jarzembowski and Batten2011) and Ross & Cook (Reference Ross and Cook1995). Petrulevičius & Jarzembowski (Reference Petrulevičius and Jarzembowski2004) described a new species and genus of the family Bittacidae from the Wealden in the county of Surrey, later restudied by Kopeć et al. (Reference Kopeć, Soszyńska-Maj, Krzemiński and Coram2016). A new family, Englathaumatidae, comprising two new species, has also recently been recognised in Surrey, as well as Sussex (Novokshonov et al. Reference Novokshonov, Ross, Cook, Krzemiński and Soszyńska-Maj2016).
Fossil Mecoptera from the Weald Clay Formation of southern England.
A new species description of the first English Wealden representative of the family Orthophlebiidae is given below.
1. Geological context
The Weald Clay Formation (Hopson et al. Reference Hopson, Wilkinson and Woods2008), outcropping in the counties of Kent, Surrey and Sussex, represents an ancient non-marine, muddy wetland with some open water; river run-off from the London area deposited terrestrial insect remains in the outcrop basin (Jarzembowski Reference Jarzembowski1995). Some 35 metres of the lower Weald Clay Formation were formerly exposed at the Clockhouse brickworks, near Capel, Surrey (Fig. 1; National grid reference [TQ 175385]; latitude 51° 8′ N., longitude 0° 19.5′ W.). The section differed from that of other Wealden localities where Mecoptera have been described (Table 1) in that the insect remains occurred in discarded siltstone lenticles and domes which originated as well-cemented scour fills in the mudstone sequence (Jarzembowski Reference Jarzembowski1991; Ruffell et al. Reference Ruffell, Ross and Taylor1996). The insects are disarticulated but numerous; the new species described below being associated, amongst others, with cockroaches (Blattodea), termites (Isoptera), plant bugs (Homoptera), true flies (Diptera) and beetles (Coleoptera). The insect-bearing sequence is dated as upper Hauterivian, below British Geological Survey beds ‘3’/3a (Rasnitsyn et al. Reference Rasnitsyn, Jarzembowski and Ross1998; Batten & Austen Reference Batten, Austen and Batten2011) ∼130 Ma (Cohen et al. Reference Cohen, Finney and Gibbard2013).
Clockhouse brickworks, near Capel, Surrey: (a) the ‘new’ pit (2005), looking East. Photo: EJ; (b) location map – brickworks marked as ‘C’.
2. Material and methods
The five fossil wings studied herein are preserved as three-dimensional impressions with brown-coloured pigmentation and veins, although the latter may be faint in unpigmented areas (Fig. 2). They occur in yellow, grey or even green calcareous siltstone. Any degagement was done with a finely-tuned Burgess vibrotool. Drawings were prepared with the help of a camera lucida mounted on an M4A Wild binocular microscope, then digitally processed using Corel X5 software. B/W photography was done on a Wild photomicroscope. Solid lines represent definite veins or margins and dashed lines represent damaged, faint or even extrapolated ones.
Forewing of Mesopanorpa brooksorum sp. nov., holotype no. II 3094 [CH200b], Weald Clay, Clockhouse. Photo: EJ.
Vein nomenclature is according to Willmann (Reference Willmann1989) with some modifications (Soszyńska-Maj et al. Reference Soszyńska-Maj, Krzemiński, Kopeć and Coram2017 (this volume)).
Collection abbreviations. NHMUK, Natural History Museum, London; BMB, Booth Museum of Natural History, Brighton. Field numbers given in parenthesis for continuity (prefixed CH, Clockhouse).
3. Systematic palaeontology
Order Mecoptera Packard, Reference Packard1886
Family Orthophlebiidae Handlirsch, Reference Handlirsch1906
Type genus. Orthophlebia Westwood in Brodie, Reference Brodie1845.
Type species. Orthophlebia liassica (Mantell, Reference Mantell1844)=‘Panorpa’ liassica Mantell, Reference Mantell1844.
Type locality. Wainlode Cliff, Gloucestershire (United Kingdom); Rhaetian (Upper Triassic).
Genus Mesopanorpa Handlirsch, Reference Handlirsch1906
Type species. Panorpa hartungi Brauer, Redtenbacher & Ganglbauer, Reference Brauer, Redtenbacher and Ganglbauer1889.
Type locality. Ust-Baley, Russia; Toarcian (Lower Jurassic).
Mesopanorpa brooksorum sp. nov.
Wing venation of Mesopanorpa brooksorum sp. nov.: (A) forewing, holotype no. II 3094 [CH200b]; (B) hindwing, paratype no. 014914.1 [CH320+774]. Abbreviations: A=anal vein; Cu=cubitus; M=media; R=radius; Rs=radial sector; Sc=subcosta. Scale bars=1mm.
Material. Five incomplete wings; holotype II 3094 [CH200b, b'], right forewing; paratypes II 3095 [CH815a, b], II 3096 [CH817c, c']; other material P1 II 3097 [CH62c, d], housed in NHMUK, London; Paratype 014914.1 [CH320], housed in BMB, Brighton.
Horizon and locality. Weald Clay Formation, Clock House Brickworks, Surrey.
Etymology. After Ken and the late Diana Brooks of Hastings, Sussex, local geologists.
Diagnosis. Wing dark coloured, with narrow transparent spots merging into bands, Rs1+2 about twice as long as Rs3+4, Sc long in forewing, reaching pterostigmal area, M4a+b very short in forewing.
Description. Forewing, narrow and elongated, more than three times longer than wide; 10.3–10.6 mm long, 3.2–3.4 mm wide; membrane with distinctive brown colour markings, comprising three connected but discrete transverse bands, and several coalesced bands in the apical one-third of the wing; basal part of wing not preserved, veins in the areas without colouring (pigmentation) weakly preserved; cross-veins very few or weakly preserved; vein Sc ending opposite first fork of Rs1, slightly beyond fork of R1; R1 with one branch surrounding the pterostigmal area; in radial sector (Rs), six veins reaching the outer margin; Rs1 with three veins reaching the outer margin; Rs1a–c slightly shorter than length of Rs stem and a little longer than Rs3+4; Rs2 simple, straight; Rs3+4 ca. half length of Rs1+2, forking with two simple veins reaching the margin; five veins in median area; M1+2 twice longer than M3+4; M4 forking with two simple veins, M4a and M4b, reaching the outer margin, M4a+b very short; two cubital veins, three anal veins present. Hindwing, vein Sc shorter than in forewing, reaching the outer margin slightly beyond end of Rs1+2 stem; four simple median veins reaching outer margin, M1+2 ca. three times longer than M3+4.
4. Discussion
Although few in number, the Wealden Mecoptera have added to our knowledge of the order in the Mesozoic. The Orthophlebiidae are described here for the first time from the Hauterivian of England. This species was already given by Jarzembowski (Reference Jarzembowski1984) as a representative of the genus Mesopanorpa Handlirsch, Reference Handlirsch1906, but without a species description. This new species is the first, but not necessarily the only representative of the genus in the Wealden; continuing insect finds including Mecoptera at the Smokejack's brickworks may well extend the range. According to the existing taxonomic system of the family Orthophlebiidae the character of Rs1+2 almost twice as long as Rs3+4 is considered as a feature of the genus Mesopanorpa with Rs1 two- or three-branched (Handlirsch Reference Handlirsch1906). This is in contrast to the genus Orthophlebia, which includes species with the radial sector forking with seven or eight simple veins to the wing margin and Rs1+2 not significantly longer than Rs3+4. However, there are some species which do not have either character Rs1+2 twice as long as Rs3+4 (Mesopanorpa) or Rs1+2 forking at the same level as Rs3+4 (Protorthophlebia). This supports the need to establish a new, updated taxonomic system of the family Orthophlebiidae. The preliminary results of this work are being submitted separately (Krzemiński et al. Reference Krzemiński, Soszyńska-Maj, Kopeć and Sukatsheva2017 (this volume); Soszyńska-Maj et al. Reference Soszyńska-Maj, Krzemiński, Kopeć and Coram2017 (this volume)). However, the final diagnoses of the genera are still under consideration.
5. Acknowledgements
Our thanks to Professor Wiesław Krzemiński and Dr Andrew Ross for commenting on the manuscript. The research was partly supported by the Polish National Science Centre (grant no. 2013/09/B/NZ8/03270) and the Chinese Academy of Sciences President's International Fellowship Initiative (2011T2Z04). EAJ is currently a Leverhulme Emeritus Fellow.
