Ergaula stonebut, Vršanský, Peter, Vidlička, Ľubomír, Barna, Peter, Bugdaeva, Eugenia & Markevich, Valentina, 2013

Vršanský, Peter, Vidlička, Ľubomír, Barna, Peter, Bugdaeva, Eugenia & Markevich, Valentina, 2013, Paleocene origin of the cockroach families Blaberidae and Corydiidae: Evidence from Amur River region of Russia, Zootaxa 3635 (2), pp. 117-126 : 123-124

Ergaula stonebut sp. n.

Holotype. IGNM FEB RAS ANHM 4/7. Both forewings; type locality, Archara-Boguchan, Belaya Gora locality, stratotype of the Tsagayan Formation, Far East, Russia; type horizon, Tsagayan Formation, Danian.

Diagnosis. Forewing narrow, length/width: 31/ 11 mm, its venation reduced to approximately 50 veins at margin. Sc branched broadly. Intercalaries distinct, coloration indistinct.

Description. Forewing fore margin slightly arcuate. Sc with both anterior (3 on left forewing, 1 on right forewing) and posterior (4, 4) branches. R more or less regularly branched, with venation more dense towards apex; veins secondarily branched (19, 16). M with secondary branches, curved posteriorly (11, 12). CuA largely simplified, reduced to 3 branches at most. Anal veins sparse (6, 7).

Remarks. E. stonebut sp. n. differs from Therea Bilberg, 1820 ( India) (the same tribe) in having costal space comparatively narrow and Sc less expanded and with branches running more longitudinally, M and R reduced to some extent and fused. Eucorydia Hebard, 1929 (SE Asia) and Miroblatta Shelford, 1906 (Borneo) have exclusively straight stem of R (without any posterior branches), the latter comprises deviant forms with extremely wide forewings, sometimes reduced to some extent. Homoeogamia Burmeiser, 1838 is limited to America ( Mexico and South America) today.

Ergaula stonebut sp. n. can be placed within Ergaula by simple exclusion and differs from its congeners only in minor characters. It is generally very similar to E. atica from the sediments of Israel (presumably Eocene in age), including the narrowness of forewings with distinct intercalaries and wide space between respective Sc branches (3 symplesiomorphies). E. atica also is very large, (forewing length 35 mm). The single preserved individual is distinctly coloured and posses numerous deformations. Undescribed specimens from the Messel, Germany are also very similar (H. Schmied, in preparation).

The E. stonebut sp. n. forewing is without deformities; it is narrower than in any living species. The type species E. carunculigera differs in having a considerably smaller forewing (21– 27 / 13.5 mm) (Gerstaecker 1861). Ergaula . capucina differs in having all Sc venation dense; E. pilosa has dense Sc venation in the anterior region only (Rehn 1951). Males of E. capensis are much larger (55–57 mm in total body length) (Hanitsch 1938).

The much smaller forewing of E. funebris (forewing length 22 mm: (Hanitsch 1933)) is monochromatic a character likely shared by E. stonebut sp. n. However, the wing of E. funebris is much wider. Ergaula nepalensis is unique in having discoidal veins straight and longitudinal (Saussure 1893), and E. silphoides , like most living species, has a rounded fore-margin of the forewing (Walker 1868).

Some distinct characters revealed in the course of study of living E. capucina are seen in forewing of the present fossil. The most distinct among them are asymmetrical sclerotisation (due to folding of wings over each other) and invagination in the base of R, which represents the huge ventral ridge serving for folding of the hind wing. Visible are also reticulations caused by sclerotisation in the costal area.

Etymology. stonebut is derived from some Slavic languages (means something).

Discussion

Based on study of terminal Mesozoic as well as Eocene cockroaches, it follows that most living cockroach genera originated directly at or around PETM (Vršanský et al. 2011, 2012b). Warming not only expanded the geographical range and the thermic optimum in more northern latitudes, but also produced conditions different from those present in the original source area. Changes on land resulted in a higher evolutionary tempo as evidenced by cockroaches (Vršanský 2011, 2012ab). Nevertheless, the present observations are direct evidence for the pre- PETM origin of some of cockroach genera, which was unexpected. It is notable that both of the species described herein belong to genera present (as codominants) in the Eocene Messel (47Ma) assemblage of Germany (Schmied 2009, unpublished observation), suggesting the characteristic Eurasian assemblage was already formed before the Paleocene side of the PETM.

Ergaula occurs also in the presumably Eocene or Oligocene mangals of Israel (Anisyutkin et al. 2008) and a leathery wing described as Netherea haatica Vršanský & Anisyutkin, 2008 seems to represent the smaller female of living Ergaula —a common sexual dimorphism of this genus. This associations are likely very similar unless identical in respect to generic content and support the Eocene stage for obscure (originally presumed to be Mesozoic) locality in Israel.

Different were some Eocene North American localities, where predominantly smaller species were preserved (Vršanský et al. 2011a, 2012).

Very little can be learned from the geography of the two specimens. Ergaula currently is widely distributed in Africa and Asia, but apparently was also present also in Europe in PETM, but absent in the Americas during the Eocene. Morphna has a similar wide pattern in Asia (absent in Africa), with occurrence in Europe during PETM. The important aspect of deformed wings is ambiguous in this respect. While no wing deformation (developmental change modifying wing geometry, most often fusion of veins or irregularity), is reported in hundreds of Eocene individuals from the Green River in Colorado, very few are present in Early Miocene localities. Deformations are common and abundant in more recent fossils and in living cockroaches. The single specimen of Morphna from the Paleocene possesses at least one such deformity, which may be stochastic.

Morphna is peculiar also in another respect in that it is not only the earliest occurrence of any living genus, but also the first occurrence of the family Blaberidae . It is possible that the original blaberid genera, representing the most advanced cockroaches of the time, survived with minor modifications to the present. In any case, the traces of plesiomorphies are valuable: branched A, branched Sc and punctuated intercalaries are all characteristics of Mesoblattinidae , and were lost in the initial stage of the evolution of the family Ectobiidae (= Blattellidae ). Therefore, it seems likely that Blaberidae originated directly from the extinct Mesoblattinidae , and not from Blattellidae as has been generally accepted (see Djernaes et al. 2012). These results do not contradict with living material-based analyses, as Blattellidae are direct descendants of the Mesoblattinidae .