comment on this calibration


 node name
Blaberidae     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Evangelista et al. 2017
  node minimum age
52 Ma
Stroiński and Szwedo (2012) reviewed the geological setting for this fossil deposit (Menat, France). K/Ar isotope analysis (Vincent et al., 1977) dated the formations around Menat to an average of 56 Ma, but the minimum age measurement given is 54 +/- 2 Ma (Vincent et al. 1977). Biostratigraphic evidence from pollen and mammals, and macrofloral analysis (Kedves, 1982; Kedves and Russell, 1982; Nel, 2008; Wappler et al., 2009) indicate older ages up to 61 Ma. We use the lower end of this age range as a hard minimum date for the calibration.
  node maximum age
0 Ma
None specified
 primary fossil used to date this node 
MNHNFr 06689
“Gyna” obesa , Piton, 1940
Location relative to the calibrated node: Stem

[show fossil details]
     Locality: Menat
     Geological age: Eocene, Paleogene, Cenozoic

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  phylogenetic justification
The characters seen in the fossil do not support a generic or subfamilial placement but they do indicate that the species is a member of Blaberidae. We base this primarily on the stout cerci, shape of the tegmina, shape of CuP (plical furrow), shape of the pronotum, shape of the posterior-most abdominal segment and overall body size. First, the visibly stout cerci are a synapomorphy of Blaberidae and are not seen in Ectobiidae, although they may be confused with convergently evolved stoutness of the cerci in some genera of Blattidae and Corydiidae. Second, the tegmina have approximately parallel edges, which is uncommon in Corydiidae but common in Blaberidae, Blattidae and Ectobiidae (Rehn, 1951). The anal area, delimited by the CuP vein, is elongated. This elongation is common in Blaberidae, Blattidae, and Ectobiidae but not seen in most Corydiidae, whose CuP typically have a sharper angulation. One trait observed in the fossil that is frequently seen in Corydiidae is the branching of CuP. However, this feature also occurs in other groups, and shows substantial intraspecific variation as well (e.g., observed in approximately one third of individuals of some Blaberidae species; Olivier Béthoux, personal commun., 2017). Piton’s original description showed the pronotum elongated postero-medially. This is rarely found outside of the Blaberidae and would be strong evidence for its placement in this family, however, our reassessment shows that the shape of the pronotum is not entirely clear. We present high resolution photos of the prothorax with hemispherical lighting in the form of an RTI image file (Appendix 3) but still cannot precisely discern the shape of the pronotum. The more posterior candidate for the edge of the pronotum could be sculpturing of the middle thoracic segment. One character Piton failed to assess is the shape of the terminal segment. We believe that the specimen is preserved lying on its dorsal side, due to at least one visible leg and lack of discernible tegminal venation on the left side of the stone. If this is the case then the terminal abdominal segment is the subgenital plate, which appears to be asymmetrical, with the right side bearing a concave margin. This is a subgenital plate shape typical of Epilamprinae, Panchlorinae and Gyninae. Considering all these characters together along with the robust proportions, and body size of 25.6 mm, we feel confident that this fossil is placed within the Blaberidae, although its subfamilial assignment is uncertain. This fossil provides a minimum age for the split between Blaberidae and its sister taxon. Djernæs et al. (2012, 2015), Maekawa et al. (2003), and Grandcolas (1996) all place Pseudophyllodromiinae as sister to Blaberidae Saussure, 1864 but other recent assessments dispute this (Figure 1 and unpublished data), so we do not set a relationship here.
  phylogenetic reference(s)
Evangelista, D.A., Djernæs, A., and Kohli, M.K. 2017. Fossil calibrations for the cockroach phylogeny (Insecta, Dictyoptera, Blattodea), comments on the use of wings for their identification, and a redescription of the oldest Blaberidae. Palaeontologia Electronica, 20.3.1FC.
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 tree image (click image for full size) 
tree image
Figure 2 from Evangelista et al. (2017).