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 node name
Sessilia     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations
Wolfe et al. 2016
  node minimum age
89.5 Ma
The oldest known locality from which B. fallax has been recovered is Pit No. 125 (Brydone, 1912), close to junction of Barnet Side Lande and King's Lane, Froxfield, Hampshire, England (A. Gale, pers. comm.). This locality bears fossils of Holaster (Sternotaxis) planus, and is thus part of the S. planus echinoid zone, which is the uppermost zone of the Turonian in English Chalk (Gale, 1996; Mortimore, 2011). The GSSP defining the global upper boundary of the Turonian remains debated (due to difficulty in identifying its index ammonite fossil, Forresteria (Harleites) petrocoriensis (Ogg et al.,2012a). Currently, the upper boundary of the Turonian is dated to 89.8Ma±0.3Myr, providing a minimum age of 89.5 Ma.
  node maximum age
521 Ma
A soft maximum age is obtained from the oldest mandibulate, Y. dianensis, which was recovered from the Yu'anshan Formation at Xiaotan section, Yongshan, Yunnan Province, attributed to the Eoredlichia–Wutingaspis Biozone (Zhang et al., 2007). Chinese Cambrian stratigraphy has been revised substantially and the Eoredlichia –Wutingaspis Biozone is no longer recognized (Peng, 2003, 2009). However, Eoredlichia is known to co-occur with Hupeidiscus, which is diagnostic of the Hupeidiscus-Sinodiscus Biozone, which is formally recognized as the second biozone of the Nangaoan Stage of the Qiandongian Series of the Cambrian of China (Peng and Babcock,2008). The Nangaoan is the proposed third stage of the Cambrian System for the International Geologic Timescale (Peng et al., 2012a).Thus, a soft maximum constraint can be established on the age of the lower boundary of the Nangaoan, which has been dated to 521 Ma (Peng et al., 2012a; Peng and Babcock, 2008).
 primary fossil used to date this node 
SM 704275
Brachylepas fallax, Withers, 1935
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Pit No. 125, Froxfield, Hampshire, England
     Geological age: Cretaceous, Mesozoic

More information in Fossilworks   PaleoBioDB

  phylogenetic justification
This species was originally described from disarticulated material by Darwin (1851) as Pollicipes fallax. Withers (1914, 1935) recognized it was a sessile, rather than pedunculate barnacle, and that it had similarities to the basal sessilian genus Pycnolepas in overall form and plate development. Synapomorphies shared by B. fallax and all crown Sessilia include: the absence of a peduncle, presence of an operculum, and absence of all lateral plates (Gale and Sørensen, 2015). B. fallax shares with crown Balanomorpha a low, hemiconical carina and rostrum (Gale and Sørensen, 2015). On the basis of these characters, a recent cladogram depicts B. fallax as one of the most distant stem lineages of Balanomorpha, which is therefore a position within the crown group of Sessilia (Gale and Sørensen, 2015).
  phylogenetic reference(s)
Gale, A.S., Sørensen, A.M. 2015. Origin of the balanomorph barnacles (Crustacea, Cirripedia, Thoracica): new evidence from the Late Cretaceous (Campanian) of Sweden. J. Syst. Palaeontol. 13, 791–824.
 tree image (click image for full size) 
tree image
Figure 12 from Wolfe et al. (2016)