comment on this calibration


 node name
Thoracica     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations
Wolfe et al. 2016
  node minimum age
306.9 Ma
Specimens are derived from the Francis Creek Shale Member of the Carbondale Formation, Mazon Creek, Illinois, of Westphalian D age (Baird et al., 1985; Shabica and Hay, 1997). The Westphalian D is equivalent to the latest Moscovian stage of the Pennsylvanian (Richards,2013). As the upper boundary of the Moscovian is 307.0 Ma± 0.1 Myr, this provides a minimum age of 306.9 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 
FMNH P32055
Illilepas damrowi, Schram, 1986
Location relative to the calibrated node: Stem

[show fossil details]
     Locality: Mazon Creek
     Stratum: Francis Creek Shale Member of the Carbondale Forma
     Geological age: Carboniferous, Paleozoic

More information in Fossilworks   PaleoBioDB

  phylogenetic justification
Schram(1975) described this fossil as Praelepas damrowi, a congener of P. jaworskii Chernyshev, 1930. Restudy led to the transfer of this fossil to the new genus Illilepas under the combination I. damrowi, as the originald escription of a carina more closely resembled a tergum, and the original tergum was more likely an enlarged spine along the margin of the aperture, similar to that seen in Ibliformes (Thoracica) (Buckeridge and Newman, 2006; Schram, 1986). However, both molecular and morphological data place Ibla as the most basal clade of Thoracica (Pérez-Losada et al., 2008, 2009a), which, if I. damrowi is on the Ibliformes stem lineage, would still situate the fossil within the crown group of Cirripedia.
  phylogenetic reference(s)
Schram, F.R. 1986. Crustacea. Oxford University Press, New York.
Buckeridge, J.S., and Newman, W.A. 2006. A revision of the Iblidae and the stalked barnacles (Crustacea: Cirripedia: Thoracica), including new ordinal, familial and generic taxa, and two new species from New Zealand and Tasmanian waters. Zootaxa 1136, 1–38
 tree image (click image for full size) 
tree image
Figure 12 from Wolfe et al. (2016).