comment on this calibration


 node name
Diapsida     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
255.9 Ma
The Kupferschiefer of Germany and the Marl Slate of NE England are correlated with each other on independent geological evidence, and defined as the basal unit of the Zechstein 1 (EZ1; Werra Folge) depositional cycle. The two units were generally assigned to the Kazanian (e.g., Benton, 1993, p. 695), but subsequent stratigraphic revisions have shown that the Zechstein falls above the Illawarra Reversal, which is at the Wordian–Capitanian boundary. Whereas Ogg (2004) moved the Zechstein I up to equate to the Capitanian, Slowakiewicz et al. (2009) move it higher to equate with the early Wuchiapingian, ranging from 260-257 Ma. Roscher and Schneider (2006) estimate a minimum age for the Kupferschiefer as 255.9 Ma, so we accept that here, as a younger estimate, based on new dating evidence, than the date of 259.7 Ma given by Benton and Donoghue (2007). This is close to the alternative suggestion of 254.7 Ma proposed by Ezcurra et al. (2014), based on a date for the Kupferschiefer (and of Protorosaurus) of 257.3 Ma ± 2.6 Myr.
  node maximum age
295.9 Ma
In order to establish the soft maximum constraint on this divergence, outgroups to Neodiapsida are considered. Ichthyosauria are known first in the Early Triassic, younger than the minimum age constraint. Younginiformes, Weigeltisauridae (Coelurosauravus), and Claudiosaurus are of similar age to Protorosaurus, or younger. Next oldest was Apsisaurus from the Archer City Formation of Texas, dated as Asselian, but this turns out to be a varanopid synapsid (Reisz et al., 2010). This is a long way below the minimum age constraint, but there is a well-known “gap” in suitable fossiliferous formations through the mid-Permian, and we retain this possibly exaggerated soft maximum constraint.
 primary fossil used to date this node 
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Kupferschiefer
     Geological age: Permian, Paleozoic

  phylogenetic justification
Protorosaurus is a member of Archosauromorpha and of crown Diapsida, based on numerous morphological synapomorphies (Benton, 1985; Gauthier et al., 1988).
  phylogenetic reference(s)
Benton, M.J. 1985. Classification and phylogeny of the diapsid reptiles. Zoological Journal of the Linnean Society, 84:97-164.
Gauthier, J.A., Kluge, A.G., and Rowe, T. 1988 Amniote phylogeny and the importance of fossils. Cladistics, 4:105–209.
 tree image (click image for full size) 
tree image
Figure 8 from Benton et al. (2015).