comment on this calibration


 node name
Lepidosauria     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
238 Ma
The Vellberg jaws are from Untere Graue Mergel, in the middle of the Erfurt Formation (formerly, Lower Keuper) of Baden-Württemberg in SW Germany. The Erfurt Formation is mid-Ladinian in age, and is dated by means of cyclostratigraphy to 238-240 Ma (Menning et al., 2005; Jones et al., 2013, p. 4).
  node maximum age
252.7 Ma
The soft maximum age is extended to the base of the Triassic, so as to accommodate the highly uncertain taxa Palacrodon and Scharschengia, formerly identified as sphenodontids, but now generally regarded as ‘enigmatic’, but also to allow for the chance that new explorations in Early and Middle Triassic formations in Africa, Russia, and North America, where new small tetrapod fossils are being extracted, might eventually yield some crown or stem lepidosaurs. The base of the Triassic is dated as 252.2 Ma ± 0.5 Myr (Gradstein et al., 2012, p. 712), so we choose 252.7 Ma.
 primary fossil used to date this node 
SMNS 91060
cf. Diphydontosaurus sp., Jones et al., 2013
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Untere Graue Mergel
     Stratum: Erfurt Formation
     Geological age: Ladinian, Middle Triassic, Triassic, Mesozoic

  phylogenetic justification
TThe jaw specimen SMNS 91060 show numerous characters of Lepidosauria (coronoid expansion, lingual subdental shelf, mix of acrodont and pleurodont teeth) and of Rhynchocephalia (absence or slow pace of tooth replacement, apparent coalescence of anteriormost teeth), and Jones et al. (2013) provide compelling evidence that this is the oldest crown lepidosaur.
  phylogenetic reference(s)
Jones, M.E.H., Anderson, C.L., Hipsley, C.A., Müller, J., Evans, S.E., and Schoch, R.R. 2013. Integration of molecules and new fossils supports a Triassic origin for Lepidosauria (lizards, snakes, and tuatara). BMC Evolutionary Biology, 13:208.
 tree image (click image for full size) 
tree image
Figure 8 from Benton et al. (2015).