comment on this calibration


 node name
Serpentes     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Head, 2015
  node minimum age
98.32 Ma
OMNH 33520 and 33520 were both collected in the uppermost Cedar Mountain Formation (Mussentuchit Member), Emery County, Utah. The Cedar Mountain Formation spans the Early Cretaceous and Early-Late Cretaceous transition (Cifelli et al., 1997). 40Ar/39Ar dating of Sanidine phenocrysts from smetitic ash horizons directly overlying snake-bearing fossil localities produced a weighted mean age of 98.39 ± 0.07 Ma, which is used as the hard minimum age for Serpentes.
  node maximum age
113 Ma
The soft maximum age is based on uncertainty in age estimates for late Albian snakes from Algeria.
 primary fossil used to date this node 
OMNH 33520
Coniophis sp., NO REFERENCE
Location relative to the calibrated node: Stem

[show fossil details]
     Locality: NO NAME
     Geological age: Modern, Holocene, Quaternary, Cenozoic

  phylogenetic justification
These specimens possess unambiguous apomorphies of all known total clade Serpentes, including a well-developed zygosphene-zygantral articulation consisting of a transversely wide zygosphene with dorsolaterally angled articular facets and a medially convex anterior margin, and a deep zygantrum with distinct ventromedially angled articular facets. Additional characters include synapophyses with distinct para- and diapophyseal articular surfaces, and well-developed intergyapophyseal ridges. These characters do not differentiate between crown and stem taxa, and there are no diagnostic characters present, or defined, for Coniophis.
  phylogenetic reference(s)
Gardner, J.D. and Cifelli, R.L. 1999. A primitive snake from the Cretaceous of Utah. Special Papers in Palaeontology, 60:87-100
 tree image (click image for full size) 
tree image
Figure 1 from Head (2015).