comment on this calibration

Heterodon + Farancia

 node name
Heterodon + Farancia     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Head et al. 2016
  node minimum age
12.08 Ma
The minimum age is based on the Swallow Ash of the lowermost Ash Hollow Formation, which succeeds the Valentine Formation (Tedford et al., 2005). The Myers Farm fauna is coeval with the Valentine Formation based on mammalian faunal composition and is considered latest Barstovian (e.g., Janis et al., 1998; Bair, 2011).
  node maximum age
None specified
 primary fossil used to date this node 
USNM 46504
Paleoheterodon tiheni, Holman, 1964
Location relative to the calibrated node: Stem

[show fossil details]
     Locality: Swallow Ash
     Stratum: Ash Hollow Formation
     Geological age: Miocene, Neogene, Cenozoic

More information in Fossilworks   PaleoBioDB

  phylogenetic justification
Assignment of UNSM 46504 to a clade including Heterodon to the exclusion of Diadophis and Pseudoboa is based on the character combination of: 1) a quadrate with a narrow and strongly recurved distal shaft and a wide, narrow suprastapedial crest; 2) a narrow ventrally curved compound bone; 3) A parietal with a broad, well-defined skull table; 4) a supraoccipital with a well-defined sagittal crest.
  phylogenetic reference(s)
The linked fossil has no phylogentic references.
 tree image (click image for full size) 
tree image
Figure 1 from Head et al. (2016).