comment on this calibration


 node name
Loxocemidae     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Head, 2015
  node minimum age
35.2 Ma
Minimum age is based on faunal correlation of Medicine Pole Hills fossil localities (Bowman County, North Dakota) with Flagstaff Rim localities (Natrona County, Wyoming), which are overlain by an ash layer (Ash B) that is 40Ar/39Ar dated at 35.41 ± 0.14 Ma (Obradovich et al., 1995). Smith (2011) recalculated the minimum estimate for the Medicine Pole Hills local fauna at 35.2 Ma.
  node maximum age
0 Ma
None specified.
 primary fossil used to date this node 
PTRM 19378
Location relative to the calibrated node: Stem

[show fossil details]
     Locality: Medicine Pole Hills
     Geological age: Eocene, Paleogene, Cenozoic

  phylogenetic justification
PTRM 19378 is united with Loxocemidae on the basis of: 1) dorsal head expanded into broad plate; 2) dorsal head lies wholly in saggital plane; 3) well-defined lip present on lateral side of dorsal margin (Smith, 2013).
  phylogenetic reference(s)
Smith, K.T. 2013. New constraints on the evolution of the snake clades Ungaliophiinae, Loxocemidae and Colubridae (Serpentes), with comments on the fossil history of Erycine boids in North America. Zoologischer Anzeiger, 252:157-182.
 tree image (click image for full size) 
tree image
Figure 1 from Head (2015).