comment on this calibration

Pan-Caenophidia

Lineage (NCBI): This node has no ancestors.
 node name
Pan-Caenophidia     Look for this name in NCBI   Wikipedia   Animal Diversity Web
 
  recommended citations
http://palaeo-electronica.org/content/fc-9 Head et al. 2016
 
  node minimum age
66 Ma
Krebsophis thobanus was recovered with a taxonomically diverse snake fauna from the Wadi Abu Hashim member of the Wadi Milk Formation of Sudan (Werner and Rage, 1999). The Wadi Milk Formation was considered Cenomanian based on palynological (Schrank,1990; Schrank and Awad, 1990) and fish data (see Werner and Rage, 1999). However, the snake fauna of Wadi Abu Hashim is much more biostratigraphically consistent with a Maastrichtian age assignment: Nigerophiids and large-bodied madtsoiids are only present in Maastrichtian sections of Madagascar and India (e.g., Prasad and Rage, 1995; Rage et al., 2004; LaDuke et al., 2010; Mohabey et al., 2011; Pritchard et al., 2014), the oldest record of palaeophiids is from the Maastrichtian of Morocco (Rage and Wouters, 1979), the oldest aniliid anatomically consistent with “Coniophis” from Wadi Abu Hashim is Australophis from the late Campanian-Early Maastrichtian of Argentina (Goméz et al., 2008, see Head [2015] for discussion of the age of Australophis), and anatomically similar “Coniophis” is known from the Maastrichtian of India (Rage et al., 2004).
 
  node maximum age
72.1 Ma
Referral to two snake specimens from Wadi Abu Hashim to Early Cretaceous “lapparentophiid-grade snakes” by Rage and Werner (1999) was admittedly based solely on plesiomorphic characters, which are taxonomically uninformative. A Cenomanian age for madtsoiids, nigerophiids, palaeophiids, and “Coniophis” form taxon aniliids would represent at least 20 million year range extension for all, of which there is no additional unambiguous evidence. Additionally, the Shendi Formation of Sudan, which shares a vertebrate fauna with the Wadi Milk Formation (J.M. pers. obs.) and previously considered a lateral extension of the Wadi Milk, has recently been dated as Campanian-Maastrichtian (Salih et al., 2015). Based on ages of comparable snake faunas from other Gondwanan landmasses and the age estimates for the Shendi Formation, we assign an age range for Krebsophis based on minima for the Campanian and Maastrichtian (Ogg et al., 2012).
 
 primary fossil used to date this node 
 
vb 681
Krebsophis thobanus, Rage and Werner, 1999
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Wadi Abu Hashim
     Stratum: Wadi Abu Hashim member of the Wadi Milk Formation
     Geological age: Cretaceous, Mesozoic


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  phylogenetic justification
Krebsophis thobanus is unambiguously included within Russellophiidae on the basis of brief, ventrolaterally angled articular facets of the prezygapophyses and compressed prezygapophyseal buttresses that form a vertical ridge, as well as more ambiguously by an elevated posterior neural arch (Rage and Werner, 1999). Characters that unite Russellophiidae, including Krebsophis, with Caenophidia include a highly elongate centrum, relatively small, circular cotyle and condyle, and well-developed subcentral paralymphatic channels defining the lateral margins of a distinct haemel keel.
 
  phylogenetic reference(s)
Rage, J.-C. and Werner, C. 1999. Mid-Cretaceous (Cenomanian) snakes from Wadi Abu Hashim, Sudan: The earliest snake assemblage. Palaeontologia Africana, 35:85-110.
 
 tree image (click image for full size) 
tree image
Figure 1 from Head et al. (2016).
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