comment on this calibration
Pan-Caenophidia
Lineage (NCBI):
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| node name Pan-Caenophidia Look for this name in NCBI Wikipedia Animal Diversity Web | ||
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recommended citations http://palaeo-electronica.org/content/fc-9 Head et al. 2016 |
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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). | ||
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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 | ||
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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. |
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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.
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| tree image (click image for full size) | ||
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Figure 1 from Head et al. (2016).
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