comment on this calibration


 node name
Squamata     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
168.9 Ma
Bharatagama and an unnamed pleurodont lizard taxon both come from the Upper Member of the Kota Formation, which is dated as Toarcian to ?Aalenian (Bandyopadhyay and Sengupta, 2006), with an age in the range 182.7 Ma ± 0.7 Myr – 170.3 Ma ± 1.4 Myr (Gradstein et al., 2012, p. 768).
  node maximum age
209.5 Ma
The soft maximum date is set somewhat deeper in time because fossil deposits with extensive materials of small-scale diapsids are rare until we reach the Rhaetian (terminal Triassic), and those units include marine Rhaetic and terrestrially derived faunas in Europe and North America. The base of the Rhaetian is dated at 208-209 Ma by Muttoni et al. (2004, 2010), based on intercontinental comparisons of magnetostratigraphic records and radiometric dating, and 209.5 Ma by Gradstein et al. (2012, p. 716), and we select the oldest of these estimates.
 primary fossil used to date this node 
Bharatagama rebbanensis, Evans et al., 2002
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Kota Formation
     Stratum: Upper Member
     Geological age: Jurassic, Mesozoic

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  phylogenetic justification
Bharatagama, represented by some 100 fragmentary specimens, shows numerous apomorphies of the acrodont Iguania: combination of a long fused angular; a short row of pleurodont anterior teeth in a shallow symphysial region; an elongate anteromedial symphysial surface restricted to the dorsal margin of the Meckelian fossa in adults; an acrodont dentition in which the teeth are broad but unflanged, and lack interstices; a pleuroacrodont additional series which follows a fully acrodont hatchling series; a strong pattern of precise dorsoventral (orthal) shear on the labial, but not lingual, surfaces of the dentary teeth; and an abutting premaxillary-maxillary contact in which a medial maxillary shelf extends behind an, apparently, narrow premaxilla (Evans et al., 2002).
  phylogenetic reference(s)
Evans, S.E., Prasad, G.V.R., and Manhas, B. 2002. An acrodont iguanian from the Mesozoic Kota Formation of India. Journal of Vertebrate Paleontology, 22:299–312.
 tree image (click image for full size) 
tree image
Figure 8 from Benton et al. (2015).