comment on this calibration

Alca torda

 node name
Alca torda     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Smith, 2015
  node minimum age
7.3 Ma
Remains of Alca aff. torda from the “Little Cove Point Beds” of the St. Mary’s Formation in Virginia, USA are the earliest records of Alca. The St. Mary's Fm. has been interpreted as Tortonian (11.62-7.246 Ma) in age on the basis of biostratigraphic correlation (de Verteuil and Norris, 1996). The earliest records of Pinguinus are from the Early Pliocene (4.4 Ma) of North Carolina (Olson and Rasmussen, 2001; Smith and Clarke, 2011).
  node maximum age
0 Ma
none specified.
 primary fossil used to date this node 
USNM 237157
Alca torda, Alca torda Linnaeus, 1758
Location relative to the calibrated node: Stem

[show fossil details]
     Locality: Little Cove Point Beds
     Stratum: St. Mary's Formation
     Geological age: Tortonian, Miocene, Neogene, Cenozoic

  phylogenetic justification
Alca and Pinguinus have been recovered as sister taxa in the results of analyses of morphological and molecular sequence data (Strauch 1985, Chandler 1990a; Moum et al. 2002; Baker et al. 2007; Pereira and Baker 2008; Smith and Clarke, 2011).
  phylogenetic reference(s)
Smith, N. A. and J. A. Clarke. 2011. An alphataxonomic revision of extinct and extant razorbills (Aves, Alcidae): a combined morphometric and phylogenetic approach. Ornithological Monographs 72:1-61.
 tree image (click image for full size) 
tree image
Figure 2 from Smith (2015).