comment on this calibration


 node name
Psittaciformes     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Ksepka and Clarke, 2015
  node minimum age
53.5 Ma
NMH A6207 was collected from the Walton Member (Division A2 of King, 1981) of the London Clay Formation at Walton-on-the-Naze, England. The Walton Member correlates to the upper part of Chron C24r and to calcareous nannoplankton zone NP10-11 (Rhodes et al. 1999). Precise dating of Chron C24r is difficult and estimates vary depending on alternate cyclostratigraphic methods applied to extrapolate the length of the stratigraphic gap between the top of C24r and horizons dated using radiometric means. Because a hard minimum calibration should be conservative, we selected the youngest estimate (inclusive of error) for the top of C24r (53.54+/-0.04) presented among the alternate estimates of Westerhold et al. (2007).
  node maximum age
0 Ma
None specified.
 primary fossil used to date this node 
Pulchrapollia gracilis, Dyke and Cooper, 2001
Location relative to the calibrated node: Stem

[show fossil details]
     Locality: Walton-on-the-Naze, England
     Stratum: Walton Member (Division A2 of King, 1981) of the L
     Geological age: Ypresian, Eocene, Paleogene, Cenozoic

  phylogenetic justification
Phylogenetic analysis of morphological data (Dyke and Cooper, 2000; Mayr, 2005), phylogenetic analysis of combined morphological and molecular data (Ksepka et al. 2011, Ksepka and Clarke, 2012).
  phylogenetic reference(s)
Dyke, G.J., and Cooper, J.H. 2000. A new psittaciform bird from the London Clay (Lower Eocene) of England. Palaeontology, 43:271-285.
ayr, G. 2002. On the osteology and phylogenetic affinities of the Pseudasturidae-Lower Eocene stem-group representatives of parrots (Aves, Psittaciformes). Zoological Journal of the Linnean Society, 136:715-729.
Ksepka, D.T., Clarke, J.A., and Grande, L. 2011. Stem parrots (Aves, Halcyornithidae) from the Green River Formation and a combined phylogeny of Pan-Psittaciformes. Journal of Paleontology, 85: 835-854.
Ksepka, D.T. and Clarke, J.A. 2012. A new stem parrot from the Green River Formation and the complex evolution of the grasping foot in Pan-Psittaciformes. Journal of Vertebrate Paleontology, 32: 395-406.
 tree image (click image for full size) 
tree image
Figure 11 from Ksepka and Clarke (2014); Phylogenetic tree showing position of Pulchrapollia gracilis, illustrating the divergence calibrated by NMH A6207.