comment on this calibration


 node name
Cetacea     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
33.9 Ma
The upper La Meseta Formation of Seymour Island, Antarctica is dated as latest Priabonian (late Eocene) on the basis of a wide variety of fossils, including palynomorphs (Mitchell, 1989). Elsewhere, the La Meseta Formation appears to be restricted in age to the eaely Eocene (Ypresian), but upper units run to the end of theEocene on Seymour Island (Reguero et al., 2013). Hence, the Priabonian record of Llanocetus serves as the minimum constraint for the crown cetacean divergence (33.9 Ma ± 0.0 Myr = 33.9 Ma).
  node maximum age
56 Ma
The presence of a diverse, early Eocene artiodactyl record, including archaeocetes but no crown cetaceans during the Ypresian, suggests the base of the Eocene may serve as a soft maximum for the odontocete-mysticete divergence, dated at 55.8 Ma ± 0.2 Myr = 56.0 Ma (Gradstein et al., 2012).
 primary fossil used to date this node 
USNM 183022
Llanocetus denticrenatus , Mitchell, 1989
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Seymour Island
     Stratum: La Meseta Formation
     Geological age: Eocene, Paleogene, Cenozoic

More information in Fossilworks   PaleoBioDB

  phylogenetic justification
Phylogenetic analysis of living and fossil mysticetes (Steeman, 2007) shows that Llanocetus is the closest relative of the toothless mysticetes (Chaeomysticeti Mitchell, 1989), based on two apomorphies: the premaxilla is straight in lateral view (not abruptly depressed anterior to nasals), and the occipital condyles are not situated on a swelling, but are rather levelled with the skull.
  phylogenetic reference(s)
Steeman, M.E. 2007. Cladistic analysis and a revised classification of fossil and recent mysticetes. Zoological Journal of the Linnean Society, 150:875–894.
 tree image (click image for full size) 
tree image
Figure 10 of Benton et al. (2014)