comment on this calibration


 node name
Annelida     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
476.5 Ma
‘‘Xanioprion’ viivei is from a larger collection of scolecodonts from Kadriorg in Tallinn, North Estonia. The unit has been correlated, based on chitinozoans, to the Paroistodus proteus Conodont Zone (Hints and Nõlvak, 2006), the top of which is dated to 476.5 Ma (Cooper and Sadler, 2012).
  node maximum age
636.1 Ma
A soft maximum constraint is based on the maximum age interpretation of the Lantian Biota (Yuan et al., 2011). This, together with the Doushantuo Biota (Yuan et al., 2002), provides a series of Lagerstätten preserving the biota in Orsten- and Burgess Shale-like modes of fossilization. None of these Lagerstätten, least of all the Lantian, preserves anything that could possibly be interpreted as even a total group eumetazoan and on this basis we define out soft maximum constraint at 635.5 Ma ± 0.6 Myr (Condon et al., 2005) and, thus, 636.1 Ma.
 primary fossil used to date this node 
GIT 424–19
Xanioprion viivei , Hints and Nõlvak, 2006
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Kadriorg in Tallinn, North Estonia
     Geological age: Ordovician, Paleozoic

  phylogenetic justification
Xanioprion shows the multi-element jaw apparatus composed of ventral mandibles and dorsal maxillae, apomorphies of scolecodonts. Scolecodonts are the jaws of annelids belonging to the extant clades Eunicida and Phyllodocida, and so located within crown-group Annelida (Parry et al. 2014).
  phylogenetic reference(s)
Parry, L., Tanner, A., and Vinther, J. 2014. The origin of annelids. Palaeontology
 tree image (click image for full size) 
tree image
Figure 1 from Benton et al. (2014).