comment on this calibration


 node name
Lophotrochozoa     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
550.25 Ma
The White Sea Biota, in which Kimberella is most common, has been dated using U-Pb zircon dates to either 558 Ma ± 1 Myr (Martin et al., 2000) or 552.85 ± 2.6 Ma (Narbonne et al., 2012; Gradstein et al., 2012). Specimens are also known from the Ediacara of Australia (Glaessner and Wade, 1966; Wade, 1972), but the age of this unit is less well constrained. We select the date published in 2012 as our minimum hard constraint.
  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 
PIN 3993/4003
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: White Sea Biota
     Geological age: Cambrian, Paleozoic

  phylogenetic justification
Kimberella preserves several features that demonstrate it is a bilateral metazoan with an anterior-posterior axis (Fedonkin and Waggoner, 1997; Fedonkin et al., 2007; Ivantsov, 2009, 2010). Specimens are often found associated with a distinct bipartite feeding trace emerging from one end of the body, indicative of a feeding apparatus with two major denticles and a grazing behavior. There appears to be a ventral creeping sole surrounded by concentric units of tissue and a dorsal soft-bodied carapace. The morphology and feeding behavior has been accredited to a molluscan affinity. No coherent argument has been presented that calls into question the lophotrochozoan affinity of Kimberella.
  phylogenetic reference(s)
Fedonkin, M.A., and Waggoner, B.M. 1997. The Late Precambrian fossil Kimberella is a mollusc-like bilaterian organism. Nature, 388:868-871.
Fedonkin, M.A., Gehling, J.G., Grey, K., Narbonne, G.M., and Vickers-Rich, P. 2007. The Rise of Animals: Evolution and Diversification of the Kingdom Animalia. Johns Hopkins, Baltimore.
Ivantsov, A.Y. 2010. Paleontological evidence for the supposed Precambrian occurrence of mollusks. Paleontological Journal, 44:1552-1559.
 tree image (click image for full size) 
tree image
Figure 1 of Benton et al. (2014).