comment on this calibration


 node name
Ambulacraria     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
515.5 Ma
The columnals were recovered from the Micmacca Breccia which encompasses the upper part of the Cephalopyge notabilis. Biozone, the Ornamentaspis frequens Biozone and, perhaps, the lower part of the Kymataspis arenosa Biozone (Geyer and Landing, 1995; Clausen and Smith, 2008). These records are effectively contemporaneous fragments of stereom that occur globally within the middle Atdabanian (= Age 3, Series 3 of GTS2012) Nevadella anabara Biozone (Kouchinsky et al., 2012; Zamora et al., 2013). This can be constrained by the latest Atdabanian date of 517.0 Ma ± 1.5 Myr from a section in Morocco (Adam C. Maloof et al. 2, 2010).
  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 
NHMUK EE6828-EE6846
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Micmacca Breccia
     Stratum: Micmacca Breccia
     Geological age: Cambrian, Paleozoic

  phylogenetic justification
The columnals exhibit a characteristic morphology and, more critically, a stereom structure is a characteristic of the echinoderm total group, acquired early in the stem-lineage (Swalla and Smith, 2008).
  phylogenetic reference(s)
Swalla, B.J. and Smith, A.B. 2008. Deciphering deuterostome phylogeny: molecular, morphological and palaeontological perspectives. Philosophical Transactions of the Royal Society B: Biological Sciences, 363:1557-1568.
 tree image (click image for full size) 
tree image
Figure 2 from Benton et al. (2014).