comment on this calibration


 node name
Echinodermata     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
509 Ma
The earliest record of Stromatocystites is of Stromatocystites walcotti from the Olenellus Beds, Taconian, upper Lower Cambrian, eastern arm of Bonne Bay, western coast of Newfoundland (Smith, 1985), which equates to Series 2, Stage 4 of the Cambrian, the top of which is dated as 509.0 Ma, the attendant errors on which are unclear (Peng et al., 2012).
  node maximum age
549 Ma
Thus, we base our soft maximum constraint on the approximate age of the Nama Group (Narbonne et al., 2012), an open marine community that preserves the earliest biomineralized animals, including Cloudina, Namacalathus and Namapoika (Wood, 2011). Since the ancestral crown-echinoderm possessed a stereom skeleton, its absence from the Nama Group, and from other Cloudina-bearing strata worldwide, establishes a basis for their absence at this interval of Earth History.
 primary fossil used to date this node 
USNM 66483
Stromatocystites walcotti, Schuchert, 1919
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Bonne Bay
     Geological age: Cambrian, Paleozoic

More information in Fossilworks   PaleoBioDB

  phylogenetic justification
Stromatocystites walcotti is identified as a crown echinoderm based on morphological phylogenetic analysis (Smith, 1985). S. walcotti exhibits crown-echinoderm synapomorphies, including a pentaradial body plan, water vascular system (inferred to be derived from the left hydrocoel) and stereom skeleton clearly place them in the crown group (Smith, 1984), as well as flat dorsal surface which distinguishes S. walcotti as a stem-eleutherozoan.
  phylogenetic reference(s)
Smith, A.B. 1985. Cambrian eleutherozoan echinoderms and the early diversification of edrioasteroids. Palaeontology, 28:715-756.
 tree image (click image for full size) 
tree image
Figure 2 of Benton et al. (2014).