comment on this calibration


 node name
Anaspidacea     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations
Wolfe et al. 2016
  node minimum age
240.5 Ma
A. antiquus was found in the Hawkesbury Sandstone at the former Brookvale Brick Quarry, New South Wales, Australia (Schram, 1984). The Hawkesbury Sandstone overlies the Narrabeen Group and underlies the Wianamatta Group (Herbert, 1997). Sequence stratigraphy places the Hawkesbury in Sequence F, including the appearance of Aratrisporites parvispinosus spores (Helby, 1973; Herbert, 1997). The A. parvispinosus spore zone indicates an age during the Anisian (middle Triassic) (Herbert, 1997). The upper boundary of the Anisian is estimated at 241.5 ± 1 Ma (Ogg, 2012), providing a minimum age at 240.5 Ma.
  node maximum age
521 Ma
A soft maximum age is obtained from the oldest mandibulate, Y. dianensis, which was recovered from the Yu'anshan Formation at Xiaotan section, Yongshan, Yunnan Province, attributed to the Eoredlichia–Wutingaspis Biozone (Zhang et al., 2007). Chinese Cambrian stratigraphy has been revised substantially and the Eoredlichia –Wutingaspis Biozone is no longer recognized (Peng, 2003, 2009). However, Eoredlichia is known to co-occur with Hupeidiscus, which is diagnostic of the Hupeidiscus-Sinodiscus Biozone, which is formally recognized as the second biozone of the Nangaoan Stage of the Qiandongian Series of the Cambrian of China (Peng and Babcock,2008). The Nangaoan is the proposed third stage of the Cambrian System for the International Geologic Timescale (Peng et al., 2012a).Thus, a soft maximum constraint can be established on the age of the lower boundary of the Nangaoan, which has been dated to 521 Ma (Peng et al., 2012a; Peng and Babcock, 2008).
 primary fossil used to date this node 
AMS Australian Muse
Anaspidites antiquus, Chilton, 1929
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Brookvale Brick Quarry
     Stratum: Hawkesbury Sandstone
     Geological age: Triassic, Mesozoic

  phylogenetic justification
Although not included in a formal phylogenetic analysis, Schram (1984) justified the membership of A. antiquus as essentially indistinguishable from living Anaspididacea. Fusion of the first thoracomere into the cephalon, uniramous pleopods, and absence of an antennal scale are noted as diagnostic characters (Schram, 1984). As the fossil lacks preservation of diagnostic mouthparts, exact family affinities within total-group Anaspidacea are uncertain.
  phylogenetic reference(s)
Schram, F.R.1984. Fossil Syncarida. Trans. San Diego Soc. Nat. Hist. 20, 189–246.
 tree image (click image for full size) 
tree image
Figure 13 from Wolfe et al. (2016)