comment on this calibration


 node name
Oligostraca     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations
Wolfe et al. 2016
  node minimum age
497 Ma
The Orsten fossils come from the lowest zone of the late Cambrian Alum Shale, formally called the Agnostus pisiformis Zone or Zone 1, previously corresponding to the Uppermost Zone of the Middle Cambrian (Babcock et al., 2005). The A. pisiformis Zone was recently redefined as the uppermost zone of the Guzhangian, at the upper boundary of Cambrian Series 3 (Nielsen et al., 2014). This age of the uppermost stage of the Cambrian Series 3 is 499 Ma ± 2 Myr. Thus the minimum age applied to Oligostraca is 497 Ma.
  node maximum age
636.1 Ma
A soft maximum constraint is based on that used by Benton et al.(2015), 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 Konservat-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 our 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 
UB W116
Boeckelericambria pelturae, Walossek and Müller, 1994
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Orsten
     Stratum: Alum Shale
     Geological age: Cambrian, Paleozoic

  phylogenetic justification
B. pelturae is likely a stem group pentastomid, based especially on the diagnostic synapomorphy of a head with two pairs of grasping hooks (similar to the extant Reighardia larva; Walossek and Müller,1994, Fig. 25a). This species is a member of the round headed (as opposed to hammer headed) morphotype (Walossek and Müller, 1994).It was resolved in the pentastomid stem-group in a cladistic analysis that sampled the extant genera by Almeida and Christoffersen (Almeida and Christoffersen, 1999). Its pentastomid identity is not dependent on whether pentastomids are interpreted as Ichthyostraca (Møller et al., 2008; Regier et al., 2010; Sanders and Lee, 2010) or early diverging euarthropods (e.g. Castellani et al., 2011). Because we accept crown pentastomids as sister group to crown branchiurans on the basis of strong support from molecular data, B. pelturae must therefore be within crown Oligostraca.
  phylogenetic reference(s)
Walossek, D., and Müller, K.J. 1994. Pentastomid parasites from the Lower Palaeozoic of Sweden. Trans. R. Soc. Edinb. Earth Sci. 85, 1–37.
 tree image (click image for full size) 
tree image
Figure 10 from Wolfe et al. (2016).