comment on this calibration


 node name
Xiphosurida     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations
Wolfe et al. 2016
  node minimum age
236 Ma
T. gadeai was discovered in the Alcover unit of the Montral site, Tarragona province, Catalonia, Spain (Vía Boada and de Villalta, 1966). Based on sequence stratigraphy, the Alcover dolomite unit is dated to the late Muschelkalk, a European regional stage of the Triassic (Calvet and Tucker, 1995; Vía Boada and de Villalta, 1966). The middle and late Muschelkalk correspond to the global Ladinian stage (Calvet and Tucker, 1995). The upper boundary of the Ladinian is 237.0 Ma ± 1 Myr (Ogg, 2012), thus, a minimum age of 236.0 Ma.
  node maximum age
0 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 
MGSB 19195
Tachypleus gadeai, Vía Boada and de Villalta, 1966
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Montral site,Tarragona province, Catalonia
     Stratum: Muschelkalk
     Geological age: Triassic, Mesozoic

More information in Fossilworks   PaleoBioDB

  phylogenetic justification
Heterolimulus gadeai Vía Boada and de Villalta, 1966 was reassigned to the extant genus Tachypleus by Diedrich (2011), who cited the presence of lateral immobile opisthosomal spines as evidence. This was validated by the phylogenetic analysis of Lamsdell and McKenzie (2015), who resolved T. gadeai as sister-taxon to a clade composed of all other members of Tachypleus. This more inclusive clade in turn resolved as sister-taxon to the extant genus Carcinoscorpius.
  phylogenetic reference(s)
Lamsdell, J.C., McKenzie, S.C., 2015. Tachypleus syriacus (Woodward)—a sexually dimorphic Cretaceous crown limulid reveals underestimated horseshoe crab divergence times. Org. Divers. Evol. 15, 681–693.
Diedrich, C.G., 2011. Middle Triassic horseshoe crab reproduction areas on intertidal flats of Europe with evidence of predation by archosaurs. Biol. J. Linn. Soc. 103, 76–105.
 tree image (click image for full size) 
tree image
Figure 3 of Wolfe et al. (2016).