comment on this calibration


 node name
Tetrapoda     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
337 Ma
The Wardie Shales are part of the Lower Oil Shale Group, dated as older than the East Kirkton locality which has also yielded several crown-group tetrapods (Rolfe et al., 1993). The Wardie Shales are assigned to the Holkerian regional stage on the basis of fossil fishes and palynomorphs (Paton et al., 1999), equivalent to the Livian in Belgium, dated as 343.5-337 Ma (Gradstein et al., 2012, p. 605), so providing the hard minimum constraint of 337 Ma.
  node maximum age
351 Ma
The soft maximum constraint is harder to determine because most of the close outgroups to the batrachomorph–reptiliomorph clade are known only from younger deposits: the oldest baphetids and crassigyrinids are from the Brigantian (Benton, 1993), the oldest colosteids from the Asbian (Benton, 1993). The whatcheeriids Whatcheeria and Pederpes, from North America and Europe, respectively, are older, however, and dated to the Ivorian regional Western European stage, and so 351-346.5 Ma. These horizons are underlain by further units of Famennian age, dated as 372.2 Ma ± 2.0 Myr – 358.9 Ma ± 0.4 Myr (Gradstein et al., 2012, p. 588), with basal tetrapods known from several continents, but no batrachomorphs or reptiliomorphs. We choose the whatcheeriids as marking the soft maximum constraint, even though they are phylogenetically more distant from crown Tetrapoda than baphetids and colosteids—but the latter two are younger than Lethiscus. Thus, we propose a date of 351 Ma as a soft maximum constraint.
 primary fossil used to date this node 
MCZ 2185
Lethiscus stocki, Wellstead, 1982
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Wardie shore, near Edinburgh
     Stratum: Wardie Shales
     Geological age: Carboniferous, Paleozoic

More information in Fossilworks   PaleoBioDB

  phylogenetic justification
Phylogenetic analyses (e.g., Panchen and Smithson 1988; Trueb and Cloutier 1991; Lombard and Sumida 1992; Ahlberg and Milner 1994; Vallin and Laurin 2004) nest Lethiscus within Aistopoda, one of a putative clade termed Lepospondyli, that was formerly placed in the Batrachomorpha, but appears more likely within Reptiliomorpha (e.g., Ruta et al., 2003). Either way, Lethiscus is the oldest crown tetrapod.
  phylogenetic reference(s)
Panchen, A. L., and Smithson, T. R. 1988. The relationships of the earliest tetrapods. The phylogeny and classification of the tetrapods 1: 1-32.
 tree image (click image for full size) 
tree image
Figure 7 from Benton et al. (2014).