comment on this calibration


 node name
Amniota     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
318 Ma
The age of the Joggins Formation has been much debated, and figures in the range from 320 to 305 Ma have been quoted. Reisz and Müller (2004) indicate an age of 316–313 Ma, while Van Tuinen and Hadly (2004) settle for 310.7 Ma ± 8.5 Myr. Detailed field logging and biostratigraphy based on palynomorphs (Falcon-Lang et al., 2006; Grey and Fink, 2010; Utting et al., 2010) confirm that the Joggins Formation falls entirely within the Langsettian European time unit, equivalent to the Westphalian A, and roughly matching the Russian Cheremshanian, in the later part of the Bashkirian Stage. Earlier dates for these units were equivocal (Menning et al., 2000), but the Langsettian is given as 319-318 Ma by Gradstein et al. (2012, p. 605), rather older than the 314.5–313.4 Ma ± 1.1 Myr given in GTS2004 (Davydov et al., 2004). This makes the classic ‘bird-mammal split’ somewhat older than has currently been assumed, at a minimum of 318 Ma.
  node maximum age
332.9 Ma
The soft maximum constraint on the bird–mammal split is based on the next richly fossiliferous units lying below these horizons. The first is the East Kirkton locality, source of a diverse fauna of batrachomorphs and reptiliomorphs (see node 41), but that has hitherto not yielded anything that could be called either a diapsid or a synapsid. Further fossiliferous sites of similar facies lie below the East Kirkton level, and they have not yielded reptile remains. We take the age of the fossiliferous Little Cliff Shale of the East Kirkton locality, assigned to the Brigantian, the fourth British regional division of the Viséan, so terminating at 330.9 Ma (Gradstein et al., 2012), and perhaps up to 2 myr in duration (Gradstein et al., 2004), as the basis for the soft maximum age constraint of 332.9 Ma.
 primary fossil used to date this node 
Hylonomus lyelli, Dawson, 1860
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Joggins Formation
     Stratum: division 4, section XV, coal group 15
     Geological age: Pennsylvanian, Carboniferous, Paleozoic

More information in Fossilworks   PaleoBioDB

  phylogenetic justification
Hylonomus was formerly assigned to the paraphyletic groups “Protorothyrididae’ or ‘Captorhinidae’ (Carroll, 1964), and it falls within Eureptilia, on the stem to Diapsida (Laurin and Reisz, 1995; deBraga and Rieppel, 1997), based on large numbers of morphological synapomorphies.
  phylogenetic reference(s)
Laurin, M. and Reisz, R.R. 1995. A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society, 113:165-223.
deBraga, M. and Rieppel, O. 1997. Reptile phylogeny and the interrelationships of turtles. Zoological Journal of the Linnean Society, 120:281–354.
 tree image (click image for full size) 
tree image
Figure 8 from Benton et al. (2015).