comment on this calibration


 node name
Caviomorpha-Phiomorpha     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Phillips, 2015
  node minimum age
40.94 Ma
Cachiyacuy contamanensis occurs in theCTA-27 locality towards the top of the Yahuarango Formation. Antoine et al. (2011) used 40Ar/39Ar step heating to date biotite grains overlying the fossil-bearing sediments to 43.44 ± 2.5 Ma, suggesting a minimum age of 40.94 Ma for CTA-27.
  node maximum age
56 Ma
No taxa presently considered as putative Caviomorpha-Phiomorpha crown members are known from earlier Lutetian (Middle Eocene) mammal faunas. However, the Lutetian is particularly poorly sampled for small mammal fossils in Africa, a potential geographic origin for this clade (Gheerbrant and Rage, 2006; Marivaux et al., 2011). Hence, the absence of any hystricognaths from the better sampled Early Eocene faunas (Marivaux et al., 2011; Coster et al., 2012) provides a more appropriate soft maximum of basal Ypresian age (56.0 Ma).
 primary fossil used to date this node 
MUSM 1871
Cachiyacuy contamanensis, Antoine et al., 2011
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Yahuarango Formation, CTA-27
     Geological age: Lutetian, Eocene, Paleogene, Cenozoic

  phylogenetic justification
Antoine et al. (2011) described five new caviomorph rodents from the Yahuarango Formation in Peru, Cachiyacuy contamanensis, Cachiyacuy kummeli, Canaanimys maquiensis, Eobranisamys sp., and Eoespinasp. All five species grouped with Caviomorpha in Antoine et al.’s (2011) cladistic analysis of dental characters. Extraordinary dental diversity among rodents as a whole precluded any unambiguous synapomorphies characterising Caviomorpha (including the new species), although the presence of a mesostyle on P4 and the absence of paracone-metacone compression on P4 are unambiguous caviomorph synapomorphies, among hystricognaths. Overall phylogenetic signal strongly supports grouping the five new taxa with Caviomorpha; my parsimony analysis of Antoine et al.’s (2011) full data matrix provided 97% bootstrap support for this grouping. I chose Cachiyacuy contamanensis as the focal species for the calibration because it has the most completely sampled dentition. Consistent with Antoine et al. (2011), caviomorphs and phiomorphs form a clade in most recent morphological assessments (e.g., Marivaux et al., 2004; Asher et al., 2005) and importantly, their living representatives are sister taxa in all recent molecular studies (e.g., Poux et al., 2006; Meredith et al., 2011).
  phylogenetic reference(s)
Antoine, P-O., Marivaux, L., Croft, D.A., Billet, G., Ganerød, M., Jaramillo, C., Martin, T., Orliac, M.J., Tejada, J., Altamirano, A.J., Duranthon, F., Fanjat, G., Rousse, S. and Gismondi, R.S. 2011. Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography. Proceedings of the Royal Society of London B, 279:1319-1326.
 tree image (click image for full size) 
tree image
Figure 1 from Phillips (2015).