For this procedure, taxa with missing or ambiguous information for these traits (4, 9 and 6 taxa for altitude, vegetation type and molar type respectively) were excluded from the analysis.
In their paper, Flynn and colleagues described Ambondro as the oldest mammal with tribosphenic molars the basic molar type of metatherian (marsupials and their extinct relatives) and eutherian (placentals and their extinct relatives) mammals, characterized by the protocone cusp on the upper molars contacting the talonid basin on the lower molars in chewing.
The BiSSE models found no support for different speciation rates associated with a particular molar type when comparing full and constrained models, although the time-dependent model performed better in AIC scores.
Molar type was coded as 0) tetralophodont, or 1) pentalophodont.
Molar type was coded as a binary character: a) tetralophodont; or b) pentalophodont.
More importantly, independent of which molar type is ancestral or derived, results suggest that the acquisition or loss of a fifth molar loph was not a key innovation in sigmodontine evolution since we found no correlation between the evolution of this trait and speciation rates.
The stochastic mapping of lifestyle or habitat type preference (elevational range and vegetation type) and the transitions between molar types using the MCC tree are shown in Additional file 8: Figure S3, Additional file 9: Figure S4, Additional file 10: Figure S5.
Similarly, it is of interest to assess if molar types are associated with differential diversification rates.
Transitions in molar types were more frequent from the tetralophodont to the pentalophodont condition; the latter morph is inferred as the derived state (see Discussion,Additional file 12: Table 7).
Of all variables recorded, only the presence of teeth (including third molars), tooth type, number and location of POPs, and tooth replacements were considered in the present study.
