None of the existing specimens shows enough detail to ascertain the phalangeal formula, but, based on other examples of Rhynchosauroides, the phalangeal formulae for both manus and pes are probably 2-3-4-5-3 (e.g., Baird 1957), which is the plesiomorphic count for Amniota
. The manus is distinctly smaller than the pes, however, and this appears to be a synapomorphy for Diapsida.
Similarities occur in the initial development stages of the copulatory organs in reptiles and mammals, which suggests that the standard of differentiation of a single penis is a basal trait in Amniota
(REINAND; PIEAU, 1998 apud RIEPPEL, 2000).
(1997): A reassessment of Eunotosaurus africanus Seeley (Amniota
For the analysis, Rieppel and deBraga compiled an extensive data matrix for amniota
(reptiles, birds, and mammals) that included 33 amniote groups and 168 characteristics of their bones -- an important physical characteristic in defining clades.