Pomatrum is a member of the
Didazoonidae, which one 2024 study has found to be a paraphyletic grade of the vetulicolians closest to
crownward chordates as shown in this simplified cladogram: An earlier study in 2014 place vetulicolians as the sister-group to tunicates, but was unable to resolve any relationships among vetulicolians as a group:
Relationship to Xidazoon Based on a comparison of the incomplete/damaged holotype with the incomplete/damaged holotype of
Pomatrum ventralis, a comprehensive examination of the vetulicolian systematics published in 2007 accepted a 2002 proposal that
X. stephanus was a junior synonym of
P. ventralis because the anterior portions of the two species are largely identical. although in some cases, notably including one co-authored by all authors of the 2007 comprehensive examination, only tentatively. Prior to this,
Xidazoon had been treated as a separate genus by workers aware of
Pomatrum, who argue that
Pomatrum has more than the seven posterior segments found in
Xidazoon. Some workers have continued to treat the genera as separate at least as recently as 2023.
Possible Relationship to Pipiscius Upon its discovery,
Xidazoon was likened to the
Carboniferous chordate
Pipiscius on account of having a similar anterior circlet, although it was noted that the similarities could be due to convergence. A recent phylogenetic analysis of vetulicolians and other early chordates did not including
Pipiscius. == See also ==