Paul Sereno et al., in 2002, considered
Cathayornis a junior synonym of
Sinornis. They interpreted the anatomies of the two as very similar and sharing key
autapomorphies of the
pygostyle. The first thorough review of
Sinornis and
Cathayornis was published by Jingmai O'Connor and Gareth Dyke in 2010. O'Connor and Dyke concluded that despite the earlier opinion of Sereno and colleagues, the two birds were not synonyms and in fact differ in several clear ways, including different proportions in the wing claws and digits, differences in the pelvis, and size of the pygostyle. Several other species –
Cathayornis aberransis,
Cathayornis chabuensis and
Cathayornis caudatus – had been classified as
Cathayornis in the past. However, their validity and/or assignment to the genus
Cathayornis has been questioned in subsequent evaluations. Jingmai O'Connor and Gareth Dyke (2010) found that many of the supposedly distinct features of
C. aberransis (such as the base of a crest on the skull) had been inaccurately described, casting doubt on the few remaining features separating it from
C. yandica, and suggested that further study was needed to determine its validity. though this has yet to be supported by rigorous study. O'Connor and colleagues noted that
Longchengornis sanyanensis, also synonymized with
C. yandica by some authors, seems to show distinct anatomy not shared with at least that species of
Cathayornis. ==References==