The quality of the fossil record of anomodonts (Synapsida, Therapsida)

The quality of the fossil record of anomodont synapsids, one of the major clades of Permian–Triassic terrestrial tetrapods, is assessed. A Character Completeness Metric (CCM2) is calculated for each taxon and consecutive time intervals at a global scale and in the South African Karoo Basin. The mean completeness score is 66.80% (globally) and 77.37% (regionally) with completeness ranging between 60.12% and 91.33% per time interval. Up-to-date taxic, phylogenetic and residual diversity estimates confirm the general biodiversity trends recovered by recent analyses. The consistently high CCM2 scores throughout their evolutionary history together with a lack of correlation with biodiversity patterns and sampling proxies document a high quality of the known anomodont fossil record. In fact, when compared to other vertebrate groups, the completeness values for anomodonts are exceptionally high. Yet, whether this pattern results from the unrivalled record of the Karoo Basin or whether it is clade-specific and unique to anomodonts remains to be tested.