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[dinosaur] Parareptilia: completeness of the fossil record

Ben Creisler

A recent paper:

Antoine Verrière, Neil Brocklehurst and Jörg Fröbisch (2016)
Assessing the completeness of the fossil record: comparison of different methods applied to parareptilian tetrapods (Vertebrata: Sauropsida).  
Paleobiology  (advance online publication)
DOI: http://dx.doi.org/10.1017/pab.2016.26 

As paleontological studies are generally distorted by gaps and biases in the fossil record, it is important to assess its completeness. Here we address the fossil record of Parareptilia, a Permian–Triassic amniote clade, applying two measures of specimen completeness: the skeletal completeness metric (SCM) and the character completeness metric (CCM). The SCM quantifies how much of the skeletal material of a taxon is preserved, whereas the CCM measures the amount of phylogenetic information available. The latter was implemented using two different approaches. In this study, we compare three completeness metrics. Two CCM implementations show a strong correlation with each other, but only the second implementation of the CCM correlates significantly with the SCM, possibly due to character selection in phylogenetic data sets. There is no correlation between diversity of parareptiles and their completeness, implying that the observed fluctuations in diversity are not driven by the completeness of the fossils. The mean completeness of parareptiles through time is consistently high compared with previously studied tetrapod clades, suggesting that most parareptile taxa are based on reasonably complete specimens. Clade-specific differences reveal no link between body size and completeness. However, the analyses confirm the impact of ecology, with aquatic mesosaurids being better preserved than terrestrial taxa.