Paleobiology, 42(4), 2016, pp. 680–695 DOI: 10.1017/pab.2016.26
Assessing the completeness of the fossil record: comparison of different methods applied to parareptilian tetrapods (Vertebrata: Sauropsida)
Antoine Verrière, Neil Brocklehurst, and Jörg Fröbisch
Abstract.—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.
Antoine Verrière, Neil Brocklehurst, and Jörg Fröbisch. Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, D-10115 Berlin, Germany. Email:
antoine.verriere@
mfn-berlin.de
Accepted: 16 June 2016 Published online: 12 August 2016 Data available from the Dryad Digital Repository:
http://dx.doi.org/10.5061/dryad.b5k79
Introduction The completeness of the fossil record is an
evident obstacle in paleontological studies. The stateofpreservation ofafossil hasanimpacton all subsequently applied analyses (Raup 1972; Benton et al. 2011). While deformation factors can be corrected for in a single specimen, analyses pertaining to a higher systematic scale and to clades’ macroevolutionary patterns, such as paleobiodiversity studies or phylogenetic analyses, have in the past often left that problem aside. However, studies of phylogeny and paleo- biodiversity arebothbuilt upon thedescription and classification of individual specimens; without considering the completeness of these specimens, it is difficult to know how robust the results are. While the authors of phylogenetic analyses often acknowledged incompleteness by giving the percentage ofmissing data in their data matrices, studies into the effect of the complete- ness of specimens have only recently become widespread, and methodologies are inconsistent.
© 2016 The Paleontological Society. All rights reserved.
There have beenmany attempts to quantify the completeness of the fossil record based on various proxies. Many attempted to infer how sampling biases have impacted taxonomic richness, for example, by comparing proxies such as the number of fossiliferous formations, number of localities, or outcrop area to diversity curves (Benton et al. 2004; Fröbisch 2008; Barrett et al. 2009; Benson et al. 2010; Benson and Upchurch 2013). Recent studies have proposed that proxies for rock volume, such as the geographic spread or outcropping surface area, could be used and measured using geographic information systems and then compared with diversity curves (Smith and McGowan 2007, 2008; Mannion et al. 2011; Upchurch et al. 2011; Dunhill et al. 2012; Fröbisch 2013). The general conclusion reached by these studies is that geological sampling biases have an impact on short-term variation of diversity, mostly at a regional or local scale, although in some cases (e.g., Alroy 2010; Benson et al. 2016),
an effect has also been noticed on large-timescale fluctuations of diversity.
0094-8373/16
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