How has our knowledge of dinosaur diversity through geologic time changed through research history?

Abstract

Assessments of dinosaur macroevolution at any given time can be biased by the historical publication record. Recent studies have analysed patterns in dinosaur diversity that are based on secular variations in the numbers of published taxa. Many of these have employed a range of approaches that account for changes in the shape of the taxonomic abundance curve, which are largely dependent on databases compiled from the primary published literature. However, how these 'corrected' diversity patterns are influenced by the history of publication remains largely unknown. Here, we investigate the influence of publication history between 1991 and 2015 on our understanding of dinosaur evolution using raw diversity estimates and shareholder quorum subsampling for the three major subgroups: Ornithischia, Sauropodomorpha, and Theropoda. We find that, while sampling generally improves through time, there remain periods and regions in dinosaur evolutionary history where diversity estimates are highly volatile (e.g. the latest Jurassic of Europe, the mid-Cretaceous of North America, and the Late Cretaceous of South America). Our results show that historical changes in database compilation can often substantially influence our interpretations of dinosaur diversity. 'Global' estimates of diversity based on the fossil record are often also based on incomplete, and distinct regional signals, each subject to their own sampling history. Changes in the record of taxon abundance distribution, either through discovery of new taxa or addition of existing taxa to improve sampling evenness, are important in improving the reliability of our interpretations of dinosaur diversity. Furthermore, the number of occurrences and newly identified dinosaurs is still rapidly increasing through time, suggesting that it is entirely possible for much of what we know about dinosaurs at the present to change within the next 20 years. Subjects Evolutionary Studies, PaleontologyChao A, Jost L. 2012. Coverage-based rarefaction and extrapolation: standardizing samples by completeness rather than size. Ecology 93 (12):

Skeletal completeness of the non‐avian theropod dinosaur fossil record

“…The high abundance of theropod remains from northern mid‐latitudes and the relative scarcity of specimens at other latitudes strongly suggests a historical focus on Europe, North America, northern Africa and East Asia, and the comparative neglect of South America, southern Africa and Australia (Benton ; Tennant et al . ). This is supported by the significantly higher completeness distributions of theropods from Asia and North America (Fig.…”

“…Benton () similarly found that recent dinosaur species described from European deposits were of the poorest quality in comparison to other continents, and attributed this to historical research efforts and an overfamiliarity with deposits, corroborated by high European theropod Good's u sampling coverage estimated by Tennant et al . (). This, however, cannot be solely driven by human sampling effort, but is more likely to reflect the lack of consistent availability of terrestrial Mesozoic horizons yielding fossiliferous material.…”

“…; Starrfelt & Liow ; Tennant et al . ) and heightened interest of these stages at the end of the dinosaur record probably explain their extensive outlying peaks in specimen number, raw diversity and the moderate completeness levels at which a majority of taxa are found and named.…”

How should we estimate diversity in the fossil record? Testing richness estimators using sampling‐standardised discovery curves

“…A key assumption of any richness estimator is that sampling is unbiased. However, palaeontological research probably exhibits a ‘novelty bias’—a tendency to prioritise publication of new taxa over new occurrences of named taxa (Alroy, ; Tennant et al., ). At least in the early phases of discovery, this bias results in inflated counts of singletons, which bias estimates of sample coverage downwards, and estimated richness upwards.…”

“…These data are exceptionally complete and well‐vetted in the PaleoDB, and there has been intense interest in reconstructing dinosaur diversity patterns (e.g. Barrett, McGowan, & Page, ; Butler, Benson, Carrano, Mannion, & Upchurch, ; Starrfelt & Liow, ; Tennant, Chiarenza, & Baron, ; Upchurch, Mannion, Benson, Butler, & Carrano, ), including in the initial publication of TRiPS. Global diversity curves suffer from profound issues with highly‐variable sampling universes (Appendix ), and here we only analyse dinosaur data at global level to enable direct comparison with Starrfelt and Liow ().…”