Ornithischians

Jonathan P. Tennant, Alfio Alessandro Chiarenza & Matthew Baron, 2018, How has our knowledge of dinosaur diversity through geologic time changed through research history?, PeerJ 4417, pp. 1-42 : 25-26

Ornithischians

The J/K interval decline in subsampled diversity remains constant and recognisable throughout publication history, with this stability suggesting a real biological signal and not a publication artefact ( Tennant, Mannion & Upchurch, 2016b). However, more focussed sampling needs to occur on J/K interval deposits to reveal the true global signal, as much of this pattern is based on fossils exclusively from historically well-sampled European localities ( Tennant et al., 2016) ( Figs. 6 , 10 and 12 ). Ornithischian subsampled diversity decreases steadily through the Early Cretaceous in Europe, with a possible radiation in the Campanian to Maastrichtian, perhaps explained by an increase of recent occurrences of latest Cretaceous dinosaurian findings mainly in Spain, Portugal, France, and Romania ( Riera et al., 2009; Csiki et al., 2010). However, many of these latest Cretaceous European dinosaur faunas are not particularly well-resolved stratigraphically compared to the well-studied North-American sections, which makes the timing of any regional extinction here and comparison with North America and Asia difficult at the present. Advanced ornithischian faunas, including ceratopsians and hadrosaurids, appear to have diversified extremely rapidly in the latest Cretaceous, but this is classically explained by the oversampling of North American Late Campanian localities, like Dinosaur Park Formation and its approximate temporal equivalents. Although a small rise in subsampled diversity is recovered from the Campanian to the Maastrichtian in Europe, this is considerably less marked than the decline in North America, where subsampling reveals that ornithischian diversity was actually declining from the Campanian to Maastrichtian ( Brusatte et al., 2015).

Ornithischian subsampled diversity in Asia has been increasing steadily through publication time in the ‘middle’ Cretaceous, filling in the gap from equivalent latitude European deposits at this time. This is plausibly due to the radiation of Parksosauridae and Ankylopollexia clades, two of the most dominant Late Cretaceous dinosaurian taxa around this time. Together with the North American record, this manifests as a great global decline across the Early–Late Cretaceous interval, a pattern that was not recognised until more recent years due to the discovery of more Konzentrat-Lagerstätten in Mongolia and China around this time, such as the Jehol Biota ( Lambert et al., 2001; Godefroit et al., 2008; Upchurch et al., 2011). A perceived Late Cretaceous subsampled diversity increase for Asian taxa, particularly hadrosauroids, could be due to a renaissance in the discovery of Cretaceous Asian dinosaurs over the past two decades (Lloyd et al., 2008; Barrett, McGowan & Page, 2009; Zhou & Wang, 2010; Upchurch et al., 2011; Mo et al., 2016). Despite the increasing availability of Early Cretaceous dinosaur-bearing formations (DBFs) in Africa in the last 20 years (e.g. Tunisia, Niger; Taquet & Russell, 1999; Anderson et al. (2007)), sampling here is still too limited to reveal any consistent patterns in ornithischian subsampled diversity ( Mannion et al., 2011; Upchurch et al., 2011; Tennant, Mannion & Upchurch, 2016b) ( Figs. 6 and 7 ).

This regional distinction could be due to the tie between ecomorphological function and biological diversity, as Asian hadrosauroids increased in morphological disparity during the latest Cretaceous, whereas in North America large-bodied bulk-feeding ornithischians decreased in their disparity ( Vavrek & Larsson, 2010; Campione & Evans, 2011; Brusatte et al., 2012; Mitchell, Roopnarine & Angielczyk, 2012). In North America, several abiotic factors, including extreme fluctuations of the Western Interior Sea, and the Laramide orogeny and proposed biogeographic provincialism, may have affected the evolution of North America dinosaurs in distinct ways from species on other continents ( Gates, Prieto-Márquez & Zanno, 2012; Arbour, Zanno & Gates, 2016), meaning that the North American record is unlikely to be representative of global diversity pattern ( Sampson et al., 2010; Brusatte et al., 2012).

Figures

Figure 7 GOOd’s u estimates fOr Ornithischians at (A) glObal and (B–F) regiOnal leVels (EurOpe, Africa, Asia, NOrth America, and SOuth America, respectiVely) based On Our published knOWledge in 1991 and 2015. Abbreviations as Fig. 4. Full-size DOI: 10.7717/peerj.4417/fig-7

Figure 10 GOOd’su estimates fOrtherOpOds at (A) glObal and (B–F)regiOnal leVels(EurOpe, Africa, Asia, NOrth America, and SOuthAmerica, respectiVely) based On Our published knOWledge in 1991 and 2015. Abbreviations as Fig. 4. Full-size DOI: 10.7717/peerj.4417/fig-10

Figure 12 Subsampled sauropodomorph diVersity at (A) global and (B–F) regional leVels (Europe, Africa, Asia, North America, and South America, respectiVely) based on our published knoWledge in 1991 and 2015. Abbreviations as Fig. 4. Full-size DOI: 10.7717/peerj.4417/fig-12

Figure6 SubsampledOrnithischiandiVersityat(A)glObal and(B–F)regiOnalleVels (EurOpe,Africa, Asia,NOrth America,and SOuthAmerica, respectiVely) based On Our published knOWledge in 1991 and 2015. Abbreviations as Fig. 4. Full-size DOI: 10.7717/peerj.4417/fig-6