From the first dinosaur discoveries until around 1950, the number of dinosaur occurrences published steadily increased through time ( Fig. 1 ). From the mid- to the end of 20th century, the number of published occurrences has increased substantially. This is mostly due to the publication of theropod and ornithischian occurrences, which reached a peak around the turn of the millennium, with occurrences of all three groups remaining high but declining in rate of publication after this. A very similar pattern is observed for genera, with the publication of newly named genera increasing exponentially since around 1990, and at an equal rate for all three groups ( Fig. 2 ). The cumulative frequency of newly named genera shows that, although the rate of growth remains approximately similar and increasing for all three groups, there are times when the relative overall number of genera between groups changes through publication history. For example, while sauropodomorphs had more named genera than theropods until around 1935, this changed at around 1960 when new theropod genera became more frequently published than sauropodomorphs. The recent rate of growth of newly named theropod genera in the last 15 years means that they are now named as frequently as newly named ornithischian genera. This recent rate of growth in the naming of new taxa is distinct from the patterns of taxonomic invalidation (e.g. through synonymy) that have occurred since 1991 ( Fig. 3 ). While we see an increase in the number of invalidated taxa between 2000 and 2010, this is variable for each group, with theropods peaking in 2007, sauropodomorphs peaking in 2002–2004, and ornithischians in 2007 and 2013.

Apparent ‘global’ empirical dinosaur diversity steadily rises until the end of the Jurassic ( Fig. 4A ). Diversity is low across the Jurassic/Cretaceous (J/K) interval until the Hauterivian, before recovering in the late Early Cretaceous. There is a second decline through the late Early to early Late Cretaceous interval, before diversity increases to its zenith in the latest Cretaceous. This general pattern remains constant throughout publication history, although diversity in the ‘middle’ Cretaceous and latest Cretaceous intervals shows the greatest increases. Subsampled global dinosaur diversity retains this overall pattern ( Fig. 4B ). The J/K interval decline is still visible, but the late Early Cretaceous apparent diversity increase supersedes Late Jurassic levels. The early Late Cretaceous decline is also still present, but the magnitude of the latest Cretaceous diversity increase is much lower than that recovered for the empirical data. The reason for this distinction between subsampled and raw diversity is that SQS estimates diversity by standardising coverage of the taxon-abundance distribution, and thereby reduces the impact of intensely sampled time intervals such as the latest Cretaceous.

Patterns of raw and subsampled diversity by group

Ornithischians Raw ‘global’ ornithischian diversity (Fig. 5A) is constant and stable throughout publication history. The apparent magnitude of longer-term trends is obscured by the relative over-sampling of the Campanian and Maastrichtian, which are almost an order of magnitude higher than any other Jurassic or Cretaceous stage interval. Indeed, the Campanian shows no sign of slowing down in increasing diversity, and is the highest and most rapidly increasing of any time interval. In spite of this, the overall trends in raw diversity remain, with steadily increasing Middle to Late Jurassic diversity, a small earliest Cretaceous decline followed by a ‘middle’ Cretaceous peak in the Aptian, a shallow decline into the early Late Cretaceous, and an increase in the Campanian. Figure 5: Raw ornithischian 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 Raw diversity in Europe shows increasing diversity across the J/K transition before an earliest Cretaceous decline (Valanginian–Hauterivian), constant ‘middle’ Cretaceous diversity, and an increase from the Campanian to Maastrichtian (Fig. 5B). Raw African ornithischian diversity is too inconsistent to analyse any changes through geological time or publication time (Fig. 5C). Raw Asian diversity is fairly constant through the Cretaceous, until an apparent major Campanian peak and Maastrichtian decline (Fig. 5D). In North America, empirical diversity is flat and low throughout the Late Jurassic and most of the Cretaceous (Fig. 5E). There is a Campanian peak, and order of magnitude higher than any prior interval, which is rapidly increasing through publication time. Diversity decreases from this into the Maastrichtian, in which diversity has remained relatively stable through publication time. Sampling in South America is also relatively poor, with apparent diversity remaining low and flat where a signal is obtained (Fig. 5F). Subsampled ‘global’ ornithischian diversity shows a distinctly different pattern from the raw curve, both in terms of overall trends, and in terms of the magnitude of the effect of publication history (Fig. 6A). The Jurassic is generally too poorly sampled to reveal a constant signal, but there is evidence of a decline through the J/K transition, which remains constant through publication time. This is followed by a middle-Cretaceous increase, in which ornithischian diversity is at its second highest level throughout their history. The magnitude of this Albian radiation has rapidly increased over publication time, the result being that originally what appeared to be increasing subsampled diversity over the Early/Late Cretaceous transition now shows a major decline from the Albian to Coniacian. Santonian subsampled diversity remains unknown, but when we see a signal emerge in the Campanian, diversity is higher than the Albian, reaching its highest level before declining by more than half into the Maastrichtian. This overall structure, besides the Albian, remains consistent throughout publication time with no major perturbations to the apparent ‘global’ curve. Figure 6: Subsampled ornithischian 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 Subsampled European diversity reveals increasing diversity across the Tithonian/Berriasian transition, followed by overall gradually decreasing diversity throughout the remainder of the Early Cretaceous (Fig. 6B). In Africa, the signal is too poor to reveal anything besides a Kimmeridgian/Tithonian subsampled diversity drop (Fig. 6C), and in Asia, there is evidence of a decline in subsampled diversity across the Albian/Cenomanian transition (Fig. 6D). In North America, subsampled diversity reveals a decline across the Early–Late Cretaceous transition, and a major decline from the Campanian to Maastrichtian, a pattern that remains stable through publication history (Fig. 6E). In South America, the subsampled signal is too poor to comment on ornithischian diversity (Fig. 6F). If we look at how coverage has changed through publication history (based on Good’s u), we should expect that subsampled diversity patterns are reflective of this pattern. At a global level, coverage in the Cretaceous is much better than the Jurassic (Fig. 7A). Much of this, however, is based on patchy regional records. In Europe, we find that coverage increases across the J/K interval (Fig. 7B), and is the only place where a consistently reliable record here can be obtained. In Africa, coverage is generally poor, besides in the latest Jurassic (Fig. 7C). In Asia, coverage is poor up until the late Early Cretaceous (Fig. 7D). In North America, coverage is good in the latest Jurassic and ‘middle’ to Late Cretaceous, but non-existent in Early to Middle Jurassic and earliest Cretaceous (Fig. 7E). Coverage is generally poor for the entire South American ornithischian record (Fig. 7F), explaining why obtaining a subsampled diversity signal here is difficult. 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