Spatiotemporal changes in fossil specimen completeness can bias our understanding of a group’s evolutionary history. The quality of the sauropodomorph fossil record was assessed a decade ago, but the number of valid species has since increased by 60%, and 17% of the taxa from that study have since undergone taxonomic revision. Here, we assess how 10 years of additional research has changed our outlook on the group’s fossil record. We quantified the completeness of all 307 sauropodomorph species currently considered valid, using the skeletal completeness metric, which calculates the proportion of a complete skeleton preserved for each taxon. Taxonomic and stratigraphic age revisions, rather than new species, are the drivers of the most significant differences between the current results and those of the previous assessment. No statistical differences are found when we use our new dataset to generate temporal completeness curves based on only the taxa known in 2009 or 1999. We now observe a severe drop in mean completeness values across the Jurassic/Cretaceous boundary that never recover to pre-Cretaceous levels. Explaining this pattern is difficult, as we find no convincing evidence it is related to environmental preferences or body size changes. Instead, it might result from: (1) reduction of terrestrial fossil preservation space due to sea level rise; (2) ecological specificities and relatively high diagnosability of Cretaceous species; and/or (3) increased sampling of newly explored sites with many previously unknown taxa. Revisiting patterns in this manner allows us to test the longevity of conclusions made in previous quantitative studies.

Completeness dataset:

Completeness data were primarily gathered from figures and descriptive text in the literature, supplemented by additional online sources, museum catalogues, first-hand observation of specimens, and via personal communications. See 'Completeness_dataset_methodology_notes.txt' for detailed description of data collection methodology.

Completeness dataset:

Specimen information, completeness scores, and spatial and temporal occurrence data for sauropodomorph dinosaurs. The whole dataset is represented in 'Completeness_Database.xlsx', while its constituent datasheets are also separated into '.csv' files ('Summary', 'SCM2', 'Specimen_scores', 'Cont._element_references', 'Skeletal_body_proportions', and 'Taxon_information'). See 'Completeness_dataset_methodology_notes.txt' for datasheet navigation and workflow details.

Supplementary material: 

Supplementary tables 1-6 provided in both '.tif' and '.csv' format, whilst supplementary figures 1-9 solely in '.tif' format.