Their Their data, taken from the Geobiodiversity Database (GBDB) ( ), span the Paleozoic through the Early Triassic. Although GBDB data are limited (largely) to China, the different continental plates that compose modern China fortuitously span multiple biogeographic realms throughout most of the Paleozoic. CONOP aligns fossil- bearing beds from different rock sections (e.g., spans of rocks from quarries, road cuts, and natural erosion on hills and mountains) by maximizing sets of species with first and last appearances in the same order in as many 4 sections as possible. By integrating these analyses with radiometric dates and other geological data ( ), the authors resolved the age of an average bed (and thus the average first and last appearance times of species) to within 26,000 years. This new level of dating specificity is similar to moving from a system in which all people who lived in the same century are considered to be contemporaries to one in which only people who lived during the same 6-month period are deemed to be contemporaries. Armed with exact first and last appearance dates for thousands of species, the authors then developed what are, as they themselves stress, a set of fairly preliminary analyses of Paleozoic diversity. The authors deliberately eschew sophisticated analyses of origination and extinction dynamics or sampling dynamics used in other works 5 6 with much coarser temporal resolution than that yielded by CONOP ( , ). This approach permits contrasting the basic patterns with those that would be implied had the authors ch osen to 'bin' these data into predefined chronostratigraphic analyses, as nearly all prior diversity studies have done. In doing so, some noteworthy patterns emerge. For example, despite failing to correct for the Signor-Lipps effect (imperfect sampling that causes sudden extinctions to look gradual or rapid radiations to look protracted) 7 ( ), CONOP results indicate rapid declines in richness of marine invertebrate species prior to the end- et al. Ordovician and end-Permian extinctions. Similarly, Fan found the rebound after the end-Ordovician extinction to be much more rapid than prior studies suggest. Furthermore, CONOP reconstructions show patterns over hundreds of thousands of years that prior studies, which lumped together occurrences over millions of years, cannot hope to reveal. 8 Analysis of the Great Ordovician Biodiversification Event (GOBE) ( ) offered a different type of unexpected et al. result. Fan 's study suggests that the GOBE began 20+ million years earlier than expected, during the late Cambrian. Given that late Cambrian sampling for many marine invertebrates is relatively poor compared to 9 their fossil records earlier in the Cambrian and in the Ordovician ( ), one would predict emergence of an opposite pattern: Any late Cambrian diversification should not have appeared until the Ordovician. The CONOP analyses of GBDB data have implications for how organismal biologists and molecular phylogeneticists perform analyses of species, including fossils, in the future. Recent years have seen a 10 11 proliferation of methods such as tip-data ( ) and fossilized birth-death models ( ), which include fossilized anatomical data and modern anatomical and molecular data. Accounting for uncertainty in the true ages of first 12 and last appearances can strongly affect the results of such analyses ( ). Current approaches for dealing with this uncertainty often assume that uncertainty is large; for example, if a species's first appearance is in the 13 Rhuddanian age, then all dates within the Rhuddanian are equally probable first appearances ( ). However, as the new study makes clear, biochronological analyses will make some dates within the Rhuddanian much more probable than others. Of course, many extant organisms do not fossilize as well as shell-bearing marine invertebrates, and their oldest fossil representatives often are known from exceptional preservation in the lagerstätte sedimentary deposits 14 15 ( ). CONOP and related biochronology methods ( ) require species from multiple beds in multiple sections to infer ages for fossil occurrences. However, fossiliferous beds preserving typical assemblages of shell- containing invertebrates usually occur above and below the lagerstätte. Constraining the ages of those beds will simultaneously constrain the ages of the lagerstätte. With respect to important evolutionary questions, the et al. development of new datasets and methods of the sort used by Fan will further evolutionary biology as a whole, not just paleontology. References and Notes

- 1. J.-x. Fan et al., Science 367, 272 (2020).

2 P. M. Sadler, R. A. Cooper, in High-Resolution Stratigraphic Approaches in Paleontology, P. Harries, Ed. (Plenum, 2003), vol. 21, pp. 49 - 94

- 3. GBDB, www.geobiodiversity.com.
- 4. P. M. Sadler, Bull. Geosci. 87, 681 (2012).