{'fraction_non_alphanumeric': 0.023474178403755867, 'fraction_numerical': 0.020657276995305163, 'mean_word_length': 5.270588235294118, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
High-resolution dating of Paleozoic fossils

Refined ages of marine fossils clarify the timing of diversification and extinction events Discussions about the quality of the fossil record frequently focus on completeness—that is, the proportion of species that existed for which scientists have fossil samples. An equally important aspect of quality is how finely the ages of fossils and durations of major evolutionary events can be resolved. Paleontologists and other biologists typically date fossils using the general ages of the chronostratigraphic units assigned to the rock strata yielding the fossils. For example, if a fossiliferous bed comes from the Rhuddanian Gasworks Sandstone, then the ages assigned to the fossils are usually 443.8 to 440.8 million years. On page 272 of this issue, Fan et al. (1) report on their use of constrained optimization (CONOP) (2) in biochronological analyses of fossil-bearing layers containing 11,000+ marine invertebrate species from 3000+ sections of sedimentary rocks, which constrain ages to a fraction of that range.