Paper No. 76-41
NGUYEN, Tuan1, MIDGLEY, Katrina M.
2, LIN, Jason Z.
1, WANG, Steve C.
3, PORTER, Susannah M.
4, MOORE, John L.
5, MALOOF, Adam C.
6, ZHOU, Heather J.
7, WANG, Daniel
3, GAI, Linda
8 and WANG, Chengying
3, (1)Mathematics and Statistics, Swarthmore College, 500 College Ave, Swarthmore, PA 19081; Computer Science, Swarthmore College, 500 College Ave, Swarthmore, PA 19081, (2)Computer Science, Swarthmore College, 500 College Ave, Swarthmore, PA 19081, (3)Mathematics and Statistics, Swarthmore College, 500 College Ave, Swarthmore, PA 19081, (4)Department of Earth Science, University of California, Santa Barbara, Santa Barbara, CA 93106, (5)Department of Earth Science, University of California, Santa Barbara, Santa Barbara, CA 93106; Earth Research Institute, University of California, Santa Barbara, Santa Barbara, CA 93106, (6)Department of Geosciences, Princeton University, Princeton, NJ 08544, (7)Mathematics and Statistics, Swarthmore College, 500 College Ave, Swarthmore, PA 19081; Economics, Swarthmore College, 500 College Ave, Swarthmore, PA 19081, (8)Biostatistics, Johns Hopkins University, Baltimore, MD 21205, tnguyen4@swarthmore.edu
Although the Signor-Lipps effect is most often associated with mass extinctions, it also plays a role in “mass origination” events. The Cambrian explosion is arguably the most important such example and a pivotal event in the history of life. The general timeline of the Cambrian explosion is well established, but details about the duration and pattern of origination events remain unclear. Maloof et al. (2010) found that a dataset of small shelly fossils through the earliest Cambrian showed three pulses of fossil appearances over approximately 16 million years. Here we attempt to provide a statistically rigorous estimate for the duration and number of pulses in the Cambrian explosion using novel methods that account for Signor-Lipps-type effects.
We used a revised dataset of fossil occurrences of 166 genera of small shelly fossils from Mongolia, Siberia, and China, dating from the earliest part of the Cambrian (Nemakit-Daldynian and Tommotian, or Terreneuvian). To estimate the duration of the origination event, we construct a confidence interval for the time span between the earliest and latest originations, by inverting a hypothesis test for whether a given duration is consistent with the observed fossil record. To estimate the number of pulses, we use a k-Nearest Neighbor classifier, which takes in a vector of Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) weights and outputs a vector indicating the posterior probability for each possible number of pulses.
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