Paleozoic geomagnetism shapes vertebrate evolution
- Published
- Accepted
- Subject Areas
- Evolutionary Studies, Paleontology
- Keywords
- Vertebrata, Paleozoic, Geomagnetism, Evolution, Paleomagnetism, Taxonomy, Phylogeny, Superchrons, Polarity reversals
- Copyright
- © 2018 Staub
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2018. Paleozoic geomagnetism shapes vertebrate evolution. PeerJ Preprints 6:e26490v1 https://doi.org/10.7287/peerj.preprints.26490v1
Abstract
Background. Despite a fifty-year failure of paleontologists to find a viable connection between geomagnetic polarity reversals and evolutionary patterns, recent databases show that the early appearance, radiation, and diversification of Paleozoic vertebrates tend to occur during periods having frequent collapses of the Earth’s geomagnetic field. The transition time during the collapse of the Earth’s protective magnetic shield can last thousands of years, and the effects on biota are unknown. Solar and cosmic radiation, volcanism, weather alteration, low-frequency electromagnetic fields, depletion of ozone, and the stripping of atmospheric oxygen have been proposed as possible causes, but previous studies have found no effects.
Methods. Using published databases, we compiled a spreadsheet that shows the first appearance of 1809 age-dated genera with each genus assigned to one of 28 taxonomic groups. From Gradstein’s Geologic Time Scale 2012, we delineated 17 Paleozoic zones with either high or low levels of polarity reversals.
Results. From our compilation, we counted 508 Paleozoic vertebrates that first appeared within 20 million-years of the origin of their clade or natural group. These genera represent the initial radiation and diversification of individual Paleozoic vertebrate clades. After compensating for sample-size and external geologic biases, the resulting Pearson’s coefficient between these genera and polarity zones equals 0.781. Using 11 commonly accepted clades and assuming a natural competition existed between them, we counted each genus from a clade’s inception until it was bypassed by a subsequent clade. Here, Pearson's equals 0.901 with a p-value of <0.000001. In a blindfold study, we separated the Paleozoic into a dozen equally-sized temporal bins, then 13 bins, up to 31 bins. The mean Pearson coefficient for these bins is 0.810. After calculating coefficients for four distinct taxonomies, two paleomagnetic systems, three systematics for age-dating within geologic stages, and seven independent spreadsheets, the results suggest a strong relationship exists between Paleozoic vertebrates and polarity reversals. In addition, the earliest species of the major divisions of Paleozoic vertebrates (jawless fish, armored fish, jawed fish, cartilage fish, fish with bones, lobe-finned fish, tetrapods, amphibians, reptiles, and synapsids) first appeared in zones with relatively high levels of polarity reversals.
Discussion. The question: is this apparent connection between geomagnetism and the evolution of Paleozoic vertebrate due to environmental or biologic factors. If biologic, why are vertebrates the only biota effected? And after an indeterminate period of time, how do vertebrate families become immune to the ongoing effects of polarity reversals?
Author Comment
This is a preprint submission to PeerJ Preprints.
Supplemental Information
Excel Data S1. Spreadsheet used in the statistical analysis of 1809 genera
Legend for Excel Data S1 for the report “Paleozoic geomagnetism shapes vertebrate evolution”. This spreadsheet was compiled from data of four sources: From paleobiology.org (Feb 9, 2017, upgraded Sept 17, 2017 ), we downloaded all occurrences of Paleozoic Chordata (accepted names only) with “output options” for “Classification”, “Stratigraphy”, and “Extended Stratigraphy”. We deleted all columns from the resulting spreadsheet except: “early_interval”, “late_interval”, “max_ma”, “min_ma”, “phylum”, “class”, “order”, “family”, “genus”, and the “stratcomments”. We added genera from Sepkoski’s 2002 Compendium of fossil marine animal genera (we used donaldkenney.x10.mx/SEPKOSKI.HTM for access). For Benton compilation we used data from “The first half of tetrapod evolution, sampling proxies, and fossil record quality” in the Dryad Digital Repository. Zhoa and Zhu’s 2010 portion of the spreadsheet is taken from their “Siluro-Devonian vertebrate biostratigraphy and biogeography of China).” We used fossilworks.org whenever needed for age-dating or taxonomy.
Column Headings in bold.
"File" names the 7 spreadsheets used in this report.
CRC Numbers represent taxonomy for CRC (Competitive Replacement Clades).
20G Numbers represent taxonomy for 20G clades (first 20 million years).
Source 4 sources (Paleobiology, Sepkoski, Benton, Zhoa&Zhu).
Clade Major clades used for this report.
SubClade Supportive taxonomy at the class level.
“Family” Supportive taxonomy at the family level.
Genus Name.
EarlyStage Earliest geologic stage for each genus.
LateStage Latest geologic stage for range of age for the earliest species.
Max Maximum age of the geologic stage (Ma, millions of years).
Min Minimum age of the geologic stage (Ma).
Mean Mean age of the geologic stage (all ages are Ma).
Diff Interval of geologic stages (ages are from Gradstein 2012 when available, otherwise Paleobiology).
The following six columns are for calculating proportional dating of stages:
DnCRC CRC Denominator (this is the total number of genera in a geologic stage).
NmCRC CRC Numerator. A series of numbers (1 to one less than the total number—the newest genera are centered in the series).
AgeCRC CRC Age (equals Max minus Diff times the numerator divided by the denominator).
Dn20G 20G Denominator.
Nm20G 20G Numerator.
Age20G 20G Age (equals Max minus Diff times numerator divided by the denominator).
ZnMd Polarity zone using the mean age of a geologic stage.
Mid+/- Polarity zone (1=high polarity zones; 0=low polarity zones).
Age1Md Age of the earliest species of a clade or natural group, using mean age of its geologic stage.
DiffMd Difference, Age1Md minus the Mean age of the genus.
ZnMx Polarity zone using the maximum age of a geologic stage.
Mx+/- Polarity zone (1=high polarity zones; 0=low polarity zones).
Age1Mx Age of the earliest species of a clade or natural group using the maximum age of its geologic stage.
DiffMx Difference in Age1Mx minus the Max age of a genus.
Genera Repeat of the genus name.
ComA Comments, generally age related.
ComT Comments, generally taxonomy related. i