View source for Physics:Appearance event ordination

'''Appearance event ordination''' or '''AEO''' is a [[Scientific method|scientific method]] for [[Physics:Biochronology|biochronology]] through the ordering of the appearance of [[Biology:Fossil|fossil]] [[Biology:Mammal|mammal]] genera by [[Multivariate analysis|multivariate analysis]], using conjunctional (overlapping) and disconjunctional (nonoverlapping) range distributions in large sets of data.<ref>{{cite journal |first=J. |last=Alroy |title=Appearance event ordination: a new biochronologic method |journal=Paleobiology |volume=20 |pages=191&ndash;207 |year=1994 |url=http://www.nceas.ucsb.edu/~alroy/pdfs/1994-Paleobiology-20-191.pdf|accessdate=30 August 2015|doi= 10.1017/S0094837300012677}}</ref>
==Process==
AEO is based on faunal overlap and stratigraphic superposition to derive a best-fit sequence of first and last appearance events.

===Step 1===
The first step is to translate patterns of overlap and [[Physics:Law of superposition|superposition]] into pairwise first-before-last statements. The wolf species ''Canis edwardii'' and ''Canis armbrusteri'' are used as example taxa for the following patterns. Each statement means ''C. edwardii'', for example, must have first appeared before ''C. armbusteri'' last appeared. This is true whenever either (1) ''C. edwardii'' and ''C. armbrusteri'' have been found together in at least one nontime-averaged fossil collection, or (2) ''C. edwardii'' is found lower in at least one [[Earth:Lithostratigraphy|lithostratigraphic]] section than ''C. armbrusteri''.

===Step 2===
A [[Multivariate statistics|multivariate]] [[Ordination (statistics)|ordination]] [[Algorithm|algorithm]] is applied to derive a first-pass, hypothesized sequence of first and last appearances. The minimal constraint on this sequence is that if there is an observed, real-world ''C. edwardii'' before ''C. armbrusteri'' statement for any pair of taxa, the hypothesized event sequence must replicate it. Then, the program shuffles the events using a maximum likelihood criterion. The criterion basically seeks to pull apart as many hypothesized age range overlaps as possible, especially if they involve common taxa. Taxa are defined as "common" if they are known to overlap with a large fraction of the taxa with which they are implied to overlap.

===Step 3===
Once the relative event sequence has been established, it is converted into numerical time with a nonlinear [[Interpolation|interpolation]] algorithm that compares event sequence positions and [[Physics:Geochronology|geochronological]] age estimates for collections that have them. The calibration only uses: 
*[[Physics:Argon–argon dating|<sup>40</sup>Argon/<sup>39</sup>Argon dates]]
*Uranium-thorium dates for some [[Earth:Pleistocene|Pleistocene]] collections
*Paleomagnetic dates that derive from unambiguous, narrow correlations inferred using nonfaunal tie points such as the position in the section of the [[Earth:Cretaceous–Paleogene boundary|Cretaceous–Paleogene boundary]], [[Earth:Paleocene–Eocene Thermal Maximum|Paleocene-Eocene boundary]], or Recent

==NALMA vs. AEO==
The North American land mammal ages procedure uses subjective opinions by published sources and/or authors, citing authors such as Michael O. Woodburne,<ref>{{cite journal|last1=Woodburne|first1=Michael O.|last2=Case|first2=Judd A.|title=Dispersal, vicariance, and the Late Cretaceous to early tertiary land mammal biogeography from South America to Australia|journal=Journal of Mammalian Evolution|date=June 1996|volume=3|issue=2|pages=121–161|doi=10.1007/BF01454359}}</ref> Robert W. Wilson,<ref>{{cite journal|last1=Wilson|first1=Robert W.|title=Evolution of the Early Tertiary Rodents|journal=Evolution|date=September 1951|volume=5|issue=3|pages=207|doi=10.2307/2405460}}</ref> and J. David Archibald.<ref>{{cite book|editor-last1=Rose|editor-first1=Kenneth D.|editor-last2=Archibald|editor-first2=J. David|title=The rise of placental mammals : origins and relationships of the Major Extant Clades|date=2005|publisher=Johns Hopkins University Press|location=Baltimore, Md.|isbn=978-0801880223}}</ref>

Appearance event ordination uses objective, explicit, recordable, repeatable, and [[Statistics|quantitative analyses]] of faunal and [[Earth:Biostratigraphy|biostratigraphic]] data to arrive at a conclusion, according to John Alroy.

==References==
{{reflist}}

[[Category:Dating methods]]

{{Sourceattribution|Appearance event ordination}}