Why Not to delete taxa A Posteriori or A Priori

So I’ve been making excursions into phylogenetic analysing, and based on advice from Mike Taylor I’ve added a dental character, Euhelopus and Brachiosaurus nougaredi. Based on what I’ve found, I can safely say that NO MATTER WHAT, all characters and taxa add to an analysis, and if there is a dissolved clade that you want resolved, add more taxa or characters.

The strict consensus, which is the only really important analysis, is resolved as (Outgroup (Cetiosaurus, H. priscus, H. delfsi, H. sp., H. utterbacki, Tataouinea, Camarasaurus, Brachiosaurus, B. nougaredi, Futalognkosaurus, Apatosaurus minimus, Atlantosaurus, Euhelopus (A. ajax + Elosaurus) ) ). Now, Atlantosaurus is a pretty bad taxa, second worst known after B. nougaredi in this analysis, so I removed it in one analysis. This generated the tree (Outgroup, all other taxa), which actually dissolves the clade of A. ajax + Elosaurus. Now for the final analysis I removed B. nougaredi, and the tree was resolved as the exact same as with all taxa except without B. nougaredi.

This shows that neither tree was improved by removing a single fragmentary taxon, but to prove my point further I decided to remove both and generate a tree. With both removed, the tree resolved the same as with only Atlantosaurus removed. Now for some reason Atlantosaurus is the taxon that supports the clade of A. ajax + Elosaurus, but I’m not sure how.

I think this is good proof that analyses are better with more information, and further analyses should put this into account before deleting A Priori or A Posteriori.


About ijreid

I am an amateur palaeontologist thats hobbies include studying extinct amniotes, specifically dinosaurs, birds, and mammals. Occasionally, I focus my time on detailed and accurate illustrations of dinosaurs, and I have completed drawings of Dysalotosaurus, Micropachycephalosaurus, Zhuchengtyrannus, Troodon, Eotyrannus, Europelta, and Achillobator. I do not believe in copyrights, and think that the world would be better if everything was open access.
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One Response to Why Not to delete taxa A Posteriori or A Priori

  1. Mike Taylor says:

    Deleting a priori is wrong, because it discards information that contributes to deriving the set of MPTs. Deleting a posteriori is just fine, because all it does is let you see your results more clearly. You’ve already used all the information. You could end up with a tree that is perfectly resolved except that Xenoposeidon could appear anywhere at all. The strict consensus tree will be a completely unresolved polytomy. But delete Xeno a posteriori and your nicely resolved tree becomes visible. You’ve not got yourself a different result: you’ve merely made the result that you already had visible.


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