Friday, May 26, 2017

Following the logic

Cladograms which are based on bootstrap/jackknife, show that there is a large polytomy at the base of the coelurosaur clade. This is because the imaginary nodes (Maniraptoriformes, Maniraptora, Pennaraptora) which are not supported have been collapsed. The result is a much more correct picture of the taxa involved.

Xu et al
http://www.ivpp.cas.cn/qt/papers/201403/P020140314389417822583.pdf
See Figure S9


AND

Brusatte et al
http://www.cell.com/cms/attachment/2019474733/2039573094/mmc1.pdf


This means (to take one example) that we cannot tell what the relationship is between oviraptorids and Paraves from the cladistic analysis. The two possibilities are that creatures similar to oviraptorids were transitional between dinosaurs and Paraves OR that oviraptorids were secondarily flightless members of  Paraves. It is important to note that the cladistic analyses cannot tell us which one is more credible.
Consequently we have to look for other indicators as to which is more credible.

We can immediately see that the alternative that oviraptorids were secondarily flightless members of Paraves means that we do not need to postulate ghost lineages. Also we do not need to postulate the pre-adaptations that are required by the idea that creatures similar to oviraptorids were transitional between dinosaurs and basal Paraves.

The same applies to ornithomimosaurs and alvarezsaurids.

3 comments:

  1. http://science.sciencemag.org/content/327/5965/571
    The new taxon confirms extreme morphological convergence between birds and derived alvarezsauroids.

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  2. https://en.wikipedia.org/wiki/Aveairfoila
    Aveairfoila is a clade of maniraptorans that contain the therizinosaurs and the pennaraptorans the latter which includes birds. The group was coined by Gregory S. Paul in his second edition of the The Princeton Field Guide to Dinosaurs. In his concept Paul argues therizinosaurs and oviraptorosaurs are closely related to Jeholornis and omnivoropterygids respectively, which are usually considered to be avialans, and that therizinosaurs and oviraptorosaurs are neoflightless birds. His evidence is based from observations in the sternum and rib morphology.[1] This is not the first time he proposed these claims as Paul made similar claims regarding the entirety of Maniraptoriformes.[2] It should be noted that Paul's taxonomy is not accepted by most scientists as often they lack any sufficient explanation or citation.[3] Regardless the name is useful to describe the clade that contains therizinosaurs and pennaraptorans as there are a lot phylogenetic support for the two taxa being sister clades.[4][5]

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  3. https://en.wikipedia.org/wiki/Therizinosaur
    Because early finds were incomplete, the strange suite of anatomical features combining features typical of theropods, prosauropods and ornithischians led some scientists, such as Gregory S. Paul, to conclude that segnosaurs (as they were called before Therizinosaurus was recognized as part of the group) represented a late-surviving suborder of primitive dinosaurs, sometimes thought of as intermediates between prosauropods and ornithischians. Because of their suspected relationship with prosauropods, early depictions of segnosaurs (including illustrations by Paul) portrayed them as semi-quadrupedal, a mode of locomotion now known to have been impossible given the bird-like nature of their wrists.[8] It also led Paul to include segnosaurs within paleontologist Robert T. Bakker's Phytodinosauria in 1986, a superorder which was to include ornithischians, prosauropods, and sauropods, typified by their "blunt, spoon-crowned teeth suitable for cropping plants."[8]

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