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 hypothesized nodes (Maniraptoriformes, Maniraptora, Pennaraptora) are not supported and 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.