[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Details on Yandangornis



Ken Kinman wrote-

>       It sounds like you are putting _Yandangornis_ very close to where
some
> workers place Alvarezsaurids.  Any chance that they are sister groups?

Well, alvarezsaurids appear further down the tree (below eumaniraptorans and
troodontids) in my analysis.  Even assuming alvarezsaurids are avialans
(which they have been before in my analysis), you would need some derived
characters shared by the two groups to support a sister group relationship.
Besides the elongate sternum (which is also seen in Sinornithosaurus,
Bambiraptor and euornithines), I cannot find any such characters.  Although
some characters (trochanteric rest, reduced fibula) are also seen in
mononykines, the absence of alvarezsaurid and Patagonykus+Mononykinae
synapomorphies (procoelous caudals, shortened forelimbs, radius and ulna
share a single humeral articular facet, radius less than 50% humeral length,
large olecranon process, manual digits II and III reduced) shows these are
more parsimoniously seen as convergences.  Also, alvarezsaurids primitively
lack the five characters I listed which show Yandangornis is more derived
than Archaeopteryx, Rahonavis, etc..  This suggests that even if
alvarezsaurids turn out to be avialans, they will be less derived than
Yandangornis.  Avimimus (currently the sister group to alvarezsaurids)
shares more characters with Yandangornis (toothless dentary, completely
fused tibiotarsus), but also lacks three out of five characters (2, 3 and 5)
that are more derived in Yandangornis than Archaeopteryx.  Thus, the
situation is similar to that of alvarezsaurids.  The best chance for a
sister group relationship that I see is with confuciusornithids (toothless
premaxilla, maxilla and dentary), especially considering both groups are
next to each other phylogenetically.  Not only is this less parsimonious
than the hypothesis it is less derived than confuciusornithids, but I don't
consider toothless elements very dependable synapomorphies considering how
many times they have evolved in other groups.

Mickey Mortimer