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Re: Eosinopteryx and the origin of birds



Dawid Mazurek <dawidmazurek@wp.pl> wrote:

> Let's leave for a moment questions regarding ontogentic age, plumage 
> reduction & cursorial abilities of _Eosinopteryx_. Having read the paper some
> time ago, IMHO it's getting increasingly probable that some kind of 
> archaeopterygid (Anchiornis/Archaeopteryx-like form) living back in Jurassic 
> was
> ancestral both to Avialae and (secondarily fligthless) deinonychosaurs...


Speaking for myself, I'm not convinced that deinonychosaurs were
secondarily flightless.  This would mean that deinonychosaurs evolved
from ancestors that flew, which is still very uncertain.  At the
moment, the jury is still out on whether basal avialans such as
_Archaeopteryx_ or _Jeholornis_ were capable of powered flight, never
mind basal paravians.


I think it's likely that the most recent common ancestor of avialans
and deinonychosaurs was capable of some kind of aerial behavior, such
as parachuting or gliding.  (This may also hold for the most recent
common ancestor of paravians and oviraptorosaurs.)


One possibility is that various lineages of Maniraptora experimented
in different kinds of non-powered aerial behaviors, as exemplified by
microraptorians, basal troodontids and basal avialans.  These aerial
behaviors were abandoned by certain descendant taxa, such as derived
dromaeosaurs and troodontids.  Only in one lineage ("advanced"
Avialae) was aerial behavior further refined to become true powered
flight.


In other words: a "long fuse" evolution of avian flight, with various
detours and dead-ends along the way.


> The weirdest thing in the Godefroit et al.'s (2013) analysis is that Archie & 
> Wellnhoferia are in politomy with deinonychosaurs and taking into account
> how this two former genera are alike morphologically, temporally and 
> biogeographically (in reality being islander sister taxa?), and similar to 
> basal
> deinonychosaurs (troodontids - Xiaotingia i Anchiornis), then, if the 
> topology presented is more or less correct, I can see no other possibility 
> than
> Archie or related taxon of similar morphology being ancestral or at least 
> archetypical for Paraves.


This seems entirely reasonable.  The question then becomes: Did this
archaeopterygid-like archetype actually fly?






Cheers

Tim