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Submitted: November 5, 2009
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Tetrapteryxby ~Albertonykus

Traditional Art / Drawings / Animals

From right to left: Anchiornis huxleyi, Microraptor zhaoianus, and Archaeopteryx lithographica

The closest relatives of birds are the deinonychosaurs, which include the infamous dromaeosaurids (such as Velociraptor mongoliensis and the like) as well as swift, omnivorous troodonts. It's been a while since it was confirmed that basal dromaeosaurids like Microraptor zhaoianus were four-winged, and we now know that early birds had hind-wings as well. (Though theirs were not as extensive as that of Microraptor zhaoianus.) With the confirmation that the also four-winged Anchiornis huxleyi as a troodont, it seems the picture is complete (or at least more complete than before): deinonychosaurs and birds evolved from an ancestor that could fly, and furthermore, it did this on four wings, possibly using the hind wings as stabilizers. (In modern birds, or neornithines, they have a tail fan to help them do this, hence, the loss of hind wings.) It's worthy to note that both deinonychosaurs and birds spawned types that returned to the ground, becoming flightless. As far as we know, deinonychosaurs seem to have done it five times, and birds countless times. I can think of about two hundred twenty examples of birds that evolved flightlessness independently, and no doubt there are more.

~SpongeBobFossilPants Mar 25, 2012

Does the utterly screwed-up phylogeny of Paraves endanger tetrapteryx being basal to the group?

~Albertonykus Mar 25, 2012

Maybe, maybe not. Not enough information to say. I still suspect that that it is indeed a basal trait though.

~SpongeBobFossilPants Mar 14, 2012

Did deinonychosaurs really lose flight five times? I can only think of two examples (or one, if the Samrukia paper's implications for Troodontidae are correct)...

~Albertonykus Mar 14, 2012

In troodonts, in unenlagiines, in eudromaeosaurs, in Mahakala, and I think I also counted Tianyuraptor as once (but it's probably actually part of the same radiation as eudromaeosaurs).

~SpongeBobFossilPants Mar 16, 2012

According to Wikipedia, Mahakala endangers the concept of secondarily flightless deinonychosaurs, although Greg Paul claims that the creature's late appearance means that deinonychosaurs could still be secondarily flightless. Who's right?

~Albertonykus Mar 16, 2012

Simple answer: we don't know.

~SpongeBobFossilPants Mar 14, 2012

And here I was thinking that microraptorines were secondarily volant...

~Albertonykus Mar 14, 2012

If deinonychosaurs aren't ancestrally volant then they might have evolved flight independently, but I don't know of any evidence to suggest that they went from flying to flightless and back to flying.

~SpongeBobFossilPants Mar 17, 2012

That makes sense, I suppose.

Wouldn't things like Pamparaptor count as once? (Oh wait, Science Marches On.)

What do you make of Paul's suggestion that microraptorines were better fliers than archaeopterygids or omnivoropterygids?

~Albertonykus Mar 17, 2012

Probably, unless it turns out to be an unenlagiine.

From what I've heard, he's probably right.

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