Hey, some interesting dinosaurs!

[Joe Botting]

I know. Amazing, isn't it?

The whole dinosaur-bird transition phase seems to get more complicated with each discovery. Unfortunately, the BBC report got rather garbled:

news.bbc.co.uk/1/hi/world/asia-pacific/4337888.stm

But then, this is the BBC, so I guess it's expected. Anyway, what the discovery says is that a Cretaceous bird-like dinosaur (a dromaeosaur, the group that was ancestral to birds) has been discovered on a separate continent from the ones that they have previously been found on. It has long arms and legs, but is certainly not a bird, as such. This is interesting, because it means that the common ancestor of these bird-like dinosaurs lived before the continents broke up, during the Jurassic.
Apparently, dromaeosaurs only appeared in the Cretaceous. Therefore, says the BBC, powered flight evolved twice, independently in the two continents.

The problem is, that it's no longer at all clear whether dromaeosaurs are the closest dinosaur group to birds. There's quite a good debate on this, which gives you an idea of the complexity, even if the technical side is beyond you (like it is for me! ;-):

www.dinosauria.com/jdp/trex/manirex.htm

The suggestion is that tyrannosaurs are actually closer to birds than dromaeosaurs are, although the whole group was at least slightly feathered.

What really scuppers the nice simplistic report is that Archaeopteryx is from the Middle Jurassic. It's a bird. And it's also, apparently, a tyrannosaur. We just can't quite confirm a semi-lunate carpal, or something, in order to be sure...

This is why I stick to sponges.

Joe

[hallucygenia]

Alright, I'm being thick. Why does the discovery of this new bird-like dinosaur mean that flight evolved independently twice? This thing only has wing-like forelimbs, according to the BBC. Unless it's been said elsewhere that the thing could actually fly?

[Joe Botting]

I've now heard from someone that read the paper for me ( , and the reason is as follows...

There's a new dromaeosaur in Argentina, only the second found in Gondwana. This is apparently (according to a cladistic analysis) closely related to the other one, from Madagascar. The Madagascan one, according to some interpretations of the limited data, might have flown.
Now, Gondwana separated from the Eurasian block in the Lower Jurassic, before the origin of powered flight in dinosaurs (we think). Therefore, if we have a non-flying dromaeosaur in that continent, closely related to a later flying dromaeosaur, and the continents separated before the first flying dromaeosaur, then... flight evolved independently in the Gondwanan and Eurasian lineages! Ta-da!

There are far too many 'ifs' for my liking. For example, the record of Mesozoic birds is very patchy. Perhaps they do go back further, or found another way to cross oceans (eg. on floating logs, as small mammals and lizards are known to do). Secondly, it all hinges on the interpretation of the Madagascan form as a flying species, and the close relationship derived from their analysis. Given that the remains are incomplete, both may be rather flawed.

So, it's probably been over-reported. Still interesting, though, I reckon.

Joe