[CT Birds] Technical question on bird evolution

Jacob Musser jacob.musser at yale.edu
Sat Apr 18 11:20:06 EDT 2015


Marty,

Great question. I am an evolutionary ornithology grad student and have 
some insight on this. Raptors are not the most primitive group. 
Actually, the word primitive must be used very carefuly, because all 
living birds have had exactly the same amount of time to evolve from 
their common ancestor. As lineages split off from each other, changes 
occur in one lineage and not another, or one part of the organism (say 
coloration on the head) but not another part. In fact, most bird species 
are a mixture of primitive (ancestral) traits and new derived traits. 
So, no single bird species or group represents the primitive condition. 
However, we can make inferences about what the ancestor may have looked 
like by constructing evolutionary trees of living and fossil taxa. If a 
particular trait is found in a series of closely related lineages we can 
infer that their common ancestor probably had that trait (because it is 
more parsimonious to assume the trait evolved once than many times 
independently in each lineage). Returning to the case of raptors, most 
raptorial traits are likely highly derived within the bird tree and are 
not ancestral traits that were found in the common ancestor of birds. 
Its difficult to know exactly what the ancestor of all living birds was 
like, but it was probably a terrestrial bird, and it was most likely not 
tearing flesh and eating meat.

In regards to the dinosaurian origins of birds, all living birds are 
descendents of a non-avian dinosaur ancestor (and no living bird is more 
dinosaur then another). I use the term non-avian dinosaurs because birds 
are still dinosaurs. This is because birds are nested deeply within the 
dinosaur tree. So, even though birds have a number of highly derived 
characteristics, they are still dinosaurs (a species does not stop being 
a member of its family just because it looks different). In fact, we 
actually run into trouble if we talk about dinosaurs and birds as 
separate groups. This is because some non-avian dinosaurs are more 
closely related to birds then they are to other non-avian dinosaurs. For 
instance, members of the genus Tyrannosaurus had feathers, whereas 
Hadrosaurs (Duck-billed Dinosaurs), likely didn't. This isn't a surprise 
if you look at the dinosaur evolutionary tree because Tyrannosaurs are 
more closely related to birds then they are to Hadrosaurs.

Here is a webpage that depicts some of the relationships among 
dinosaurs: http://palaeos.com/vertebrates/theropoda/dinosaurs-birds.html

Hope this was useful!

All the best,
Jake

On 4/18/15 10:15 AM, Marty via CTBirds wrote:
> I just watched an episode of Wild Kratts on PBS about raptors.  The show stated that raptors are direct descendants of dinosaurs due to their characteristics - nothing new there.
>
> My question is - Are raptors the most primitive 'group' of birds and did other groups branched off of them?
>
> Marty
> Woodbury
>
> Sent from my iPhone
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