PSA: Anchiornis feet were scaly AND fully feathered

[Dinoguy2]

There is evidence that other maniraptorans also has connected fingers, especially in some oviraptorosaurs, and this might explain why some species reduce or lose digit 3, like in Caudipteryx.

Anchiornis having its second and third fingers connected by skin has made me wonder to what extent this feature was present in other dinosaurs.  Maybe it was present in dromaeosaurids, troodontids and avialans at least?  I would've thought oviraptorosaurs too, but I feel quite uncertain about that after seeing the positions those fingers are preserved in on specimens of Citipati and Similicaudipteryx.  What evidence is there for oviraptorosaurs having the second and third fingers connected?

Caudipteryx barely even has a third finger, and the third finger of caenagnathids is also very thin/reduced and I've seen someone mention these as evidence that their digits were bound as well. If Anchiornis has this feature, and oviraotorosaurs have it, its probably a basal pennaraptoran trait and should be assumed for dromaeosaurids too. I wouldn't take much stock in the actual positions the hand bones are preserved in especially for 3D specimens like Citipati. But in many specimens including Similicaudipteryx, the third finger is touching the second along its entire length up to the last joint. So it looks like the tip of the finger was free but most wasn't. You can see the same pattern in a lot of feathered Dino specimens.

As for what they used the claws for... have you ever seen birds fight? Many species have gone so far as to re-evolve a "wing claw" in the form of a bony wrist spur, probably for the same purpose. It hurts more when you beat your opponent via numerous high-energy wing flaps if you have spikes on your wings!

By the way, Dave Peters (pre-crazytown) predicted bound fingers and patagia back in the '90s!

[Papi-Anon]

And with that the feathered version of my Velociraptor action figure shall have mittened wing-claws.

Still, the hoatzin has two articulated digits as a chick that I believe wither as they grow into adulthood (or maybe they fuse with digit-3?). Any other extant birds that have this feature post-hatching?

[Dinoguy2]

And with that the feathered version of my Velociraptor action figure shall have mittened wing-claws.

Still, the hoatzin has two articulated digits as a chick that I believe wither as they grow into adulthood (or maybe they fuse with digit-3?). Any other extant birds that have this feature post-hatching?

Hoatzin fingers don't wither, they just fuse together like a normal bird wing. All birds have three fingers, but 2 and 3 fuse to each other and all fuse to the wrist so they can't move.

[Papi-Anon]

Ah, well in in that case maybe I'll do hoatzin chick clawed wings for my project. Mittens are neat but in remembering the 'stink-bird' that seems feasible.

[PaleoMatt]

Are there any other birds that have claws like that when they are young? I think the Moorhen might but I'm not sure. (Btw Moorhen is my archenemy).

[Dinoguy2]

Are there any other birds that have claws like that when they are young? I think the Moorhen might but I'm not sure. (Btw Moorhen is my archenemy).

There are plenty of birds that have claws when they're old! Search up emu claws. Or better yet look at the claws on a chicken next time you eat one. Most birds have claws, the hoatzin is only unique because of the separation of the fingers in babies, which seem to be necessary for climbing.

Emu wing:

[Sim]

Thanks for your reply about the connected fingers, Dinoguy2!  It was very informative.  I've spent time looking at lots of pennaraptoran forelimbs (mostly oviraptorosaurs, dromaeosaurids and (extinct and extant) avialans) and pennaraptorans having fingers 2 and 3 connected seems to make so much sense (the patagia too).  It makes their wings really look like wings, as opposed to forelimbs with feathers there because they have to be.


What I'm surprised hasn't been discussed yet is Anchiornis having scales on its hands...  I was really surprised it had that.  Based on what I've seen, my understanding is the top of the fingers of Anchiornis were fully feathered, while there are scales on the underside of its third finger.  What I don't know is whether it also had scales on the underside of the first and second finger, and whether there were also feathers on the scaly underside of the fingers.

I wonder why Anchiornis had scales on its fingers?  Maybe to help protect the hand while climbing?  It also makes me wonder what the integument of the fingers of other Mesozoic pennaraptorans might have been like, excluding remiges.  Besides what I described for Anchiornis above, as far as I know:

- The holotype of Caudipteryx dongi preserves skin impressions from the underside of its fingers and hand that look similar to what is preserved on the underside of the third finger of Anchiornis.  I don't know if it's been established exactly what the integument on the fingers of C. dongi is though.

- In Confuciusornis, the first finger appears to be unusual, being free of feathers and independent of the rest of the wing, and having a large claw.

- NGMC 91 aka Dave, which is considered to be a juvenile Sinornithosaurus, appears to have its hands completely covered in feathers (except for the claws), although I'm not sure if the feathers could be only on one side of the hand (e.g. the top side).

[Dinoguy2]

Thanks for your reply about the connected fingers, Dinoguy2!  It was very informative.  I've spent time looking at lots of pennaraptoran forelimbs (mostly oviraptorosaurs, dromaeosaurids and (extinct and extant) avialans) and pennaraptorans having fingers 2 and 3 connected seems to make so much sense (the patagia too).  It makes their wings really look like wings, as opposed to forelimbs with feathers there because they have to be.


What I'm surprised hasn't been discussed yet is Anchiornis having scales on its hands...  I was really surprised it had that.  Based on what I've seen, my understanding is the top of the fingers of Anchiornis were fully feathered, while there are scales on the underside of its third finger.  What I don't know is whether it also had scales on the underside of the first and second finger, and whether there were also feathers on the scaly underside of the fingers.

I wonder why Anchiornis had scales on its fingers?  Maybe to help protect the hand while climbing?  It also makes me wonder what the integument of the fingers of other Mesozoic pennaraptorans might have been like, excluding remiges.  Besides what I described for Anchiornis above, as far as I know:

- The holotype of Caudipteryx dongi preserves skin impressions from the underside of its fingers and hand that look similar to what is preserved on the underside of the third finger of Anchiornis.  I don't know if it's been established exactly what the integument on the fingers of C. dongi is though.

- In Confuciusornis, the first finger appears to be unusual, being free of feathers and independent of the rest of the wing, and having a large claw.

- NGMC 91 aka Dave, which is considered to be a juvenile Sinornithosaurus, appears to have its hands completely covered in feathers (except for the claws), although I'm not sure if the feathers could be only on one side of the hand (e.g. the top side).

Well, my guess for what it's worth is that scaly fingers is just the primitive trait. Many modern birds have partly bare fingers (see emu pic again) and obviously scales and feathers used to intermingle on more parts of the body than they do now. Climbing or digging (nests?) seem like good hypotheses. Alternately, feathers were lost in these areas and scales remained having been under the feathers all along like on the tibia of Anchiornis. If an Anchiornis lost (in life or by evolution) it's leg feathers, it would have scaly legs too.