Humanoid avians with six limbs, how to modify their bodyplan so that their ribcage won't constrain certain movements?

Question

Thundercats 2011 was great. I mean, it even had Thanos and infinity stones before it was cool. Such a good remake simply couldn't survive in final-stage capitalism, as those who worked on it didn't sacrifice quality to more efficiently promote plastic landfill. Well, at least my secret network of spies across the WWW managed to track down one of the art directors (well, his DA page), here I found something interesting I didn't even notice while watching the show.

See where the wings are? Well, I think this image shows it even better. They're closer to the waist. In paper, this solves problems with balance, but people who praised this idea forgot that now these bird people have a big, rigid bone in the area of their stomachs, making basic things, like bending down to grab something, an impossible task. I have very, very similar creatures in my world (please don't sue) and I haven't actually thought about this... HECK!

My two other six-limbed creatures, centaurs and dragons avoid this anatomical problem. Centaurs have their human body where normally a horse's neck would be, which is pretty flexible; and dragons are still rather snakey, despite their bigger chests, plus their forelegs have been dialed down to reduce the TPK-capability of an all-out "paw-paw-bite-and-set-on-fire" pounce.

Bird people aren't particularly snakey, neither are they short kings like the aarakocra. I still wanted to keep the bird people's weight low, because I won't go through the same headaches, estimating dragon flight-capability had brought.

Alexander Zass, the guy who could bend steel, was only 167 cm and 80 kg. So I guess we will be safe with a total mass of 70 kilograms for bird people, plus what Marden said that around 20-25% of a bird's weight is their flight muscles, we get either 56-52.5 kilograms to make the rest of the body. As I said before, I'm more lenient with height (they can be taller if that helps the issue), but weight is still a constraint.

Sure, they aren't supposed to be strong, yet taking away even more of the pecs sounds like a bad idea, as they still need to do things like wielding weapons and coffee covfefe mugs, but then the lengthening of their ribcage is inevitable and I am Iron Man. But seriously, how can I keep these bird people out of the uncanny valley while also giving them enough flight muscles without compromising their ability to do ab crunches?

Answer 1

Hip joints

I should preface this by saying I'm not by any means an expert on birds' anatomy. That said, if you feel the need to keep some scientific accuracy so that these bird folk have a rigid sternum in their mid section, a possible way to circumvent their innability to bend forward would be setting their hip joints further apart.

Just like in goold ol' regular birds, this would allow them to bend down in more of a squatting fashion if need be. It wouldn't really solve the problem of the ab crunches, but I believe it might improve their mobility as long as you allow for some hip torque.

Answer 2

Your birds just need prehensile feet

Forget about making rib cages flexible, they don't need to bend over, they have muscular legs and good enough balance to lift whatever they need with their feet.

Answer 3

The wings could be anchored to something like a second set of shoulder blades that attach near the bottom of the ribcage. This would allow for an open area between the ribs and pelvis but not quite as big as a human's.

Some birds barely have a separation at all between ribs and hips. They make up for it with flexible hip joints and the ability to fly.

Alternatively you could extend the pelvis upward with an outcropping on either side for wing joints to fit into. This may put your wings too low, or maybe not.

Those of us who are human get a couple of less connected ribs that don't come all the way around like the rest. Your birdfolk could have even more of those to anchor your extra bones on.

In the end though, who's gonna check if the fictional species you created is biologically accurate? Give those bird people wings.

Answer 4

I think this image from the answer by Len to this Anatomically correct multiarmed humanoids SE question is probably what you're looking for. Obviously the lower pair of arms become your wings.

Just scale your bird men accordingly to achieve the height you want.

Naturally the wings are going to be longer & the bird sternum & its muscles (which should be somewhat bigger than human pecs) replacing the lower ribcage will provide a different 'chest' shape in the upper body area than shown.

You probably want to relocate the wings shoulders back a little closer to the spine than normal shoulders to help avoid the two sets of limbs interfering with each other.

But I don't see a problem with waist flexibility in this skeletal structure, hope that helps.

Answer 5

What I think a lot of people are forgetting about is a keel, it is vital for flight, it is where the birds flight muscles connect. I also am working on hexapodle bird aliens and I have also ran into these problems in the past. I have settled on a longer abdomen with shorter yet more stable legs, the type of legs the elites in Halo have I forgot the name for it. This will balance out the body as you bird will have to deal with the weight of the wings that have been attached to its humanoid body. So lets say lighter bones (obviously) longer torso to allow a normal human ribcage then as we go lower the keel for the wings and below you can shove whatever alien organs you want and then the legs which will be those weird three jointed legs that most four legged aninals have in the back. So we have mostly everything set but theirs a few slight problems. Without proper feet or feathers, your bird creature will not be able to traditionally swim like a human does and will have to use its wings or if its adapted for it, its feet. Also, your creatures head will be slightly lowered during flight due to the wings being placed lower on the spine and will most likely fly like a secretary bird whos legs are all poking iut at the end due to there length.

Answer 6

Add an extra joint to the wing

By adding an additional segment to the wing, you can have the flapping motion start off to the sides, where the arms and body won't get in the way. If you'll forgive the crude drawing, it would look something like this:

The main joints are highlighted in red. Note that the first segments of the wings would not be positioned directly back, but would be angled towards the sides to allow for more freedom of movement for the wings proper.

These first segments would probably have an unusual bone setup to allow them to easily lock into place with little muscular effort. the first "elbow" joint would probably be very large and bulbous to support flight muscles.

Answer 7

Switch out the torso

I like the answer by Pelinore!

But also, this might be helpful:

http://www.sciencepartners.info/module-6-birds/bird-anatomy-bones-muscles/

There's a nice diagram in there of both bird and human skeletons, that shows how both bodies work and you can use your imagination to combine the parts you want. What I imagined changes the skeletal structure away from the pics you offered though. Their torsos would be different.

In short, it might be more realistic to have a bird torso with human appendages, rather than a human torso with bird appendages.

Answer 8

Flying skills required ?

Opening: "I still wanted to keep the bird people's weight low, because I won't go through the same headaches, estimating dragon flight-capability had brought."

Weight is an important consideration, but wing shape and wing span are also relevant. Correct anatomy would depend on the flying skills you want to give these creatures. When your scenario is involving say 50kG body weight and actual flight in a planetary atmosphere at Earthly G-forces, a wing span as depicted will be insufficient to take off from the ground, especially when helmets, armour and weaponry are needed. You'd require very big muscles for take off, allowing for hummingbird like wing speeds.

There are other ways.. a creature like this could jump off a cliff or tower, and proceed gliding considerable distances, make use of thermals. A wing suit type of flight would be feasible, even with the above proportions.

Gliding could be made easier and more agile, with a different set of wings, having less prominent feathers. Rather a smooth, wide surface, like seagulls have.. the gliding action does not involve much energy, so the muscles can remain small and the wings could be attached to a large, solid waist bone or "waist shoulder" or "hump shoulder" in some way, it should not require too much muscle strength during flight. Note some muscles will certainly be needed to fold the wings, as you show. The support bone may need to be hinged, to fold and unfold the wings.