Tag Archives: metacarpal

Tapejara’s hands and feet

It was challenging to make such small bones. The metacarpals were the thinnest ones and the phalanges of the feet the smallest. I obviously didn’t make them hollow since they are thinner than my 2mm thick sheet of foam, but I did try to. I made hollow fingers, but later reduced their width by pressing and by using fire. That made them stronger (although the result was a bit thicker than I expected). Since they are small and very fragile, I can’t pin them together (I would need some micropins for that), so I already covered them with epoxi resin. Here are the pictures.

This is a metatarsi from one of the feet, before treating with fire and resin.

Metatarsal

Here I try to fit the bones in place to make adjustments. The images from SMNK PAL 1137 are very bad but I used it to get the proportions of the metatarsi and the first toe phalanx and toenail. I initially then used as sources individual photos of Tapejara foot bones, but they are usually in unprepared blocks and not always entirely visible, and sometimes damaged. So my measurements didn’t match. I also looked at several well-preserved photos of different species (like SMNK PAL 3830) but then adapted a generic layout from Wellnhofer’s handbook for Pteranodon, scaled for Tapejara. It seems that the smalled phalanges are a bit smaller in Tapejara, and I tried to make them a bit smaller. Here are the bones of the feet after attempting an assembly.

assembly

And these are the hand fingers (I made the phalanges hollow).

finger assembly

I pinned the fingers to the wing metacarpal to try it out.

hand testing 2

hand testing

Then I pinned all these little bones on a surface to apply the epoxi resin.

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I feel like leaving it this way ūüôā A Tapejara bone graveyard under an unknown Azhdarchoid skull.

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Here are all the shiny parts after the resin dried.

shiny

These are the toe bones. Each square measures 5mm (remember this Tapejara was scaled up 25%).

toe set

And the bones in place (I will make more adjustments when I connect the bones together with silicone rubber).

toe assembly

Get these rocks and assemble a pair of hands?

finger set 2

finger and metacarpal 2

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Tapejara wings

The wing is a giant finger, and fingers are connected to the radio/ulna pair by several small bones called carpals and metacarpals. I’ll leave the carpals for another opportunity and concentrate on the metacarpal and four phalanges of the wing.

The wing metacarpal is a big bone, about the size of the radius and ulna and even wider on one end. The wider end articulates with the radio-ulna pair through the carpal bones, and the other is a hinge for the first phalange of the wing – the longest bone in the Tapejara body.

I used SMNK PAL 1137 as a source, but had to rely on Tupuxuara for some details. They are similar. I got the length dimensions from Brian Andres’s database (scaled 25%). I used the same process I employed on the other long bones. Cut two halves, shape, glue together, fix with fire, add ends in thicker foam and reshape.

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After the metacarpal comes the long first phalanx. This one I could rely on a picture I have from IMCF 1061 (which was perfect, since the quality of the pictures in SMNK PAL 1137 is very bad).

This bone has a flattened shaft, so it has greater resistance to anteroposterior forces than to dorsoventral ones.

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You can see I added a thin strip of plastic to the middle of the bone. Does that increase resistance?¬†I measured it. A strip of 2mm foam 20 cm long ¬†and 7mm wide attached on one end (1cm for attachment) can support 7 grams on the other end before folding (forcing the weak narrower side). Treating it with fire made it resist more, but it cracked with 9 grams. The phalanx has two of these strips, and is a bit hollow (I glue them on the edges, slightly curved). I made a prototype which supported 20 grams before cracking. Adding the strip won’t keep it from bending, but will avoid a destructive bend in one place or cracking. I expect that resistance to increase when I add the acrylic resin, and even more after the epoxy resin coating. Anyway, the maximum of weight the phalange will have to bear (considering only support on the proximal end) is 7 grams (considering the other three phalanges already coated with resin and epoxy and connected with silicone rubber). They currently weigh less than 5 grams (no epoxy coating yet) and they still have some water from the acrylic resin to evaporate.

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Here are the finished bones of the first phalanx compared to an unfinished humerus and the neurocranium.

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Some closeups and other angles.

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Testing the articulation with the metacarpal.

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The articulation with the radius-ulna pair is still not possible because there are yet no carpals.

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Next step: the other three phalanges. In fact I already had them all cut out and the haves attached before I did metacarpals and radius-ulna pairs. All these unfinished bones fit nicely on top my computer.

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So I tested the wings before I made these bones.

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And here is the final result. I used IMCF 1061 as sources for phalanges 2 and 3, and Tupuxuara for the last phalanx. I also used measurements from Brian Andres (scaled 25% as usual, since this is a larger specimen).

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Here is a detail of the last phalanx and articulation.

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And the full wing (I still hadn’t finished the humerus).

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Now we can place the bones on a surface and imagine the full skeleton.

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Pterosaur claws

I have several photos of individual finger bones from yet undescribed species which might be Tupuxuara. I also have pictures of the fingers of Tapejara wellnhoferi. But I only have photos of the bones of Tapejara from one angle, in black and white and in low resolution, so I can’t really see if they are flattened out, or curved in some direction. I assume they are straight comparing to the other photos I have (unfortunately I can’t post any of those pictures here, since they are all unpublished research). I compared different drawings of pterosaur hands and they seem quite similar. The number of phalanges is the same in all pterosaurs. Including the nails, the pattern for fingers 1-4 (where 4 is the wing)¬†is 2-3-4-4. The sizes, the widths and the shape (curved, straight, flattened) of the phalanges differ across different species. As to the proportions, I found no great differences between some drawings of Tupuxuara hands (from which I have no sources), Tapejara and Pteranodon. So I used¬†this drawing by Wellnhofer, scaled it to mach the size of my Tupuxuara skeleton, and used it as a guide to carve the fingers.

Here are the fingers and metacarpals after carving.

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These are the finger bones and nails before assembly. I already pinned the metacarpals together.

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I have to turn the metacarpals a bit, but this is how the fingers will be assembled.

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Here are Tupuxuara’s claws after assembly. I am using pins to test, but I will later keep the fingers and metacarpals together using some cartilage (silicone rubber). If I use pins all the time it will weaken the foam.

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Now I placed the metacarpals back on the skeleton with the claws in place.

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Here are some other angles showing the left hand.

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This is the right hand.

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A hand bone

Tupuxuara has four metacarpals. One for each finger. The fourth finger, of course, has a larger one. This post is about metacarpal #4.

DCF 1.0

We only have four views of each one. Very good pictures, but no distal and proximal views of the bone ends. So I have to guess what they look like from the pictures.

The bone shafts are somewhat cone shaped, a bit flat on one side, narrow and rounded near one end (distal) and triangular at the other end (proximal). I started with a sheet of 5 mm foam for each one.

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Folded and twisted until I could roll it into shape.

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Rolled it. Held everything in place with rubber bands. Then I made the bone ends with thicker (3 cm) XPS foam. I made the shaft slightly longer so I could insert it into the wheel-shaped distal end.

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When they were dry, I did some trimming, shaping and texturing with a knife and a lighter.

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And this is the result. Four views. The pencil is 16 cm long.

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This is the distal end (the end that connects to the first phalanx of the fourth finger).

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And this is the proximal end which connects to the distal carpal (wrist).

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That’s only one metacarpal. I need three more for the small fingers. They run parallel to the big one and are connected through¬†cartilage¬†and muscles. But I will finish the humeri and radio-ulna pairs before making them.

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