The Reaping lizards: The Therizinosaurs

[Bokisaurus]

Something ugly joins the group
[]
I would not pay full price for schleich figures. I found these guys on sale for $2, so I got them
That beak on this figure, what on earth are they thinking? It looks like an ingrown nail stuck on the mouth

[LophoLeeVT]

ugly indeed!!!

[Derek.McManus]

  Your photo actually looks much better than the one in the catalogue lol

[Archinto]

Kindof bringing this slightly aged topic back to life, but really curious on their hands. Im going to make models of some therizinosaurs as time goes on, and looking at their hands, i find a lot of reconstructions to be somewhat not beleivable. Giant claws on separated fingers. One would think that under force, whether it be while feeding or defending itself, this creature would have often suffered from broken hand bones, which isnt really evident in the fossils. My thoughts are that the fingers would be flesh bonded with the claws close together much like a modern day three toed sloth. It would aid the animal greatly for grabbing heavy branches and stripping leaves off of smaller branches. It seems more beleivable to me if their phalanges were flesh bonded. What are your guys thoughts on this idea?

[stargatedalek]

Kindof bringing this slightly aged topic back to life, but really curious on their hands. Im going to make models of some therizinosaurs as time goes on, and looking at their hands, i find a lot of reconstructions to be somewhat not beleivable. Giant claws on separated fingers. One would think that under force, whether it be while feeding or defending itself, this creature would have often suffered from broken hand bones, which isnt really evident in the fossils. My thoughts are that the fingers would be flesh bonded with the claws close together much like a modern day three toed sloth. It would aid the animal greatly for grabbing heavy branches and stripping leaves off of smaller branches. It seems more beleivable to me if their phalanges were flesh bonded. What are your guys thoughts on this idea?

Most therizinosaurs are known from wet areas, Therizinosaurus itself was actually from a forested swamp if I recall correctly. They were probably decent swimmers, an idea also encouraged by the enlarged fourth toe. I'm not sure what that would mean in regards to fused fingers, but potentially relevant.

It's also possible they weren't using the claws so much to strip or even pull branches as to lift lower or even aquatic greenery within reach, while the long neck on its own was already enough to reach almost any branches the claws could. The claws don't really extend the reach that much further than the neck already does, even in the largest species it's only a couple more feet of reach.

The main evidence in favour of the fingers being separate is that they are quite mobile, and we see no change in this between large and small members. If the fingers were conjoined, there would likely be a decrease in individual digits mobility over time.

[Halichoeres]

That's a really fascinating hypothesis. Sloth phalanges have a really odd phalangeal morphology, with limited mobility relative to, say, armadillos. I looked up the hand anatomy in the Therizinosauroidea chapter in The Dinosauria (Clark et al.), because I didn't really know anything about it. In Therizinosaurus, the phalanges all have well-developed trochlear surfaces, which is consistent with a pretty high degree of mobility, at least in one plane (so they could curl their fingers, but probably not spread them apart very well). If that's true, then if the digits were going to be bound (syndactylous), they would have to have the joints precisely aligned so that they bent in unison. At first glance, at least, that's not what this looks like to me:



But I dunno, there's plenty of precedent for syndactyly: Ichthyostega, Anchiornis, lots of diprotodonts like this koala foot.


Or this kangaroo foot.


It's easy to make syndactyly happen, from a developmental genetics standpoint. Most vertebrates form the manus in a continuous mitten, and the digits are formed by programmed cell death of the tissue between them. It's not that difficult to change the degree of cell death, which is why semi-aquatic animals can evolve webbing so easily, and why humans are sometimes born with digits fused (I'll let you Google "human syndactyly" on your own). If fused digits had even a relatively minor adaptive advantage, you could evolve them without too much trouble.

I wonder if anybody has done finite element analysis of therizinosaur digits to see how much stress they can take. It might be more than it looks like, especially if they're well muscled, as Clark et. al suggest is the case based on ligament and muscle insertion points.

[Archinto]

Looking at several different skeletal hands, it looks lie the 2nd and third digits could be syndactylous up to the first knuckle, as the bones align up to that point. The hands were probably a lot fatter with muscle than some reconstructions show. I would imagine they would pull down tall thin trunked trees for feeding, or used their claws to dig up tender roots and other plants. Syndactyly would allow for stronger hands I think than fingers that are totally free flexing. It's an interesting concept to think on. Ill have to take a look at other therizinosaurids and see what their hands look like.

[ZoPteryx]

Looking at several different skeletal hands, it looks lie the 2nd and third digits could be syndactylous up to the first knuckle, as the bones align up to that point. The hands were probably a lot fatter with muscle than some reconstructions show. I would imagine they would pull down tall thin trunked trees for feeding, or used their claws to dig up tender roots and other plants. Syndactyly would allow for stronger hands I think than fingers that are totally free flexing. It's an interesting concept to think on. Ill have to take a look at other therizinosaurids and see what their hands look like.

Possibly relevant: there's an undescribed therizinosaur with a vestigial (or nearly so) third digit.  Almost certainly would've been bound to the second digit.

[Vidusaurus]

Looking at several different skeletal hands, it looks lie the 2nd and third digits could be syndactylous up to the first knuckle, as the bones align up to that point. The hands were probably a lot fatter with muscle than some reconstructions show. I would imagine they would pull down tall thin trunked trees for feeding, or used their claws to dig up tender roots and other plants. Syndactyly would allow for stronger hands I think than fingers that are totally free flexing. It's an interesting concept to think on. Ill have to take a look at other therizinosaurids and see what their hands look like.

The strengthening of the hand through syndactyly makes sense, especially with regards to your digging/semiaquatic hypotheses. I feel like they'd also have a lot more musculature in the arms and shoulders compared to what we usually see.
As an aside, it really grinds my gears that Therizinosaurs are the only major group of dinosaur that we don't have a decent model for at this stage.

[Halichoeres]

Hypothesis: it stinks.

Discuss.

[Halichoeres]

"Tiantai(o)saurus" by Vitae:

[Shonisaurus]

Thanks for posting that beautiful photo Halichoeres, without a doubt I really like Vitae's tiantaiosaurus especially because its sculpture is clean in the sense that it is not excessively sculpted in terms of exaggerated and marked reliefs of feathers, muscles and hair. I like the smooth texture of that Vitae figure, it is a very elegant detail from this brand.

[Fembrogon]

Hypothesis: it stinks.

Discuss.

I'm coming in on this very late, but it kills me that Papo managed to mess up the most distinctive trait of the dinosaur: the hands. Where are the 3-ft scythe claws??? Those look more like Deinocheirus hands!

[Stuckasaurus (Dino Dad Reviews)]

You know, the Therezinosaurus from the Jurassic World Captivz "blind bag" eggs makes for a really nice 1:40-ish Nothronychus!