Alvarezsauroid forelimb range of motion and myology support digging function (free pdf)

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

Free pdf:

Sidney Leedham, Zichuan Qin, Benjamin William Griffin, Antonio Ballell, Yilun Yu, Xing Xu & Emily Rayfield (2026)
Range of motion and myology support a digging function for the forelimbs of alvarezsauroid dinosaurs
Proceedings of the Royal Society B: Biological Sciences 293(2070): 20260565
doi: https://doi.org/10.1098/rspb.2026.0565
https://royalsocietypublishing.org/rspb/article/293/2070/20260565/481630/Range-of-motion-and-myology-support-a-digging


Numerous lineages of theropod dinosaurs display notable modification of the forelimb, particularly reduction in size and number of digits. Alvarezsauroids are one of the most striking examples of this, exhibiting extreme shortening and increased robusticity of forelimb elements, with a functionally monodactylous manus in late-diverging taxa. These features are generally interpreted as adaptations for digging, possibly as part of a myrmecophagous ecology. Here, we test this hypothesis, using computational range of motion analysis of the shoulder and elbow joints to demonstrate the feasibility of digging behaviours in Mononykus olecranus, a highly specialized alvarezsauroid, and the less specialized Bannykus wulatensis. We find that Bannykus has the capacity for various digging styles and generalized forelimb function, while Mononykus has more restricted motion and may have employed a highly specialized digging style. We also identify similarities in forelimb muscle moment arms between alvarezsaurs and specialized mammalian diggers, supporting adaptation for digging. These findings are consistent with interpretations of insectivory in alvarezsauroids, and suggest increasing specialization to myrmecophagy throughout their evolutionary history, shedding new light on the evolution of this enigmatic clade and the ecological diversity of non-avian theropod dinosaurs.

====

[Gregory Paul]

Mark Witton posted a podcast that favored the inflated Jackie Gleason mass values for Tyrannosaurus that have become the fashion these days, with up to 13 tonnes (2 X too heavy) for Sue! While disparaging my profile-skeletals and mass estimates, yet not bothering to show where they are in actual error in any particular regard. 

My reply is at https://gspaulscienceofnonreligion.substack.com/p/the-science-of-dinosaurs-more-tyrannosaurus

Its shows that digital scans of mounted skeletons can be fundamentally proportionally errant, and sometimes in surprising ways that I was not aware of until doing this. 

Enjoy, 

GSPaul

[Milo Gaillard]

Can you please post a link to the podcast you’re referring to in question?

Thank you,

-Milo

Sent from my iPhone

On May 13, 2026, at 15:02, 'Gregory Paul' via Dinosaur Mailing Group <DinosaurMa...@googlegroups.com> wrote:



--
You received this message because you are subscribed to the Google Groups "Dinosaur Mailing Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to DinosaurMailingG...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/261936577.1121884.1778709756783%40mail.yahoo.com.

[Gregory Paul]

It is at the beginning of the post, but here it is in case that one is not working. 

https://www.youtube.com/watch?v=-EGbqEEEQ0Y

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/9175D568-A6DC-4F49-B422-60991A46E280%40gmail.com.

[Milo Gaillard]

I saw that video. I didn’t know that Mark Witton “posted” it. Maybe he shared it somewhere.

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/848042680.1133079.1778716464435%40mail.yahoo.com.

[Gregory Paul]

Thanks for the clarification.

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CALaRhVz%2BiZp%2B%2B836VJ012G9TyOoYtA7bLCLpVoRxMF8Xwt57gQ%40mail.gmail.com.

[Milo Gaillard]

No problem. I’m only saying that, because the video was not made by Mark Witton. It was made by the Vividen.

Sent from my iPhone

On May 13, 2026, at 20:33, 'Gregory Paul' via Dinosaur Mailing Group <DinosaurMa...@googlegroups.com> wrote:



To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/732948162.1175386.1778729631288%40mail.yahoo.com.

[Tim Williams]

If I'm understanding the hypothesis here, the relatively longer forelimbs of _Bannykus_ could be used in an opportunistic manner to extract wood-boring termites.  The forelimbs of _Bannykus_ are relatively longer and less specialized than those of _Mononykus_, and therefore inferred by Leedham &c to have had a "wider functional repertoire than later-branching, highly derived parvicursorines" and is consistent with a "more generalist, faunivorous lifestyle" for _Bannykus_.  By contrast, in parvicursorines like _Mononykus_, the extremely short and highly specialized forelimbs were used to make the initial breach in rotting wood, after which it stuck its entire head in to extract termites. 

However, although the forelimbs of _Bannykus_ are not as reduced as those of _Mononykus_, they are nonetheless still very short.  I doubt they could have been used for predation.  Intestinal contents suggest _Bannykus_ had a carnivorous diet, but the forelimbs look way too short to have been used for catching prey.  (I suspect the same was even true for _Alnashetri_, where the "unreduced forelimbs" are only around ~60% the length of the hindlimbs.)  

The prevailing hypothesis is that as the forelimbs of parvicursorines became extremely short and highly specialized, they lost the prey-catching function of early-diverging alvarezsauroids.  But I doubt alvarezsauroid forelimbs had any prey-catching function to begin with.  

There was a time when I was skeptical of the idea that alvarezsaurids were myrmecophagous, and that their forelimbs were used for hook-and-pull digging.  That was until I read  Albertonykus' blog ( https://albertonykus.blogspot.com/2020/05/making-sense-of-alvarezsaurid.html ), which convinced me this was currently the best supported hypothesis.  Plus, as frequently mentioned, unlike myrmecophagous mammals, alvarezsaurids are obligate bipeds, so the forelimbs can be reduced because they don't use them for locomotion.  

Nevertheless, parvicursorine forelimbs aren't just short - they're *extremely* short.  This has perplexed me, and Leedham &c have come up with an explanation: the slender head and jaws took over the function of the forelimbs to extract termite prey.  

--

You received this message because you are subscribed to the Google Groups "Dinosaur Mailing Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to DinosaurMailingG...@googlegroups.com.

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CAMR9O1JvS2F8qRA1Ddfrxt9FxZcU%3DYzNdTpCt7MXJvOC%2B83w-Q%40mail.gmail.com.

[Jura]

Yes, I also don't buy much into the argument that being bipedal means that one can reduce one's forelimbs to nubs and still have them be "useful". Pangolins are bipeds and still have "regular" length forelimbs (long enough that people thought they were quadrupeds until they saw them moving). Stocky forelimbs are good for digging (e.g., moles). Short forelimbs are not the same thing.

[Mickey Mortimer]

The authors write "For the elbow joints, four simulations were run each for Mononykus and Bannykus; using CCFs [Cartilage Correction Factors] calculated from both the radius and ulna cartilage of Gallus, and for the radius and ulna values of Coturnix ... This was done to reflect the full spectrum of possible articular cartilage thicknesses...", as Coturnix values are more limited than Gallus (taken from Holliday et al. 2010). This makes sense as domestic chickens are generally not given time to ossify fully before adult size is reached. 

Under Results, they first say "Both simulations (table 1; MECgu, MECgr) using Gallus-derived CCFs for the elbow of Mononykus resulted in very large volumes of viable ROM [Range Of Motion], which are uninformative for interpretation of in vivo forelimb function so are not discussed further. Additional simulations run using the Gallus-derived CCFs, with a higher overlap threshold of 80% (significantly more conservative than thresholds used in other ROM studies, which often consider 50% overlap still to be in articulation [6,40]), also yield very large volumes of viable ROM, indicating that Gallus-derived CCFs are inappropriate for use in Mononykus. Therefore, the Mononykus simulation using CCFs derived from measurements of the ulna of Coturnix (table 1; MECcu) is selected as most appropriate for further discussion and for comparison with the results for Bannykus. Both Bannykus elbow simulations using CCFs derived from Gallus (table 1; BECgu, BECgr) retrieve similar results; the ulna CCF simulation results (table 1; BECgu) are selected for further discussion and comparison, and the radius CCF simulation is not discussed further. Henceforth, discussion of ‘6DOF’ or ‘cartilage’ ROM simulations for the elbow joints refer to the Mononykus-Coturnix ulna simulation MECcu, and the Bannykus-Gallus ulna simulation BECgu (table 1)."

So this is not my area of expertise, but wouldn't the large volume of viable range of motion using Gallus for Mononykus actually mean that we can't use these simulations to tell us much about whatever limits Mononykus had, since we can't say it DIDN'T have Gallus-level thickness? Instead the authors seem to want SOME answer, so they arbitrarily go with Coturnix-level thickness that provides more limitations.  Which wouldn't be THAT bad except their conclusion is-

"We find that Bannykus has the capacity for various digging styles and generalized forelimb function, while Mononykus has more restricted motion and may have employed a highly specialized digging style."  (from the abstract)
"Large extents of elbow flexion and extension are feasible in Bannykus; these are greater than in Mononykus."
"In Mononykus, however, the highly modified morphology of the forelimb appears to have resulted in a reduction in ROM at the shoulder and elbow joints. Elevation and depression of the humerus are lessened, as are extension and flexion of the elbow, indicating that forelimb function may have been more specialized."

So surprise surprise- Mononykus has more limited elbow mobility when constrained to have thinner elbow cartilage. The fact four of six mobility measurements using Gallus-level thickness are LESS restricted for Mononykus' elbow than Bannykus' would really seem to argue against a more restricted elbow in the former if anything. This is especially true given long-axis rotation and elbow adduction are actually MORE restricted in Gallus-level Bannykus than even Cotunix-level Mononykus! 

Now of course the authors measured one other joint too- the shoulder joint. "For the alvarezsauroid shoulder joint, avian CCFs were insufficient to fulfil the overlap requirements of the APSE algorithm, so the offsets were iteratively increased to find the closest viable offset", which is fine. I would say this supports Mononykus having at least a more limited range of motion in the shoulder than Bannykus, except we have sentences like-

"In fact, the degree of [shoulder] retraction retrieved is anatomically unfeasible, taking the humerus underneath the scapular blade..."
"Similarly to Mononykus, biologically unfeasible humeral retraction is reconstructed..."
"A large degree of possible elbow abduction is retrieved; this is biologically unfeasible..."

As far as I can tell, there's no table listing ranges of motion when biologically unfeasible positions are excluded, so the provided numbers seem less useful. Overall I'm skeptical this type of analysis can tell us much, especially based on Table 5 of Carpenter and Wilson (2008), who found the following in Gallus for all soft tissues intact versus no skin or muscle-
Shoulder flexion- 40 degrees vs. 90
Shoulder extension- 10 degrees vs. 70
Elbow flexion- 5 degrees vs. 90
Elbow extension- 60 degrees vs. 70

So the in vivo range of motions looks to be less than what bone and cartilage would suggest by themselves, sometimes but not always by a huge margin. And considering just how different alvarezsauroid shoulder and elbow joints are from chickens', I don't think it would be safe at all to extrapolate and say "reduce the calculated shoulder flexion by 55%" or something. So did Mononykus have a smaller range of forelimb motion than Bannykus? I don't think this study can tell us.

Reference-  Carpenter and Wilson, 2008. A new species of Camptosaurus (Ornithopoda: Dinosauria) from the Morrison Formation (Upper Jurassic) of Dinosaur National Monument, Utah, and a biomechanical analysis of its forelimb. Annals of Carnegie Museum. 76, 227-263.

Mickey Mortimer

[Alberta Claw]

Almost all species of pangolins are habitual quadrupeds that occasionally use bipedal locomotion, as described in the detailed species accounts in Challender et al. (2020). The ground (or Temminck's) pangolin is the only one that is mostly bipedal (though not entirely—"the forelimbs are used to scale obstacles"), and indeed the "forelimbs are considerably reduced" compared to those of other pangolins.

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/8ca165e2-2e7b-4852-87b4-9bb04ad2cb09n%40googlegroups.com.

[Jura]

Define "considerably reduced".

[Jura]

So, I did some digging (LOL) into the Challender et al. book and I can see the part where they mention the considerable reduction of the forelimbs. I also noticed this:

"Further, because Temminck’s pangolins are mostly bipedal, and do little digging, their forelimbs are considerably reduced compared with giant pangolins, which have a preponderance of bone and muscle at the front end (Kingdon, 1971). This difference is also noticeable in the structure of the pelvis, which is robust, elongated and more horizontal in the former, whereas the pelvis is more lightly built, shorter and more vertical in the latter (Kingdon, 1971)"

According to this, our obligate biped is not much of a digger at all. Kingdon gets cited a lot. Unfortunately, Kingdon is a textbook with no real citations behind what the author states. The tone is fairly laid back. According to Kingdon 1971:

"The ground pangolin, Manis temmincki, does very little digging and has relatively insignificant forelegs, this species is capable of bipedal walking and running and carries most weight on the hindlegs. An opportunity to appreciate the relative unimportance of digging for this species was offered a when I was sent an old female M. temmincki that had lost a front leg at the elbow. The stump had healed perfectly and was clearly several years old, note withstanding this she was fat, healthy, pregnant and also with a young one at heel."

It's all very qualitative, and the purported evidence for unimportance of digging is pretty weak. There is a study by Steyn et al. (2018) on the forelimbs of (now) Smutsia temminckii, but it's done in isolation with no mention of hind limb proportions.

[Alberta Claw]

The Challender et al. volume has a bit more context on what is known about the role of digging in that species, the most relevant passages probably being: 

• "The species tends not to dig burrows, instead using the abandoned burrows of other species [...], modifying them to some degree."
• "Rarely, dispersing individuals may dig a burrow in soft sand, but these are typically not very deep (<0.5 m in depth) and do not afford much protection (D.W. Pietersen and W. Panaino, pers. obs.)."
• "The muscular forelimbs and strong front claws are used to tear open terrestrial ant nests, scratch away cartilaginous material from termite mounds, and tear away bark on dead trees when foraging, enabling access to prey. At epigeal ant nests, the species typically digs only shallow holes (5–10 cm deep) [...]"

Many of the field observations in the chapter are cited to Swart's ground pangolin entry in the Mammals of Africa series (edited by Kingdon et al., 2013), though Swart et al. (1999) covers some feeding behavior.

Based on this, they certainly seem less inclined to dig than some other terrestrial pangolin species (the Chinese pangolin for example has been recorded making burrows over 5 m and allegedly up to 10 m deep), but do dig for foraging purposes and limited burrow construction/modification.

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/a6f411a6-1305-4e7b-ac66-fb3ee686f701n%40googlegroups.com.