Hypothetical armless T. rex descendant

[Vladimír Socha]

Good day!

I was also wondering, if T. rex wasn't wiped out by the K-Pg catastrophe 66 mya, and would be able to evolve a few more million years, could it then become completely armless? So that the rudiments of its front legs would be completely covered by the skin and soft tissue, as the hind limb remnants of some recent cetaceans? Also, could its skull grow even larger and more robust? Thank you in advance! Sincerely, VS.

[Mike Taylor]

Could we maybe have just ONE thread that's not about tyrannosaurs? Even Tom Holtz must be getting bored of them by now.

…

Just kidding, do go on. Of course, this group is for discussion whatever its members want to discuss. But it's quite striking how completely that one insignificant family is dominating this group now. Maybe we should rename it the TMG.

-- Mike.

On Wed, 16 Jul 2025 at 13:03, Vladimír Socha <vladimir....@gmail.com> wrote:

Good day!

I was also wondering, if T. rex wasn't wiped out by the K-Pg catastrophe 66 mya, and would be able to evolve a few more million years, could it then become completely armless? So that the rudiments of its front legs would be completely covered by the skin and soft tissue, as the hind limb remnants of some recent cetaceans? Also, could its skull grow even larger and more robust? Thank you in advance! Sincerely, VS.

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[Andreas Johansson]

There was a similar discussion here a while ago. 

The only (known) example of theropods completely losing their forelimbs is the moa, while there are plenty of lineages that strongly reduced them but didn’t go entirely armless. So while it has to be *possible* that Tyrannosaurus descendants would completely lose their arms, it’s probably not very likely. 

—
Andreas Johansson

On Wed, 16 Jul 2025 at 14:03, Vladimír Socha <vladimir....@gmail.com> wrote:

Good day!

I was also wondering, if T. rex wasn't wiped out by the K-Pg catastrophe 66 mya, and would be able to evolve a few more million years, could it then become completely armless? So that the rudiments of its front legs would be completely covered by the skin and soft tissue, as the hind limb remnants of some recent cetaceans? Also, could its skull grow even larger and more robust? Thank you in advance! Sincerely, VS.

--

[Thomas Richard Holtz]

Hah!!!

But yes, to be fair: it would be refreshing to see more threads not about either tyrannosaurs, etymology/nomenclature, or the origin(s) of flight.

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[Thomas Richard Holtz]

Greg Paul himself speculated (and illustrated!) this in his review of Dougal Dixon's The New Dinosaurs back in 1990. Thankfully, Paul has a pdf of that paper publicly available at his website, at http://gspauldino.com/Tertiary.pdf 

On Wed, Jul 16, 2025 at 8:03 AM Vladimír Socha <vladimir....@gmail.com> wrote:

Good day!

I was also wondering, if T. rex wasn't wiped out by the K-Pg catastrophe 66 mya, and would be able to evolve a few more million years, could it then become completely armless? So that the rudiments of its front legs would be completely covered by the skin and soft tissue, as the hind limb remnants of some recent cetaceans? Also, could its skull grow even larger and more robust? Thank you in advance! Sincerely, VS.

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[Gregory Paul]

I did that piece as a counter to what I thought was Dixon's going too far with his speculations. 

Whether if the many sorts of tyrannosaurs running hinder and yon at the end of the Mesozoic would have lost their forelimbs entirely is open to question. After the teeny armed tyrannosaurids appeared in the Campanian they were not showing dramatic signs of further reduction. 

Also of interest is what robust T. rex and comparatively gracile T. regina living at the same time at the end of the Maastrichtian, would they have continued to divergently evolve into distinct genera, like albertosaurs and daspletosaurs dwelling in the same habitat? 

GSPaul

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[Gregory Paul]

And moas were island animals, not continental. I remain very irritated that people ate them all just a thousand years ago. 

GSPaul

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[Milo Gaillard]

To Gregory Paul,

Actually, more like 580 years ago. Moas are said to have went extinct on 1445. Sorry, I just felt like saying that.

Thank you,

-Milo Gaillard 

[Milo Gaillard]

To Mike Taylor,

You don't get it man, T. rex is THE KING! T. rex can destroy ANYTHING! T. rex grows like a teleost fish, which is crazier than any amniote, man. Young T. rex ate and outcompeted every mid-sized predator in its sight, with none being able to COPE or COMPETE against the almighty king! T. rex was also as smart as baboons (but still not as smart as elephants, lol). Why? Because a neurologist (someone who works on brains) said so! T. REX CULTURE MAN!

Ergo, its sheer royalty means that it's part of a royal bloodline. Therefore, tyrannosauroids (as a whole) are 1000000% more significant than ANY OTHER DINO! INCLUDING THOSE SCRAWNY ALLOSAUROIDS!

(BTW, this is a joke in case that wasn't obvious)

BOW TO THE KING

-Milo Gaillard (ultimate T. rex fanboy)

[Gregory Paul]

About a 1000 years ago the moas were doing fine:) In a few hundred years wiped out for drumsticks and omelets:(

Elephant birds lasted until about 1000 years ago despite Madagascar being inhabited for a long time prior. Apparently hunting adults was discouraged. Their eggs made fine eating though. 

GSPaul

https://groups.google.com/d/msgid/DinosaurMailingGroup/bb5abfba-d876-4ca2-a01b-d15703a01c84n%40googlegroups.com

.

[Gregory Paul]

Of course the big downside of eating moas was no spicy buffalo wings. Or white breast meat. 

https://groups.google.com/d/msgid/DinosaurMailingGroup/788213442.1220820.1752677972279%40mail.yahoo.com

.

[Jaime Headden]

In order to advance this idea for one, it'd probably be more likely at this point to see armless pachycephalosaurs, noasaurids, or carnotaurine abelisaurids, to be frank.

Cheers,

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Jaime A. Headden

The Bite Stuff: http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth" - P. B. Medawar (1969)

[Jacqueline Silviria]

Maybe some of them could have their brownie batter eaten by paraselenodonts. ;)

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[Dawid Mazurek]

My idea was that tyrannosaurids' arms were RELATIVELY small, but nowhere on a path to becoming vestiges. Abelisauroids would be better candidates, but I think the realm of the what-ifs is far from scientific way of thinking. Reminds me of "who would win a fight, a tyrannosaur or a godzilla?"

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[Gregory Paul]

Well obviously Godzilla since it was vastly bigger and had the atomic breath and all. 

GSPaul

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[Jaime Headden]

You'd be right:

Tyrannosaurin forelimbs remain functional, despite their size, without the reduced joint surfaces or deformation that happens when there's a reduced constraint on the limb's mechanical loading. The limbs were functional, and employed, as muscle attachment sites attest.

In contract, almost all abelisaurid, especially carnotaurine, forelimbs known are effectively a squat, small humerus with hypotrophies epiphyseal and articular surfaces, indicated a reduction in loading and strain on the forearm and manus, which have been reduced to mere gnarled digits. Not even the flat, non-functional joints seen in some avialaean phalanges when there's a lack of flexure. Those limbs become glorified humeri, not unlike that seen in hesperornithines or kiwis (or, hypothetically, Sharovipteryx).

Noasaurids maintain what seems to be a functionally tridactyl manus at the end of a functionally reduced forelimb, except when you get to the ostensibly herbivorous taxa, in which case not only does the forelimb get smaller, they lose the third digit. Yet the forelimbs maintain functional degrees of movement and muscle attachment without any distinct reduction in articular range of motion or a lack of constraint on their morphology given loading strain and the like. So the limbs were being used as such. Similarly, oviraptorosaurs show two independent forelimb reduction events: first with Caudipterids, reducing both element size and digit count; then again with heyuannine oviraptorids, in which the forelimb became reduced overall, but was relatively robust; and then a third further event with Oksoko (digit reduction and forelimb size). This happened gradually towards the end point of these derived groups, although we lack intermediate taxa between a Masiakasaurus-like noasaurid and a Limusaurus-like one.

Similar to noasaurids, pachycephalosaurids also show extremely reduced forelimbs, with some of the proportionally shortest humerus-femur ratios in all Archosauria (when both are present), but retain articular and morphological "limb-ness,"  indicating that, like tyrannosaurids and almost all other taxa mentioned, the manus was likely still engaging foodstuffs or conspecifics, such as through combat. I'm not actually familiar whether a complete pachycephalosaurid forelimb is known, but digit reduction would be likely down from four functional to perhaps three, or even two.

All these taxa arrived at their forelimb reduction regimes independently. Vestigialization would need to be accounted for with high sampling and phylogenetic constraints, showing a trend towards reduction, muscle attachment reduction, articular mobility reduction, reduced constraints on functional use of the limbs, or some combination of the above; this isn't an exhaustive list. The trends are typically distal to proximal, suggesting that the humerus may still have functional constraints even devoid of any mechanic value for the limb, such as supporting shoulder muscles---as, indeed, almost all short-forelimbed taxa mentioned here tend also to have extremely large scapulae, coracoids, or both, and may even have enlarged sternae, demonstrating a movement of forelimb-relation function to the shoulder. Given that several important shoulder muscles insert onto the humerus (e.g., mm. pectoralis, components of the serratus group and latissimus dorsi, which stabilize the scapula relative to the trunk and neck.

Some arguments for tyrannosaurin forelimb reduction apply here: Reduction of forelimbs advantages transfer of muscle mass to the shoulder-supporting muscles of the neck and torso, which can equate in some taxa to increased use of the head and neck for incurring high strain (tyrannosaurs, abelisaurids, pachycephalosaurs) or as a passive effect of reduced reliance on forelimb function relative to the hindlimbs or head in food acquisition or agonistic behavior.

Cheers,

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[Tim Williams]

Were the hands of a pachycephalosaur able to reach the mouth?

(The shuvosaurids, also herbivores, have forelimbs that are highly reduced - though not the scapula.)

[Jaime Headden]

I'd argue it was possible without doing any range of motion or flexibility analyses: the necks of some pachycephalosaurids (e.g., Sandy) suggest a strong upturn that may have inhibited ventroflexion, though Bakker et al (2006; "Dracorex") illustrated the partial neck of TCMI 2004.17.1 as being largely straight, CV9(?) has a typical slightly upturned cranial facet of the centrum. While this may be exaggerated with ontogeny (as "Dracorex" is based on an immature specimen with open neurocentral and cranial sutures), I doubt that would impair hand-mouth contact or manual grooming. The size of the head could offset limited ventroflexion, while the occipital condyle is large and offset from the neck, with large, ventrally positioned basal tuberae. The shoulders should be mobile.

Cheers,

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[Ethan Schoales]

What did tyrannosaurs use their arms for if they were functional?

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[Jaime Headden]

I think the best option we have is (barring some miraculous discovery that they could, in fact, do a push up) sexual and fitness signaling. It's plausible they would have been ornamented, colored, and been able to engage in some manner with their social-sexual partner, or helped groom one another.

Cheers,

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[Tim Williams]

Andreas Johansson <andr...@gmail.com> wrote:

> The only (known) example of theropods completely losing their forelimbs is the moa, 

Yes, in moa the only remnant of the wing is a diminutive scapulocoracoid.

Someone should write a book about moa evolution - call it "A Farewell to Arms".  Or is that title already taken...?

[Gregory Paul]

The recent Tyranno chat was associated with the publication of my megapaper on the subject. And I was the one who happened to kill off most of it off with my post on Friday where I complained about aspects of the discussion up to then. Including apparent failure of many to be famiiar with the published data and analysis. To my surprise it came the thread came to a screeching halt. I like to think because I pointed out that actual juvenile Tyrannosaurus specimens are very different from the basal eutyrannosaurs that are not juveniles. And because it is pretty apparent that the ETRH will soon collapse when Bloodly Mary is described, so why defend the zombie theory. 

GSPaul

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[Richard W. Travsky]

For those remains where the forearm claws themselves are present, what type of wear do they show (that might indicate what they were used for)?

 

From: dinosaurma...@googlegroups.com <dinosaurma...@googlegroups.com> On Behalf Of Jaime Headden
Sent: Wednesday, July 16, 2025 11:04 PM
To: DinosaurMa...@googlegroups.com
Subject: Re: [DMG] Hypothetical armless T. rex descendant

 

I think the best option we have is (barring some miraculous discovery that they could, in fact, do a push up) sexual and fitness signaling. It's plausible they would have been ornamented, colored, and been able to engage in some manner with their social-sexual partner, or helped groom one another.

 

On Wed, Jul 16, 2025 at 7:25 PM Ethan Schoales <ethan.s...@gmail.com> wrote:

 

[…]

[Sean McKelvey]

I don't think the bony core of the manual unguals would show any wear as they would have been covered in a keratin sheath in life?

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