Titanosaur front feet

[andrewsaurus rex]

when I got the Mattel  Dreadnoughtus, it was pointed out that it should not have any front toes and thus no toe nails or claws....after researching a bit I discovered this is because it is basically walking on its knuckles, so no toe nails or claws would be present.

After reading the review on Collecta's really nice Ruyangosaurus, I noticed it does have nails on the front feet and a claw on each inner toe....which I presume is correct.

So then, not all titanosaurs had the same arrangement to their front feet?  Some walked on their knuckles, while others essentially walked on their fingers and palms?

[DinoToyForum]

I asked sauropod researcher Mike Taylor this on Mastodon and he replied

"Off the top of my head, I think you're right [all titanosaurs completely lacked manual unguals]. But I've not really done much with titanosaurs, so take my opinion with a pinch of salt."

[Flaffy]

A couple of titanosaur genus have been found with phalanges preserved, with Diamantinasaurus and Tapuisaurus being the only two were we've recovered manual unguals.

Other basal members of Titanosauria might have retained their manual ungual, but advanced members most likely lost them alltogether.
Trackways from Late Cretaceous Australia indicate that some Australian taxa display the basal condition, but considering the geographic isolation of Australia, along with direct evidence of other advanced Titanosaurs lacking complex phalanges, it can be assumed that Australian titanosaurs were just doing their own thing.

Mind you, certain aspects of Titanosaur phylogeny is still a big mess, so things may or may not change in the future.

[andrewsaurus rex]

Interesting.  Are there any theories as to why they lost their manual unguals?  Was it simply because it gives a more solid support for the front feet?  Did they actually lose the toe, or I guess finger bones or did they just curl under, resulting in the animal essentially walking on its knuckles?

[Flaffy]

Interesting.  Are there any theories as to why they lost their manual unguals?  Was it simply because it gives a more solid support for the front feet?  Did they actually lose the toe, or I guess finger bones or did they just curl under, resulting in the animal essentially walking on its knuckles?

Probably the same reason why equids only have 1 digit nowadays, with vestigial structures being gradually phased out.

Sauropods have been loosing the individual functionality of their digits in favour of bearing weight throughout their evolution; so loosing them altogether would be the natural conclusion of that process.

Titanosaurs had highly reduced phalanges, to the point where in advanced taxa they were entirely absent. Meaning they walked on their metacarpals. Entire structures were lost. I guess you could say they walked on their knuckles; but instead of your fingers being curled under your palm, the fingers weren't there to begin with.

So then, not all titanosaurs had the same arrangement to their front feet?  Some walked on their knuckles, while others essentially walked on their fingers and palms?

No sauropods walk on their palms. They had digitigrade front limbs and plantigrade hindlimbs.

[andrewsaurus rex]

that's all very interesting thanks.

[Shane]

Titanosaurs had highly reduced phalanges, to the point where in advanced taxa they were entirely absent. Meaning they walked on their metacarpals. Entire structures were lost. I guess you could say they walked on their knuckles; but instead of your fingers being curled under your palm, the fingers weren't there to begin with.

I think, though this is the prevailing thinking, it's also theorized that some of this may be preservation bias. There is I believe some potential evidence of phalanges (or at least one phalanx) found in later titanosaurs, like Opisthocoelicaudia, which may indicate that phalanges might have existed in these dinosaurs, but might have not been preserved after death.

I think most paleontologists currently accept that derived titanosaurs probably lost their phalanges, but the matter isn't quite as settled (but what ever is in paleontology?).

[Halichoeres]

Which species exactly may have lacked phalanges is hard to know, since sauropod feet are notoriously rarely preserved (like their heads). You're left trying to interpolate from the small handful of taxa with a known manus, and even then, as Shane points out, whether the distalmost element never existed or has just been washed away is hard to know as well. But in terms of a reason that it might be useful to lack phalanges, it gives them one less point of failure in the forelimb. If you need little more than a pillar, having one less joint in it makes it more stable, uses less energy during walking, and reduces the risk of injury.