Comments on: A Mysterious Thumb

By: the layman

the layman — Thu, 05 Jan 2012 17:53:50 +0000

I’m thinking it probably was a weapon. It is true that Iguanodon would have to be within biting range to use it but, it surely wasn´t running after theropods to stab them!- it would have used its thumb spike as a desperate measure once the theropod had already caught him!
Just like platypus will only stab when caught, they always prefer to swim away. Why would Iguanodon be any different?

By: Zach Miller

Zach Miller — Thu, 29 Dec 2011 19:51:27 +0000

It IS a modified digit I.

By: Matt Martyniuk

Matt Martyniuk — Wed, 28 Dec 2011 20:48:50 +0000

“The peculiar false thumb of Iguanodon”

Wait, is it really a false thumb, i.e. modified carpals like that of a panda? I always assumed it was a modified digit I.

By: Leigh

Leigh — Wed, 28 Dec 2011 03:16:03 +0000

He stuck in his thumb, and pulled out a plum, and said what a good dinosaur am I?

Seriously, it would be nice to know what the critter was eating. Its hands are so interesting, with the thumb spike on one side and another thumb on the other – an opposable pinkie? It was doing something really interesting with its hands.

By: HCA

HCA — Wed, 28 Dec 2011 01:53:58 +0000

Just FYI for testing these hypotheses – trabecular bone will align with principle axes of loading. Look at the inside of a femur for an excellent example. If the trabeculae show no alignment, it must’ve been exposed to minimal forces, while alignment will show whether it was loaded in shear, compression, bending, etc. A good mini-CT scan should work, or a micro-CT with a large bore.

By: Heinrich Mallison

Heinrich Mallison — Tue, 27 Dec 2011 22:50:51 +0000

Quite obviously, those thumbs were designed for eviscerating and obliterating obnoxious bloggers!

By: Torbjörn Larsson, OM

Torbjörn Larsson, OM — Tue, 27 Dec 2011 21:38:07 +0000

Okay, I give, it is a twitter # tag. Dunno what it stands for, but it looks to be a result of a Switek – Young mock fight.

By: Torbjörn Larsson, OM

Torbjörn Larsson, OM — Tue, 27 Dec 2011 21:35:38 +0000

“What’s “GRAWR!”?”

It is googleable, that’s what it is. Also fun, when you locate it – take a gander at Ed Young’s birfday cakez.

By: Mike Keesey

Mike Keesey — Tue, 27 Dec 2011 20:22:48 +0000

What’s “GRAWR!”?

Interesting about the brotothere and ruminant parallels.

Come to think of it, the hadrosauriform Ouranosaurus has a (secondarily?) small thumb spike, and a rather prominent display(?) structure, although it’s a dorsal sail rather than a head crest.

This doesn’t quite explain all those hadrosaurs with no cranial ornamentation (including many basal forms), though. But it’s an interesting angle, nonetheless.

By: Kathy

Kathy — Tue, 27 Dec 2011 19:26:41 +0000

Maybe, its purpose was for some sort of grooming.
I know that this might be far-fetched. But, some animals have adaptations for grooming.

By: Anonymous

Anonymous — Tue, 27 Dec 2011 18:36:55 +0000

“2.Maybe they were used for reviewing movies or determining the fate of gladiators.”

This totally needs to go on GRAWR!

“3.In seriousness, though, the evolutionary trajectory of the thumb spike is odd. Starts off small, in basal ankylopollexians, reaches its maximum in Iguanodon, then abruptly shrinks again in basal hadrosauriforms, only for the digit to be completely lost by the time hadrosaurids appear. (At least that’s my understanding of its trajectory–not sure if that’s out of date or not.)”

Actually, that might actually point to something. In many groups of horned mammals like brontotheres and deer, basal forms have large canine teeth used for intraspecific combat (and also defense). But once horns start showing up, the canine teeth become less and less prominent, until they are completely lost altogether. Perhaps this is what occured in iguanodontians. The thumb-spike functioned as some sort of intraspecific combat weapon (perhaps akin to the spurs of male chickens), and then as flashy crests and vocalization began to become more prominent the thumb spike starts shrinking and eventually vanishes.

By: Mike Keesey

Mike Keesey — Tue, 27 Dec 2011 16:29:06 +0000

In seriousness, though, the evolutionary trajectory of the thumb spike is odd. Starts off small, in basal ankylopollexians, reaches its maximum in Iguanodon, then abruptly shrinks again in basal hadrosauriforms, only for the digit to be completely lost by the time hadrosaurids appear. (At least that’s my understanding of its trajectory–not sure if that’s out of date or not.)

I don’t have an answer for why it’s so large in Iguanodon, but I’ll bet figuring out its function in other ankylopollexians would shed some light.

By: Mike Keesey

Mike Keesey — Tue, 27 Dec 2011 16:24:23 +0000

Maybe they were used for reviewing movies or determining the fate of gladiators.

By: Jon Tennant

Jon Tennant — Tue, 27 Dec 2011 14:26:16 +0000

An interesting point! It is an odd structure, especially compared to the ‘standard’ morphology in other ornithopods. We need to find a fully articulated forelimb and manus, and then test ranges of non-linear motion etc. Or find one stuck inside a Mesozoic coconut..