• Question from:Ed Dowdall

Hello.

The question has been continually asked "what purpose did the small strong forearms of t-rex serve?".
Theories seem to be few and far between, so I'd like to add my voice to the discussion and perhaps you can tell me if my line of thinking has any possibility of being plausible!

My theory hinges totally on an associated question of what the habitat was like where t-rex lived.
All of the "dinosaur-book" pictures usually show t-rex running across a sparsely vegetated rocky plain, in hot pursuit of some other creature, or in a death grip with a triceratops.  (reference i.e. http://www.prehistory.com/timeline/cretace.htm)

What I want to believe is that the world of t-rex was anything BUT arid.
I'm thinking instead thick vegetation, jungles, swamps, trees and brush so thick that we would find such a world completely impassable.  But not t-rex nor many of the other giant creatures of the Cretaceous period.

Can you answer that first question for me?
Could the normal habitat of t-rex have been densely vegetated jungle?

Once I have that answer, I'd like to share my idea of the possible purpose of those short fore-arms, if you haven't guessed at my thinking already!

Thanks,

Ed Dowdall
Granite Springs, NY
P.S.  I suggested this theory to someone in your field a number of years ago, but never received any response.  I hope to hear back from someone, if even to say "no one knows for sure".

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  • Horniman Museum, London, UK
  • Posts: 1,105

Hi Ed, sorry you've waited so long for a reply - I assumed one of our resident palaeontologists would have tackled this question ages ago - I guess they've been away on fieldwork.

To the best of my knowledge T. rex lived in well vegetated habitats, but since this is not my field of expertise I'll need to check some more literature.

I think the idea that the reduced limbs are an adaptation to moving about in a dense environment has merit. My personal opinion is that T. rex relied mostly on it's jaws for manipulating prey and longer arms were simply not advantageous (and possibly disadvantageous due to habitat constraints). I can imagine the arms being useful during mating or for getting onto the hind legs after laying or falling down.

I hope some more ideas are added!

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  • School of Earth Sciences, University of Bristol, Bristol, UK
  • Posts: 306

I don't think the habitat in which T. rex lived in was a dense jungle like the Amazon. I haven't read much on palaeoenvironments so I may be wrong, but my impression is that the Late Cretaceous of North America is pretty arid.

That aside, the reduction of forelimbs in tyrannosaurs coincide with an increase in skull robustness so it may have something to do with compensating mass-distribution?

I don't think there's any single right answer to this question yet.

Tyrannosaurus inhabited a fairly wide area (from as far south as New Mexico to as north as Saskatchewan), and must have occurred across a wide variety of habitats: from fairly arid scrublands to well-vegetated, moist, sub-tropical woodlands. The locations that have yielded most Tyrannosaurus fossils however - the various locations in Montana, for example - also preserve a flora, and an assortment of sediments, that suggest sub-tropical woodland habitats with frequent rainfall. This habitat wouldn't be called 'jungle', it is properly called riparian woodland (riparian means 'associated with the banks of streams or rivers').