Spinosaur bones hollow?

[Daze]

I recently purchased this metatarsal that was described as coming from a Spinosaurus. A small piece at the end of the bone (bottom end on the photo) came loose so I had a chance to look inside the bone with a flashlight and noticed the bone is hollow inside. As far as I understand most theropod bones are hollow but Spinosaur bones are said to be very dense, to make it easier for them to submerge into water.

 

Now I'm a little confused, is it possible this isn't a Spinosaur bone but possibly from a Carcharodontosaur? @Troodon? 

Edited May 20, 2023 by Daze

[Opabinia Blues]

Do either of those two taxa have formally described metatarsals? If not then this bone may only be describable as Theropoda indet. but I suppose you could compare from closely related taxa.

 

As I understand it the bone density in Spinosaurus is based on the compactness of the spongy bone, so I don’t think that would necessarily preclude hollow bones as are typical for theropods. With aquatic vertebrates the greater bone density is usually most pronounced in the ribs and vertebrae and I would assume this would also be the case for Spinosaurus, so I don’t know how the appendicular bones would actually be affected if at all.

[Troodon]

These are not formally described but we have some photos/illustrations of Spinosaurus.  I would have called yours a Spinosaurid but agree with you it should not be hollow so that has me confused.   There are multiple Spinosaurids in the KK so not sure if there is a difference is bone density?

From Ibrahim et al. papers

Compare the proximal end of yours to the dorsal view "c"

 

 

 

 

On the Carch side we can look at the Holotype of the recently described Meraxes gigas from Argentina,   Canale et al. 2022.  Really not sure how these would compare to the Carcharodontosaurids in the KK?

 

[Daze]

Thanks guys and @Troodon thanks a lot for the photos. If I compare the proximal end of my bone to dorsal view 'C' of Spinosaurus I think it's a pretty good match with metatarsal II. Still a mystery why it's hollow though 

[Troodon]

I would call it Spinosaurid unless we learn something different.  I think the bone density studies were looking at least a femur, might be different on other bones or might be different on other Spinosaurids