Re: gastroliths (was Re:Giant carnivorous geese)

["Steve Brusatte" <dinoland@lycos.com>]

On Sat, 24 Aug 2002 23:27:02  
 calzola wrote:
>***as I wrote, I've heard use of gastroliths has been reported for crocs (in
>that case they were talking about Nile crocs) ...and they're certainly
>carnivorous

Yeah, but up until your post I hadn't heard about that.  But, after searching 
through the archives, I found a post by HP Darren Naish that mentioned, among 
other carnivorous animals, some crocodylians, otariids, and predatory birds 
possess gastroliths.  In addition, the ant/termite eater _Proteles_ also does.  
Interesting.  Not widespread...but some carnivores do indeed use them.  

>phillidor11@snet.net  commented:
><<The implicit question is whether use of gastroliths could develop
>in a carnivore or might it be an indication that the animal was
>a herbivore that became an omnivore or carnivore?
>No axe, or stone, to grind, but I'm wondering if use of gastroliths
>has anything to say about ancestry.>>
>
>***** I _think_ erbivorous diets have never been really common amongst crocs
>; therefore I assume the use of  gastrolithgs _by crocs_  has always had to
>do with their carnivorous diets (i.e. evolved  in animals that were already
>eating flesh, as it more likely for extant crocs to have had meat-eating
>ancestors than plant-eating ones if what i said before is correct  )

Certainly herbivorous crocodylians are rare.  _Simosuchus_, the pug-nosed 
Malagasy form, immediately comes to mind (it's so crazy looking), but it's long 
extinct.  AFAIK, no modern crocs are exclusively herbivorous.  So, in the Nile 
crocodile, I would tend to say that gastrolith possession represents a unique 
adaptation or behavior unrelated to ancestry, but I could be wrong.

>Since we've seen how those stones have been found in association with
>presumed strictly carnivorous and erbivorous forms (fossil or living ones),
>i think their presence may have little ,if anything, to say about the
>ancestry of the animal those pebbles are found in; it's, however,
>interesting to note how solutions to different feeding "problems"  evolved
>convergently.

It certainly is interesting.  I'm also unsure about ancestry...especially 
regarding long-term trends in the fossil record.  What I do know is that 
various theropods (from quite different clades) possessed gastroliths: 
_Poekilopleuron_, _Lourinhanosaurus_, _Baryonyx_, and apparently some sort of 
tyrannosaurid.  This behavior appears to be something that might indeed have 
been widespread, but perhaps isn't well represented in the fossil record.  Or, 
perhaps, in the past paleontologists have dismissed gastrolith-like stones 
found near theropod dinosaurs, relying on the a priori assumption that 
carnivorous animals don't use gastroliths, and hence the stones couldn't 
possibly be gastroliths.  

But, I think the new discoveries of theropod gastroliths will certainly make 
paleontologists keep their eyes open (or so I hope).

Steve

---
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Steve Brusatte-DINO LAND PALEONTOLOGY
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