Re: Guts-Eating Spinosaurs

["Adam Britton" <abritton@wmi.com.au>]

I haven't been following this thread, so perhaps I'm getting the wrong end
of the stick (never make assumptions based on limited conversation data!),
but there seem to be some misconceptions about what modern crocs subsist on.
Given that there's a lot of analogising between croc diets and Spinosaurus
diets going on, this probably needs clarifying.

First, if you're a crocodile, having a slender, longirostrine snout does not
limit one to piscivory. Clearly, a slender snout is ideal for sweeping
through the water, but if it's robust enough then it's quite capable of
taking a wide range of different prey. All modern longirostrine species (eg.
Tomistoma schlegelii, Crocodylus cataphractus, C. johnstoni etc) have diets
that include all manner of vertebrates and invertebrates, and the largest
individuals will often take small to medium-sized mammals (an 18 foot long
Tomistoma is a powerful predator that can easily take macaques and -
reportedly - even the occasional small deer). Even Gavialis is not the
complete fish specialist that most believe it to be. Fish may form the
majority of its diet, but firstly juveniles take all kinds of invertebrates,
and large adults have been known to eat birds, reptiles and other relatively
small vertebrates. It may not be the norm, but if the animal has an
opportunity and ability to catch, overpower and swallow a particular animal,
then why forgo useful protein? That's why all crocs will also scavenge when
the opportunity presents itself.

A second misconception seems to be that large crocodylians only eat large
prey. This is what the Discovery Channel wants you to believe, but in
reality most large crocs eat primarily small prey: crustaceans, molluscs,
fish, reptiles, birds, small mammals etc.  That's another reason why a
longirostrine species like Tomistoma is not a fish specialist - it's jaws
might not be capable of taking down a water buffalo, but they can easily be
used to catch relatively small reptiles, birds and mammals. Crocodylus
porosus males reach sizes of 16 to 20 feet on animals no larger than large
mudcrabs for the most part, with perhaps the occasional slightly larger
mammal such as wallabies, small buffalo or pigs.

Therefore, is there any reason to believe that medium- or even large-sized
dinosaurs limited their diet to large prey or fish? Even if they were
homeothermic unlike crocs, there were still plenty of small to medium-sized
vertebrates and invertebrates that could have taken up a reasonable
proportion of, say, a Spinosaurus' normal diet. I doubt we have sufficient
information from fossilised stomach contents to answer such a question,
especially if the animals in question ceased feeding normally before they
died.

Adam Britton


----- Original Message -----
From: "Steve Brusatte" <dinoland@lycos.com>
To: <dinosaur@usc.edu>
Sent: Wednesday, January 09, 2002 8:21 AM
Subject: Guts-Eating Spinosaurs


> Hey,
> Here is a reply from Marco Mendez (who is currently off-list) regarding
the ongoing "spinosaurids as specialized innards-eaters thread":
>
> "About spinosaur feeding, well that is a problem, due to the fact they
> are fragmentary and enigmatic. However, we can still discern some things
> just from the bones we have. I do believe that spinosaurs ate other
dinosaurs
> along with fish. Modern crocodiles do this sort of stuff, except they
> eat other crocs, mammals, and fish (Sarco is the one who ate dinos).
>
>
> I do not completely object to spinosaurs being able to stick their mouths
> into sauropod bellies or what not, however, they have to take down this
> animal as well. (there might be another explanation, I'll get to this
> a bit later). Spinosaur skulls and necks are not very strong to take
> down a big animal. Their skulls are long and narrow, with no much width
> they really cannot clamp down on such prey. Spinosaurine teeth have no
> serrations in them, and they are straight, kind of like gharial teeth
> or crocodile teeth. Baryonichid (suchomimus and baryonyx) teeth have
> serrations, but not curved back toward the throat. There is some
curvature,
> however it is not so great that it woulc convince me. Both spinosaur
> types seem not to have very strong teeth, as seen in T. rex or the other
> gigantic predators.
>
> Tooth comparison:
> If you were to take a tooth of _Suchomimus_ and that of
_Carcharodontosaurus_
> and compare them, you'd see some obvious differences. While the Carch.
> tooth is narrow, it is curved back and has  big serrations. While the
> Sucho. tooth has serrations, it lacks the knife-like serrations of Carch.
> More oval-ish, the Sucho. tooth  is smaller. Now in the jaws, the teeth
> are curved back in Carch. to hold in prey. In spinosaurs the teeth are
> much more numerous and not so curved.
>
> About the other theory, they may have poked around, however they were
> scavangers. Not very likely, since they are animals that lived near the
> river shores and tended to eat fish. In the belly of Baryonyx, some fish
> cales along with acid-etched bone has been found, suggesting spinosaurs
> ate fish and dinosaur meat. I do not doubt other spinosaurs ate meat
> along with fish. The claws are most widely though to be used while
fishing,
> since they do have to drag out 300pds+  of fish out of the water. In
> Spinosaurus' time there was a huge meat eater who had the dinosaurs,
> Carcharodontosaurus. I think he would be the main predator in land,
followed
> maybe by Spinosaurus, until other fossil material arises.
>
> I cant say the sail helped in hunting, however it migth have helped to
> intimidate other dinosaurs.
>
> As for eating inside tummies, well I dont know, spinosaurs could have
> done this, just not as a long term habit. A long snout would be more
> useful to catch slippery prey, I would argue that a short snout be more
> useful in poking into stomach crevises, since it allows for more grab
> than a spino skull (I dont know much about this argument, I am just
putting
> this out there).
>
> -marco"
>
> Regards,
> Steve
>
> ---
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