[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

DIET OF LIOPLEURODON...



Nick Longrich writes..

>  They have found fish scales in the belly of a rhamphorhynch- I
> think it had big forward-pointing teeth and tricuspid teeth in back to
> puncture heavy scale.

Sounds like you're referring to the Triassic _Eudimorphodon_ (yes, a
'rhamphorhynchoid' [=paraphyletic non-pterodactyloid pterosaurs], but not a
'rhamphorhynch' [=family Rhamphorhynchidae]). Tricuspid teeth in this pterosaur
have been interpreted as aiding a diet of fish (consistent with stomach
contents.. if there are stomach contents preserved, I don't remember), but it's
interesting that elsewhere tricuspid teeth are interpreted differently. Baby
_Tanystropheus_ have them, and Rupert Wild suggested that they were for
arthropod-eating. I would guess that eudimorphodonts were shallow-water/shore
generalists.

> Some plesiosaurs had this to varying degree.
> Liopleurodon has forward pointing teeth (a shortneck- I don't know what it
> ate) Elasmosaurus has it a little in the forward teeth. I can't find good
> pictures, though. 

No plesiosaur (s.l.) has procumbent teeth in the fashion of a piscivorous
pterosaur like _Rhamphorhynchus_, but a great many of them have sharp, slender
teeth that point out from the jaws all around the margin, and interlace with
their opposites when the jaws are closed. Cryptoclidids have absolutely loads
of them, and some elasmosaurids have proportionally elongate ones at the front,
or sometimes just at the side (_Styxosaurus_ I think). Cryptoclidids were
probably as near to filter-feeding as reptiles ever got - the late Cret S.
American form, _Aristonectes_, literally has hundreds of little teeth.
Elasmosaurid teeth are apparently adapted for small-medium fish prey, but some
data from stomach contents suggests (surprise surprise) that they were doing
things weirder than we'd imagined (e.g. grazing on benthos!).

They contrast with the huge, robust deep-rooted conical teeth of big pliosaurs
and mosasaurs - real big-game hunters. As Nick says, the teeth in _Liopleurodon_
do point forward somewhat, as they also do in the basilosaur cetaceans (not
really in orcas though). What does a big pliosaur eat? Whatever it wants to! By
inference, these things (up to 11 m and more..) could eat other marine reptiles,
the biggest ammonites, swimming dinosaurs, each other.. you name it. BUT..
stomach contents do not reveal equivocal evidence of this having been the case!

Scutes from a thyreophoran dinosaur _have_ been described in close association
with a pliosaur skeleton, but apparently the association is not close enough for
evidence of diet (debatable). A subadult _Liopleurodon_ from Peterborough
revealed lovely stomach contents - mostly belemnite hooklets and a few fish
scales. So, despite their dental armoury and large size, were these animals like
sperm whales: formidably adapted, but subsisting on puny prey? (yes, puny prey:
forget Jules Verne and Cousteau, about 95% of the cephalopods sperm whales eat
are less than 1 m long). Or did they eat (almost exclusively) cephalopods when
they were youngsters, later switching to macroprey? Or, most likely IMHO, were
they just dustbins that swallowed anything within reach? We have a pathetic
sample size and cannot make assertions based on one, perhaps aberrant,
individual. However, find me a dinosaur in a marine sediment that has been
bitten in half and I'll be _very_ interested...

> It seems to me that a porpoise skull I
> saw had the teeth sticking slightly out to the sides, so I wonder if they
> grab their food from the sides of the mouth (anyone know?). How do
> gharials stack up? Do their teeth stick out to the sides at all?

Many delphinids do grab fish and other prey in the length of the jaw, rather
than with the tip, but this isn't because of a marked sideways strike. Jaw
length and acceleration during prey capture just means that the prey is some
distance within the jaws before it is seized. Gharials (and presumably most
other longirostrine crocodilians), with their similarly slightly-sideways
pointing teeth, grab fish with a swift sideways strike. Despite claims to the
contrary, it's unlikely that pliosaurs did this: their skulls are streamlined
for forward motion, not like platyrostral croc snouts. Delphinid teeth that I
have seen do point out to the side somewhat - even in orcas which grab seal
pups head-on and take chunks out of baleen whales. Most cetaceans have
comparatively little cervical flexibility, and they also hunt with head-on
strikes. Mosasaurs seem to have ambushed large prey similarly (no sideways
strike), but unlike pliosaurs (biggest teeth around symphysis) their teeth get
bigger toward the middle of the jaws. Presumably this adaptation is a result of
the streptostyly and highly mobile dentary-surangular joint they inherited from
their ancestors.

"Size matters not. Judge me by my size do you?"

DARREN NAISH