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RE: Carcharias [Was Re: Oviraptorids as Parrots?}



Colin McHenry wrote:

The placement of sand tigers/ grey nurses/ ragged tooths in the top ten list of 'maneaters' may be a little dated. Every recent piece of info I've found on them stresses their inoffensive nature as far as humans goes.

I found the exact same thing. I have heard/read that the sand tiger (or grey nurse) was once *assumed* to be a man-eater because of its outwardly fearsome appearance. However, this fearsome appearance might have been the reason why they were blamed for attacks committed by other shark species (as Colin mentioned); all along, they were probably just innocent bystanders. Sand tigers are typically slow smimmers that often hover motionless in shallow, coastal water (such as near where Colin swims). This makes them very easy to kill. At one time they were killed by trophy-hunters, and I believe _Carcharias taurus_ is the first shark species to be officially protected. We humans are far more dangerous to sand tigers than they are to us.


They are certainly popular as a large shark for aquaria...

Their toothy, "sharky" appearance is one of the reasons why they are so popular in public aquaria - plus the fact that they are relatively easy to keep in captivity.


..or alternatively, the bad reputation is a hangover from days when its 'offensive' nature was presumed from its (admittedly impressive) appearance:

That's my bet.

Well, there are _Carcharias_ teeth in the Cretaceous of Queensland. Funny to think that a very similar animal to something that lived alongside plesiosaurs is still swimming around off the beach where I swim every day...

Oh yes, this is a dinosaur list... OK, ahem.... The thing about shark teeth is that they are notoriously difficult to assign to individual taxa. With _Carcharias_, although the dental record goes back to the Aptian, this assignment is very controversial, and it is not really clear how ancient _Carcharias_ is. (_C. taurus_ itself reportedly goes back to the Miocene.) That's the problem with fossil sharks: the vast majority of species are known only from teeth, which are usually found isolated and disarticulated. So while it is possible that a _Carcharias_-like shark was swimming around at the time of the dinosaurs (phew, got it in!), all we can really be sure of was that there were sharks with _Carcharias_-like teeth around at this time. Having said that, the overall morphology of modern _C. taurus_ appears to be quite plesiomorphic by lamniform standards, so Colin may be absolutely right in saying that Cretaceous _Carcharias_ was very similar to the modern sand tiger in appearance. (Something for you paleo-artists out there.)


Can you imagine trying to reconstruct a phylogeny of theropods based almost entirely upon teeth? That's the kind of task fossil shark experts are up against. The occasional fossil shark skeleton does turn up (like _Scapanorhynchus_, the Cretaceous goblin shark), but these are few and far between compared to the huge abundance of isolated teeth.

Cheers

Tim





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Dann Pigdon
GIS / Archaeologist         http://heretichides.soffiles.com
Melbourne, Australia        http://www.geocities.com/dannsdinosaurs
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