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

RE: Sauropod-eating snakes

I interpreted Wilson &c's paper a little differently.  I didn't think they were 
arguing that "narrow-gaped" snakes like scolecophidians or anilioids should be 
models for _Sanajeh_ (or any other Cretaceous snake).  Nor did I think that 
Wilson &c were arguing for a dichotomy between "narrow" and "wide"-gaped 
snakes.  _Sanajeh_ was "narrow-gaped" in the sense that the oral gap was 
comparable to that of anilioids, even though it had enhanced Macrostomata-like 
intraoral mobility... that's what I thought Wilson &c were saying.  

There is no doubt that the components of the specialized jaw apparatus of the 
Macrostomata (pythons, boas, colubroids, etc) were accrued in stages.  Whether 
madtsoiids represent a transitional stage depends on their exact phylogenetic 
position within the snake clade.

Also, a 3.5m long snake like _Sanajeh_ swallowing a 50 cm long titanosaur 
hatchling is not all that impressive - especially considering that over half of 
the hatchling's body length was made up of neck and tail.  Constriction would 
probably have been unnecessary.  If this is the best that Cretaceous snakes 
could do (and I'm not necessarily suggesting that it is), then the _Madtsoia_ 
vs _Laplatasaurus_ scenario in the artwork is out of the question.  The 
_Madtsoia_ wouldn't have bothered trying to bring down such a large animal.

Cenozoic madtsoiids might certainly have done a lot better, especially given 
the elongation of the supratemporal bone.  Yep, Cenozoic madtsoiids might 
therefore have been constrictors that brought down very large mammals.  But my 
query was specifically referring to Cretaceous snakes, and whether any of them 
had boa constrictor-like behavior, including targeting much larger dinosaurs 
(not just hatchlings).



--- On Wed, 3/3/10, John Scanlon <riversleigh@outbackatisa.com.au> wrote:

> From: John Scanlon <riversleigh@outbackatisa.com.au>
> Subject: RE: Sauropod-eating snakes
> To: "'Tim Williams'" <tijawi@yahoo.com>, dinosaur@usc.edu
> Cc: bchoo@museum.vic.gov.au
> Received: Wednesday, 3 Marc
:54 PM
> There's no particular anatomical
> signature for constriction, but I can't see any reason to
> assume madtsoiids or other basal snakes couldnât do it.
> But there are lots of different components to
> 'macrostomatan' adaptations for swallowing large prey, and
> some of them are actually primitive for snakes, so 'wide'
> vs. 'narrow' gape is a false dichotomy: scolecophidians and
> 'anilioids' absolutely do not represent ancestral stages or
> adequate models for large Cretaceous snakes, which is indeed
> one of the main conclusions drawn by Wilson et al. Also,
> their phylogeny (Jason Head's work, which I think is his
> first published phylogenetic analysis) is just one of
> several recent morphology-based versions, and they all need
> testing against the very significant molecular data sets now
> available for extant groups... in fact somebody is working
> on it already ;)
> If 3.5 m Sanajeh (95 mm skull length with very short
> supratemporals) could swallow 50 cm sauropods, what does
> that tell us about 6 m madtsoiids with 150 mm skulls and
> long supratemporals (but still short quadrates) like
> Yurlunggur? Presumably, few Miocene mammals would be safe.
> Then you've got your 9 m Madtsoia bai (the one in the
> fantasy painting) or Gigantophis from the Fayum. They'd have
> been serious predators even without the palatal kinesis of
> modern snakes, and maybe just had to work a bit harder to
> eat the same-sized prey.
> -----------------------------------------------
> Dr John D. Scanlon, FCD
> Riversleigh Fossil Centre, Outback at Isa
> riversleigh@outbackatisa.com.au
> http://www.outbackatisa.com.au/Fossil-Education/Palaeontologist.aspx
> "Get this $%#@* python off me!", said Tom laocoonically.
> -----Original Message-----
> From: Tim Williams [mailto:tijawi@yahoo.com]
> Sent: 03 March, 2010 4:44 PM
> To: dinosaur@usc.edu
> Cc: bchoo@museum.vic.gov.au;
> tijawi@yahoo.com
> Subject: RE: Sauropod-eating snakes
> Brian Choo <bchoo@museum.vic.gov.au>
> wrote:
> > Wasn't too d
 the accompanying William
> Service
> > narration describes the engagement as an unsuccesful
> attack
> > that seems plausible:  the serpent instinctively
> > strikes the young sauropod and coils around it. 
> It
> > constricts but fails to suffocate the prey item, then
> > finally relinquishes its grip and retreats.
> But would any Cretaceous snake coil itself around live prey
> to suffocate it, prior to swallowing?  Madtsoiids like
> _Sanajeh_ were narrow-gaped snakes.  The authors of the
> _Sanajeh_ paper suggest that titanosaur eggs had to be
> crushed by constriction before swallowing.  I assume
> that small prey items (like titanosaur hatchlings!) were
> eaten alive.  AFAIK, there are no known wide-gaped
> (macrostomatous) snakes in the Cretaceous.  So no
> Cretaceous snakes were capable of swallowing very large
> prey, in the manner of a boa constrictor (for example). 
> The phylogeny in the _Sanajeh_ paper recovers the
> pachyophiids as sister taxon to the macrostomatous
> snakes.  This would drag the origin of the wide-gaped
> snakes back to the mid-Cretaceous, suggesting that
> macrostomatous snakes were around in the later
> Cretaceous.  But the phylogenetic relationships of
> pachyophiids are controversial.  Pachyophiids like
> _Pachyrhachis_ retain fairly well-developed hindlimbs, and
> some phylogenetic analyses place them outside the
> crown-group, as very primitive snakes.
> I wish I still had my Service/Stout book.  :-(  
> Cheers
> Tim