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RE: Segregated vs age-mixed sauropod herds



Dann asked: Is there any way of telling from fossil skulls whether these
snakes had thermal sensing abilities?

Potentially yes, but we'll have to wait for more detailed illustration of
the maxilla and mandible of _Sanajeh_. But a priori it is not expected:
facial heat-sensory pits have evolved three times (in different anatomical
positions) in pythons, boas, and crotaline vipers, but the EPB for basal
snakes (or basal alethinophidians, _fide_ Wilson et al) implies their
absence in madtsoiids. In modern snakes, pits correlate with enlarged
trigeminal foramina in the maxilla, dentary and/or surangular (pythons and
boas) or a cavity in the maxillary bone itself (pitvipers). No such obvious
enlargement or excavation is seen in Australian madtsoiids (but this
comparison ought to be quantified), but most madtsoiid dentaries do have two
or three (smallish) mental foramina rather than the single one usual for
snakes, so it's possible there was a specialized sensory function for these,
evolved independently of modern lineages.

"Never underestimate the stealth abilities of snakes" - assuming the
sauropods piled some sort of soil/vegetation mound over the eggs (which the
paper supported based on density of pores in eggshell, though this could not
be confirmed geologically), it would have been relatively easy for snakes to
move around the nesting area under cover. Even in daylight, many snakes have
incredibly cryptic behaviour: e.g. Australian brownsnakes (_Pseudonaja_) up
to 2m long can cross open areas of short grass almost invisibly by
semi-burrowing below the horizontal rhizomes. 

-----------------------------------------------
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: Dann Pigdon [mailto:dannj@alphalink.com.au] 
Sent: 15 March, 2010 8:11 AM
To: dinosaur@usc.edu
Subject: Re: Segregated vs age-mixed sauropod herds


On Mon, Mar 15th, 2010 at 8:24 AM, Mike Habib <habib@jhmi.edu> wrote:

> > Let's not forget, snakes are MAJOR predators of baby birds today, 
> 
> > even for species with biparental care.
> >
> > Parental care =/= total immunity of the babies from all attacks!!
> 
> Excellent point. Never underestimate the stealth abilities of snakes.

Especially at night. Navigating via scent, or perhaps thermal-detecting
pits, night allow the snakes 
to slip into the nesting grounds under cover of darkness. If they were
constrictors, then they could 
have dispatched any lone hatchlings relatively silently.

Is there any way of telling from fossil skulls whether these snakes had
thermal sensing abilities? 
Even if they didn't, there are nocturnal snakes around today that rely
mostly on large sensitive 
eyes, like the 'night tiger' here in Australia that has done so much damage
in Guam when it was 
accidentally introduced there.

-- 
_____________________________________________________________

Dann Pigdon
GIS Specialist                         Australian Dinosaurs
Melbourne, Australia               http://home.alphalink.com.au/~dannj
_____________________________________________________________