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

Re: Sauroparental care



The comment about the claw shows the type of thinking that I am trying to 
change on DML. It is important to look at the whole picture and not just a 
single feature (in this case). A dinosaur is more than a single bone (or set of 
closely related bones). (BUT don't feel too bad, my professional colleagues 
fall into this same trap with cladistic anaylses of a taxon based on a single 
bone, make behavioral inferences from a single structure, etc.) 

In the case of digging, we can look at all the known digging vertebrates today 
and see certain characteristics that they all share. The results are more 
meaningful if the animals are not closely related because similar adaptations 
had to have arisen independently (i.e., the characters were not inherited, but 
developed because of similar life-style, etc.). In the case of diggers (e.g. 
armadillo and mole, which are unrelated), we can see that the claws (not just 
one) are enlarged and occupy the entire width of the hand in order to maximize 
the amount of dirt the hands/paws can move. Digging in dirt puts a great deal 
of stress on the bones, so short stocky arm bones are better than long, slender 
ones (which would more easily break). Digging involves a downward stroke to 
scrape through the earth, so that means powerful retractors (muscles that pull 
the arm backwards). Such muscles need a large attachment point, which has 
resulted in an elongated elbow (olecronon process on the u!
 ln!
a) and large crests on the humerus. The stresses are also great at the point of 
origin for these retractors, so the shoulder blade is short and deep (a 
counter-shape to the short arms).  This much is frequently cited as the 
evidence for diggers, but is not the whole story. Diggers also have short necks 
so that the short arms can reach ahead of the snout as the animalburrows, and 
that also means a mobile shoulder than allows the arms to reach forwards. 

Now applying these morphological features to the sauropod, and we see that the 
only two features they have that even remotely corresponds to diggers is a 
large claw on the paw and a moderately large olecronon in SOME titanosaurs 
(which also happen to be clawless). I think that you can see the problem 
already. The single claw faces more inwards than forwards, has a small surface 
area for digging, and is actually rather short when compared with the elongated 
claws of diggers. The elongated elbow of some titanosaurs is actually short in 
comparison to the ratio of elbow length to arm length or ulna length. Because 
titanosaurids with such structures are clawless on the hand, there must be some 
other reason why there was a need for relatively powerful retractors. Now 
before anyone gets carried away with wild just-so stories, take into account 
the rest of the body.

Ken


>>> zone65 <zone65@telstra.com> 12/21/03 16:44 PM >>>

> You could indeed look for traces of mounds (I doubt sauropods 
> burrowed, they lack any of the morphological features of a burrower). 

I'm sure they were capable of digging. See that spiked claw on their front feet?

> However, a mound would tell you nothing about parent care. 

It'd be a start, wouldn't it? The very existence of a mound (or deep hole in 
the ground) would indeed be an indicator of basic parental care, as any nest 
is. Is it better not to look for anything in case it isn't there? Don't have 
ideas in case they're wrong? Wait for evidence to fall into your lap without 
first pondering possibilities??

>Just the structure of the nest.
> Ken

And maybe evidence of regurgitation. Hey, or maybe not - but it's worth 
thinking about and looking into rather than dismissing as unprovable or 
likening to Creationist claptrap.

Peter Markmann
Canberra

> Perhaps it can be tested, by looking for evidence of mounds or burrows
> in known sauropod-inhabited areas.
>
> In any 
eent, I used the words "idea" and "possibility" to suggest
> these things. Even if I had said "hypothesis", that is merely a
> proposition. Had I lazily bandied about the word "theory", well, then
> you would have had a point.
>
> Peter Markmann
> Canberra
>
>
> On Monday, December 22, 2003, at 12:50  AM, Ken Carpenter wrote:
>
>> Again, I raise the point of how do you test your hypothesis? I can
>> just as as well say that little green men come to earth and took care
>> of the babies. The point is that this idea is not testable, nor, as
>> you'll note, can you disprove it as structured. A hypothesis needs to
>> be framed in such a way that it can be disproved. That is one reason
>> why debates with Creationists are futile. They tend to make statements
>> that cannot be tested.
>> Ken
>>
>>>>> <zone65@bigpond.com> 12/20/03 22:53 PM >>>
>> OK, the question of how Saurpods avoided trampling their young into
>> brontoburgers must be considered... one idea is that the eggs were 

>> laid
>> in rather deep/wide burrows dug in the ground. The hatchlings would
>> then live there until they were large enough to emerge, and clever
>> enough to avoid their elders' feet. Another possibility is the young
>> lived on mud-islands created by the adults in lakes.
>>
>> Peter Markmann
>> Canberra