Re: Seasonal "Day Care" Hypothesis for Maiasaura (Speculation about speculation)

["Rob Gay" <rob_redwing@hotmail.com>]

> If anyone wants to comment or criticize it, feel free, as it is my first 
> feeble attempt to dabble in dinosaur behavior.<
Ah, behavior. Something that I am really quite interested in, since these 
were, after all, living breathing animals, and had to have behaved in some 
way! But, much of behavior of extinct animals must be speculation. That 
being said, here's my take on the idea:
I personally don't see this as being too likely. This obviously does not 
mean it didn't happen, I just view it as unlikely. Here's my reasoning, 
which, no doubt, has some flaws.
I know of know modern animal that has this tactic for reproduction/infant 
survival. However, I don't think this itself is a strong argument. Most 
egg-laying animals don't migrate, and this itself mitigates the value of 
this observation. But I think it's an important one to make.
Secondly, from a "survival of the fittest" perspective, this would not make 
too much sense. If, for example, you are leaving mostly the elderly/sick 
animals behind, this would make the nest more vulnerable to raiding. Larger 
predators (Albertasaurus) in the area would presumably favor elderly/sick 
individuals in a normally diverse herd. Leaving these animals behind to 
guard the nests makes them more susceptible to attack from large carnivores. 
So if the guarding animals are decreased in number, this makes it easier for 
egg-raiding animals (like Troodon, presumably) to get into the nests. Of 
course, this argument assumes that the large predators wouldn't follow the 
herd in the first place. The day care scenario also makes assumtions about 
gestation periods for the eggs. The animals migrating would have to be on a 
fairly precise schedule (not too impossible to do, though), to return to the 
breeding site in time for the eggs to hatch. Otherwise, the day care parents 
would be forced to try to protect a lot of moving hatchlings, as opposed to 
large, unmoving nests.
Also, there is no direct proof (as far as I know) that Maiasaura migrated. I 
agree that it probably did, and the evidence from fossil trackways seems to 
show that groups of animals moved in herds, but until we find Maiasaura on 
the north slope of Alaska (there are some hadrosaurs from there, right?), we 
can't say for certain. I must say, the evidence for Maiasaura migrating is 
probably pretty good (Two Medicine Bone Bed), however, you must consider 
that the bone bed is in the same geographic area as the nests, so there's no 
direct proof that this group actually went anywhere.
Finally, there is the fossil evidence. The Maiasaura nests are not directly 
associated with many (any?) Maiasaura remains. The bone beds and the nests 
are in different (overlying) parts of the Two Medicine Formation.
Just some of my thoughts and my own speculation on what I find to be some of 
the most fascinating aspects of paleontology (behavior).
Peace,
Rob

Student of Geology
Northern Arizona University
P.O. Box 20840
Flagstaff, Az. 86011
AIM: TarryAGoat
"A _Coelophysis_ with feathers?"

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