sauropod breeding

[Brian Lauret <zthemanvirus@hotmail.com>]

Dear all,

I'd like to ask the other people on the list how likely some of my ideas 
about sauropod breeding are to be true or at least realistic. For purpose of 
illustration the example I'm using is the Morrison fauna.

I used to think WWD was off when they proposed Diplodocus females laid their 
eggs and left them after that. Undoubtedly inspired by the assumptions about 
parental care in dinosaurs, I felt Diplodocus would have practised at least 
some parental care. Thinking the whole matter over however, made me 
reconsider that belief. It would have been impossible for an adult 
Diplodocus to look after its eggs or offspring. I've come to think the whole 
WWD dinosaurs might have been quite feasible,though the youngsters might not 
have taken as long to grow as the WWD Diplodocus did.

As shown in WWD, infant mortality would have been extremely high. In 
reality, the number of predators would have been even higher. Not only would 
Ornitholestes and Allosaurus have been present, but we also have 
Coelurus,'Beleemosaurus' (sic?),Tanycolagreus, Koparion, Stokesosaurus, 
Avetyrannus, Ceratosaurus, ?Elaphrosaurus, Marshosaurus,Torvosaurus and 
Saurophaganax as potential predators, as well as 
crocodiles,lizards,rhynchocephalians and perhaps mammals and the occasional 
avialean. Add to that all kinds of other hazards and it seems surprising any 
of the little ones ever became adult. Especially considering the fact we 
seem to be dealing with (comparitively) small creatures without 
spikes,clubs,speed or any other obvious weapons or defenses.

The fact that infant mortality must have been very high makes me think that 
not only numerous nests were laid by female sauropods at once, but also that 
this must have occured very regularly, if only to replenish numbers. 
Considering the fact sauropod eggs were very small compared to female body 
size and that after being laid,neither eggs nor youngsters require any help 
from the adult, or at least don't receive it, i think it would have been 
possible or even neccesary for a female to lay often, perhaps even every 
year.

This would have meant there was a presence of reasonable to large numbers of 
young Diplodoci of various stages of development at any given time. Perhaps 
the presence of so many theropods at once can be partially attributed to 
this fact. In fact, I've been considering Ornitholestes as a possible young 
sauropod specialist. After all, we seem to be dealing with a small but 
robust theropod that does not seem to have been much of a cursor. (Or at 
least,that's what I've read about the beastie.) Young sauropods would have 
been small and probably not very fast. Could it be possible Ornitholestes' 
main prey consisted of very small sauropods, or that they at least 
constituted an important part of its diet? Its robust build would seem to 
indicate it was used to killing prey too large to be consumed whole and 
required some more power to tackle.

I'd suspect the few Diplodocus to survive to sexual maturity and reasonable 
size would have joined the others at the moment they did. Or perhaps infant 
groups stayed together as a herd for all their life. To prevent inbreeding 
or for other reasons males might have been ousted from the group at that 
point and might have had to lead a solitary life or in small groups with 
related males. It would seem realistic to me if male sauropods were only 
allowed close to the herd in the breeding season.

Are any of these thoughts reasonable or are there reasons why they are 
unlikely to be true?

Thanks in advance,

Brian