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

Reproduction



On Wed, 8 Mar 1995, Ralph Chapman wrote:

> 2) On sauropod eggs, one line of research by John Damuth would seem to
> suggest that they probably did lay eggs. John has data that suggests that
> the reason dinos were able to get as big as they did is because they were
> egg layers as opposed to live-bearers. In mammals, the bigger you get, the
> bigger the offspring and the longer the gestation time.

Does he say why he thinks this is?  Is it a possible strategy for mammals
to produce many small offspring (with presumably a shorter gestation 
period)?  Constraints might be the forces exerted during birth, surface 
area and volume of the uterus/uteri, number of teats and 'squishing' during
suckling.  However, it might also be due to K-selection (in a loose sense)
favouring large body size in adults and in juveniles.

> Now dinos that lay eggs don't have that problem and John's initial research
> suggests they even had a correlation between egg number and dino size, which
> would be typical for most organisms.

Typical for most organisms, yes, but is it typical for vertebrates?  I don't
know.  You would expect this correlation as a result of the constraint on
egg size, given that larger dinosaurs will invest absolutely more in 
reproduction.  Mammals go the other way of course, with proboscideans, 
cetaceans, sirenians and large primates and ungulates having litters of 1.
Is John saying that with a mode of reproduction with no size constraints, 
animals would follow the dinosaur pattern rather than the mammal one?

The reverse seems more likely to me: dinosaur oviparity forced them to
have small offspring but mammals were free to optimise litter size.
Oviparity would be a disadvantage for individual dinosaurs but (as I
suggested in my last post) they were stuck with it.  There could be an
advantage at the level of species selection: big dinosaurs would be less 
prone to extinction than equally large mammals.

By the way, do you have references for Damuth's work?
                                                                Bill Adlam