Dinosaur reproduction strategy contributed to gigantism

[Ben Creisler <bscreisler@yahoo.com>]

From: Ben Creisler
bscreisler@yahoo.com
 
New in PLoS ONE:
 
Werner, J. & Griebeler, E.M. (2011)
Reproductive Biology and Its Impact on Body Size: Comparative Analysis of 
Mammalian, Avian and Dinosaurian Reproduction. 
PLoS ONE 6(12): e28442. 
doi:10.1371/journal.pone.0028442
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0028442

Janis and Carrano (1992) suggested that large dinosaurs might have faced a 
lower risk of extinction under ecological changes than similar-sized mammals 
because large dinosaurs had a higher potential reproductive output than 
similar-sized mammals (JC hypothesis). First, we tested the assumption 
underlying the JC hypothesis. We therefore analysed the potential reproductive 
output (reflected in clutch/litter size and annual offspring number) of extant 
terrestrial mammals and birds (as "dinosaur analogs") and of extinct dinosaurs. 
With the exception of rodents, the differences in the reproductive output of 
similar-sized birds and mammals proposed by Janis and Carrano (1992) existed 
even at the level of single orders. Fossil dinosaur clutches were larger than 
litters of similar-sized mammals, and dinosaur clutch sizes were comparable to 
those of similar-sized birds. Because the extinction risk of extant species 
often correlates with a low reproductive output,
 the latter difference suggests a lower risk of population extinction in 
dinosaurs than in mammals. Second, we present a very simple, mathematical model 
that demonstrates the advantage of a high reproductive output underlying the JC 
hypothesis. It predicts that a species with a high reproductive output that 
usually faces very high juvenile mortalities will benefit more strongly in 
terms of population size from reduced juvenile mortalities (e.g., resulting 
from a stochastic reduction in population size) than a species with a low 
reproductive output that usually comprises low juvenile mortalities. Based on 
our results, we suggest that reproductive strategy could have contributed to 
the evolution of the exceptional gigantism seen in dinosaurs that does not 
exist in extant terrestrial mammals. Large dinosaurs, e.g., the sauropods, may 
have easily sustained populations of very large-bodied species over 
evolutionary time.