Table 2 Summary table comparing life history distribution across amniotes
| Â | Characteristics of distribution |
|---|---|
Body mass | All unimodal and right skewed Squamata < Aves <  < Mammals |
Offspring/female size | Offspring/female size ratio approximately the same across placental mammals, birds and squamates (7–8%) marsupials <  <  < turtles <  < birds ≈ placentals ≈ squamates |
Brood size | Mode is 1 in mammals, 2 in birds and squamates |
Reproductive frequency | The overall mode and distribution of reproductive frequency is extremely similar across amniote groups |
Relative brood mass | All unimodal and right skewed. But no placental mammal has a relative brood mass higher than 70%. Small in turtles, very small in marsupials |
Yearly fecundity | Distribution of reptiles and birds very similar (right skewed distribution with a mode of 4–6 young). Mammalian mode is 1–2 offspring per year |
Reproductive output | Similar overall in squamates, birds and mammals (low intercepts associated with steep slopes), low intercept in turtles, very low intercept, and shallow slope in marsupials |