| Some interesting exceptions to the correlation between body size and pneumaticity occur in birds that dive underwater to feed, such as grebes, loons, and penguins. |
| Postcranial pneumaticity is absent in all other extant vertebrates with the known exceptions of osteoglossomorph fish and the hyoid bone in howler monkeys. |
| Perhaps the most striking feature of the endoskeleton of birds is its pneumaticity. |
