Types of birth: Oviparous or viviparous
In the animal world there are two main methods used for the birthing of offspring. The main difference between oviparous (egg laying) and viviparous (live young) animals is that oviparous creatures do not undergo embryonic development within the mother, whereas viviparous animals develop within the female's body. A subset of viviparous is ovoviviparous – it gets technical, but the result is a live birth!
A few species can even do both. Our Australian three-toed skink Saiphos equalis may lay eggs or deliver live young! This phenomenon is called bimodal reproduction.
Oviparous (egg laying): Birds, most reptiles, amphibians, most fish, most insects, molluscs, arachnids and monotremes are oviparous.
Most eggs from a vertebrate: Ocean sunfish Mola mola, 300,000,000 at a time.
Most eggs from an invertebrate: Giant clam Tridacna gigas, 500,000,000
Viviparous (live bearing): Most mammals such as dogs, bats, whales, and humans, some reptiles. If you can read this newsletter, you're a viviparous species.
Most live babies from a vertebrate: Tailless tenrec Tenrec ecaudatus, up to 32
Not all females gestate their young. Seahorses and pipefish both have the males carry and birth their young!
Baby turtles have recently been studied and it has been found that they communicate to each other while still inside the egg. Scientists theorise that this communication is used to determine a hatching timeline, so they hatch in staggered stages rather than all at once. This can help ensuring some of each egg cluster can make it to the water before predators eat them, ensuring a higher survival rate.