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The Science of Reptile Eggs

The Science of Reptile Eggs

What Came First? The Chicken or the Snake?

Actually, turtles and tortoises came first. The group Testudines or Chelonii that includes all turtles and tortoises dates back to 220 million years. Crocodilians came second; they are about 98 million years old. Today, turtles and crocodilians share a very unique feature that makes their eggs especially weird: the sex of the offspring inside is not determined by genetics, it’s determined by temperature.

Some Like it Hot, Some Like it Cold

Being ectothermic, or cold-blooded, a turtle or crocodilian’s life is dependent on temperature for energy, digestion, reproduction and yes, even whether or not they are male or female. This phenomenon is called Temperature-Dependent Sex Determination (TDSD).

All reptile eggs are laid on land, usually buried underground or in a covered nest to help regulate the temperature. If you’re a Nile crocodile egg incubating between 31.7 – 34.5 C (89 – 94 F), you’ll be a male. Above or below that, you’ll be female. If you’re a spotted turtle egg, males will be produced below 30 C (86 F) and females will happen above that temperature.

Snakes and Lizards

The squamates, or scaled reptiles, are more recent in the fossil record. Snake and lizard eggs are similar to turtles and crocodilians in that their eggs are usually of round or oval shape with a tough leathery shell; they are however not dependent on temperature in the same ways. Some snakes and lizards can do something unbelievable though: they can give birth to live young!

I know what you’re thinking: “I thought only mammals did that?” What happens is the female snake doesn’t just lay the eggs; she retains them inside of her and incubates them there. This strategy ensures that eggs are kept at a warm, comfortable temperature and minimizes the chances that a predator will eat them. Unfortunately, a female snake can be slowed down by the extra weight and can be vulnerable to predation in turn. However this strategy has worked for snakes such as boas, and more locally, rattlesnakes, garter snakes and water snakes!

The Flying Reptiles

I’m not talking about pterodactyls; I’m talking about the cute feathery creatures flying around living today: birds. Unbelievable, isn’t it? Birds have more in common with some extinct dinosaurs and living crocodiles than crocodiles do with other reptiles today. Birds have officially been classified as a reptile since 2009 and rightly so.

They do have some key differences though, many of which are related to their eggs. Birds are endothermic or warm-blooded, so they do not rely on the same mechanisms to survive and grow as their other reptilian family members. The shell on a bird’s egg is hard and calcified. This makes the egg much more resistant to the environment as most birds’ eggs are laid in nests, exposed, not hidden in the ground. Bird’s eggs also have a slightly conical shape; this is to ensure that the egg rolls in a circle.

The other major difference is that when a baby bird emerges from its egg, it is helpless. The parents must feed and nurture the young. With a few exceptions, reptiles are born completely independent of their parents and are ready to go as soon as they emerge.

Eggs at Science North

At Science North, our grey rat snakes successfully mated recently and produced a clutch of 11 eggs, out of which we’ve welcomed ten baby snakes!

Watch the video posted at the top of the blog for a time-lapse video of the first snakelet hatching!

Brought to you by Meghan Mitchell, Science Communicator at Science North.


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Author: suzanne

1 Comment to “The Science of Reptile Eggs”
  1. simply that’s all are dangerous beautiful

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