Amphibians emerged about 370 million years ago. They are typically born underwater, start their life breathing through gills, and undergo a metamorphosis that allows them to breath air and live on land as adults. They are particularly sensitive to their environments, and can serve as “canaries in the coalmine” for ecological disturbances.

Current scientific consensus is that birds are the world’s last surviving dinosaurs, though they are warm-blooded and have four-chambered hearts like mammals. True birds began showing up about 100 million years ago; they all have feathers (though not all can fly), lay eggs, and have toothless beaks.

If it has a skull and backbone, gills, and its limbs (if present) are fins, it is probably a fish. But fish are actually a collection of several populations, such as lampreys, ray-finned fish, and sharks – animals of wildly different shapes, sizes and behaviors. A few even spend much of their lives on land!

As the name suggests, invertebrates are animals that do not possess a vertebral column (spine or backbone). With just one feature to define them, this makes for a huge group of animals: insects, snails, octopuses and many more. In fact, invertebrates make up 97% of all living animals on the earth!

Mammals are the only animal on earth with real hair, but that’s far from their only defining feature! Mammals are warm blooded, birth and nurse their young (with a few exceptions), and their brains possess a neocortex. Humans are mammals, as is the largest known animal to ever live: the Blue Whale!

Reptiles are ectothermic vertebrates who possess watertight scale or scute-covered skin, and (usually) lay hard-shelled eggs. Reptiles first appeared about 315 million years ago and are still plentiful today, with many types of crocodiles, lizards, and snakes serving as easily recognizable representatives.