We know one when we see one. A dog is an animal. We are animals. What about a sponge? Sponges are animals, too. That's right—we mean SpongeBob.All life is divided into six kingdoms: BacteriaArcha...

Life on Earth didn't start out with animals. All life on earth started from the primordial ooze, where inorganic molecules produced organic molecules, organic molecules formed bigger molecules, and...

We are family. All animals are related, but figuring out the relationships is not straightforward. Traditionally, the family tree has been based on body plan and how embryos develop. Animals with c...

It's alive! Sponges are animals, the oldest ones around. The first branching in the animal family tree is the split between the parazoa and eumetazoa. The difference between these two groups of ani...

Muscles and Nervous Systems and Organs, Oh MyThis is the beginning of the rest of the animal kingdom, the eumetazoa, or "true animals" (we eumetazoans are a little biased). Eumetazoans have tissues...

From here on out, we're going to be talking about the Bilateria, or animals that have a body plan that is bilaterally symmetrical. The remaining animals in the animal kingdom have a front and back,...

The rest of the animal kingdom fits nicely into the next two big branches of the animal family tree: the protostomes and the deuterostomes. In this section, we'll cover one of the three protostome...

Segmented worms like earthworms and leeches are found all over the place—from our compost to under the sea. Annelida means "little rings," which is how these worms look on the outside, like the b...

We see arthropods everywhere we go. Arthropoda, the third protostome phylum, is everywhere. Arthropods live on the land and in the sea. They swim, run, and fly. Arthropods mean a lot to us, too. We...

Four invertebrate phyla remain to be discussed: Phoronida, Bryozoa, Brachiopoda, and Echinodermata. LophophoresPhoronida, Bryozoa, and Brachiopoda have in one thing in common that no one else has:...

When we think "animal," we usually think of a vertebrate. Sorry, we're a bit biased. We'll first look at what a chordate is and then at the earliest vertebrates, the fish.What's a Chordate?We are m...

First, the ancestors of frogs and salamanders crawled out of the deep blue sea. Then, for a while, dinosaurs ruled the earth. AmphibiansWeather has always been unreliable. What do you do if water,...

If there is space, someone will move in. With flying dinosaurs going away, airspace opened for birds. Flight takes a lot of energy, but it offers access to flying insects and the ability to see foo...

Mammals evolved from reptile ancestors, just like birds. Mammals, however, came first and they came from a different reptilian stock: therapsids, descendants of the synapsids. Small mammal ancestor...

You'll appreciate your thumb so much more after this.We are primates, as are monkeys, apes, and those cute little lemurs in Madagascar. Primates are one of the newer orders of eutherian mammals. Se...

What is an Animal? When we think of life, we generally remember plants and animals. Try a mnemonic to get them all:All Boy Pilots Fly Paper Airplanes (Archaea, Bacteria, Protista, Fungi, Plantae, A...

What is an Animal? 1. The six kingdoms of life are:2. Animals are:  a. Prokaryoticb. Heterotrophicc. Haploidd. a. and b.e. b. and c.3. What unique tissues are characteristic of animals:4....