Animals Diversity

Animals are classified into at least 30 groups called "phyla". Nine of these phyla contain most of the animals that exist on Earth today.

Phylogeny

A phylogeny is a branching diagram that shows evolutionary relationships between species. 

Scientists usually determine these relationships based on DNA evidence.

Cladogram

A cladogram is similar to a phylogeny, but it shows hypothesized relationships between species based on shared physical traits.

For this class, we will treat phylogenies and cladograms as essentially the same.

Phylogenies

You read a phylogeny much like you read a family tree. 

The root of the tree represents the ancestral lineage, and the tips of the branches represent the descendants of that ancestor.

As you move from the root to the tips, you are moving forward in time.

Phylogenies

Recall that traits are passed down from generation to generation. 

As species evolve and traits are inherited, their evolutionary paths may split.

When one lineage splits into two, a new species may arise. We call that 'speciation'. 

Phylogenies

Phylogenies trace patterns of shared ancestry between lineages. 

Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages.​

Phylogenies

Similarly, each lineage has ancestors that are unique to that lineage and ancestors that are shared with other lineages (common ancestors).

Shared lineage = common ancestry!

Phylogenies

A clade is a grouping that includes a common ancestor and all the descendants (living and extinct) of that ancestor. 

Imagine clipping a single branch off the phylogeny — all of the organisms on that clipped branch make up a clade.

Different styles of phylogeny / cladogram

Each of these show the same relationships between species. It is the branching pattern that is important, so the shape can vary.

Cladograms

Cladograms use physical features to distinguish the evolutionary relationships between species.

Each branch represents a different lineage.

Each new feature (vertebrae, bony skeleton, etc) applies only to the species HIGHER UP in the tree.

Cladograms

If you trace a species lineage from top to base, it includes all the features on the line.

So the rodents & rabbits have hair, amniotic eggs, four limbs, bony skeletons, and vertebrae.