Autapomorphy vs. Synapomorphy

We’ve finally made it to our first tip: the sponges!

We see here our node is dated at 758 MYA. This node is not telling us sponges appeared 758 MYA - rather,  that the most recent common ancestor between all metazoans and Porifera exist here.

Sponges possess an autapomorphy; a trait present only in their group. Sponges have cell-level organisation.
All other metazoans have at least a tissue-level of organisation, meaning similar cells are organised into tissues. This tissue-level organisation is a synapomorphy between all metazoans but sponges. A synapomorphy is a unique trait shared by a group.
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Spatial Proximity Bias

A common misconception is that the order of tips on a tree can indicate relatedness, where tips closer together are more closely related. This is incorrect. Tips can be rotated around a node and represent the same relationship.  Here, we can see that the same relationship can be represented in multiple ways.
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We’ve now reached the current day, and the terminus of our tree of life. Phylogenetic trees are useful diagrams that allow us to draw conclusions about relationships between different taxa and generate hypotheses about genetic and morphological evolutions on macro scales. The ability to correctly read and interpret them allows us to properly understand evolution. The ability to conceptualise the amount of time these processes occur over also allows us to understand evolution.
Just as life evolves, so does the tree. As branches disappear due to extinction, new branches appear as the inevitable result of evolution. Who knows how our phylogenetic tree will continue to grow and branch as another billion years go by.
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