Answer to Question 1a:
40 million years ago ✔
---
Explanation (in red font):
The common ancestor of all the organisms shown on this phylogenetic tree is located at the
base (root) of the tree, which corresponds to the point where all branches originate. According to the time scale at the top of the tree, this root is aligned with
40 million years ago.
This means that approximately
40 million years ago, a single ancestral species existed from which all the modern organisms in this tree — including raccoons, red pandas, giant pandas, and various bear species — evolved through speciation events over time.
Each branching point (node) represents a divergence event where one lineage split into two separate evolutionary paths. The farther back a node is on the timeline, the more ancient the shared ancestor.
So, since the
first major split occurs at 40 million years ago, this is when the common ancestor of all these species lived.
---
✔ Final Answer:
40 million years ago
Parent Tip: Review the logic above to help your child master the concept of constructing a phylogenetic tree worksheet.
