Phylogeny worksheet - Free Printable

Let’s go step by step through the phylogenetic tree questions.

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First Tree (with timeline from 100 million years ago to Present Time):

1. Which organism is the ancestor of all of the other organisms on this tree?
→ Look at the bottom of the tree — that’s where evolution started for this group. Organism A is at the base, and all branches come from it. So, A is the ancestor of all others.

2. Which organisms (species) are still on Earth presently?
→ The “Present Time” line has dots labeled J, K, M, O, P. These are the ones that survived until now. So: J, K, M, O, P

3. Approximately, when did species A have a speciation event? which organisms resulted from this event?
→ Speciation means one species splits into two. At point A (100 million years ago), the branch splits into two main lines: one leading to B/C/D/E/F/G/H/I/J/K/L/M/N/O/P, and another? Wait — actually, looking closely, A splits into two branches: one going to B (and then C/D), and the other going to E (then F, etc.). But note: the first split after A leads to two major groups — let’s call them left side (B, C, D) and right side (E, F, G, H, I, J, K, L, M, N, O, P). Actually, re-examining:
- From A, one branch goes to B (which later gives C and D), and another branch goes to E (which leads to everything else).
→ So speciation event at A happened ~100 million years ago, resulting in B and E as the first two descendant lineages.

*Wait — correction:* Looking again, A connects directly to two points: one is B, and the other is E? No — actually, A connects to a node that then splits into B and E? Let me trace:

Actually, in standard phylogenetic trees, each dot is either an organism or a speciation event. In this diagram:
- A is at 100 mya.
- From A, two branches emerge: one goes up to B, the other goes up to E.
→ So yes, speciation at A produced B and E.

Answer: ~100 million years ago; organisms B and E

4. Which organisms went extinct? how do you know?
→ Any branch that does NOT reach “Present Time” went extinct. That includes:
B, C, D, E, F, G, H, I, L, N
Why? Because their branches stop before reaching the top (“Present Time”) line. Only J, K, M, O, P make it to present.

5. Which organism is the most recent common ancestor of J, K and M?
→ Find where the branches for J, K, and M meet.
- J and K share ancestor I.
- I and M share ancestor G? Wait — let’s trace:
- J and K come from I.
- I comes from G.
- M comes from... also G? Yes! G splits into I and M.
→ So G is the common ancestor of J, K, and M. And since no more recent node connects all three, G is the most recent common ancestor.

6. When did the speciation event occur that gave rise to organisms J and K?
→ Look at where J and K diverge — they split from I. Where is I located? On the timeline, I is between 25 million years ago and Present Time — specifically, just below Present Time. The horizontal dashed line for 25 million years ago is above I? Wait — let's check:

Timeline:
- Present Time
- 25 million years ago ← I is here? Actually, I is drawn at about the same level as 25 million years ago? Or slightly above?

Looking carefully:
- The branch to I starts around 25 million years ago? Actually, the node I is positioned just below the 25 million years ago line? Or on it?

Standard interpretation: if a node is drawn at a certain height, its age corresponds to that time. Node I is aligned with the 25 million years ago mark? Actually, no — looking again:

The vertical axis:
- Present Time — J, K, M, O, P
- 25 million years ago — I, L, N
- 50 million years ago — G, F
- etc.

So I is at 25 million years ago. That means the speciation event that created J and K happened at I — so approximately 25 million years ago.

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Second Tree (simpler, only 10 million years ago to present):

7. Which species is the common ancestor of all of the other species?
→ Bottom of the tree: K is at the base, and all branches lead upward from it. So K is the common ancestor.

8. Explain why species B and C are more related than species A and C.
→ To find relatedness, look at how recently two species shared a common ancestor.
- B and C share a common ancestor at F (very recent — close to present time).
- A and C share a common ancestor at K (much older — 10 million years ago).
→ Since B and C split off from each other more recently than A and C did, they are more closely related.

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Now, compiling final answers clearly:

Final Answer:
For the first tree:
- Ancestor of all: A
- Still on Earth: J, K, M, O, P
- Speciation event of A: ~100 million years ago; resulted in B and E
- Went extinct: B, C, D, E, F, G, H, I, L, N — because their branches don’t reach present time
- Most recent common ancestor of J, K, M: G
- Speciation event for J and K: ~25 million years ago

For the second tree:
- Common ancestor of all: K
- Why B and C are more related than A and C: B and C share a more recent common ancestor (F) than A and C do (K).