Cladogram interactive worksheet - Free Printable

Let’s go step by step to fill in the table and answer all the questions using the cladogram.

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Step 1: Understand the Cladogram

The cladogram shows how different animals are related based on shared traits (called “derived traits”). Each node (numbered 1–6) represents a point where a new trait evolved, and all organisms after that node have that trait — unless they branched off before it.

Traits from bottom to top:
- Vertebrae → appears at node 0 (base), so ALL animals here have vertebrae.
- Bony skeleton → node 1 → tuna, frog, human, hare, caiman, parrot have it. Shark does NOT (shark has cartilage).
- Four limbs → node 2 → frog, human, hare, caiman, parrot have it. Tuna and shark do not.
- Amniotic egg → node 3 → human, hare, caiman, parrot have it. Frog does not (frogs lay eggs in water without amnion).
- 2 skull openings → node 4 → caiman and parrot have it. Human and hare do NOT (they’re mammals with one opening or modified).
Wait — actually, looking again: In standard biology, mammals (human, hare) have ONE temporal fenestra (skull opening), while reptiles/birds (caiman, parrot) have TWO. But in this diagram, “2 skull openings” is placed at node 5? Let me recheck the image description.

Actually, in the provided cladogram:

Looking at the branching:

After “amniotic egg” (node 3), we split into two lines:
- One leads to human/hare → then gets “hair” at node 6.
- Other leads to caiman/parrot → then gets “2 skull openings” at node 5? Wait, no — let's trace carefully.

From the diagram description:

Node 1: bony skeleton → after this: tuna, frog, human, hare, caiman, parrot (not shark)

Node 2: four limbs → after this: frog, human, hare, caiman, parrot (not tuna or shark)

Node 3: amniotic egg → after this: human, hare, caiman, parrot (not frog)

Then from node 3, it splits:
- Left branch → human & hare → then node 6: hair
- Right branch → caiman & parrot → then node 5: 2 skull openings? Actually, looking at labels:

In the original text:
“hair” is labeled near node 6 (for human/hare)
“2 skull openings” is labeled near node 5 (for caiman/parrot)
But wait — node numbers might be assigned differently.

Actually, let’s assign traits per organism by tracing their path from root:

Start from bottom (vertebrae = everyone):

Shark: only has vertebrae → no bony skeleton (cartilaginous), no four limbs, etc.

Tuna: vertebrae + bony skeleton → stops there. No four limbs.

Frog: vertebrae + bony skeleton + four limbs → no amniotic egg.

Human: vertebrae + bony skeleton + four limbs + amniotic egg + hair → but NOT 2 skull openings (mammals have one)

Hare: same as human → vertebrae, bony skeleton, four limbs, amniotic egg, hair → no 2 skull openings

Caiman: vertebrae + bony skeleton + four limbs + amniotic egg + 2 skull openings → no hair

Parrot: same as caiman → vertebrae, bony skeleton, four limbs, amniotic egg, 2 skull openings → no hair

So now we can fill the table.

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Fill the Table:

We put an “X” if the organism HAS the trait.

| | vertebrae | Bony skeleton | Four limbs | Amniotic egg | 2 skull openings | hair |
|----------|-----------|---------------|------------|--------------|------------------|------|
| Shark | X | | | | | |
| Tuna | X | X | | | | |
| Frog | X | X | X | | | |
| Human | X | X | X | X | | X |
| Hare | X | X | X | X | | X |
| Caiman | X | X | X | X | X | |
| Parrot | X | X | X | X | X | |

Note: For “2 skull openings”, humans and hares do NOT have them — they are mammals with a single temporal fenestra (or secondarily closed). So leave blank for human/hare.

Hair is only for human and hare.

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Now Answer Questions:

#### What do nodes 1-6 represent?
→ They represent derived traits (new evolutionary features that appear at that point and are passed to descendants).

Specifically:
- Node 1: bony skeleton
- Node 2: four limbs
- Node 3: amniotic egg
- Node 4: ? (actually in diagram, node 4 isn’t labeled — maybe typo? From context, node 5 is “2 skull openings”, node 6 is “hair”)
Wait — in the user’s image description, nodes are labeled with traits:

Looking back:
“vertebrae” at base (node 0?)
Then node 1: bony skeleton
Node 2: four limbs
Node 3: amniotic egg
Then branch: left to human/hare → node 6: hair
Right to caiman/parrot → node 5: 2 skull openings
And node 4 is between amniotic egg and the split? Maybe node 4 is just the common ancestor of amniotes?

Actually, in many cladograms, nodes represent common ancestors, and the tick marks represent derived traits.

But the question says: “What do nodes 1-6 represent?” and gives options: derived trait OR common ancestor.

In cladistics, nodes represent common ancestors, and the tick marks (or labels along branches) represent derived traits.

But in this diagram, the numbers 1-6 are placed ON THE BRANCHES next to the trait names — so likely, each number corresponds to the evolution of that trait.

However, strictly speaking, in phylogenetics:

→ Nodes = common ancestors
→ Traits evolve along branches leading to nodes.

Given the way the question is phrased (“nodes 1-6”), and since they’re numbered along the branches with traits, I think here they mean the points where traits arise — so perhaps they’re referring to the traits themselves as represented by those nodes.

But let’s look at the exact wording: “What do nodes 1-6 represent? derived trait / common ancestor”

Standard answer: Nodes represent common ancestors.

Even though traits are written beside them, the node itself is the ancestor.

For example, node 3 is the common ancestor of human, hare, caiman, parrot — which had the amniotic egg.

So correct answer: common ancestor

But let’s confirm with later questions.

Next question: “What are the traits that are shared by the human, hare, caiman and parrot?”

These four all come after node 3 → so they share: vertebrae, bony skeleton, four limbs, amniotic egg.

They do NOT all share 2 skull openings (only caiman/parrot) or hair (only human/hare).

So shared traits: vertebrae, bony skeleton, four limbs, amniotic egg.

Similarly, traits NOT shared by all four: 2 skull openings and hair.

Trait common to ALL organisms listed (shark to parrot): only vertebrae — because shark doesn’t have bony skeleton, etc.

Most recent common ancestor of human and hare: look at where their lines meet — that’s node 6? Or the node just before hair? Actually, human and hare share a more recent common ancestor than either does with caiman. That ancestor would be the one right after node 3, before splitting into mammal line and reptile/bird line. But specifically for human and hare, their MRCA is the node where hair evolved — node 6? Or the node immediately preceding both?

In cladograms, the most recent common ancestor of two species is the node where their lineages converge.

For human and hare: they branch off from the same point after node 3 — so their MRCA is the ancestor at the base of the “hair” clade — which is node 6? Or is node 6 the trait?

This is confusing due to labeling.

Perhaps better to think:

- All organisms after node 3 have amniotic egg.
- Then the lineage splits: one leads to mammals (human/hare), other to sauropsids (caiman/parrot).
- Within mammals, human and hare share a more recent ancestor — which is the one that first developed hair — so node 6 represents that ancestor? Or the trait?

I think for simplicity, since the question asks “what is the most recent common ancestor”, and nodes are numbered, we refer to the node number.

Looking at the diagram structure:

After node 3 (amniotic egg), the branch goes up and splits into two:
- Left: goes to human and hare — and along that branch, node 6 is marked with “hair”
- Right: goes to caiman and parrot — node 5 marked with “2 skull openings”

So the common ancestor of human and hare is the node just before they split — which might be unlabeled, but since node 6 is on the branch leading to both, perhaps node 6 is considered their MRCA.

Actually, typically, the node is the point of divergence. So if human and hare diverge from each other at a certain point, that point is their MRCA.

In this diagram, human and hare are shown as sister taxa — meaning they share a direct common ancestor not shared with others. That ancestor would be at the node where the “hair” trait appears — so node 6.

Similarly, human and caiman: their MRCA is node 3 (the amniotic egg ancestor), because after that, they went separate ways.

Now, “Would it matter if the hare and the human swapped places?” — No, because they are sister taxa; swapping them doesn’t change relationships.

Organisms with amniotic eggs: human, hare, caiman, parrot (all after node 3)

Outgroup: The outgroup is the organism that branches off earliest and is least related to the rest. Here, shark is the outgroup — it only has vertebrae, nothing else. So yes, there is an outgroup: shark.

Which organisms are more closely related: frog and tuna, or shark and frog?

Look at the cladogram:

- Shark branches off first.
- Then tuna branches off.
- Then frog branches off.

So frog and tuna share a more recent common ancestor (node 1: bony skeleton) than shark and frog do (their MRCA is node 0: vertebrae).

Therefore, frog and tuna are more closely related.

Criteria: We look at how recently they shared a common ancestor — the fewer nodes between them, the closer the relationship.

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Final Answers Compiled:

#### Table:

| | vertebrae | Bony skeleton | Four limbs | Amniotic egg | 2 skull openings | hair |
|----------|-----------|---------------|------------|--------------|------------------|------|
| Shark | X | | | | | |
| Tuna | X | X | | | | |
| Frog | X | X | X | | | |
| Human | X | X | X | X | | X |
| Hare | X | X | X | X | | X |
| Caiman | X | X | X | X | X | |
| Parrot | X | X | X | X | X | |

#### Questions:

1. What do nodes 1-6 represent? → common ancestor

2. Traits shared by human, hare, caiman, parrot? → vertebrae, bony skeleton, four limbs, amniotic egg

3. Traits NOT shared by all four? → 2 skull openings, hair

4. Trait common to all organisms? → vertebrae

5. Most recent common ancestor of human and hare? → node 6 (since that’s where their lineage shares the hair trait, and they are sister groups)

6. Most recent common ancestor of human and caiman? → node 3 (amniotic egg ancestor)

7. Would it matter if hare and human swapped places? → no

8. Which organisms have amniotic eggs? → human, hare, caiman, parrot

9. Is there an outgroup? → yes (shark)

10. Which organisms are more closely related? → frog and the tuna

11. Why? → Because they share a more recent common ancestor (at node 1, bony skeleton) than shark and frog do (who only share vertebrae at the base).

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Final Answer:

Table filled as above.

Answers to questions:

- Nodes 1-6 represent: common ancestor
- Shared traits by human, hare, caiman, parrot: vertebrae, bony skeleton, four limbs, amniotic egg
- Traits not shared by all four: 2 skull openings, hair
- Common trait to all: vertebrae
- MRCA of human and hare: node 6
- MRCA of human and caiman: node 3
- Swap hare and human? no
- Organisms with amniotic eggs: human, hare, caiman, parrot
- Outgroup? yes
- More closely related: frog and the tuna
- Criteria: They share a more recent common ancestor (node 1) compared to shark and frog (who share only node 0).