Phylogeny and Cladistics | CK-12 Foundation - Free Printable

To solve this problem, we need to fill in the missing "X" marks in the table by looking at the evolutionary tree (cladogram) above it. The tree shows which traits each group of animals has developed.

Step 1: Understand how to read the chart
* The diagonal line represents evolution over time.
* Traits written below the line (like "amniotic egg") appeared earlier. Any animal branching off *after* that point has that trait.
* Traits written above the line (like "wings") appeared later. Only animals branching off *after* that specific tick mark have that trait.
* An "X" in the table means the animal has that trait. A blank space means it does not.

Step 2: Fill in the row for Mammals
* Look at where "Mammals" branch off on the tree. It is the last branch on the right.
* Trace back down the line from Mammals. You pass these traits: wings, all have legs, no outer shell, nucleated RBC, and amniotic egg.
* Wait, look closely at the "wings" trait. The tick mark for "wings" is *before* the mammal branch? No, let's look closer. The branch for Birds goes up *after* the "wings" mark. The branch for Mammals goes up *before* the "wings" mark but *after* the "all have legs" mark.
* Actually, let's re-read the tree structure carefully.
* The main line goes from left to right.
* Trait 1: Amniotic egg. All groups (Lizards/Snakes, Crocodiles, Birds, Turtles, Mammals) are to the right of this. So all have an amniotic egg. (The table already has Xs for all).
* Trait 2: Nucleated RBC. The next branch to the left is Lizards & Snakes. They branch off *before* this trait? No, the branch for Lizards & Snakes comes off *before* the "nucleated RBC" mark? Let's trace the lines.
* The first branch on the far left is Lizards & Snakes. It branches off *after* "amniotic egg" but *before* "nucleated RBC". However, the table says Lizards & Snakes HAVE nucleated RBCs (there is an X). This implies the trait "nucleated RBC" applies to everything to the right of that tick mark, including the branch that splits off there? Or perhaps the diagram implies that Lizards/Snakes branched off, and then the lineage leading to the others developed nucleated RBCs?
* Let's look at the table again.
* Lizards & Snakes: Amniotic egg (X), Nucleated RBC (X), No outer shell (X).
* Turtles: Amniotic egg (X), Nucleated RBC (X). Blanks for the rest.
* Crocodiles: Amniotic egg (X), Nucleated RBC (X), No outer shell (X), All have legs (X).
* Birds: All Xs.
* Mammals: Amniotic egg (X). Blanks for the rest.

* Let's re-evaluate the tree based on the standard interpretation of cladograms where traits listed on the main stem apply to all descendants branching off after that point.
* Amniotic egg: First trait. All 5 groups branch off after this. Table confirms all have X.
* Nucleated RBC: Second trait.
* The branch for Lizards & Snakes comes off *before* the "Nucleated RBC" tick mark? If so, they shouldn't have it. But the table *gives* them an X. This suggests my initial reading of the branch order might be slightly off, or the table provided in the prompt has pre-filled data that defines the rules. Let's trust the pre-filled Xs to deduce the rule.
* Lizards & Snakes have: Amniotic egg, Nucleated RBC, No outer shell.
* Turtles have: Amniotic egg, Nucleated RBC. (They do NOT have "No outer shell", "All have legs", or "Wings").
* Crocodiles have: Amniotic egg, Nucleated RBC, No outer shell, All have legs.
* Birds have: All traits.
* Mammals have: Amniotic egg. We need to find the rest.

* Let's look at the position of the Mammals branch on the tree.
* The Mammals branch is the second one from the right.
* The Birds branch is the one on the far right.
* The trait "all have legs" is located on the main line *before* the Bird branch splits off, but *after* the Turtle branch splits off? Let's trace the vertical lines up from the labels.
* Label "all have legs": The tick mark is between the Turtle branch and the Crocodile/Bird/Mammal cluster? No, that doesn't fit the table.
* Let's look at the table for Crocodiles. They have "All have legs".
* Let's look at the table for Turtles. They do *not* have "All have legs".
* Therefore, the trait "All have legs" must have evolved *after* Turtles branched off but *before* Crocodiles branched off.
* Now look at Mammals. Where does the Mammal branch split?
* In the diagram, the branches from left to right are:
1. Lizards & Snakes
2. Crocodiles (Wait, the label is under the second box, but the branch line connects to the main stem...)
Let's trace the black lines from the boxes to the main diagonal line.
- Box 1 (Lizards & Snakes): Line connects to the stem *after* "amniotic egg" and *before* "nucleated RBC"? But the table says they have nucleated RBC. This is confusing. Let's look at the tick marks again.

Actually, usually in these diagrams, if a group branches off *before* a trait, they don't have it. If they branch off *after*, they do.

Let's look at Mammals specifically.
The Mammal branch connects to the main diagonal line. Let's see which traits are "below" (earlier than) that connection point and which are "above" (later than).

Looking at the diagonal line from bottom-left to top-right:
1. Tick: amniotic egg
2. Branch: Lizards & Snakes (connects here?) -> If so, they have amniotic egg. Do they have nucleated RBC? The next tick is "nucleated RBC". If the branch is before the tick, they don't. BUT the table says they DO.
*Correction*: Maybe the branch for Lizards/Snakes is actually *after* the Nucleated RBC tick? Let's look at the spacing. The red circle for Lizards/Snakes is in the first box. The line drops down. It seems to drop down *between* "amniotic egg" and "nucleated RBC". This contradicts the table.

Let's try another interpretation. Maybe the table is partially filled and we just need to complete the Mammal row based on the visual position of the Mammal branch relative to the traits.

Let's look at the Mammal branch line. It originates from the main diagonal line.
Which trait ticks are *below* (to the left of) the Mammal branch origin?
- amniotic egg: Yes. (Table has X)
- nucleated RBC: The Mammal branch is clearly to the right of this tick. So Mammals should have Nucleated RBC.
- no outer shell: The Mammal branch is to the right of this tick. So Mammals should have No outer shell.
- all have legs: The Mammal branch is to the right of this tick. So Mammals should have Legs.
- wings: The Mammal branch is to the *left* of the "wings" tick mark. The "wings" tick is further up the line, closer to the Birds. Therefore, Mammals do *not* have wings.

Let's double check this logic against the other animals to ensure consistency.

* Turtles: Branch is after "amniotic egg" and "nucleated RBC". But before "no outer shell"?
* Table says Turtles do NOT have "no outer shell". This fits if the Turtle branch is *before* the "no outer shell" tick.
* Table says Turtles do NOT have "all have legs". This fits if the Turtle branch is *before* the "all have legs" tick.
* Table says Turtles do NOT have "wings". Fits.

* Crocodiles: Branch is after "amniotic egg", "nucleated RBC", "no outer shell", and "all have legs".
* Table says Crocodiles HAVE all these. This fits.
* Table says Crocodiles do NOT have wings. This fits if the Crocodile branch is *before* the "wings" tick. Looking at the diagram, the Crocodile branch (2nd from left? No, let's identify the branches properly).

Let's identify the branches from Left to Right based on the image layout:
1. Lizards & Snakes: Leftmost box. Line connects to stem.
2. Crocodiles: Second box. Line connects to stem.
3. Birds: Third box. Line connects to stem.
4. Turtles: Fourth box. Line connects to stem.
5. Mammals: Fifth box. Line connects to stem.

Wait, the labels at the bottom are:
[Lizards & Snakes] [Crocodiles] [Birds] [Turtles] [Mammals]

But the branches on the tree don't necessarily match that left-to-right order perfectly if we just look at the boxes. We must follow the lines.

Let's trace the lines from the boxes to the diagonal axis:
- Box 1 (Lizards & Snakes): Line hits the axis *after* "amniotic egg" but *before* "nucleated RBC".
*Contradiction Check*: The table says Lizards & Snakes HAVE Nucleated RBC. This implies the diagram might be drawn such that the trait applies to the group branching off at that node, OR the branch is actually after the tick. Let's look really closely at the tick marks vs branch points.

Actually, looking at the "No outer shell" tick. The branch for Lizards & Snakes is definitely before it. The table says they HAVE "No outer shell".
The branch for Turtles is... where? The 4th box. Its line goes down to the axis. It looks like it hits *before* "no outer shell". The table says Turtles do NOT have "no outer shell". This is consistent.

The branch for Crocodiles (2nd box). Its line hits the axis *after* "no outer shell" and *after* "all have legs". The table says they HAVE both. Consistent.

The branch for Birds (3rd box). Its line hits the axis *after* "wings". The table says they HAVE wings. Consistent.

The branch for Mammals (5th box). Its line hits the axis... wait. Let's look at the order of branches on the diagonal line from bottom-left to top-right:
1. Branch for Lizards & Snakes?
2. Branch for ...?

Let's look at the traits again.
Trait: Amniotic Egg. All groups have it.
Trait: Nucleated RBC.
Trait: No Outer Shell.
Trait: All Have Legs.
Trait: Wings.

Let's determine the status of Mammals by comparing their branch position to the trait ticks.

1. Nucleated RBC: The Mammal branch connects to the main line significantly to the right (upstream) of the "Nucleated RBC" tick mark. Therefore, Mammals have Nucleated RBCs.
2. No Outer Shell: The Mammal branch connects to the main line to the right of the "No outer shell" tick mark. Therefore, Mammals have No outer shell.
3. All Have Legs: The Mammal branch connects to the main line to the right of the "All have legs" tick mark. Therefore, Mammals have legs.
4. Wings: The "Wings" tick mark is located further up the line, *after* the Mammal branch has already split off. The Bird branch is the only one that splits off after the "Wings" tick. Therefore, Mammals do not have wings.

Conclusion for Mammals Row:
- Amniotic egg: X (Given)
- Nucleated RBC: X (Because the branch is after this trait evolved)
- No outer shell: X (Because the branch is after this trait evolved)
- All have legs: X (Because the branch is after this trait evolved)
- Wings: [Blank] (Because the branch is before this trait evolved)

Let's double check with general biological knowledge to be sure the diagram isn't tricking us.
- Mammals have amniotic eggs (yes, though internal).
- Mammals have nucleated red blood cells? NO. Wait. Mature mammalian red blood cells do *not* have nuclei. Birds, reptiles, amphibians, and fish DO have nucleated RBCs.

This creates a conflict between standard biology and the likely intended logic of the diagram.
- In many simplified cladograms for schools, "Nucleated RBC" is often used as a trait for Reptiles/Birds, and Mammals are distinguished by *losing* it or having different blood traits. However, looking at the diagram strictly:
- The trait "Nucleated RBC" is placed early on the line.
- The Mammal branch is *after* this trait.
- If we follow the diagram's logic strictly (which is what these tests usually require), Mammals would inherit the traits of their ancestors unless a later trait overrides it. There is no later trait saying "non-nucleated RBC".
- HOWEVER, look at the table for Lizards & Snakes. They have an X for Nucleated RBC.
- Look at Crocodiles. X for Nucleated RBC.
- Look at Birds. X for Nucleated RBC.
- Look at Turtles. X for Nucleated RBC.

If the diagram implies that Mammals branch off *after* the "Nucleated RBC" trait appears, then according to the diagram's internal logic, Mammals should have them. But biologically, they don't.

Let's re-examine the branch positions. Is it possible the Mammal branch is *before* the Nucleated RBC trait?
- The "Amniotic egg" tick is first.
- The "Lizards & Snakes" branch is next.
- The "Nucleated RBC" tick is next.
- If Mammals branched off *before* Nucleated RBC, they wouldn't have it. But the Mammal branch is clearly on the far right of the tree, near Birds. It is physically located after all those early ticks.

Is there a mistake in my biological fact?
- Non-mammalian vertebrates have nucleated RBCs.
- Mammals have non-nucleated RBCs.

So, if the table is scientifically accurate, Mammals should NOT have an X for Nucleated RBC.
Does the diagram support this?
For the diagram to support Mammals NOT having Nucleated RBC, the Mammal branch would have to split off *before* the "Nucleated RBC" tick. But visually, the Mammal branch is the second to last one, splitting off way after that tick.

Alternative interpretation: Maybe the traits listed are derived traits *unique* to the clade starting there?
- "Nucleated RBC" might label the clade containing Lizards, Crocs, Birds, Turtles.
- If Mammals are outside that clade, they don't have it.
- But the line is a single continuum. Usually, traits on the main line are ancestral to all subsequent branches.

Let's look at the "No outer shell" trait.
- Turtles have shells. The table correctly leaves "No outer shell" blank for Turtles.
- The Turtle branch splits off *before* the "No outer shell" tick. This matches the visual.
- Mammals do not have shells. The Mammal branch splits off *after* the "No outer shell" tick. This matches the visual.

Let's look at "All have legs".
- Snakes don't have legs. Lizards do. The group is "Lizards & Snakes". The table puts an X for "All have legs" as BLANK for Lizards & Snakes. This is correct (because snakes don't).
- The "Lizards & Snakes" branch splits off *before* the "All have legs" tick. This matches the visual.
- Mammals have legs. The Mammal branch splits off *after* the "All have legs" tick. This matches the visual.

So, visually and logically within the chart's system:
- Mammals are after "Nucleated RBC".
- Mammals are after "No outer shell".
- Mammals are after "All have legs".
- Mammals are before "Wings".

This leads to the conclusion that Mammals HAVE Nucleated RBCs *according to this specific diagram*. Even though it is biologically incorrect for mature mammalian RBCs, in the context of interpreting this specific educational graphic, we must follow the visual evidence provided. The diagram likely simplifies "vertebrate blood" or ignores the enucleation process in mammals, or perhaps refers to the presence of the gene/capability in the lineage before specialization. Or, more likely, it's a flawed diagram regarding that specific trait, but the student is expected to read the graph, not use outside knowledge that contradicts the graph's explicit topology.

However, let's look closer at the "Nucleated RBC" tick.
Is it possible the tick applies to the branch *starting* there?
The tick is between the Lizard/Snake branch and the next segment.
If the trait evolves *on* the segment leading to Crocs/Birds/Turtles/Mammals, then all those groups have it.

Let's check the solution for "No outer shell".
Tick is after Turtle branch.
Crocs, Birds, Mammals are after. They have no outer shell.
Turtles, Lizards/Snakes are before. They have outer shells (or lack the "no outer shell" trait).
Table: Turtles blank. Lizards/Snakes X? Wait.
Table says Lizards & Snakes HAVE "No outer shell".
But the Lizard/Snake branch is BEFORE the "No outer shell" tick.
This is a contradiction in my previous analysis.

Let's re-read the table for Lizards & Snakes.
Amniotic egg: X
Nucleated RBC: X
No outer shell: X
All have legs: Blank
Wings: Blank

Visually:
Lizard/Snake branch is BEFORE "No outer shell" tick.
Yet table says they HAVE it.

Why?
Maybe the ticks indicate where a trait is *lost* or changed? No, "Amniotic egg" is a gain. "Wings" is a gain.

Let's look at the position of the Lizard/Snake branch again.
Maybe I am misidentifying which line belongs to which box.
Box 1: Lizards & Snakes. Line goes to the first branch point.
Box 2: Crocodiles. Line goes to the third branch point?
Box 3: Birds. Line goes to the last branch point.
Box 4: Turtles. Line goes to the second branch point?
Box 5: Mammals. Line goes to the fourth branch point?

Let's trace the lines very carefully from the boxes to the diagonal.
1. Lizards & Snakes (Box 1): The line drops down and hits the diagonal line at the first intersection point (after amniotic egg, before nucleated RBC).
- If this is true, they should ONLY have Amniotic Egg.
- But the table says they also have Nucleated RBC and No Outer Shell.
- This implies the table might be pre-filled incorrectly in my head? No, I'm reading the image provided. The image HAS the Xs for Lizards/Snakes.

Is it possible the labels on the diagonal are not "traits evolved here" but "traits present in groups above this point"?

Let's reconsider the standard way these questions work. Often, you just match the group to the traits that appear on the line *leading up to* them.

Let's look at Mammals again.
Traits on the line before the Mammal branch:
1. Amniotic egg
2. Nucleated RBC
3. No outer shell
4. All have legs

Traits on the line after the Mammal branch:
1. Wings

Therefore, Mammals have traits 1-4. They do not have trait 5.

Let's verify this pattern with Birds.
Traits before Bird branch: All 5.
Table: All 5 are X. Matches.

Let's verify with Crocodiles.
Where is the Croc branch?
If the order of branches (left to right on diagonal) corresponds to the complexity/traits:
The branches seem to be:
1. Lizards/Snakes
2. Turtles? (If Turtles branch off before "No outer shell", they don't have it. Table agrees.)
3. Crocodiles? (If Crocs branch off after "No outer shell" and "Legs", they have them. Table agrees.)
4. Mammals?
5. Birds?

Let's check the position of the Mammal line vs the Crocodile line.
In the diagram:
- The line from Mammals (Box 5) connects to the diagonal line.
- The line from Crocodiles (Box 2) connects to the diagonal line.
- The line from Turtles (Box 4) connects to the diagonal line.

Let's look at the intersections on the diagonal line from bottom-left to top-right:
Intersection 1: Branch for Lizards & Snakes.
Intersection 2: Branch for Turtles? (It's the line coming from Box 4).
Intersection 3: Branch for Crocodiles? (Line from Box 2).
Intersection 4: Branch for Mammals? (Line from Box 5).
Intersection 5: Branch for Birds? (Line from Box 3).

Let's test this branching order against the traits:

Trait: Nucleated RBC (Tick is between Intersection 1 and 2).
- Lizards/Snakes (Intersect 1): Before tick. Should NOT have it. BUT TABLE SAYS THEY DO.

This is the sticking point. Why does the table say Lizards/Snakes have Nucleated RBCs if they branch off before the tick?

Possibility A: The tick marks indicate the trait is present in the group *branching off at that point* and all subsequent ones?
- If "Nucleated RBC" tick is associated with the Lizard/Snake branch, then Lizards/Snakes have it.
- Then who doesn't? Everyone before? No one is before except maybe fish/amphibians not shown.

Possibility B: The diagram is drawn loosely, and we should rely on the vertical alignment of the boxes and traits?
- Look at the columns.
- There are no grid columns aligning boxes to traits directly.

Possibility C: I am misinterpreting the "No outer shell" entry for Lizards/Snakes.
- Lizards have scales, not shells. Snakes have scales. So "No outer shell" is TRUE for them.
- Turtles HAVE shells. So "No outer shell" is FALSE for them.
- The table reflects reality.
- The diagram MUST reflect reality.
- Therefore, the Lizard/Snake branch MUST be considered "after" the "No outer shell" trait evolution?
- But visually it is before.

Let's look at the Mammals again.
Regardless of the confusion with the earlier branches, the position of the Mammal branch is clear relative to the traits near it.

1. Wings: The Mammal branch is clearly BEFORE the wing tick. (Birds are the only ones after). So Mammals = No Wings.
2. All have legs: The Mammal branch is AFTER the "all have legs" tick. So Mammals = Have Legs.
3. No outer shell: The Mammal branch is AFTER the "no outer shell" tick. So Mammals = No Outer Shell.
4. Nucleated RBC: The Mammal branch is AFTER the "nucleated RBC" tick. So Mammals = Have Nucleated RBC (per diagram logic).

Let's check if there is any reason to doubt "Nucleated RBC" for Mammals in this specific homework context.
- If the student marks "No X" for Nucleated RBC, they are using outside knowledge.
- If they mark "X", they are reading the graph.
- In graph-reading tasks, reading the graph is almost always the required skill. The graph establishes a hypothetical or simplified evolutionary history. We must follow the internal logic of the graph.
- Internal Logic: Trait appears on line -> All subsequent branches have it.
- Mammal branch is subsequent to "Nucleated RBC".
- Therefore, Mammal has "Nucleated RBC".

Final Check of the Mammal Row:
- Amniotic egg: X (Pre-filled)
- Nucleated RBC: X (Branch is after trait)
- No outer shell: X (Branch is after trait)
- All have legs: X (Branch is after trait)
- Wings: [Blank] (Branch is before trait)

Let's quickly verify the "Turtle" row to see if this logic holds for them, as they are the tricky "exception" in the middle.
- Turtle branch is after "Amniotic" and "Nucleated RBC".
- Turtle branch is BEFORE "No outer shell".
- Table: Turtle has Amniotic (X), Nucleated (X), No outer shell (Blank).
- This perfectly matches the "Branch Position" logic.

Since the logic holds perfectly for Turtles (who are correctly placed before the "No outer shell" tick), it must also hold for Mammals (who are correctly placed after the "No outer shell" and "Legs" ticks).

Therefore, the biological inaccuracy regarding mammalian RBCs is an error in the question's design, but the correct answer *for the test* is derived from the visual position.

Step-by-step derivation for the final output:
1. Locate the "Mammals" branch on the evolutionary tree. It is the second branch from the top/right.
2. Identify which trait markers are located on the main line *before* (below/left of) the Mammals branch. These traits are inherited by Mammals.
- "amniotic egg" is before.
- "nucleated red blood cells (RBC)" is before.
- "no outer shell" is before.
- "all have legs" is before.
3. Identify which trait markers are located on the main line *after* (above/right of) the Mammals branch. These traits are NOT inherited by Mammals.
- "wings" is after. (Only the Bird branch is after this mark).
4. Mark an 'X' for every trait found in step 2. Leave blank for step 3.

Resulting Mammals Row:
- Amniotic egg: X
- Nucleated RBC: X
- No outer shell: X
- All have legs: X
- Wings: (blank)

Final Answer:
The completed row for Mammals should have X marks under Nucleated RBC, No outer shell, and All have legs. The column for Wings should remain blank.

| | Amniotic egg | Nucleated RBC | No outer shell | All have legs | Wings |
| :--- | :---: | :---: | :---: | :---: | :---: |
| Mammals | X | X | X | X | |