Question

The table shows the presence (+) / absence (-) of features 1 - 5 for animals P - U.

Based on the table, the correct statement is:

• A. If Q and R represent lamprey and fish respectively, then feature 4 could be jaws.
• B. Feature 5 is the most recently evolved trait.
• C. If S, T and U are respectively amphibian, reptile and mammal, then feature 3 could be amniotic egg.
• D. If S, T and U respectively are salamander, turtle and leopard, then features 1 and 2 could respectively represent hair and four legs.

Hint:

In cladistics, shared derived characters (synapomorphies) are nested. A trait present in many taxa (like Feature 5) is ancestral (plesiomorphic), while a trait unique to a terminal taxon (like Feature 1) is recently derived (apomorphic).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This question asks to identify the correct evolutionary statement based on a character matrix showing the presence (+) or absence (-) of five morphological features across six animal taxa (P to U).

Step 2: Detailed Explanation:

• Let us analyze the character matrix to reconstruct the order of trait evolution: itemize

• Taxon P has none of the features (all -). This represents the outgroup.

• Taxon Q has only feature 5 (+), while all other features are absent (-).

• Taxon R has features 4 and 5 (+).

• Taxon S has features 3, 4, and 5 (+).

• Taxon T has features 2, 3, 4, and 5 (+).

• Taxon U has all five features (+).

From this nested pattern, we can infer that the evolutionary sequence of characters is: Feature 5 $\rightarrow$ Feature 4 $\rightarrow$ Feature 3 $\rightarrow$ Feature 2 $\rightarrow$ Feature 1.
Let us evaluate the options:

• In Option A, Q represents a lamprey (a jawless vertebrate) and R represents a jawed fish. Lampreys have a vertebral column (Feature 5) but lack jaws. Gnathostomes (jawed vertebrates, starting with fish, R) possess jaws. Thus, Feature 4, which is present in R, S, T, U but absent in Q, perfectly represents the evolution of jaws. This is a highly consistent evolutionary scenario.

• Option B is incorrect because Feature 5 is present in almost all taxa, indicating it is the most ancestral trait, not the most recently evolved.

• Option C is incorrect because if S is an amphibian and T is a reptile, then Feature 3 (present in S) cannot be the amniotic egg, as amphibians are anamniotes and do not lay amniotic eggs.

• Option D is incorrect because salamanders (S) do not have four legs and hair represented by features 1 and 2 in that order.

itemize

Step 3: Final Answer:
Therefore, if Q and R represent lamprey and fish respectively, then feature 4 could be jaws.