Anapsid skull defines a primitive reptilian condition with no temporal fenestrae, a solid bony roof over the temporal region. For Q.24—”An anapsid skull is a characteristic of”—the correct answer is option 4: turtles, as they retain this ancestral trait among modern reptiles.

Option Analysis

Option 1: Lizards
Lizards belong to Squamata and possess diapsid skulls with two pairs of temporal fenestrae (antorbital and subtemporal), allowing jaw muscle expansion. These openings evolved for lighter skulls and stronger bite force.
Incorrect, as lizards lost the anapsid condition early in reptilian evolution.​

Option 2: Crocodiles
Crocodiles have diapsid skulls, featuring two temporal openings, though the upper one is often reduced (forming the “diapsid grade”). This supports powerful jaw adduction via enlarged temporalis muscles.
Wrong, as crocodilians diverged from anapsid ancestors but developed fenestrae.​

Option 3: Alligators
Alligators, like crocodiles, exhibit diapsid skull morphology with dual temporal fenestrae, adapted for aquatic predation. Their skulls show the characteristic arch between openings.
Incorrect for the same reasons as crocodiles; they are archosaurs with advanced diapsid features.​

Option 4: Turtles
Turtles (Testudines) uniquely retain the anapsid skull among living reptiles—no temporal fenestrae, fully roofed by dermal bones. This solid structure suits their shelled, protective lifestyle.
Correct, confirmed by embryology and fossils; early anapsids like pareiasaurs also shared this.

Skull Types Overview

Anapsid skulls originated in Carboniferous reptiles (~310 MYA), providing maximal cranial protection but limiting muscle attachment sites.

Exam Relevance

Key for CSIR NET/GATE Zoology: Anapsids represent the basal amniote skull, contrasting diapsid dominance in Sauria. Note: Molecular data debates turtle phylogeny, but skull morphology defines classification.