Difference between Diapsid and Synapsid


They are amniotes that developed two temporal fenestra or skull holes about millions of years ago. Here, two holes are present on each side of the skull. Diapsids include organisms like lizards, snakes, crocodiles, turtles, tuatara and birds. Some of them, like lizards, have lost one of their holes in recent years. Turtles and snakes have lost both holes, and the bird’s skull has been heavily restructured in modern days. However, all these organisms are classified under diapsid based on their ancestral skull structure.

Most diapsids show unique characteristics like strong jaw muscles and long radial bone. They were originally classified under the class Reptilia.


They include mammals and mammal-like animals with one skull hole on each side. Their temporal fenestrae are fused. Synapsids were the largest vertebrates during the Permian period.

Their special characteristics include differentiated teeth – incisors, molars and canines. Thus, they have versatile feeding behaviour. Their jaw transitioned from a reptile-like to a more mammalian-like feature. They developed a secondary palate that separates the nasal cavity and mouth. Body hair and other mammalian features are also unique to synapsids. They have evolved to become more mammalian than reptilian. Present-day synapsids include most mammals like humans, blue-whale and even monotremes.

Also Refer: Vertebrates

Difference between Diapsid and Synapsid



They are vertebrates with two skull holes or temporal fenestra.

They are vertebrates with one skull hole or temporal fenestra.

Two holes are at each side of the skull.

The holes are behind each eye in the skull region.

They support strong jaw muscles.

They have comparatively weaker jaws.

Their teeth are not differentiated.

Their teeth are differentiated into canines, incisors and molars.

They have less versatile feeding niches.

They show more versatile feeding behaviours.

They include most reptiles and birds.

They mostly include mammals.

They are reptile-like organisms that are less evolved.

They are more evolved into mammal-like creatures.

Also Read: Difference between Aves and Mammals

Frequently Asked Questions on Difference between Diapsid and Synapsid

What is temporal fenestra?

It is a skull opening behind the eye cavity (orbit) in some vertebrates. It was a common feature in the fossilised skulls of most dinosaurs. Their main role is to reduce the skull weight.

What are sauropsids?

Sauropsids are lizard-like amniotes that are considered as a sister group to the synapsids. They were once the largest animals on water, air and land. Most of them died out in mass extinction. At present, they include most birds and reptiles. Diapsida is a subclade under Sauropsida.

What are anapsids?

Amniotes with no skull openings are termed anapsids. They are primitive organisms that had Permian turtles, terrapins and tortoises.

Explore: Reptilia

Keep exploring BYJU’S Biology for more exciting topics

Leave a Comment

Your Mobile number and Email id will not be published. Required fields are marked *




App Now