Temporal fenestra

Massospondylus Skull Steveoc 86

Temporal fenestra are openings in the skull of certain vertebrate animals, located behind the orbits of the eyes. These openings are significant in the study of the evolution of vertebrates, particularly in the classification of amniotes, which include modern reptiles, birds, and mammals. Temporal fenestrae allow for the attachment of muscles that control the jaws, thereby facilitating a stronger bite. The classification of amniotes into different groups is largely based on the number and arrangement of these fenestrae.

Types of Temporal Fenestrae

There are three main types of temporal fenestrae arrangements found in amniotes:

1. Anapsid: Skulls with no temporal fenestrae. This condition is primitive and is seen in early amniotes. Modern examples include turtles, which are often considered anapsids, though this classification is subject to ongoing research and debate.

2. Synapsid: Skulls with a single temporal fenestra on each side. This arrangement is characteristic of mammals and their extinct relatives, such as the pelycosaurs and therapsids. The single opening allows for the expansion of the jaw muscles, contributing to the more powerful bite of mammals compared to other vertebrates.

3. Diapsid: Skulls with two temporal fenestrae on each side. Most modern reptiles, including lizards, snakes, and crocodilians, as well as birds, exhibit this pattern. The additional fenestra provides more space for muscle attachment, allowing for a wide range of jaw movements and bite strengths.

Evolutionary Significance

The evolution of temporal fenestrae is a key aspect of vertebrate evolution, providing insights into the dietary habits, ecological niches, and phylogenetic relationships of extinct animals. The transition from anapsid to synapsid and diapsid conditions marks significant evolutionary events, reflecting adaptations to changing environments and prey availability.

Function

The primary function of temporal fenestrae is to allow for the expansion and more efficient arrangement of jaw muscles, which can increase bite force and efficiency. This adaptation is particularly important for predators and herbivores that rely on strong bites to capture and process food.

Classification Based on Temporal Fenestrae

The classification of amniotes based on the presence and arrangement of temporal fenestrae is a fundamental aspect of vertebrate paleontology. This classification system has undergone revisions as new fossil evidence comes to light, but it remains a crucial tool for understanding the evolutionary history of terrestrial vertebrates.

See Also

• Skull
• Vertebrate
• Amniote
• Evolution of reptiles