Synapsids and Sauropsids Overview

A specialized egg that develops an amnion, allantois, chorion, and yolk sac, providing protection, gas exchange, and nourishment.

The inner membrane surrounding the embryo within the amniotic egg, providing a fluid-filled environment.

A structure that helps with gas exchange and waste disposal in the amniotic egg.

An outer membrane in the amniotic egg that contributes to gas exchange and, in mammals, becomes part of the placenta.

A sac within the amniotic egg that provides nutrients to the developing embryo.

A clade of amphibians that includes the ancestors of amniotes.

A skull with solid dermal plates and no temporal fenestrae. This is found in turtles and early reptiles.

A skull with two temporal fenestrae. This is found in dinosaurs and all extant reptiles except turtles.

A skull with one temporal fenestra located below the postorbital-squamosal suture. This is found in mammals and their ancestors.

A skull with one temporal fenestra located high on the skull. This is found in several extinct marine groups.

A sheet of muscle that separates the abdomen and helps with breathing. It flattens when it contracts, pulling air into the lungs.

This is a change in the vertebral column, specifically the division into thoracic and lumbar sections, connected to the development of the diaphragm in synapsids.

A type of lung common in mammals, characterized by a tree-like branching pattern with alveoli where gas exchange occurs.

Type of lung common in sauropsids (reptiles and birds), featuring cup-like chambers that line the airways (parabronchi).

A structure found in birds, these air sacs do not participate in gas exchange but store air, aiding in respiration.

The ankle joint in amniotes is characterized by a calcaneum and astragalus bone, with the mesotarsal joint being the original point of articulation.

The maintenance of a body temperature higher than the ambient temperature, leading to higher metabolic rates and greater activity levels.

A theory explaining the evolution of endothermy, where early mammals may have been nocturnal and higher temperatures were beneficial for their activity.

The principal nitrogenous waste product excreted by mammals, requiring a lot of water for elimination.

The primary nitrogenous waste product excreted by reptiles, requiring less water for elimination. This is made possible by the presence of small glomeruli in the kidneys.

The amniotic egg is a revolutionary adaptation that allowed vertebrates to reproduce on land. It consists of four extra-embryonic membranes: the amnion, allantois, chorion, and yolk sac, each with a specific function.

Amniotes exhibit internal fertilization and lack a larval stage, unlike their amphibian ancestors. This allows for more direct development and eliminates the need for an aquatic larval stage, freeing them from dependence on water.

Synapsids, the group that includes mammals and their ancestors, are characterized by a single temporal fenestra (opening) in their skull, right below the postorbital-squamosal suture. This unique feature distinguishes them from other amniotes.

The evolution of the diaphragm in synapsids was a crucial adaptation that enabled them to breathe more efficiently. It separates the chest cavity from the abdomen, allowing for negative pressure breathing.

Sauropsids, the group that includes reptiles and birds, have a different type of lung structure known as faveolar lungs. These lungs feature cup-like chambers called faveoli that line the airways, allowing for efficient gas exchange.

The earliest group of amniotes, characterized by a skull with solid dermal plates and no temporal fenestrae.

A large Mesozoic radiation of amniotes, characterized by a skull with two temporal fenestrae. Ancestors of all living reptiles and birds.

The first large radiation of amniotes, characterized by a skull with a single temporal fenestra located below the postorbital-squamosal suture. Includes ancestors of mammals.

An extinct group of amniotes characterized by a single temporal fenestra located high on the skull.

The process of breathing in synapsids is coupled with locomotion, allowing efficient ventilation without interfering with movement.

Animals (clade Amniota) distinguished by having an amniotic egg and internal fertilization.

Membranes (amnion, allantois, chorion, yolk sac) that surround the embryo, providing protection, nutrition, and waste management.

Ventilation achieved by rib movement creating negative pressure to draw air in, augmented in some by cloacal or pharyngeal gas exchange.

Keratinized structures like scales, hair, feathers, etc., combined with high lipid concentration which minimizes water loss in amniotes.

A key characteristic of amniotes is the complete absence of gills in all life stages.

Tetrapods initially moved like salamanders, compressing one lung while bending.

A sheet of muscle separating the abdomen, aiding breathing without locomotion interference.

The boundary where the diaphragm develops and lumbar ribs are lost.

Ventral ribs used by some bipedal dinosaurs and birds for lung ventilation.

Anterior and posterior sacs that store air but don't participate in gas exchange.

Site of gas exchange, branching from parabronchi.

Connects to the fibula.

Connects to the tibia.

Being active in cool nights and colder temperatures.

Ancestral mammals being nocturnal.

Can influence phenotype of offspring through temperature.

Excreting uric acid and reabsorbing sodium/potassium.

Secreting salt; allows for excess ions in blood to be secreted.