Discuss the progression of changes that took place during th

Discuss the progression of changes that took place during the transition from pelycosaurs to true mammals that may have promoted the evolution of endothermic homeothermy according to the changing body size hypothesis of McNab. Include the influences of changing body size in the ancestors of mammals, inertial homeothermy, and shifting to nocturnality.

Solution

There are major changes took place during transition from pelycosaurs to mammals . First Locomotion, Mammals locomotion process involved a change in limb posture from sprawling in Pelycosaurs to erect. Erect body posture places the hands and feet closer to the body, resulting in less need for large ventral limb muscles just to hold the body up off the ground. Movement of the limb goes into rotation back and forward. The long bones of mammalian limbs in conjunction with the shift to more erect body posture. The vertebral column becomes more rigid.More neck bones are added and a more rounded occipital condyle develops which allow more flexible movement of the head. The major changes in jaws , teeth and jaw muscles are modified. Increased complexity in the cheek teeth included the growth of additional cusps on the crowns . This helps to chew and crush food particles. As the complexity increases , it forms firm anchorage. One of the features in mammals is evolution of two sets of teeth juvenile teeth and adult teeth. This feature in mammalsis due to presence of interlocking teeth which results in improved chewing.The interlocking cusps of upper and lower teeth cannot be maintained if the teeth are continuously lost and replaced So this feature is enabled . It is believed that the pelycosaurs, like their living mammal relatives, were endothermic, which means that they maintained a constant internal body temperature. These are the changes from pelycosaurs to mammals.