Presence of diaphragm is an exclusive character of mammals which is not found in any other class.
Homeothermy is also found in class aves; so it cannot be
considered as an exclusive character.
Four chambered heart is found in crocodiles which belongs
to reptilia.
So diaphragm is the organ found exclusively in mammals which differentiates it from other classes.

Hope it helps!!

Presence of Diaphragm

The correct answer is option 'B': Presence of diaphragm. The diaphragm is a unique feature of the mammalian body. It is a dome-shaped, muscular partition that separates the thoracic and abdominal cavities. This structure plays a crucial role in the process of respiration and is responsible for the mechanical aspect of breathing.

The diaphragm is located at the base of the rib cage and is attached to the lower ribs and the lumbar vertebrae. It is composed mainly of skeletal muscle fibers, which are under voluntary control. However, the diaphragm also contains smooth muscle fibers, which are involuntary and help in maintaining its shape.

Function of the Diaphragm

The diaphragm has several important functions in the mammalian body:

1. Breathing: The main function of the diaphragm is to aid in the process of respiration. When it contracts, it flattens and moves downward, increasing the volume of the thoracic cavity. This expansion creates a negative pressure within the lungs, causing air to rush in and fill the lungs during inhalation. When the diaphragm relaxes, it returns to its dome shape, reducing the volume of the thoracic cavity and causing exhalation.

2. Separation of Thoracic and Abdominal Cavities: The diaphragm acts as a physical barrier between the thoracic and abdominal cavities. It prevents the organs in the abdominal cavity, such as the liver, stomach, and intestines, from pushing up into the thoracic cavity.

3. Core Stability: The diaphragm is an essential component of the core musculature. It works in coordination with other muscles, such as the transverse abdominis, pelvic floor muscles, and deep back muscles, to provide stability and support to the spine and pelvis.

Evolutionary Significance

The presence of a diaphragm is unique to mammals. It is believed to have evolved as a result of the transition from a quadrupedal to a bipedal posture. The diaphragm enables mammals to breathe efficiently by enhancing the exchange of gases in the lungs. Additionally, the diaphragm's role in core stability is crucial for the maintenance of an upright posture.

In conclusion, the presence of a diaphragm is a very unique feature of the mammalian body. It plays a vital role in respiration, separates the thoracic and abdominal cavities, and contributes to core stability. This evolutionary adaptation has provided mammals with efficient breathing mechanisms and improved posture.