California Sea Lion

California Sea Lion

The California sea Iion (Zalophus californianus) is the most commonly stranded pinniped in California. California sea lions are light to chocolate brown in color and exhibit marked sexual dimorphism. Males can weigh up to 390kg (850lbs) and have a distinctive raised bony bump on their head known as a sagittal crest. Females are smaller and weigh up to 110kg (220lbs) and have no sagittal crest. California sea lions can sometimes be confused with the Stellar sea lion which are found rarely in central and northern California. These two species are distinguished most easily by the presence of a thumb-sized gap between the most rear tooth and the next tooth in the skull which is present in Stellar sea lions but not in California sea lions. This gap is called a diastema. You can further explore the anatomy of the California sea lion below.

The special sensory organs in pinnipeds include the eyes, ears, nose, and vibrissae. Marine mammals, especially pinnipeds, have quite a challenge to overcome because they have to function in air, in water, in bright light, and in low light.

The integument (skin or pelt) of marine mammals is a very special organ! In cetaceans (dolphins, porpoises, whales) the skin is smooth and sleek and feels very similar to a hard boiled egg. In pinnipeds (seals, sea lions, and fur seals), the skin is covered in a layer of hair which can vary greatly in its thickness depending on the species.

The musculoskeletal system consists of the muscles, bones, ligaments, and tendons. In marine mammals, one of the first noticeable differences during a necropsy is the dark red color of the muscles compared with terrestrial animals.

Fish anyone? The digestive system of marine mammals consists of the mouth, esophagus, stomach, small and large intestine, colon, and rectum. Accessory organs are also critical for digestive function including the liver and pancreas.

The cardiopulmonary system includes the heart and blood vessels, the lymphatic system, nose, nasopharynx, trachea, bronchi and lungs.  These interdependent systems are responsible for picking up and carrying oxygen to the cells of the body and transporting and discarding carbon dioxide.

The lymphoreticular system consists of the spleen, lymphnodes, lymphatic vessels, thymus, and bone marrow. The functions of these systems include immune defense, transport of fats throughout the body, and collection and transport of interstitial fluid (the fluid bathing the cells) back to the circulatory system.

The endocrine system consists of the thyroid and parathyroid glands, pancreas and adrenal glands although other organs are also critical players in the endocrine system as well including the liver, adipose (fat) tissue, the hypothalamus, and pituitary glands.

The nervous system is made up of the brain and spinal cord (the central nervous system or CNS) and the all the other nerves of the body (the peripheral nervous system or PNS).

The urinary system consists of the kidneys, ureters, bladder, and urethra. The most striking difference between the urinary system of marine mammals and that of most terrestrial animals is that marine mammals have reniculated kidneys.

Like all mammals, the female reproductive tract consists of the ovaries, uterus, cervix, and vagina. Examination of the reproductive tract during necropsy can reveal a lot of life history information about an individual. For example, the presence and number of CORPUS ALBINCANS (white bodies) can tell you the approximate number of pregnancies that the animal has experienced.

The male reproductive system consists of the testicles, vas deferens, epididymis, prostate, and penis. In pinnipeds, males have a bone inside their penis called a baculum. This bone is not present in cetaceans. As in females, significant life history information can be gained by careful examination of the male reproductive tract. For example, determination of whether an animal is an adult or sub-adult can be determined by looking for the presence of sperm in the epididymis and the relative size of the testicles.