Sirenia

Sirenia is an order of large, fully aquatic, herbivorous mammals that inhabit warm waters around the world. They are the only extant members of the infraorder Tethytheria, which also includes the extinct “sea cows” and “land sloths.” Sirenians are characterized by their streamlined bodies, paddle-shaped tails, and dense bones that aid in buoyancy. Unlike their terrestrial relatives, Sirenians have evolved to live completely aquatic lifestyles. These adaptations include: forelimbs modified into flippers, nostrils located on top of their heads, and the absence of external ear pinnae. Their diet consists primarily of aquatic plants, which they graze on using their large, sensitive upper lips and strong, grinding teeth.

Common Names

Sirenians are commonly known as "sea cows" or "manatees." The term "sea cow" is more broadly used to describe all sirenians, while "manatee" specifically refers to members of the family Trichechidae. Other common names include dugong, "sea pigs," and "sea monsters," though the latter two terms are often used colloquially and are not scientifically recognized.

Characteristics

Key characteristics of sirenians include:

  • Large size: Sirenians are among the largest living mammals, with adults typically weighing between 400 and 1,500 kg (880–3,300 lb).
  • Streamlined bodies: Their bodies are well-adapted for swimming, with a fusiform shape and lack of external ear pinnae.
  • Paddle-shaped tails: The tail is horizontally flattened and used for propulsion.
  • Herbivorous diet: Sirenians are obligate herbivores, feeding on aquatic plants.
  • Dense bones: Their bones are dense, providing ballast and aiding in buoyancy.
  • Thick, wrinkled skin: Their skin is thick and wrinkled, with few hair follicles.
  • Nostrils on top of their heads: This allows them to breathe easily while submerged.
  • Forelimbs modified into flippers: Their forelimbs are used for steering and maneuvering.
  • Rudimentary hind limbs: Sirenians have only vestigial hind limbs, located internally and not visible externally.

Environments

Sirenians inhabit warm, shallow waters of tropical and subtropical regions around the world. They are found in coastal areas, rivers, estuaries, and lagoons, where they have access to abundant vegetation. They are commonly associated with seagrass beds, mangroves, and freshwater wetlands.

References

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