sirenid

Sirenids are a family of marine mammals belonging to the order Cetacea, commonly known as whales and dolphins. The family includes two extant genera: *Ziphius* (the bottlenose whale) and *Mesoplodon* (beaked whales), as well as several extinct relatives. Sirenids are often confused with sirens from mythology, but they are unrelated; the name "sirenid" is derived from their resemblance to mythological sirens in some early classifications.

The most well-known living sirenid is the bottlenose whale (*Ziphius cavirostris*), a deep-diving species found in temperate and tropical oceans worldwide. It is characterized by its robust, conical snout, large eyes, and dark, streamlined body. Beaked whales (*Mesoplodon* spp.) are smaller, with a distinct beak-like snout and a series of teeth in the lower jaw. These whales are known for their deep dives, often reaching depths of over 2,000 meters, and their elusive behavior, making them difficult to study.

Fossil records indicate that sirenids evolved from earlier cetaceans around 15–20 million years ago. Some extinct genera, such as *Hyperoodon* (now classified under *Berardius*), were much larger, with species like *Hyperoodon planifrons* reaching lengths of up to 20 meters. Sirenids are adapted for deep-sea life, with specialized physiological traits like high blood oxygen capacity and collapsible lungs to withstand extreme pressures.

Behaviorally, sirenids are generally solitary or found in small groups. They communicate using low-frequency sounds, which can travel long distances underwater. Due to their deep-diving habits and remote habitats, much about their ecology and behavior remains poorly understood. Conservation efforts focus on protecting critical habitats and reducing threats such as ship strikes and entanglement in fishing gear.