Longman's beaked whales, sometimes known as "tropical bottlenose" or "Indo-Pacific beaked whales," are one of the rarest and least known members of the beaked whale family (Ziphiidae). As adults, Longman's beaked whales can reach estimated lengths of about 20-30 ft (6-9 m); their weight is unknown. Compared to other beaked whales, this species is relatively large.
Longman's beaked whales have a large, robust body with a fairly large, "falcate" "dorsal" fin located far down their back. This species has dark, small, rounded, narrow flippers that fit into a depression on either side of the body. They have a well-defined "melon" (forehead) that is almost perpendicular to their long, tube-shaped beak. A crease may distinguish the melon from the beak. As they grow older, the melon develops into a steeper more bulbous shape that may hang over the beak. Like other beaked whales, they have V-shaped paired throat creases. As scientists have learned more about this species' external appearance and physical description, they have resolved confusion in various at sea sightings.
Longman's beaked whales have a relatively small, low, bushy blow that is usually visible and slightly angled forward. Longman's beaked whales generally have a darker grayish, bronze, brown, or olive coloration that extends from their blowhole and eye down their back, as well as a facial band. The melon and defined "thoracic" patch is lighter in color, sometimes described as "creamy" or pale. The upper jaw of the beak is darker and the lower jaw is lighter. The lower jaw has two conical shaped teeth located at the tip. Adult males have visible, erupted teeth (difficult to see in the field, especially when the mouth is closed), and may have linear and oval-shaped scars (e.g., bites from cookie-cutter sharks and lampreys) along their body.
Many species of beaked whales (especially those in the genus Mesoplodon) are very difficult to distinguish from one another (even when dead). At sea, they are challenging to observe and identify to the species level due to their cryptic, skittish behavior, a low profile, and a small, inconspicuous blow at the waters surface; therefore, much of the available characterization for beaked whales is to genus level only. Uncertainty regarding species identification of beaked whales often exists because of a lack of easily discernable or distinct physical characteristics.
Longman's beaked whales are usually found in tight groups averaging between 10-20 individuals, but occasionally have been seen in larger groups of up to 100 animals. They have sometimes been observed associating with other marine mammals such as pilot whales, spinner dolphins, and bottlenose dolphins. Dives may last from 14-33 minutes and their swimming style has been described as aggressive. This species is commonly misidentified when observed at sea.
The feeding behavior and prey of these cetaceans is generally unknown, but scientists believe it is similar to that of other beaked whales. Beaked whales are known to dive deep to forage for their food, possibly into the "sound channel." The analysis of stomach contents from one stranded specimen implies that cephalopods (e.g., squid and octopus) comprise the majority of the whale's diet.
Nothing is known about the reproduction or lifespan of this species. Due to the rarity, behavior, and infrequent encounters with this species, much of the information available is unreliable. A single young neonate calf was measured at 9.5 ft (2.9 m).