Baleen whale

Baleen whales[1] Fossil range: latest Eocene - Recent Humpback Whale breaching Scientific classification Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Cetacea Suborder: Mysticeti Cope, 1891 Families Balaenidae Balaenopteridae Eschrichtiidae Neobalaenidae Janjucetidae† Cetotheriidae† Diversity Around 15 species Baleen

The blue whales, also called whalebone whales or great whales, form the Mysticeti, one of two suborders of the Cetacea (whales, dolphins, and porpoises). Baleen whales are characterized by having baleen plates for filtering food from water, rather than having teeth. This distinguishes them from the other suborder of cetaceans, the toothed whales or Odontoceti. Living Mysticeti species have teeth only during the embryonal phase. Fossil Mysticeti had teeth before baleen evolved.

The suborder contains four families and fifteen species.

Etymology

The taxonomic name Mysticeti apparently derives from a transmission error in early copies of Aristotle's Historia Animalium in which "ο μυς το κητος" ("the whale known as 'the mouse' or 'Gutter whale' ") was mistakenly run together as "ο μυστικητος" ("the Mysticetus").^[2] An alternate name for the suborder is Mystacoceti (from Greek μυσταξ "moustache" + κητος "whale").^[3]

Anatomy

Baleen whales are generally larger than toothed whales, and females are bigger than males. This group includes the largest known animal species, the Blue Whale.

Humpback whale with two blowholes clearly visible

Baleen whales have two blowholes, causing a V-shaped blow.

Ecology and life history

Behavioral ecology

Solitary or in small groups called pods.

Breaching

In spite of their enormous size, baleen whales are able to leap completely out of the water. They can grow to 190,000 kilograms (420,000 lb) in weight and 33.5 metres (110 ft) in length.^[4] Particularly known for its acrobatics is the Humpback Whale, but other baleen whales also break through the water surface with their body or beat it loudly with their fins. Some believe that the male baleen whales try to show off in the presence of females to increase their mating success. Scientists speculate that baleen whales and other cetaceans may engage in breaching to dislodge parasites, or scratch irritated skin. Breaching, and other behaviors like lobtailing, are also used to stun or kill nearby fish or krill.

Importance to humans

From the 11th to the late 20th centuries, baleen whales were hunted commercially for their oil and baleen. Their oil was used to make margarine and cooking oils, whilst their baleen was used to stiffen corsets, as parasol ribs and to crease paper.

Evolutionary history

Parietobalaena palmeri (extinct) skull

Early baleen whales first appeared as far back as Early Oligocene, or perhaps the latest Eocene (39–29 million years ago; e.g., Llanocetus). Early baleen whales possessed teeth inherited from their ancestors, as opposed to baleen, in modern species. The Oligocene species Aetiocetus cotylalveus is considered the evolutionary link between toothed and baleen whales. It was discovered by renowned fossil collector Douglas Emlong in 1964 near Seal Rock State Recreation Site, Oregon, in a sandstone formation.^[5] In the early 1990s, the species Janjucetus hunderi was discovered in Victoria, Australia by a surfer and was described in 2006 by E. M. G. Fitzgerald.^[6] Janjucetus was a baleen whale with sharp teeth that hunted fish and squid as well as larger prey, potentially including sharks and dolphin-like cetaceans. These fossils hint that early baleen whales were predatory and eventually evolved into the gentler, toothless whales known today. A recent study identified palatal foramina (bony impressions of blood vessels that 'feed' the baleen racks) in the palate of a toothed mysticete, Aetiocetus weltoni. The scientists involved indicated that this discovery implies that this whale possessed both teeth and baleen, and serves as an intermediate adaptive role between primitive toothed mysticetes and more advanced toothless mysticetes.^[7] The first baleen-bearing, toothless baleen whales (such as Eomysticetus, and Micromysticetus) appeared in the late Oligocene.^[8] Early baleen whales probably could not echolocate; no anatomical evidence preserved in the skulls and ear regions of any fossil baleen whales show any of the adaptations associated with echolocation as in 'toothed whales' (Odontoceti).^[6]

Taxonomic classification

• ORDER CETACEA

The earliest-known baleen whale is Llanocetus denticrenatus, discovered on Seymour Island, Antarctica, by E.D. Mitchell in 1989. The species lived during the Late Eocene, about 45 mya.

References