Balaenidae (/bəˈlɛnɪdeɪ,-diː/) is afamily ofwhales of theparvorderMysticeti (baleen whales) that contains mostly fossil taxa and two living genera: the right whale (genusEubalaena), and the closely related bowhead whale (genusBalaena).[3][4]
Until recently, all right whales of the genusEubalaena were considered a single species—E. glacialis. In 2000, genetic studies of right whales from the different ocean basins led scientists to conclude that the populations in the North Atlantic, North Pacific and Southern Hemisphere constitute three distinct species.[5] Further genetic analysis in 2005 using mitochondrial DNA and nuclear DNA has supported the conclusion that the three populations should be treated as separate species,[6] and the separation has been adopted for management purposes by the U.S. National Marine Fisheries Service and the International Whaling Commission.[7]
Thecladogram is a tool for visualizing and comparing the evolutionary relationships betweentaxa. The point where a node branches off is analogous to an evolutionary branching – the diagram can be read left-to-right, much like a timeline. The following cladogram of the family Balaenidae serves to illustrate the current scientific consensus as to the relationships between the North Pacific right whale and the other members of its family:[8]
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Baleen whales belong to a monophyletic lineage ofMysticeti. Mysticeti are large filter-feedingcetaceans that also include some of the largest animals on earth as well as some of the most critically endangered.[9][10] Based on morphology and molecular data, four extant family-level clades are recognized within Mysticeti: Balaenidae (bowhead and right whales), Neobalaenidae (pygmy right whales), Eschirichtiidae (gray whales), and Balaenopteridae (rorquals).[10] Phylogenetic relationships of the mysticeti order remain unclear due to legal and logistical challenges.[10] However, recent morphological analysis, support Balaenidae as a monophyletic group that is the sister group to Neobalaenidae.
Balaenids are large whales, with an average adult length of 15 to 17 metres (45–50 feet), and weighing 50-80 tonnes. Their principle distinguishing feature is their narrow, arched, upper jaw, which gives the animals a deeply curved jawline. This shape allows for especially longbaleen plates. The animals utilise these byram feeding, swimming at or near the surface with their mouth open for minutes at a time, and straining food from the water, which they then scrape off the baleen with their tongues[11] – a feeding method that contrasts with those of therorquals and thegray whale.[12] Their diet consists of smallcrustaceans, primarilycopepods, although some species also eat a significant amount ofkrill.[13] Similarities in terms of physical appearances of jawlines and usages between balaenidae andflamingo have been pointed as a result of possibleconvergent evolution.[14]
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Balaenids are also robustly built by comparison with the rorquals, and lack the grooves along the throat that are distinctive of those animals. They have exceptionally large heads in comparison with their bodies, reaching 40% of the total length in the case of thebowhead whale. They have short, broad, flippers, and lack a dorsal fin.
All species are at least somewhat migratory, moving into warmer waters during the winter, during which they both mate and give birth.Gestation lasts 10–11 months, results in the birth of a single young, and typically occurs once every three years.[13]
The four species of the Balaenidae are found in temperate and polar waters;Eubalaena glacialis (North Atlantic right whale),Eubalaena japonica (North Pacific right whale),Eubalaena australis (southern right whale), andBalaena mysticetus (bowhead whale). Bowhead and right whales can reach up to 18 meters in length and over 100 tons at maturity.[15][16]
Members of Balaenidae can live over 70 years and were hunted extensively in the late 1800s for their blubber. Approximately 40% of right whales' body mass is blubber, and thus they were known as the "right" whale to kill.[17][18]
After death, the large blubber deposits caused right whales to float to the surface, which facilitated an easier oil harvest. With a population estimated at between 300-350 individuals,[19] the North Atlantic right whale is the most critically endangered great whale. The Northern Pacific right whale is also endangered with only about 500 individuals extant.[16][17] The Southern right whale (~7500 individuals in 1997) and the Bowhead whale (20,000 to 40,000) have made stronger recoveries since whale hunting was significantly curtailed by international agreement.[16]
Although Rice believed that all right whales belong with the bowhead in the genusBalaena, recent genetic analysis have recognized three separate right whale species, in the genusEubalaena: in the North Atlantic (E. glacialis); in the North Atlantic (E. japonica); and in the Southern Hemisphere (E. australis).
The study by Churchill (2007) now has provided the evidence to conclude that the three living right whale species do comprise a phylogenetic lineage distinct from the bowhead and are rightly classified into a separate genus.
Media related toBalaenidae at Wikimedia Commons
Data related toBalaenidae at Wikispecies
