Balaenopteridaerorquals

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This family includes 6 species placed in 2 genera. It includes minke, Bryde's, sei, fin, humpback, and blue whales. These range in size from the relatively small minke whale, about 8-10 m in length, to the giant blue whale, at 20 - 28 m length and almost 200,000 kg weight. The shape and color of the body, and the size and shape of fins, varies considerably among species. A shared external trait is the presence of deep longitudinal grooves in the skin, running over the entire throat and chest.

The skulls of these mysticetes can be recognized by a combination of the following technical characteristics: the nasals and the nasal processes of the premaxillae extend backward beyond the supraorbital processes of the frontals; the nasals are reduced in size; the frontals are small and barely or not exposed on the dorsal surface; the supraoccipital extends forward beyond the zygomatic process of the squamosal; the rostrum is broad and flat.

The baleen plates of rorquals are short and broad. These species feed by gulping large quantities of water and straining crustaceans and fish by shooting the water out between the baleen plates.

Rorquals feed in cold currents at high latitudes during the summer, mostly on the eastern sides of the oceans. Some species range mostly offshore, others are more often found in coastal waters. Their food is primarily krill, euphausiid crustaceans, which congregate near the surface in cold water. Blue whales eat little but euphausiids; other species have a broader diet, even including some fish. During the fall, most species migrate toward equatorial latitudes. They fast for several month, living by metabolizing blubber.

Rorquals are usually seen in groups ("pods") of 2-5 individuals. Their populations have been much reduced by whaling, and most are now fully protected by international treaty.

References and literature cited:

Nowak, R.M. and J.L. Paradiso. 1983. Walker's Mammals of the World, 4th edition . John Hopkins University Press, Baltimore, MD.

Savage, R. J. G. and M. R. Long. 1986. Mammal Evolution: An Illustrated Guide. Facts on File Publications, UK. 251 pp.

Rice, D. W. 1984. Cetaceans. Pp. 447-490 in Anderson, S. and J. K. Jones, Jr. (eds). Orders and Families of Recent Mammals of the World. John Wiley and Sons, N.Y. xii+686 pp.

Vaughan, T. A. 1986. Mammalogy. Third Edition. Saunders College Publishing, N.Y. vii+576 pp.

Wilson, D. E., and D. M. Reeder. 1993. Mammal Species of the World, A Taxonomic and Geographic Reference. 2nd edition. Smithsonian Institution Press, Washington. xviii+1206 pp.


Species included in database:

Contributors

Phil Myers (author), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

motile

having the capacity to move from one place to another.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate