PlatanistidaeIndian river dolphins

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This family includes 5 species in 4 genera. In many accounts of cetaceans, its members are placed in four separate families: Iniidae (South American river dolphin), Lipotidae (Chinese river dolphin), Platanistidae (Indian river dolphins), and Pontoporidae ( La Plata river dolphin). Members of these families are found in fresh-water rivers and coastal waters in Asia and South America.

These dolphins are generally small, ranging from 1-3 m in length and from roughly 20 to 225 kg in weight, depending on species. They have a long, slender beak, above which rises a sharply differentiated, bulging forehead. The eyes are small, and in some species, appear atrophied. Unlike most other cetaceans, platanistids have a distinct neck. The flippers are broad and either rounded or sharply curved. The dorsal fin is low in all but the La Plata dolphin, in which it is moderately high. Colors tend to be muted grays, pinks, and browns, usually darker above and paler below.

Technically, these species are characterized by narrow facial depressions, with the lateral edges of the depression (formed by maxilla and frontal bones) not roofing over the temporal fossa and concealing the zygomatic arch. The zygomatic arch is strongly developed and arched. The rostrum is very long and slender; the mandibular symphysis is long, from 46 to 72% of the length of the ramus; and the teeth are numerous, ranging from 25/24 to 61/61. The teeth of most species are simple pegs, but in one species the posterior teeth are slightly tricusped, and in another they have a well defined cingulum.

The rivers used by most platanistids are muddy, and these animals probably rely on echolocation more than vision to locate their prey. They feed on fish and invertebrates, making dives that rarely last more than a few minutes. Group size varies from single individuals to 10 or 12. In general, little is known about their ecology and social behavior.

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.

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