Monodontidaebeluga and narwhal

The two species of this fam­ily are found at high lat­i­tudes in the arc­tic seas and in most of the major rivers drain­ing into them, south to the Saint Lawrence River. These are medium-sized whales, rang­ing from 4 - 6 m in length and up to around 1600 kg weight. Bel­u­gas have a very short, broad snout, while nar­whales have a square head and ap­pear to lack a snout al­to­gether. The fore­head in both species is high and glo­bose. Mem­bers of this fam­ily lack a dor­sal fin, al­though nar­whals do have a dis­tinc­tive ridge run­ning along their backs. Adults are white (bel­u­gas) or white and black (nar­whals).

As in the closely re­lated del­phinids, both species have a broadly ex­panded fa­cial de­pres­sion; this holds the melon, a fatty de­posit be­lieved to func­tion in echolo­ca­tion. The max­illa and frontal are ex­panded lat­er­ally, hid­ing the small zy­go­matic arch from dor­sal view. The pre­max­il­lae lie flat in front of the nares, which are at the base of the short and broad ros­trum. The length of the mandibu­lar sym­ph­ysis is less than 20% the length of the ramus, and in the upper jaw, the toothrows di­verge pos­te­ri­orly. Teeth are usu­ally sim­ple pegs in bel­uga (5/2 to 11/11 in num­ber) but oc­ca­sion­ally slightly 3-cusped. Nar­whals have but two teeth, the one on the left is de­vel­oped into a spi­raled, for­ward-pro­ject­ing tusk up to 2.7 m in length, and the other is rudi­men­tary. The tusk of nar­whals is found only in males; the teeth of fe­males re­main imbed­ded in their jaws.

Mon­odon­tids are gen­er­ally found in schools, some­times in­clud­ing more than 100 in­di­vid­u­als. They mi­grate in re­sponse to the shift­ing ice pack. Both species feed mainly on the bot­tom, con­sum­ing a num­ber of species of fish and in­ver­te­brates. The tusks pre­sum­ably func­tion in so­cial be­hav­ior; males have been seen to fence with these struc­tures, and oc­ca­sion­ally bro­ken-off pieces of tusk have been found imbed­ded in the heads of males of this species. Both species are highly vocal. Bel­u­gas make a sort of trilling sound and are some­times known as "sea ca­naries."

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.

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