Animal Diversity Web

Cur­rently, this fam­ily in­cludes 38 species placed in 1 genus, but pat­terns of vari­a­tion within and among species are very poorly un­der­stood, and the num­ber of species may change con­sid­er­ably as tax­on­o­mists con­tinue to work on the fam­ily. Cteno­myids are found in cen­tral and south­ern South Amer­ica.

Tucos are small to medium in size, rang­ing up to around 700 gms body weight. Their bod­ies are heav­ily built, with short, pow­er­ful legs. The skin seems loosely ap­plied to the body, and it has been sug­gested that this makes it eas­ier for tucos to turn around in nar­row bur­rows. The forefeet have ex­tremely long and strong claws that are used for loos­en­ing packed earth. The hind­feet also have well-de­vel­oped claws, but they are not as long as those on the forefeet. The soles of the feet are sur­rounded by a fringe of very stiff hairs, func­tion­ally in­creas­ing their sur­face area for push­ing earth and serv­ing as combs for re­mov­ing dirt from fur. Tucos have large heads. Their eyes are of medium size, not as re­duced as in many other fos­so­r­ial ro­dents. Their ex­ter­nal ears, how­ever, are very small. Tails are short and very sparsely haired. Ex­ter­nally, tucos re­sem­ble pocket go­phers ( Ge­omyi­dae), but they lack the ex­ter­nal cheek pouches pos­sessed by mem­bers of that fam­ily.

The pelage of tucos varies con­sid­er­ably in color and tex­ture among and within species. Gen­er­ally, the fur is thick and long.

As is the case in many other fos­so­r­ial ro­dents, tucos have mas­sively con­structed, broad and flat­tened skulls. They lack a sagit­tal crest, but promi­nent ridges often run along the pari­etals. The ros­trum is ex­cep­tion­ally broad. Zy­go­matic arches bow strongly out­ward. Tucos are hys­tri­co­mor­phous, with a greatly en­larged in­fra­or­bital fora­men that lacks the ven­tral ac­ces­sory fora­men for the pas­sage of nerves to the ros­trum that is seen in some hys­tri­co­morphs. The jugal does not con­tact the lacrimal, but it does have a promi­nent process that pro­jects dor­sally. The bul­lae are large, and be­hind them the paroc­cip­i­tal processes are also large and pressed against the bul­lae. The lower jaws are strongly hys­tricog­nathous and have an ex­cep­tion­ally well de­vel­oped coro­noid process. A deep groove sep­a­rates the mas­se­teric ridge from the lower toothrow.

The teeth of tucos are sim­i­lar to those of the Octodon­ti­dae, kid­ney-shaped (lack­ing re-en­trant folds) and with a much-re­duced third molar. They are hyp­sodont. In­cisors are wide and pow­er­fully built. The roots of the upper in­cisors can clearly be seen to ex­tend through the in­fra­or­bital fora­men to the start of the cheek­teeth. The den­tal for­mula is 1/1, 0/1, 1/1, 3/3 = 20.

Tucos are strongly fos­so­r­ial. They pre­fer to dig in sandy or loamy soils, in which they build com­plex, branch­ing tun­nel sys­tems. These sys­tems may be very long, and they in­clude nest­ing cham­bers and spe­cial cham­bers for stor­ing food. Earth is piled at bur­row en­trances, and the ac­tual bur­row open­ing is some­times plugged. Tucos dig by loos­en­ing earth with their in­cisors, then sweep­ing it out of the tun­nel with their hind feet. In­di­vid­u­als of at least one species uri­nate on packed earth to soften it while they are dig­ging. When threat­ened, tucos may back rapidly through their bur­rows, using their tail as a sense organ.

Tucos feed on roots, stems, and grasses.

Tucos often ap­pear to be colo­nial, but in part that may be due to the patchy dis­tri­b­u­tion of soils that are ap­pro­pri­ate for their ac­tiv­i­ties. In many species, bur­row sys­tems within these colonies are oc­cu­pied by sin­gle in­di­vid­u­als or moth­ers with young. In a few species, how­ever, the so­cial sys­tem is more com­plex and bur­rows may be used by sev­eral in­di­vid­u­als. The name "tuco-tuco" comes from alarm calls in re­sponse to dan­ger; other calls are also known in the more so­cial species.

Tucos are def­i­nitely not ap­pre­ci­ated by ranch­ers and farm­ers, with whom they may com­pete for crops. They also some­times dam­age roots and bark in cit­rus plan­ta­tions, and their bur­rows may pre­sent some dan­ger to live­stock. On the other hand, a num­ber of other species of mam­mals, lizards, toads, in­ver­te­brates, and even birds rely on their bur­rows for shel­ter.

The fos­sil record of tucos ex­tends to the early Pliocene. Tucos are prob­a­bly closely re­lated to the fam­ily Octodon­ti­dae. Like pocket go­phers, they seem to live in fairly small pop­u­la­tions that are par­tially iso­lated from other pop­u­la­tions by in­hos­pitable soils, which has re­sulted in the dif­fer­en­ti­a­tion of a large num­ber of taxa. Whether these taxa should be con­sid­ered species is an issue that may never be re­solved.

Ref­er­ences and lit­er­a­ture cited:

Feld­hamer, G. A., L. C. Drick­amer, S. H. Vessey, and J. F. Mer­ritt. 1999. Mam­mal­ogy. Adap­ta­tion, Di­ver­sity, and Ecol­ogy. WCB Mc­Graw-Hill, Boston. xii+563pp.

Mac­don­ald, David. 1984. The en­cy­clo­pe­dia of mam­mals. Facts on File Pub­li­ca­tions, New York.

Nowak, R. M. and J. L. Par­adiso. 1983. Walker's mam­mals of the world. The Johns Hop­kins Uni­ver­sity Press, Bal­ti­more and Lon­don, pp 803-810.

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

Vaughan, T. A., J. M. Ryan, N. J. Czaplewski. 2000. Mam­mal­ogy. Fourth Edi­tion. Saun­ders Col­lege Pub­lish­ing, Philadel­phia. vii+565pp.

Wil­son, D. E. and D. M. Reeder (eds.). 1993. Mam­mal species of the world: A tax­o­nomic and ge­o­graphic ref­er­ence, 2nd ed.. Smith­son­ian In­sti­tu­tion Press, Wash­ing­ton and Lon­don.

Woods, C. A. 1984. Hys­tricog­nath ro­dents. Pp. 389-446 in An­der­son, S. and J. K. Jones, Jr. (eds.). Or­ders and familes of mam­mals of the world. John Wiley and Sons, New York.

Con­trib­u­tors

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