Ctenomyidaetuco-tucos

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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.

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