>SPECIES of DEGU<

There are currently four different sub-species of degu26, one species (O. pacificus) has only relatively recently been discovered. All are herbivorous and similar in appearance24. The four species include: 

The degu (or common degu)
Bridges' degu Octodon bridgesii
The moon-toothed degu
And the Mocha Island degu Octodon pacificus

The common degu is the species most of us in the UK, USA and Europe keep as pets, and the species referred to as 'degu'. The degu was classified as a species in 1782 by Father Juan Ignacio Molina, a Chilean priest and naturalist. 

Bridges' degu was classified as a species in 1844 by George Robert Waterhouse, an English naturalist. Waterhouse named the species after Victorian botanist Thomas Bridges who collected the first specimen172.

The moon-toothed degu was classified as a species in 1943 by Wilfred Hudson Osgood, an American zoologist.

The Mocha island degu was classified in 1994 by Dr. Rainer Hutterer, a German mammalogist.

Although all these degus look similar, not all the species have the same circadian patterns (the moon-toothed degu and Bridges' degu are nocturnal, while the common degu and the Mocha island degu are diurnal24 , 143). The ventral (belly) fur of the common degu and Bridges' degu has also been found to be markedly more UV reflective than that of the moon-toothed degu24, possibly due to its strict nocturnal lifestyle. Bridges' degu is reported to be less well adapted than the common degu for digging143. The Mocha island degu appears more primitive27 and has long, soft fur and a long, poorly tufted tail27. The common degu is reported to have the most tufted tail of all species52, despite being the least well haired52. The common degu's molars differ from the moon-tooth and Bridges' degu as it has only moderate indentations in the enamel surface, whereas the other species have marked molar indentations52. The moon-toothed degu also lacks a fold on the inside of the last molar52, whereas Bridges' degu has a deep fold52. Other differences include the distribution; the common degu, as it's name suggests, is the most common and endemic in most open scrub areas of central 24 ,26. The next most common is Bridges' degu, which inhabits denser rocky areas, forest52 and farmland24 , 26 in the southern portion of 26, although this species is becoming increasingly uncommon33, possibly as a result of deforestation in the area143. Bridges' degu has some climbing ability, dependent on tree stem diameter154. The moon-toothed degu is rarer, inhabiting dense scrubland near the coast26, thickets52 and small forests from sea level to 1,200m in the Andes24 near 26. Rarer still is the Mocha island degu, having been discovered in the last few decades on alone26. Mocha island is a small costal island in the Valdivian rainforest zone of central Chile27.

In addition to these four octodons, there is also an offshoot genus called Octodontomys, or long-tailed octodons20. This genus includes the mountain degu (chozchoz)20 .

>RELATIVES<

The order Caviomorpha is divided into four lineages25 (and includes 16 families24): 

Cavioidea (including the guinea pig)
Erethizontoidea (including the porcupine)
Chinchilloidea (including the chinchilla)
Octodontoidea (including our friend the degu)

Which shows that degus are closely related to guinea pigs and chinchillas18, as well as tree porcupines. In particular, the hystricognath group includes the degus' close relatives the wild guinea pig19 , the capybara19 , the mara23 , the yellow toothed cavies23 ( (the cui), (the mountain cavy)) and the plains viscacha19 . Hystricognaths have 230 species in 68 genera and 17 families25, and all share characteristic mandible and cranial morphology120.

Although there are only four sub-species of degu, there are a total of six species of Octodontoids occupying central Chile26 on both sides of the Andes mountains between 16-41° south115.  Other Octodontids include the rock rabbit (pika)20 , the tuco tuco25 , the casiragua25 , the white-faced tree rat25 , the nutria25 , the Cuban hutia25 and the mountain viscacha20 .

Caviomorphs in the Erethizontoid group include the North American porcupine25 .

Caviomorphs in the Cavioid group include the paca25 , the pacarana25 , the capybara25 and of course the guinea pig25.

Caviomorphs in the Chinchilloid group include the chinchilla25 and the chinchilla rat25 .