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Viscacha rats (genus Tympanoctomys Yepes, 1942) are ecologically, physiologically, and behaviorally unusual octodontid rodents endemic to the Monte and Patagonian desert biomes of Argentina. The geographic ranges of the different species of Tympanoctomys have been described in general terms but have not been associated with spatial and climate data. Within species, populations are patchily distributed and genetically distinct. We investigated the predicted distribution of Tympanoctomys and the influence of climate fluctuations on their geographic range in historical, current, and future, scenarios. Our objectives were to characterize the environmental niche of the genus, propose a paleoclimatic context for the oldest fossils, characterize the environmental niches for T. barrerae and T. kirchnerorum, and forecast potential future distributions for these taxa. Ecological niche models were constructed using occurrence records from 1941 to the present wherein we identified several precipitation and temperature variables as important predictors of the geographic distributions of the genus, and the species T. barrerae and T. kirchnerorum. Based on our models’ results, we hypothesize that the distribution of Tympanoctomys has contracted from historical to modern times. At the species level, T. kirchnerorum likely experienced the most dramatic change, suffering a large contraction of its historical distribution resulting in its limited present distribution. Given these findings, projected future climate fluctuations and global warming are expected to affect the distributions and persistence of these species.

The Andean degu, Octodontomys gliroides Gervais & d'Orbigny, 1844, has a broad distribution inhabiting pre-Andean pre-Puna and Puna environments of tropical South America. In order to understand the phylogeographic patterns of Octodontomys gliroides, we sequenced 579 bp of the mitochondrial DNA control region from 100 individuals collected from 20 populations across its entire distributional range. The phylogenetic and parsimony network, in conjunction with analysis of molecular variance (AMOVA), revealed a structured pattern of geographic differentiation of O. gliroides, with the occurrence of two well-defined evolutionary lineages: lineage A, restricted to Bolivia and Chile, and lineage B, restricted mainly to Argentina. Analysis of population structure inferred three genetic clusters along the distribution of O. gliroides that mostly agree with the four major barriers inferred by BARRIER analysis (e.g. rivers, salt flats, deserts, and mountain systems). In addition to the significant differentiation found among all levels studied, a positive correlation was identified between genetic and geographic distance, similar to as expected under the isolation-by-distance model. The most recent common ancestor of O. gliroides was estimated as c. 5.99 Mya, and the divergence between lineages A and B is estimated to have occurred by the Middle Pleistocene, about 0.69 Mya. The mismatch distributions and neutrality tests suggested a signal of population range expansion for both lineages coincident with major climatic changes that occurred during the wet–dry events of the Pleistocene in the Andean Puna region. Bayesian skyline plots (BSPs) for lineage A suggest a long history of constant population size followed by a period of slight to moderate demographic expansion at c. 0.04 Mya, whereas lineage B remained unclear after BSP analysis, probably because of the limited sample size.

Rodents are important components of nearly every terrestrial ecosystem and display considerable ecological diversity. Nevertheless, a lack of data on the ecomorphology of rodents has led to them being largely overlooked in palaeoecological reconstructions. Here, geometric and linear morphometrics are used to examine how cranial and dental shapes reflect the diets of living rodent species. Although most rodents are omnivores or generalist herbivores, some species have evolved highly specialized carnivorous, insectivorous, and herbivorous diets. Results show that living rodents with similar diets display convergent morphology, despite their independent evolutionary histories. Carnivores have relatively elongate incisors, elongate and narrow incisor blades, orthodont incisor angles, reduced cheek tooth areas, and enlarged temporal fossae. Insectivores display relatively degenerate dentition, elongate rostra, narrow and thin zygomatic arches, and smaller temporal fossae. Herbivores are characterized by relatively broader incisor blades, longer molar tooth rows, larger cheek tooth areas, wider skull and rostrum, thicker and broader zygomatic arches, and larger temporal fossae. These results suggest that cranial and dental morphology can be used to accurately infer extinct rodent diets regardless of ancestry. Application to extinct beavers suggests that most had highly specialized herbivorous diets.

By comparison with murine rodents such as rats, the middle ear structures of many subterranean mammals appear to be enlarged and thus adapted toward low-frequency sound transmission. However, comparison with closely related terrestrial outgroups has not always been undertaken, and apparent specializations in some cases might reflect phylogeny rather than habitat. Examination of the middle ear of the nonsubterranean degu (Octodon degus) under light microscopy revealed a septated middle ear cavity, a circular tympanic membrane lacking a pars flaccida, a malleus with elongated head, synostosed with the incus, a typically bicrurate stapes, and no stapedius muscle. Many of these features are shared with closely related, subterranean octodontoids in the genera Ctenomys (tuco-tucos) and Spalacopus (coruro). Caviomorph rodents in general share a very similar middle ear morphology, regardless of habitat, which suggests that sensitive low-frequency hearing is plesiomorphic for this group, rather than being specifically associated with a subterranean lifestyle.

To examine the evolution of burrowing specializations in the sister families Octodontidae and Ctenomyidae (Rodentia: Caviomorpha), we produced a synthetic phylogeny (supertree), combining both molecular and morphological phylogenies, and including both fossil and extant genera. We mapped morphological specializations of the digging apparatus onto our phylogenetic hypothesis and attempted to match morphological diversity with information on the ecology and behaviour of octodontoid taxa. Burrowing for sheltering and rearing is the rule among octodontids and ctenomyids, and adaptations for digging have been known from the Early Pliocene onward. However, only a few taxa have evolved fully subterranean habits. Scratch-digging is widespread among both semifossorial and fully subterranean lineages, and morphological changes associated with scratch-digging are not restricted to subterranean lineages. By contrast, various adaptations for chisel-tooth digging are restricted to some subterranean lineages and are combined differently in the octodontid Spalacopus, the fossil ctenomyid Eucelophorus, and some living Ctenomys. Some octodontid taxa are able to dig complex burrows in spite of having no substantial changes in musculoskeletal attributes. Hence, we suggest that, during the early evolution of those branches giving rise to fully subterranean ctenomyids and octodontids, a change in behaviour probably preceded the origin of structural adaptations. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 267–283. ADDITIONAL KEYWORDS: behaviour – Ctenomyidae – evolutionary morphology – Octodontidae – subterranean niche.

The discovery of tetraploidy in the red viscacha rat, Tympanoctomys barrerae (4 n = 102) has emphasized the evolutionary role of genome duplication in mammals. The tetraploid status of this species is corroborated here by in situ PCR and Southern blot analysis of a single-copy gene. The species meiotic configuration strongly suggests a hybrid derivation. To investigate the origin of T. barrerae further, the recently described Pipanacoctomys aureus was studied. This 92-chromosome species also has a duplicated genome size, redundant gene copy number and diploid-like meiotic pairing, consistent with an event of allotetraploidization. Phylogenetic analysis of mitochondrial sequences indicates sister-group relationships between these two tetraploid rodents. The new karyotypic data and the phylogenetic relationships suggest the participation of the ancestral lineages of Octomys mimax in the genesis of P. aureus . The high overall DNA similarity and shared band homology revealed by genomic Southern hybridization as well as matching chromosome numbers between O. mimax and the descendant tetraploid species support the notion of introgressive hybridization between these taxa. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 443‐451. ADDITIONAL KEYWORDS: allotetraploidy ‐ genome size ‐ hybridization ‐ octodontids ‐ polyploidy ‐ Tympanoctomys barrerae .

Molecular phylogenetic relationships were investigated in 6 species of Chinchillidae (Chinchilla lanigera, C. brevicaudata, Lagidium peruanum, L. viscacia, L. wolffsohni, and Lagostomus maximus), 1 species of Dinomyidae (Dinomys branickii), 1 of Abrocomidae (Abrocoma cinerea), and 1 of Octodontidae (Octodon degus) using the first 548 base pairs of the mitochondrial cytochrome-b gene. Maximum-parsimony and maximumlikelihood analyses consistently showed Chinchillidae as a robust clade and confirmed a close relationship with Dinomyidae. Both Chinchilla species differed at 22 sites, and 3 were nonsilent; average genetic distances were approximately 6%. Sequences from domestic C. lanigeraand wild C. brevicaudatashowed low levels of variation. Although all topologies obtained were congruent with current taxonomy, Lagidium exhibited large genetic distances (range 5.9‐8.9%), suggesting the existence of more than the 3 species currently recognized. Chinchillids are endemic South American rodents (Rodentia, Hystricognathi, Chinchillidae) and occur along the Andes. They include chinchillas (Chinchilla), mountain viscachas (Lagidium), and pampas viscachas (Lagostomus).

The middle ear of the solitary subterranean rodent Ctenomys talarum was studied. The most significant features observed were the enlarged middle-ear cavity, a round and larger eardrum without pars flaccida, no connection between malleus and the tympanic bone, partial fusion of malleus with incus, a nearly flat stapedial footplate, absence of stapedial artery, reduced tensor tympani, and absence of stapedial muscle. Some of these features are shared with unrelated subterranean rodents like Spalax ehrenbergi and geomyids, possibly as adaptations for low-frequency hearing.

Sperm quantity and quality were examined in 2 populations (from Mar de Cobo and Necochea, Argentina) of the subterranean rodent Ctenomys talarum (tuco-tuco) for which polygyny was confirmed as their mating system. Nonetheless, differential population attributes allow us to propose that polygyny may be exerted at different levels. Mean epididymal sperm counts were not different, but the Necochea population was characterized by higher variance in sperm counts. Low sperm production, with little variance, in the Mar de Cobo population is consistent with a more extreme polygyny, with aggression playing an important role in the males securing monopolization of females. In the Necochea population, where males were less likely to maintain female exclusivity, subordinant males are not driven away and may invest more in sperm production than in male-male interactions. However, C. talarum males from both populations produce high-quality sperm cells, based on their motility, percentage of live sperm cells, and morphology.

The red viscacha rat, Tympanoctomys barrerae , is an octodontid rodent endemic to the Monte and Patagonian deserts of Argentina. It lives in burrows with numerous portals facing different directions. We studied climatic factors as possible determinants of burrow architecture and portal orientation, in 2 populations. Climatic factors examined were sunlight, direction of sun’s rays, and wind frequency and intensity. Variables analyzed for burrow architecture were portal orientation, slope, and depth at the 1st turn. Mean number of portals per burrow was significantly different between populations. Burrows had few portals oriented toward predominantly cold and intense winds. More portals faced direct solar light in winter. Burrows are so constructed as to allow openings to receive direct sunlight in winter and indirect sunlight in summer.

We studied morphological and functional variations in jaws of coastal and mountain populations of subterranean Spalacopus cyanus inhabiting soils with contrasting hardness. We found almost no morphological differentiation between populations in the variables we measured. However, there were clear differences in incisor resistance between them. Apparently, soil hardness did not represent a selective pressure on cururos' digging apparatus. An Andean origin of this genus could explain our results.

Daily patterns of activity were studied under laboratory conditions in 12 coruros, Spalacopus cyanus, subterranean social rodents originally from Chile. When able to burrow, coruros spent 90% of the total time underground, and surface activity occurred during the 1st hours of darkness. When prevented from burrowing, locomotory activity of coruro groups peaked near the onset of darkness but also occurred during episodes of light. Individually housed coruros displayed a clear nocturnal activity pattern. Coruros exhibited endogenous circadian rhythms entrained by a light–dark cycle.

A chromosomal study that included the use of uniform stain, G-, C-banding and digestion with restriction enzymes Alu I and Sau 3A was completed in 13 male and two female Ctenomys perrensi collected six localities in Corrientes (NE Argentina). The specimens studied had diploid numbers of 50–57 and FN ranging from 84 to 88. These differences resulted from the presence in heterozygosis or homozygosis of one or two fission products involving chromosomes 1, 2, 4, 7 and 8. In addition, in two localities karyotypes with 2 n=51, 53, 54, 55 and 56 were found, due to the presence of 1–4 C-negative supernumerary chromosomes. All specimens, except for one male and two females, showed more than one different karyotype. Our results suggest that in the localities studied, individuals heterozygous for one or two fission products and/or with a variable number of supernumerary chromosomes are frequently found.

A cytogenetic chromosome study was carried out on specimens of four species of Ctenomys—C. talarum, C. rionegrensis, C. pearsoni and C. dorbignyi—from 10 different populations. The analysis of chromosomes was performed through sequential uniform stain, G and C-banding, and with restriction enzymes. The results obtained are discussed in relation to phylogeny. Chromosome evolution in the species studied suggests that the chromosome number has increased due to fissions, and that a reduction of the amount of constitutive heterochromatin has occurred. Different types of heterochromatin, with different patterns, have been added in parallel during evolution. Some taxonomic suggestions can be deduced from this cytogenetic study.

Genetic variability measured by allozymic electrophoresis has been studied in several species of the subterranean rodent genus Ctenomys (Octodontidae). The study was carried out with the main purpose of analysing a special group known as the 'Corrientes group' which inhabits the province of Corrientes in Argentina. The members of the group are, with high probability, isolated reproductively due to their karyotypic differences (diploid numbers are between 49 and 70). To evaluate whether the chromosomal differences were the causes of speciation or if they arose a posteriori, we compared the level of the genetic distance among taxa within the Corrientes group with all those measured between intraspecific populations in Ctenomys. The results indicate that the distances among the populations of the Corrientes group are at or below the level of those measured among intraspecific populations in Ctenomys. Thus, it is unlikely that genetic differentiation triggered speciation. It is shown that this low level of genetic differentiation is not in contradiction with the high levels expected for species originating from one of the possible mechanisms of chromosomal speciation named, chromosomal transilience. Although for geographical reasons it seems obvious that gene flow is precluded among the members of the Corrientes group, the Slatkin method for estimating Nm values was also used. Because high values of Nm exist but no isolation by distance could be detected, it is suggested that reproductive and geographical isolation are very recent. Finally, analysis of population variability suggests that the high levels of heterozygosity observed (a) can be explained by the population structure, and (b) are within the range of expected values if bottlenecks have occurred in the recent history of the Corrientes group. As a general conclusion, the results indicate that in the Corrientes group the genetic data support a putative causal role for chromosomes in speciation.

Predation by owls upon two sympatric species of subterranean rodents of the genus Ctenomys was studied by comparing characteristics of individuals that were field-trapped and preyed upon. Predators took a greater proportion of the smaller C. talarum than of the larger C. australis in comparison to that estimated from their respective field densities. Only subadult individuals of C. australis were found among pellets. For C. talarum , a greater proportion of subadults than of adults was observed in pellets. We suggest that this pattern is determined both by constraints imposed by size of prey on the ability of a predator to handle large prey and by greater exposure of dispersing subadults to predation. Differential predation possibly maintains the habitat segregation observed between C. talarum and C. australis .

Morphological variation in the glans penis of the six genera and most species of octodontid rodents was studied and compared to members of the Abrocomidae and Ctenomyidae. Most specimens of Octodon degus, O. lunatus, O. bridgesi, Octodontomys gliroides, Aconaemys fuscus , and A. sagei presented two spikes on each side at the bottom of the intromitent sac (2–2 pattern), although the number of spikes varies from 1–2 to 4–5. The largest variability in number of spikes was shown by Spalacopus cyanus , ranging from 1–1 to 4–5; although they were rather short. The 1–1 pattern characterized Tympanoctomys barrerae and Octomys mimax . This pattern was found in the species of the genera Abrocoma and Ctenomys , which belong to the related families Abrocomidae and Ctenomyidae. Our results support the view that the 1–1 pattern is ancestral and that other patterns are derived states. Within the octodontids, only Tympanoctomys barrerae and Octomys mimax showed the ancestral condition shared with Ctenomyidae and Abrocomidae. All other octodontid genera share the derived state 2–2 or modifications of it.

Six geographic samples of the fossorial genus Aconaemys were studied to determine differences in cranial morphometrics, pelage coloration, and karyotype. Results showed variation that departs significantly from previous works. Distinct karyotypes were found for each nominal form. Using cluster analysis and discriminant-function analysis, contrasting patterns of cranial morphology are demonstrated that show A. fuscus to be as distinct from A. sagei as is A. porteri . Despite a certain degree of overlap in qualitative cranial characters and pelage coloration, three monotypic species of Aconaemys are recognized.

Karyotypic evolution in the Octodontidae and Abrocomidae is examined by use of C-bands. Karyotypic pathways illustrate chromosomal rearrangements that are more varied than previously thought. A superimposition of tandem fusions and non-Robertsonian mechanisms involving euchromatic segments accounts for the pattern of variation observed. Hetero-chromatic short arms, although present, do not explain the general biarmed karyotypic condition observed across the genera. Evolution of heterochromatin has proceeded through whole-arm additions and euchromatin transformation, and has been independent of the bidirectional changes in diploid number. The magnitude of the karyotypic differences within the Octodontidae reflects its extensive adaptive radiation in the past, although the family is now represented by relatively few species.

Coevolution was studied in six species of rodents of the genus Ctenomys and their parasitic nematodes of the genus Paraspidodera, collected in Bolivia. Representatives of the families Octodontidae and Caviidae were used as outgroups for the mammals, and nematodes from caviids were used as outgroups of the nematodes from ctenomyids. For the nematodes, quantitative and qualitative morphological characteristics of both males and females and electrophoretic characters of both sexes were used to generate phylogenetic hypotheses of evolutionary relationships of the OTes occurring in hosts of different species. Concordance estimates of cladograms generated from biochemical-genetic and morphological data of the nematodes show a percentage incongruence (Mickevich-Farris Incongruence Statistic or 1"r) of 8.23"0 in the character sets. Parsimony mapping, testing concordance of topologies between the trees derived from both analysis of both morphological and biochemical-genetic data indicates an overall agreement of82.3° 0 . Comparisons of topologies of the host and parasite cladograms, as measured with parsimony mapping, showed 70. 8 o/" concordance, indicating substantially more cospeciation than host-switching in the Ctenomys-Paraspidodera host-parasite system. Nematodes of the genus Paraspidodera appear to have invaded the Ctenomys lineage from an origin in caviids sometime before the ctenomyids began to diversify in early Pleistocene time.

Subterranean rodents have been used frequently as examples of explosive speciation in mammals. We tested for differential rates of diversification by using information from molecular phylogenies to focus primarily on tuco-tucos (Rodentia: Octodontidae), the most speciose lineage of subterranean rodents. Tuco-tucos were not significantly more diverse than their sister taxon (octodontines); however, a lineages-through-time analysis suggests an increase in diversification at the base of the tuco-tuco clade.

ROBERTSHAW, J. D., AND R. H. HARDEN. 1986. The ecology of the dingo in northeastern New South Wales. IV. Prey selection and its effect on the major prey species, the swamp wallaby Wallabia bicolor (Desmarest). Australian Wildl. Res., 13:141-164. RUSSELL, E. M. 1982. Patterns of parental care and parental investment in marsupials. Biol. Rev., 57: 423-486. SCHLAGER, F. 1981. The distribution, status and ecology of the rufous rat-kangaroo, Aepyprymnus rufescens, in northern New South Wales. Unpubl. M. Nat. Res. thesis, Univ. New England, Armidale, New South Wales, 190 pp.

We studied the glans penis of Ctenomys from 8 localities in western and southern Uruguay. Three of them, representing C. rionegrensis , are characterized by a trilobed bacular tip and a pair of spikes (length = 2.412 ± 0.093 mm, mean ± SD ) within the intromittent sac. Five samples representing the C. pearsoni complex exhibit a paddle-shaped baculum with a simple, rounded tip, and peculiar spiny bulbs. These paired structures consist of an evagination of the dorsolateral inner surface of the intromittent sac, and bear a large number of spines. A variable number of small spikes (length = 0.861 ± 0.034) may be present at the base of the spiny bulbs. The spikes may be absent, present only on one side or on both. Phallic structural variation is congruent with cranial morphology and karyotypes. The observed variation in pattern of spikes, as well as the striking differences between the species considered, suggest that penial structures of caviomorph rodents might be useful for diagnosing species as well as for tracing macroevo-lutionary relationships.

NEVO, E. 1979. Adaptative convergence and divergence of subterranean mammals. Ann. Rev. Ecol. Syst., 10:269-308. 1982. Speciation in subterranean mammals. Pp. 191-218, in Mechanisms of speciation (C. Barigozzi, G. Montalenti, and M. J. D. White, eds.). Liss Publ., New York, 546 pp. PEARSON, O. P. 1959. Biology of subterranean rodents, Ctenomys, in Perui. Mem. Mus. Hist. Nat. "Javier Prado," 9:1-56. PEARSON, O. P. ET AL. 1968. Estructura social, distribuci6n espacial y composicion por edades de una poblaci6n de tuco-tucos (Ctenomys talarum). Invest. Zool. Chilenas, 13:47-80. PETRUSEWICZ, K. 1983. Numbers: the concept and definitions. Acta Theriol., 28:89-101. REIG, O. A., AND P. KIBLISKY. 1969. Chromosome multiformity in the genus Ctenomys (Rodentia, Octodontidae). Chromosoma, 28:211-244. SMOLEN, M. J., H. H. GENOWAYS, AND R. J. BAKER. 1980. Demographic and reproductive parameters of the yellow-che ked pocket gopher (Pappogeomys castanops). J. Mamm., 61:224-236. WEIR, B. J. 1974. Reproductive characteristics of hystricomorph rodents. Symp. Zool. Soc. London, 34:265-301. WILSON, A. C., G. L. BUSCH, S. M. CASE, AND M. C. KING. 1975. Social structuring of mammalian populations and rate of chromosomal evolution. Proc. Natl. Acad. Sci., 72:5061-5065.

La morphologie du penis chez le genre Ctenomys est examinee en relation avec les hypotheses de Patterson (1983) sur l'evolution du penis, et la signification et l'utilisation des caracteres phalliques en systematique

Two chromosomal forms of Ctenomys torquatus are found in southern Brasil: 2n = 44 and 2n = 46, both showing AN = 72. The patterns of the G and C bands and the nucleolar organizer regions are presented. The two chromosomal forms do not show important differences in their morphology.

Chromosomes obtained from bone-marrow, spleen and testes were studied in samples from five populations of Spalacopus cyanus of Central Chile. Animals of four low-land coastal localities and animals of a high Andean valley showed a karyotype of 2n = 58 chromosomes, with almost no variation, either in number or in structure, both within each population or among the various populations. This karyotype was found to be very similar to that of Octodon degus, but very different to those in species of Ctenomys. The evolutionary and systematic significance of these results is discussed. The lack of karyotypic variation found in Spalacopus is correlated with its taxonomic uniformity, and both could be the result of the high vagility of the populations of this rodent, suggested by previous studies. This high capacity of dispersal is supposed to have enhanced gene flow, and therewith chromosome uniformity and low taxonomic diversification. The occurrence of a case of dimorphism for the presence of a secondary constriction in one of the autosome pairs is reported and discussed.

In the coastal region of central Chile the coruro, Spalacopus cyanus, lives in large populations consisting of many small, nomadic colonies. One colony contained 15 members belonging to no less than three generations. A colony of coruros occupies a common burrow system and apparently wanders continuously in search of food. Coruros feed primarily, if not exclusively, on the tubers and underground stems of the lily, Leucoryne ixiodes. S. cyanus has a higher metabolic rate than similar-sized fossorial species of Ctenomys. In February, adult males were sexually active and two of six adult females were pregnant, each bearing three small fetuses.

Allusions appear frequently in the literature to the idea that a special relationship exists between the African hystricomorph rodents Petromys and Thry-onomys and the Octodontidae and Myocastoridae (Capromyidae auct .), respectively, of South America. I have elsewhere ( In press ) reviewed the history of this arrangement and attempted to show that few positive reasons for classifying these two genera with South American families have ever been advanced. The idea derives ultimately from the unsupported assertion of Waterhouse (1839). Ellerman (1940) classified both Petromys and Thryonomys as sole representatives of the subfamilies Petromurinae and Thryonomyinae of the Echimyidae. This “Echimyidae” is roughly the equivalent of Simpson's (1945) “Octodontoidea,” so these two authors really classified Petromys and Thryonomys in the same way, as Simpson lists them under Petromyidae and Thryonomyidae of the Octodontoidea, stating (p. 212), “… Thryonomys and Petromys are morphologically octodontoid and it has been common practice to refer them to neotropical families and subfamilies, for instance, placing Petromys with Octodon and Thryonomys with Capromys .” Wood (1955) separates Thryonomys and Petromys from the South American hystricomorphs in his splitting apart of the suborder Hystricomorpha. He divides the hystricomorphs into two suborders: Hystricomorpha (Old World forms) and Caviomorpha (New World forms). He still asserts, however, that there is “morphological similarity” between Petromys and Thryonomys and New World families. He says (p. 184), “There are many obvious similarities to the Octodontidae and Echimyidae respectively. These are so great that formerly the African genera were placed in South American families. This is still done sometimes, the latest example being Ellerman, Morrison-Scott and Hayman (1953: 237–239) who consider the Thryonomyinae, Petromurinae and Echi-myinae to be subfamilies of the Octodontidae.” As a matter of fact, Ellerman, Morrison-Scott and Hayman (1953) concede that there may be some doubt about the classification of Thryonomys , …