Molecular Relationships Among Octodontidae (Mammalia: Rodentia: Caviomorpha)

We examined ten species of octodontid rodents and representatives of three outgroups in a complete 13 × 13 DNA-hybridization matrix. The results were indexed as differences in median melting-point depressions (T,_ms), symmetrized, subjected to phylogenetic analysis using FITCH, bootstrapped, and exhaustively taxon-jackknifed. Within Octodontidae, four clades were recovered with 100% bootstrap and complete jackknife support: Tympanoctomys barrerae with Octomys mimax, Octodontomys gliroides alone, Octodon spp., and Aconaemys spp. with Spalacopus cyanus; the latter two clades were closer to each other than either was to Octodontomys or Octomys-Tympanoctomys, but were slightly nearer to and united with Octodontomys, with 89% bootstrap support. However, relationships among the three Aconaemys species and Spalacopus were not completely resolved by our experiments. Ctenomys coyhaiquensis, Abrocoma bennetti, and Lagostomus maximus represented successive outgroups to Octodontidae, while one-way comparisons with Cavia porcellus and Microcavia australis suggested that these caviids are almost as distant from octodontoids as is the chinchilloid Lagostomus. When the data were suitably corrected for percentage hybridization and saturation, division of the distances by the rate previously determined for most amniotes (0.48%/myr) suggested that the basal divergence among the caviomorph rodents examined occurred about 59 myrbp, and that Octodontidae originated 40 myrbp and diversified into extant lineages beginning 14 myr ago. Calibration against the date of the earliest known caviomorph (late Eocene or about 37.5 myrbp) gave a rate of 0.75%/myr, which would suggest later dates for subsequent caviomorph cladogenesis. It is notable that, based respectively on the slower or faster rates, the tetraploid Tympanoctomys barrerae must have diverged from its sister-taxon Octomys mimax 10 or 6.5 myr ago.     

Taxonomic identity of Chionomys nivalis spitzenbergerae (Mammalia: Rodentia)

The most genetically divergent populations of the European snow vole Chionomys nivalis occupy the extreme eastern range of the Black Sea and the Caspian Sea. It was recently suggested that subspecies C. n. spitzenbergerae from the Central Taurus Mountains (Turkey) represents a highly divergent lineage of C. nivalis from the Alada? Range which induced us to address its status by examining topotype specimens. Two females karyotyped displayed 54 mitotic chromosomes of 25 acrocentric autosomal pairs. One of the smallest autosomal pairs was heteromorphic in both specimens, consisting of a submetacentric and an acrocentric chromosomes (NFa = 53). Cytochrome b sequences however unambiguously clustered both individuals with reference sequences from C. nivalis from Turkey. We conclude that a deviant haplotype from the Alada? Range does not represent C. n. spitzenbergerae. Its taxonomic identity was not resolved in our study. Further attention should be devoted to snow voles from Central Anatolia and Western Iran, which are characterized by cranial peculiarities.     

Chromosome studies in some members of the family Caviidae (Mammalia: Rodentia)

A study of the chromosomes of Cavia aperea and Galea musteloides has been made following the introduction into captivity of these two cavies from Argentina. The evolutionary relationships of the two genera have been considered, and the possible ancestry of C. porcellus from C. aperea was investigated in hybrids of the two species.     

Additions to the knowledge on fossil rodents of Uruguay (Mammalia: Rodentia)

Additions to the knowledge on fossil rodents of Uruguay (Mammalia: Rodentia). — This paper brings new information on fossil rodents of Uruguay. Four new species are described:Microcavia (M.) aua n. sp. (Caviidae),Ctenomys mesorhinus n. sp. (Octodontidae),Isostylomys intermedius n. sp. andIsostylomys magnus n. sp. (Dinomyidae), the latter from Argentina. Apart from this,Palmiramys waltheri Kraglievich, 1932, illustrated here for the first time, is considered a Lower Oligocene (Deseadan) ?Dasyproctidae. The first records for Uruguay ofEucardiodon cf.marshi (Ameghino) (Hydrochoeridae), and +Holochilus brasiliensis (Desmarest) are reported.     

The evolution of fossoriality and the adaptive role of horns in the Mylagaulidae (Mammalia: Rodentia)

Ceratogaulus, a member of the extinct fossorial rodent clade Mylagaulidae, is the only known rodent with horns and the smallest known horned mammal. The function of the large, dorsally projecting nasal horns on this burrowing animal has been the subject of wide speculation among palaeontologists; suggested uses range from sexual combat to burrowing. Mammals have evolved adaptations for digging repeatedly; horns and other cranial appendages have also evolved numerous times. These two adaptations co-occur in mammals extremely rarely: only two fossil genera (Ceratogaulus and the xenarthran Peltephilus) and no extant mammals are both horned and fossorial. Tracing the evolution of fossoriality in aplodontoid rodents (the larger clade to which Ceratogaulus belongs) reveals that Ceratogaulus descended from ancestors who dug by head-lifting. Whereas this suggests an obvious explanation for the horns of this rodent, evidence from functional morphology, anatomy, phylogeny and geologic context indicates that the horns in Ceratogaulus were used for defence, rather than digging, and evolved to offset increased predation costs associated with spending more time foraging above ground as body size increased.     

Karyotypes of field mice of the genus Apodemus(Mammalia:Rodentia) from China

Karyotypes of four Chinese species of field mice of the genus Apodemus were examined, including Apodemus chevrieri(diploid chromosome number,2 n=48, fundamental number of autosomal arms,FNa=56), A. draco(2 n=48, FNa=48), A. ilex(2 n=48, FNa=48), and A. latronum(2 n=48, FNa=48).Karyotypes of A. chevrieri, A. draco, and A. ilex are reported here for the first time, providing useful information for their species taxonomy. Determining the karyotypes of all species of Apodemus in Asia,both in this and previous studies, provides a solid overview of the chromosome evolution and species differentiation of the genus in East Asia. In addition to allopatric speciation, chromosome rearrangements likely played an important role in the formation of the four Apodemus species groups as well as speciation within each group in East Asia. For example, increased centromeric heterochromatin in A. latronum may have contributed to the post-mating reproductive isolation from the A. draco-A. ilex-A. semotus clade.     

新疆准噶尔盆地北缘中中新世早期的原圆齿鼠(Promylagaulinae,Mylagaulidae)(英文)

<正>1988年吴文裕描述了产自新疆准噶尔盆地北缘铁尔斯哈巴合地点哈拉玛盖组下部层位的一枚圆齿鼠的P4,定名为Sinomylagaulus halamagaiensis。1997年中国科学院古脊椎动物与古人类研究所新疆考察队又在铁尔斯哈巴合的哈拉玛盖组下部层位中采集到两枚p4。1988年的研究工作仅依据一枚上前臼齿(P4),标本的稀缺决定了当时研究成果的局限性。新材料无疑为认识新疆的圆齿鼠类提供了新的信息     

New Late Miocene murids from China (Mammalia, Rodentia)

New murids of Late Miocene (medial Baodean Chinese Mammal Unit) age from Inner Mongolia, northern China, and from Yunnan Province, southern China, are described. Hansdebruijnia perpusilla nov. sp. represents the earliest known and morphologically most primitive species of the genus, which is known from the latest Miocene of Europe and western Asia. The new species suggests an eastern Palaearctic origin of Hansdebruijnia. “Progonomys” yunnanensisQIU and STORCH, 1990 from Lufeng, Yunnan Province, is referred to Linomys nov. gen. New samples from Leilao, Yuanmou County, Yunnan Province, are included in this species, although this population is somewhat more primitive than that from Lufeng. Leilaomys zhudingi nov. gen. and sp. from Leilao shows a unique combination of apomorphic and plesiomorphic characters, which suggest an early divergence from the murid stem. The new findings indicate that our knowledge of the early radiation of murids in southeast Asia is still in its infancy.     

A ctenodactylid rodent (Mammalia: Rodentia) from the Middle Miocene of Chios Island (Greece)

Field work carried out in 1991 and 1993 at the Middle Miocene locality of Thymiana (Chios Island, Greece), produced much rodent material including a number of ctenodactylid dental specimens. They represent a single taxon whose upper and lower cheek tooth morphology clearly differs from Prosayimys flynni and all Sayimys species known so far, except for Sayimys intermedius. The ctenodactylid teeth from the Middle Miocene of Chios are identified as pertaining to the latter species, despite minor differences from the Pakistani and Saudi Arabian representatives of S. intermedius.     

Allometry and chromosomal speciation of the casiraguas Proechimys (Mammalia, Rodentia)

Morphometric characters (linear measurements) of the skull and mandible of the rodent Proechimys occurring in Venezuela and Columbia were investigated through multivariate techniques in order to describe static allometry and to relate allometric patterns to the recent evolution of these taxa. At least five species originated during the recent Pleistocene period in the upper Orinoco basin, all characterized by different karyotypes, one of them (P. guairae) being a Rassenkreis of karyomorphs. Species are characterized by unique static allometric patterns and the study of these patterns suggests a phylogenetic rather than an ecogenetic origin for these patterns; modifications in the shape of the skull and the mandible have originated during phyletic speciation and there is no apparent sign of functional adaptation.     

Geomorphometric differences among four species of Microtus in Turkey (Mammalia: Rodentia)

In order to determine the phenotypic associations of four morphologically similar species of Microtus occurring in Turkey, we applied landmark-based shape analysis. The skulls of Microtus anatolicus, M. dogramacii, M. guentheri and M. levis (= M. rossiaemeridionalis) were found to differ significantly in terms of both size and shape. M. guentheri had the biggest skull, while M. levis had the smallest. Sexual dimorphism was found in the shape of the skull in M. dogramacii and M. levis. The tympanic bulla area is enlarged in M. anatolicus compared to the other species. Mahalanobis distances (the distance between a point and the group mean, taking into account the within-group covariance-variance matrix) confirm the distinction of the arvalis group (M. levis) and socialis group (Microtus anatolicus, M. dogramacii, M. guentheri).     

Distribution of sibling species of the Praomys (Mastomys) natalensis group in Rhodesia (Mammalia: Rodentia)

The taxon Praomys ( Mastomys ) natalensis, the multimammate mouse, comprises at least two biological species in Rhodesia. Species-specific haemoglobin phenotypes which were previously documented for sympatric populations near Salisbury are shown to apply throughout Rhodesia. Several areas of sympatry were revealed which encompassed various habitats. No hybrids for diploid number or haemoglobin phenotype were found.     

Multivariate morphometries of the Ethiopian populations of harsh-furred rat (Lophuromys: Mammalia, Rodentia)

We investigated the geographic variation of eight Ethiopian populations of the rodent Lophuromys flavopunctatus and compared them to the Bale endemic species L. melanonyx. We used multivariate morphometrics and analysed independently skull and external body linear measurements, in an attempt to relate morphological variability to geography (latitude, longitude, altitude). There is a high morphological diversity in these Ethiopian populations, which form three distinct recognizable groups, with the Bale population being the most distinct. The results of analyses on the two character sets corroborate each other and indicate that the kind of variation is not 'ecological' but rather there is a phylogenetic cause, and relations at higher taxonomic level are suggested. There is a homogeneous group with five populations within which there is a recognizable pattern of clinal variation related to altitude, with a decrease in body size and a change in skull shape.