New Bovid fossils from the Late Miocene Hasnot (Siwaliks,Pakistan)

The Siwalik Late Miocene bovids from the Hasnot deposits of Northern Pakistan are described here. The bovids are represented predominantly by boselaphines. The Hasnot outcrops range 7–5 Ma and correspond to the fauna of the Late Miocene–Early Pliocene of Eurasia and Africa. The associated fauna of Hasnot is suggestive a vast open land environment depicting sporadic dry and flood seasons, forcing a mosaic of ecotonal habitats with countless number of niches.     

Dietary Ecology of Murinae (Muridae,Rodentia): A Geometric Morphometric Approach

Murine rodents represent a highly diverse group, which displays great ecological versatility. In the present paper we analyse the relationship between dental morphology, on one hand, using geometric morphometrics based upon the outline of first upper molar and the dietary preference of extant murine genera, on the other. This ecomorphological study of extant murine rodents demonstrates that dietary groups can be distinguished with the use of a quantitative geometric morphometric approach based on first upper molar outline. A discriminant analysis of the geometric morphometric variables of the first upper molars enables us to infer the dietary preferences of extinct murine genera from the Iberian Peninsula. Most of the extinct genera were omnivore; only Stephanomys showed a pattern of dental morphology alike that of the herbivore genera.     

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.     

Fossil Mice and Rats Show Isotopic Evidence of Niche Partitioning and Change in Dental Ecomorphology Related to Dietary Shift in Late Miocene of Pakistan

Stable carbon isotope analysis in tooth enamel is a well-established approach to infer C₃ and C₄ dietary composition in fossil mammals. The bulk of past work has been conducted on large herbivorous mammals. One important finding is that their dietary habits of fossil large mammals track the late Miocene ecological shift from C₃ forest and woodland to C₄ savannah. However, few studies on carbon isotopes of fossil small mammals exist due to limitations imposed by the size of rodent teeth, and the isotopic ecological and dietary behaviors of small mammals to climate change remain unknown. Here we evaluate the impact of ecological change on small mammals by fine-scale comparisons of carbon isotope ratios (δ¹³C) with dental morphology of murine rodents, spanning 13.8 to ∼2.0 Ma, across the C₃ to C₄ vegetation shift in the Miocene Siwalik sequence of Pakistan. We applied in-situ laser ablation GC-IRMS to lower first molars and measured two grazing indices on upper first molars. Murine rodents yield a distinct, but related, record of past ecological conditions from large herbivorous mammals, reflecting available foods in their much smaller home ranges. In general, larger murine species show more positive δ¹³C values and have higher grazing indices than smaller species inhabiting the same area at any given age. Two clades of murine rodents experienced different rates of morphological change. In the faster-evolving clade, the timing and trend of morphological innovations are closely tied to consumption of C₄ diet during the vegetation shift. This study provides quantitative evidence of linkages among diet, niche partitioning, and dental morphology at a more detailed level than previously possible.     

Neocometes (Rodentia,Platacanthomyinae) from the early Miocene of Echzell,Germany

The dental material described in this paper represents the largest known sample of molar material of the extinct platacanthomyine rodent Neocometes Schaub and Zapfe. It can be attributed to Neocometes similis Fahlbusch, the stratigraphically oldest and most primitive of the two species recognized in the European Miocene. This rich material provides sufficient samples of all molar positions to evaluate and confirm the morphologic and morphometric characters given for N. similis. The evolutionary stage of the Neocometes population from Echzell is only slightly more derived than the one from the type locality Erkertshofen 2, and supports the biostratigraphic setting of Echzell given by earlier authors. N. similis is the first mammal described in detail from the fossiliferous ash layers of Echzell, a locality situated at the southwestern margin of the Vogelsberg volcanic complex in central Germany.     

Structural Features of Spines in Some Rodents (Rodentia: Myomorpha, Hystricomorpha)

The architectonics of spines and hair was studied in Neacomys spinosus, Tokudaia osimensis, Arvicanthis somalicus, Leopoldamys sabanus, L. edwardsi, Maxomys moi, M. surifer, Niviventer fulvescens, N. confucianus, N. cremoriventer, Acomys cahirinus, A. somalica, Hystrix indica, H. cristata, Atherurus macrourus, Erethizon dorsatum, Proechimys steerei, and Lonchotrix emiliae. The presence of a dorsal longitudinal furrow covered by a modified cuticle is a common structural feature of spines in all studied species except E. dorsatum, H. indica, and H. cristata. The frontal surface of the mosaic (scales located side by side) and terrace cuticle (steps between scales) varies in different species from smooth to rib-folded. A terminology has been proposed to describe the main structures of spine and hair. The adaptive significance of the spine architectonics in rodents is discussed.     

The complete mitochondrial genome of the Korean red-backed vole, Myodes regulus (Rodentia, Murinae) from Korea

We have determined the complete mitochondrial genome (NC_016427) of the Korean red-backed vole, Myodes regulus, which is distributed in South Korea. The total length of the M. regulus mitogenome is 16,379?bp, with a base composition of 33.0% A, 26.7% T, 27.1% C, and 13.2% G. The total length of the 13 protein-coding genes is 11,396?bp long.     

The complete mitochondrial genome of the striped field mouse, Apodemus agrarius (Rodentia, Murinae) from Korea

The striped field mouse, Apodemus agrarius, is the most common rodents in temperate forests of the Korean peninsula. We have determined the complete mitochondrial genome (JN629047) of A. agrarius from Korea. Apodemus agrarius mitogenome is 16,263 bp in length and has a base composition of 33.9% A, 29.9% T, 23.6% C, and 12.5% G. The total length of the 13 protein-coding genes is 11,398 bp long.     

The complete mitochondrial genome of the Korean field mouse Apodemus peninsulae (Rodentia, Murinae) from Korea

We have determined the complete mitochondrial genome of a subspecies of the Korean field mouse, Apodemus peninsulae peninsulae, from South Korea. The total length of the A. p. peninsulae genome is 16,268 bp with a base composition of 34.5% A, 30.7% T, 22.6% C, and 12.2% G.     

B chromosomes of Korean field mouse Apodemus peninsulae (Rodentia,Murinae) analysed by microdissection and FISH

Organization of B chromosomes in the Korean field mouse Apodemus peninsulae was analyzed. We painted its metaphase chromosomes with whole and partial chromosome paints generated by microdissection and DOP-PCR. The results of the painting indicated that all B chromosomes contained a large amount of repeated DNA sequences. The repeats could be classified in terms of their homology and predominant location. Pericentromeric repeats of B chromosomes were present in many copies in pericentromeric C-blocks of all autosomes and in non-centromeric C-blocks of the sex chromosomes. B arm specific type 1 repeats comprised the main body of the arms of almost all B chromosomes and were present in the arms of A chromosomes as interspersed sequences. B arm-specific type 2 repeats were found at the ends of some B chromosomes that did not undergo compaction at the interphase- metaphase transition and remained uncondensed. On the basis of comparative analysis of localization of B chromosome repeats in the chromosomes of two related species, A. peninsulae and A. agrarius, we suggest a hypothesis of B chromosome origin and evolution in the genus Apodemus.     

Relationship between the Social Structure and Potential Reproductive Success in Muroid Rodents (Rodentia,Myomorpha)

Biology Bulletin - In many systematic groups of mammalian species, the evolution of sociality leads to the formation of large social groups (group-size evolution). In rodents, however, the most...     

Molecular phylogeny of the African pygmy mice, subgenus Nannomys (Rodentia, Murinae, Mus): implications for chromosomal evolution

Molecular phylogenies based on sequences of mitochondrial cytochrome b and nuclear IRBP genes are assessed on a comprehensive taxonomic sampling of African pygmy mice (subgenus Nannomys of the genus Mus). They represent a taxonomically diversified group of morphologically similar species, and exhibit an important chromosomal diversity, particularly involving sex-autosome translocations, one of the rarest and most deleterious chromosomal changes among mammals. The results show that the species sampled are genetically well differentiated, and that chromosomal rearrangements offer accurate diagnostic characters for discriminating most species. Furthermore, the species carrying different sex-autosome translocations appear monophyletic, suggesting that a genome modification allowing a higher rate of occurrence and/or fixation of such translocations took place, leading to the emergence of this lineage. In addition to taxonomic and biogeographical clarifications, we provide a temporal framework within which patterns of genic and chromosomal evolution are discussed.     

Tooth Replacement in Late Jurassic Dryolestidae (Eupantotheria, Mammalia)

The discovery of juvenile dentitions of late Jurassic (Kimmeridgian) Dryolestidae (Eupantotheria, Mammalia) from Guimarota, Portugal, yields for the first time information on the mode of tooth replacement in therian mammals prior to the dichotomy of placentals and marsupials. As in extant placentals, tooth replacement occurs at all antemolar positions [incisors (I1–I4), canine (C), premolars (P1–P4)]. P1 and P2 have premolariform milk predecessors, whereas the large premolariform third (P3) and fourth premolars (P4) are preceded by molariform deciduous premolars (dP3, dP4). Tooth replacement takes place in two waves, at least in the lower jaw, with I₂, I₄, P₁, and P₃ in the first series and I₁, I₃, C, P₂, and P₄ in the second. P₄ is the last premolar to erupt, and it is present when the sixth molar (M₆) starts to break through. The reduced tooth replacement pattern of marsupials (with only dP3 being replaced postnatally) evolved secondarily from the primitive or plesiomorphic mammalian condition, which was retained in Dryolestidae and Eutheria.     

A Transitional Gundi (Rodentia: Ctenodactylidae) from the Miocene of Israel

We describe a new species of gundi (Rodentia: Ctenodactylidae: Ctenodactylinae), Sayimys negevensis, on the basis of cheek teeth from the Early Miocene of the Rotem Basin, southern Israel. The Rotem ctenodactylid differs from all known ctenodactylid species, including Sayimys intermedius, which was first described from the Middle Miocene of Saudi Arabia. Instead, it most resembles Sayimys baskini from the Early Miocene of Pakistan in characters of the m1-2 (e.g., the mesoflexid shorter than the metaflexid, the obliquely orientated hypolophid, and the presence of a strong posterolabial ledge) and the upper molars (e.g., the paraflexus that is longer than the metaflexus). However, morphological (e.g., presence of a well-developed paraflexus on unworn upper molars) and dimensional (regarding, in particular, the DP4 and M1 or M2) differences between the Rotem gundi and Sayimys baskini distinguish them and testify to the novelty and endemicity of the former. In its dental morphology, Sayimys negevensis sp. nov. shows a combination of both the ultimate apparition of key-characters and incipient features that would be maintained and strengthened in latter ctenodactylines. Thus, it is a pivotal species that bridges the gap between an array of primitive ctenodactylines and the most derived, Early Miocene and later, gundis.     

Hippotraginae (Bovidae,Artiodactyla, Mammalia) from the Late Miocene of Tuva

Fossil remains of Late Miocene (Baode, NMU10-NMU11) horse antelopes from Tuva (Russia) are described, including Tragoreas sp., Protoryx tuvaensis sp. nov. from the Taralyk Cher locality and Quirliqnoria sp. from the Kholu locality. A new species, Protoryx tuvaensis Dmitrieva et Serdyuk, is described. These taxa compose a Late Miocene antelope assemblage of a new eastern geographical point (Russia, Tuva, Baode, NMU10-MN11).     

Early Miocene cricetids (Rodentia) from the Junggar basin (Xinjiang, China) and their biochronological implications

Among the 14 small mammal species from the early Miocene locality of the northern area of the Junggar basin (northern Xinjiang, China), four species are cricetids (Rodentia): unnamed species of Cricetodon and Eumyarion, and two new species, Karydomys debruijni nov. sp. and Megacricetodon beijiangensis nov. sp. Some aspects of the morphology of Cricetodon sp. are shared by Eucricetodon from the late Oligocene, suggesting that these specimens could be of intermediate form between Eucricetodon and Cricetodon. One tooth of Eumyarion sp. was found, making its determination uncertain, but its morphology is clearly differentiated from the one of Cricetodon sp. The species K. debruijni nov. sp. is established based on its primitive features compared to the species known in Europe and Anatolia, and its specific association of characters compared to Karydomys dzerzhinskii. M. beijiangensis nov. sp. shows many plesiomorphic features compared to the species already described in the middle Miocene of China. Based on both the whole assemblage of rodents and the species of cricetids, the biochronologic position and the age of the locality are discussed. The locality appears to be biochronologically very close to the fauna from the Chul’adyr Formation in Aktau Mountains, but we propose an age slightly older than the one proposed for this fauna, probably equivalent to the MN3 biozone in Europe.     

Chromosomal characterization of Arvicanthis species (Rodentia,Murinae) from western and central Africa: implications for taxonomy

A chromosome study of unstriped grass rats of the genus Arvicanthis (Rodentia, Murinae) in western and central Africa is presented. The observations extend the data available to 242 specimens from 59 localities. All individuals karyotyped belong to four karyotypic forms, or cytotypes, earlier described as ANI-1, ANI-2, ANI-3, and ANI-4 and are presumed to correspond to four distinct species. In order to provide diagnostic characters for these western and one central African Arvicanthis species, we standardized the chromosomal data available and developed a G- and C-banded chromosome nomenclature that allows easy species identification. Each form is characterized by a distinct geographical distribution, roughly following the biogeographical domains of western Africa, although their precise limits remain to be assessed. The sole area of sympatry detected is the region of the inner delta of the Niger River, where both ANI-1 and ANI-3 can be found. It is proposed that the three western African species ANI-1, ANI-3, and ANI-4 be renamed as A. niloticus, A. ansorgei, and A. rufinus, respectively.     

Polymorphism and polytypy for pericentric inversions in 38-chromosome Mastomys (Rodentia, Murinae) and possible taxonomic implications.

Chromosome banding analysis (R- and C-bands) of two 38-chromosome Mastomys specimens originating from the Ivory Coast and Uganda revealed different numbers of autosome arms (NFa), equal to 51 and 60, respectively. Comparison of their chromosome banding patterns with those of Mastomys specimens from the Sudan (NFa = 41) and Senegal (NFa = 51-54), studied previously, showed that variation of the NFa from 40 to 60 throughout the species distribution is the result of a pericentric inversion polymorphism involving 3-12 chromosome pairs. At the population level, this variation is much narrower and never results from more than two chromosome pairs involved in inversion polymorphism. Taking into account that the NFa values recorded to date form a well-defined discontinuous row, we presume that introgressive hybridization between populations differing from each other by 3-5 to 11-12 pericentric inversions is interrupted. From there, the hypothesis of the existence of at least three cryptic species (designated provisionally as MER-1, MER-2, and MER-3) within 38-chromosome Mastomys populations previously assigned to M. erythroleucus can be made. It looks likely that one of them, possessing a karyotype with an NFa = 50-56, is widely distributed throughout sub-Saharan Africa and includes karyotyped populations from Senegal, the Ivory Coast, Mali, Benin, Cameroon, Zaire, and the Sudan. The second species (MER-2) includes the specimens karyotyped (NFa = 40-41) from Chad and the Sudan. Finally, a third tentative species (MER-3) corresponds to specimens with NFa = 59-60 found in East Zaire and Uganda, as well as possibly Mali and Chad.     

The Impact of Tooth Wear on Occlusal Shape and the Identification of Fossils of New World Porcupines (Rodentia: Erethizontidae)

Although isolated dental remains are a central source of data in mammalian paleontology, the teeth of many taxa remain unidentifiable at low taxonomic levels because of intraspecific variation. Extant New World porcupines, Erethizontinae, illustrate this problem. Since being declared unusually variable over 50 years ago, molar occlusal morphology has been neglected as a potential source of diagnostic traits. Here, we use geometric morphometrics to re-evaluate the occlusal morphology of the third lower molar of erethizontines as the basis for identification of genera while accounting for variation, particularly changes in shape caused by progressive tooth wear. We model the impact and predictability of this source of variation by using CT-based digital sectioning. We use modelled occlusal shapes to analytically search for traits that can be used to improve identification of isolated dental remains, as well as training machine-learning models to assign occlusal surfaces to genus. Nearly half of all shape variation can be explained by variables such as wear and size. Resulting models of shape predict six univariate traits that may diagnose the two extant genera, especially when specimens are compared at the same wear stage. However, high levels of variation previously noted qualitatively also influence quantitative analyses, rendering machine learning models unreliable. Overall, although the identity of some specimens that are highly worn or contain certain combinations of traits will remain ambiguous, large segments of the gnathic erethizontine fossil record have renewed utility when analyzed using these methods.

     

A chromosomal study on Greek populations of the genusApodemus (Rodentia, Murinae) reveals new data on B chromosome distribution

During this study, 94 specimens (51 males, 43 females) of the wood mouseApodemus sylvaticus (Linnaeus, 1758), the yellow-necked mouseA. flavicollis (Melchior, 1834) and the western broad-toothed mouseA. epimelas (Nehring, 1902) from 20 localities of Greece were karyologically examined. The first two species were found to be widely distributed and their otherwise very similar karyotype (2n=48, FN=48) could be clearly distinguished, based on C-banding pattern. The third species appeared to have a more limited geographical distribution and its karyotype was distinguished from that of the previous two species, since it contained two pairs of small metacentric autosomes (2n=48, FN=52). The chromosomal study further revealed that nine individuals ofA. flavicollis possessed supernumerary B chromosomes (2n=49–50, FN=49–50). Meiotic chromosome preparations revealed that in contrast to sex chromosomes and autosomes, B chromosomes do not participate in bivalent formation. On the other hand, no supernumerary chromosomes were found in the studiedA. sylvaticus andA. epimelas material.