Allometry of the limb long bones of insectivores and rodents

In an attempt to investigate the relationships between allometry and locomotory adaptations, we studied the long limb bones of 45 species of insectivores and rodents. Animals ranged from a few grams to about 50 kilograms. Diameter and length of the bones and body mass (when known) were recorded. Regressions of diameter to length, diameter to body mass, and length to body mass were calculated by the least-squares and Model II, or major axis, methods. The results obtained do not agree with the predictions of either the theory of geometric similarity or the theory of elastic similarity. The discrepancies could be due to the fact that animals studied exhibit various modes of locomotion. Moreover, the allometric relationships of the different locomotor patterns are better reflected in insectivores and rodents than in other groups of mammals. The use of a single regression analysis seems to be inadequate when the sample includes a large range of body sizes.     

Phylogeny and adaptive diversity of rodents of the family Ctenomyidae (Caviomorpha): delimiting lineages and genera in the fossil record

Differentiation of genera of the modern (Late Miocene to Recent) South American rodent family Ctenomyidae would have been linked to the acquisition of disparate adaptations to digging and life underground. In accordance with this hypothesis, the delimitation of lineages and genera in the ctenomyid fossil record is evaluated here following an adaptation-rooted criterion that involves both an assessment of the monophyly and of the adaptive profiles of recognized clades. The application of such a criterion, including morphofunctional information, delimited four cohesive lineages among crown ctenomyids (i.e. euhypsodont species of the Late Miocene to Recent): Eucelophorus (Early Pliocene–Middle Pleistocene), Xenodontomys-Actenomys (Late Miocene–Pliocene), Praectenomys (Pliocene) and Ctenomys (including Paractenomys ; Pliocene–Recent); in addition, the results supported the status of Xenodontomys as a paraphyletic ancestor of Actenomys . The cladogenesis that gave rise to the crown group would have occurred immediately after the acquisition of euhypsodonty in a Xenodontomys simpsoni -like ancestor during the Late Miocene. This putative ancestor would have had fossorial habits and moderate digging specializations, an adaptive profile maintained in Xenodontomys-Actenomys . Eucelophorus and Ctenomys would have independently evolved subterranean habits at least since the Pliocene. Although the earliest history of the only living representative, Ctenomys , is known only fragmentarily, remains from Esquina Blanca (Uquía Formation), in north-western Argentina, suggest a minimum age of around 3.5 Ma (Early–Late Pliocene) for the differentiation of the genus. This date agrees with recent molecular estimates.     

Arvicolidae (Rodentia) from the Pliocene of Tollo de Chiclana (Granada, SE Spain)

Several new fossiliferous Pliocene localities have been identified in the continental deposits of the area of Tollo de Chiclana (Guadix Basin, SE Spain), that have yielded a rich rodent and insectivore fauna. In this paper, we study the Arvicolidae from these localities. Remains adscribed to the genera Dolomys, Mimomys and Kislangia have been found, which are very interesting from a biostratigraphical point of view.     

Allometry and curvature in the long bones of quadrupedal mammals

The allometric relationships between basic structural proportions in long bones are examined in the humerus, radius, femur and tibia for a diverse group of 42 terrestrial quadrupedal mammals that span a size range from 0.02–6000 kg. Non-linear scaling is found for length vs. diameter in the tibia and radius, suggesting that the mechanical constraints on the skeleton differ within large and small body-size mammals. Curvature normalized to mid-shaft radius scales differently in the different long bones. Curvature is poorly related to size in the proximal limb bones (humerus and femur) while it decreases systematically with size in the tibia (mass exponent −0.13). The scaling of normalized curvature in the radius is unique among long bones. Variability of curvature in the radius is reduced at any size in comparison to that found in the other long bones. Normalized curvature is constant within the small body size group (0.02 to approximately 100 kg) while it decreases sharply with size within animals over 100 kg body mass. The unusual scaling found in the radius is probably the result of this bone's close alignment with the extrinsic forces which act on it during locomotion. The change in scaling within the radius for animals of different size may be indicative of more general size-dependent mechanical trade-offs which are masked by the complex loading circumstances of the other long bones.     

Re-interpreting the biochronology of the La Celia and Los Gargantones mammal sites (Late Miocene,Murcia, Spain)

The biochronological age of the small-mammal populations of Los Gargantones 1, 2 and La Celia (upper Miocene, La Celia sub-basin, Murcia, Spain) is re-interpreted. The presence in Los Gargantones of Occitanomys adroveri, Parapodemus barbarae, Parapodemus cf. gaudryi, Huerzelerimys turoliensis, Atlantoxerus cf. adroveri, and Alilepus evidences a correlation to MN12 (∼7.5–7 Ma) rather than to MN11 (∼9–7.5 Ma), as inferred previously. The assemblage corresponds to that of the more eastern, near-coast sites of Crevillente 8 and 15, situated in the Alicante area. The stratigraphically highest site of La Celia contains Hispanomys adroveri, a species also indicative of MN12. The presence of Castromys cf. littoralis together with an advanced O. adroveri points to a slightly younger age than that of Los Gargantones, approaching that of MN13 sites. The assemblage best matches that of Crevillente 17. Other species described in this paper are Prolagus crusafonti, Prolagus sp., Parasorex cf. ibericus, Panelimnoecus cf. repenningi, and Blarinella aut Petenyia sp. indet.     

Craniodental and forelimb specializations for digging in the South American subterranean rodent Ctenomys (Hystricomorpha,Ctenomyidae)

We explored the distribution of tooth- and scratch-digging specializations in species of the subterranean rodent Ctenomys (tuco-tucos) from diverse environments and representing different clades. Principal component analysis of craniodental and postcranial indexes with functional relevance showed that specializations for tooth-digging on one hand, and scratch- digging on the other, formed two uncorrelated groups of variables; functionally significant enamel traits varied concurrently with the tooth-digging specialization axis. Species occupied all sectors of the morphospace showing that craniodental and forelimb specializations have not been mutually exclusive in the evolution of the genus.     

Allometry of the leg bones of moas (Dinornithes) and other birds

The body masses of various moas have been estimated, measurements have been made of their leg bones and allometric equations have been calculated. Corresponding equations have been calculated for various groups of living birds, using new data and data from the literature. The two families of moas are compared with each other, with modern ratites and with flying birds. Shortening of the tarsometatarsus in moas and narrowing of the pelvis in other ratites are interpreted as adaptations concerned with balancing the bird on its feet. following reduction of the wings.     

Additional cricetid and dipodid rodent material from the Erden Obo section,Erlian Basin (Nei Mongol,China) and its biochronological implications

New cricetid (Cricetops dormitor, Eocricetodon sp., Eucricetodon cf. E. wangae, Pappocricetodon schaubi) and dipodid (Allosminthus gobiensis n. sp., Allosminthus ernos, Allosminthus uniconjugatus, Allosminthus cf. A. majusculus, Primisminthus shanghenus, Sinosminthus sp.) occurrences from the “Lower Red”, “Middle Red”, “Middle White” and “Upper White” beds of the Erden Obo section in Nei Mongol, China are reported. They are first discovered in these horizons. On the basis of the comparison of the rodent assemblages, we consider that the age of the “Upper White” beds is early Oligocene, the age of the “Middle Red” and “Middle White” beds is probable more similar to the age of late Eocene Houldjin Formation and lower part of Chaijiachong Formation, and the age of the “Lower Red” beds is correlative to the Sharamurunian. The diversity of ctenodactyloid, dipodid, and cricetid appears to change, and the turnover in rodent fauna possibly responded to the environmental and climate change towards the end of middle Eocene.     

Phylogenetic Analysis of the Cytochrome P450 3 (CYP3) Gene Family

Cytochrome P450 genes (CYP) constitute a superfamily with members known from the Bacteria, Archaea, and Eukarya. The CYP3 gene family includes the CYP3A and CYP3B subfamilies. Members of the CYP3A subfamily represent the dominant CYP forms expressed in the digestive and respiratory tracts of vertebrates. The CYP3A enzymes metabolize a wide variety of chemically diverse lipophilic organic compounds. To understand vertebrate CYP3 diversity better, we determined the killifish (Fundulus heteroclitus) CYP3A30 and CYP3A56 and the ball python (Python regius) CYP3A42 sequences. We performed phylogenetic analyses of 45 vertebrate CYP3 amino acid sequences using a Bayesian approach. Our analyses indicate that teleost, diapsid, and mammalian CYP3A genes have undergone independent diversification and that the ancestral vertebrate genome contained a single CYP3A gene. Most CYP3A diversity is the product of recent gene duplication events. There is strong support for placement of the guinea pig CYP3A genes within the rodent CYP3A diversification. The rat, mouse, and hamster CYP3A genes are mixed among several rodent CYP3A subclades, indicative of a complex history involving speciation and gene duplication. Phylogenetic analyses suggest two CYP3A gene duplication events early in rodent history, with the rat CYP3A9 and mouse Cyp3a13 clade having a sister relationship to all other rodent CYP3A genes. In primate history, the human CYP3A43 gene appears to have a sister relationship to all other known primate CYP3A genes. Other, more recent gene duplications are hypothesized to have occurred independently within the human, pig, rat, mouse, guinea pig, and fish genomes. Functional analyses suggest that gene duplication is strongly tied to acquisition of new function and that convergent evolution of CYP3A function may be frequent among independent gene copies. Current address (Rachel L. Cox): Laboratory of Aquatic Biomedicine, Marine Biology Laboratory, Woods Hole, MA 02543, USA     

Geometry and evolutionary parallelism in the long bones of cavioid rodents and small artiodactyls

Morphological parallelism between South American cavioid rodents and small artiodactyls from the Old World has been postulated for a long time. Our study deals with this question from the point of view of biomechanical characteristics of the long bones. For this, cross-sectional area, second moment of the area, polar moment, athletic ability indicators and strength were calculated for the long bones (i.e. humerus, radius, femur and tibia) of five species of cavioids and two species of artiodactyls. Regressions of all these variables to body mass were established. Regarding the cross-sectional area, the confidence intervals show that the exponents calculated are not significantly different from the geometrical predicted value. The exponents obtained for the second moment of area and the polar moment are not significantly different from the geometrical prediction, except for the humerus. The two indicators of athletic ability scaled as expected, but the bending indicator of athletic ability of the femur was not correlated to body mass. The exponent calculated for femur strength is not different from zero, while the strength of the humerus decreases slightly with the body mass. Additional statistical tests (ANCOVAs) showed no difference between the values of these variables calculated for the samples studied of artiodactyls and rodents. The present results are consistent with the hypothesis that there is significant evolutionary parallelism between cavioid rodents and small artiodactyls.     

Allometry of the limb bones of mammals from shrews (Sorex) to elephant (Loxodonta)

Measurements have been made of the principal leg bones of 37 species representing almost the full range of sizes of terrestrial mammals. The lengths of corresponding bones tend to be proportional to (body mass)^0·35 and the diameters to (body mass)^0·36, except in the family Bovidae in which the exponents for length are much nearer the value of 0·25 predicted by McMahon's (1973) theory of elastic similarity. Comparisons are made between mammals of similar size belonging to different orders.     

Arboreal gaits in three sympatric rodents Apodemus agrarius,Apodemus flavicollis (Rodentia,Muridae) and Myodes glareolus (Rodentia,Cricetidae)

Vertical stratification of the arboreal habitat allows the coexistence of several species in a given area, because the complex arboreal strata can be used in different ways by arboreal and scansorial mammals. The present report experimentally investigated the gait metrics on different arboreal substrates, of three sympatric rodents living in a deciduous forest in Poznań, Poland. Arboreal locomotion was compared between the burrowing striped field mouse, Apodemus agrarius, the scansorial bank vole, Myodes glareolus, and the more arboreal yellow-necked mouse, Apodemus flavicollis. We filmed two wild-caught individuals from each species walking on four different substrate diameters (2 mm, 5 mm, 10 mm, 25 mm) and three different inclinations (45° descending, horizontal, 45° ascending) at 240 fps and collected a set of gait parameters from a total of 273 complete cycles. Our results did not demonstrate clear relationships between arboreal locomotion and the ecology of the three species. Only A. flavicollis exhibited locomotor features partly associated with arboreal competence, including lower velocity and diagonality on narrow substrates and asymmetrical gaits on wider ones. On the other hand, the two Apodemus species, despite their different ecologies, shared a few locomotor similarities, such as velocity regulation primarily by stride frequency, and similar effects of substrate size and inclination on diagonality, duty factor, and duty factor index indicating the possibility of a phylogenetic signal. Because the selected gait parameters provided limited insight into the ability of small mammals to move competently through an arboreal habitat, these findings indicate that the relationship between behaviour and ecology is complex.     

New dipodid rodents from the Late Eocene of Erden Obo (Nei Mongol,China)

New dipodid occurrences (Heosminthus nomogenesis sp. nov., Sinosminthus sp., Allosminthus cf. A. majusculus, Allosminthus ernos and Allosminthus cf. A. diconjugatus) are reported from the ‘Upper Red’ beds of the Erden Obo section in Nei Mongol, China. Heosminthus nomogenesis is similar to Heosminthus primiveris from the Caijiachong Formation, and it is more primitive than Heosminthus chimidae of the Mongolian biozone A. Allosminthus cf. A. majusculus has a more variable mesolophid and metalophid in m1-2. Based on the dipodid assemblage, the age of the ‘Upper Red’ of the Erden Obo section is late Eocene and correlative to the Ergilian. Based on the comparison of their morphological characters, we recognize some differences between the stem dipodoids and muroids.     

Allometry and adaptation in the catarrhine postcranial skeleton

Seven measurements were taken on the postcranial skeleton of 249 specimens representing ten species of catarrhine primates and tested to determine their relationship with size. Size was measured as skeletal weight on each individual. It was found that the interspecific line based on the entire sample was in some cases determined not only by morphological adjustments for size variation but also by changes in locomotor adaptations of differently sized species within the sample. It is suggested that it is consequently preferable to study allometric relationships within a species or within a group of species that differ in size but are similar in their mode of locomotion. The allometric analysis reveals some interesting patterns within the data. Limb lengths scaled with either negative allometry or isometry over the entire sample. Within the species groups isometry was the rule except for pongid femurs, which showed negative scaling. Humerus length scaled at the same rate in pongids as in cercopithecoids but had a slightly higher intercept value. While colobines and cercopithecines scaled at similar rates for all seven dimensions, the colobine line was shifted to a position above that for cercopithecines in every case. It is suggested that this is a result of adaptation for leaping in the former group. Other implications of the allometric results are discussed.     

Large apeomyine rodents (Mammalia,Eomyidae) from the early Miocene of Echzell,Germany

The dental material described in this paper was collected from fossiliferous ash layers of the Vogelsberg volcanic complex at Echzell, Germany. It consists of 32 teeth of a new large Apeomys species, Apeomys oldrichi n. sp., and 19 teeth of Megapeomys lindsayi Fejfar, Rummel and Tomida. Both species are extremely rare faunal elements in the early Miocene of Europe. Apeomys oldrichi n. sp. is the largest known Apeomys species, and occurs in a number of MN 3 – 4 sites in southern Germany and Czech Republic. Megapeomys lindsayi, the largest Eurasian apeomyine, was described on the basis of a single lower premolar. Herein both lower and upper cheek teeth as well as the lower deciduous premolar are described for the first time. In comparison with related populations from other localities, the evolutionary stage of the two apeomyine species clearly indicates a middle Orleanian age (MN 4) for Echzell which concurs with previous studies.

http://zoobank.org/urn:lsid:zoobank.org:pub:1F9E49BE-C4B6-4597-A116-234E13D86BA9     

Parallel evolution in molar outline of murine rodents: the case of the extinct Malpaisomys insularis (Eastern Canary Islands)

The lava mouse Malpaisomys was part of Pleistocene and Holocene faunas of the eastern Canary Islands; it became extinct during historical times. In order to evaluate the evolutionary processes of this endemic species, we set out to identify its relationships with possible mainland relatives. Its dental morphology was compared to a set of fossil and modern murine rodents from various phylogenetic groups, characterized by different diets and dental patterns, using a quantitative method based on a Fourier analysis of the outline of the first upper and lower molars. This morphometric analysis identified different evolutionary grades that are independent of the phylogenetic group. The first cluster is associated with primitive, asymmetric dental outlines, the second with intermediate forms linked to a more herbivorous diet. Highly differentiated forms diverge not only from the second cluster but also from each other. Our investigations reveal Malpaisomys to have had an intermediate dental pattern, a result which confirms previous palaeoecological interpretations of this taxon. However, conclusions about its closest mainland relative remain tentative. Based on a comparison of dental size and shape, as well as geographical considerations, a possible mainland ancestor could be either Paraethomys (North-African Pliocene) or Occitanomys (South-western European Pliocene). Such results support the hypothesis of a Pliocene colonization event, in which case Malpaisomys would display a normal evolutionary rate in dental size and shape, in spite of the insular context. In contrast, a late colonization by a modern representative of the African fauna would imply exceptionally high evolutionary rates compared to the background morphological evolution and a decrease in size that is unlikely under insular conditions.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 142 , 555–572.     

Higher-level systematics of rodents (Mammalia,Rodentia): Evidence from the mitochondrial 12S rRNA gene

Phylogenetic relationships among major rodent superfamilies traditionally have been difficult to establish because of the apparent high level of convergence and parallelism seen among morphological characters and/or rapid differentiation of rodent groups in the Paleocene/Eocene. Nucleotide sequence data from the mitochondrial 12S rRNA gene were used to clarify phylogenetic relationships among the major groups of rodents as defined by Brandt (1855) and Tullberg (1899). Based on the approximately 800 bp analyzed for the 12S rRNA gene in 59 mammalian species, including 25 of the 32 extant rodent families, the major rodent groups that could be defined as monophyletic clades were the Hystricognathi, the Muroidea, and the Geomyoidea. In addition, support for superfamilial sister-group relationships was found for Aplodontoidea with Sciuroidea and Dipodoidea with Muroidea.