Morphological differences in skulls and feeding apparatuses between Antarctic and common minke whales, and the implication for their feeding ecology

The differences in rorqual feeding ecology have been linked to the presence of different morphological markers. The Antarctic minke whale (Balaenoptera bonaerensis Burmeister, 1867) and common minke whale (Balaenoptera acutorostrata Lacépède, 1804) are closely related species, but their morphological differences have not been fully investigated. In this study, we compared 21 skull and 11 feeding apparatuses (baleen and mouth-related parts) measurement points between these two species using hundreds of individuals covering a wide range of body lengths in both sexes. Their engulfment capacities were estimated using these measurements. Our results show that Antarctic minke whales have (1) proportionally larger skulls to the body length, (2) more dorsoventrally and laterally curved rostra, (3) proportionally larger feeding apparatuses to the condylobasal length, and (4) significantly larger engulfment capacity than common minke whales. These differences could indicate that Antarctic minke whales have developed a feeding strategy suitable for feeding on krill, which forms large schools. In contrast, common minke whales have adapted to prey on small pelagic fishes that are agile and form small schools.

Using osteological measurements to estimate body length in Amazonian manatees

ABSTRACT Body length is an important parameter in morphological, ecological and behavioral studies of a species and contributes to the understanding of the body condition of individuals. This parameter is essential for conservation and management strategies by informing studies evaluating growth rates, physical maturity and classification of individuals into age groups, promoting better accuracy for the biological parameters of the species. The aim of this study was to identify predictors of body length for Amazonian manatees (Trichechus inunguis) using metric characters of osteological materials. Eleven linear measurements of skull, jaw, scapulae and humeri were collected from 41 Amazonian manatee skeletons of different age classes (calf, juvenile and adult). Data were analyzed by simple linear regression. The condylobasal length was the best predictor of body length for the species (R = 0.943), however, all bones evaluated showed at least one measurement with the capacity to predict body size (R2 > 0.9). Results of this study are useful for inferring body length of Amazonian manatees using bones deposited in museums and biological collections, expanding the informative potential of these materials.

Sexual dimorphism and variability in the skull of Martes foina

Morphometry can help to understand morphology and clarify taxonomy of species. The morphometric variability of the skull and sexual dimorphism of stone martens (Martes foina), obtained from various geographical regions of Turkey, were investigated. Measurements were made regarding 14 characters on skulls of the samples. Adults have significantly bigger skulls compared to juveniles. Regarding their sexual dimorphism, descriptive statistics revealed variability in the size of the skull between sexes, with mean values of males being higher than those of females. The most significant sexual dimorphisms (the highest variabilities) were observed in palatal width and especially frontal width. The strongest positive correlations were found between the basilar length and condylobasal length in males and between the mandibular length and total skull length in females. Furthermore, principal component analysis confirmed strong correlations between some characters of the skull in both sexes. By comparing characters with those of European populations this study contributes to a general model of the skull of Martes foina.

Variation of craniometrical characters in an artificial population of Cervus nippon from Askania-Nova, Ukraine

Craniometrical characters of adult sika deer from an artificial population, which was created by import of animals from a natural population from the Primorsky Krai of Russia, are analysed. It was revealed that the mean value of variation (by 11 characters) of skulls of sika deer is 3.56 ± 0.35 in males and 3.89 ± 0.33 in females. Males are significantly larger than females (p < 0.001) by all characters. The study of craniometrical characters of the sika deer using principal component analysis showed that 93.3 % of total variance is described by the first principal component (PC1). The highest, though quite equal, factor loadings on PC1 have characters of length (full length, condylobasal length, basic length). Study results suggest that sex-related differences in C. nippon by craniometrical characters are expressed by general linear dimensions and by proportions of the skull. The correlation matrix of craniometrical characters of adult sika deer from the Askanian subpopulation shows a relatively weak dependence between different parameters. It was established that the coefficient of correlation in most pairs of characters varies from 0.02 to 0.96 in males and from 0.01 to 0.97 in females. The highest coefficients of correlation in both males and females (r = 0.96 and r = 0.97, respectively) are revealed between the condylobasal and basal lengths of the skull. Correlations between cranial indices are significantly lower compared to craniometrical characters. The highest coefficient of correlation in both males and females has the variation of the index of mastoid width in relation to the relative largest skull width (r = 0.72). Skulls of sika deer from the Askanian subpopulation (of both males and females) have significantly larger dimensions compared to those in animals from the natural population from the Primorsky Krai.

Sibling mice species of the genus Sylvaemus Ognev, 1924 (Mammalia, Rodentia) in the Ukrainian Carpathians

Three species of the genus Sylvaemus occur in the region of the Ukrainian Carpathians: the yellow-necked field mouse (S. tauricus), the long-tailed field mouse (S. sylvaticus) and the pygmy field mouse (S. uralensis). Issues of the genus’s taxonomy and identification of species have remained controversial in some parts of the geographic range, while in the Ukrainian Carpathians they have been studied scarcely at all. We studied about 250 mice specimens from the Ukrainian Carpathians belonging to the genus Sylvaemus, among which 216 were analysed morphometrically based on 4 external and 11 cranial characters. Results indicate that by linear body dimension only S. uralensis can be differentiated with high probability. For the pair of species tauricus–sylvaticus, the hind foot length is the least variable among linear body characters, which might be considered diagnostic, although values of this character also tend to overlap. To identify species correctly, it is necessary to use craniometrical characters. For the pair of tauricus–sylvaticus, the least variable among the 11 studied characters are the upper molars length (M13), braincase width (CRB), and braincase height (CRH). Mixed samples of adult specimens of the three species can be differentiated with minimal or practically no overlap by using the relation of the upper molars length to braincase width, condylobasal length, and auditory bulla length. Analysis of characters’ uniformity in adult specimens showed that S. tauricus and S. sylvaticus differ from one another the most by the upper molars length (M13), braincase width (CRB), braincase height (CRH), condylobasal length (CBL), and auditory bulla length (BUL). A similar tendency was revealed for the pair of S. sylvaticus and S. uralensis. A regional identification key was developed for differentiation of adult mice, which allows identifying reliably 93.5% of specimens. Results of the revision of samples suggest that S. tauricus has the widest altitudinal and habitat preferences, S. sylvaticus occurs mainly in humid floodplain biotopes (shrubs, woods) entering far into the mountains along river valleys, while S. uralensis is represented only by few records from lowland floodplain habitats.

Diagnostic Criteria for Identification of Microtus s. l. Species (Rodentia, Arvicolidae) of the Ukrainian Carpathians

The present paper deals with the issues of diagnostics of morphologically similar vole species (Microtus s. l.) common in the fauna of the Ukrainian Carpathians. Three groups of characters have been analysed: external traits (linear body dimensions, coloration features, etc.), morphological and anatomical features of the skull (size of its structures, form of certain bones and sutures, etc.), and morphology of molar teeth (number and form of enamel lobes and triangles). The analysis of museum specimens of voles collected in the region of the Ukrainian Carpathians has shown that external and cranial non-metric characters allow reliable identification to genus level, while for species diagnostics it is necessary to use a complex of characters including structural features of molars and dimensions of skull structures. The height and width of the braincase have the largest diagnostic value among cranial characters for the sibling species complex Terricola subterraneus–Terricola tatricus, while for the pair of morphologically similar species Microtus agrestis–Microtus arvalis such value have the upper molars length, condylobasal length, and braincase height. The most significant, revised and newly described, diagnostic characters have been generalized into an identification key, especially convenient for use during work with collection materials.

Sex- and age-related variations in cranial measurements and suture closure in the Australian sea lion, Neophoca cinerea (Peron, 1816)

A total of 65 skulls of the Australian sealion, Neophoca cinerea, was examined to investigate the extent to which sexual dimorphism is reflected in cranial dimensions (n = 32) and skull growth, and to determine whether cranial sutures (n = 18) can be useful in age determination. All adult skull dimensions studied display significant sexual dimorphism. Skull growth ceases close to 4–7 years of age for females (Suture Fusion Rating, SFR 25–34) but skull growth in males continues until at least 16 years of age. In animals with a SFR ≥� 25, male skulls have a minimum condylobasal length of 272 mm, whereas female skulls have a maximum condylobasal length of 259 mm. The relatively early closure of the cranial vault sutures (cessation of brain growth) is balanced by the continued growth of the bony projections that provide muscle attachment (e.g. mastoid width). The later fusion of the snout and palate sutures corresponds with the continued growth of the snout and palate to match the prolonged growth of the mandibles. The upper sixth postcanine tooth was present in 43% of the adult female skulls, but only 15% of the adult male skulls. The data suggest that it may be possible to determine age(s) from examination of the sequence of fusion of cranial sutures as well as by calculation of an overall suture fusion rating for the skull.

Geographic variation in skull characters of fur seals and sea lions (family Otariidae)

Geographic variation was observed in skulls of several otariid species, with a general change in size corresponding with a change in latitude and primary productivity. The largest specimens were from cool temperate localities, conforming mostly to Rensch's rule. Skulls of Australian sea lions from Western Australia were generally smaller in condylobasal length, but were more robust than those from South Australia. The subantarctic fur seal did not conform to Bergmann's rule: skulls from Amsterdam Island (37�55´S) were largest, those from Gough Island (40�20´S) intermediate and those from Marion Island (46�55´S) the smallest. For both sexes, skulls of southern sea lions from the Falkland Islands were smaller than their equivalents from mainland South America. Similarly, skulls of South African fur seals from south-east South Africa appeared smaller than those from the west coast of South Africa and Namibia; skulls from Namibia grouped separately from those of south-east and west coast, South Africa. We postulate that the Otariidae are in the process of species divergence, much of which may be driven by local factors, particularly latitude and resources.

A comparative review of condylobasal lengths and other craniometric characters in 30 species of pinniped

ABSTRACTThe condylobasal length (CBL) of skulls from 999 sexually mature seal, sealion, and fur seals of 30 different species was measured. Additional data gathered from previous studies were also included to give an indication of variation within each species, particularly where there is a wide geographical dispersion. Where possible, means and ranges of CBL were given separately for each sex, so that the degree of sexual dimorphism could be assessed. Previous studies have indicated that CBL continues to increase after sexual maturity has been reached. In order to assess this, three species (Mirounga leonina, Otaria byronia (flavescens), and Halichoerus grypus) that contained individuals of known age were included in the study. Other craniometric characters are often expressed as a percentage of CBL when assessing taxonomic relationships. Some of these characters were reassessed using the new data.

Sexual dimorphism in the baiji, Lipotes vexillifer

Dimorphism was detected in body length and in skull dimensions of the baiji, Lipotes vexillifer. The age of a sample comprising 22 females and 14 males was estimated. A single-phase Laird growth model was fitted to the body length versus age data for females. Two curves were required for the males, one for those with 4 dentinal growth layer groups (GLGs) and another for those above that age, i.e., with more than 4 GLGs. Males and females have about the same growth rate until they have about 4 GLGs, after which males grow more slowly than females. Sexual dimorphism was also found in 9 external measurements, based on t-tests. Analysis of covariance showed that once the effect of body length was removed, only 1 of the 9 measurements, from the tip of the upper jaw to the genital aperture, differed significantly between males and females. Differences in skull measurements resulted mainly from an early slowdown in the rate of longitudinal growth of the male, before the increase in body length slowed. Females and males could be correctly sexed by discriminant analysis using the body length, condylobasal length, and zygomatic width, and also the condylobasal length, width of the rostrum at the base, and the zygomatic width, except for one young female. Eight skull length measurements were greater in adult females than in adult males after the effect of body length was removed, and five skull width measurements were greater in males when the effect of condylobasal length was removed. Asymmetry in the position of the blowhole and in skew of the skull is pronounced and is independent of body length and sex.