Morphological Characteristics of Retinal Ganglion Cells in the Retinas of Giant Pandas (Ailuropoda melanoleuca).

Vision plays a crucial role in the survival of animals, and the visual system has particularly selectively evolved in response to the visual environment, ecological niche, and species habitats in vertebrate species. To date, a horizontal streak of retinal ganglion cell (RGC) distribution pattern is observed across mammal species. Here, we report that the giant panda's vertically oriented visual streak, combined with current evidence of the animal's forward-placed eyes, ocular structure, and retinal neural topographic distribution patterns, presents the emergence of a well-adapted binocular visual system. Our results suggest that the giant panda may use a unique way to processing binocular visual information. Results of mathematical simulation are in favor of this hypothesis. The topographic distribution properties of RGCs reported here could be essential for understanding the visual adaptation and evolution of this living fossil.

First description of the baubellum in the spectacled bear Tremarctos ornatus (Mammalia: Ursidae).

The baubellum (os clitoridis) is a bone found in the clitoris of many female eutherian mammals and is homologous to the baculum in males. In contrast to the baculum, the baubellum has received very little attention regarding its morphological or interspecific diversity, or on hypotheses for its function. The presence of the baubellum in bears (Ursidae) has only been established and mentioned in the literature for the Ursus genus, and not for the other genera of bears. Moreover, no scaled photographs are available for baubella of this clade, and the sizes reported vary between sources. We hereby present and describe the baubellum of a spectacled bear (Tremarctos ornatus), providing a detailed account of baubella in a basal ursid species. The baubellum of Tremarctos is slightly bowed dorsally, with two small prominences at the distal apex. The length of the Tremarctos baubellum in this study is comparable to that of Ursus americanus (American black bear). We infer the specific shape, with longitudinal ridges, of the baubellum in Tremarctos could indicate a discrete function during copulation or sexual arousal. However, future studies, especially regarding the associated soft tissues, will be required to confirm whether this is indeed the case. Our study expands the understanding of baubella within Ursidae, providing new data (including a three-dimensional model) that can be used to further explore the morphological diversity and function of this enigmatic extra-skeletal bone.

Polar bear paw pad surface roughness and its relevance to contact mechanics on snow.

Microscopic papillae on polar bear paw pads are considered adaptations for increased friction on ice/snow, yet this assertion is based on a single study of one species. The lack of comparative data from species that exploit different habitats renders the ecomorphological associations of papillae unclear. Here, we quantify the surface roughness of the paw pads of four species of bear over five orders of magnitude by calculating their surface roughness power spectral density. We find that interspecific variation in papillae base diameter can be explained by paw pad width, but that polar bear paw pads have 1.5 times taller papillae and 1.3 times more true surface area than paw pads of the American black bear and brown bear. Based on friction experiments with three-dimensional printed model surfaces and snow, we conclude that these factors increase the frictional shear stress of the polar bear paw pad on snow by a factor of 1.3-1.5 compared with the other species. Absolute frictional forces, however, are estimated to be similar among species once paw pad area is accounted for, suggesting that taller papillae may compensate for frictional losses resulting from the relatively smaller paw pads of polar bears compared with their close relatives.

Earliest giant panda false thumb suggests conflicting demands for locomotion and feeding.

Of the many peculiarities that enable the giant panda (Ailuropoda melanoleuca), a member of the order Carnivora, to adapt to life as a dedicated bamboo feeder, its extra "thumb" is arguably the most celebrated yet enigmatic. In addition to the normal five digits in the hands of most mammals, the giant panda has a greatly enlarged wrist bone, the radial sesamoid, that acts as a sixth digit, an opposable "thumb" for manipulating bamboo. We report the earliest enlarged radial sesamoid, already a functional opposable "thumb," in the ancestral panda Ailurarctos from the late Miocene site of Shuitangba in Yunnan Province, China. However, since the late Miocene, the "thumb" has not enlarged further because it must be balanced with the constraints of weight bearing while walking in a plantigrade posture. This morphological adaptation in panda evolution thus reflects a dual function of the radial sesamoid for both bamboo manipulation and weight distribution. The latter constraint could be the main reason why the panda's false thumb never evolved into a full digit. This crude "thumb" suggests that the origin of the panda's dedicated bamboo diet goes back to as early as 6-7 Ma.

Footprint evidence of early hominin locomotor diversity at Laetoli, Tanzania.

Bipedal trackways discovered in 1978 at Laetoli site G, Tanzania and dated to 3.66 million years ago are widely accepted as the oldest unequivocal evidence of obligate bipedalism in the human lineage1-3. Another trackway discovered two years earlier at nearby site A was partially excavated and attributed to a hominin, but curious affinities with bears (ursids) marginalized its importance to the paleoanthropological community, and the location of these footprints fell into obscurity3-5. In 2019, we located, excavated and cleaned the site A trackway, producing a digital archive using 3D photogrammetry and laser scanning. Here we compare the footprints at this site with those of American black bears, chimpanzees and humans, and we show that they resemble those of hominins more than ursids. In fact, the narrow step width corroborates the original interpretation of a small, cross-stepping bipedal hominin. However, the inferred foot proportions, gait parameters and 3D morphologies of footprints at site A are readily distinguished from those at site G, indicating that a minimum of two hominin taxa with different feet and gaits coexisted at Laetoli.

Mobility of the forearm skeleton in the Asiatic black (Ursus thibetanus), brown (U. arctos) and polar (U. maritimus) bears.

In several primates and carnivores, pronation/supination angles of the forearm skeleton were examined, and it is thought that a larger angle is useful to acquire dexterous behaviors in feeding and/or life style, including climbing. In this study, the pronation/supination angles in Asiatic black, brown and polar bears were nondestructively examined. These specimens were classified as adult or non-adult. Three or four carcasses of each group of Asiatic black and brown bears were used for CT analysis, whereas only one adult polar bear was used. The forearms were positioned within the gantry of a CT scanner in both maximally supinated and pronated states. Extracted cross-sectional CT images of two positions were superimposed by overlapping the outlines of each ulna. The centroids of the radii were detected, and then the centroid of each radius and the midpoint of a line which connects between both ends of the surface of each radius facing the ulna, were connected by lines to measure the angle of rotation as an index of pronation/supination. In adult brown and polar bears, the angles were smaller as compared with the other groups (Asiatic black and non-adult brown bears). Asiatic black and non-adult brown bears can climb trees, whereas adult brown bears and polar bears cannot. This suggests that the pronation/supination angle is related to arboreal activity in Ursidae.

Macroanatomic and morphometric analysis of the brown bear (Ursus arctos horribilis) mandible / Análisis macro anatómico y morfométrico de la mandíbula del oso pardo (Ursus arctos horribilis)

SUMMARY: Brown bear (Ursus arctos horribilis) is a wild animal from the bear (Ursidae) family. In this study, it was aimed to determine the morphometric values and anatomical structure of the brown bear mandible. After the superficial muscles of the mandible were dissected, the muscles were completely separated from the bones by boiling. 17 morphometric measurements were taken from the right and left mandible of each animal with the help of digital calipers. The mean and standard deviation values of the taken morphometric measurements were analyzed in the SPSS (20.0 version) package program. The mandible length was measured as 250.37 ± 9.75 mm on the right side and 246.83 ± 5.92 mm on the left side. The mandible height was determined as 105.76 ± 4.18 mm on the right and 108.62 ± 3.33 mm on the left. Consequently, the mandible was submitted to the results of the brown bear in the diversity of wildlife found in Turkey. We believe that the presented results will contribute to anatomical, surgical and archaeological studies.

RESUMEN: El oso pardo (Ursus arctos horribilis) es un animal salvaje de la familia de los osos (Ursidae). El objetivo de este estudio fue determinar los valores morfométricos y la estructura anatómica de la mandíbula del oso pardo, luego de la disección de los músculos superficiales de la mandíbula. Los músculos fueron separados por completo de los huesos mediante ebullición. Se tomaron 17 medidas morfométricas de la mandíbula derecha e izquierda de cada animal con la ayuda de calibradores digitales. Los valores de desviación estándar y media de las medidas morfométricas tomadas se anali- zaron en el programa SPSS (versión 20.0). El largo determiando de la mandíbula fue de 250,37 ± 9,75 mm en el lado derecho y 246,83 ± 5,92 mm en el lado izquierdo; la altura de la mandíbula era de 105,76 ± 4,18 mm en el lado derecho y 108,62 ± 3,33 mm en el izquierdo. Los resultados morfométricos obtenidos de la mandíbula del oso pardo en la diversidad de vida silvestre que se encuentra en Turquía contribuirán con el conocimiento anatómico y para los estudios quirúrgicos y arqueológicos.

Biomechanical simulations reveal a trade-off between adaptation to glacial climate and dietary niche versatility in European cave bears.

The cave bear is one of the best known extinct large mammals that inhabited Europe during the "Ice Age," becoming extinct ≈24,000 years ago along with other members of the Pleistocene megafauna. Long-standing hypotheses speculate that many cave bears died during their long hibernation periods, which were necessary to overcome the severe and prolonged winters of the Last Glacial. Here, we investigate how long hibernation periods in cave bears would have directly affected their feeding biomechanics using CT-based biomechanical simulations of skulls of cave and extant bears. Our results demonstrate that although large paranasal sinuses were necessary for, and consistent with, long hibernation periods, trade-offs in sinus-associated cranial biomechanical traits restricted cave bears to feed exclusively on low energetic vegetal resources during the predormancy period. This biomechanical trade-off constitutes a new key factor to mechanistically explain the demise of this dominant Pleistocene megafaunal species as a direct consequence of climate cooling.

Comparative skeletal anatomy of neonatal ursids and the extreme altriciality of the giant panda.

Mammalian neonates are born at a wide range of maturity levels. Altricial newborns are born with limited sensory agency and require extensive parental care. In contrast, precocial neonates are relatively mature physically and often capable of independent function shortly after birth. In extant mammals, placental newborns vary from altricial to precocial, while marsupials and monotremes are all extremely altricial at birth. Bears (family Ursidae) have one of the lowest neonatal-maternal mass ratios in placental mammals, and are thought to also have the most altricial placental newborns. In particular, giant pandas (Ailuropoda melanoleuca) are thought to be exceptionally altricial at birth, and possibly marsupial-like. Here we used micro-computer (micro-computed) tomography scanning to visualize the skeletal anatomy of ursid neonates and compare their skeletal maturity with the neonates of other caniform outgroups. Specifically, we asked whether ursid neonates have exceptionally altricial skeletons at birth compared with other caniform neonates. We found that most bear neonates are similar to outgroup neonates in levels of skeletal ossification, with little variation in degree of ossification between ursine bears neonates (i.e. bears of the subfamily Ursinae). Perinatal giant pandas, however, have skeletal maturity levels most similar to a 42-45-day-old beagle fetus (~70% of total beagle gestation period). No bear exhibits the skeletal heterochronies seen in marsupial development. With regards to skeletal development, ursine bears are not exceptionally altricial relative to other caniform outgroups, but characterized largely by the drastic difference between newborn and adult body sizes. A review on the existing hypotheses for ursids' unique reproductive strategy suggests that the extremely small neonatal-maternal mass ratio of ursids may be related to the recent evolution of large adult body size, while life history characteristics retained an ancestral condition. A relatively short post-implantation gestation time may be the proximal mechanism behind the giant panda neonates' small size relative to maternal size and altricial skeletal development at birth.

The bears from Dmanisi and the first dispersal of early Homo out of Africa.

We report on the taxonomy and paleodiet of the bear population that inhabited the emblematic palaeoanthropological Early Pleistocene (1.8 Ma) site of Dmanisi (Georgia), based on a dual approach combining morphometrics and microwear of upper and lower teeth. Given that the teeth of Ursus etruscus Cuvier, 1823 from Dmanisi show considerable size variability, their systematic position has been debated. However, a comparative study of the coefficients of variation for tooth size measurements in several modern bear species shows that the variability in tooth size of the ursid population from Dmanisi could result from sexual dimorphism. The analysis of tooth microwear indicates that these bears inhabited a mixed environment of open plain with forest patches, where they had a browsing diet with a substantial contribution of meat and/or fish. Comparative tooth morphometric analyses of modern ursids and fossil U. etruscus indicate that this extinct species had an omnivorous behavior similar to that of extant brown bears. The ecological interactions of the Dmanisi bears with other members of the large mammals community, including the first hominins that dispersed out of Africa, are discussed in the light of this new evidence.

Does hard mast production affect patterns of cementum annuli formation in premolar teeth of Asian black bears (Ursus thibetanus)?

Cementum annuli widths in mammals are is influenced by the nutrition of mammals. Reproductive stress has been is suggested to reduce the width of lead to narrower cementum annuli widths in female Asian black bears (Ursus thibetanus); however, food availability in autumn strongly impacts bear nutrition and likely impacts cementum widths as well. This study aimed to test how cementum annuli widths and the formation of false annuli were influenced by hard mast production. We established two hypotheses: (1) cementum annuli widths become narrower in poor mast years owing to inadequate nutritional conditions and (2) false annuli occur more frequently in poor mast years. We used teeth samples from male bears to avoid reproductive influences and separated width data into "adult" and "subadult" groups. We calculated the proportional width index (PWI) and used linear mixed models to estimate the masting effects on PWI. Generalized linear mixed models estimated the masting effects on false annuli frequency. True annuli widths and false annuli formation showed no significant relationship with mast production in adults. In subadults, poor mast production weak negative influence on false annuli formation. These new data resolve previous questions, allowing us to deduce that cementum annuli widths are a reliable index of reproductive success in female bears.

Palaeohistology and life history evolution in cave bears, Ursus spelaeus sensu lato.

The abundance of skeletal remains of cave bears in Pleistocene deposits can offer crucial information on the biology and life history of this megafaunal element. The histological study of 62 femora from 23 different European localities and comparisons with specimens of five extant ursid species revealed novel data on tissue types and growth patterns. Cave bear's femoral bone microstructure is characterized by a fibrolamellar complex with increasing amounts of parallel-fibered and lamellar bone towards the outer cortex. Remodelling of the primary bone tissue initially occurs close to the perimedullary margin of the bone cortex around the linea aspera. Although similar histological traits can be observed in many extant bear species, the composition of the fibrolamellar complex can vary greatly. Cave bears reached skeletal maturity between the ages of 10 and 14, which is late compared to other bear species. There is a significant correlation between altitude and growth, which reflects the different body sizes of cave bears from different altitudes.

Lectin histochemical studies on the olfactory gland and two types of gland in vomeronasal organ of the brown bear.

Olfaction is mediated by the vomeronasal and main olfactory systems, and the peripheral vomeronasal organ (VNO) processes species-specific chemicals that are associated with various behaviors in mammals. Sensory epithelial surfaces of the olfactory mucosa and VNO are covered by mucosal fluid that contains secretory products derived from associated glands, and glycoconjugates in the mucosal fluid are involved in odorant reception. The VNO of brown bears contains two types of glands; submucosal vomeronasal glands (VNG) and multicellular intraepithelial glands (MIG). The present study determined the labelling profiles of 21 lectins in the olfactory glands (OG), VNG and MIG of young male brown bears. The OG reacted with 12 lectins, and the VNG and MIG were positive for seven and eight lectins, respectively. Six lectins bound only to the OG, while four reacted with both or either of the VNG and MIG, but not the OG. The differences of lectin labelling pattern between the OG and glands in the VNO suggest that glycans in covering mucosal fluids differ between the olfactory mucosa and VNO. In addition, Bandeiraea simplicifolia lectin-I, Sophora japonica agglutinin and Jacalin reacted with the MIG but not the VNG, whereas Datura stramonium lectin and concanavalin A bound to the VNG, but not the MIG. These findings indicate that the properties of secretory substances differ between the two types of glands in the bear VNO, and that the various secretions from these two types of glands may function in the lumen of VNO together.

A cerebellar substrate for cognition evolved multiple times independently in mammals.

Given that complex behavior evolved multiple times independently in different lineages, a crucial question is whether these independent evolutionary events coincided with modifications to common neural systems. To test this question in mammals, we investigate the lateral cerebellum, a neurobiological system that is novel to mammals, and is associated with higher cognitive functions. We map the evolutionary diversification of the mammalian cerebellum and find that relative volumetric changes of the lateral cerebellar hemispheres (independent of cerebellar size) are correlated with measures of domain-general cognition in primates, and are characterized by a combination of parallel and convergent shifts towards similar levels of expansion in distantly related mammalian lineages. Results suggest that multiple independent evolutionary occurrences of increased behavioral complexity in mammals may at least partly be explained by selection on a common neural system, the cerebellum, which may have been subject to multiple independent neurodevelopmental remodeling events during mammalian evolution.

Frequency of appearance of transverse (Harris) lines reflects living conditions of the Pleistocene bear-Ursus ingressus-(Sudety Mts., Poland).

Transverse lines, called Harris Lines (HL), osteological markers of recovery from growth arrest episodes, are visible in radiograms of recent and Pleistocene fossil bones. Since on the one hand they mark stressful episodes in life, and on the other are mainly used to trace health fluctuations in prehistoric human communities, I used a cave bear population to check if the processes that could affect the specie' condition were in any way reflected in the bone structure. 392 bear bones from Bear Cave in Kletno (collection: Department of Palaeozoology, University of Wroclaw), dated as 32 100 ±1300 to >49 000 years BP, were radiologically examined. The bones were found in a non-anatomical position; morphological analysis indicated that they belonged to different individuals. HL shadows were observed on 9 tibiae and 3 radii: 8.8% out of the 59 tibiae and 77 radii and 3.1% of all the bones. At least 3 transverse lines were recognised in those cases; the specimens were histologically examined. The bear individuals in question experienced regular malnutrition periods during their ontogeny. Starvation resulting in growth inhibition involved young individuals, aged 1 to 4 years. Juveniles aged 6 months, i.e. before weaning, or younger, showed no signs of nutritional stress. Starvation periods associated with seasonal food deficit were not long or common and had no significant effect on the development and welfare of the species. This is the first description of the occurrence of transverse lines in the Pleistocene bear.

Accounting for Age Structure and Spatial Structure in Eco-Evolutionary Analyses of a Large, Mobile Vertebrate.

The idealized concept of a population is integral to ecology, evolutionary biology, and natural resource management. To make analyses tractable, most models adopt simplifying assumptions, which almost inevitably are violated by real species in nature. Here, we focus on both demographic and genetic estimates of effective population size per generation (Ne), the effective number of breeders per year (Nb), and Wright's neighborhood size (NS) for black bears (Ursus americanus) that are continuously distributed in the northern lower peninsula of Michigan, United States. We illustrate practical application of recently developed methods to account for violations of 2 common, simplifying assumptions about populations: 1) reproduction occurs in discrete generations and 2) mating occurs randomly among all individuals. We use a 9-year harvest dataset of >3300 individuals, together with genetic determination of 221 parent-offspring pairs, to estimate male and female vital rates, including age-specific survival, age-specific fecundity, and age-specific variance in fecundity (for which empirical data are rare). We find strong evidence for overdispersed variance in reproductive success of same-age individuals in both sexes, and we show that constraints on litter size have a strong influence on results. We also estimate that another life-history trait that is often ignored (skip breeding by females) has a relatively modest influence, reducing Nb by 9% and increasing Ne by 3%. We conclude that isolation by distance depresses genetic estimates of Nb, which implicitly assume a randomly mating population. Estimated demographic NS (100, based on parent-offspring dispersal) was similar to genetic NS (85, based on regression of genetic distance and geographic distance), indicating that the >36000 km2 study area includes about 4-5 black-bear neighborhoods. Results from this expansive data set provide important insight into effects of violating assumptions when estimating evolutionary parameters for long-lived, free-ranging species. In conjunction with recently developed analytical methodology, the ready availability of nonlethal DNA sampling methods and the ability to rapidly and cheaply survey many thousands of molecular markers should facilitate eco-evolutionary studies like this for many more species in nature.

Persistent organic pollutants, skull size and bone density of polar bears (Ursus maritimus) from East Greenland 1892-2015 and Svalbard 1964-2004.

We investigated skull size (condylobasal length; CBL) and bone mineral density (BMD) in polar bears (Ursus maritimus) from East Greenland (n = 307) and Svalbard (n = 173) sampled during the period 1892-2015 in East Greenland and 1964-2004 at Svalbard. Adult males from East Greenland showed a continuous decrease in BMD from 1892 to 2015 (linear regression: p < 0.01) indicating that adult male skulls collected in the early pre-pollution period had the highest BMD. A similar decrease in BMD over time was not found for the East Greenland adult females. However, there was a non-significant trend that the skull size of adult East Greenland females was negatively correlated with collection year 1892-2015 (linear regression: p = 0.06). No temporal change was found for BMD or skull size in Svalbard polar bears (ANOVA: all p > 0.05) nor was there any significant difference in BMD between Svalbard and East Greenland subpopulations. Skull size was larger in polar bears from Svalbard than from East Greenland (two-way ANOVA: p = 0.003). T-scores reflecting risk of osteoporosis showed that adult males from both East Greenland and Svalbard are at risk of developing osteopenia. Finally, when correcting for age and sex, BMD in East Greenland polar bears increased with increasing concentrations of persistent organic pollutants (POPs) i.e. ΣPCB (polychlorinated biphenyls), ΣHCH (hexachlorohexane), HCB (hexachlorobenzene) and ΣPBDE (polybrominated diphenyl ethers) while skull size increased with ΣHCH concentrations all in the period 1999-2014 (multiple linear regression: all p < 0.05, n = 175). The results suggest that environmental changes over time, including exposure to POPs, may affect bone density and size of polar bears.

Morphology of the lingual papillae of the polar bear (Ursus maritimus).

We examined the dorsal lingual surfaces of a newborn and an old polar bears by using scanning electron microscopy. In the newborn polar bear, the filiform papilla on the lingual apex was cylindrical in shape. The connective tissue core of the filiform papillae was needle-shaped and that of the fungiform papillae was funnel-shaped. The filiform papillae on the lingual body was dome-shaped. The connective tissue core of the filiform papillae was U-shaped and that of the fungiform papillae was column-shaped. On the lingual apex and body, there could not distinguish the filiform from fungiform papillae. The connective tissue core of the filiform papilla was different from the fungiform papilla. The vallate papillae were surrounded by a groove and pad and the surface was smooth. In the old bear, the filiform papilla on the lingual apex had several pointed processes. The processes of the filiform papilla on the lingual body were larger than those of the lingual apex. The vallate papillae were surrounded by a groove and pad and the surface was rough. There are no foliate papillae.

Rediscovery of the sun bear (Helarctos malayanus) in Yingjiang County,Yunnan Province,China.

The sun bear, Helarctos malayanus (Raffles, 1821), is a forest-dependent bear species distributed in tropical Southeast Asia. The species was previously reported from scattered localities in southwestern China, which is at the northeastern edge of its global range. Due to the scarcity of reliable recent records, some authorities cast doubt on the continued existence of sun bear in China. Here we present the rediscovery of this species in Yingjiang County, western Yunnan Province, China, near the international border with Myanmar's Kachin State.

Morphological and histological features of the vomeronasal organ in the brown bear.

The vomeronasal organ (VNO) is a peripheral receptor structure that is involved in reproductive behavior and is part of the vomeronasal system. Male bears exhibit flehmen behavior that is regarded as the uptake of pheromones into the VNO to detect estrus in females. However, the morphological and histological features of the VNO in bears have not been comprehensively studied. The present study investigated the properties and degree of development of the VNO of the brown bear by histological, histochemical and ultrastructural methods. The VNO of bears was located at the same position as that of many other mammals, and it opened to the mouth like the VNO of most carnivores. The shape of the vomeronasal cartilages and the histological features of the sensory epithelium in the bear VNO were essentially similar to those of dogs. Receptor cells in the VNO of the bear possessed both cilia and microvilli like those of dogs. The dendritic knobs of receptor cells were positive for anti-G protein alpha-i2 subunit (Gαi2 ) but negative for anti-G protein alpha-o subunit, indicating preferential use of the V1R-Gαi2 pathway in the vomeronasal system of bears, as in other carnivores. The VNO of the bear possessed three types of secretory cells (secretory cells of the vomeronasal gland, multicellular intraepithelial gland cells and goblet cells), and the present findings showed that the secretory granules in these cells also had various properties. The vomeronasal lumen at the middle region of the VNO invaginated toward the ventral region, and this invagination contained tightly packed multicellular intraepithelial gland cells. To our knowledge, this invagination and intraepithelial gland masses in the VNO are unique features of brown bears. The VNO in the brown bear, especially the secretory system, is morphologically well-developed, suggesting that this organ is significant for information transmission in this species.