A quantitative test of the "Ecomorphotype Hypothesis" for fossil true seals (Family Phocidae).

The fossil record of true seals (Family Phocidae) is mostly made up of isolated bones, some of which are type specimens. Previous studies have sought to increase referral of non-overlapping and unrelated fossils to these taxa using the 'Ecomorphotype Hypothesis', which stipulates that certain differences in morphology between taxa represent adaptations to differing ecology. On this basis, bulk fossil material could be lumped to a specific ecomorphotype, and then referred to species in that ecomorphotype, even if they are different bones. This qualitative and subjective method has been used often to expand the taxonomy of fossil phocids, but has never been quantitatively tested. We test the proposed ecomorphotypes using morphometric analysis of fossil and extant northern true seal limb bones, specifically principal components analysis and discriminant function analysis. A large amount of morphological overlap between ecomorphotypes, and poor discrimination between them, suggests that the 'Ecomorphotype Hypothesis' is not a valid approach. Further, the analysis failed to assign fossils to ecomorphotypes designated in previous studies, with some fossils from the same taxa being designated as different ecomorphotypes. The failure of this approach suggests that all fossils referred using this method should be considered to have unknown taxonomic status. In light of this, and previous findings that phocid limb bones have limited utility as type specimens, we revise the status of named fossil phocid species. We conclude that the majority of named fossil phocid taxa should be considered nomina dubia.

Morphology of sweat glands in the skin of Saimaa (Pusa hispida saimensis) and Baltic ringed (Pusa hispida botnica) seals.

The endangered Saimaa ringed seal (Pusa hispida saimensis) is an endemic freshwater subspecies inhabiting Lake Saimaa in Finland. The Baltic ringed seal (Pusa hispida botnica) inhabits the brackish Baltic Sea, which is almost entirely landlocked. Recent research shows that Saimaa and Baltic ringed seals may be genetically even further apart from each other than from other ringed seal subspecies. We documented histologically the integument microstructure of Saimaa and Baltic ringed seals to determine whether the geographic and genetic isolation was manifested as variation in the integument microstructure of these subspecies adapted to icy aquatic environments. The skin structures of these subspecies were similar to those of other phocids. The association of the sweat glands with hair follicles in both subspecies suggested that they were small apocrine sweat glands described previously in terrestrial or aquatic mammals. None of the apocrine glands had large lumina, and some of the ducts were relatively straight and short. Further studies analysing the mode of secretion, for example, apocrine versus eccrine, in the sweat glands are necessary to confirm the types of sweat glands in seals.

Microarchitecture of the penis bone (baculum) of a seal: A 3D morphometric examination using synchrotron and laboratory micro-computed tomography.

We examined the ultrastructure of the mammalian os penis at the high-resolution synchrotron level. Previously, bacular microanatomy had only been investigated histologically. We studied the baculum of the harp seal (Pagophilus groenlandicus), in which the baculum varies more in size and shape than does a mechanically constrained bone (humerus). We (1) investigated the microarchitecture of bacula and humeri from the same seal specimens, and (2) described changes in bone micro- and macro-morphology associated with age (n = 15, age range = 1-35 years) and bone type. We analyzed cross-sectional geometry non-destructively through laboratory micro-computed tomography. We suggest that the midshaft may resist axial compression while the proximal region may resist torsion, based on measurements of cross-sectional and cortical areas, perimeter, ratio of maximum and minimum moments of inertia, and polar moment of inertia. In addition, midshaft bacula may be less mechanosensitive than humeri, based on microstructural variables (e.g., volume, surface area, diameter associated with lacunae and cortical porosity) analyzed across age groupings. Our findings related to the microarchitecture of the pinniped baculum provide a basis for further studies on development, mechanical properties, functions, and adaptations in this and other pinniped species. Our use of a multi-modal imaging approach was minimally destructive for reproducible and accurate comparison of three-dimensional bone ultrastructure. Such methods, coupled with multidisciplinary analyses, enable diverse studies of bone biology, life history, and evolution using museum collections.

Report on the brain of the monk seal (Monachus monachus, Hermann, 1779).

The Mediterranean monk seal (Monachus monachus, Hermann, 1779) is an endangered species of pinniped endemic to few areas of the Mediterranean Sea. Extensive hunting and poaching over the last two centuries have rendered it a rare sight, scattered mainly in the Aegean Sea and the western coast of North Africa. In a rare event, a female monk seal calf stranded and died in southern Italy (Brindisi, Puglia). During due necropsy, the brain was extracted and fixed. The present report is the first of a monk seal brain. The features reported are remarkably typical of a true seal brain, with some specific characteristics. The brain cortical circonvolutions, main fissures and the external parts are described, and an EQ was calculated. Overall, this carnivore adapted to aquatic life shares some aspects of its neuroanatomy and physiology with other seemingly distant aquatic mammals.

Comparative examination of pinniped craniofacial musculature and its role in aquatic feeding.

Secondarily aquatic tetrapods have many unique morphologic adaptations for life underwater compared with their terrestrial counterparts. A key innovation during the land-to-water transition was feeding. Pinnipeds, a clade of air-breathing marine carnivorans that include seals, sea lions, and walruses, have evolved multiple strategies for aquatic feeding (e.g., biting, suction feeding). Numerous studies have examined the pinniped skull and dental specializations for underwater feeding. However, data on the pinniped craniofacial musculoskeletal system and its role in aquatic feeding are rare. Therefore, the objectives of this study were to conduct a comparative analysis of pinniped craniofacial musculature and examine the function of the craniofacial musculature in facilitating different aquatic feeding strategies. We performed anatomic dissections of 35 specimens across six pinniped species. We describe 32 pinniped craniofacial muscles-including facial expression, mastication, tongue, hyoid, and soft palate muscles. Pinnipeds broadly conform to mammalian patterns of craniofacial muscle morphology. Pinnipeds also exhibit unique musculoskeletal morphologies-in muscle position, attachments, and size-that likely represent adaptations for different aquatic feeding strategies. Suction feeding specialists (bearded and northern elephant seals) have a significantly larger masseter than biters. Further, northern elephant seals have large and unique tongue and hyoid muscle morphologies compared with other pinniped species. These morphologic changes likely help generate and withstand suction pressures necessary for drawing water and prey into the mouth. In contrast, biting taxa (California sea lions, harbor, ringed, and Weddell seals) do not exhibit consistent craniofacial musculoskeletal adaptations that differentiate them from suction feeders. Generally, we discover that all pinnipeds have well-developed and robust craniofacial musculature. Pinniped head musculature plays an important role in facilitating different aquatic feeding strategies. Together with behavioral and kinematic studies, our data suggest that pinnipeds' robust facial morphology allows animals to switch feeding strategies depending on the environmental context-a critical skill in a heterogeneous and rapidly changing underwater habitat.

Neuroanatomy of the grey seal brain: bringing pinnipeds into the neurobiological study of vocal learning.

Comparative animal studies of complex behavioural traits, and their neurobiological underpinnings, can increase our understanding of their evolution, including in humans. Vocal learning, a potential precursor to human speech, is one such trait. Mammalian vocal learning is under-studied: most research has either focused on vocal learning in songbirds or its absence in non-human primates. Here, we focus on a highly promising model species for the neurobiology of vocal learning: grey seals (Halichoerus grypus). We provide a neuroanatomical atlas (based on dissected brain slices and magnetic resonance images), a labelled MRI template, a three-dimensional model with volumetric measurements of brain regions, and histological cortical stainings. Four main features of the grey seal brain stand out: (i) it is relatively big and highly convoluted; (ii) it hosts a relatively large temporal lobe and cerebellum; (iii) the cortex is similar to that of humans in thickness and shows the expected six-layered mammalian structure; (iv) there is expression of FoxP2 present in deeper layers of the cortex; FoxP2 is a gene involved in motor learning, vocal learning, and spoken language. Our results could facilitate future studies targeting the neural and genetic underpinnings of mammalian vocal learning, thus bridging the research gap from songbirds to humans and non-human primates. Our findings are relevant not only to vocal learning research but also to the study of mammalian neurobiology and cognition more in general. This article is part of the theme issue 'Vocal learning in animals and humans'.

Term placenta of the southern elephant seal (Mirounga leonina).

INTRODUCTION: The pinnipeds' placenta has been described as zonary, annular, labyrinthic and endotheliochorial, like that of the terrestrial carnivores. This article describes the placenta of Mirounga leonina, a phocid pinniped, focusing on some morphological features related to fetal nutrition. METHODS: Placental samples from three elephant seals were collected and conditioned after natural delivery at the Antarctic Specially Protected Area 132. Histological and ultrastructural studies were conducted; cytokeratins, vimentin, α-smooth muscle actin, and desmin proteins were detected using immunohistochemistry. RESULTS: The placentas were zonary, lobed, belt-shaped, and showed multiple vivid orange areas, which corresponded to bilirubin crystalline pigment found among chorionic villi and inside trophoblast cells. In the labyrinth, cytotrophoblast cells were isolated and there was a scant syncytium interposed between maternal and fetal vessels. Fetal vessels were small, round, and frequently intratrophoblastic, while maternal vessels were large, irregular, sinuous, and thin-walled. Vimentin and actin were detected in some scattered non-vascular cells throughout the labyrinth. Broad areas of degenerated and necrotic maternal components were also observed. DISCUSSION: The placentas of pinniped and fissiped carnivores share several traits. However, some remarkable features might maximize respiratory efficiency, collaborating to endure deep-diving hypoxia. Some of them, as the notably large sinuous maternal capillaries and fetal capillary indentation into the syncytium, are shared, e.g., by Phocidae and Mustelidae. Besides hemotropic nutrition taking place through an extremely narrow barrier, the abundant necrotic material and hematic products might allow substantial endocytosis of detritus even in term placentas, in this species giving birth to precocious offspring.

Comparative feeding strategies and kinematics in phocid seals: suction without specialized skull morphology.

Feeding kinematic studies inform our understanding of behavioral diversity and provide a framework for studying the flexibility and constraints of different prey acquisition strategies. However, little is known about the feeding behaviors used by many marine mammals. We characterized the feeding behaviors and associated kinematics of captive bearded (Erignathus barbatus), harbor (Phoca vitulina), ringed (Pusa hispida) and spotted (Phoca largha) seals through controlled feeding trials. All species primarily used a suction feeding strategy but were also observed using a biting strategy, specifically pierce feeding. Suction feeding was distinct from pierce feeding and was characterized by significantly faster feeding times, smaller gapes and gape angles, smaller gular depressions and fewer jaw motions. Most species showed higher variability in suction feeding performance than in pierce feeding, indicating that suction feeding is a behaviorally flexible strategy. Bearded seals were the only species for which there was strong correspondence between skull and dental morphology and feeding strategy, providing further support for their classification as suction feeding specialists. Harbor, ringed and spotted seals have been classified as pierce feeders based on skull and dental morphologies. Our behavioral and kinematic analyses show that suction feeding is also an important feeding strategy for these species, indicating that skull morphology alone does not capture the true diversity of feeding behaviors used by pinnipeds. The ability of all four species to use more than one feeding strategy is likely advantageous for foraging in spatially and temporally dynamic marine ecosystems that favor opportunistic predators.

Adaptations to deep and prolonged diving in phocid seals.

This Review focuses on the original papers that have made a difference to our thinking and were first in describing an adaptation to diving, and less on those that later repeated the findings with better equipment. It describes some important anatomical peculiarities of phocid seals, as well as their many physiological responses to diving. In so doing, it is argued that the persistent discussions on the relevance and differences between responses seen in forced dives in the laboratory and those during free diving in the wild are futile. In fact, both are two sides of the same coin, aimed at protecting the body against asphyxic insult and extending diving performance.

An evaluation of three-dimensional photogrammetric and morphometric techniques for estimating volume and mass in Weddell seals Leptonychotes weddellii.

Body mass dynamics of animals can indicate critical associations between extrinsic factors and population vital rates. Photogrammetry can be used to estimate mass of individuals in species whose life histories make it logistically difficult to obtain direct body mass measurements. Such studies typically use equations to relate volume estimates from photogrammetry to mass; however, most fail to identify the sources of error between the estimated and actual mass. Our objective was to identify the sources of error that prevent photogrammetric mass estimation from directly predicting actual mass, and develop a methodology to correct this issue. To do this, we obtained mass, body measurements, and scaled photos for 56 sedated Weddell seals (Leptonychotes weddellii). After creating a three-dimensional silhouette in the image processing program PhotoModeler Pro, we used horizontal scale bars to define the ground plane, then removed the below-ground portion of the animal's estimated silhouette. We then re-calculated body volume and applied an expected density to estimate animal mass. We compared the body mass estimates derived from this silhouette slice method with estimates derived from two other published methodologies: body mass calculated using photogrammetry coupled with a species-specific correction factor, and estimates using elliptical cones and measured tissue densities. The estimated mass values (mean ± standard deviation 345±71 kg for correction equation, 346±75 kg for silhouette slice, 343±76 kg for cones) were not statistically distinguishable from each other or from actual mass (346±73 kg) (ANOVA with Tukey HSD post-hoc, p>0.05 for all pairwise comparisons). We conclude that volume overestimates from photogrammetry are likely due to the inability of photo modeling software to properly render the ventral surface of the animal where it contacts the ground. Due to logistical differences between the "correction equation", "silhouette slicing", and "cones" approaches, researchers may find one technique more useful for certain study programs. In combination or exclusively, these three-dimensional mass estimation techniques have great utility in field studies with repeated measures sampling designs or where logistic constraints preclude weighing animals.

Sensory anatomy of the most aquatic of carnivorans: the Antarctic Ross seal, and convergences with other mammals.

Transitions to and from aquatic life involve transformations in sensory systems. The Ross seal, Ommatophoca rossii, offers the chance to investigate the cranio-sensory anatomy in the most aquatic of all seals. The use of non-invasive computed tomography on specimens of this rare animal reveals, relative to other species of phocids, a reduction in the diameters of the semicircular canals and the parafloccular volume. These features are independent of size effects. These transformations parallel those recorded in cetaceans, but these do not extend to other morphological features such as the reduction in eye muscles and the length of the neck, emphasizing the independence of some traits in convergent evolution to aquatic life.

Ultrastructural, Sensory and Functional Anatomy of the Northern Elephant Seal (Mirounga angustirostris) Facial Vibrissae.

Vibrissae (whiskers) play a key role in underwater orientation in foraging phocids through vibrotactile sensation processing. Our aim was to evaluate the structure of northern elephant seal (NES) vibrissae by means of light (LM) and transmission electron microscopy (TEM), in order to elucidate their function. Vibrissal follicles were processed using standardized laboratory methods and LM/TEM techniques. Individual follicular axonal numbers were counted and axonal diameter measured and averaged. NES have mystacial, rhinal, supraorbital and labial vibrissae. The vibrissal follicles are histologically subdivided into a ring, upper and lower cavernous sinuses (LCS). Each vibrissa is innervated by the deep vibrissal nerve. The average number of axons per large mystacial vibrissa is 1804 (±123), rhinal 985 (±241), supraorbital 1,064 (±204) and 374 (±65) in labial vibrissa. The entire vibrissal system carries an estimated 148 573 axons, and mystacial vibrissae alone have 125 323 axons. Axonal conduction velocity for each vibrissal type is 55.26 m/s for labial, 56.58 m/s for rhinal and 35.88 m/s for mystacial vibrissae. TEM and LM revealed a plethora of mechanoreceptors within the vibrissal follicles: Merkel cell-neurite complexes, lanceolate and pilo-Ruffini end organs. A vast number of sensory axons projecting from the entire vibrissal system indicate that the vibrissal sensory area takes up a large proportion of phocids' somatosensory cortex. In conclusion, NES has highly sensitive and finely tuned vibrotactile vibrissal sense organs.

Optic nerve, superior colliculus, visual thalamus, and primary visual cortex of the northern elephant seal (Mirounga angustirostris) and California sea lion (Zalophus californianus).

The northern elephant seal (Mirounga angustirostris) and California sea lion (Zalophus californianus) are members of a diverse clade of carnivorous mammals known as pinnipeds. Pinnipeds are notable for their large, ape-sized brains, yet little is known about their central nervous system. Both the northern elephant seal and California sea lion spend most of their lives at sea, but each also spends time on land to breed and give birth. These unique coastal niches may be reflected in specific evolutionary adaptations to their sensory systems. Here, we report on components of the visual pathway in these two species. We found evidence for two classes of myelinated fibers within the pinniped optic nerve, those with thick myelin sheaths (elephant seal: 9%, sea lion: 7%) and thin myelin sheaths (elephant seal: 91%, sea lion: 93%). In order to investigate the architecture of the lateral geniculate nucleus, superior colliculus, and primary visual cortex, we processed brain sections from seal and sea lion pups for Nissl substance, cytochrome oxidase, and vesicular glutamate transporters. As in other carnivores, the dorsal lateral geniculate nucleus consisted of three main layers, A, A1, and C, while each superior colliculus similarly consisted of seven distinct layers. The sea lion visual cortex is located at the posterior side of cortex between the upper and lower banks of the postlateral sulcus, while the elephant seal visual cortex extends far more anteriorly along the dorsal surface and medial wall. These results are relevant to comparative studies related to the evolution of large brains.

Morphology of the Bearded Seal (Erignathus barbatus) Muscular-Vibrissal Complex: A Functional Model for Phocid Subambient Pressure Generation.

Bearded seals possess a broad muscular snout with large mystacial vibrissal fields that are involved in tactile sensation and prey identification. Although the microstructure of bearded seal vibrissae and their feeding performance have been investigated their orofacial morphology has not. Such morphological studies are important to understand the underlying mechanisms of feeding performance and to test proposed functional hypotheses. Therefore, the facial musculature was examined in bearded seals to test functional hypotheses regarding feeding performance. The orofacial musculature is composed primarily of three enlarged muscular layers, the M. levator nasolabialis, M. orbicularis oris, and M. buccinatorius (superficial), M. maxillonasolabialis (intermediate), and the M. lateralis nasi and M. dilator nasi (deep). The expansion of these muscles, the three dimensionality of the entire muscular array, the soft tissue insertions, and constant volume fit the model of a muscular hydrostat, and explains the detailed and varied mobility of their snout. An anastomosing network of CN VII innervates these facial muscles. The disproportionately large infraorbital nerve of CN V courses toward the snout and divides into numerous branches that penetrate the external capsule of every Follicle Sinus-Complex. The anatomical evidence support that the M. orbicularis oris, M. buccinatorius, and M. maxillonasolabialis form a robust lateral lip complex that can occluded lateral gape during subambient pressure generation. The rostral portion of the M. orbicularis oris, M. dilator nasi, and M. mentalis function to pursue the rostral lips to form a circular aperture important for projecting steep pressure gradients rostral to the lips for prey acquisition. Anat Rec, 299:1043-1053, 2016. © 2016 Wiley Periodicals, Inc.

Localization of the high-resolution area in the ganglion cell layer of the Baikal seal Pusa sibirica Gm.1788.

The morphological and functional density of the retinal ganglion cells of the Baikal Lake endemic seal Pusa sibirica was studied using cresyl-violet-stained whole-mounts. An area of the highest concentration of ganglion cells has been identified by drawing up a density map. This was an ellipsoid spot in the upper temporal part of the retina 6-7 mm from the visual nerve output. The maximum cell density in this area was 3800 cells/mm(2). The retinal resolution estimated from the maximum density of ganglion cells and the posterior nodal distance (24 mm) was 2.4' in the water and 3' in the air, and this can be used as an estimation of the retina resolving power.

Eye Histology and Ganglion Cell Topography of Northern Elephant Seals (Mirounga angustirostris).

Northern elephant seals are one of the deepest diving marine mammals. As northern elephant seals often reach the bathypelagic zone, it is usually assumed that their eyes possess evolutionary adaptations that provide better ability to see in dim or scotopic environments. The purpose of this study was to carefully describe anatomical and histological traits of the eye that may improve light sensitivity. Northern elephant seals have large, somewhat elliptical eyes, with equatorial and anteroposterior diameters of 5.03 and 4.4 cm, respectively. The cornea is large in diameter and the lens is completely spherical. The iris has pronounced constrictor and dilator muscles, whereas the ciliary muscle is notably less developed. The tapetum lucidum is more prominent than in other pinnipeds, making up about 63% of retinal thickness in the posterior aspect of the globe. Within the retina, the pigmented epithelium lacks pigment except for the region close to the ora serrata. Parts of the photoreceptor and outer nuclear layers are folded. Although the photoreceptor layer is composed predominantly of rods, cone photoreceptors were also observed. Cells within the retinal ganglion cell layer are arranged in a single level. Ganglion cells reach their maximum density (∼1,300 cells per mm(2) ) dorsal to the optic disc, whereas the periphery of the retina is sparsely populated (<100 cells per mm(2) ). All above mentioned features are consistent with the predicted evolutionary adaptations to the photic environment of the bathypelagic zone. Anat Rec, 299:798-805, 2016. © 2016 Wiley Periodicals, Inc.

The better to eat you with: the comparative feeding morphology of phocid seals (Pinnipedia, Phocidae).

One adaptation crucial to the survival of mammalian lineages that secondarily transitioned from land to water environments was the ability to capture and consume prey underwater. Phocid seals have evolved diverse feeding strategies to feed in the marine environment, and the objectives of this study were to document the specialized feeding morphologies and identify feeding strategies used by extant phocids. This study used principal component analysis (PCA) to determine the major axes of diversification in the skull for all extant phocid taxa and the recently extinct Caribbean monk seal (n = 19). Prey data gathered from the literature and musculoskeletal data from dissections were included to provide a comprehensive description of each feeding strategy. Random Forest analysis was used to determine the morphological, ecological and phylogenetic variables that best described each feeding strategy. There is morphological evidence for four feeding strategies in phocids: filter; grip and tear; suction; and pierce feeding. These feeding strategies are supported by quantitative cranial and mandibular characters, dietary information, musculoskeletal data and, for some species, behavioral observations. Most phocid species are pierce feeders, using a combination of biting and suction to opportunistically catch prey. Grip and tear and filter feeding are specialized strategies with specific morphological adaptations. These unique adaptations have allowed leopard seals (Hydrurga leptonyx) and crabeater seals (Lobodon carcinophaga) to exploit novel ecological niches and prey types. This study provides the first cranial and mandibular morphological evidence for the use of specialized suction feeding in hooded seals (Cystophora cristata), northern elephant seals (Mirounga angustirostris) and southern elephant seals (Mirounga leonina). The most important variables in determining the feeding strategy of a given phocid species were cranial and mandibular shape, diet, and phylogeny. These results provide a framework for understanding the evolution and adaptability of feeding strategies employed by extant phocid species, and these findings can be applied to other pinniped lineages and extinct taxa.

Field use of ultrasonography to characterize the reproductive tract and early pregnancy in a phocid, the Weddell seal (Leptonychotes weddellii).

The utility of transrectal ultrasonography was tested in a field setting to characterize the reproductive tract and detect early pregnancy (embryonic vesicles < 3 mm in diameter) in 17 multiparous female Weddell seals (Leptonychotes weddellii). Female Weddell seals give birth in October/November each year, followed by the breeding season (December) and embryonic diapause. Transrectal ultrasonography was attempted in January/February 2014 to examine the entire reproductive tract (uterine horns and body, ovaries with follicles and corpora lutea) using a 5-10 MHz linear-array probe with a 70 cm-long extension. A single pregnancy was detected in 14 of 17 seals (82.4%) as a circular or guitar-pick shaped nonechogenic (black) vesicle with a clearly visible echogenic border within the lumen of the uterus. The stage of embryonic development (ostensibly the gestational age) varied markedly among individuals, ranging from a vesicle with no embryo proper to a large fetus with an ocular orbit, nose/mouth, limb buds, spinal column, umbilical cord, and prominent vasculature. Two of the pregnant seals were re-examined 3-6 days after the initial examination to obtain longitudinal growth rates. Images of one or both ovaries were obtained in nine and seven of the 19 examinations, respectively. Numerous ovarian follicles (3 to 12 mm diameter) were detected and animals typically had a single well-perfused corpus luteum (determined by Doppler color-flow) ipsilateral to the uterine horn containing the pregnancy. We conclude that real-time transrectal ultrasonography is an effective tool for characterizing reproductive events in phocids including ovarian dynamics, and for elucidating the nature of embryonic diapause.

Comparisons and Uncertainty in Fat and Adipose Tissue Estimation Techniques: The Northern Elephant Seal as a Case Study.

Fat mass and body condition are important metrics in bioenergetics and physiological studies. They can also link foraging success with demographic rates, making them key components of models that predict population-level outcomes of environmental change. Therefore, it is important to incorporate uncertainty in physiological indicators if results will lead to species management decisions. Maternal fat mass in elephant seals (Mirounga spp) can predict reproductive rate and pup survival, but no one has quantified or identified the sources of uncertainty for the two fat mass estimation techniques (labeled-water and truncated cones). The current cones method can provide estimates of proportion adipose tissue in adult females and proportion fat of juveniles in northern elephant seals (M. angustirostris) comparable to labeled-water methods, but it does not work for all cases or species. We reviewed components and assumptions of the technique via measurements of seven early-molt and seven late-molt adult females. We show that seals are elliptical on land, rather than the assumed circular shape, and skin may account for a high proportion of what is often defined as blubber. Also, blubber extends past the neck-to-pelvis region, and comparisons of new and old ultrasound instrumentation indicate previous measurements of sculp thickness may be biased low. Accounting for such differences, and incorporating new measurements of blubber density and proportion of fat in blubber, we propose a modified cones method that can isolate blubber from non-blubber adipose tissue and separate fat into skin, blubber, and core compartments. Lastly, we found that adipose tissue and fat estimates using tritiated water may be biased high during the early molt. Both the tritiated water and modified cones methods had high, but reducible, uncertainty. The improved cones method for estimating body condition allows for more accurate quantification of the various tissue masses and may also be transferrable to other species.

Morphology of the tympanic-basicranial region in Mirounga leonina (Phocidae, Carnivora), postnatal ontogeny and sexual dimorphism.

The auditory region of pinnipeds has seldom been described. Here we describe and analyze the ontogenetic trajectory of the tympanic bulla of the southern elephant seal, Mirounga leonina (Phocidae, Mammalia). This species is extremely sexually dimorphic and highly polygynous (organized in harems). We examined 118 specimens, arranged in three age classes (CI, CII, and CIII), ranging from newborn to adults (males and females). To analyze the overall size and shape of the tympanic bulla we performed a geometric morphometric analysis including 87 skulls. Females reach definitive shape and size of the bulla at earlier ontogenetic stages than males, in agreement with their earlier involvement in reproductive activities. The internal anatomy of the tympanic region (e.g. form and extension of the paries) does not show remarkable differences between sexes or age classes. The greatest differences between age classes are related to bone thickness, resulting from the apposition of new annual layers. An examination of possible sex-related external differences among age classes shows significant shape differences between males and females in CIII. The morphology observed in neonates is conserved across all individuals from CI, which included specimens up to 1 year old. Clear morphological differences were observed between CI individuals, on one hand, and CII individuals plus CIII females on the other. During cranial development of both male and females, the glenoid cavity expands and compresses the bulla; this condition reaches its maximum expression in CIII males. CIII males showed the greatest morphological differences, with respect to both CI and CII individuals, and CIII females.