The teeth of odontocetes commonly display growth layers in their dentine and cementum. Sets of dentinal growth layers are called Growth Layer Groups (GLGs) and display an annual pattern, allowing them to be used in age estima-tion. Typically, GLGs have been counted on cut and polished or thin-sectioned teeth, a laborsome and destructive process. Herein, we investigate whether micro-CT scanning can provide an effec-tive means to count GLGs. Ages of similar to 400 Eastern Chukchi Sea stock belugas were estimated using micro-CT scans. For a subsample of our collec-tion, physically sectioned teeth had been prepared for scanned individuals and yielded ages that were similar. We selected micro-CT scanner parameters that balanced image quality with scan times and are suitable for an efficient workflow, aided by scanning batches of teeth and using macros to speed image processing and assist in counting GLGs. In addition to the non-destructive nature of the micro-CT, benefits include ease of opti-mizing virtual planes of section and the ability to scroll through a correctly oriented stack of scans to examine multiple image planes. If sampling of dentine from a GLG is needed, micro-CT scans can guide optimal tooth selection for analytical study by providing a preview of the internal tooth structure which can be used to guide sampling. Using this method, we introduce an explicit scor-ing system to categorize quality of age estimates as there is clear variation between individuals in how distinct GLGs appear.

Introduction: Ontogenetic brain growth in cetaceans is essential for understanding their development and evolution. This study investigates brain size changes relative to body growth in bowhead (Balaena mysticetus) and beluga (Delphinapterus leucas) whales in the framework of age estimates of pre- and postnatal specimens. Methods: We collected specimens in the field, determined brain size and endocranial volumes, as well as size of endocranial adnexa, either by direct measurement or by CT. We estimated age using baleen length (bowhead), growth layers in teeth (belugas), or fetal stages. We fitted Gompertz growth models to our data. Results: Our findings show that both bowhead and beluga whales reach nearly their full brain size by the end of weaning, unlike dolphins and humans, whose brains continue growing after weaning. Bowhead brains grow faster than those of belugas, and much faster than those of humans, and their rete mirabile occupies a much larger portion of the cranial cavity than in belugas. Encephalization quotients decline with age due to continued body growth after brain maturation. Conclusion: Brain growth in these cetacean species plateaus early, challenging the assumption that cetacean brains grow throughout life. In bowhead, the brain is significantly smaller than the cranial cavity, and this is not the case in beluga. If this observation can be generalized to all mysticetes and odontocetes, it implies that no single equation can capture the proportional volumes of the brain and cranial cavity across the entire cetacean clade.

“My first contact with Rod Feldmann was his voicemail message: ‘An incredible set of circumstances makes it impossible for me to come to the phone right now. Please leave a message and I will get back to you as soon as possible.’ I was considering coming to Kent for graduate school and I thought, ‘Wow, this guy is either really important or really arrogant.’ I was right and wrong. He was never arrogant, but always important, and eventually of utmost importance to me.

Toothed whales (odontocetes) make use of high-frequency sounds to echolocate, differing significantly from their sister group baleen whales (mysticetes), which make use of low-frequency sound for long-distance communication. This divergence in auditory ability has led to considerable speculation as to how hearing functioned in the ancestral archaeocetes, and when the specializations of modern species arose. Numerous studies have attempted to infer auditory capabilities from morphological correlates valid in modern species. Here, we build upon these previous methods with a focus on cochlear structures that have well-understood links to function. We combine this with information on the sound conduction apparatus to chart the evolutionary trajectory of cetacean hearing. Our results suggest an initial move toward low-frequency specialization in early Eocene cetaceans, which coincides with the appearance of new sound conduction pathways. This paved the way for the later movement toward higher-frequency hearing in protocetids; however, the ultra-high- and low-frequency hearing specializations of both modern cetacean clades evolved after their divergence. We use these data to test the hypotheses that evolutionary brain size increases in cetaceans were related to the origin of high-frequency echolocation. We show that no shift in relative brain size coincides with any changes toward high-frequency perception. However, this does not rule out a role for other changes in hearing ability such as some simple forms of echolocation, similar to that suggested for hippopotamuses or bowhead whales, which may have been present in even the earliest cetaceans.

As bones age in most mammals, they typically become more fragile. This state of bone fragility is often associated with more homogenous collagen fiber orientations (CFO). Unlike most mammals, bats maintain mechanically competent bone throughout their lifespans, but little is known of positional and age-related changes in CFO within wing bones. This study tests the hypothesis that age-related changes in CFO in big brown bats (Eptesicus fuscus) differ from those of the standard mammalian model for skeletal aging, the C57BL/6 laboratory mouse. We used data from quantitative polarized light microscopy (qPLM) to compare CFO across the lifespan of long-lived big brown bats and age matched C57BL/6 mice. Eptesicus and C57BL/6 mice displayed idiosyncratic patterns of CFO. Consistent age-related changes were only apparent in the outer cortical bone of Eptesicus, where bone tissue is more longitudinally arranged and more anisotropic in older individuals. Both taxa displayed a ring of more transversely oriented bone tissue surrounding the medullary cavity. In Eptesicus, this tissue represents a greater proportion of the overall cross-section, and is more clearly helically aligned (arranged at 45° to the bone long axis) than similar bone tissue in mice. Bat wing bones displayed a proximodistal gradient in CFO anisotropy and longitudinal orientation in both outer and inner cortical bone compartments. This study lays a methodological foundation for the quantitative evaluation of bone tissue architecture in volant and non-volant mammals that may be expanded in the future.

newly discovered fossil of an extinct whale from Peru indicates that the animal’s skeleton was unexpectedly enormous. This finding challenges our understanding of body-size evolution.

The cetacean visual system is a product of selection pressures favoring underwater vision, yet relatively little is known about it across taxa. Previous studies report several mutations in the opsin genetic sequence in cetaceans, suggesting the evolutionary complete or partial loss of retinal cone photoreceptor function in mysticete and odontocete lineages, respectively. Despite this, limited anatomical evidence suggests cone structures are partially maintained but with absent outer and inner segments in the bowhead retina. The functional consequence and anatomical distributions associated with these unique cone morphologies remain unclear. The current study further investigates the morphology and distribution of cone photoreceptors in the bowhead whale and beluga retina and evaluates the potential functional capacity of these cells' alternative to photoreception. Refined histological and advanced microscopic techniques revealed two additional cone morphologies in the bowhead and beluga retina that have not been previously described. Two proteins involved in magnetosensation were present in these cone structures suggesting the possibility for an alternative functional role in responding to changes in geomagnetic fields. These findings highlight a revised understanding of the unique evolution of cone and gross retinal anatomy in cetaceans, and provide prefatory evidence of potential functional reassignment of these cells.

Most authors have identified two rapid increases in relative brain size (encephalization quotient, EQ) in cetacean evolution: first at the origin of the modern suborders (odontocetes and mysticetes) around the Eocene-Oligocene transition, and a second at the origin of the delphinoid odontocetes during the middle Miocene. We explore how methods used to estimate brain and body mass alter this perceived timing and rate of cetacean EQ evolution. We provide new data on modern mammals (mysticetes, odontocetes, and terrestrial artiodactyls) and show that brain mass and endocranial volume scale allometrically, and that endocranial volume is not a direct proxy for brain mass. We demonstrate that inconsistencies in the methods used to estimate body size across the Eocene-Oligocene boundary have caused a spurious pattern in earlier relative brain size studies. Instead, we employ a single method, using occipital condyle width as a skeletal proxy for body mass using a new dataset of extant cetaceans, to clarify this pattern. We suggest that cetacean relative brain size is most accurately portrayed using EQs based on the scaling coefficients as observed in the closely related terrestrial artiodactyls. Finally, we include additional data for an Eocene whale, raising the sample size of Eocene archaeocetes to seven. Our analysis of fossil cetacean EQ is different from previous works which had shown that a sudden increase in EQ coincided with the origin of odontocetes at the Eocene-Oligocene boundary. Instead, our data show that brain size increased at the origin of basilosaurids, 5 million years before the Eocene-Oligocene transition, and we do not observe a significant increase in relative brain size at the origin of odontocetes.

The lake deposits of the informal Ruby Paper Shale unit, part of the Renova Formation of Montana, have yielded abundant plant fossils that document Late Eocene – Early Oligocene global cooling in western North America. A nearly complete small bird with feather impressions was recovered from this unit in in 1959, but has only been informally mentioned. Here we describe this fossil and identify it as a new species of Zygodactylus, a stem lineage passerine with a zygodactyl foot. The new taxon shows morphological traits that are convergent on crown Passeriformes, including an elongate hallux, reduced body size, and a comparative shortening of proximal limb elements. The fossil documents the persistence of this lineage into the earliest Oligocene (~ 33 Ma) in North America. It is the latest occurring North American species of a group that persists in Europe until the Miocene. Eocene-Oligocene global cooling is known to have significantly remodeled both Palearctic and Nearctic mammal faunas but its impact on related avifaunas has remained poorly understood. The geographic and temporal range expansion provided by the new taxon together with avian other taxa with limited fossil records suggests a similar pattern of retraction in North America followed by Europe.

Tympanic bullae and baleen plates from bowhead whales of the Western Arctic population were examined. Growth layer groups (GLGs) in the involucrum of the tympanic bone were used to estimate age of the whales, and compared to stable isotope signatures along transects of baleen plates and the involucrum. The involucrum of the tympanic bone consists of three regions that form in utero, during nursing in the first year, and during the first decades of life, respectively. Life history events, such as annual migration, are recorded in the bowhead tympanic bulla. It is likely that bone growth in the bowhead tympanic occurs during periods of high food intake, while slow or arrested growth occurs during periods of low food intake. Comparisons between numbers of GLGs in the tympanic, number of isotopic oscillations in a baleen plate, length of the baleen plate, and total whale length show correlation coefficients as high as 0.97. The tympanic GLG method is particularly useful for estimating the age of whales up to 20 yr old.

Counts of Growth Layer Groups (GLGs) in the dentin of marine mammal teeth are widely used as indicators of age. In most marine mammals, observations document that GLGs are deposited yearly, but in beluga whales, some studies have supported the view that two GLGs are deposited each year. Our understanding of beluga life-history differs substantially depending on assumptions regarding the timing of GLG deposition; therefore, resolving this issue has important considerations for population assessments. In this study, we used incremental lines that represent daily pulses of dentin mineralization to test the hypothesis that GLGs in beluga dentin are deposited on a yearly basis. Our estimate of the number of daily growth lines within one GLG is remarkably close to 365 days within error, supporting the hypothesis that GLGs are deposited annually in beluga. We show that measurement of daily growth increments can be used to validate the time represented by GLGs in beluga. Furthermore, we believe this methodology may have broader applications to age estimation in other taxa.

Eleven concretions containing the nephropid lobster, Palaeonephrops browni (Whitfield, 1907), from the Upper Cretaceous (Campanian), Bearpaw Formation in northeastern Montana, were examined using visual and geochemical methods. The concretions were zoned, with an axial, phosphate-rich core also containing calcium surrounding the lobster remains and an outer, calcium-rich zone lacking phosphate. The overall composition documents these as carbonate concretions, not phosphatic concretions. Where visible, the inner zone is sheathed in a thin layer dominated by framboidal pyrite, suggesting formation by a microbial film. The different geochemical settings in the inner versus outer zones suggest reduced pH conditions during formation of the inner core and normal pH conditions resulting in formation of the outer zone. The pattern is suggestive of extremely rapid preservation of the lobster remains within a microbial sheath in which a calcium phosphate mineral, probably francolite, delicately replaced the lobster cuticle, and traces of worm (?) burrows and fecal pellets were preserved. The remainder of the concretion, the outer zone, formed under normal pH conditions and was probably induced by the chemistry of the core. Size of the concretions relative to the size of the enclosed lobsters, lack of evidence of a burrow complex in the surrounding sediment, and central positioning of the lobster remains within the concretions do not support the contention that the lobsters were entombed within a burrow.

In an effort to use aspects of the cuticle as taxonomic characters in phylogenies of fossil and extant decapods, variation due to gender, growth, sample location on the carapace, and molt cycle must be understood so that taxonomically important characters can be identified. In this study, effects of sample location on the carapace and carapace size were examined. A series of male Callinectes Sapidus Rathbun, 1896, specimens from 2-6 cm in length were collected on the Rhode River of the Chesapeake Bay, MD. USA. To study the effects of sample location and carapace size on parameters of the cuticle, the cuticle was examined in thin section and oil the surface of the dorsal carapace. The distributional density Of setal pits and nodes and node size were measured on the surface. In thin section, thickness of the cuticle and construction of the nodes and setal pits was examined. Thickness of the cuticle, node size, and setal pit density increased during growth of the crab. Node density decreased with growth. Construction of nodes and setal pits remained constant in all specimens and sample locations. Morphometric parameters of the cuticle were consistent with previously reported growth rates of the carapace in C. sapidus. Differences in the rate of change for the cuticle metrics studied occurred at carapace sizes that are attained upon reaching sexual maturity. Growth rates Of Cuticular features provide context for comparison with similar data in other species. In addition, the change ir growth rates of these features, if recognized in fossil crab populations, may allow the determination of population age structures and size it maturity.