Pinnipeds (true seals, eared seals and walruses) are the only mammals that can hear effectively in both air and water. How and when they achieved the ability to negotiate such contrasting auditory media remains unknown. Here, we apply 3D shape and phylogenetic comparative analyses to a large dataset of extant and extinct caniform carnivorans (119 species, 217 specimens) to study the emergence of amphibious hearing in pinnipeds despite significant evolutionary constraints. We find support for the cavernous tissue as a functional and evolutionary mechanism for amphibious hearing. This tissue fills with blood during diving to equalize air pressure in the ear, enabling a shift from in-air to underwater hearing by matching the ear's acoustic impedance to that of the surrounding water. We found that early diverging freshwater pinnipeds had impaired hearing underwater. The first ancestral marine pinnipeds could hear amphibiously but with limited hearing ranges, probably reducing attenuation and harm from loud underwater sounds. Subsequently, otariids (eared seals) and phocids (true seals) independently acquired middle ear adaptations that expanded their underwater hearing range. This iterative evolution probably facilitated the exploration of novel auditory adaptive zones by crown pinnipeds, resulting in rare acoustic abilities like ultrasonic singing, vocal learning and rhythm.

Seals (pinnipeds) are the only mammals that can hear in both air and water. How and when they achieved the ability to negotiate such contrasting auditory media remains unknown. Here, we apply 3D shape and phylogenetic comparative analyses to a large dataset of caniform carnivorans (119 species, 217 specimens) to study the emergence of amphibious hearing in pinnipeds despite significant evolutionary constraints. We find support for the cavernous tissue as a functional and evolutionary mechanism for amphibious hearing. This tissue, which fills with blood during diving to equalise air pressure in the ear, enables a shift from in-air to underwater hearing by matching the acoustic impedance of the ear to that of the surrounding water. Early diverging freshwater pinnipeds had impaired hearing underwater. The first marine pinnipeds could hear amphibiously but were limited by a functional tradeoff between hearing abilities and the need to prevent damage from loud underwater sounds. Subsequently, otariids (eared seals) and phocids (true seals) independently acquired middle ear adaptations that expanded their underwater hearing range. This iterative evolution likely facilitated the exploration of novel auditory adaptive zones by crown pinnipeds, resulting in rare acoustic abilities like ultrasonic singing, vocal learning, and keeping rhythm. ### Competing Interest Statement The authors have declared no competing interest. UK Research and Innovation, https://ror.org/001aqnf71, EP/X021238/1 Marie Skłodowska-Curie Actions, 748167/ECHO CAPES, 4240/08-1 UCL, Small Grant 2009/10 DE-TAF, DE-TAF-273 Slovak Research and Development Agency, APVV-20-0079 NSF, NSF-DEB 1257572 John Templeton Foundation, JTF 62574 Leverhulme Trust, ECF-2025-468 Australian Research Council, DP230100613 Anatomy and Developmental Biology, Monash University Center for Functional Anatomy and Evolution at John Hopkins School of Medicine Canadian Museum of Nature Young researcher award from the Fondation des Treilles French-U.S. Fulbright Researcher program grant AMNH Frick Fund University of Poitiers

The Dasyurid species Sarcophilus harrisii, Dasyurus maculatus, and Dasyurus viverrinus, occupying diverse ecological niches and forming a guild structure in Tasmania, provide a basis for examining the roles of various forelimb muscle groups in prey capture and locomotion. Muscle fiber architecture is a key contributor to muscle force and can indicate specialized, repeated forelimb engagement. We performed wet dissections and virtual dissections via computed tomography to provide the first modern descriptions for the three species. We also quantified intrinsic forelimb muscles and compared normalized physiological cross-sectional area (PCSA) across species for individual and grouped muscles. The topology and muscle PCSAs are similar across species with select functional groups showing slight deviations. Overall proportions and ratios between antagonistic muscle groups reveal that D. viverrinus shows an overall reduction in muscle PCSA, whereas S. harrisii and D. maculatus appear to show an emphasis on muscle groups engaging in specialized behaviors for prey processing and arboreal locomotion, respectively. The results support the known trend of conserved forelimb musculature in marsupials. Nevertheless, muscle PCSA remains an important biomechanical indicator for specialized forelimb use in dasyurids.

Venomous snakes owe their evolutionary success in part to the effectiveness of their strike. The success of a strike depends on reaching the prey quickly before it startles and has the chance to escape. Here, we present the first ever large-scale experiment comparing strike performance across 36 venomous snake species from three families (31 Viperidae, 4 Elapidae and 1 Colubridae). We used two high-speed video cameras (1000 frames s-1) to capture strikes at a ballistics gel prey and tracked the strike trajectory in three dimensions. The 3D coordinates were used to measure strike kinematics and performance. Kinematic performance was compared within Viperidae across predation style, diel activity pattern, diet, habitat type, temperature and first jaw contact with prey. Kinematic variables (peak velocity, peak acceleration, gape angle, start distance, contact angle, head size) varied by the part of the jaw that first contacts the prey. Start distance to prey also varied by peak acceleration, jaw gape angle and contact angle with prey. Vipers typically reached higher peak velocities than elapids; however, some elapids such as Acanthophis rugosus reached equally high velocities. Peak velocities were found to be higher in ambush predators and in snakes that prey on mammalian prey. Prey was often reached within 100 ms, which falls within the mammalian startle response. Behavioural differences across the three families were also observed: Viperidae performed a smooth strike that was often followed by fang repositioning; Elapidae reached their prey quickly, bit and repeatedly squeezed prey with their jaws; and Colubridae used their rear-positioned fangs by alternate jaw movement to damage the prey's surface.

As teeth develop, their mineralised composition is a bio-recorder of diet, environment, and growth. High-resolution elemental mapping provides a tool to reveal records of life history within teeth. The relative concentrations of a range of trace elements change between in utero development, birth, and weaning in eutherian mammals. Marsupials, however, have a different mode of development: altricial birth and growth within the pouch facilitated by compositional transitions in milk. How these differences alter patterns of elemental mineralisation and become recorded in marsupial teeth is previously unknown. This study analyses the distribution of calcium (major element), zinc (actively incorporated trace element), and strontium (passively incorporated trace element) in the teeth of five species of diprotodontian marsupial using synchrotron X-ray fluorescence microscopy. We find that the diprotodontian lower incisor concatenates elemental variation from across the molariform dentition, preserving a prolonged record of life history in four of the five species. Patterns of elemental incorporation in enamel, dentine, and cementum are presented, with Ca, Zn, and Sr having differing distributions. Zn accretion indicates a role in mineralisation and/or prevention of tooth degradation. Zn also demarcates incremental cementum lines. Sr is shown to be passively incorporated into marsupial teeth, with increasing Sr concentration in milk recorded in dental tissues formed contemporaneously. Older individuals have oscillatory signals in Sr that appear linked to seasonality. These findings highlight some similarities between eutherian and marsupial trace element incorporation, particularly in the distribution of Zn. Sr signals in marsupial teeth record key aspects of life history.

“Saber teeth”—elongate, blade-like canines—are a classic example of convergence, having evolved repeatedly throughout mammalian history. Within canine teeth, there is a trade-off between the aspects of shape that improve food fracture and those that increase tooth strength. Optimal morphologies strike a balance between these antagonistic functional criteria. The extreme saber-tooth morphology is thought to confer functional advantage for more specialized predatory adaptations and optimization; however, the adaptive bases underpinning their evolution remain unclear. To determine whether saber-tooth shape reflects selection for functionally optimal morphologies, we generated a morphospace of the 3D shape of 70 non-saber and 25 saber-tooth species, a subset of which were used to quantify functional metrics of puncture performance and breakage resistance. These data were combined using a Pareto rank-ratio algorithm to evaluate optimality. We demonstrate that extreme saber-tooth morphologies are functionally optimal, occupying a localized peak in our optimality landscape. Unlike other optimal canine morphologies, extreme saber teeth optimize puncture performance at the expense of breakage resistance. This identifies functional optimality as a key driver underpinning the repeated evolution of this iconic tooth.

As teeth wear, their shapes change and functional features can be dulled or lost, presumably making them less effective for feeding. However, we do not know the magnitude and effect of this wear. Using Tasmanian devil canines as a case study, we investigated the impact of wear on puncture in pointed teeth. We measured aspects of shape impacted by wear (tip sharpness, height and volume) in teeth of varying wear followed by 3D printing of real and theoretical forms to carry out physical puncture tests. Tooth wear acts in two ways: by blunting tooth tips, and decreasing height and volume, both of which impact performance. Sharper tips in unworn teeth decrease the force and energy required to puncture compared with blunter worn teeth, while taller unworn teeth provide the continuous energy necessary to propagate fracture relative to shorter worn teeth. These wearmodulated changes in shape necessitate more than twice the force to drive worn teeth into ductile food and decrease the likelihood of puncture success.

While terrestrial breeding in polygynous species of pinnipeds allows for observations of reproductive behavior (Atkinson, 1997), similar opportunities are limited for cryptic, nonpolygynous, aquatic-breeding species. The isolated nature of solitary leopard seals (Hydrurga leptonyx; Southwell et al., 2012) restricts data collection on their reproductive behavior. Observations on reproductive behavior are limited to mating calls (Rogers, 2017; Rogers et al., 1996) and pupping (van der Linde et al., 2022). Leopard seal mating has been observed in captivity (Marlow, 1967), but not in the wild (Kooyman, 1981). Currently, the leopard seal is thought to mate aquatically, with males defending territories for mating (Atkinson, 1997). Inferences on leopard seal reproduction are further confounded by the lack of basic anatomical data for their reproductive anatomy, currently limited to the female reproductive tract (Hamilton, 1939; Harrison et al., 1952) and the ex situ baculum (Didier, 1952; Hamilton, 1939). The baculum (os penis) size and structure has been shown to be related to reproductive life history strategies in pinnipeds (Brassey et al., 2020; Dixson, 1995; Fitzpatrick et al., 2012). Any additional anatomical data for the baculum anatomy of the leopard seal, particularly its relationship with soft tissues (Harrison et al., 1952), would therefore represent a notable contribution to understanding their reproductive mating strategies. Here we provide some basic soft tissue and in situ skeletal data on the reproductive anatomy of an adult male leopard seal specimen, based on observations made during dissection and CT scanning. The leopard seal was observed hauled out on a beach at Point Ricardo prior to October 9, 2018, roughly 9 km west of Cape Conran, Victoria, Australia. It is suspected to have died on that day, and was collected by the Department of Environment, Land, Water and Planning (DEWLP) on October 10, 2018 (stranding specimen record ORB 0516). The specimen was donated to Museums Victoria and registered in the Mammalogy collections as NMV C39957. After collection, the specimen was stored at −20°C until it was thawed for dissection (the specimen had previously undergone a freeze–thaw cycle for another study, see Hocking et al., 2021). A full-body dissection of NMV C39957 was done from April 4–5, 2022. The soft tissue anatomy of the penis was observed while partitioning the hindquarters from the trunk section. After full separation, the hindquarters were CT scanned with a Siemens Somatom Go.UP at Monash Biomedical Imaging. CT scans were processed in Avizo Version 2022.1 (ThermoFisher Scientific), and measurements were taken using Meshlab (Cignoni et al., 2008). Available comparative baculum material was studied and photographed in the Mammalogy collections of Museums Victoria: a southern elephant seal (Mirounga leonina, NMV C33585), a juvenile leopard seal (NMV C39957), an immature crabeater seal (Lobodon carcinophaga, NMV C25039), and a fur seal (Arctocephalus sp., NMV C33579). A walrus specimen (Odobenus rosmarus, unregistered) from the Zoology teaching collections at Monash University was also studied. All specimens were measured with tape measure and linear calipers, except for those measured digitally (NMV C39957, unregistered walrus specimen Monash teaching collection). The walrus baculum was also CT scanned, processed, and measured on the same equipment and programs as the leopard seal. 3D scan files are available on MorphoSource (project ID 000487269). Due to the rarity of baculum specimens in pinnipeds, the comparisons are supplemented with observations in the literature (Didier, 1953; Hamilton, 1939; Miller, 2009; Miller & Burton, 2001; Miller et al., 1999, 2000; Morejohn, 2001; Oosthuizen & Miller, 2000; Scheffer, 1950; Yurkowski et al., 2011). Before dissection, we observed that the preputial opening of NMV C39957 was small, 5 cm in length (Table 1) and located just anterior to the hips. The epidermis and dermis were thick around the genital area (Figure 1b,c), although the blubber was much thinner in this region (~0.2 cm) compared to the rest of the external body cavity (~0.9 cm; Table 1, Figure 2). Phocid blubber thickness is known to vary in different parts of the body to act as thermal windows (Mellish et al., 2007), and hence this may be an adaptation for temperature regulation of the testes to avoid overheating. The testes were located between the skin/blubber and abdominal muscles. Despite testis size having a long history of study in pinnipeds (Fitzpatrick et al., 2012; Harrison et al., 1952), this is (to our knowledge) the first observation of thinning of blubber in this region. However, it is possible that the thin blubber was due to malnourishment and poor health, as the blubber thickness of the leopard seal was well below the average for phocids (~3.8 cm, Liwanag et al., 2012) and the expected variability outside of winter (>1.2 cm; Mellish et al., 2007). In a relaxed, retracted state, the penis itself was located entirely within the body cavity, in the midline ventral to the pelvis (in the scan it is displaced; Figure 3). When extended out of the preputial opening, the penis was mostly straight, although there is a slight ventral curve of the glans relative to the shaft (Figure 1c). The prepuce was elastic and stayed retracted when the penis was extended beyond the preputial opening. The CT scan revealed that the glans protrudes slightly distoventrally from the baculum (Figure 2c), with a slight projection of soft tissue at the terminal end of the glans (Figure 1b,c). The soft tissue of the glans took up most of the distal penis in cross-section (Figure 2a), although the shaft was substantially thinner relative to the baculum at mid-shaft (Figure 2b). When retracted, the preputial skin was clearly distinguishable from the penile shaft in CT images, due to the presence of radio-opaque sand particles lodged between its folds (Figure 2c). Proximally, the penis extends beyond the baculum, ending posterior to the pelvis (Figure 3). The baculum appears to be over 50% of the length of the flaccid penis (Figure 3), similar proportions to those in the walrus, Odobenus rosmarus (Fay, 1982). The data reported in this study represent the first observations of penile soft tissues in a leopard seal (Figures 1-3), and only the third observation for a monachine (southern true seal, subfamily Monachinae; Laws, 1956; Tedman, 1991). The soft tissue anatomy of the leopard seal appears to have broad similarities with harbor (Phoca vitulina), gray (Halichoerus grypus), and elephant (Harrison et al., 1952; Laws, 1956) seals described in the literature. Having soft tissue of the glans distal to the apex of the baculum appears to be a characteristic shared among phocids (Figure 2c), in contrast to otariids (Harrison et al., 1952; Laws, 1956). The prepuce appears to retract in all four of these phocid seals (Figure 1b,c; Harrison et al., 1952; Laws, 1956). One difference between the leopard seal and the two phocine seals (harbor and gray) is that the longitudinal striations noted on the glans of phocines (Harrison et al., 1952) were absent on NMV C39957; but it is possible that those striations may be artifacts caused by the formalin fixation employed in that study. We segmented out the baculum of NMV C39957 from the CT data to make observations of skeletal anatomy. The distal baculum appears laterally compressed, and much thinner compared to its shaft (Figure 4a). There is a shallow concavity on the posterior surface of the distal baculum, presumably homologous to the groove for the urethra in terrestrial carnivorans (Figure 4c) (Evans & de Lahunta, 2012). The ventral surface of the distal end of the baculum is mostly flattened (Figure 4). Immediately proximal to this flattened section, the shaft is mostly ovoid. At the midshaft, there is a ventral protuberance in the body (Figure 4b,c); this protuberance is only slightly flattened and appears to have the same thickness as the immediate dorsal surface. Proximal to this protuberance, the body is subcircular (slightly ovoid horizontally) in cross section. The base is quite short and tapers to a smaller circumference than the rest of the body (Figure 4a,b). Proximal-distally, the baculum has a slight lateral S-shaped bend when viewed dorsally or ventrally. In overall shape, the juvenile leopard seal (NMV C5603, Figure 5d) is more similar to other phocids, including juveniles of other species (Figure 5e), than it is to the adult specimen NMV C39957 (Figure 5c; Hamilton, 1939); as such, the leopard seal baculum appears to undergo substantial shape change during pubertal development (Hamilton, 1939), as it does in other pinnipeds reported in the literature such as otariids and phocines (Miller, 2009; Miller & Burton, 2001; Miller et al., 1999, 2000; Oosthuizen & Miller, 2000; Scheffer, 1950; Yurkowski et al., 2011). Overall, the baculum morphology of the adult leopard seal NMV C39957 is similar to the lobodontins described in the literature; the Weddell seal (Leptonychotes weddellii), the Ross seal (Ommatophoca rossii), and the crabeater seal are also asymmetrical and have a flattened distal apex (Didier, 1953; Morejohn, 2001). The leopard and Weddell seals both have a distinct ventral protuberance (Morejohn, 2001), although the ventral protuberance might vary in leopard seals (Hamilton, 1939). The anatomical characteristics shared amongst the lobodontins set them apart from the other pinnipeds (Figure 5b–e; Miller, 2009). The baculum of the adult leopard seal NMV C39957 is curved, similar to the hooded seal (Cystophora cristata; Miller et al., 1999), walrus (Figure 5a), and fur seal (Arctocephalus sp.; Figure 5f); however, the ventral curvature differs in the leopard seal (and the Weddell seal) by the interruption in profile from the ventral protuberance. It should be noted that this ventral protuberance has not been described in other observations of leopard seal bacula (Didier, 1952; Hamilton, 1939), and while the overall profile is consistent there appears to be some intraspecific variation in the ventral curvature. The intraspecific variation in leopard seal bacula (Didier, 1952; Hamilton, 1939) appears to be consistent with intraspecific variation observed in other phocid seals (Miller & Burton, 2001; Miller et al., 1999; Yurkowski et al., 2011). However, intraspecific variation in leopard seal bacula (and most pinnipeds) has likely not been adequately characterized and should be explored in future studies. This is important to establish, as early observations of morphological changes in leopard seal bacula in the third year of life (Hamilton, 1939) closely match when male leopard seals reach sexual maturity (Kooyman, 1981; Rogers, 2007). Noting both inter- and intraspecific variation in pinniped baculum morphology is important, as it has the potential to help infer the life history of more cryptic species (Dixson, 1995; Fitzpatrick et al., 2012; Yurkowski et al., 2011). Baculum size has been proposed to be related to intromission time (Dixson, 1995) and reproductive life history (Fitzpatrick et al., 2012). Intromission in captive leopard seals has been observed to last 10 min (Marlow, 1967). At 26 cm (Table 2), the baculum length of NMV C39957 is roughly 10% of the body length, making it the largest baculum recorded for a leopard seal, both absolutely and scaled to body size (the next largest being 24 cm; Hamilton, 1939; Scheffer & Kenyon, 1963). This places the leopard seal as having one of the larger baculum in pinnipeds (Scheffer & Kenyon, 1963). This is consistent with most phocids having larger bacula (scaled to body size) compared to most otariids and elephant seals (~6% body length), although they are still dwarfed by that of the walrus (~18% body length) (Scheffer & Kenyon, 1963). This larger relative size of the baculum in the leopard seal suggests prolonged intromission in this species, consistent with captive observations (Marlow, 1967), due to the established scaling relationship between these two variables (Dixson, 1995). In addition to size, shape complexity of bacula has also been noted to be related to reproductive strategy in carnivores, with socially monogamous taxa having more complex baculum shape, and "group-living" taxa having more simple shapes (Brassey et al., 2020). Pinnipeds, including the leopard seal, have been noted to have simple baculum shapes, on account of pinnipeds having group-living mating behavior such as land-based harems or aquatic lek-type mating (Boness et al., 2006; Brassey et al., 2020). This would imply that the leopard seal would have some form of group-living mating behavior, contrasting to their known solitary nature (Southwell et al., 2012). While the baculum of NMV C39957 is simple in shape, it should be noted that it is slightly more complex than the juvenile specimen (NMV C5603); therefore, ontogeny may need to be accounted for when making these life history inferences. When making inferences regarding leopard seal reproduction, both males and females need to be considered. The reproductive anatomy of female leopard seals has been described briefly (Hamilton, 1939; Harrison et al., 1952), based on a few individuals. The general morphology of the reproductive tract of female pinnipeds is known (Atkinson, 1997), and a study on vaginal endocasts in marine mammals found pinnipeds to have relatively simple shape complexity (Orbach et al., 2021). This seems to be the case for leopard, crabeater, Weddell, and harbor seals (Hamilton, 1939; Harrison et al., 1952). There are few descriptions of the baubellum (os clitoridis) in pinnipeds, the exception being the walrus (Fay, 1982). While some individual female pinnipeds are known to lack a baubellum completely (Lough-Stevens et al., 2018), we have no knowledge of the morphological variation in this structure. A leopard seal baubellum does not appear to have ever been reported in the literature. As such, future studies should also aim to expand on the anatomy of the baubellum. In conclusion, the soft tissue anatomy of the leopard seal penis seems to show broad similarities with other phocid seals. While the baculum of NMV C39957 largely agreed with other descriptions of leopard seal bacula, there were also some clear differences, namely the ventral protuberance, highlighting the presence of intraspecific variation. The baculum of NMV C39957 is the largest recorded for the leopard seal, and its large size is likely linked to longer intromission. Future studies should focus on recording the variation in baculum morphology of leopard seals, as well as expanding on knowledge on the reproductive anatomy of female leopard seals. James P. Rule was supported by an Australian Research Council Discovery Project (DP180101797). Thanks to Monash University's Anatomy and Developmental Biology department (in particular, Bonnie Dopheide, Stephen Thompson, Justin Adams) for providing space for the dissection. Thanks also go to Museums Victoria for access to dissection equipment and the Mammalogy collection (in particular, Karen Roberts and Steven Sparrey). The following members of the Evans EvoMorph lab and Adams Lab also assisted with the dissection: Lucy Costello, Kathleen Garland, Ruairidh Duncan, William Parker, Jake Kotevski, Jack O'Connor, Natasha Nosiara, Jonathan Edwards, and Ramon Ciccone. CT scanning was performed with the valuable assistance of Alexander McDonald and Dr. Michael De Veer at Monash Biomedical Imaging. The authors acknowledge the facilities and technical assistance of the National Imaging Facility (NIF), a National Collaborative Research Infrastructure Strategy (NCRIS) capability at Monash Biomedical Imaging (MBI), a Technology Research Platform at Monash University. Thanks to Daniel Latorre for discussions around anatomical terminology. The quality of this manuscript was improved thanks to feedback from the associate editor Frank Fish, Krista van der Linde, and two anonymous reviewers. Open access publishing facilitated by Monash University, as part of the Wiley - Monash University agreement via the Council of Australian University Librarians. James Patrick Rule: Conceptualization; data curation; formal analysis; investigation; project administration; writing – original draft; writing – review and editing. Hazel L Richards: Conceptualization; investigation; writing – review and editing. Tahlia I Pollock: Investigation; writing – review and editing. David P Hocking: Investigation; writing – review and editing. Alistair R Evans: Conceptualization; investigation; project administration; writing – review and editing.

Teeth are the primary tool used by most mammals to capture and process food. Over the lifetime of an individual, they progressively wear through contact with each other (attrition) and with food (abrasion), creating distinctive patterns that reflect function and diet. Unlike their terrestrial cousins, many marine mammals capture prey via suction, which so far has not been associated with a specific wear pattern. Here, we describe two new types of tooth wear across 18 species of modern marine mammal (beaked whales, belugas, killer whales, globicephalines, and various seals) that likely stem from this behaviour: "glossowear", which primarily affects the lingual side of the crown and plausibly records piston-like tongue movements during suction feeding; and "hydrowear", which wraps around the sides of the crown and occurs as water is expelled from the mouth. Both wear types differ from attrition and biting-related abrasion in their surface characteristics and location on the crown. Horizontal scratches suggest a physical wear process, rather than dental erosion (acid corrosion) and tooth abfraction (microfracture). Since suction specifically exploits the liquid properties of water, physical evidence of this behaviour may help to elucidate marine mammal feeding ecology and evolution. For example, glossowear is found in the toothed ancestors of baleen whales (mammalodontids, at least one aetiocetid, and likely Mystacodon), where it suggests an important role for suction in the emergence of filter feeding. By contrast, it is absent in most long-snouted toothed whales and dolphins, indicating that these animals mostly bite, rather than suck in, their prey.

Albatross are the largest seabirds on Earth and have a suite of adaptations for their pelagic lifestyle. Rather than having a bill made of a single piece of keratin, Procellariiformes have a compound rhamphotheca, made of several joined plates. Drivers of the shape of the albatross bill have not been explored. Here we use three-dimensional scans of 61 upper bills from 12 species of albatross to understand whether intrinsic (species assignment & size) or extrinsic (diet) factors predict bill shape. Diet is a significant predictor of bill shape with coarse dietary categories providing higher R2 values than dietary proportion data. We also find that of the intrinsic factors, species assignment accounts for ten times more of the variation than size (72% versus 6.8%) and that there is a common allometric vector of shape change between all species. When considering species averages in a phylogenetic framework, there are significant Blomberg's K results for both shape and size (K = 0.29 & 1.10) with the first axis of variation having a much higher K value (K = 1.9), reflecting the split in shape at the root of the tree. The influence of size on bill shape is limited, with species assignment and diet predicting far more of the variation. The results show that both intrinsic and extrinsic factors are needed to understand morphological evolution.

Context. The behaviours used by mammalian predators to track, kill, and consume prey are some of the most dynamic interspecific interactions in nature. However, they are often challenging to follow through the landscape and observe directly without disturbing the animals being watched. Aims. We describe the behaviours used by wild dingoes while hunting macropods in Namadgi National Park, Australian Capital Territory, Australia. Methods. Footage was initially captured by wildlife cinematographers on behalf of documentary programs and was made available for viewing after production. Hunting events were filmed from an altitude of > 50 m by using a "long lens' fitted to either a drone or helicopter. Results. We recorded a suite of hunting behaviours that would have been extremely challenging to observe from the ground via traditional methods. This includes some of the first video records published in the scientific literature of the behaviours used by dingoes to hunt and kill macropod prey, as well as some rare observations of mother and pup hunting dynamics. We did not observe any signs of disturbance as a result of filming for either predator or prey. Conclusions. The varied repertoire of predatory behaviours displayed by dingoes is similar to that documented in wolves and asserts them as a behaviourally complex top predator in the Australian landscape. In addition, we highlight the use of drones as a valuable approach for directly observing wild behaviours. They offer a minimally invasive and relatively inexpensive and accessible alternative to helicopters. This project is also a case study exemplifying the value of collaborations between filmmakers and researchers that enable the sharing of archival documentary footage for the study of wild animal behaviour. Implications. Future studies of wild animal behaviour should consider employing drones (at a safe distance and in accordance with published best practices and guidelines) as an additional tool to collect types of data that would be challenging using other methods.

Canine teeth are vital to carnivore feeding ecology, facilitating behaviours related to prey capture and consumption. Forms vary with specific feeding ecologies; however, the biomechanics that drive these relationships have not been comprehensively investigated. Using a combination of beam theory analysis (BTA) and finite-element analysis (FEA) we assessed how aspects of canine shape impact tooth stress, relating this to feeding ecology. The degree of tooth lateral compression influenced tolerance of multidirectional loads, whereby canines with more circular cross-sections experienced similar maximum stresses under pulling and shaking loads, while more ellipsoid canines experienced higher stresses under shaking loads. Robusticity impacted a tooth's ability to tolerate stress and appears to be related to prey materials. Robust canines experience lower stresses and are found in carnivores regularly encountering hard foods. Slender canines experience higher stresses and are associated with carnivores biting into muscle and flesh. Curvature did not correlate with tooth stress; however, it did impact bending during biting. Our simulations help identify scenarios where canine forms are likely to break and pinpoint areas where this breakage may occur. These patterns demonstrate how canine shape relates to tolerating the stresses experienced when killing and feeding, revealing some of the form–function relationships that underpin mammalian carnivore ecologies.

Drones have become popular with the general public for viewing and filming marine life. One amateur enthusiast platform, DroneSharkApp, films marine life in the waters off Sydney, Australia year-round and posts their observations on social media. The drone observations include the behaviours of a variety of coastal marine wildlife species, including sharks, rays, fur seals, dolphins and fish, as well as migratory species such as migrating humpback whales. Given the extensive effort and multiple recordings of the presence, behaviour and interactions of various species with humans provided by DroneSharkApp, we explored its utility for providing biologically meaningful observations of marine wildlife. Using social media posts from the DroneSharkApp Instagram page, a total of 678 wildlife videos were assessed from 432 days of observation collected by a single observer. This included 94 feeding behaviours or events for fur seals (n = 58) and dolphins (n = 33), two feeding events for white sharks and one feeding event for a humpback whale. DroneSharkApp documented 101 interactions with sharks and humans (swimmers and surfers), demonstrating the frequent, mainly innocuous human–shark overlap off some of Australia’s busiest beaches. Finally, DroneSharkApp provided multiple observations of humpback and dwarf minke whales with calves travelling north, indicating calving occurring well south of traditional northern Queensland breeding waters. Collaboration between scientists and citizen scientists such as those involved with DroneSharkApp can greatly and quantitatively increase the biological understanding of marine wildlife data.

Often the first point of contact between predator and prey, mammalian canine teeth are essential for killing, dismembering and consuming prey. Yet despite their importance, few associations among shape, function and phylogeny are established. We undertook the first comprehensive analysis of canine tooth shape across predatory mammals (Carnivora, Didelphimorphia and Dasyuromorphia), integrating shape analysis with function of this fundamental feature. Shape was quantified using three-dimensional geometric morphometrics and cross-sectional sharpness. Canines vary in three main ways (sharpness, robustness and curvature) which vary with diet, killing behaviour and phylogeny. Slender, sharp canines are associated with carnivores such as felids that target the neck of their prey and primarily consume the ‘softer’ parts of a carcass. Robust, blunt canines are found in mustelids and dasyurids that typically consume ‘harder’ materials, such as bone, or bite into skulls. Differences in the killing behaviours of felids and canids probably result in more curved canines in the latter, which act as hooks to hold prey. We find functional specialization in the upper and lower canines of individuals and across the major mammalian clades. These patterns demonstrate how canine teeth are adapted to suit diverse diets and hunting styles, enabling mammals to become some of nature's most successful predators.

The success of carnivorous mammals is determined not only by their ability to locate and kill prey, but also their efficiency at consuming it. Breaking large prey into small pieces is challenging due to the strong and tough materials that make up a carcass (e.g. hide, muscle, and bone). Carnivores therefore require a diverse suite of prey-processing behaviours to utilise their catch. Tasmanian devils are Australia’s only large marsupial scavengers and have the ability to consume almost all of a carcass. To determine how they do this we analysed 5.5 hours of footage from 21 captive and wild devils feeding at carcasses. We documented 6320 bouts of 12 distinct prey-processing behaviours, performed at frequencies that varied throughout feeds and between groups. The time point in the feed influenced the types of behaviours used. This is likely due to changing prey size, as different techniques appear better suited to handling whole carcasses or large pieces (pulling and pinning) or smaller pieces (holding and manipulating). Group size impacted the frequency of social pulling behaviours, which increased with the number of animals. Our findings highlight the range of prey-processing behaviours performed by scavenging devils when handling, breaking down, and consuming a carcass. The devils’ repertoire shares similarities with large carnivores that handle and consume whole carcasses as well as small carnivores that are adept in grasping and handling smaller prey.

A predator's preferred prey often changes over the course of its life as it grows from an inexperienced juvenile through to a sexually mature adult. For species with highly specialised feeding strategies, this may require its anatomy to change over the course of its life. The dugite (Pseudonaja affinis, Gunther 1872) is a venomous snake from Australia that displays such a diet shift, with juveniles feeding on small reptiles, while adults mainly target mammals. We examined the morphology of fangs across both sexes and throughout ontogeny using geometric morphometrics and cross-sectional sharpness measurements of key functional regions on these teeth. This highlighted key differences in shape that likely relate to the varied properties of their adult and juvenile diet. We found that juveniles display a more robust and blunter fang, which likely relates to feeding on scaly lizard prey, whereas adults have slender fangs with sharper tips, which reflects their diet of softer mammalian prey. There were also differences between males and females, with male snakes having significantly more slender fangs than females, which might be an indication of niche partitioning between the sexes. Using snout-vent length as a proxy for age, we found that the ontogenetic shift in fang shape occurs when P. affinis is around 60 cm long, corresponding with previous studies that found this size to be the moment where these snakes switch from their juvenile to adult diet.

A predator's preferred prey often changes over the course of its life as it grows from an inexperienced juvenile through to a sexually mature adult. For species with highly specialised feeding strategies, this may require its anatomy to change over the course of its life. The dugite (Pseudonaja affinis, Günther 1872) is a venomous snake from Australia that displays such a diet shift, with juveniles feeding on small reptiles, while adults mainly target mammals. We examined the morphology of fangs across both sexes and throughout ontogeny using geometric morphometrics and cross‐sectional sharpness measurements of key functional regions on these teeth. This highlighted key differences in shape that likely relate to the varied properties of their adult and juvenile diet. We found that juveniles display a more robust and blunter fang, which likely relates to feeding on scaly lizard prey, whereas adults have slender fangs with sharper tips, which reflects their diet of softer mammalian prey. There were also differences between males and females, with male snakes having significantly more slender fangs than females, which might be an indication of niche partitioning between the sexes. Using snout‐vent length as a proxy for age, we found that the ontogenetic shift in fang shape occurs when P. affinis is around 60 cm long, corresponding with previous studies that found this size to be the moment where these snakes switch from their juvenile to adult diet.

Venomous snakes are among the world's most specialized predators. During feeding, they use fangs to penetrate the body tissues of their prey, but the success of this penetration depends on the shape of these highly specialized teeth. Here, we examined the evolution of fang shape in a wide range of snakes using 3D geometric morphometrics (3DGM) and cross-sectional tooth sharpness measurements. We investigated the relationship of these variables with six diet categories based on the prey's biomechanical properties, and tested for evolutionary convergence using two methods. Our results show that slender elongate fangs with sharp tips are used by snakes that target soft-skinned prey (e.g., mammals), whereas fangs become more robust and blunter as the target's skin becomes scaly (e.g., fish and reptiles) and eventually hard-shelled (e.g., crustaceans), both with and without correction for evolutionary allometry. Convergence in fang shape is present, indicating that fangs of snakes with the same diet are more similar than those of closely related species with different diets. Establishing the relationship between fang morphology and diet helps to explain how snakes became adapted to different lifestyles, while also providing a proxy to infer diet in lesser known species or extinct snakes from the fossil record.

Otarioids (fur seals, sea lions and the walrus, Odobenus rosmarus) are an ancient group of marine mammals that have adapted to feeding in water in a variety of ways. Fur seals and sea lions (otariids) primarily feed on fish and cephalopods, but opportunistically target a wide range of prey types and sizes, including sharks, penguins, and even their own kind. Like their terrestrial carnivoran relatives, otariids primarily rely on their teeth to catch and process their food. Suction—the ability to lower the pressure inside the oral cavity to draw in water and prey—also plays an important role, however, especially when ingested items are small. Osteological adaptations for suction are seemingly absent, but the behavior is nonetheless facilitated by the shape of the soft tissues surrounding the mouth. Walruses are suction specialists, as reflected in their robust skull, muscular lips and strong throat muscles. They primarily feed on benthic bivalves, gastropods and annelids, but sometimes also target larger prey, including birds and other pinnipeds. Their foraging activities affect vast areas of the (sub)Arctic seafloor, affecting the structure of benthic communities and leading to major increases in nutrient flux. These large-scale effects, plus a voracious appetite, make walruses a major ecosystem engineer.