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First insights into the function of the sawshark rostrum through examination of rostral tooth microwear: rostral tooth microwear in sawsharks
Journal of Fish Biology
Abstract
Potential roles of the rostrum of sawsharks (Pristiophoridae), including predation and self-defence, were assessed through a variety of inferential methods. Comparison of microwear on the surface of the rostral teeth of sawsharks and sawfishes (Pristidae) show that microwear patterns are alike and suggest that the elongate rostra in these two elasmobranch families are used for a similar purpose (predation). Raman spectroscopy indicates that the rostral teeth of both sawsharks and sawfishes are composed of hydroxyapatite, but differ in their collagen content. Sawfishes possess collagen throughout their rostral teeth whereas collagen is present only in the centre of the rostral teeth of sawsharks, which may relate to differences in ecological use. The ratio of rostrum length to total length in the common sawshark Pristiophorus cirratus was found to be similar to the largetooth sawfish Pristis pristis but not the knifetooth sawfish Anoxypristis cuspidata. Analysis of the stomach contents of P. cirratus indicates that the diet consists of demersal fishes and crustaceans, with shrimp from the family Pandalidae being the most important dietary component. No prey item showed evidence of wounds inflicted by the rostral teeth. In light of the similarities in microwear patterns, rostral tooth chemistry and diet with sawfishes, it is hypothesised that sawsharks use their rostrum in a similar manner for predation (sensing and capturing prey) and possibly for self-defence.
... The distribution of ventral LLG in this long-nose chimaera is similar to that in sawsharks and sawfishes 91,92 (notwithstanding the presence of mandibular, supratemporal, and angular grooves); an observation which would form the basis for a prediction that the two very different groups of chondrichthyans use their sensory systems in similar ways, specifically for the detection of benthic prey. In fact, the rhinochimaerid-like rostrum of sawsharks and sawfishes is thought to assist with the detection of demersal fishes and crustaceans [91][92][93]94 . Table 3. Ampullary pore counts for each study species (n = 3 specimens), expressed as number ± standard deviation (SD) and percentage of the total count. ...
... Mean pore number for H. avia (1,245 ± 137) is relatively high for an holocephalan. Similar pore numbers occur in the southern sawshark Pristiophorus nudipinnis (1,283) 91,94 and the dwarf sawfish Pristis clavata (1,267) 105 . This reinforces the hypothesis that H. avia uses its rostrum to locate infaunal prey 91,93,94,105 . ...
... Similar pore numbers occur in the southern sawshark Pristiophorus nudipinnis (1,283) 91,94 and the dwarf sawfish Pristis clavata (1,267) 105 . This reinforces the hypothesis that H. avia uses its rostrum to locate infaunal prey 91,93,94,105 . The high pore number in H. avia could also be an example of a species that fulfils the 'enhanced electrosensory hypothesis' postulated for some species of shovelnose rays (Rhinobatidae) 57 and hammerhead sharks (Sphyrnidae) 103 . ...
The mechanosensory (lateral line) and electrosensory systems are two important non-visual sensory modalities, especially in low light environments. Despite their importance, these sensory systems have received little attention in deepwater chondrichthyans. Here, we describe the morphological organisation of the peripheral lateral line and electrosensory systems in two species of chimaeras; the pale ghost shark Hydrolagus bemisi (Chimaeridae) and the Australasia narrow-nosed spookfish Harriotta avia (Rhinochimaeridae), occupying depth ranges of 400–1,100 m and 260–1,278 m, respectively. Using topographic mapping, computed tomography, histology, and scanning electron microscopy, the distribution, abundance, size, and microstructure of lateral line grooves and organs (neuromasts), and ampullary organs (pores, canals, and bulbs) are described. The arrangement of the peripheral sense organs in both these systems may reflect comparable feeding strategies for detecting benthic prey. While the elongated rostrum of Harriotta avia is likely used as a sensory probe, providing spatially-resolved information about minute hydrodynamic disturbances and electric fields of potential prey beneath the animal, the arrangement of sense organs in Hydrolagus bemisi indicates that this species may rely less on electroreception. The study compares the morphology and provides information on the relative importance of two (non-visual) sensory modalities in two demersal holocephalans that remain vulnerable to anthropogenic disturbances.
... Sawfish (Pristidae) and sawsharks (Prostiophoridae) have adapted their elongate rostra to bear lateral teeth on the outside. The function of these toothed-rostrums ('saws') has been widely hypothesised (Breder, 1952;Nevatte et al., 2017a;Slaughter & Springer, 1968;Wueringer et al., 2012). The sawfish rostrum bears large, broad, flattened and triangular shaped teeth that grow continuously but are not replaced if lost (Slaughter & Springer, 1968). ...
... Sawfish rostral use has been successfully explored through a number of behavioural experiments in aquaria and laboratory settings (Wueringer et al., 2012). The function of the saw in sawsharks is less clear as maintaining them in aquaria has proved difficult (Nevatte et al., 2017a;Wueringer et al., 2020). Sawsharks possess a rostrum containing a pair of barbels and a series of alternating large and small slender teeth that are sequentially replaced on loss (Ebert & Cailliet, 2011). ...
... The common sawshark Pristiophorus cirratus (Latham 1794) is a small, benthic-associated species that occurs in waters along the southern half of Australia, to depths of 40 m to 630 m (Last & Stevens, 2009;Nevatte & Williamson, 2020;Nevatte et al., 2019). Limited information exists for this species, with the exception of recent studies on aspects of their diet (Raoult et al., 2015), fisheries interactions (Raoult et al., 2017, biological features (Nevatte et al., 2017a(Nevatte et al., , 2017bWueringer et al., 2020) and longevity concerns (Burke et al., 2020). Initial studies focusing on ecological aspects of the common sawshark have observed a diet based in teleosts and crustaceans (Nevatte et al., 2017a;Raoult et al., 2015). ...
Prey manipulation through headfirst ingestion is a common foraging tactic in predatory taxa. Sawsharks possess a toothed rostrum that is thought to assist in prey capture, but the process from prey contact to ingestion is unknown. This study provides evidence of headfirst ingestion and possible prey orientation in situ through the use of cone beam CT scans in the common sawshark (Pristiophorus cirratus). CT scans provide an efficient method for assessing ingestion and proposing plausible behavioural tactics for food manipulation in a species difficult to observe in the wild or maintain in captivity.
... Two species of sawshark-the common sawshark Pristiophorus cirratus (Latham, 1794) and the southern sawshark Pristiophorus nudipinnis (Günther, 1870)-occur in waters off southeast Australia (Nevatte and Williamson 2020). These species overlap in distribution and depth and are considered benthic consumers with P. nudipinnis feeding at a higher trophic level than P. cirratus, reducing trophic niche overlap through diet partitioning (Nevatte et al. 2017;Raoult et al. 2020a, b;Raoult et al. 2015). Most of what is known about the distribution and ecology of these sharks is derived from fisheries-dependent data, particularly benthic associated fisheries, i.e. demersal trawl and gillnet (Raoult et al. 2020a, b) or population-scale genetic analyses (Nevatte et al. 2021). ...
... There is no trophic enrichment for δ 34 S, so the discrimination value was left at 0, but a standard deviation of 0.5 was added to reflect measurement error of the spectrometer and uncertainty around trophic fractionation (Raoult et al. 2019). Mixing models were run with informed priors set as benthic fish (0.9), benthic invertebrates (3.0), benthopelagic (0.09), and pelagic (0.09) based on stomach contents found in this study and Nevatte et al. (2017). Model run length was set to 'extreme' to assure Gelman and Geweke diagnostics were within acceptable ranges as described in Stock et al. (2018). ...
Quantifying the trophic role of a species is key to understanding its ecology and ecological role. Their trophic role can influence community composition, ecosystem stability, and nutrient transport and cycling between habitats through ingestion, egestion, and excretion, which requires an understanding of species diet and habitat use. Despite the regular occurrence of sawsharks in Australian temperate fisheries, there remains limited information on their trophic ecology or habitat use, but they are assumed to be benthic consumers. We used fatty acid and stable isotope profiles along with stomach content analysis to investigate the trophic ecology of two sympatric species of sawsharks, the common sawshark (Pristiophorus cirratus) and southern sawshark (Pristiophorus nudipinnis) in south-eastern Australia. Stable isotope analysis of δ¹³C, δ¹⁵N, and δ³⁴S in sawshark muscle revealed that P. nudipinnis fed at a higher trophic level than P. cirratus, and mixing models and stomach contents indicated P. nudipinnis was surprisingly reliant on pelagic and benthopelagic prey sources. In contrast, P. cirratus preyed on more benthic invertebrate species, not found in P. nudipinnis. This bentho-pelagic partitioning between species was supported by P. nudipinnis fatty acid profiles having higher levels of tracers associated with dinoflagellate basal sources (16:1/16:0, 22:6ω3) than P. cirratus, indicating a reliance on pelagic food webs. These data demonstrate that sawsharks are mesopredators that play a substantial role linking pelagic and benthic food webs and highlights the value of incorporating multiple biochemical tracers to provide a comprehensive representation of an animal’s trophic ecology and role in and between ecosystems.
... In these taxa, this feature lies in the upper jaw or rostrum. In the chondrichthyan groups, their rostra are equipped with sensory organs that allow detection and monitoring of movement near the animal through electroreception [66][67][68], although this is not limited to elongated jaws. Their teeth are used as a tool with the rostrum to strike the prey after detection [68]. ...
... In the chondrichthyan groups, their rostra are equipped with sensory organs that allow detection and monitoring of movement near the animal through electroreception [66][67][68], although this is not limited to elongated jaws. Their teeth are used as a tool with the rostrum to strike the prey after detection [68]. Micro-teeth were reported and studied in three billfishes (Kajikia audax, Istiophorus platypterus and Makaira nigricans), for which they were also used to perform high speed dashes or precise strikes to attack prey of various sizes (large prey for Makaira and smaller prey from schools for Kajikia and Istiophorus) [69]. ...
Jaws are a key vertebrate feature that arose early in our evolution.
Placoderms are among the first jawed vertebrates; their fossils yield essential knowledge about the early diversification of gnathostome feeding strategies, diets and modularity. Modularity can be expressed through disproportional lengths of lower and upper jaws as in swordfish or halfbeaks. Alienacanthus malkowskii is an arthrodire from the Famennian of Morocco and Poland, whose most remarkable feature is its lower jaw, which is twice as long as the skull. This is the
oldest record of such extreme jaw elongation and modularity in vertebrates. The gnathal plates of Alienacanthus possess sharp, posteriorly recurved teeth that continue anterior of the occlusion in the inferognathals. The dentition suggests a catching and trapping live prey function, and the jaw occlusion is unique among placoderms. This armoured ‘fish’ expands the morphological and ecological diversity during one of the first radiations of jawed vertebrates with a combination of features so far unrecorded for arthrodires.
... The micro-tooth morphology of blue marlin rostral tips was in accordance with our predictions; compared to other billfish species, it was more similar to that of striped marlin than sailfish, with a relatively high percentage of broken micro-teeth and a low regrowth rate. A comparative approach has previously been successful in identifying feeding-related functions of morphological structures in a variety of different taxa, such as birds (Olsen, 2017), marine mammals (Franco-Moreno et al., 2021), elasmobranchs (Nevatte et al., 2017;Wueringer et al., 2012), and other species of billfishes Habegger et al., 2015;Hansen et al., 2020). Notably, Hansen et al. (2020) have linked lower percentages of broken teeth and an increased regrowth rate on the sailfish rostrum to a higher investment F I G U R E 3 Analysis of micro-tooth variables from micro-CT (computed tomography) measurements for Makaira nigricans, Istiophorus platypterus, and Kajikia audax. ...
... We found lateral micro-teeth to be the longest in all three billfish species. Even though the multifunctionality of the billfish rostrum is under discussion Häge et al., 2022;Videler et al., 2016), inflicting physical damage on prey is regarded as the main purpose of rostral teeth (Domenici et al., 2014;Hansen et al., 2020;Nevatte et al., 2017). This is well documented in sailfish, which are known to swim in close proximity to schooling prey and repeatedly injure fish with precise rostrum strikes, thus negatively affecting the prey's swimming performance and increasing the predators' hunting success Krause et al., 2017;Kurvers et al., 2017). ...
Billfish rostra potentially have several functions; however, their role in feeding is unequivocal in some species. Recent work linked morphological variation in rostral micro‐teeth to differences in feeding behavior in two billfish species, the striped marlin (Kajikia audax) and the sailfish (Istiophorus platypterus). Here, we present the rostral micro‐tooth morphology for a third billfish species, the blue marlin (Makaira nigricans), for which the use of the rostrum in feeding behavior is still undocumented from systematic observations in the wild. We measured the micro‐teeth on rostrum tips of blue marlin, striped marlin, and sailfish using a micro–computed tomography approach and compared the tooth morphology among the three species. This was done after an analysis of video‐recorded hunting behavior of striped marlin and sailfish revealed that both species strike prey predominantly with the first third of the rostrum, which provided the justification to focus our analysis on the rostrum tips. In blue marlin, intact micro‐teeth were longer compared to striped marlin but not to sailfish. Blue marlin had a higher fraction of broken teeth than both striped marlin and sailfish, and broken teeth were distributed more evenly on the rostrum. Micro‐tooth regrowth was equally low in both marlin species but higher in sailfish. Based on the differences and similarities in the micro‐tooth morphology between the billfish species, we discuss potential feeding‐related rostrum use in blue marlin. We put forward the hypothesis that blue marlin might use their rostra in high‐speed dashes as observed in striped marlin, rather than in the high‐precision rostral strikes described for sailfish, possibly focusing on larger prey organisms.
... Many aspects of the biology of these species remain poorly known, with detailed investigations having occurred only in recent years. These include studies of age and growth (Raoult et al. 2017;Burke et al. 2020b), trophic ecology and possible feeding behaviour (Raoult et al. 2015;Nevatte et al. 2017b;Burke and Williamson 2021), movement and population structure (Burke et al. 2020a;Nevatte et al. 2021), and sensory systems (Nevatte et al. 2017a;Wueringer et al. 2021). ...
... bite wounds from males (Pratt and Carrier 2001; Ritter and Amin 2019)] and this may also be true for sawsharks. While their mating behaviour has not been observed, the toothed rostrum used by sawsharks for sensing, capturing, and manipulating prey (Nevatte et al. 2017b;Burke and Williamson 2021;Wueringer et al. 2021) could inflict injuries when copulating. ...
Context
Knowledge of sawshark reproductive biology is limited to general parameters such as reproductive mode and litter size. The mating system is currently unknown.
Aim
To test for multiple paternity in the common (Pristiophorus cirratus) and southern (Pristiophorus nudipinnis) sawshark and investigate the occurrence of hybridisation between these two species.
Methods
Pups from a single litter of each species and an adult P. nudipinnis displaying mismatches in its morphology and mitochondrial DNA were genotyped with nuclear single-nucleotide polymorphisms (SNPs). Multiple paternity was assessed using pairwise relatedness and sibship analysis, and hybridisation was examined using three approaches (principal-component analysis, admixture analysis and clustering with NewHybrids).
Key results
Multiple paternity was detected in both species, with two males siring the seven-pup litter in P. cirratus and two males siring the two-pup litter in P. nudipinnis. Hybridisation between the two species was also confirmed, with the mismatched adult identified as a first-generation hybrid.
Conclusions
The mating system of sawsharks involves polyandry, and hybridisation between the two co-occurring Australian species is possible.
Implications
These results provide new information on sawshark reproductive biology and highlight the need for combined use of mitochondrial and nuclear markers in future genetic studies involving these species.
... The common sawshark Pristiophorus cirratus (Latham, 1794) is a small, benthic-associated shark endemic to south eastern Australia and occurs from shallow to deep-sea environments (25). Very little information is known about this species and what is known is primarily from recent studies relating to aspects of their diet (26), longevity concerns (27), and biological features (28,29). These animals are a regular facet of nontarget catch in the trawl, gill-net, and Danish-seine sheries of south eastern Australia (19) and despite over 90 years of continued shing there remains a dearth of biological data on P. cirratus, particularly in movement ecology. ...
... Diel mediated vertical movement patterns are common in large epipelagic shes (52,53), however, this phenomena is not well documented in small, benthic-associated shes (48). Current literature suggests common sawsharks feed primarily on benthic primary consumers (26,29), so it is plausible that the observed vertical movements are predatory events following the well documented diel movements of primary consumers (60)(61)(62). Furthermore, similar 'yo-yo' vertical movements where the animal makes regular rapid vertical ascents then descents have been linked in other shark species for prey detection (53). ...
Background
Understanding movement patterns of a species is vital for optimising conservation and management strategies. This information is often difficult to obtain in the marine realm for species that regularly occur at depth. The common sawshark (Pristiophorus cirratus) is a small, benthic associated elasmobranch species that occurs from shallow to deep-sea environments. No information is known regarding its movement ecology. Despite this, P. cirrata are still regularly landed as nontargeted catch in the south eastern Australian fisheries. Three individuals were tagged with pop-up satellite archival tags (PSATs) off the coast of Tasmania, Australia, to test the viability of satellite tagging on these small elasmobranchs and to provide novel insights into their movement.
Results
Tags were successfully retained for up to three weeks, but movement differed on an individual basis. All three individuals displayed a post-release response to tagging and limited vertical movement was observed for up to 5 – 7 days post-tagging. Temperature loggers on the tags suggest the animals were not stationary but moved horizontally during this time, presumably in a flight response. After this response, continuous wavelet transformations identified diel vertical movements in one individual at cyclical intervals of 12- and 24-hour periods, however, two others did not display as clear a pattern. Temperature was not significantly correlated with movement in the study period. The deepest depths recorded during the deployments for all individuals was approximately 120 meters and the shallowest was 5 meters.
Conclusions
This study demonstrates that sawsharks can be successfully tagged by pop-up satellite archival tags. The data presented here show that sawsharks regularly move both horizontally and vertically in the water column, which was an unexpected result for this small benthic species. Additional research aimed at resolving the trophic ecology will help identify the drivers of these movements and help to better define the ecological, behavioural and physiological roles of these sharks in their ecosystems. These data describe a substantial ability to move in the common sawshark that was previously unknown and provides the first account of movement ecology on the family of sawsharks: Pristiophoridae.
... The common sawshark Pristiophorus cirratus (Latham, 1794) is a small, benthic-associated shark endemic to south eastern Australia and occurs from shallow to deepsea environments [25]. Very little information is known about this species and what is known is primarily from recent studies relating to aspects of their diet [26], longevity concerns [27], and biological features [28,29]. These animals are a regular facet of nontarget catch in the trawl, gillnet, and Danish-seine fisheries of south eastern Australia [19] and despite over 90 years of continued fishing there remains a dearth of biological data on P. cirratus, particularly in movement ecology. ...
... Diel mediated vertical movement patterns are common in large epipelagic fishes [52,53]; however, this phenomena is not well documented in small, benthic-associated fishes [48]. Current literature suggests common sawsharks feed primarily on benthic primary consumers [26,29], so it is plausible that the observed vertical movements are predatory events following the well documented diel movements of primary consumers [60][61][62]. Furthermore, similar 'yo-yo' vertical movements, where the animal makes regular rapid vertical ascents then descents have been linked in other shark species for prey detection [53]. ...
Background
Understanding movement patterns of a species is vital for optimising conservation and management strategies. This information is often difficult to obtain in the marine realm for species that regularly occur at depth. The common sawshark (Pristiophorus cirratus) is a small, benthic-associated elasmobranch species that occurs from shallow to deep-sea environments. No information is known regarding its movement ecology. Despite this, P. cirrata are still regularly landed as nontargeted catch in the south eastern Australian fisheries. Three individuals were tagged with pop-up satellite archival tags (PSATs) off the coast of Tasmania, Australia, to test the viability of satellite tagging on these small elasmobranchs and to provide novel insights into their movement.
Results
Tags were successfully retained for up to 3 weeks, but movement differed on an individual basis. All three individuals displayed a post-release response to tagging and limited vertical movement was observed for up to 5–7 days post-tagging. Temperature loggers on the tags suggest the animals were not stationary but moved horizontally during this time, presumably in a flight response. After this response, continuous wavelet transformations identified diel vertical movements in one individual at cyclical intervals of 12- and 24-hour periods; however, two others did not display as clear a pattern. Temperature was not significantly correlated with movement in the study period. The deepest depths recorded during the deployments for all individuals was approximately 120 m and the shallowest was 5 m.
Conclusions
This study demonstrates that sawsharks can be successfully tagged by pop-up satellite archival tags. The data presented here show that sawsharks regularly move both horizontally and vertically in the water column, which was an unexpected result for this small benthic species. Additional research aimed at resolving the trophic ecology will help identify the drivers of these movements and help to better define the ecological, behavioural and physiological roles of these sharks in their ecosystems. These data describe a substantial ability to move in the common sawshark that was previously unknown and provides the first account of movement ecology on the family of sawsharks: Pristiophoridae.
... mature at around 300 cm total length (Peverell, 2009). Despite this size difference, the rostrum constitutes a comparable but speciesspecific percentage of the total body length (Nevatte et al., 2017a;Wueringer, 2012). Interestingly, rostral teeth are lost and replaced in pristiophorids, whereas they grow continuously in pristids (Slaughter & Springer, 1968). ...
... The pristiophorid rostrum may also have a defensive role. Puncture marks and slashes on the pristiophorid trunk have been reported (Ebert & Cailliet, 2011;Nevatte et al., 2017a). Moreover, P. nudipinnis have been observed to swipe their saw defensively in response to perceived threats (pers. ...
It has long been assumed that the elongated rostra (the saws) of sawsharks (family: Pristiophoridae) and sawfish (family: Pristidae) serve a similar function. Recent behavioural and anatomical studies have shed light on the dual function of the pristid rostrum in mechanosensory and electrosensory prey detection and prey manipulation. Here, the authors examine the distributions of the mechanosensory lateral line canals and electrosensory ampullae of Lorenzini in the southern sawshark, Pristiophorus nudipinnis and the longnose sawshark, Pristiophorus cirratus. In both species, the receptive fields of the mechano‐ and electrosensory systems extend the full length of the rostrum indicating that the sawshark rostrum serves a sensory function. Interestingly, despite recent findings suggesting they feed at different trophic levels, minimal interspecific variation between the two species was recorded. Nonetheless, compared to pristids, the pristiophorid rostrum possesses a reduced mechanosensory sampling field but higher electrosensory resolution, which suggests that pristiophorids may not use their rostrums to disable large prey like pristids do.
... Saws are multifunctional and primarily used for hunting and feeding. They stun or kill prey through rapid, lateral strikes and manipulate it towards the mouth, sometimes by pinning it to the substrate (Wueringer et al., 2012a;Nevatte et al., 2017;Burke & Williamson, 2021). They are also covered in hundreds of sensory organs, the ampullae of Lorenzini, that detect the electric fields emitted by prey (Wueringer et al., 2011(Wueringer et al., , 2012b(Wueringer et al., , 2021. ...
Convergent evolution is the development of analogous structures or bauplans in at least two independent lineages of organisms. Convergence is driven by the occupation of similar ecological niches and by various physical and phylogenetic constraints (McGhee, 2011). Despite the wide recognition of this phenomenon in evolutionary biology, formal terms and definitions for specific examples are rare. The most notable is carcinisation, which refers to the appearances of a crab-like bauplan among crustaceans (Keiler et al., 2017). Here the term ‘pristification’ is proposed for the convergence of saws in sharks and rays. It was coined previously in a preliminary publication (Greenfield, 2021a) but is formally defined for the first time. Not only does it highlight a remarkable convergent structure, but it also serves as a template for future terminology.
... Saws are multifunctional tools primarily used for hunting and feeding. They stun or kill prey through rapid, lateral strikes and manipulate it towards the mouth, sometimes by pinning it to the substrate (Wueringer et al., 2012a;Nevatte et al., 2017;Burke & Williamson, 2021). They are also covered in hundreds of sensory organs, the ampullae of Lorenzini, that detect the electric fields emitted by prey (Wueringer et al., 2011;2012b;. ...
Saws are elongated rostra with enlarged denticles that are used for hunting and feeding. They convergently evolved in three groups of sharks and rays, the extinct sawskates and the extant sawsharks and sawfishes. Saws and saw-bearing fishes are briefly reviewed here, including their anatomy, ecology, and phylogeny. The term 'pristification' is proposed for this convergence and defined. It is an example of repeated, iso-convergent evolution and is the evolution of a structure without an associated bauplan.
... The closest extant analogues of this feeding apparatus would be observed in sawfish and sawsharks, which have long flattened rostra with teeth-like rostral spines lining the edges [48]. Recent studies showed evidence that sawfish and sawsharks use their 'saw' to slash prey items in order to injure or kill [49,50]. Billfish such as Xiphias gladius do not have teeth along their rostra (homologous to the posterior two thirds of the rostrum of N. matakoi), and use their bill to stun or injure prey using lateral strikes [51]. ...
All extant toothed whales (Cetacea, Odontoceti) are aquatic mammals with homodont dentitions. Fossil evidence from the late Oligocene suggests a greater diversity of tooth forms among odontocetes, including heterodont species with a variety of tooth shapes and orientations. A new fossil dolphin from the late Oligocene of New Zealand, Nihohae matakoi gen. et sp. nov., consisting of a near complete skull, earbones, dentition and some postcranial material, represents this diverse dentition. Several preserved teeth are horizontally procumbent, including all incisors and canines. These tusk-like teeth suggest adaptive advantages for horizontally procumbent teeth in basal dolphins. Phylogenetic analysis places Nihohae among the poorly constrained basal waipatiid group, many with similarly procumbent teeth. Features of N. matakoi such as its dorsoventrally flattened and long rostrum, long mandibular symphysis, unfused cervical vertebrae, lack of attritional or occlusal wear on the teeth and thin enamel cover suggest the rostrum and horizontally procumbent teeth were used to injure and stun prey though swift lateral head movements, a feeding mode that did not persist in extant odontocetes.
... (i) Introduction. Dental microwear has been studied across vertebrates (Purnell, 1995;Purnell et al., 2006;Nevatte et al., 2017;Bestwick, Unwin & Purnell, 2019;Ungar, 2019;Winkler et al., 2019). Dental microwear describes the surface scarring of tooth enamel at a microscopic level, which can provide insight into the hardness (resistance to fracture) and toughness (resistance to tearing) of an animal's last meals, typically within the last few days of its life (Ungar, 2019). ...
Birds are some of the most diverse organisms on Earth, with species inhabiting a wide variety of niches across every major biome. As such, birds are vital to our understanding of modern ecosystems. Unfortunately, our understanding of the evolutionary history of modern ecosystems is hampered by knowledge gaps in the origin of modern bird diversity and ecosystem ecology. A crucial part of addressing these shortcomings is improving our understanding of the earliest birds, the non‐avian avialans (i.e. non‐crown birds), particularly of their diet. The diet of non‐avian avialans has been a matter of debate, in large part because of the ambiguous qualitative approaches that have been used to reconstruct it. Here we review methods for determining diet in modern and fossil avians (i.e. crown birds) as well as non‐avian theropods, and comment on their usefulness when applied to non‐avian avialans. We use this to propose a set of comparable, quantitative approaches to ascertain fossil bird diet and on this basis provide a consensus of what we currently know about fossil bird diet. While no single approach can precisely predict diet in birds, each can exclude some diets and narrow the dietary possibilities. We recommend combining (i) dental microwear, (ii) landmark‐based muscular reconstruction, (iii) stable isotope geochemistry, (iv) body mass estimations, (v) traditional and/or geometric morphometric analysis, (vi) lever modelling, and (vii) finite element analysis to reconstruct fossil bird diet accurately. Our review provides specific methodologies to implement each approach and discusses complications future researchers should keep in mind. We note that current forms of assessment of dental mesowear, skull traditional morphometrics, geometric morphometrics, and certain stable isotope systems have yet to be proven effective at discerning fossil bird diet. On this basis we report the current state of knowledge of non‐avian avialan diet which remains very incomplete. The ancestral dietary condition in non‐avian avialans remains unclear due to scarce data and contradictory evidence in Archaeopteryx. Among early non‐avian pygostylians, Confuciusornis has finite element analysis and mechanical advantage evidence pointing to herbivory, whilst Sapeornis only has mechanical advantage evidence indicating granivory, agreeing with fossilised ingested material known for this taxon. The enantiornithine ornithothoracine Shenqiornis has mechanical advantage and pedal morphometric evidence pointing to carnivory. In the hongshanornithid ornithuromorph Hongshanornis only mechanical advantage evidence indicates granivory, but this agrees with evidence of gastrolith ingestion in this taxon. Mechanical advantage and ingested fish support carnivory in the songlingornithid ornithuromorph Yanornis. Due to the sparsity of robust dietary assignments, no clear trends in non‐avian avialan dietary evolution have yet emerged. Dietary diversity seems to increase through time, but this is a preservational bias associated with a predominance of data from the Early Cretaceous Jehol Lagerstätte. With this new framework and our synthesis of the current knowledge of non‐avian avialan diet, we expect dietary knowledge and evolutionary trends to become much clearer in the coming years, especially as fossils from other locations and climates are found. This will allow for a deeper and more robust understanding of the role birds played in Mesozoic ecosystems and how this developed into their pivotal role in modern ecosystems. Video abstract
... While the rostral teeth in both groups are modified dermal denticles composed of hydroxyapatite (Nevatte, Wueringer, Jacob, Park, & Williamson, 2017;Welten et al., 2015), morphologically, the rostral teeth of the two groups are very different. Sawfish possess broad, triangular-shaped teeth that are uniform in size, whereas sawsharks possess small, roughly uniform teeth on the ventral surface and needle-like teeth of varying sizes (small, medium and large) along the lateral edges. ...
Sawsharks (Order: Pristiophoriformes, Family: Pristiophoridae) are a highly distinctive group of sharks, characterized by a tapering saw‐like rostrum with a pair of elongate barbels on the ventral surface. Their unusual characteristics should attract attention; however, very few studies have been dedicated to sawsharks. As a result, our understanding of their biology and ecology is limited. However, information on aspects of their biology and ecology can be found in studies not directly focussing on sawsharks. This review provides a synthesis of information pertaining to the 10 recognized sawshark species following a comprehensive search of the scientific literature. We cover their distributions, habitat utilization, life histories, reproduction, trophic dynamics and sensory biology. Current knowledge on their unique rostral structures, the evolutionary history of pristiophorids, taxonomy, behaviour and threats to sawshark populations are also reviewed. This compilation serves as a foundation for sawshark researchers and highlights key knowledge gaps in this unique group of elasmobranchs, thereby beginning the sawshark redemption.
... The common sawshark Pristiophorus cirratus (Latham, 1794) is a small, benthic-associated shark endemic to south eastern Australia and occurs from shallow to deep-sea environments (25). Very little information is known about this species and what is known is primarily from recent studies relating to aspects of their diet (26) and biological features (27,28). These animals are a regular facet of nontarget catch in the trawl sheries of south eastern Australia (19) and despite over 90 years of continued shing there remains a dearth of biological data on P. cirratus, particularly in movement ecology. ...
Background
Understanding movement patterns of a species is vital for optimising conservation and management strategies. This information is often difficult to obtain in the marine realm for species that regularly occur at depth. The common sawshark (Pristiophorus cirratus) is a small, benthic associated elasmobranch species that occurs from shallow to deep-sea environments. No information is known regarding its movement ecology. Despite this, P. cirrata are still regularly landed as nontargeted catch in the south eastern Australian trawl fisheries. Three individuals were tagged with pop-up satellite archival tags (PSATs) off the coast of Tasmania, Australia, to test the viability of satellite tagging on these small elasmobranchs and to provide novel insights into their movement.
Results
Tags were successfully retained for up to three weeks, but movement results differed on an individual basis. All three individuals displayed a post-release response to tagging and limited vertical movement was observed for up to 5–7 days post-tagging. Temperature loggers on the tags suggest the animals were not stationary but moved horizontally during this time, presumably in a flight response. After this response, continuous wavelet transformations identified diel vertical movements in one individual at cyclical intervals of 12- and 24-hour periods, however, two others did not display as clear a pattern. Temperature was not significantly correlated with movement in the study period. The deepest depths recorded during the deployments for all individuals was approximately 120 meters and the shallowest was 5 meters.
Conclusions
This study demonstrates that sawsharks can be successfully tagged by pop-up satellite archival tags. The data presented here show that sawsharks regularly move both horizontally and vertically in the water column, which was an unexpected result for this small benthic species. Additional research aimed at resolving the trophic ecology will help identify the drivers of these movements and help to better define the ecological, behavioural and physiological roles of these sharks in their ecosystems. These data describe a substantial ability to move in the common sawshark that was previously unknown and provides the first account of movement ecology on the family of sawsharks: Pristiophoridae.
... Tuck (2018) also highlighted a potential decline in standardised catch rate of sawshark for gillnet fisheries that required verification with a different catch per unit effort (CPUE) metric (per net length rather than per shot). Generic biological information (Raoult et al. 2017), apparent resource partitioning between P. cirratus and P. nudipinnis (Raoult et al. 2015) and information on barbel and rostrum use (Nevatte et al. 2017a(Nevatte et al. , 2017b are only recent discoveries for this enigmatic shark. ...
Sawsharks are one of the least well-known groups of sharks globally, yet they are caught in large numbers in south-eastern Australia. In this study we assessed spatiotemporal patterns of distribution of two co-occurring species of sawsharks, namely the common sawshark (Pristiophorus cirratus) and the southern sawshark (Pristiophorus nudipinnis), to guide future research in this area. To identify where the animals may occur in greater numbers, this study used the major commercial fishery datasets in the region, containing nearly 180 000 catch records from 1990 to 2017. Several general patterns were evident. Sawsharks occurred at shallower and deeper depths than previously thought, and their geographical range was larger than documented in previous studies. Depth distributions of both species overlapped, but P. cirratus appeared more common in deeper water (at depths up to 500 m), with peak common sawshark catch rates at ~400 m. Seasonal standardised catch patterns across fishing methods suggested that migrations from deeper to shallower waters may occur in the Australasian autumn and winter. The greatest concentration of sawsharks, inferred by standardised catch rates, occurred to the east and west of Bass Strait between Tasmania and mainland Australia. Although standardised catch rates of sawsharks declined in gill-net fisheries by ~30%, primarily in the Bass Strait and Tasmania, sawsharks appear to be caught at consistent rates since the 1990s, inferring a possible resilience of these sharks to current levels of fishing pressure.
... As typical of pristid rostral spines, the proximal parasagittal surface exhibits a porous texture that originates by the presence of a plethora of very small-sized nutrient foramina (HERMAN et al., 1997;MARSILI, 2006) (Fig. 4.E). Differing from other fossil (e.g., COLLARETA et al., 2017b) and extant (e.g., NEVATTE et al., 2017) rostral spines of sawfish, no obliquely-oriented shallow incisions that might evoke the abrasive action of water laden with sediment flowing at the sides of the rostrum could be detected on the rostra spines of CPI-7937. ...
Modern sawfishes (Rhinopristiformes: Pristidae) are circumglobally distributed in warm waters and are common in proximal marine and even freshwater habitats. The fossil record of modern pristid genera (i.e., Pristis and Anoxypristis) dates back to the early Eocene and is mostly represented by isolated rostral spines and oral teeth, with phosphatised rostra representing exceptional occurrences. Here, we report on a partial pristid rostrum, exhibiting several articulated rostral spines, from middle Eocene strata of the Paracas Formation (Yumaque Member) exposed in the southern Peruvian East Pisco Basin. This finely preserved specimen shows anatomical structures that are unlikely to leave a fossil record, e.g., the paracentral grooves that extend along the ventral surface of the rostrum. Based on the morphology of the rostral spines, this fossil sawfish is here identified as belonging to Pristis. To our knowledge, this discovery represents the geologically oldest known occurrence of Pristidae from the Pacific Coast of South America. Although the fossil record of pristids from the East Pisco Basin spans from the middle Eocene to the late Miocene, sawfishes are no longer present in the modern cool, upwelling-influenced coastal waters of southern Peru. Given the ecological preferences of the extant members of Pristis, the occurrence of this genus in the Paracas deposits suggests that middle Eocene nearshore waters in southern Peru were warmer than today. The eventual disappearance of pristids from the coastal waters off southern Peru might be interpreted as reflecting the late Cenozoic trend of strengthening of the Humboldt Current.
... Previous comparative work on fishes with toothed rostra (common sawshark (Pristiophorus cirratus), largetooth sawfish (Pristis pristis) and knifetooth sawfish (Anoxypristis cuspidata)) examined rostrum function through an analysis of rostral tooth microwear and stomach analysis [27], and related research explored the feeding strategy of captive sawfish via examination of the transitional probabilities between behavioural states [28]. Our study builds upon this illuminating work and suggests that matching the physical properties of rostra to behavioural strategies in the wild is a productive methodology, especially when capture success can be quantified. ...
Linking morphological differences in foraging adaptations to prey choice and feeding strategies has provided major evolutionary insights across taxa. Here, we combine behavioural and morphological approaches to explore and compare the role of the rostrum (bill) and micro-teeth in the feeding behaviour of sailfish (Istiophorus platypterus) and striped marlin (Kajikia audax) when attacking schooling sardine prey. Behavioural results from high-speed videos showed that sailfish and striped marlin both regularly made rostrum contact with prey but displayed distinct strategies. Marlin used high-speed dashes, breaking schools apart, often contacting prey incidentally or tapping at isolated prey with their rostra; while sailfish used their rostra more frequently and tended to use a slower, less disruptive approach with more horizontal rostral slashes on cohesive prey schools. Capture success per attack was similar between species, but striped marlin had higher capture rates per minute. The rostra of both species are covered with micro-teeth, and micro-CT imaging showed that species did not differ in average micro-tooth length, but sailfish had a higher density of micro-teeth on the dorsal and ventral sides of their rostra and a higher amount of micro-teeth regrowth, suggesting a greater amount of rostrum use is associated with more investment in micro-teeth. Our analysis shows that the rostra of billfish are used in distinct ways and we discuss our results in the broader context of relationships between morphological and behavioural feeding adaptations across species.
... Pristiophorus cirratus (Latham 1794) is an Australian endemic found on the continental shelf and slope, typically at water depths of 40-630 m (Last & Stevens, 2009). Little is known about the species, with the exception of recent work on its biology and behaviour by Nevatte et al., (2017aNevatte et al., ( , 2017b and Raoult et al. (2015Raoult et al. ( , 2017. Pristiophorus cirratus grows to a total length of 149 cm and has the widest native range of the three Australian pristiophorid species, which at present is considered to span the waters surrounding the entire southern half of the country, from Coffs Harbour in New South Wales to Jurien Bay in Western Australia, as well as Tasmania (Figure 1a; Last & Stevens, 2009;Walker, 2016). ...
In 2011, a male pristiophorid was caught by a prawn trawler north east of Cape Moreton, Queensland, Australia. Molecular analyses confirmed the specimen to be the common sawshark Pristiophorus cirratus. Historical catch data indicate the occurrence of the species in the region but this is the first verified record of P. cirratus occurring in the waters of southern Queensland. Together, these records extend the recognised northern limit of P. cirratus by c. 500 km, which suggests that further investigation of its distribution is warranted.
... The rostrum of Pristis microdon is used both to sense and to capture prey, by stunning or impaling them or by pinning them to the substrate (Wueringer et al., 2012). Observations of microwear on rostral teeth of the sawshark Pristiophorus cirratus suggest that it also uses its rostrum to capture prey, though not necessarily to impale them (Nevatte et al., 2017). In that work, numbers of scratches were counted, but the directional distributions of the scratches were assessed only qualitatively. ...
The symphyseal tooth whorls of the Carboniferous chondrichthyan Edestus consist
of files of teeth having sharply-pointed, serrated crowns, joined at their bases. A single tooth whorl was present in each jaw. How these tooth whorls functioned is unclear, since their convex curvature allows only a few of the most lingual crowns of opposing tooth whorls to occlude. Rather than working in opposition, like scissors, the more labial teeth might have been used to cut and disable prey with a vertical motion of the anterior part of the body. Provided the scratches observed on the surface of Edestus teeth can be inferred to have been generated in the process of feeding, their orientation might be used to distinguish whether the teeth were used mainly in occlusion, to cut prey trapped between the jaws, or mainly to cut prey situated outside the oral cavity. Edestus minor teeth having unusually good surface preservation were examined for microwear. The teeth are from the Strawn Group (Desmoinesian, Middle Pennsylvanian) of San Saba County, Texas, USA. The best-preserved crown surfaces display scratches 50 to 500 micrometers long. The scratches are oriented predominantly transversely to the basal-apical axis. This observation appears to support the vertical slashing hypothesis. However, the possibility that interaction with the substrate contributed to the observed wear cannot be discounted.
... Armaments such as saws and swords in fish (e.g. see Fig. 4 in Emlen, 2008) have been related to feeding and defence against predators (Wueringer et al., 2012;Domenici et al., 2014;Habegger et al., 2015;Nevatte et al., 2017) but never to intraspecific fights. Our methods allowed us to exclude exaggerated structures that were previously considered as weapons (cf . ...
We propose a practical concept that distinguishes the particular kind of weaponry that has evolved to be used in combat between individuals of the same species and sex, which we term intrasexually selected weapons (ISWs). We present a treatise of ISWs in nature, aiming to understand their distinction and evolution from other secondary sex traits, including from ‘sexually selected weapons’, and from sexually dimorphic and monomorphic weaponry. We focus on the subset of secondary sex traits that are the result of same‐sex combat, defined here as ISWs, provide not previously reported evolutionary patterns, and offer hypotheses to answer questions such as: why have only some species evolved weapons to fight for the opposite sex or breeding resources? We examined traits that seem to have evolved as ISWs in the entire animal phylogeny, restricting the classification of ISW to traits that are only present or enlarged in adults of one of the sexes, and are used as weapons during intrasexual fights. Because of the absence of behavioural data and, in many cases, lack of sexually discriminated series from juveniles to adults, we exclude the fossil record from this review. We merge morphological, ontogenetic, and behavioural information, and for the first time thoroughly review the tree of life to identify separate evolution of ISWs. We found that ISWs are only found in bilateral animals, appearing independently in nematodes, various groups of arthropods, and vertebrates. Our review sets a reference point to explore other taxa that we identify with potential ISWs for which behavioural or morphological studies are warranted. We establish that most ISWs come in pairs, are located in or near the head, are endo‐ or exoskeletal modifications, are overdeveloped structures compared with those found in females, are modified feeding structures and/or locomotor appendages, are most common in terrestrial taxa, are frequently used to guard females, territories, or both, and are also used in signalling displays to deter rivals and/or attract females. We also found that most taxa lack ISWs, that females of only a few species possess better‐developed weapons than males, that the cases of independent evolution of ISWs are not evenly distributed across the phylogeny, and that animals possessing the most developed ISWs have non‐hunting habits (e.g. herbivores) or are faunivores that prey on very small prey relative to their body size (e.g. insectivores). Bringing together perspectives from studies on a variety of taxa, we conceptualize that there are five ways in which a sexually dimorphic trait, apart from the primary sex traits, can be fixed: sexual selection, fecundity selection, parental role division, differential niche occupation between the sexes, and interference competition. We discuss these trends and the factors involved in the evolution of intrasexually selected weaponry in nature.
... Of course, only the latter function (capturing prey) is thought to be analogous to Edestus. In the absence of direct observational data, studies of microwear of rostral teeth of the extant sawshark Pristiophorus cirratus suggest that it also uses its rostrum to capture prey, though not necessarily to impale them ( Nevatte et al. 2017). Among both extant and extinct chondrichthyans possessing sawfish-like rostra, Schizorhiza, from the Upper Cretaceous, is the one most closely analogous to Edestus. ...
Edestus is a Middle Pennsylvanian chondrichthyan possessing symphyseal tooth whorls in both the upper and lower jaws. The curvature of the tooth whorls prevents most of the crowns of the opposing whorls from occluding with each other. For that reason, it has recently been hypothesized that the tooth whorls were used to slash prey with a vertical motion of the anterior part of the body, not to cut prey caught between them. A tooth of Edestus minor having a truncated, smoothly worn apex has been reported previously. Here, a partial tooth whorl of a different species, Edestus heinrichi, is described. The apices of the crowns are worn, so that the crown heights are reduced by about one third. The more labial (older) of the two preserved crowns shows more wear than the more lingual (younger) one. In contrast to the previously reported E. minor tooth, wear is observed to the serrations as well as to the apices of the crowns. The observed wear on both the E. minor tooth and on the E. heinrichi tooth whorl supports the recent hypothesis on the function of the tooth whorls. In both cases, the apices might have been abraded by attempted predation on or scavenging of large fish having skin covered with denticles or scales.
... Many terms have been proposed and are currently utilized to indicate the highly derived placoid scales which take place along the lateral margins of the rostrum of pristids, including "rostral teeth" (e.g., Cappetta & Case, 2016;Bradney et al., 2017;Jabado et al., 2017;Landini et al., 2017a;Leeney, 2017;Seitz & Hoover, 2017;Nevatte et al., in press), "saw-teeth" (e.g., Smith et al., 2015;Welten et al., 2015), and "rostral spines" (e.g., Carrillo-Briceño et al., 2015;Di Celma et al., 2017;Landini et al., 2017b). Since Welten et al. (2015) provided wide evidence that these tooth-like elements are not homologous to oral teeth, representing instead an independent derivation from dermal denticles, we argue that terms such as "rostral teeth" and "saw-teeth" could sound somewhat ambiguous. ...
In this paper we report on a partially preserved rostral spine attributed to Anoxypristis? sp. from lower Pliocene (Zanclean) marine deposits exposed at Lucciolabella (Province of Siena, Tuscany, central Italy). This finding represents the first unambiguous record of pristids in lower Pliocene deposits of Italy, corroborating the persistence of sawfish in the Mediterranean basin after the so-called Messinian Salinity Crisis. Our finding supports the hypothesis of the persistence of climatic and ecological conditions propitious to warm-water marine vertebrates along the early Pliocene coasts of Tuscany and suggests that, after centuries of scientific study, the Pliocene elasmobranch palaeocommunities of Tuscany can still bring surprises.
Nel presente lavoro è descritta una spina rostrale parziale di un pesce sega (identificato come Anoxypristis? sp.) da depositi marini del Pliocene inferiore (Zancleano) affioranti presso Lucciolabella (Provincia di Siena, Toscana, Italia centrale). Si tratta del primo rinvenimento di un pristide in depositi italiani di età zancleana. Esso conferma la persistenza della famiglia Pristidae nel bacino Mediterraneo a segui-to della nota "crisi di salinità del Messiniano". Questo ritrovamento permette di inferire condizioni climatiche ed ecologiche favorevoli alla presenza di vertebrati marini di acque calde lungo le coste della Toscana durante il Pliocene inferiore e suggerisce che, dopo secoli di studi paleontologici, le paleocomunità ad elasmobranchi del Pliocene toscano possano ancora riservare delle sorprese.
... Observed post-birth variations in zinc distributions may be driven by diet or environment [17]. The Common Sawshark is a benthic predator with a diet mainly consisting of invertebrates such as shrimp [58][59][60]. Decapod shells are known to absorb environmentally available zinc [61], implying that high concentrations of zinc post-birth in this species may, therefore, be related to diet. Conversely, the Southern Sawshark is a piscivorous species that is sympatric with the Common Sawshark over much of its distribution, does not have a similar pattern of zinc deposition, despite feeding at a higher trophic level [58]. ...
The development of shark vertebrae and the possible drivers of inter- and intra-specific differences in vertebral structure are poorly understood. Shark vertebrae are used to examine life-history traits related to trophic ecology, movement patterns, and the management of fisheries; a better understanding of their development would be beneficial to many fields of research that rely on these calcified structures. This study used Scanning X-ray Fluorescence Microscopy to observe zinc distribution within vertebrae of ten shark species from five different orders. Zinc was mostly localised within the intermedialis and was generally detected at levels an order of magnitude lower in the corpus calcareum. In most species, zinc concentrations were higher pre-birth mark, indicating a high rate of pre-natal zinc deposition. These results suggest there are inter-specific differences in elemental deposition within vertebrae. Since the deposition of zinc is physiologically-driven, these differences suggest that the processes of growth and deposition are potentially different in the intermedialis and corpus calcareum, and that caution should be taken when extrapolating information such as annual growth bands from one structure to the other. Together these results suggest that the high inter-specific variation in vertebral zinc deposition and associated physiologies may explain the varying effectiveness of ageing methodologies applied to elasmobranch vertebrae.
548 shark species were considered in this paper. They were classified in function of their depth of occurrence: 218 deep, 114 transitory and 210 shallow. The diets of the 332 deep and transitory species are reviewed. 10 prey categories are recognized here: Chondrichthyes, Teleosts, Cephalopods, Crustaceans, Marine mammals, Annelids, Ctenophores, Egg of Chondrichthyes, Siphonophores, and Bivalves. There is a complete lack of data for 210 species, and 59 have only a limited amount of information available. In general, teleosts, crustaceans, and cephalopods were the main prey found in deep-water sharks. However, some species have a specialized diet. A simple index of dietary knowledge has been developed to highlight the current state of knowledge on the subject, further illustrating the lack of information. The proportion of empty and regurgitated stomachs varies significantly between species and studies. Most data on deep and transitory sharks come from stomach content analysis. Stable isotope analysis provides additional insight into their trophic ecology. Fatty acid profiling and DNA metabarcoding can also add important information, but their use is currently limited with deep-water sharks. The most important conclusion from this synthesis is the lack or scarcity of information for most deep and transitory species.
Serving in a foraging or self‐defense capacity, pristiophorids, pristids, and the extinct sclerorhynchoids independently evolved an elongated rostrum lined with modified dermal denticles called rostral denticles. Isolated rostral denticles of the sclerorhynchoid Ischyrhiza mira are commonly recovered from Late Cretaceous North American marine deposits. Although the external morphology has been thoroughly presented in the literature, very little is known about the histological composition and organization of these curious structures. Using acid‐etching techniques and scanning electron microscopy, we show that the microstructure of I. mira rostral denticles are considerably more complex than that of previously described dermal denticles situated elsewhere on the body. The apical cap consists of outer single crystallite enameloid (SCE) and inner bundled crystallite enameloid (BCE) overlying a region of orthodentine. The BCE has distinct parallel bundled enameloid (PBE), tangled bundled enameloid (TBE), and radial bundled enameloid (RBE) components. Additionally, the cutting edge of the rostral denticle is produced by a superficial layer of SCE and a deeper ridges/cutting edge layer (RCEL) of the BCE. The highly organized enameloid observed in the rostral denticles of this batomorph resembles that of the multifaceted tissue architecture observed in the oral teeth of selachimorphs and demonstrates that dermal scales have the capacity to evolve histologically similar complex tooth‐like structures both inside and outside the oropharyngeal cavity. The highly organized enameloid observed in the rostral denticles of the sclerorhynchoid Ischyrhiza mira resembles that of the multifaceted tissue architecture observed in the oral teeth of selachimorphs and demonstrates that dermal scales have the capacity to evolve histologically similar complex tooth‐like structures both inside and outside the oropharyngeal cavity.
In the waters of southeast Australia, two species of sawshark—the common (Pristiophorus cirratus) and southern (Pristiophorus nudipinnis) sawshark—are frequent by-catch in commercial fisheries. While harvesting of both species is currently considered sustainable, there has been no investigation of whether P. cirratus and P. nudipinnis display genetically distinct populations throughout their ranges. Such information is necessary for effective management of these species in commercial fisheries. This study examined population structure in both sawshark species through analysis of two mitochondrial genes: cytochrome b (Cyt-b) and NADH dehydrogenase subunit 5 (ND5). Results indicated contrasting levels of population structure, with P. cirratus consisting of two, possibly three, genetically distinct populations with two mitochondrial lineages and P. nudipinnis consisting of a single population. Tests for population expansion also highlighted differences between the two species. Population expansion was detected for the entire P. nudipinnis population, whereas this was only the case for one mitochondrial lineage in P. cirratus. The entire P. cirratus population displayed signals of demographic stability. It is hypothesised that the opening and closing of Bass Strait during glacial-interglacial cycles played a major role in shaping the population structure and expansion signatures observed in this study. Mitochondrial data also suggest that patterned and uniform brown P. cirratus are the same species. Fisheries managers should consider adopting two management units in southern Australia—one along the east coast (for the eastern P. cirratus population) and one along the south coast (for the southern P. cirratus population and the single P. nudipinnis population).
Extensive oral processing of food through dental occlusion and orbital mandibular movement is often cited as a uniquely mammalian trait that contributed to their evolutionary success. Save for mandibular translation, these adaptations are not seen in extant archosaurs or lepidosaurs. In contrast, some ornithischian dinosaurs show evidence of precise dental occlusion, habitual intraoral trituration and complex jaw motion. To date, however, a robust understanding of the diversity of jaw mechanics within non-avian dinosaurs, and its comparison with other vertebrates, remains unrealized. Large dental batteries, well-developed dental wear facets, and robust jaws suggests that neoceratopsian (horned) dinosaurs were capable chewers. But, biomechanical analyses have assumed a relatively simple, scissor-like (orthal) jaw mechanism for these animals. New analyses of dental microwear, presented here, show curvilinear striations on the teeth of Leptoceratops . These features indicate a rostral to caudal orbital motion of the mandible during chewing. A rostrocaudal mandibular orbit is seen in multituberculates, haramiyid allotherians, and some rodents, and its identification in Leptoceratops gracilis is the first evidence of complex, mammal-like chewing in a ceratopsian dinosaur. The term circumpalinal is here proposed to distinguish this new style of chewing from other models of ceratopsian mastication that also involve a palinal component. This previously unrecognized complexity in dinosaurian jaw mechanics indicates that some neoceratopsian dinosaurs achieved a mammalian level of masticatory efficiency through novel adaptive solutions.
Two species of angel shark (Squatina australis, S. albipunctata) and two species of sawshark (Pristiophorus nudipinnis, P. cirratus) are frequently caught in south-eastern Australia. Little is known of the biology of these elasmobranchs, despite being caught as secondary target species in large numbers. The present study collected morphometric and reproductive data from sharks caught in shark-control nets, commercial fishing trawlers and research trawlers in south-eastern Australia. All four species had female-biased sexual size dimorphism, but growth curves between sexes did not differ. Male S. australis individuals were fully mature at ~800-mm total length, male P. nudipinnis at ~900 mm, and male P. cirratus at ~800 mm. Anterior pectoral margins could be used to determine total length in all species. No morphometric measurement could reliably separate Squatina spp. or Pristiophorus spp., although S. albipunctata over 1000-mm total length had larger eyes than did S. australis.
The description of a partial but well preserved head of the sclerorhynchid batoid Sclerorhynchus atavus Woodward 1889 gave the first clear indication of the presence of a puzzling group of extinct rostrum-bearing rays that resembled both the Pristidae (rays) and the Pristophoridae (sharks). Despite recognizing similarities and differences to these extant groups, Woodward (1889, 1892) suggested that Sclerorhynchus be assigned to the Pristidae, although the rostra are very different. Woodward did note similarities of Sclerorhynchus rostrum saw-teeth to those of the Pristiophoridae, including the location of these along the margin of the rostrum, rather than in deep sockets, as seen along the pristid rostrum. In addition, the type specimen of Sclerorhynchus has very distinct saw-tooth denticles not only along the rostrum, but modified denticles along the sides of the head, as in the Pristiophoridae. The enlarged rostral denticles of Sclerorhynchus also appear to rotate into position, another feature seen in the pristiophorids but not in the pristids, and in other sclerorhynchids such as Libanopristis. Although individual fossil rostral tooth-like denticles had been earlier described, Woodward’s description of a rostrum and associated rostral tooth-like denticles meant that for the first time a fossil rostrum could be compared to living forms, highlighting the extreme variation in rostrum saw-tooth morphology among sharks and rays.
A well-known characteristic of chondrichthyans (e.g. sharks, rays) is their covering of external skin denticles (placoid scales), but less well understood is the wide morphological diversity that these skin denticles can show. Some of the more unusual of these are the tooth-like structures associated with the elongate cartilaginous rostrum ‘saw’ in three chondrichthyan groups: Pristiophoridae (sawsharks; Selachii), Pristidae (sawfish; Batoidea) and the fossil Sclerorhynchoidea (Batoidea). Comparative topographic and developmental studies of the ‘saw-teeth’ were undertaken in adults and embryos of these groups, by means of three-dimensional-rendered volumes from X-ray computed tomography. This provided data on development and relative arrangement in embryos, with regenerative replacement in adults. Saw-teeth are morphologically similar on the rostra of the Pristiophoridae and the Sclerorhynchoidea, with the same replacement modes, despite the lack of a close phylogenetic relationship. In both, tooth-like structures develop under the skin of the embryos, aligned with the rostrum surface, before rotating into lateral position and then attaching through a pedicel to the rostrum cartilage. As well, saw-teeth are replaced and added to as space becomes available. By contrast, saw-teeth in Pristidae insert into sockets in the rostrum cartilage, growing continuously and are not replaced. Despite superficial similarity to oral tooth developmental organization, saw-tooth spatial initiation arrangement is associated with rostrum growth. Replacement is space-dependent and more comparable to that of dermal skin denticles. We suggest these saw-teeth represent modified dermal denticles and lack the ‘many-for-one’ replacement characteristic of elasmobranch oral dentitions.
Despite the global distribution of sawsharks, little is known about their diets or their role in the marine biosphere. As species in higher trophic positions are generally considered to be more at risk to perturbations such as fishing, understanding their role in the food chain will enable better conservation and management strategies for these species. Two sawshark species (Pristiophorus cirratus, Pristiophorus nudipinnis) co-occur in waters off east Tasmania, Australia. This study determined the trophic positions of these sawsharks and whether they avoided competing with each other through resource partitioning. Isotopic analysis of muscle tissue revealed that P.cirratus and P.nudipinnis had significantly different trophic levels, with P.cirratus likely to have a diet of primary consumers and P.nudipinnis likely to have a piscivorous diet. Owing to their different isotopic signatures, it is also likely that the sawshark rostrum has multiple functions. Both species shifted to higher trophic levels during ontogeny. Maternal isotopic signatures were detectable in P.cirratus juveniles.
This study reports and characterises an anomalous condition in teeth of captive sand tiger sharks Carcharias taurus. Abnormal shed teeth from captive sand tiger sharks which were soft to the touch were structurally and chemically characterised and compared to the structure and composition of normal teeth of the species. Normal specimens exhibited the expected tooth morphology with a well-developed tooth crown consisting of a central cusp and two lateral cusplets with smooth and sharp margins, while in the anomalous specimens the crown height was much reduced and the overall shape did not follow this pattern. Lateral cusplets were also considerably reduced in size and with blunt margins. Scanning electron images showed a distinct absence of crystalline structures in the anomalous specimens. Raman microscopy analysis confirmed the low volume of fluoroapatite in the outer layers of the anomalous teeth, while the composition of the inner layers corresponding to dentine was comparable to the normal tooth specimens. Nanoindentation-derived mechanical properties showed significant differences between the anomalous and normal teeth. The mean values for enameloid elastic modulus and hardness of all three normal teeth were 75.92±3.4 GPa and 3.27±0.41 GPa, respectively. On the other hand, mean values of elastic modulus and hardness for anomalous teeth were 7.81±3.27 GPa and 0.39±0.25 GPa, respectively. However, mechanical property values of the dentine of normal and anomalous teeth were similar. The mean values of dentine elastic modulus and hardness of the normal teeth were 25.66±2.14 GPa and 0.89±0.01 GPa, respectively, while mean values for the anomalous teeth were 25.34±1.54 GPa and 0.83±0.03 GPa. Although the morphological, mechanical and chemical differences between the normal and anomalous teeth are quite evident, establishing the causes of this condition are not possible at this stage.
Identifying essential habitat for large, mobile endangered species is difficult, particularly marine species where visual observations are limited. Though various methods of telemetry are available, each suffers from limitations and only provides satisfactory information over a specific temporal or spatial scale. Sawfish are one of the most imperilled groups of fishes, with every species worldwide listed as endangered or critically endangered. Whereas movements of juvenile sawfish are fairly well studied, much less is known about adults due to their rarity and the challenging environments they live in. Previous encounter records have identified Florida Bay in the Everglades National Park as a potentially important habitat for adults of the critically endangered smalltooth sawfish (Pristis pectinata). We used a combination of acoustic and satellite telemetry, as well as conventional tagging, to determine patterns of movement and residency by sub-adult and adult sawfish. Over short time periods, movements appeared primarily tidal driven with some evidence that animals moved into shallow water during the ebbing or flooding tides. Adult sawfish sexually segregated seasonally with males found by mangrove-lined canals in the spring and females predominantly found in outer parts of the bay. Males migrated from canals starting in late May potentially as temperatures increased above 30°C. Some males and females migrated north during the summer, while others may have remained within deeper portions of Florida Bay. Male sawfish displayed site fidelity to Florida Bay as some individuals were recaptured 1–2 years after originally being tagged. We hypothesize that mating occurs in Florida Bay based on aggregations of mature animals coinciding with the proposed mating period, initial sexual segregation of adults followed by some evidence of females moving through areas where males show seasonal residency, and a high percentage of animals showing evidence of rostrum inflicted injuries. The combination of methods providing movement data over a range of spatial and temporal scales reveals that sub-tropical embayments serve as essential habitat for adult smalltooth sawfish.
Perhaps the most striking feature of billfishes is the extreme elongation of the premaxillary bones forming their rostra. Surprisingly, the exact role of this structure in feeding is still controversial. The goal of this study is to investigate the use of the rostrum from a functional, biomechanical, and morphological standpoint to ultimately infer its possible role during feeding. Using beam theory, experimental and theoretical loading tests were performed on the rostra from two morphologically different billfish, the blue marlin (Makaira nigricans) and the swordfish (Xiphias gladius). Two loading regimes were applied (dorso-ventral and lateral) to simulate possible striking behaviors. Histological samples and material properties of the rostra were obtained along their lengths to further characterize structure and mechanical performance. Intraspecific results show similar stress distributions for most regions of the rostra, suggesting this structure may be designed to withstand continuous loadings with no particular region of stress concentration. Although material stiffness increased distally, flexural stiffness increased proximally owing to higher second moment of area. The blue marlin rostrum was stiffer and resisted considerably higher loads for both loading planes as compared to that of the swordfish. However, when a continuous load along the rostrum was considered, simulating the rostrum swinging through the water, swordfish exhibited lower stress and drag during lateral loading. Our combined results suggest the swordfish rostrum is suited for lateral swiping to incapacitate their prey, whereas the blue marlin rostrum is better suited to strike prey from a wider variety of directions.
Among the various functions of the paddlefish rostrum, it is also believed to serve as a stabilizer to counteract the downward force that would otherwise occur during the process of filter feeding. From its unique shape, it is hypothesized that the paddlefish rostrum serves to generate a substantial amount of lift that naturally occurs as the rostrum is elevated at the same time the fish opens its mouth. The present, numerical study is an attempt to quantify the amount of lift (and drag) that is generated by the rostrum of a juvenile paddlefish. Additionally, this data is compared with other hydrofoils. The results suggest that the paddlefish rostrum does indeed produce substantial lift at certain angles of attack. In fact, the results indicate that the amount of lift is comparable to that produced by a symmetric foil (NACA 0012).
Tooth microwear feature densities were significantly increased in a population of laboratory-reared three-spined stickleback Gasterosteus aculeatus in four days, after they were transferred from a limnetic feeding regime to a benthic feeding regime. These results show that even in aquatic vertebrates with non-occluding teeth, changes in feeding can cause changes in tooth microwear in just a few days, as in mammals.© 2014 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of The Fisheries Society of the British Isles.
The istiophorid family of billfishes is characterized by an extended rostrum or 'bill'. While various functions (e.g. foraging and hydrodynamic benefits) have been proposed for this structure, until now no study has directly investigated the mechanisms by which billfishes use their rostrum to feed on prey. Here, we present the first unequivocal evidence of how the bill is used by Atlantic sailfish (Istiophorus albicans) to attack schooling sardines in the open ocean. Using high-speed video-analysis, we show that (i) sailfish manage to insert their bill into sardine schools without eliciting an evasive response and (ii) subsequently use their bill to either tap on individual prey targets or to slash through the school with powerful lateral motions characterized by one of the highest accelerations ever recorded in an aquatic vertebrate. Our results demonstrate that the combination of stealth and rapid motion make the sailfish bill an extremely effective feeding adaptation for capturing schooling prey.
A new species of sawshark, Pristiophorus nancyae sp. nov., is described from eight specimens collected off mozambique. The new species is the second member of the family pristiophoridae and first member of the genus Pristiophorus described from the western indian ocean. The new Pristiophorus species can be distinguished from the sympatric occurring six-gilled sawshark, Pliotrema warreni regan, 1906, most notably by having five paired gill openings as opposed to six. The new species is distinguished from all other Pristiophorus species by several distinctive characteristics. most notably, the new species differs by having a very distinctive double row of four to five conspicuous large pits anterior to the nasal barbels on the underside of its snout. other distinguishing characteristics include a broad, triangular first dorsal fin with a rear tip that extends behind the pelvic midbases, barbels much closer to mouth than snout tip, two rows of enlarged pits on the underside of the pre-barbel rostrum, ridges on the base of its large lateral rostral teeth, mostly tricuspidate, flat, imbricated lateral trunk denticles, and plain color pattern. The new species is compared to the five other known Pristiophorus species and a revised key to the genus is presented.
The sailfish and swordfish are known as the fastest sea animals, reaching their maximum speeds of around 100 km/h. In the present study, we investigate the hydrodynamic characteristics of these fishes in their cruise speeds of about 1 body length per second. We install a taxidermy specimen of each fish in a wind tunnel, and measure the drag on its body and boundary-layer velocity above its body surface at the Reynolds number corresponding to its cruising condition. The drag coefficients of the sailfish and swordfish based on the free-stream velocity and their wetted areas are measured to be 0.0075 and 0.0091, respectively, at their cruising conditions. These drag coefficients are very low and comparable to those of tuna and pike and smaller than those of dogfish and small-size trout. On the other hand, the long bill is one of the most distinguished features of these fishes from other fishes, and we study its role on the ability of drag modification. The drag on the fish without the bill or with an artificially-made shorter one is slightly smaller than that with the original bill, indicating that the bill itself does not contribute to any drag reduction at its cruise speed. From the velocity measurement near the body surface, we find that at the cruise speed flow separation does not occur over the whole body even without the bill, and the boundary layer flow is affected only at the anterior part of the body by the bill.
Available fragmentary data on tactile sensie of fish are summed up for the first time. Data are presented on morphology and distribution of tactile receptors (free nerve endings, Merkel cells, Rohon-Beard cells, etc.) and on their innervation. Main tactile organs of fish are considered—barbels and various other cutaneous outgrowths, free rays of fins, rostrum, breeding tubercles, dermal teeth. Information is presented on functional parameters of tactile reception and its significance in orientation and in manifestation by fish of reproductive, defensive, social, exploratory, and food searching behavior. An important role is shown of the intraoral tactile reception in estimation by fish of texture and attractiveness of food objects. Time of formation of tactile sensitivity in fish ontogenesis is indicated and dynamics of its formation is analyzed. A low level of knowledge of structure and function of the tactile system is noted. The majority of the available data are mostly facts indicating the importance of tactile sense in various life manifestations of fish but not disclosing the functional potential of the system.
The goal of this work was to evaluate the ability of Raman spectroscopy to identify molecular organization and chemical composition of extracellular matrix such as the collagen fibers arrangement, the level of mineralization, and the carbonate accumulation in mineral phase in spongy bone of the human head of the femur. Changes in composition and structure of the spongy bone tissue were illustrated using maps of polarized Raman spectra. In particular, the purpose of the present study was determination of arrangement of mineralized collagen on surface of trabecula by using transformations of Raman spectra maps. Transformations of Raman spectra maps were needed in order to remove impact of chemical composition on images of Raman spectra map, which display the collagen fibers orientation. These transformations allow to obtain simultaneously the distribution of constituents of bone and arrangement of collagen fibers on tissue surface. A method to indicate the collagen orientations is developed to understand the molecular organization in healthy and unhealthy bone at the microstructural level.
Sharks represent 78% of the total catch by weight of a Taiwanese surface gill-net fishery off northern Australia. Two carcharhinids, Carcharhrnus tilstoni (previously described as C. limbatus) and C. sorrah, together comprise 83% of this shark catch by number. C. tilstoni is distinguished from C. limbatus by differences in enzyme systems, vertebral counts, size data and pelvic fin coloration. Of the specimens of C. tilstoni and C. sorrah caught in the Arafura and Timor Seas from 1981 to 1983, 43% and 47%, respectively, were female; at birth these proportions were 46% and 50%, respectively. In both species, females tended to be relatively more abundant in catches of mature fish, except around March, when males predominated. In northern Australia, the usual size at maturity for C. tilstoni is 110 cm for males and 115 cm for females; for C. sorrah, it is 90 cm and 95 cm, respectively. Both species exhibit placental viviparity and have almost identical restricted reproductive cycles. Mating occurs in February-March, ovulation in March-April and the main parturition period is in January. The gestation period is 10 months and individual fish breed each year. The average litter size for both species is three. The size at birth is about 60 cm for C. tilstoni and 50 cm for C. sorrah. Stomach contents indicate that teleost fish are an important component of the diet of both species and there is some indication of a change in feeding depth with shark size.
Stomach contents were analysed to investigate the diets of 52 commercial species of fish. Fish were collected from Bass Strait and adjacent Victorian waters, south-eastern Australia; samples effectively covered the whole of the Victorian coast. Particular emphasis was placed on estimating the importance of arrow squid, Nototodarus gouldri in the diets of the species investigated. For most of the species investigated, the major food items (expressed as the proportion of stomach contents by number, weight and volume or through the calculation of the Index of Relative Importance) were fish or crustaceans. Cephalopods were found in the diets of 21 species but provided a major proportion of the stomach contents in only six species. Arrow squid did not appear to be a major item in the diets of any of the species investigated. For those species that eat large amounts of cephalopods, it appears to be octopus, rather than squid, that is of most significance in the diet.
Stomachs from 433 specimens of Rhizoprionodon taylori caught by gill-nets and otter trawls in Cleveland Bay, north Queensland, were examined. At least 5.3% of specimens examined had regurgitated. Of the remaining 410 specimens 59.0% had empty stomachs and only 19.3% contained food items identifiable to the family level. The diet comprised mostly small teleosts from the families Leiognathidae, Clupeidae, Teraponidae and Engraulidae. Penaeid prawns and loliginid squid were also important in the diet. Average weight of individual recently ingested food items was 28.5 g, which represented 2.3% of body weight. The high diversity of potential prey groups, high rate of regurgitation, and high proportion of empty stomachs meant that although a large number of specimens were examined the sample size was probably insufficient to provide a thorough analysis of the diet of R. taylori in Cleveland Bay.
Understanding how endangered marine species rely on coastal habitats is vital for population recovery planning. The smalltooth sawfish (Pristis pectinata) is one of several critically endangered sawfishes worldwide known to use estuaries and rivers during their early life history. In a Florida estuary designated as critical habitat by the USA government, juveniles were monitored to characterise seasonality, recruitment, and habitat use. Stretched total length ranged from 671 to 2172 mm (n = 137, mean = 1248 mm). Sawfish were captured year round. Captures of neonates with embryonic rostral sheaths allowed refinement of the size at birth (671–812 mm) and confirmed a protracted timing of parturition (November–July), which peaked between April and May. Although sampling occurred throughout the estuary, five locations had the greatest catch rates. Most juvenile sawfish had an affinity for water <1 m deep, water >30°C, dissolved oxygen >6 mg L–1, and salinity between 18 and 30. Greater catch rates for sawfish >1 year old were associated with shoreline habitats with overhanging vegetation such as mangroves. These results detail habitat use within a recognised nursery that can be used for conservation of the first endangered marine fish species in the USA.
The diet of the broadnose sevengill shark Notorynchus cepedianus was investigated over 3 years from 2 coastal locations in south-east Tasmania: the Derwent Estuary and Norfolk Bay. In general, individuals from both locations consumed the same broad dietary categories (sharks, batoids, teleosts and mammals). However, within these categories, species composition differed. Variations in chondrichthyan prey consumed matched estimations of prey abundance: Mustelus antarcticus was the primary prey in Norfolk Bay, where it was also the most abundant prey species; similarly, Squalus acanthias was an important prey and the most abundant in the Derwent Estuary. A decline in the catch rates of N. cepedianus and elasmobranch prey, in particular M. antarcticus over 3 years coincided with declines in dietary occurrence of M. antarcticus. Also, N. cepedianus and M. antarcticus abundances were both higher in Norfolk Bay than the Derwent Estuary. The correlation with diet and estimations of predator and prey relative abundance suggests N. cepedianus may move into coastal areas to exploit regular seasonal abundant resources, but they can also be versatile opportunistic predators that exploit a temporarily abundant resource.
In the aquatic environment, living organisms emit weak dipole electric fields, which spread in the surrounding water. Elasmobranchs detect these dipole electric fields with their highly sensitive electroreceptors, the ampullae of Lorenzini. Freshwater sawfish, Pristis microdon, and two species of shovelnose rays, Glaucostegus typus and Aptychotrema rostrata were tested for their reactions towards weak artificial electric dipole fields. The comparison of sawfishes and shovelnose rays sheds light on the evolution and function of the elongated rostrum ('saw') of sawfish, as both groups evolved from a shovelnose ray-like ancestor. Electric stimuli were presented both on the substrate (to mimic benthic prey) and suspended in the water column (to mimic free-swimming prey). Analysis of around 480 behavioural sequences shows that all three species are highly sensitive towards weak electric dipole fields, and initiate behavioural responses at median field strengths between 5.15 and 79.6 nV cm(-1). The response behaviours used by sawfish and shovelnose rays depended on the location of the dipoles. The elongation of the sawfish's rostrum clearly expanded their electroreceptive search area into the water column and enables them to target free-swimming prey.
The internal anatomy of the barbels of the common sawshark Pristiophorus cirratus was examined with light microscopy to clarify their sensory role. No sensory structures such as taste buds (chemoreception), ampullae of Lorenzini (electroreception) or free neuromasts (lateral line mechanoreception) could be located in the barbels. The presence of bundles of nerve fibres, however, indicates a tactile function for the barbels. Conveyance of information regarding potentially damaging stimuli (nociception) and temperature (thermoception) cannot be excluded at this stage. It is hypothesized that the barbels are used by P. cirratus to locate prey in both the water column and on the substratum via wake detection and sensing changes in surface texture. The barbels may also be involved in the detection of water currents for rheotaxis. Regression analyses on P. cirratus morphometric data showed that the width of the rostrum at two sections (the barbels and the rostrum tip) does not significantly correlate with total length. The regression analyses also suggested that the barbels of P. cirratus may be lateralised.
Detailed computational fluid dynamics simulations for the rostrum of three species of sawfish (Pristidae) revealed that negligible turbulent flow is generated from all rostra during lateral swipe prey manipulation and swimming. These results suggest that sawfishes are effective stealth hunters that may not be detected by their teleost prey's lateral line sensory system during pursuits. Moreover, during lateral swipes, the rostra were found to induce little velocity into the surrounding fluid. Consistent with previous data of sawfish feeding behaviour, these data indicate that the rostrum is therefore unlikely to be used to stir up the bottom to uncover benthic prey. Whilst swimming with the rostrum inclined at a small angle to the horizontal, the coefficient of drag of the rostrum is relatively low and the coefficient of lift is zero.
Since 1966, an extensive tagging program has demonstrated beyond any further doubt (Thorson, 1971) that the sharks move from the Caribbean Sea to Lake Nicaragua and vice versa. At the time of this writing, of 1450 post-juvenile sharks tagged at the various river mouths on the Caribbean Coast, ten have been recovered in Lake Nicaragua; and of 146 tagged at San Carlos, where the river leaves the lake, 28 have been recovered along the Caribbean Coast, most of them at the various outlets of the Rio San Juan. Except for these basic facts, the results of the tagging program have not yet been published.
To make a biophysical standard for histological identification of fish teeth, fluorescence and Raman-spectra are employed for typical teeth of various fish, such as the sea-bream, shark, trout, and hagfish in comparison with human teeth. The tooth tissues of sea-bream, mainly containing hydroxyapatite, resemble those of human teeth. In the teeth of the trout and hagfish, no difference can be found between the surface and deep layers and they appear like decalcified human cement. Shark teeth, rich in fluoroapatite, are much different from both human enamel and dentin. According to the similarity of Raman-band patterns, it is possible to arrange them in order from trout to sea-bream through the human enamel and finally to the shark. These suggest that the structural characteristics off teeth in the fish kingdom do not coincide with differentiation of human tooth tissues.
In recent sawfishes, Pristis (order Batoidei), rostral teeth that are lost are not replaced and those not severely damaged in use increase in size throughout life. Presumably similar conditions pertain to fossil sawfish genera having socket-like attachments for rostral teeth. In recent sawsharks, Pristiophorus and Pliotrema (order Selachii), rostral teeth are replaced if lost and do not increase in size after reaching a functional position. Similarities in tooth development and the process of replacement were observed in recent sawsharks (Selachii) and in the Cretaceous sawfish genus Sclerorhynchus (Batoidei). Also, the pattern of varying length of rostral teeth in adults of recent sawsharks (Selachii), which is explained by the appearance of both new and replacement teeth at intervals during growth, offers a possible explanation for the presence of rostral teeth of various lengths in the Cretaceous ganopristid sawfish Onchopristis numidus (Batoidei).
Seven species of the family Istiophoridae and Xiphias gladius were identified using only features of their rostrum. In the Istiophoridae, two rostral regions were emphasized, one-fourth and one-half the distance between the distal tip and the orbital margin of the lateral ethmoid bone. Characters studied in each region were the depth and width of rostrum and height, width, and position of nutrient canals (as seen in cross-section). Characters studied without reference to region were the distribution of denticles on both dorsal and ventral surfaces of the bill and position of the prenasal bone. In the Xiphiidae, the only characters studied were the depth and width of the rostrum at the level of the dermethmoid bone and the presence and placement of central chambers as seen in radiographs. A total of 32 characters were analyzed as ratios using both multivariate and univariate statistics. The rostrum of X. gladius was separated from the Istiophoridae by its fiat shape, Tetrapturus angustirostris from all other istiophorids by its widely separated nutrient canals, and the complex of T. audax/T. pfluegeri/Makaira nigricans/M. indica from the complex of Istiophorus platypterus/T. al bidus by having a smaller area of denticles on the dorsal surface. Tetrapturus pfluegeri was separated from T. audax, M. nigricans, and M. indica by having a longer denticle-free midline on the ventral surface of the rostrum. Tetrapturus audax was separated from M. nigricans and M. indica by the location of its nutrient canals. The complexes of Makaira nigricans/M. indica and L platypterus/T. albidus were each separated using multivariate discriminant analysis. We show the study has application in identifying rostral fragments found as fossils and impaled in animate and inanimate objects such as marine turtles and wooden ships and should have application wherever rostral fragments are found.
The bull shark or cub shark, Carcharhinus leucas, occurs in tropical and subtropical waters of the Atlantic, Pacific, and Indian oceans. In the western Atlantic it occurs from New York to southern Brazil.
Methods for analysing fish stomach contents are listed and critically assessed with a view to their suitability for determining dietary importance—this term is defined. Difficulties in the application of these methods are discussed and, where appropriate, alternative approaches proposed. Modifications which have practical value are also considered. The necessity of linking measurements of dietary importance to stomach capacity is emphasized and the effects of differential digestion upon interpretation of stomach contents outlined. The best measure of dietary importance is proposed as one where both the amount and bulk of a food category are recorded.
Billfishes (Istiophoridae and Xiphiidae) are notorious for driving their rostra into animate and inanimate objects, a behavior usually resulting in transverse fracture of the bill and leaving the distal segment embedded (Gudger, 1940; Frazier et aI., 1994). Some billfishes recover from this loss because there are records ofapparently healthy fish with missing rostra (Frazier et aI., 1994). Generally only one rostral fragment is found in each object, but multiple stabbings have been reported. For example, fragments of three swordfish bills were discovered in a whale during flensing (Jonsgard, 1962), several "marlin" spears were found impaled in bales of rubber that were floating at sea (Smith, 1956), and two istiophorid rostra were identified in the timber of a vessel that was brought in for repair (Gudger, 1940; Fierstine and Crimmen, 1996). The following is a detailed account of a large Atlantic blue marlin with two rostral fragments embedded in its head and is the first record of a fish with multiple wounds. I briefly discuss whether impalement was the result of a predator-prey interaction, if embedded rostra aid in understanding migration patterns in both prey and predator, and the effect of impalement on a predator.
Effective management of critically endangered sawfishes can be a difficult task, in part due to interspecies misidentification. Current methods for identifying sawfishes can be impractical as they are based on morphological features that are often unobservable. Further exploration is required to develop a more reliable means of identification.
This study explored the utility of sawfish rostra in determining the species, size and sex of sawfishes, as rostra are commonly the only feature of a sawfish observed by fishers or present in public and private collections.
A morphometric and meristic database consisting of over 1100 narrow sawfish ( Anoxypristis cuspidata ), dwarf sawfish ( Pristis clavata ), largetooth (or freshwater) sawfish ( Pristis pristis ; formerly Pristis microdon ) and green sawfish ( Pristis zijsron ) rostra from Australian waters, was statistically analysed.
Identification of sawfishes was found to be possible through the use of the variables: inter‐tooth spacing, standard rostrum width/standard rostrum length, standard rostrum length/total rostrum length, rostrum tip width/standard rostrum length, and/or rostral tooth count range, although the distinguishing variables were species‐dependent.
The relationship between standard rostrum length and total length was also observed to vary substantially between most species. Models for estimating total length from standard rostrum length are provided.
This study has provided a tool that can be used to identify accurately the species and size of sawfishes by their rostra, and therefore can assist in clarifying historical and contemporary sawfish records, nomenclature and distributions. A better understanding of these issues should allow sawfish conservation strategies to become more focused, and thus more effective.
Copyright © 2013 John Wiley & Sons, Ltd.
The lateral line sense organs of sharks include ampullae of Lorenzini and neuromasts. Each of these two classes of receptors is highly specialized and therefore can be expected to biologically respond to one specific modality of stimulus of minimal threshold intensity. Current anatomical, electro-physiological and behavioral evidence indicates that the ampullae are organized to respond to very weak DC and low frequency AC electric fields that originate from external sources in the environment and that this information is used in the detection of prey. Neuromasts consist of canal receptors and pit organs and are mechanoreceptors that are sensitive to water movements caused by external sources as well as the animal's own swimming movements. There is no convincing experimental evidence of the behavioral role that neuromasts play in the life of sharks, but they can orient toward a source that causes water displacements and perhaps use the neuromast system in the coordination of locomotor activity.Ampullae and neuromasts are innervated by different components of the lateral line nerves that project to special terminal areas within the central nervous system. The dorsal root of the anterior lateral line nerve, which is believed to carry nerve fibers from the ampullae of Lorenzini exclusively, enters and terminates within the anterior lateral line lobe of the medulla. Neuromasts (canal and pit organs) are innervated by the ventral root of the anterior lateral line nerve and posterior lateral line nerve, which project to the posterior lateral line lobe (nucleus medialis) of the medulla and, in addition, distribute to the eminentia granularis of the cerebellum, superior and inferior lobes of the auricle, and to the spinal cord. There is no apparent overlap between those central terminal fields that receive fibers from electroreceptors and those that receive fibers from mechanoreceptors nor with the central terminal field of VIII th nerve neurons. This supports the contention that different functional classes of lateral line receptors are specialized to perform a particular function, but the central coordinating and integrating mechanisms are unknown.
A new species of the rock shrimp genus Sicyonia, S. australiensis sp. nov. (Decapoda, Sicyoniidae) is described and illustrated based on specimens collected from south-eastern Australia. The new species has the first two abdominal somites with an anteriorly directed dorsomedian spine; consequently it resembles closely the following four species: S. laevis Bate, 1888, S. nebulosa (Kubo, 1949), S. truncata (Kubo, 1949) and S. nasica Burukovsky, 1990. However, S. australiensis can be distinguished from its congeners by a combination of features, having the pleuron of the fifth abdominal somites with a posteroventral spine and the rostrum moderately high throughout the entire length, with the distal end posteriorly inclined to ventrad. The genital structures also distinguish the Australian specimens from the related species.
Six species of prawns (four penaeid and two carid) provide most of the catch of a trawl fishery on the continental slope of north-western Australia. The occurrence and volume of prey in the stomach contents of demersally trawled animals (315-485 m) were examined and related to diel changes in the commercial catch rates of each species. The prey included midwater (siphonophores, chaetognaths, heteropods and pteropods) and benthic forms (sponges, polychaetes, other gastropods, bivalves and echinoderms). The dominant prey were decapod crustaceans (7.9-67.2% by volume) and fish (0.5-33.0%), most of which could not be identified as midwater or demersal in origin; significant quantities of foraminiferans (1.8-15%) and squid (0.5-6.5%) were also eaten. The penaeids Aristeus virilis, Haliporoides sibogae and Plesiopenaeus edwardsianus ate mainly benthic or demersal animals. The catch rates of these prawns were 1.4-2.0 times greater during the day than at night, with the lower night-time catches probably resulting from some nocturnal swimming above the bottom. The penaeid Aristaeomorpha foliacea and the carid Heterocarpus sibogae ate both midwater and demersal animals, while the carid Heterocarpus woodmasoni ate mainly midwater animals. The catch rates of these prawns were 2.6-16.5 times higher during the day than at night, which suggests that a large proportion of them migrate into the water column at night, possibly to feed.
Extant billfishes of the family Istiophoridae (Teleostei: Perciformes: Scombroidei) often use their rostra to impale or slash prey (Gudger, 1940; Nakamura, 1983; Frazier et aI., 1994). Although it is generally assumed that fossil and living representatives of the same species have similar behaviors and physiology (Fierstine, 200I), there is no docu mentation of a fossil istiophorid billfish using its rostrum for food cap ture. The Yorktown Formation (early Pliocene) at Lee Creek Mine, eastern North Carolina, USA, has yielded thc world's largest collection of fossils of the family Istiophoridae (Fierstine, 2001), and an abundant number of vertebrae belonging to tunas of the genus Thunnus (Purdy et aI., 2001). Most of the fossil istiophorids at Lee Creek Mine belong to four extant species. The genus Thunnus, although not identifiable to species at Lee Creek Mine (Purdy et al., 2001), has five extant species, all of which are prey of istiophorid billfishes (Nakamura, 1983). We offer evidence that punch marks in fi ve tuna vertebrae collected at Lee Creek Mine were the result of impalement by istiophorids.
We report the Raman spectra of a series of fluorochloroapatites Ca5(PO4)3F1−xClx, where x = 0.0, 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 0.9 and 1.0 (i.e. from pure fluorapatite to chlorapatite). The series did not appear to exhibit any immiscibility, however peak broadening and additional Raman and NMR spectral features on chlorine addition could be interpreted as reduction in symmetry and ordering in the ion channels. All Raman bands showed significant broadening with chlorine substitution, indicating disordering of the crystal lattice or ordering into fluorine and chlorine rich environments. There was also a general trend of the Raman bands to shift to lower wavenumber linearly with chlorine substitution with the ν1 phosphate band decreasing from 966 cm−1 for x = 0.0 to 961 cm−1 for x = 1.0. The full width half maximum (FWHM) of this band increases linearly with chlorine addition from 5 cm−1 for x = 0.0 to 10 cm−1 for x = 1.0. The shift in a component in the ν3 phosphate band with chlorine addition at around 1035 cm−1 agrees with data in the literature on chlorine containing geological apatites. An additional component was seen at around 586 cm−1 in the ν4 phosphate region for chlorapatite and the area of this band decreased linearly to zero as fluorine replaced chlorine. This could be due to Eg symmetry phonons splitting into Ag and Bg modes due to a symmetry change such as hexagonal to monoclinic with chlorine addition. 19F magic angle spinning nuclear magnetic resonance (MAS-NMR) spectra showed a shift to lower ppm values with chlorine addition and a broadening of resonances, consistent with the Raman data. The 31P spectra developed additional shoulders (at around 2 and 4 ppm) with chlorine addition with the main peak position (3.3 ppm for x = 0) decreasing for compositions moving away from x = 0.5 indicating maximum phosphorous nuclear shielding occurs at an approximate F:Cl ratio of 1:1. This discontinuity is a possible indication of a structural transition at x = 0.5 related to local short scale phosphate order ↔ disorder or a change in crystal symmetry.