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First insights into the function of the sawshark rostrum through examination of rostral tooth microwear: rostral tooth microwear in sawsharks

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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.

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... 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). ...
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Prey manipulation through headfirst ingestion is a common foraging tactic in predatory taxa. Sawsharks possesses a toothed rostrum that is thought to assist in prey capture, but the process from prey contact to ingestion is unknown. Here we provide 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. This article is protected by copyright. All rights reserved.
... 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). ...
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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]. ...
Article
Full-text available
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. ...
Article
It has long been assumed that the elongated rostra (the saws) of sawsharks (Fam. Pristiophoridae) and sawfish (Fam. 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, we 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, we recorded minimal interspecific variation between the two species. However, compared to pristids, the pristiophorid rostrum possesses a reduced mechanosensory sampling field but higher electro-sensory resolution, which suggests pristiophorids may not use their rostrums to disable large prey like pristids do. This article is protected by copyright. All rights reserved.
... 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]. ...
Article
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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.
... 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. ...
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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.
... 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. ...
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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.
... 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. ...
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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.
... 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 . ...
Article
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.
... 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. ...
Article
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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.
... 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. ...
Article
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 180000 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 500m), with peak common sawshark catch rates at ~400m. 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. ...
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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.
... (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). ...
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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
... 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. ...
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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.
... 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. ...
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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.
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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.
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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).
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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.
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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.
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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.
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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. © 2015, National Research Council of Canada. All rights reserved.
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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.
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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.
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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.
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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).
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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).
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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.
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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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
Abramoff, M.D., Magelhaes, P.J., Ram, S.J. "Image Processing with ImageJ". Biophotonics International, volume 11, issue 7, pp. 36-42, 2004.