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Peter T Madsen - One of the best experts on this subject based on the ideXlab platform.
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narrow acoustic field of view drives frequency scaling in Toothed Whale biosonar
Current Biology, 2018Co-Authors: Michael Ladegaard, Frants H Jensen, Mark P Johnson, Danuta M Wisniewska, Peter T MadsenAbstract:Summary Toothed Whales are apex predators varying in size from 40-kg porpoises to 50-ton sperm Whales that all forage by emitting high-amplitude ultrasonic clicks and listening for weak returning echoes [ 1 , 2 ]. The sensory field of view of these echolocating animals depends on the characteristics of the biosonar signals and the morphology of the sound generator, yet it is poorly understood how these biophysical relationships have shaped the evolution of biosonar parameters as Toothed Whales adapted to different foraging niches. Here we test how biosonar output, frequency, and directivity vary with body size to understand the co-evolution of biosonar signals and sound-generating structures. We show that the radiated power increases twice as steeply with body mass (P ∝ M1.47 ± 0.25) than expected from typical scaling laws of call intensity [ 3 ], indicating an evolutionary hyperallometric investment into sound production structures that may be driven by a strong selective pressure for long-range biosonar. We find that biosonar frequency scales inversely with body size (F ∝ M−0.19 ± 0.03), resulting in remarkably stable biosonar beamwidth that is independent of body size. We discuss why the three main hypotheses for inverse frequency scaling in animal communication signals [ 3 , 4 , 5 ] do not explain frequency scaling in Toothed Whale biosonar. We instead propose that a narrow acoustic field of view, analogous to the fovea of many visual predators, is the primary evolutionary driver of biosonar frequency in Toothed Whales, serving as a spatial filter to reduce clutter levels and facilitate long-range prey detection.
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First-year sperm Whale calves echolocate and perform long, deep dives
Behavioral Ecology and Sociobiology, 2018Co-Authors: Pernille Tønnesen, Michael Ladegaard, Shane Gero, Mark Johnson, Peter T MadsenAbstract:Deep-diving sperm Whales have a complex social structure and the largest brain of any animal, but very little is known about the ontogeny of their diving, foraging, echolocation, and communication skills. In large-brained terrestrial species, social skills develop earlier than locomotor abilities, but this may not be feasible for sperm Whales, which require locomotor skills from birth to breathe, swim, and suckle. Here, we shed new light on the relative development of social and locomotor capabilities of a wild Toothed Whale. Sound and movement recording tags deployed on three first-year sperm Whale calves for a total of 15 h revealed that these calves rarely produced codas for communication with adult Whales, but likely tracked the ample passive acoustic cues emitted by clicking adults. The calves’ diving capabilities were well developed (maximum dive depth: 285, 337, and 662 m; maximum dive time: 11, 31, and 44 min) and they all produced clicks in a way that is consistent with echolocation. The calf performing the longest and deepest dives additionally emitted two echolocation buzzes, suggesting that it could have attempted to forage. Thus, sperm Whale calves may supplement their milk diet with food caught independently at depth much earlier than previously believed. Contrary to terrestrial mammals, we propose that the maturation of locomotor, diving, and echolocation skills may be favored over investment in developing social communication skills at an early age in sperm Whales. Significance statement The life of deep-diving Toothed Whales has up until recently been a mystery and the understanding of their behavior has generally been limited to surface observations and captive studies. Fortunately, the rapid development of animal-borne bio-logging devices has markedly improved our knowledge of the behavior of adult Whales. The behavior and development of young calves are, however, still largely unknown. Sperm Whale calves are challenged by being air-breathing marine mammals, which must learn to hunt prey at great depths. Using Dtags, we here show that sperm Whale calves have much more pronounced diving capabilities than previously thought. The onset of independent foraging and foraging effort seems linked to the diving capability of the calf. These results show that young members of this otherwise slowly maturing species of apex predators do learn to dive and may hunt much earlier than previously believed.
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functional convergence in bat and Toothed Whale biosonars
Physiology, 2013Co-Authors: Peter T Madsen, Annemarie SurlykkeAbstract:Echolocating bats and Toothed Whales display a remarkable functional convergence in the way they sense actively with sound.
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clicking in shallow rivers short range echolocation of irrawaddy and ganges river dolphins in a shallow acoustically complex habitat
PLOS ONE, 2013Co-Authors: Frants H Jensen, Alice Rocco, Rubaiyat M Mansur, Brian D Smith, Vincent M Janik, Peter T MadsenAbstract:Toothed Whales (Cetacea, odontoceti) use biosonar to navigate their environment and to find and catch prey. All studied Toothed Whale species have evolved highly directional, high-amplitude ultrasonic clicks suited for long-range echolocation of prey in open water. Little is known about the biosonar signals of Toothed Whale species inhabiting freshwater habitats such as endangered river dolphins. To address the evolutionary pressures shaping the echolocation signal parameters of non-marine Toothed Whales, we investigated the biosonar source parameters of Ganges river dolphins (Platanista gangetica gangetica) and Irrawaddy dolphins (Orcaella brevirostris) within the river systems of the Sundarban mangrove forest. Both Ganges and Irrawaddy dolphins produced echolocation clicks with a high repetition rate and low source level compared to marine species. Irrawaddy dolphins, inhabiting coastal and riverine habitats, produced a mean source level of 195 dB (max 203 dB) re 1 µPapp whereas Ganges river dolphins, living exclusively upriver, produced a mean source level of 184 dB (max 191) re 1 µPapp. These source levels are 1–2 orders of magnitude lower than those of similar sized marine delphinids and may reflect an adaptation to a shallow, acoustically complex freshwater habitat with high reverberation and acoustic clutter. The centroid frequency of Ganges river dolphin clicks are an octave lower than predicted from scaling, but with an estimated beamwidth comparable to that of porpoises. The unique bony maxillary crests found in the Platanista forehead may help achieve a higher directionality than expected using clicks nearly an octave lower than similar sized odontocetes.
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Sperm Whale coda communication studied with multiple acoustic tags
Journal of the Acoustical Society of America, 2012Co-Authors: Peter T MadsenAbstract:Female sperm Whales spend their entire lives in matrilineal groups with long term social bonds. However, contrary to other Toothed Whale species with a complex, long term social structure, sperm Whales seemingly only use stereotyped patterns of clicks, named coda, to radiate acoustic clan identity with little or no signature encoding. Due to their deep diving behavior in offshore water, it is difficult to study the acoustic behavior and source properties of sperm Whale communication signals. To alleviate that, multiple acoustic Dtags was deployed on sperm Whales to study the behavioral context and source parameters of coda production. It is shown that more than 50% of all codas are produced during deep dives where the active space can cover the entire foot print of the social group despite low apparent source levels of around 180 dB re 1uPa. Intra click information in the form of spectral and IPI information is heavily distorted as a function of aspect with little room for individual encoding. The unequiv...
Graham J. Pierce - One of the best experts on this subject based on the ideXlab platform.
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Vocal foragers and silent crowds: context-dependent vocal variation in Northeast Atlantic long-finned pilot Whales.
Behavioral Ecology and Sociobiology, 2017Co-Authors: Fleur Visser, Graham J. Pierce, Machiel G. Oudejans, Lindesay A. S. Scott-hayward, Stacy L. Deruiter, Ana Alves, Ricardo Antunes, Saana Isojunno, Hans SlabbekoornAbstract:Vocalisations form a key component of the social interactions and foraging behaviour of Toothed Whales. We investigated changes in calling and echolocation behaviour of long-finned pilot Whales between foraging and non-foraging periods, by combining acoustic recordings and diving depth data from tagged individuals with concurrent surface observations on social behaviour of their group. The pilot Whales showed marked vocal variation, specific to foraging and social context. During periods of foraging, pilot Whales showed more vocal activity than during non-foraging periods (rest, travel). In addition to the expected increase in echolocation activity, call rates also increased, suggesting that pilot Whales communicate more during foraging. Furthermore, calls with multiple inflections occurred more often immediately before and after foraging dives and during the early descent and late ascent phases of foraging dives. However, these calls were almost never detected at diving depths of the tagged Whale beyond 350 m. Calls with no or few inflections were produced at all times, irrespective of diving depth of the tagged Whale. We discuss possible explanations for the distinct vocal variation associated with foraging periods. In addition, during non-foraging periods, the pilot Whales were found to be more silent (no calling or echolocation) in larger, more closely spaced groups. This indicates that increased levels of social cohesion may release the need to stay in touch acoustically. Social Toothed Whales rely on vocalisations to find prey and interact with conspecifics. Species are often highly vocal and can have elaborate call repertoires. However, it often remains unclear how their repertoire use correlates to specific social and behavioural contexts, which is vital to understand Toothed Whale foraging strategies and sociality. Combining on-animal tag recordings of diving and acoustic behaviour with observations of social behaviour, we found that pilot Whales produce more calls during foraging than during non-foraging periods. Moreover, highly inflected calls were closely associated to the periods around and during foraging dives. This indicates enhanced communication during foraging, which may, for example, enable relocation of conspecifics or sharing of information. Whales reduced their vocal activity (calling and echolocation) at increased levels of social cohesion, indicating that in certain behavioural contexts, closer association (i.e. more closely spaced) may release the need to stay in touch acoustically.
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Vocal foragers and silent crowds: context-dependent vocal variation in Northeast Atlantic long-finned pilot Whales
Behavioral Ecology and Sociobiology, 2017Co-Authors: Fleur Visser, Graham J. Pierce, Machiel G. Oudejans, Lindesay A. S. Scott-hayward, Stacy L. Deruiter, Saana Isojunno, Hans Slabbekoorn, Ana C. Alves, Ricardo N. Antunes, Jef HuismanAbstract:Vocalisations form a key component of the social interactions and foraging behaviour of Toothed Whales. We investigated changes in calling and echolocation behaviour of long-finned pilot Whales between foraging and non-foraging periods, by combining acoustic recordings and diving depth data from tagged individuals with concurrent surface observations on social behaviour of their group. The pilot Whales showed marked vocal variation, specific to foraging and social context. During periods of foraging, pilot Whales showed more vocal activity than during non-foraging periods (rest, travel). In addition to the expected increase in echolocation activity, call rates also increased, suggesting that pilot Whales communicate more during foraging. Furthermore, calls with multiple inflections occurred more often immediately before and after foraging dives and during the early descent and late ascent phases of foraging dives. However, these calls were almost never detected at diving depths of the tagged Whale beyond 350 m. Calls with no or few inflections were produced at all times, irrespective of diving depth of the tagged Whale. We discuss possible explanations for the distinct vocal variation associated with foraging periods. In addition, during non-foraging periods, the pilot Whales were found to be more silent (no calling or echolocation) in larger, more closely spaced groups. This indicates that increased levels of social cohesion may release the need to stay in touch acoustically. Significance statement Social Toothed Whales rely on vocalisations to find prey and interact with conspecifics. Species are often highly vocal and can have elaborate call repertoires. However, it often remains unclear how their repertoire use correlates to specific social and behavioural contexts, which is vital to understand Toothed Whale foraging strategies and sociality. Combining on-animal tag recordings of diving and acoustic behaviour with observations of social behaviour, we found that pilot Whales produce more calls during foraging than during non-foraging periods. Moreover, highly inflected calls were closely associated to the periods around and during foraging dives. This indicates enhanced communication during foraging, which may, for example, enable relocation of conspecifics or sharing of information. Whales reduced their vocal activity (calling and echolocation) at increased levels of social cohesion, indicating that in certain behavioural contexts, closer association (i.e. more closely spaced) may release the need to stay in touch acoustically.
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Ecological niche segregation among five Toothed Whale species off the NW Iberian Peninsula using ecological tracers as multi-approach
Marine Biology, 2013Co-Authors: Paula Méndez-fernandez, Tiphaine Chouvelon, Marisa Ferreira, Angel F Gonzalez, Graham J. Pierce, Fiona L. Read, M. Begoña Santos, Paco Bustamante, Alfredo Lopez, Jerome SpitzAbstract:This study aims to assess niche segregation among the five main Toothed Whales that frequent the NW Iberian Peninsula waters: the common dolphin, the harbour porpoise, the bottlenose dolphin, the striped dolphin and the long-finned pilot Whale. We used cadmium (Cd) and stable isotope ratios (δ^13C and δ^15N) as ecological tracers to assess degree of segregation in diet/trophic level and in foraging habitat, over various time-scales. δ^13C values highlighted different habitats, while Cd concentrations highlighted feeding differences between oceanic and neritic species. Moreover, δ^15N values suggest different trophic levels of prey targeted within oceanic and neritic species. Hence, results revealed long-term ecological segregation among five Toothed Whales that coexist in the NWIP and demonstrated the ability of ecological tracers to discriminate ecological niches among closely related species.
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Relative prey size consumption in Toothed Whales: implications for prey selection and level of specialisation
Marine Ecology Progress Series, 2006Co-Authors: Colin D Macleod, M. B. Santos, Alfredo Lopez, Graham J. PierceAbstract:3 Coordinadora para o Estudio dos Mamiferos Marinos (CEMMA), Apdo. 15, 36380 Gondomar, Pontevedra, Spain ABSTRACT: We investigated whether Toothed Whales consume prey in relation to their availability in the local environment based on the fact that availability of potential prey is likely to decrease expo- nentially with increasing size, reflecting the usual size-abundance relationships found in marine communities. We calculated relative prey size frequency spectra for 13 species of Toothed Whale from the northeast Atlantic. These differed considerably from an exponential distribution, suggesting that Toothed Whales preferentially consume larger, less abundant organisms over smaller, more abundant ones. The prey size spectra of the various cetacean species could be separated into 3 distinct groups based on the strength of the mode, maximum value and inter-quartile range. Group 1 species, such as the common dolphin, consume a wide range of relatively large organisms. In contrast, Group 2 and 3 species, such as the northern bottlenose Whale and the sperm Whale respectively, specialise on nar- row ranges of relatively small organisms. We hypothesise that these differences are related to the mode of prey capture. Group 1 species can capture prey using pincer-like movement of jaws contain- ing a large number of small, homodont teeth, as well as suction-feeding, allowing them to be rela- tively generalist in terms of relative prey size. In contrast, Group 2 and 3 species have a greatly reduced dentition and specialise on using suction to capture prey. The morphological adaptations that make suction-feeding more efficient restrict the size of prey that can be ingested, so that suction- feeders are limited to relatively small prey.
Christopher R. Mchenry - One of the best experts on this subject based on the ideXlab platform.
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The remarkable convergence of skull shape in crocodilians and Toothed Whales.
Proceedings of The Royal Society B: Biological Sciences, 2017Co-Authors: Matthew R Mccurry, Erich M G Fitzgerald, Justin W Adams, Philip Clausen, Alistair R Evans, Christopher R. MchenryAbstract:The striking resemblance of long-snouted aquatic mammals and reptiles has long been considered an example of morphological convergence, yet the true cause of this similarity remains untested. We addressed this deficit through three-dimensional morphometric analysis of the full diversity of crocodilian and Toothed Whale (Odontoceti) skull shapes. Our focus on biomechanically important aspects of shape allowed us to overcome difficulties involved in comparing mammals and reptiles, which have fundamental differences in the number and position of skull bones. We examined whether diet, habitat and prey size correlated with skull shape using phylogenetically informed statistical procedures. Crocodilians and Toothed Whales have a similar range of skull shapes, varying from extremely short and broad to extremely elongate. This spectrum of shapes represented more of the total variation in our dataset than between phylogenetic groups. The most elongate species (river dolphins and gharials) are extremely convergent in skull shape, clustering outside of the range of the other taxa. Our results suggest the remarkable convergence between long-snouted river dolphins and gharials is driven by diet rather than physical factors intrinsic to riverine environments. Despite diverging approximately 288 million years ago, crocodilians and odontocetes have evolved a remarkably similar morphological solution to feeding on similar prey.
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Supplementary section S4 from The remarkable convergence of skull shape in crocodilians and Toothed Whales
2017Co-Authors: Matthew R Mccurry, Erich M G Fitzgerald, Justin W Adams, Alistair R Evans, Philip D. Clausen, Christopher R. MchenryAbstract:The striking resemblance of long-snouted aquatic mammals and reptiles has long been considered an example of morphological convergence, yet the true cause of this similarity remains untested. We addressed this deficit through three-dimensional morphometric analysis of the full diversity of crocodilian and Toothed Whale (Odontoceti) skull shapes. Our focus on biomechanically important aspects of shape allowed us to overcome difficulties involved in comparing mammals and reptiles, which have fundamental differences in the number and position of skull bones. We examined whether diet, habitat and prey size correlated with skull shape using phylogenetically informed statistical procedures. Crocodilians and Toothed Whales have a similar range of skull shapes, varying from extremely short and broad to extremely elongate. This spectrum of shapes represented more of the total variation in our dataset than between phylogenetic groups. The most elongate species (river dolphins and gharials) are extremely convergent in skull shape, clustering outside of the range of the other taxa. Our results suggest the remarkable convergence between long-snouted river dolphins and gharials is driven by diet rather than physical factors intrinsic to riverine environments. Despite diverging approximately 288 million years ago, crocodilians and odontocetes have evolved a remarkably similar morphological solution to feeding on similar prey
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Supplementary S5 from The remarkable convergence of skull shape in crocodilians and Toothed Whales
2017Co-Authors: Matthew R Mccurry, Erich M G Fitzgerald, Justin W Adams, Alistair R Evans, Philip D. Clausen, Christopher R. MchenryAbstract:The striking resemblance of long-snouted aquatic mammals and reptiles has long been considered an example of morphological convergence, yet the true cause of this similarity remains untested. We addressed this deficit through three-dimensional morphometric analysis of the full diversity of crocodilian and Toothed Whale (Odontoceti) skull shapes. Our focus on biomechanically important aspects of shape allowed us to overcome difficulties involved in comparing mammals and reptiles, which have fundamental differences in the number and position of skull bones. We examined whether diet, habitat and prey size correlated with skull shape using phylogenetically informed statistical procedures. Crocodilians and Toothed Whales have a similar range of skull shapes, varying from extremely short and broad to extremely elongate. This spectrum of shapes represented more of the total variation in our dataset than between phylogenetic groups. The most elongate species (river dolphins and gharials) are extremely convergent in skull shape, clustering outside of the range of the other taxa. Our results suggest the remarkable convergence between long-snouted river dolphins and gharials is driven by diet rather than physical factors intrinsic to riverine environments. Despite diverging approximately 288 million years ago, crocodilians and odontocetes have evolved a remarkably similar morphological solution to feeding on similar prey
Frants H Jensen - One of the best experts on this subject based on the ideXlab platform.
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narrow acoustic field of view drives frequency scaling in Toothed Whale biosonar
Current Biology, 2018Co-Authors: Michael Ladegaard, Frants H Jensen, Mark P Johnson, Danuta M Wisniewska, Peter T MadsenAbstract:Summary Toothed Whales are apex predators varying in size from 40-kg porpoises to 50-ton sperm Whales that all forage by emitting high-amplitude ultrasonic clicks and listening for weak returning echoes [ 1 , 2 ]. The sensory field of view of these echolocating animals depends on the characteristics of the biosonar signals and the morphology of the sound generator, yet it is poorly understood how these biophysical relationships have shaped the evolution of biosonar parameters as Toothed Whales adapted to different foraging niches. Here we test how biosonar output, frequency, and directivity vary with body size to understand the co-evolution of biosonar signals and sound-generating structures. We show that the radiated power increases twice as steeply with body mass (P ∝ M1.47 ± 0.25) than expected from typical scaling laws of call intensity [ 3 ], indicating an evolutionary hyperallometric investment into sound production structures that may be driven by a strong selective pressure for long-range biosonar. We find that biosonar frequency scales inversely with body size (F ∝ M−0.19 ± 0.03), resulting in remarkably stable biosonar beamwidth that is independent of body size. We discuss why the three main hypotheses for inverse frequency scaling in animal communication signals [ 3 , 4 , 5 ] do not explain frequency scaling in Toothed Whale biosonar. We instead propose that a narrow acoustic field of view, analogous to the fovea of many visual predators, is the primary evolutionary driver of biosonar frequency in Toothed Whales, serving as a spatial filter to reduce clutter levels and facilitate long-range prey detection.
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clicking in shallow rivers short range echolocation of irrawaddy and ganges river dolphins in a shallow acoustically complex habitat
PLOS ONE, 2013Co-Authors: Frants H Jensen, Alice Rocco, Rubaiyat M Mansur, Brian D Smith, Vincent M Janik, Peter T MadsenAbstract:Toothed Whales (Cetacea, odontoceti) use biosonar to navigate their environment and to find and catch prey. All studied Toothed Whale species have evolved highly directional, high-amplitude ultrasonic clicks suited for long-range echolocation of prey in open water. Little is known about the biosonar signals of Toothed Whale species inhabiting freshwater habitats such as endangered river dolphins. To address the evolutionary pressures shaping the echolocation signal parameters of non-marine Toothed Whales, we investigated the biosonar source parameters of Ganges river dolphins (Platanista gangetica gangetica) and Irrawaddy dolphins (Orcaella brevirostris) within the river systems of the Sundarban mangrove forest. Both Ganges and Irrawaddy dolphins produced echolocation clicks with a high repetition rate and low source level compared to marine species. Irrawaddy dolphins, inhabiting coastal and riverine habitats, produced a mean source level of 195 dB (max 203 dB) re 1 µPapp whereas Ganges river dolphins, living exclusively upriver, produced a mean source level of 184 dB (max 191) re 1 µPapp. These source levels are 1–2 orders of magnitude lower than those of similar sized marine delphinids and may reflect an adaptation to a shallow, acoustically complex freshwater habitat with high reverberation and acoustic clutter. The centroid frequency of Ganges river dolphin clicks are an octave lower than predicted from scaling, but with an estimated beamwidth comparable to that of porpoises. The unique bony maxillary crests found in the Platanista forehead may help achieve a higher directionality than expected using clicks nearly an octave lower than similar sized odontocetes.
Matthew R Mccurry - One of the best experts on this subject based on the ideXlab platform.
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The remarkable convergence of skull shape in crocodilians and Toothed Whales.
Proceedings of The Royal Society B: Biological Sciences, 2017Co-Authors: Matthew R Mccurry, Erich M G Fitzgerald, Justin W Adams, Philip Clausen, Alistair R Evans, Christopher R. MchenryAbstract:The striking resemblance of long-snouted aquatic mammals and reptiles has long been considered an example of morphological convergence, yet the true cause of this similarity remains untested. We addressed this deficit through three-dimensional morphometric analysis of the full diversity of crocodilian and Toothed Whale (Odontoceti) skull shapes. Our focus on biomechanically important aspects of shape allowed us to overcome difficulties involved in comparing mammals and reptiles, which have fundamental differences in the number and position of skull bones. We examined whether diet, habitat and prey size correlated with skull shape using phylogenetically informed statistical procedures. Crocodilians and Toothed Whales have a similar range of skull shapes, varying from extremely short and broad to extremely elongate. This spectrum of shapes represented more of the total variation in our dataset than between phylogenetic groups. The most elongate species (river dolphins and gharials) are extremely convergent in skull shape, clustering outside of the range of the other taxa. Our results suggest the remarkable convergence between long-snouted river dolphins and gharials is driven by diet rather than physical factors intrinsic to riverine environments. Despite diverging approximately 288 million years ago, crocodilians and odontocetes have evolved a remarkably similar morphological solution to feeding on similar prey.
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Supplementary section S4 from The remarkable convergence of skull shape in crocodilians and Toothed Whales
2017Co-Authors: Matthew R Mccurry, Erich M G Fitzgerald, Justin W Adams, Alistair R Evans, Philip D. Clausen, Christopher R. MchenryAbstract:The striking resemblance of long-snouted aquatic mammals and reptiles has long been considered an example of morphological convergence, yet the true cause of this similarity remains untested. We addressed this deficit through three-dimensional morphometric analysis of the full diversity of crocodilian and Toothed Whale (Odontoceti) skull shapes. Our focus on biomechanically important aspects of shape allowed us to overcome difficulties involved in comparing mammals and reptiles, which have fundamental differences in the number and position of skull bones. We examined whether diet, habitat and prey size correlated with skull shape using phylogenetically informed statistical procedures. Crocodilians and Toothed Whales have a similar range of skull shapes, varying from extremely short and broad to extremely elongate. This spectrum of shapes represented more of the total variation in our dataset than between phylogenetic groups. The most elongate species (river dolphins and gharials) are extremely convergent in skull shape, clustering outside of the range of the other taxa. Our results suggest the remarkable convergence between long-snouted river dolphins and gharials is driven by diet rather than physical factors intrinsic to riverine environments. Despite diverging approximately 288 million years ago, crocodilians and odontocetes have evolved a remarkably similar morphological solution to feeding on similar prey
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Supplementary S5 from The remarkable convergence of skull shape in crocodilians and Toothed Whales
2017Co-Authors: Matthew R Mccurry, Erich M G Fitzgerald, Justin W Adams, Alistair R Evans, Philip D. Clausen, Christopher R. MchenryAbstract:The striking resemblance of long-snouted aquatic mammals and reptiles has long been considered an example of morphological convergence, yet the true cause of this similarity remains untested. We addressed this deficit through three-dimensional morphometric analysis of the full diversity of crocodilian and Toothed Whale (Odontoceti) skull shapes. Our focus on biomechanically important aspects of shape allowed us to overcome difficulties involved in comparing mammals and reptiles, which have fundamental differences in the number and position of skull bones. We examined whether diet, habitat and prey size correlated with skull shape using phylogenetically informed statistical procedures. Crocodilians and Toothed Whales have a similar range of skull shapes, varying from extremely short and broad to extremely elongate. This spectrum of shapes represented more of the total variation in our dataset than between phylogenetic groups. The most elongate species (river dolphins and gharials) are extremely convergent in skull shape, clustering outside of the range of the other taxa. Our results suggest the remarkable convergence between long-snouted river dolphins and gharials is driven by diet rather than physical factors intrinsic to riverine environments. Despite diverging approximately 288 million years ago, crocodilians and odontocetes have evolved a remarkably similar morphological solution to feeding on similar prey
