Cetaceans (whales and dolphins) have some of the largest and most complex brains in the animal ki... more Cetaceans (whales and dolphins) have some of the largest and most complex brains in the animal kingdom. When and why this trait evolved remains controversial, with proposed drivers ranging from echolocation to foraging complexity and high-level sociality. This uncertainty partially reflects a lack of data on extinct baleen whales (mysticetes), which has obscured deep-time patterns of brain size evolution in non-echolocating cetaceans. Building on new measurements from mysticete fossils, we show that the evolution of large brains preceded that of echolocation, and subsequently followed a complex trajectory involving several independent increases (e.g. in rorquals and oceanic dolphins) and decreases (e.g. in right whales and ‘river dolphins’). Echolocating whales show a greater tendency towards large brain size, thus reaffirming cognitive demands associated with sound processing as a plausible driver of cetacean encephalization. Nevertheless, our results suggest that other factors such as sociality were also important.
Modern pinnipeds (true and eared seals) employ two radically different swimming styles, with true... more Modern pinnipeds (true and eared seals) employ two radically different swimming styles, with true seals (phocids) propelling themselves primarily with their hindlimbs, whereas eared seals (otariids) rely on their wing-like foreflippers.Current explanations of this functional dichotomy invoke either pinniped diphyly or independent colonizations of the ocean by related but still largely terrestrial ancestors. Here, we show that pinniped swimming styles form an anatomical, functional, and behavioral continuum, within which adaptations for forelimb swimming can arise directly from a hindlimb-propelled bauplan. Within phocids, southern seals (monachines) show a convergent trend toward wing-like, hydrodynamically efficient forelimbs used for propulsion during slow swimming, turning, ursts of speed, or when initiating movement. This condition is most evident in leopard eals, which have well-integrated foreflippers with little digit mobility, reduced claws, and hydrodynamic characteristics comparable to those of forelimb-propelled otariids. Using monachines as a model, we suggest that the last common ancestor of modern seals may have been hindlimb-propelled and aquatically adapted, thus resolving the apparent contradiction at the root of pinniped evolution.
Understanding feeding ecology of extinct kangaroos is fundamental to understanding the evolution ... more Understanding feeding ecology of extinct kangaroos is fundamental to understanding the evolution of kangaroos and the Australia paleoenvironment during the Oligo-Miocene. Comparisons with extant species have suggested that the macropodiforms of the Oligo/Miocene (kangaroos and allies) from the Riversleigh World Heritage Area, northern Australia, were predominantly folivorous browsers or fungivores, unlike the majority of extant species. To further test this hypothesis, we investigate the relationship between variation in cranial and mandibular shape of extant and extinct macropodiforms and ecological factors such as diet, locomotion, and body mass using 3D geometric morphometric analysis of 42 living species and eight extinct species from two radiations (the extinct clade of Balbaridae and some early representatives of the extant Macropodidae. Dietary class (fungivore, browser, grazer, and mixed feeder) correlated strongly with variation in cranial shape (20–25% of variance explained). There was also significant association between cranial shape, and both locomotor mode and body mass. In a principal component analysis of shape variation for crania (including the shape of the molar row), Riversleigh macropodiforms cluster with extant folivorous browsers on principal components (PC) 1 and 3, providing support for previous interpretations of these species as browsing kangaroos.However, as a group and regardless of phylogenetic association, the shape centroid of extinct species differs significantly from that of extant species. Riversleigh macropodiforms cluster with regularhoppers or arboreal tree kangaroos, but this may be a result of the correlation between diet and locomotor mode in kangaroos. Their similarity to extant browsers supports previous interpretations of rainforest and woodland environments at Riversleigh during the early andmiddleMiocene, respectively. Procrustes ANOVA Analysis of the full shape dataset and diet also shows that diet accounts for a significant portion of variation; however, when phylogeny is taken into account these results become nonsignificant. In analyses of dentary shape, some balbarid species cluster with extant mixed feeders, although this may reflect phylogenetic differences rather than ecological signal.
Background/Question/Methods Macroecologists often focus on body size as a factor of interest beca... more Background/Question/Methods Macroecologists often focus on body size as a factor of interest because it serves as a proxy for many different aspects of an organism's biology. Size results from a complex and dynamic tradeoff between physiology, life history, environment, phylogenetic constraints, and past geologic and/or climatic history. Nonetheless, certain 'invariant'size-dependent scaling relationships and broad-scale distributional patterns are repeatedly observed for mammals and other taxa. Do these ...
Neobalaenines are an enigmatic group of baleen whales represented today by a single living specie... more Neobalaenines are an enigmatic group of baleen whales represented today by a single living species: the pygmy right whale, Caperea marginata, found only in the Southern Hemisphere. Molecular divergence estimates date the origin of pygmy right whales to 22–26 Ma, yet so far there are only three confirmed fossil occurrences. Here, we describe an isolated periotic from the latest Miocene of Victoria (Australia). The new fossil shows all the hallmarks of Caperea, making it the second-oldest described neobalaenine, and the oldest record of the genus. Overall, the new specimen resembles C. marginata in its external morphology and details of the cochlea, but is more archaic in it having a hypertrophied suprameatal area and a greater number of cochlear turns. The presence of Caperea in Australian waters during the Late Miocene matches the distribution of the living species, and supports a southern origin for pygmy right whales.
Animals with dietary specializations can be used to link climate to specific ecological drivers o... more Animals with dietary specializations can be used to link climate to specific ecological drivers of endangerment. Only two mammals, the giant panda (Ailuropoda melanoleuca) in Asia and the greater bamboo lemur (Prolemur simus) in Madagascar, consume the nutritionally poor and mechanically challenging culm or trunk of woody bamboos [1, 2, 3]. Even though the greater bamboo lemur is critically endangered, paleontological evidence shows that it was once broadly distributed [4, 5]. Here, integrating morphological, paleontological, and ecological evidence, we project the effects of climate change on greater bamboo lemurs. Both the giant panda and the greater bamboo lemur are shown to share diagnostic dental features indicative of a bamboo diet, thereby providing an ecometric indicator [6, 7] of diet preserved in the fossil record. Analyses of bamboo feeding in living populations show that bamboo culm is consumed only during the dry season and that the greater bamboo lemur is currently found in regions with the shortest dry season. In contrast, paleontological localities of the greater bamboo lemurs have the longest dry seasons. Future projections show that many present-day greater bamboo lemur populations will experience prolonged dry seasons similar to those of the localities where only fossils of the greater bamboo lemur are found. Whereas abundant foods such as bamboo allow feeding specialists to thrive, even a moderate change in seasonality may outstrip the capacity of greater bamboo lemurs to persist on their mechanically demanding food source. Coupling known changes in species distribution with high-resolution ecological and historical data helps to identify extinction risks.
Kienle et al. [1] suggest amendments to our framework for feeding in predatory
aquatic mammals [2... more Kienle et al. [1] suggest amendments to our framework for feeding in predatory aquatic mammals [2]. Below we reply to their suggestions and demonstrate that they are fundamentally flawed from both a mechanical (feeding cycle, strategies) and an evolutionary perspective. They do, however, inspire an important addition to the range and structuring of capture behaviours encoded in our framework.
The pygmy right whale, Caperea marginata, is the least understood extant baleen whale (Cetacea, M... more The pygmy right whale, Caperea marginata, is the least understood extant baleen whale (Cetacea, Mysticeti). Knowledge on its basic anatomy, ecology, and fossil record is limited, even though its singular position outside both balaenids (right whales) and balaenopteroids (rorquals 1 grey whales) gives Caperea a pivotal role in mysticete evolution. Recent investigations of the cetacean cochlea have provided new insights into sensory capabilities and phylogeny. Here, we extend this advance to Caperea by describing, for the first time, the inner ear of this enigmatic species. The cochlea is large and appears to be sensitive to low-frequency sounds, but its hearing limit is relatively high. The presence of a well-developed tympanal recess links Caperea with cetotheriids and balaenopteroids, rather than balaenids, contrary to the traditional morphological view of a close Caperea-balaenid relationship. Nevertheless, a broader sample of the cetotheriid Herpetocetus demonstrates that the presence of a tympanal recess can be variable at the specific and possibly even the intraspecific level. We describe the cochlea of the pygmy right whale. The cochlea is large and sensitive to low-frequency sounds. Possession of a tympanal recess links Caperea with Plicogulae (cetotheriids and balaenopteroids). However, this feature may be more variable than previously thought.
2016. Suction feeding preceded filtering in baleen whale evolution. Memoirs of Museum Victoria 75... more 2016. Suction feeding preceded filtering in baleen whale evolution. Memoirs of Museum Victoria 75: 71–82. The origin of baleen, the key adaptation of modern whales (Mysticeti), marks a profound yet poorly understood transition in vertebrate evolution, triggering the rise of the largest animals on Earth. Baleen is thought to have appeared in archaic tooth-bearing mysticetes during a transitional phase that combined raptorial feeding with incipient bulk filtering. Here we show that tooth wear in a new Late Oligocene mysticete belonging to the putatively transitional family Aetiocetidae is inconsistent with the presence of baleen, and instead indicative of suction feeding. Our findings suggest that baleen arose much closer to the origin of toothless mysticete whales than previously thought. In addition, they suggest an entirely new evolutionary scenario in which the transition from raptorial to baleen-assisted filter feeding was mediated by suction, thereby avoiding the problem of functional interference between teeth and the baleen rack.
The reliability of finite element analysis (FEA) in biomechanical investigations depends upon und... more The reliability of finite element analysis (FEA) in biomechanical investigations depends upon understanding the influence of model assumptions. In producing finite element models, surface mesh resolution is influenced by the resolution of input geometry, and influences the resolution of the ensuing solid mesh used for numerical analysis. Despite a large number of studies incorporating sensitivity studies of the effects of solid mesh resolution there has not yet been any investigation into the effect of surface mesh resolution upon results in a comparative context. Here we use a dataset of crocodile crania to examine the effects of surface resolution on FEA results in a comparative context. Seven high-resolution surface meshes were each down-sampled to varying degrees while keeping the resulting number of solid elements constant. These models were then subjected to bite and shake load cases using finite element analysis. The results show that incremental decreases in surface resolution can result in fluctuations in strain magnitudes, but that it is possible to obtain stable results using lower resolution surface in a comparative FEA study. As surface mesh resolution links input geometry with the resulting solid mesh, the implication of these results is that low resolution input geometry and solid meshes may provide valid results in a comparative context.
Scanning of the small dinosaur Leaellynasaura amicagraphica at the Australian Synchrotron is maki... more Scanning of the small dinosaur Leaellynasaura amicagraphica at the Australian Synchrotron is making possible the eventual reconstruction of its entire skeleton. Embedded in extremely hard rock, its bones are simply too fragile to ever physically extract from rock. However, by making a 3D rapid prototype print of the scanned bones, it will be possible to reconstruct a skeletal mount for study and display. Currently disarticulated, it will be possible to reconstruct the skull by manipulation of 3D rapid prototypes of the various preserved components. Microscanning of tiny teeth of mammals contemporaneous with Leaellynsaura and other South Polar dinosaurs dinosaurs has permitted production of 3D rapid prototype prints X10 natural size, facilitating both their study and exhibition. Particularly critical, such scans have also made possible precise measuring of fossils still partially embedded in the rock. The same scan data have been used for non-destructive histological investigations o...
Evolution; international journal of organic evolution, 2016
The reversibility of phenotypic evolution is likely to be strongly influenced by the ability of u... more The reversibility of phenotypic evolution is likely to be strongly influenced by the ability of underlying developmental systems to generate ancestral traits. However, few studies have quantitatively linked these developmental dynamics to traits that reevolve. In this study, we assess how changes in the inhibitory cascade, a developmental system that regulates relative tooth size in mammals, influenced the loss and reversals of the posthypocristid, a molar tooth crest, in the kangaroo superfamily Macropodoidea. We find that posthypocristid loss is linked with reduced levels of posterior molar inhibition, potentially driven by selection for lophodont, higher-crowned molar teeth. There is strong support for two posthypocristid reversals, each occurring after more than 15 million years of absence, in large-bodied species of Macropus, and two giant extinct species of short-faced sthenurine kangaroo (Procoptodon). We find that whereas primitive posthypocristid expression is linked to hig...
Vertebrate Paleobiology and Paleoanthropology, 2010
The remains of fossil rhinoceroses from Laetoli represent at least three taxa: Ceratotherium effi... more The remains of fossil rhinoceroses from Laetoli represent at least three taxa: Ceratotherium efficax, Ceratotherium cf. simum, and Diceros sp. The great majority of the material from the Pliocene Laetolil Beds belongs to C. efficax, for which we provide a revised diagnosis. This taxon has been frequently misidentified and inaccurately referred to as C. praecox, C. germanoafricanum, or C. mauritanicum.
During wild foraging, Australian fur seals (Arctocephalus pusillus doriferus) encounter many diff... more During wild foraging, Australian fur seals (Arctocephalus pusillus doriferus) encounter many different types of prey in a wide range of scenarios, yet in captive environments they are typically provided with a narrower range of opportunities to display their full repertoire of behaviours. This study aimed to quantitatively explore the effect of foraging-based enrichment on the behaviour and activity patterns displayed by two captive Australian fur seals at Melbourne Zoo, Australia. Food was presented as a scatter in open water, in a free-floating ball device, or in a static box device, with each treatment separated by control trials with no enrichment. Both subjects spent more time interacting with the ball and static box devices than the scatter feed. The total time spent pattern swimming was reduced in the enrichment treatments compared to the controls, while the time spent performing random swimming behaviours increased. There was also a significant increase in the total number of bouts of behaviour performed in all three enrichment treatments compared to controls. Each enrichment method also promoted a different suit of foraging behaviours. Hence, rather than choosing one method, the most effective way to increase the diversity of foraging behaviours, while also increasing variation in general activity patterns, is to provide seals with a wide range of foraging scenarios where food is encountered in different ways.
Cetaceans (whales and dolphins) have some of the largest and most complex brains in the animal ki... more Cetaceans (whales and dolphins) have some of the largest and most complex brains in the animal kingdom. When and why this trait evolved remains controversial, with proposed drivers ranging from echolocation to foraging complexity and high-level sociality. This uncertainty partially reflects a lack of data on extinct baleen whales (mysticetes), which has obscured deep-time patterns of brain size evolution in non-echolocating cetaceans. Building on new measurements from mysticete fossils, we show that the evolution of large brains preceded that of echolocation, and subsequently followed a complex trajectory involving several independent increases (e.g. in rorquals and oceanic dolphins) and decreases (e.g. in right whales and ‘river dolphins’). Echolocating whales show a greater tendency towards large brain size, thus reaffirming cognitive demands associated with sound processing as a plausible driver of cetacean encephalization. Nevertheless, our results suggest that other factors such as sociality were also important.
Modern pinnipeds (true and eared seals) employ two radically different swimming styles, with true... more Modern pinnipeds (true and eared seals) employ two radically different swimming styles, with true seals (phocids) propelling themselves primarily with their hindlimbs, whereas eared seals (otariids) rely on their wing-like foreflippers.Current explanations of this functional dichotomy invoke either pinniped diphyly or independent colonizations of the ocean by related but still largely terrestrial ancestors. Here, we show that pinniped swimming styles form an anatomical, functional, and behavioral continuum, within which adaptations for forelimb swimming can arise directly from a hindlimb-propelled bauplan. Within phocids, southern seals (monachines) show a convergent trend toward wing-like, hydrodynamically efficient forelimbs used for propulsion during slow swimming, turning, ursts of speed, or when initiating movement. This condition is most evident in leopard eals, which have well-integrated foreflippers with little digit mobility, reduced claws, and hydrodynamic characteristics comparable to those of forelimb-propelled otariids. Using monachines as a model, we suggest that the last common ancestor of modern seals may have been hindlimb-propelled and aquatically adapted, thus resolving the apparent contradiction at the root of pinniped evolution.
Understanding feeding ecology of extinct kangaroos is fundamental to understanding the evolution ... more Understanding feeding ecology of extinct kangaroos is fundamental to understanding the evolution of kangaroos and the Australia paleoenvironment during the Oligo-Miocene. Comparisons with extant species have suggested that the macropodiforms of the Oligo/Miocene (kangaroos and allies) from the Riversleigh World Heritage Area, northern Australia, were predominantly folivorous browsers or fungivores, unlike the majority of extant species. To further test this hypothesis, we investigate the relationship between variation in cranial and mandibular shape of extant and extinct macropodiforms and ecological factors such as diet, locomotion, and body mass using 3D geometric morphometric analysis of 42 living species and eight extinct species from two radiations (the extinct clade of Balbaridae and some early representatives of the extant Macropodidae. Dietary class (fungivore, browser, grazer, and mixed feeder) correlated strongly with variation in cranial shape (20–25% of variance explained). There was also significant association between cranial shape, and both locomotor mode and body mass. In a principal component analysis of shape variation for crania (including the shape of the molar row), Riversleigh macropodiforms cluster with extant folivorous browsers on principal components (PC) 1 and 3, providing support for previous interpretations of these species as browsing kangaroos.However, as a group and regardless of phylogenetic association, the shape centroid of extinct species differs significantly from that of extant species. Riversleigh macropodiforms cluster with regularhoppers or arboreal tree kangaroos, but this may be a result of the correlation between diet and locomotor mode in kangaroos. Their similarity to extant browsers supports previous interpretations of rainforest and woodland environments at Riversleigh during the early andmiddleMiocene, respectively. Procrustes ANOVA Analysis of the full shape dataset and diet also shows that diet accounts for a significant portion of variation; however, when phylogeny is taken into account these results become nonsignificant. In analyses of dentary shape, some balbarid species cluster with extant mixed feeders, although this may reflect phylogenetic differences rather than ecological signal.
Background/Question/Methods Macroecologists often focus on body size as a factor of interest beca... more Background/Question/Methods Macroecologists often focus on body size as a factor of interest because it serves as a proxy for many different aspects of an organism's biology. Size results from a complex and dynamic tradeoff between physiology, life history, environment, phylogenetic constraints, and past geologic and/or climatic history. Nonetheless, certain 'invariant'size-dependent scaling relationships and broad-scale distributional patterns are repeatedly observed for mammals and other taxa. Do these ...
Neobalaenines are an enigmatic group of baleen whales represented today by a single living specie... more Neobalaenines are an enigmatic group of baleen whales represented today by a single living species: the pygmy right whale, Caperea marginata, found only in the Southern Hemisphere. Molecular divergence estimates date the origin of pygmy right whales to 22–26 Ma, yet so far there are only three confirmed fossil occurrences. Here, we describe an isolated periotic from the latest Miocene of Victoria (Australia). The new fossil shows all the hallmarks of Caperea, making it the second-oldest described neobalaenine, and the oldest record of the genus. Overall, the new specimen resembles C. marginata in its external morphology and details of the cochlea, but is more archaic in it having a hypertrophied suprameatal area and a greater number of cochlear turns. The presence of Caperea in Australian waters during the Late Miocene matches the distribution of the living species, and supports a southern origin for pygmy right whales.
Animals with dietary specializations can be used to link climate to specific ecological drivers o... more Animals with dietary specializations can be used to link climate to specific ecological drivers of endangerment. Only two mammals, the giant panda (Ailuropoda melanoleuca) in Asia and the greater bamboo lemur (Prolemur simus) in Madagascar, consume the nutritionally poor and mechanically challenging culm or trunk of woody bamboos [1, 2, 3]. Even though the greater bamboo lemur is critically endangered, paleontological evidence shows that it was once broadly distributed [4, 5]. Here, integrating morphological, paleontological, and ecological evidence, we project the effects of climate change on greater bamboo lemurs. Both the giant panda and the greater bamboo lemur are shown to share diagnostic dental features indicative of a bamboo diet, thereby providing an ecometric indicator [6, 7] of diet preserved in the fossil record. Analyses of bamboo feeding in living populations show that bamboo culm is consumed only during the dry season and that the greater bamboo lemur is currently found in regions with the shortest dry season. In contrast, paleontological localities of the greater bamboo lemurs have the longest dry seasons. Future projections show that many present-day greater bamboo lemur populations will experience prolonged dry seasons similar to those of the localities where only fossils of the greater bamboo lemur are found. Whereas abundant foods such as bamboo allow feeding specialists to thrive, even a moderate change in seasonality may outstrip the capacity of greater bamboo lemurs to persist on their mechanically demanding food source. Coupling known changes in species distribution with high-resolution ecological and historical data helps to identify extinction risks.
Kienle et al. [1] suggest amendments to our framework for feeding in predatory
aquatic mammals [2... more Kienle et al. [1] suggest amendments to our framework for feeding in predatory aquatic mammals [2]. Below we reply to their suggestions and demonstrate that they are fundamentally flawed from both a mechanical (feeding cycle, strategies) and an evolutionary perspective. They do, however, inspire an important addition to the range and structuring of capture behaviours encoded in our framework.
The pygmy right whale, Caperea marginata, is the least understood extant baleen whale (Cetacea, M... more The pygmy right whale, Caperea marginata, is the least understood extant baleen whale (Cetacea, Mysticeti). Knowledge on its basic anatomy, ecology, and fossil record is limited, even though its singular position outside both balaenids (right whales) and balaenopteroids (rorquals 1 grey whales) gives Caperea a pivotal role in mysticete evolution. Recent investigations of the cetacean cochlea have provided new insights into sensory capabilities and phylogeny. Here, we extend this advance to Caperea by describing, for the first time, the inner ear of this enigmatic species. The cochlea is large and appears to be sensitive to low-frequency sounds, but its hearing limit is relatively high. The presence of a well-developed tympanal recess links Caperea with cetotheriids and balaenopteroids, rather than balaenids, contrary to the traditional morphological view of a close Caperea-balaenid relationship. Nevertheless, a broader sample of the cetotheriid Herpetocetus demonstrates that the presence of a tympanal recess can be variable at the specific and possibly even the intraspecific level. We describe the cochlea of the pygmy right whale. The cochlea is large and sensitive to low-frequency sounds. Possession of a tympanal recess links Caperea with Plicogulae (cetotheriids and balaenopteroids). However, this feature may be more variable than previously thought.
2016. Suction feeding preceded filtering in baleen whale evolution. Memoirs of Museum Victoria 75... more 2016. Suction feeding preceded filtering in baleen whale evolution. Memoirs of Museum Victoria 75: 71–82. The origin of baleen, the key adaptation of modern whales (Mysticeti), marks a profound yet poorly understood transition in vertebrate evolution, triggering the rise of the largest animals on Earth. Baleen is thought to have appeared in archaic tooth-bearing mysticetes during a transitional phase that combined raptorial feeding with incipient bulk filtering. Here we show that tooth wear in a new Late Oligocene mysticete belonging to the putatively transitional family Aetiocetidae is inconsistent with the presence of baleen, and instead indicative of suction feeding. Our findings suggest that baleen arose much closer to the origin of toothless mysticete whales than previously thought. In addition, they suggest an entirely new evolutionary scenario in which the transition from raptorial to baleen-assisted filter feeding was mediated by suction, thereby avoiding the problem of functional interference between teeth and the baleen rack.
The reliability of finite element analysis (FEA) in biomechanical investigations depends upon und... more The reliability of finite element analysis (FEA) in biomechanical investigations depends upon understanding the influence of model assumptions. In producing finite element models, surface mesh resolution is influenced by the resolution of input geometry, and influences the resolution of the ensuing solid mesh used for numerical analysis. Despite a large number of studies incorporating sensitivity studies of the effects of solid mesh resolution there has not yet been any investigation into the effect of surface mesh resolution upon results in a comparative context. Here we use a dataset of crocodile crania to examine the effects of surface resolution on FEA results in a comparative context. Seven high-resolution surface meshes were each down-sampled to varying degrees while keeping the resulting number of solid elements constant. These models were then subjected to bite and shake load cases using finite element analysis. The results show that incremental decreases in surface resolution can result in fluctuations in strain magnitudes, but that it is possible to obtain stable results using lower resolution surface in a comparative FEA study. As surface mesh resolution links input geometry with the resulting solid mesh, the implication of these results is that low resolution input geometry and solid meshes may provide valid results in a comparative context.
Scanning of the small dinosaur Leaellynasaura amicagraphica at the Australian Synchrotron is maki... more Scanning of the small dinosaur Leaellynasaura amicagraphica at the Australian Synchrotron is making possible the eventual reconstruction of its entire skeleton. Embedded in extremely hard rock, its bones are simply too fragile to ever physically extract from rock. However, by making a 3D rapid prototype print of the scanned bones, it will be possible to reconstruct a skeletal mount for study and display. Currently disarticulated, it will be possible to reconstruct the skull by manipulation of 3D rapid prototypes of the various preserved components. Microscanning of tiny teeth of mammals contemporaneous with Leaellynsaura and other South Polar dinosaurs dinosaurs has permitted production of 3D rapid prototype prints X10 natural size, facilitating both their study and exhibition. Particularly critical, such scans have also made possible precise measuring of fossils still partially embedded in the rock. The same scan data have been used for non-destructive histological investigations o...
Evolution; international journal of organic evolution, 2016
The reversibility of phenotypic evolution is likely to be strongly influenced by the ability of u... more The reversibility of phenotypic evolution is likely to be strongly influenced by the ability of underlying developmental systems to generate ancestral traits. However, few studies have quantitatively linked these developmental dynamics to traits that reevolve. In this study, we assess how changes in the inhibitory cascade, a developmental system that regulates relative tooth size in mammals, influenced the loss and reversals of the posthypocristid, a molar tooth crest, in the kangaroo superfamily Macropodoidea. We find that posthypocristid loss is linked with reduced levels of posterior molar inhibition, potentially driven by selection for lophodont, higher-crowned molar teeth. There is strong support for two posthypocristid reversals, each occurring after more than 15 million years of absence, in large-bodied species of Macropus, and two giant extinct species of short-faced sthenurine kangaroo (Procoptodon). We find that whereas primitive posthypocristid expression is linked to hig...
Vertebrate Paleobiology and Paleoanthropology, 2010
The remains of fossil rhinoceroses from Laetoli represent at least three taxa: Ceratotherium effi... more The remains of fossil rhinoceroses from Laetoli represent at least three taxa: Ceratotherium efficax, Ceratotherium cf. simum, and Diceros sp. The great majority of the material from the Pliocene Laetolil Beds belongs to C. efficax, for which we provide a revised diagnosis. This taxon has been frequently misidentified and inaccurately referred to as C. praecox, C. germanoafricanum, or C. mauritanicum.
During wild foraging, Australian fur seals (Arctocephalus pusillus doriferus) encounter many diff... more During wild foraging, Australian fur seals (Arctocephalus pusillus doriferus) encounter many different types of prey in a wide range of scenarios, yet in captive environments they are typically provided with a narrower range of opportunities to display their full repertoire of behaviours. This study aimed to quantitatively explore the effect of foraging-based enrichment on the behaviour and activity patterns displayed by two captive Australian fur seals at Melbourne Zoo, Australia. Food was presented as a scatter in open water, in a free-floating ball device, or in a static box device, with each treatment separated by control trials with no enrichment. Both subjects spent more time interacting with the ball and static box devices than the scatter feed. The total time spent pattern swimming was reduced in the enrichment treatments compared to the controls, while the time spent performing random swimming behaviours increased. There was also a significant increase in the total number of bouts of behaviour performed in all three enrichment treatments compared to controls. Each enrichment method also promoted a different suit of foraging behaviours. Hence, rather than choosing one method, the most effective way to increase the diversity of foraging behaviours, while also increasing variation in general activity patterns, is to provide seals with a wide range of foraging scenarios where food is encountered in different ways.
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Papers by Alistair Evans
obscured deep-time patterns of brain size evolution in non-echolocating cetaceans. Building on new measurements from mysticete fossils, we show that the evolution of large brains preceded that of echolocation, and subsequently followed a complex trajectory involving several independent increases (e.g. in rorquals and oceanic dolphins) and decreases (e.g. in right whales and ‘river dolphins’). Echolocating whales show a greater tendency towards large brain size, thus reaffirming cognitive demands associated with sound processing as a plausible driver of cetacean encephalization. Nevertheless, our results suggest that other factors such as sociality were also important.
Australia paleoenvironment during the Oligo-Miocene. Comparisons with extant species have suggested that the
macropodiforms of the Oligo/Miocene (kangaroos and allies) from the Riversleigh World Heritage Area, northern Australia,
were predominantly folivorous browsers or fungivores, unlike the majority of extant species. To further test this hypothesis, we
investigate the relationship between variation in cranial and mandibular shape of extant and extinct macropodiforms and
ecological factors such as diet, locomotion, and body mass using 3D geometric morphometric analysis of 42 living species
and eight extinct species from two radiations (the extinct clade of Balbaridae and some early representatives of the extant
Macropodidae. Dietary class (fungivore, browser, grazer, and mixed feeder) correlated strongly with variation in cranial shape
(20–25% of variance explained). There was also significant association between cranial shape, and both locomotor mode and
body mass. In a principal component analysis of shape variation for crania (including the shape of the molar row), Riversleigh
macropodiforms cluster with extant folivorous browsers on principal components (PC) 1 and 3, providing support for previous
interpretations of these species as browsing kangaroos.However, as a group and regardless of phylogenetic association, the shape
centroid of extinct species differs significantly from that of extant species. Riversleigh macropodiforms cluster with regularhoppers or arboreal tree kangaroos, but this may be a result of the correlation between diet and locomotor mode in kangaroos.
Their similarity to extant browsers supports previous interpretations of rainforest and woodland environments at Riversleigh
during the early andmiddleMiocene, respectively. Procrustes ANOVA Analysis of the full shape dataset and diet also shows that
diet accounts for a significant portion of variation; however, when phylogeny is taken into account these results become
nonsignificant. In analyses of dentary shape, some balbarid species cluster with extant mixed feeders, although this may reflect
phylogenetic differences rather than ecological signal.
aquatic mammals [2]. Below we reply to their suggestions and demonstrate that
they are fundamentally flawed from both a mechanical (feeding cycle, strategies)
and an evolutionary perspective. They do, however, inspire an
important addition to the range and structuring of capture behaviours encoded
in our framework.
obscured deep-time patterns of brain size evolution in non-echolocating cetaceans. Building on new measurements from mysticete fossils, we show that the evolution of large brains preceded that of echolocation, and subsequently followed a complex trajectory involving several independent increases (e.g. in rorquals and oceanic dolphins) and decreases (e.g. in right whales and ‘river dolphins’). Echolocating whales show a greater tendency towards large brain size, thus reaffirming cognitive demands associated with sound processing as a plausible driver of cetacean encephalization. Nevertheless, our results suggest that other factors such as sociality were also important.
Australia paleoenvironment during the Oligo-Miocene. Comparisons with extant species have suggested that the
macropodiforms of the Oligo/Miocene (kangaroos and allies) from the Riversleigh World Heritage Area, northern Australia,
were predominantly folivorous browsers or fungivores, unlike the majority of extant species. To further test this hypothesis, we
investigate the relationship between variation in cranial and mandibular shape of extant and extinct macropodiforms and
ecological factors such as diet, locomotion, and body mass using 3D geometric morphometric analysis of 42 living species
and eight extinct species from two radiations (the extinct clade of Balbaridae and some early representatives of the extant
Macropodidae. Dietary class (fungivore, browser, grazer, and mixed feeder) correlated strongly with variation in cranial shape
(20–25% of variance explained). There was also significant association between cranial shape, and both locomotor mode and
body mass. In a principal component analysis of shape variation for crania (including the shape of the molar row), Riversleigh
macropodiforms cluster with extant folivorous browsers on principal components (PC) 1 and 3, providing support for previous
interpretations of these species as browsing kangaroos.However, as a group and regardless of phylogenetic association, the shape
centroid of extinct species differs significantly from that of extant species. Riversleigh macropodiforms cluster with regularhoppers or arboreal tree kangaroos, but this may be a result of the correlation between diet and locomotor mode in kangaroos.
Their similarity to extant browsers supports previous interpretations of rainforest and woodland environments at Riversleigh
during the early andmiddleMiocene, respectively. Procrustes ANOVA Analysis of the full shape dataset and diet also shows that
diet accounts for a significant portion of variation; however, when phylogeny is taken into account these results become
nonsignificant. In analyses of dentary shape, some balbarid species cluster with extant mixed feeders, although this may reflect
phylogenetic differences rather than ecological signal.
aquatic mammals [2]. Below we reply to their suggestions and demonstrate that
they are fundamentally flawed from both a mechanical (feeding cycle, strategies)
and an evolutionary perspective. They do, however, inspire an
important addition to the range and structuring of capture behaviours encoded
in our framework.