Amphibians are different from most other tetrapods because they have a biphasic life cycle, with ... more Amphibians are different from most other tetrapods because they have a biphasic life cycle, with larval forms showing a dramatically different cranial anatomy and feeding strategy compared to adults. Amphibians with their exceptional diversity in habitats, lifestyles and reproductive modes are also excellent models for studying the evolutionary divergence in feeding systems. In the present chapter, we review the literature on amphibian feeding anatomy and function published since 2000. We also present some novel unpublished data on caecilian feeding biomechanics. This review shows that over the past two decades important new insights in our understanding of amphibian feeding anatomy and function have been made possible, thanks to a better understanding of the phylogenetic relationships between taxa, analyses of development and the use of biomechanical modelling. In terms of functional analyses, important advances involve the temperature-dependent nature of tongue projection mechanis...
Lissamphibia, the only extant, non-amniote tetrapod clade, are morphologically incredibly diverse... more Lissamphibia, the only extant, non-amniote tetrapod clade, are morphologically incredibly diverse. However, to date, studies of morphological evolution, phenotypic integration (covariation) and modularity (the division of a structure into sets of integrated traits) have concentrated overwhelmingly on amniotes. In this thesis I quantified cranial morphological variation across two lissamphibian clades, with representative specimens from every extant genus (caecilians) and family (frogs). Shape was captured in detail, using a high-dimensional surface-based geometric morphometric approach, to test alternative models of cranial organisation and reconstruct cranial evolution across caecilians and frogs. I found both frog and caecilian crania are highly modular, and the pattern of cranial integration is strongly conserved across the clades. Of particular interest is the highly integrated, fast-evolving jaw suspensorium region of both frogs and caecilians, suggesting feeding mechanics may ...
Habitat is one of the most important factors shaping organismal morphology, but it may vary acros... more Habitat is one of the most important factors shaping organismal morphology, but it may vary across life history stages. Ontogenetic shifts in ecology may introduce antagonistic selection that constrains adult phenotype, particularly with ecologically distinct developmental phases such as the free-living, feeding larval stage of many frogs (Lissamphibia: Anura). We test the relative influences of developmental and ecological factors on the diversification of adult skull morphology with a detailed analysis of 15 individual cranial regions across 173 anuran species, representing every extant family. Skull size, adult microhabitat, larval feeding, and ossification timing are all significant factors shaping aspects of cranial evolution in frogs, with late-ossifying elements showing the greatest disparity and fastest evolutionary rates. Size and microhabitat show the strongest effects on cranial shape, and we identify a “large size-wide skull” pattern of anuran, and possibly amphibian, ev...
Metamorphosis is widespread across the animal kingdom and induces fundamental changes in the morp... more Metamorphosis is widespread across the animal kingdom and induces fundamental changes in the morphology, habitat and resources used by an organism during its lifetime. Metamorphic species are likely to experience more dynamic selective pressures through ontogeny compared with species with single-phase life cycles, which may drive divergent evolutionary dynamics. Here, we reconstruct the cranial evolution of the salamander using geometric morphometric data from 148 species spanning the order’s full phylogenetic, developmental and ecological diversity. We demonstrate that life cycle influences cranial shape diversity and rate of evolution. Shifts in the rate of cranial evolution are consistently associated with transitions from biphasic to either direct-developing or paedomorphic life cycle strategies. Direct-developers exhibit the slowest rates of evolution and the lowest disparity, and paedomorphic species the highest. Species undergoing complete metamorphosis (biphasic and direct-developing) exhibit greater cranial modularity (evolutionary independence among regions) than do paedomorphic species, which undergo differential metamorphosis. Biphasic and direct-developing species also display elevated disparity relative to the evolutionary rate for bones associated with feeding, whereas this is not the case for paedomorphic species. Metamorphosis has profoundly influenced salamander cranial evolution, requiring greater autonomy of cranial elements and facilitating the rapid evolution of regions that are remodelled through ontogeny. Rather than compounding functional constraints on variation, metamorphosis seems to have promoted the morphological evolution of salamanders over 180 million years, which may explain the ubiquity of this complex life cycle strategy across disparate organisms. An analysis of geometric morphometric data from 148 species of salamanders shows how life cycle influences cranial shape diversity and rate of evolution.
Phenotypic integration and modularity are concepts that represent the pattern of connectivity of ... more Phenotypic integration and modularity are concepts that represent the pattern of connectivity of morphological structures within an organism. Integration describes the coordinated variation of traits, and analyses of these relationships among traits often reveals the presence of modules, sets of traits that are highly integrated but relatively independent of other traits. Phenotypic integration and modularity have been studied at both the evolutionary and static level across a variety of clades, although most studies thus far are focused on amniotes, and especially mammals. Using a high-dimensional geometric morphometric approach, we investigated the pattern of cranial integration and modularity of the Italian fire salamander (Salamandra salamandra giglioli). We recovered a highly modular pattern, but this pattern did not support either entirely developmental or functional hypotheses of cranial organisation, possibly reflecting complex interactions amongst multiple influencing facto...
Advances in imaging technologies, such as computed tomography (CT) and surface scanning, have fac... more Advances in imaging technologies, such as computed tomography (CT) and surface scanning, have facilitated the rapid generation of large datasets of high-resolution 3D specimen reconstructions in recent years. The wealth of phenotypic information available from these datasets has the potential to inform our understanding of morphological variation and evolution. However, the ever-increasing ease of compiling 3D datasets has created an urgent need for sophisticated methods of capturing high-density shape data that reflect the biological complexity in form. Landmarks often do not take full advantage of the rich shape information available from high-resolution 3D specimen reconstructions, as they are typically restricted to sutures or processes that can be reliably identified across specimens and exclude most of the surficial morphology. The development of sliding and surface semilandmark techniques has greatly enhanced the quantification of shape, but their application to diverse datas...
Advances in imaging technologies, such as computed tomography (CT) and surface scanning, have fac... more Advances in imaging technologies, such as computed tomography (CT) and surface scanning, have facilitated the rapid generation of large datasets of high-resolution 3D specimen reconstructions in recent years. The wealth of phenotypic information available from these datasets has the potential to inform our understanding of morphological variation and evolution. However, the ever-increasing ease of compiling 3D datasets has created an urgent need for sophisticated methods of capturing high-density shape data that reflect the biological complexity in form. Landmarks often do not take full advantage of the rich shape information available from high-resolution 3D specimen reconstructions, as they are typically restricted to sutures or processes that can be reliably identified across specimens and exclude most of the surficial morphology. The development of sliding and surface semilandmark techniques has greatly enhanced the quantification of shape, but their application to diverse datas...
Amphibians are different from most other tetrapods because they have a biphasic life cycle, with ... more Amphibians are different from most other tetrapods because they have a biphasic life cycle, with larval forms showing a dramatically different cranial anatomy and feeding strategy compared to adults. Amphibians with their exceptional diversity in habitats, lifestyles and reproductive modes are also excellent models for studying the evolutionary divergence in feeding systems. In the present chapter, we review the literature on amphibian feeding anatomy and function published since 2000. We also present some novel unpublished data on caecilian feeding biomechanics. This review shows that over the past two decades important new insights in our understanding of amphibian feeding anatomy and function have been made possible, thanks to a better understanding of the phylogenetic relationships between taxa, analyses of development and the use of biomechanical modelling. In terms of functional analyses, important advances involve the temperature-dependent nature of tongue projection mechanis...
Lissamphibia, the only extant, non-amniote tetrapod clade, are morphologically incredibly diverse... more Lissamphibia, the only extant, non-amniote tetrapod clade, are morphologically incredibly diverse. However, to date, studies of morphological evolution, phenotypic integration (covariation) and modularity (the division of a structure into sets of integrated traits) have concentrated overwhelmingly on amniotes. In this thesis I quantified cranial morphological variation across two lissamphibian clades, with representative specimens from every extant genus (caecilians) and family (frogs). Shape was captured in detail, using a high-dimensional surface-based geometric morphometric approach, to test alternative models of cranial organisation and reconstruct cranial evolution across caecilians and frogs. I found both frog and caecilian crania are highly modular, and the pattern of cranial integration is strongly conserved across the clades. Of particular interest is the highly integrated, fast-evolving jaw suspensorium region of both frogs and caecilians, suggesting feeding mechanics may ...
Habitat is one of the most important factors shaping organismal morphology, but it may vary acros... more Habitat is one of the most important factors shaping organismal morphology, but it may vary across life history stages. Ontogenetic shifts in ecology may introduce antagonistic selection that constrains adult phenotype, particularly with ecologically distinct developmental phases such as the free-living, feeding larval stage of many frogs (Lissamphibia: Anura). We test the relative influences of developmental and ecological factors on the diversification of adult skull morphology with a detailed analysis of 15 individual cranial regions across 173 anuran species, representing every extant family. Skull size, adult microhabitat, larval feeding, and ossification timing are all significant factors shaping aspects of cranial evolution in frogs, with late-ossifying elements showing the greatest disparity and fastest evolutionary rates. Size and microhabitat show the strongest effects on cranial shape, and we identify a “large size-wide skull” pattern of anuran, and possibly amphibian, ev...
Metamorphosis is widespread across the animal kingdom and induces fundamental changes in the morp... more Metamorphosis is widespread across the animal kingdom and induces fundamental changes in the morphology, habitat and resources used by an organism during its lifetime. Metamorphic species are likely to experience more dynamic selective pressures through ontogeny compared with species with single-phase life cycles, which may drive divergent evolutionary dynamics. Here, we reconstruct the cranial evolution of the salamander using geometric morphometric data from 148 species spanning the order’s full phylogenetic, developmental and ecological diversity. We demonstrate that life cycle influences cranial shape diversity and rate of evolution. Shifts in the rate of cranial evolution are consistently associated with transitions from biphasic to either direct-developing or paedomorphic life cycle strategies. Direct-developers exhibit the slowest rates of evolution and the lowest disparity, and paedomorphic species the highest. Species undergoing complete metamorphosis (biphasic and direct-developing) exhibit greater cranial modularity (evolutionary independence among regions) than do paedomorphic species, which undergo differential metamorphosis. Biphasic and direct-developing species also display elevated disparity relative to the evolutionary rate for bones associated with feeding, whereas this is not the case for paedomorphic species. Metamorphosis has profoundly influenced salamander cranial evolution, requiring greater autonomy of cranial elements and facilitating the rapid evolution of regions that are remodelled through ontogeny. Rather than compounding functional constraints on variation, metamorphosis seems to have promoted the morphological evolution of salamanders over 180 million years, which may explain the ubiquity of this complex life cycle strategy across disparate organisms. An analysis of geometric morphometric data from 148 species of salamanders shows how life cycle influences cranial shape diversity and rate of evolution.
Phenotypic integration and modularity are concepts that represent the pattern of connectivity of ... more Phenotypic integration and modularity are concepts that represent the pattern of connectivity of morphological structures within an organism. Integration describes the coordinated variation of traits, and analyses of these relationships among traits often reveals the presence of modules, sets of traits that are highly integrated but relatively independent of other traits. Phenotypic integration and modularity have been studied at both the evolutionary and static level across a variety of clades, although most studies thus far are focused on amniotes, and especially mammals. Using a high-dimensional geometric morphometric approach, we investigated the pattern of cranial integration and modularity of the Italian fire salamander (Salamandra salamandra giglioli). We recovered a highly modular pattern, but this pattern did not support either entirely developmental or functional hypotheses of cranial organisation, possibly reflecting complex interactions amongst multiple influencing facto...
Advances in imaging technologies, such as computed tomography (CT) and surface scanning, have fac... more Advances in imaging technologies, such as computed tomography (CT) and surface scanning, have facilitated the rapid generation of large datasets of high-resolution 3D specimen reconstructions in recent years. The wealth of phenotypic information available from these datasets has the potential to inform our understanding of morphological variation and evolution. However, the ever-increasing ease of compiling 3D datasets has created an urgent need for sophisticated methods of capturing high-density shape data that reflect the biological complexity in form. Landmarks often do not take full advantage of the rich shape information available from high-resolution 3D specimen reconstructions, as they are typically restricted to sutures or processes that can be reliably identified across specimens and exclude most of the surficial morphology. The development of sliding and surface semilandmark techniques has greatly enhanced the quantification of shape, but their application to diverse datas...
Advances in imaging technologies, such as computed tomography (CT) and surface scanning, have fac... more Advances in imaging technologies, such as computed tomography (CT) and surface scanning, have facilitated the rapid generation of large datasets of high-resolution 3D specimen reconstructions in recent years. The wealth of phenotypic information available from these datasets has the potential to inform our understanding of morphological variation and evolution. However, the ever-increasing ease of compiling 3D datasets has created an urgent need for sophisticated methods of capturing high-density shape data that reflect the biological complexity in form. Landmarks often do not take full advantage of the rich shape information available from high-resolution 3D specimen reconstructions, as they are typically restricted to sutures or processes that can be reliably identified across specimens and exclude most of the surficial morphology. The development of sliding and surface semilandmark techniques has greatly enhanced the quantification of shape, but their application to diverse datas...
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Papers by Carla Bardua