For decades, theoretical morphological studies of different groups of organisms have been success... more For decades, theoretical morphological studies of different groups of organisms have been successfully pursued in biological, paleontological, and computational contexts, often with distinct modeling approaches and research questions. A regular influx of new perspectives and varied expertise has contributed to the emergence of a veritable multidisciplinary outlook for theoretical morphology. The broadening of this discipline is reflected in a substantial increase in the number of models, leading to a bewildering diversity that has yet to be scrutinized. In this work, we tackle this issue in a synthetic fashion, with a quantitative meta-analysis that allows an objective comparison of theoretical morphological models treated as entities. By analogy with empirical morphospace analyses of actual organisms, we performed a multivariate ordination of a representative sample of models, producing a metaspace of models in which patterns of similarity and difference are visualized. A phenetic tree was used to characterize the relationships between models. Four major groups have been identified, and their disparity analyzed. We suggest this typology as a useful starting point to identify a core set of fundamental principles and protocols for better interpretation of the plethora of current models and for more efficient construction of models in the future. This in turn can help in diversifying the scope of macroevolutionary, developmental, and bioenvironmental questions in theoretical morphology.
The joint quantification of disparity and diversity is an important aspect of recent macroevoluti... more The joint quantification of disparity and diversity is an important aspect of recent macroevolutionary studies, and is usually motivated by theoretical considerations on the pace of innovation and the filling of morphospace. In practice, varying protocols of data collection and analysis have rendered comparisons among studies difficult. The basic question remains, how sensitive is any given disparity signal to different aspects of sampling and data analysis? Here we address this issue in the context of the radiation of the echinoid order Spatangoida during the Cretaceous. We compare patterns at the genus-and species-level, with time subdivision into subepochs and into stages, and with morphological sampling based on landmarks, traditional morphometrics, and discrete characters. In terms of temporal scale, similarity of disparity pattern accrues despite a change in temporal resolution. Different morphometric methods, however, produce somewhat different signals early in the radiation. Both the landmark analysis and the discrete character analysis suggest relatively high early disparity, whereas the analysis based on traditional morphometrics records a much lower value. This difference appears to reflect primarily the measurement of different aspects of overall morphology. Notwithstanding, a general deceleration in morphological diversification is apparent at both the genus and the species level. Moreover, inclusion or exclusion of the sister-order Holasteroida and stem-group Disasteroida in the reference morphospace did not affect proportional Villier and Eble, p. 3 changes in spatangoid disparity. The relative robustness of these patterns implies that the choice of temporal scale, morphometric scheme, and taxonomic level may not substantially affect the representation of large-scale morphospace structure and of broad trends in disparity. However, the choice need not be arbitrary, as particular questions may demand certain protocols.
Temporal asymmetries in clade histories have often been studied in lower Paleozoic radiations. Po... more Temporal asymmetries in clade histories have often been studied in lower Paleozoic radiations. Post-Paleozoic patterns, however, are less well understood. In this paper, disparity and diversity changes in Mesozoic heart urchins were analyzed at the ordinal level, with contrasts among the sister groups Holasteroida and Spatangoida, their paraphyletic stem group Disasteroida, and the more inclusive clade, the superorder Atelostomata. A 38-dimensional landmark-based morphospace representing test architecture was used to describe morphological evolution in terms of total variance and total range. Discordances between disparity and diversity were evident and were expressed both as deceleration in morphological diversification in all groups and as disproportionately higher disparity early in the histories of the Atelostomata, Holasteroida, and Spatangoida. The finding that the early atelostomate disparity peak coincides with the origin of the orders Holasteroida and Spatangoida lends support to the perception of orders as semi-independent entities in the biological hierarchy and as meaningful proxies for morphological distinctness. A comparison of holasteroid and spatangoid responses to the end-Cretaceous mass extinction revealed morphological selectivity. Paleocene spatangoid survivors showed no change in disparity relative to the Campanian-Maastrichtian sample, suggesting nonselectivity. Holasteroids suffered a pronounced loss in disparity (despite a rather high Late Cretaceous level of disparity), indicating morphological selectivity of extinction. Partitioning of disparity into plastral and nonplastral components, reflecting different degrees of developmental entrenchment and functionality, suggests that the origin of holasteroids and spatangoids is more consistent with an exploration of the developmental flexibility of nonplastral constructions than with uniform ecospace occupation. Within groups, several patterns were also most consistent with intrinsic controls. For plastral landmarks, there is an apparent increase in developmental modularity and decrease in developmental constraint from disasteroids to holasteroids and spatangoids. For nonplastral landmarks, no substantial change in disparity was observed from disasteroids to holasteroids and spatangoids, suggesting the maintenance of a developmental constraint despite the passage of time and ecological differentiation. More generally, this study suggests that certain topologies of disparity and evolutionary mechanisms potentially characteristic of the lower Paleozoic radiations of higher taxa (e.g., developmental flexibility) need not be confined to any given time period or hierarchical level.
Proceedings of The Royal Society B: Biological Sciences, Jun 22, 1999
Recent Fourier analyses of fossil extinction data have indicated that the power spectrum of extin... more Recent Fourier analyses of fossil extinction data have indicated that the power spectrum of extinction during the Phanerozoic may take the form of 1/f noise, a result which, it has been suggested, could be indicative of the presence of "critical dynamics" in the processes giving rise to extinction. In this paper we examine extinction power spectra in some detail, using family-level data from a variety of different sources. We find that although the average form of the power spectrum roughly obeys the 1/f law, the spectrum can be represented more accurately by dividing it into two regimes: a low-frequency one which is well fit by an exponential, and a high-frequency one in which it follows a power law with a 1/f 2 form. We give explanations for the occurrence of each of these behaviours and for the position of the cross-over between them.
Two major research themes in Evolutionary Developmental Biology and in Paleobiology, respectively... more Two major research themes in Evolutionary Developmental Biology and in Paleobiology, respectively, have each become central for the analysis and interpretation of morphological changes in evolution: the study of ontogeny/ phylogeny connections, mainly within the widespread and controversial framework of heterochrony; and the study of morphological disparity, the morphological signal of biodiversity, describing secular changes in morphospace occupation during the history of any given clade. Although enriching in their respective fields, these two themes have remained rather isolated to date, despite the potential value of integrating them as some recent studies begin to suggest. Here, we explore the recent notion of developmental morpho-spaceFmorphospace carrying ontogenetic informationFas a potential tool for bridging the gap between disparity dynamics and developmental dynamics. We elaborate this approach with a case study of Early Jurassic ammonite family Hildoceratidae (Mollusca, Cephalopoda). Morphometric analyses of the shell shape of 20 species spanning the morphological spectrum of the family are used to quantify and contrast juvenile and adult disparity levels. Adult disparity is significantly greater than juvenile disparity at the family level; yet, some subclades also display different patterns. In addition, comparisons of ontogenetic trajectories underline the prevalence of heterochrony-based evolutionary modifications within subfamilies (via ontogenetic scaling); they also point to the probable existence of pervasive developmental constraints structuring inhomogeneous morphospace occupation. Morphological disparity and developmental dynamics 473 Gerber et al.
Here, we advance novel uses of allometric spaces-multidimensional spaces specifically defined by ... more Here, we advance novel uses of allometric spaces-multidimensional spaces specifically defined by allometric coefficients-with the goal of investigating the focal role of development in shaping the evolution of morphological disparity. From their examination, operational measures of allometric disparity can be derived, complementing standard signals of morphological disparity through an intuitive and process-oriented refinement of established analytical protocols used in disparity studies. Allometric spaces thereby become a promising context to reveal different patterns of evolutionary developmental changes and to assess their relative prevalence and importance. Such spaces offer a novel domain of investigation of phenotypic variation and should help in detecting large-scale trends, thus placing various macroevolutionary phenomena in an explicitly developmental context. Ammonoidea (Cephalopoda) at the Lower-Middle Jurassic transition were chosen as a case study to illustrate this methodological approach. We constructed two phenotypic spaces: a static, adult one (adult morphospace) and a dynamic, developmental one (allometric space). Comparative disparity analyses show a strikingly stable occupation in both spaces, despite extensive change in taxonomic composition. In contrast, disparity analyses of subclades reveal clearly distinct morphological and allometric disparity dynamics. Allometric approaches allow developmental insights into morphological diversification otherwise intractable from the analysis of adult morphospace alone.
A good fossil record of life on earth is available since the beginning of the Cambrian Period abo... more A good fossil record of life on earth is available since the beginning of the Cambrian Period about 545 million years ago. Over the interval between then and now, there has been a substantial increase in biodiversity interrupted by many extinction events which caused sharp but relatively brief dips in biodiversity. Modern-day biodiversity is close to the highest it has ever been.
We show that the decline in the extinction rate during the Phanerozoic can be accurately paramete... more We show that the decline in the extinction rate during the Phanerozoic can be accurately parameterized by a logarithmic fit to the cumulative total extinction. This implies that extinction intensity is falling off approximately as the reciprocal of time. We demonstrate that this observation alone is sufficient to explain the existence of the proposed power-law forms in the distribution of the sizes of extinction events and in the power spectrum of Phanerozoic extinction, results which previously have been explained by appealing to self-organized critical theories of evolutionary dynamics.
What is Complexity? - The philosophy of complexity per se with application to some examples in ev... more What is Complexity? - The philosophy of complexity per se with application to some examples in evolution B. Edmonds. The Growth of Structural and Functional Complexity during Evolution F. Heylighen. Involution: On the Structure and Process of Existence D.M. Keirsey. The Nature, Development, and Destiny of Organization in the Universe A. Mansueto. Physical Models of Biological Evolution N. Vandewalle, M. Ausloos. A Simple Mathematical Theory of Evolution Showing that Taxonomic Complexity is a Logistic Variable R.L. Coren. Diversity and Complexity: Two Sides of the Same Coin J.B.C. Garcia, et al. Chaos in Mathematics, Physics, and Computer Science: Similarities and Dissimilarities B. Codenotti, L. Margara. Metacomputation of Language Hierarchies R. Glueck, A. Klimov. Eigenmechanism - An Explanatory Principle and an Artful Exemplar J. Hu. Forgetting in Self-Organising Systems B.C.E. Scott. Invertibility and the Evolution of Complex Systems G. Nagarjuna. Lest We Forget Our Inheritance A.J. Hirst. Mind as Evolution and Evolution as Such R. Pallbo. The Evolution of Complexity in the Evolution of Language: grammaticalization, pidgin languages, and language acquisition K.C. Diller. Memetics: On a conceptual framework for cultural evolution H.C. Speel. Parasite Ecology and the Evolution of Religion B. Cullen. Innovation, Increasing Complexity and the Need for a New Paradigm in Economics B.H. Martens. Use of Complex Adaptive Systems in Organizational Studies E.A. Garcia. Responsive Accounting: a grounding of the informational domain in the operational domain of an organisation R. Espejo, A. Reyes. Application of Complexity Theories to Evolutionary System Development G.S. Percivall. Cognitive Complexity vs. Connectivity: efficiency analysis of hypertext networks J. Bollen. Index.
Temporal asymmetries in clade histories have often been studied in lower Paleozoic radiations. Po... more Temporal asymmetries in clade histories have often been studied in lower Paleozoic radiations. Post-Paleozoic patterns, however, are less well understood. In this paper, disparity and diversity changes in Mesozoic heart urchins were analyzed at the ordinal level, with contrasts among the sister groups Holasteroida and Spatangoida, their paraphyletic stem group Disasteroida, and the more inclusive clade, the superorder Atelostomata. A 38-dimensional landmark-based morphospace representing test architecture was used to describe morphological evolution in terms of total variance and total range. Discordances between disparity and diversity were evident and were expressed both as deceleration in morphological diversification in all groups and as disproportionately higher disparity early in the histories of the Atelostomata, Holasteroida, and Spatangoida. The finding that the early atelostomate disparity peak coincides with the origin of the orders Holasteroida and Spatangoida lends support to the perception of orders as semi-independent entities in the biological hierarchy and as meaningful proxies for morphological distinctness. A comparison of holasteroid and spatangoid responses to the end-Cretaceous mass extinction revealed morphological selectivity. Paleocene spatangoid survivors showed no change in disparity relative to the Campanian-Maastrichtian sample, suggesting nonselectivity. Holasteroids suffered a pronounced loss in disparity (despite a rather high Late Cretaceous level of disparity), indicating morphological selectivity of extinction. Partitioning of disparity into plastral and nonplastral components, reflecting different degrees of developmental entrenchment and functionality, suggests that the origin of holasteroids and spatangoids is more consistent with an exploration of the developmental flexibility of nonplastral constructions than with uniform ecospace occupation. Within groups, several patterns were also most consistent with intrinsic controls. For plastral landmarks, there is an apparent increase in developmental modularity and decrease in developmental constraint from disasteroids to holasteroids and spatangoids. For nonplastral landmarks, no substantial change in disparity was observed from disasteroids to holasteroids and spatangoids, suggesting the maintenance of a developmental constraint despite the passage of time and ecological differentiation. More generally, this study suggests that certain topologies of disparity and evolutionary mechanisms potentially characteristic of the lower Paleozoic radiations of higher taxa (e.g., developmental flexibility) need not be confined to any given time period or hierarchical level.
The fossil record of insects documents a high proportion of modern higher-level taxa (67% for fam... more The fossil record of insects documents a high proportion of modern higher-level taxa (67% for families), although this capture rate drops off considerably for lower-level taxa. This record is Lagerstätten-driven, and is deployed by complementary, parallel body-and trace-fossil components that reveal a wealth of taxonomic and ecological detail. A family-level analysis of this record shows that past insect diversity is governed by low origination and extinction rates, both decreasing toward the Recent. This feature, in addition to prolonged taxal durations, has conferred on insects significant immunity from extinction. Nevertheless, the most profound event in insect history, the end-Permian extinction, decimated the Paleozoic Insect Fauna but allowed survival of lineages that gave rise to the Modern Insect Fauna of the Mesozoic and Cenozoic. Past insect ecomorphologic disparity can be documented as feeding attributes from the traceand body-fossil records. Three such attributes are assessed in the insect fossil record: mouthpart class, functional feeding group, and dietary guild, which collectively are divided into 74 distinctive categories. A plot of durations of these categories disclose a distinct trend of
For decades, theoretical morphological studies of different groups of organisms have been success... more For decades, theoretical morphological studies of different groups of organisms have been successfully pursued in biological, paleontological, and computational contexts, often with distinct modeling approaches and research questions. A regular influx of new perspectives and varied expertise has contributed to the emergence of a veritable multidisciplinary outlook for theoretical morphology. The broadening of this discipline is reflected in a substantial increase in the number of models, leading to a bewildering diversity that has yet to be scrutinized. In this work, we tackle this issue in a synthetic fashion, with a quantitative meta-analysis that allows an objective comparison of theoretical morphological models treated as entities. By analogy with empirical morphospace analyses of actual organisms, we performed a multivariate ordination of a representative sample of models, producing a metaspace of models in which patterns of similarity and difference are visualized. A phenetic tree was used to characterize the relationships between models. Four major groups have been identified, and their disparity analyzed. We suggest this typology as a useful starting point to identify a core set of fundamental principles and protocols for better interpretation of the plethora of current models and for more efficient construction of models in the future. This in turn can help in diversifying the scope of macroevolutionary, developmental, and bioenvironmental questions in theoretical morphology.
The joint quantification of disparity and diversity is an important aspect of recent macroevoluti... more The joint quantification of disparity and diversity is an important aspect of recent macroevolutionary studies, and is usually motivated by theoretical considerations on the pace of innovation and the filling of morphospace. In practice, varying protocols of data collection and analysis have rendered comparisons among studies difficult. The basic question remains, how sensitive is any given disparity signal to different aspects of sampling and data analysis? Here we address this issue in the context of the radiation of the echinoid order Spatangoida during the Cretaceous. We compare patterns at the genus-and species-level, with time subdivision into subepochs and into stages, and with morphological sampling based on landmarks, traditional morphometrics, and discrete characters. In terms of temporal scale, similarity of disparity pattern accrues despite a change in temporal resolution. Different morphometric methods, however, produce somewhat different signals early in the radiation. Both the landmark analysis and the discrete character analysis suggest relatively high early disparity, whereas the analysis based on traditional morphometrics records a much lower value. This difference appears to reflect primarily the measurement of different aspects of overall morphology. Notwithstanding, a general deceleration in morphological diversification is apparent at both the genus and the species level. Moreover, inclusion or exclusion of the sister-order Holasteroida and stem-group Disasteroida in the reference morphospace did not affect proportional Villier and Eble, p. 3 changes in spatangoid disparity. The relative robustness of these patterns implies that the choice of temporal scale, morphometric scheme, and taxonomic level may not substantially affect the representation of large-scale morphospace structure and of broad trends in disparity. However, the choice need not be arbitrary, as particular questions may demand certain protocols.
Temporal asymmetries in clade histories have often been studied in lower Paleozoic radiations. Po... more Temporal asymmetries in clade histories have often been studied in lower Paleozoic radiations. Post-Paleozoic patterns, however, are less well understood. In this paper, disparity and diversity changes in Mesozoic heart urchins were analyzed at the ordinal level, with contrasts among the sister groups Holasteroida and Spatangoida, their paraphyletic stem group Disasteroida, and the more inclusive clade, the superorder Atelostomata. A 38-dimensional landmark-based morphospace representing test architecture was used to describe morphological evolution in terms of total variance and total range. Discordances between disparity and diversity were evident and were expressed both as deceleration in morphological diversification in all groups and as disproportionately higher disparity early in the histories of the Atelostomata, Holasteroida, and Spatangoida. The finding that the early atelostomate disparity peak coincides with the origin of the orders Holasteroida and Spatangoida lends support to the perception of orders as semi-independent entities in the biological hierarchy and as meaningful proxies for morphological distinctness. A comparison of holasteroid and spatangoid responses to the end-Cretaceous mass extinction revealed morphological selectivity. Paleocene spatangoid survivors showed no change in disparity relative to the Campanian-Maastrichtian sample, suggesting nonselectivity. Holasteroids suffered a pronounced loss in disparity (despite a rather high Late Cretaceous level of disparity), indicating morphological selectivity of extinction. Partitioning of disparity into plastral and nonplastral components, reflecting different degrees of developmental entrenchment and functionality, suggests that the origin of holasteroids and spatangoids is more consistent with an exploration of the developmental flexibility of nonplastral constructions than with uniform ecospace occupation. Within groups, several patterns were also most consistent with intrinsic controls. For plastral landmarks, there is an apparent increase in developmental modularity and decrease in developmental constraint from disasteroids to holasteroids and spatangoids. For nonplastral landmarks, no substantial change in disparity was observed from disasteroids to holasteroids and spatangoids, suggesting the maintenance of a developmental constraint despite the passage of time and ecological differentiation. More generally, this study suggests that certain topologies of disparity and evolutionary mechanisms potentially characteristic of the lower Paleozoic radiations of higher taxa (e.g., developmental flexibility) need not be confined to any given time period or hierarchical level.
Proceedings of The Royal Society B: Biological Sciences, Jun 22, 1999
Recent Fourier analyses of fossil extinction data have indicated that the power spectrum of extin... more Recent Fourier analyses of fossil extinction data have indicated that the power spectrum of extinction during the Phanerozoic may take the form of 1/f noise, a result which, it has been suggested, could be indicative of the presence of "critical dynamics" in the processes giving rise to extinction. In this paper we examine extinction power spectra in some detail, using family-level data from a variety of different sources. We find that although the average form of the power spectrum roughly obeys the 1/f law, the spectrum can be represented more accurately by dividing it into two regimes: a low-frequency one which is well fit by an exponential, and a high-frequency one in which it follows a power law with a 1/f 2 form. We give explanations for the occurrence of each of these behaviours and for the position of the cross-over between them.
Two major research themes in Evolutionary Developmental Biology and in Paleobiology, respectively... more Two major research themes in Evolutionary Developmental Biology and in Paleobiology, respectively, have each become central for the analysis and interpretation of morphological changes in evolution: the study of ontogeny/ phylogeny connections, mainly within the widespread and controversial framework of heterochrony; and the study of morphological disparity, the morphological signal of biodiversity, describing secular changes in morphospace occupation during the history of any given clade. Although enriching in their respective fields, these two themes have remained rather isolated to date, despite the potential value of integrating them as some recent studies begin to suggest. Here, we explore the recent notion of developmental morpho-spaceFmorphospace carrying ontogenetic informationFas a potential tool for bridging the gap between disparity dynamics and developmental dynamics. We elaborate this approach with a case study of Early Jurassic ammonite family Hildoceratidae (Mollusca, Cephalopoda). Morphometric analyses of the shell shape of 20 species spanning the morphological spectrum of the family are used to quantify and contrast juvenile and adult disparity levels. Adult disparity is significantly greater than juvenile disparity at the family level; yet, some subclades also display different patterns. In addition, comparisons of ontogenetic trajectories underline the prevalence of heterochrony-based evolutionary modifications within subfamilies (via ontogenetic scaling); they also point to the probable existence of pervasive developmental constraints structuring inhomogeneous morphospace occupation. Morphological disparity and developmental dynamics 473 Gerber et al.
Here, we advance novel uses of allometric spaces-multidimensional spaces specifically defined by ... more Here, we advance novel uses of allometric spaces-multidimensional spaces specifically defined by allometric coefficients-with the goal of investigating the focal role of development in shaping the evolution of morphological disparity. From their examination, operational measures of allometric disparity can be derived, complementing standard signals of morphological disparity through an intuitive and process-oriented refinement of established analytical protocols used in disparity studies. Allometric spaces thereby become a promising context to reveal different patterns of evolutionary developmental changes and to assess their relative prevalence and importance. Such spaces offer a novel domain of investigation of phenotypic variation and should help in detecting large-scale trends, thus placing various macroevolutionary phenomena in an explicitly developmental context. Ammonoidea (Cephalopoda) at the Lower-Middle Jurassic transition were chosen as a case study to illustrate this methodological approach. We constructed two phenotypic spaces: a static, adult one (adult morphospace) and a dynamic, developmental one (allometric space). Comparative disparity analyses show a strikingly stable occupation in both spaces, despite extensive change in taxonomic composition. In contrast, disparity analyses of subclades reveal clearly distinct morphological and allometric disparity dynamics. Allometric approaches allow developmental insights into morphological diversification otherwise intractable from the analysis of adult morphospace alone.
A good fossil record of life on earth is available since the beginning of the Cambrian Period abo... more A good fossil record of life on earth is available since the beginning of the Cambrian Period about 545 million years ago. Over the interval between then and now, there has been a substantial increase in biodiversity interrupted by many extinction events which caused sharp but relatively brief dips in biodiversity. Modern-day biodiversity is close to the highest it has ever been.
We show that the decline in the extinction rate during the Phanerozoic can be accurately paramete... more We show that the decline in the extinction rate during the Phanerozoic can be accurately parameterized by a logarithmic fit to the cumulative total extinction. This implies that extinction intensity is falling off approximately as the reciprocal of time. We demonstrate that this observation alone is sufficient to explain the existence of the proposed power-law forms in the distribution of the sizes of extinction events and in the power spectrum of Phanerozoic extinction, results which previously have been explained by appealing to self-organized critical theories of evolutionary dynamics.
What is Complexity? - The philosophy of complexity per se with application to some examples in ev... more What is Complexity? - The philosophy of complexity per se with application to some examples in evolution B. Edmonds. The Growth of Structural and Functional Complexity during Evolution F. Heylighen. Involution: On the Structure and Process of Existence D.M. Keirsey. The Nature, Development, and Destiny of Organization in the Universe A. Mansueto. Physical Models of Biological Evolution N. Vandewalle, M. Ausloos. A Simple Mathematical Theory of Evolution Showing that Taxonomic Complexity is a Logistic Variable R.L. Coren. Diversity and Complexity: Two Sides of the Same Coin J.B.C. Garcia, et al. Chaos in Mathematics, Physics, and Computer Science: Similarities and Dissimilarities B. Codenotti, L. Margara. Metacomputation of Language Hierarchies R. Glueck, A. Klimov. Eigenmechanism - An Explanatory Principle and an Artful Exemplar J. Hu. Forgetting in Self-Organising Systems B.C.E. Scott. Invertibility and the Evolution of Complex Systems G. Nagarjuna. Lest We Forget Our Inheritance A.J. Hirst. Mind as Evolution and Evolution as Such R. Pallbo. The Evolution of Complexity in the Evolution of Language: grammaticalization, pidgin languages, and language acquisition K.C. Diller. Memetics: On a conceptual framework for cultural evolution H.C. Speel. Parasite Ecology and the Evolution of Religion B. Cullen. Innovation, Increasing Complexity and the Need for a New Paradigm in Economics B.H. Martens. Use of Complex Adaptive Systems in Organizational Studies E.A. Garcia. Responsive Accounting: a grounding of the informational domain in the operational domain of an organisation R. Espejo, A. Reyes. Application of Complexity Theories to Evolutionary System Development G.S. Percivall. Cognitive Complexity vs. Connectivity: efficiency analysis of hypertext networks J. Bollen. Index.
Temporal asymmetries in clade histories have often been studied in lower Paleozoic radiations. Po... more Temporal asymmetries in clade histories have often been studied in lower Paleozoic radiations. Post-Paleozoic patterns, however, are less well understood. In this paper, disparity and diversity changes in Mesozoic heart urchins were analyzed at the ordinal level, with contrasts among the sister groups Holasteroida and Spatangoida, their paraphyletic stem group Disasteroida, and the more inclusive clade, the superorder Atelostomata. A 38-dimensional landmark-based morphospace representing test architecture was used to describe morphological evolution in terms of total variance and total range. Discordances between disparity and diversity were evident and were expressed both as deceleration in morphological diversification in all groups and as disproportionately higher disparity early in the histories of the Atelostomata, Holasteroida, and Spatangoida. The finding that the early atelostomate disparity peak coincides with the origin of the orders Holasteroida and Spatangoida lends support to the perception of orders as semi-independent entities in the biological hierarchy and as meaningful proxies for morphological distinctness. A comparison of holasteroid and spatangoid responses to the end-Cretaceous mass extinction revealed morphological selectivity. Paleocene spatangoid survivors showed no change in disparity relative to the Campanian-Maastrichtian sample, suggesting nonselectivity. Holasteroids suffered a pronounced loss in disparity (despite a rather high Late Cretaceous level of disparity), indicating morphological selectivity of extinction. Partitioning of disparity into plastral and nonplastral components, reflecting different degrees of developmental entrenchment and functionality, suggests that the origin of holasteroids and spatangoids is more consistent with an exploration of the developmental flexibility of nonplastral constructions than with uniform ecospace occupation. Within groups, several patterns were also most consistent with intrinsic controls. For plastral landmarks, there is an apparent increase in developmental modularity and decrease in developmental constraint from disasteroids to holasteroids and spatangoids. For nonplastral landmarks, no substantial change in disparity was observed from disasteroids to holasteroids and spatangoids, suggesting the maintenance of a developmental constraint despite the passage of time and ecological differentiation. More generally, this study suggests that certain topologies of disparity and evolutionary mechanisms potentially characteristic of the lower Paleozoic radiations of higher taxa (e.g., developmental flexibility) need not be confined to any given time period or hierarchical level.
The fossil record of insects documents a high proportion of modern higher-level taxa (67% for fam... more The fossil record of insects documents a high proportion of modern higher-level taxa (67% for families), although this capture rate drops off considerably for lower-level taxa. This record is Lagerstätten-driven, and is deployed by complementary, parallel body-and trace-fossil components that reveal a wealth of taxonomic and ecological detail. A family-level analysis of this record shows that past insect diversity is governed by low origination and extinction rates, both decreasing toward the Recent. This feature, in addition to prolonged taxal durations, has conferred on insects significant immunity from extinction. Nevertheless, the most profound event in insect history, the end-Permian extinction, decimated the Paleozoic Insect Fauna but allowed survival of lineages that gave rise to the Modern Insect Fauna of the Mesozoic and Cenozoic. Past insect ecomorphologic disparity can be documented as feeding attributes from the traceand body-fossil records. Three such attributes are assessed in the insect fossil record: mouthpart class, functional feeding group, and dietary guild, which collectively are divided into 74 distinctive categories. A plot of durations of these categories disclose a distinct trend of
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Papers by Gunther Eble