Hans Larsson - Academia.edu (original) (raw)
Papers by Hans Larsson
Microscopy and Microanalysis, 2007
... M. de Boef* and HCE Larsson* * Redpath Museum, McGill University, 859 Sherbrooke St West, Mon... more ... M. de Boef* and HCE Larsson* * Redpath Museum, McGill University, 859 Sherbrooke St West, Montreal, QC, H3A 2K6, Canada ... Page 2. [2] R. Reid, in Encyclopedia of Dinosaurs, P. Currie and K. Padian, Eds. Academic Press, San Diego (1997) 329 [3] Scion Corporation. ...
The Journal of experimental zoology, Jan 15, 2002
The issue of the homology of bird fingers with those of pentadactyl amniotes has been a topic of ... more The issue of the homology of bird fingers with those of pentadactyl amniotes has been a topic of contention for nearly 200 years. Data from the fossil record and phylogenetic systematics ascribe bird digit homologies to digits I, II, and III of pentadactyl amniotes while embryological evidence supports digital homologies of II, III, and IV. Using a molecular marker specific for condensation competent mesenchymal cells, we describe a pentadactyl arrangement of prechondrogenic digital anlagen in the wings of stage 29 chick embryos. Only the middle three anlagen develop into mature fingers. This pattern supports the hypothesis that bird fingers develop from digital anlagen II, III, and IV of pentadactylous amniotes. In addition, this result rejects a model assuming a shift in the primary axis in bird digit development and shows that a prechondrogenic digital anlage has been maintained in the bird lineage for at least 220 million years since the last known pentadactylous ancestor of the...
Science (New York, N.Y.), Jan 13, 1998
Fossils discovered in Lower Cretaceous (Aptian) rocks in the Tenere Desert of central Niger provi... more Fossils discovered in Lower Cretaceous (Aptian) rocks in the Tenere Desert of central Niger provide new information about spinosaurids, a peculiar group of piscivorous theropod dinosaurs. The remains, which represent a new genus and species, reveal the extreme elongation and transverse compression of the spinosaurid snout. The postcranial bones include blade-shaped vertebral spines that form a low sail over the hips. Phylogenetic analysis suggests that the enlarged thumb claw and robust forelimb evolved during the Jurassic, before the elongated snout and other fish-eating adaptations in the skull. The close phylogenetic relationship between the new African spinosaurid and Baryonyx from Europe provides evidence of dispersal across the Tethys seaway during the Early Cretaceous.
Systematic biology, 2015
Likelihood-based methods are commonplace in phylogenetic systematics. Although much effort has be... more Likelihood-based methods are commonplace in phylogenetic systematics. Although much effort has been directed toward likelihood-based models for molecular data, comparatively less work has addressed models for discrete morphological character (DMC) data. Among-character rate variation (ACRV) may confound phylogenetic analysis, but there have been few analyses of the magnitude and distribution of rate heterogeneity among DMCs. Using 76 data sets covering a range of plants, invertebrate, and vertebrate animals, we used a modified version of MrBayes to test equal, gamma-distributed and lognormally distributed models of ACRV, integrating across phylogenetic uncertainty using Bayesian model selection. We found that in approximately 80% of data sets, unequal-rates models outperformed equal-rates models, especially among larger data sets. Moreover, although most data sets were equivocal, more data sets favored the lognormal rate distribution relative to the gamma rate distribution, lending ...
Nature, 2014
The origin of tetrapods from their fish antecedents, approximately 400 million years ago, was cou... more The origin of tetrapods from their fish antecedents, approximately 400 million years ago, was coupled with the origin of terrestrial locomotion and the evolution of supporting limbs. Polypterus is a member of the basal-most group of ray-finned fish (actinopterygians) and has many plesiomorphic morphologies that are comparable to elpistostegid fishes, which are stem tetrapods. Polypterus therefore serves as an extant analogue of stem tetrapods, allowing us to examine how developmental plasticity affects the 'terrestrialization' of fish. We measured the developmental plasticity of anatomical and biomechanical responses in Polypterus reared on land. Here we show the remarkable correspondence between the environmentally induced phenotypes of terrestrialized Polypterus and the ancient anatomical changes in stem tetrapods, and we provide insight into stem tetrapod behavioural evolution. Our results raise the possibility that environmentally induced developmental plasticity facilitated the origin of the terrestrial traits that led to tetrapods.
Zoological Journal of the Linnean Society, 2007
The evolutionary history of Mesozoic crocodyliform reptiles from Africa is still poorly understoo... more The evolutionary history of Mesozoic crocodyliform reptiles from Africa is still poorly understood. Most of the relatively few forms known to date are Cretaceous in age. Stromer (1914, 1925, 1933, 1936) described a series of crocodyliform taxa from the Upper Cretaceous (Cenomanian) of the Bahariya Oasis in the Western Desert of Egypt. Most noteworthy among these are Libycosuchus brevirostris (Stromer, 1914; Buffetaut, 1976b) and the huge,'duck-billed'Stomatosuchus inermis (Stromer, 1925, 1936; the holotype was ...
ZooKeys, 2009
This work is licensed under a Creative Commons Attribution 3.0 License.
Systematic Biology, 2008
Developmental biology often yields data in a temporal context. Temporal data in phylogenetic syst... more Developmental biology often yields data in a temporal context. Temporal data in phylogenetic systematics has important uses in the field of evolutionary developmental biology and, in general, comparative biology. The evolution of temporal sequences, specifically developmental sequences, has proven difficult to examine due to the highly variable temporal progression of development. Issues concerning the analysis of temporal sequences and problems with current methods of analysis are discussed. We present here an algorithm to infer ancestral temporal sequences, quantify sequence heterochronies, and estimate pseudoreplicate consensus support for sequence changes using Parsimov-based genetic inference [PGi]. Real temporal developmental sequence data sets are used to compare PGi with currently used approaches, and PGi is shown to be the most efficient, accurate, and practical method to examine biological data and infer ancestral states on a phylogeny. The method is also expandable to address further issues in developmental evolution, namely modularity. [Developmental biology; developmental sequences; evolutionary developmental biology; event-pairs; heterochrony; phylogenetics; sequence heterochrony.] 378 by guest on May 17, 2016 http://sysbio.oxfordjournals.org/ Downloaded from a Tree length is based on the shortest optimization of event-pairs (either ACCTRAN or DELTRAN). b Ancestral sequences with simultaneity excluded (see text). c Forelimb events only.
Science, 1999
These results demonstrate the ability of present-day ultrashort-laser-driven x-ray sources to stu... more These results demonstrate the ability of present-day ultrashort-laser-driven x-ray sources to study transiently generated extreme states of matter. Although further studies of important outstanding problems related to the structure of superheated solids and transient liquid phases (1, 2) are natural extensions of this work, foreseeable improvements already in development in tabletop laser-driven plasma sources should expand the scope of ultrafast x-ray diffraction to the dynamic study of many other ultrafast processes in physics, chemistry, and biology, including the ultrafast atomic and molecular dynamics by which other solid-state processes and chemical and biochemical reactions take place. 454 (1983); Phys. Rev. Lett. 51, 900 (1983). 16. H.
PLoS ONE, 2008
Background: Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dor... more Background: Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dorsally-anchored lung and several compliant air sacs that operate as bellows, driving inspired air through the lung. Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence.
Paleobiology, 2009
The evolution of powered flight has traditionally been associated with the origin of birds, the m... more The evolution of powered flight has traditionally been associated with the origin of birds, the most successful clade of modern tetrapods, as exemplified by the nearly 10,000 species alive today. Flight requires a suite of morphological changes to skeletal anatomy to create a light yet resistant framework for an airfoil and advanced nervous motor control. Given the level of morphological integration necessary to create a suitable aerofoil, the origin of flight may be intuitively assumed to be coupled with high evolutionary rates of wing-related morphologies. Here we show that the origin of birds is associated with little or no evolutionary change to the skeletal anatomy of the forelimb, and thus Archaeopteryx is unlikely to be the ''Rosetta Stone'' for the origin of flight it was once believed to be. Using comparative statistics and time-series analyses on a data set constructed from all known forelimb skeletal anatomy of non-avian theropod dinosaurs and a diverse assemblage of early birds, we demonstrate three focused peaks of rapid forelimb evolution at Tetanurae, Eumaniraptora, and Ornithothoraces. The peaks are not associated with missing data and remain stable under multiple perturbations to the phylogenetic arrangements. Different regions of the forelimbs are demonstrated to have undergone asynchronous periods of evolutionary peaks and stasis. Our results evince a more complicated stepwise mode of forelimb evolution before and after the origin of Aves than previously supposed.
Journal of Vertebrate Paleontology, 1999
Extant crocodylians possess a remarkably uniform dental morphology, typified by simple, unserrate... more Extant crocodylians possess a remarkably uniform dental morphology, typified by simple, unserrated and conical teeth (Wettstein, 1937; Edmund, 1969; Langston, 1973). The limited deviation from this morphology observed in most fossil crocodyliforms has prompted suggestions of ecological and functional homogeneity throughout the group's 200 million year history (but see Colbert [1946] for a notable exception). Recent paleontological finds from the Mesozoic Era, however, have demonstrated a heretofore unsuspected range of ...
Journal of Vertebrate Paleontology, 2005
We describe hindlimb elements of the large captorhinid Moradisaurus grandis (Reptilia: Captorhini... more We describe hindlimb elements of the large captorhinid Moradisaurus grandis (Reptilia: Captorhinidae) recently collected from the Upper Permian Moradi Formation of north-central Niger. This description is based primarily on an associated partial skeleton comprising a hemimandible, vertebral column, and partial left and nearly complete right hindlimb. Additionally, we report on a well-preserved, articulated, and essentially complete juvenile pes that provides important information on the ontogeny of the captorhinid tarsus. The hindlimb of Moradisaurus is stout and more massively built than in any other known captorhinid. The femur displays several features interpreted as adaptations to the demands of large body size, and the tibia and fibula have short, wide shafts and hypertrophied condyles and epicondyles. The astragalus is very derived, possessing two accessory ossifications and a relatively horizontal tibial articulation, indicating that the tibia was held more vertically than in other captorhinids. The calcaneum is co-ossified with distal tarsal five. The juvenile pes indicates that the captorhinid centrale arose from the fusion of two ossification centers, and that the captorhinid astragalus arose from the fusion of at least three ossification centers.
Canadian Journal of Earth Sciences, 2007
... St. West, Montréal, QC H3A 2K6, Canada. N. Rybczynski. Canadian Museum of Nature, PO Box 3443... more ... St. West, Montréal, QC H3A 2K6, Canada. N. Rybczynski. Canadian Museum of Nature, PO Box 3443, Station D, Ottawa, ON K1P 6P4, Canada. 1Corresponding author (e-mail: matthew.vavrek@mcgill.ca). Page 2. Hills 1988 ...
Journal of anatomy, 2015
Polypterus, a member of the most primitive living group of ray-finned fishes, has demonstrated th... more Polypterus, a member of the most primitive living group of ray-finned fishes, has demonstrated the ability to perform fin-assisted terrestrial locomotion, a behavior that indicates a complex pectoral musculoskeletal system. Review of the literature reveals that many aspects of the pectoral muscular anatomy of Polypterus are still unclear, with a number of conflicting descriptions. We provide a new interpretation of the pectoral musculature using soft tissue-enhanced microCT scanning and gross anatomical dissection. The results demonstrate a complex musculature, with six independent muscles crossing the glenoid-fin joint. Comparisons with other bony-fish (Osteichthyes), including both ray-finned (Actinopterygii) and lobed-fin (Sarcopterygii) fish, indicate the presence of novel muscles within Polypterus: coracometapterygialis I+II and the zonopropterygialis medialis. Examination of these muscular additions in the context of osteichthyan phylogeny indicates that this represents a prev...
Journal of experimental zoology. Part B, Molecular and developmental evolution, Jan 15, 2003
Microscopy and Microanalysis, 2007
... M. de Boef* and HCE Larsson* * Redpath Museum, McGill University, 859 Sherbrooke St West, Mon... more ... M. de Boef* and HCE Larsson* * Redpath Museum, McGill University, 859 Sherbrooke St West, Montreal, QC, H3A 2K6, Canada ... Page 2. [2] R. Reid, in Encyclopedia of Dinosaurs, P. Currie and K. Padian, Eds. Academic Press, San Diego (1997) 329 [3] Scion Corporation. ...
The Journal of experimental zoology, Jan 15, 2002
The issue of the homology of bird fingers with those of pentadactyl amniotes has been a topic of ... more The issue of the homology of bird fingers with those of pentadactyl amniotes has been a topic of contention for nearly 200 years. Data from the fossil record and phylogenetic systematics ascribe bird digit homologies to digits I, II, and III of pentadactyl amniotes while embryological evidence supports digital homologies of II, III, and IV. Using a molecular marker specific for condensation competent mesenchymal cells, we describe a pentadactyl arrangement of prechondrogenic digital anlagen in the wings of stage 29 chick embryos. Only the middle three anlagen develop into mature fingers. This pattern supports the hypothesis that bird fingers develop from digital anlagen II, III, and IV of pentadactylous amniotes. In addition, this result rejects a model assuming a shift in the primary axis in bird digit development and shows that a prechondrogenic digital anlage has been maintained in the bird lineage for at least 220 million years since the last known pentadactylous ancestor of the...
Science (New York, N.Y.), Jan 13, 1998
Fossils discovered in Lower Cretaceous (Aptian) rocks in the Tenere Desert of central Niger provi... more Fossils discovered in Lower Cretaceous (Aptian) rocks in the Tenere Desert of central Niger provide new information about spinosaurids, a peculiar group of piscivorous theropod dinosaurs. The remains, which represent a new genus and species, reveal the extreme elongation and transverse compression of the spinosaurid snout. The postcranial bones include blade-shaped vertebral spines that form a low sail over the hips. Phylogenetic analysis suggests that the enlarged thumb claw and robust forelimb evolved during the Jurassic, before the elongated snout and other fish-eating adaptations in the skull. The close phylogenetic relationship between the new African spinosaurid and Baryonyx from Europe provides evidence of dispersal across the Tethys seaway during the Early Cretaceous.
Systematic biology, 2015
Likelihood-based methods are commonplace in phylogenetic systematics. Although much effort has be... more Likelihood-based methods are commonplace in phylogenetic systematics. Although much effort has been directed toward likelihood-based models for molecular data, comparatively less work has addressed models for discrete morphological character (DMC) data. Among-character rate variation (ACRV) may confound phylogenetic analysis, but there have been few analyses of the magnitude and distribution of rate heterogeneity among DMCs. Using 76 data sets covering a range of plants, invertebrate, and vertebrate animals, we used a modified version of MrBayes to test equal, gamma-distributed and lognormally distributed models of ACRV, integrating across phylogenetic uncertainty using Bayesian model selection. We found that in approximately 80% of data sets, unequal-rates models outperformed equal-rates models, especially among larger data sets. Moreover, although most data sets were equivocal, more data sets favored the lognormal rate distribution relative to the gamma rate distribution, lending ...
Nature, 2014
The origin of tetrapods from their fish antecedents, approximately 400 million years ago, was cou... more The origin of tetrapods from their fish antecedents, approximately 400 million years ago, was coupled with the origin of terrestrial locomotion and the evolution of supporting limbs. Polypterus is a member of the basal-most group of ray-finned fish (actinopterygians) and has many plesiomorphic morphologies that are comparable to elpistostegid fishes, which are stem tetrapods. Polypterus therefore serves as an extant analogue of stem tetrapods, allowing us to examine how developmental plasticity affects the 'terrestrialization' of fish. We measured the developmental plasticity of anatomical and biomechanical responses in Polypterus reared on land. Here we show the remarkable correspondence between the environmentally induced phenotypes of terrestrialized Polypterus and the ancient anatomical changes in stem tetrapods, and we provide insight into stem tetrapod behavioural evolution. Our results raise the possibility that environmentally induced developmental plasticity facilitated the origin of the terrestrial traits that led to tetrapods.
Zoological Journal of the Linnean Society, 2007
The evolutionary history of Mesozoic crocodyliform reptiles from Africa is still poorly understoo... more The evolutionary history of Mesozoic crocodyliform reptiles from Africa is still poorly understood. Most of the relatively few forms known to date are Cretaceous in age. Stromer (1914, 1925, 1933, 1936) described a series of crocodyliform taxa from the Upper Cretaceous (Cenomanian) of the Bahariya Oasis in the Western Desert of Egypt. Most noteworthy among these are Libycosuchus brevirostris (Stromer, 1914; Buffetaut, 1976b) and the huge,'duck-billed'Stomatosuchus inermis (Stromer, 1925, 1936; the holotype was ...
ZooKeys, 2009
This work is licensed under a Creative Commons Attribution 3.0 License.
Systematic Biology, 2008
Developmental biology often yields data in a temporal context. Temporal data in phylogenetic syst... more Developmental biology often yields data in a temporal context. Temporal data in phylogenetic systematics has important uses in the field of evolutionary developmental biology and, in general, comparative biology. The evolution of temporal sequences, specifically developmental sequences, has proven difficult to examine due to the highly variable temporal progression of development. Issues concerning the analysis of temporal sequences and problems with current methods of analysis are discussed. We present here an algorithm to infer ancestral temporal sequences, quantify sequence heterochronies, and estimate pseudoreplicate consensus support for sequence changes using Parsimov-based genetic inference [PGi]. Real temporal developmental sequence data sets are used to compare PGi with currently used approaches, and PGi is shown to be the most efficient, accurate, and practical method to examine biological data and infer ancestral states on a phylogeny. The method is also expandable to address further issues in developmental evolution, namely modularity. [Developmental biology; developmental sequences; evolutionary developmental biology; event-pairs; heterochrony; phylogenetics; sequence heterochrony.] 378 by guest on May 17, 2016 http://sysbio.oxfordjournals.org/ Downloaded from a Tree length is based on the shortest optimization of event-pairs (either ACCTRAN or DELTRAN). b Ancestral sequences with simultaneity excluded (see text). c Forelimb events only.
Science, 1999
These results demonstrate the ability of present-day ultrashort-laser-driven x-ray sources to stu... more These results demonstrate the ability of present-day ultrashort-laser-driven x-ray sources to study transiently generated extreme states of matter. Although further studies of important outstanding problems related to the structure of superheated solids and transient liquid phases (1, 2) are natural extensions of this work, foreseeable improvements already in development in tabletop laser-driven plasma sources should expand the scope of ultrafast x-ray diffraction to the dynamic study of many other ultrafast processes in physics, chemistry, and biology, including the ultrafast atomic and molecular dynamics by which other solid-state processes and chemical and biochemical reactions take place. 454 (1983); Phys. Rev. Lett. 51, 900 (1983). 16. H.
PLoS ONE, 2008
Background: Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dor... more Background: Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dorsally-anchored lung and several compliant air sacs that operate as bellows, driving inspired air through the lung. Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence.
Paleobiology, 2009
The evolution of powered flight has traditionally been associated with the origin of birds, the m... more The evolution of powered flight has traditionally been associated with the origin of birds, the most successful clade of modern tetrapods, as exemplified by the nearly 10,000 species alive today. Flight requires a suite of morphological changes to skeletal anatomy to create a light yet resistant framework for an airfoil and advanced nervous motor control. Given the level of morphological integration necessary to create a suitable aerofoil, the origin of flight may be intuitively assumed to be coupled with high evolutionary rates of wing-related morphologies. Here we show that the origin of birds is associated with little or no evolutionary change to the skeletal anatomy of the forelimb, and thus Archaeopteryx is unlikely to be the ''Rosetta Stone'' for the origin of flight it was once believed to be. Using comparative statistics and time-series analyses on a data set constructed from all known forelimb skeletal anatomy of non-avian theropod dinosaurs and a diverse assemblage of early birds, we demonstrate three focused peaks of rapid forelimb evolution at Tetanurae, Eumaniraptora, and Ornithothoraces. The peaks are not associated with missing data and remain stable under multiple perturbations to the phylogenetic arrangements. Different regions of the forelimbs are demonstrated to have undergone asynchronous periods of evolutionary peaks and stasis. Our results evince a more complicated stepwise mode of forelimb evolution before and after the origin of Aves than previously supposed.
Journal of Vertebrate Paleontology, 1999
Extant crocodylians possess a remarkably uniform dental morphology, typified by simple, unserrate... more Extant crocodylians possess a remarkably uniform dental morphology, typified by simple, unserrated and conical teeth (Wettstein, 1937; Edmund, 1969; Langston, 1973). The limited deviation from this morphology observed in most fossil crocodyliforms has prompted suggestions of ecological and functional homogeneity throughout the group's 200 million year history (but see Colbert [1946] for a notable exception). Recent paleontological finds from the Mesozoic Era, however, have demonstrated a heretofore unsuspected range of ...
Journal of Vertebrate Paleontology, 2005
We describe hindlimb elements of the large captorhinid Moradisaurus grandis (Reptilia: Captorhini... more We describe hindlimb elements of the large captorhinid Moradisaurus grandis (Reptilia: Captorhinidae) recently collected from the Upper Permian Moradi Formation of north-central Niger. This description is based primarily on an associated partial skeleton comprising a hemimandible, vertebral column, and partial left and nearly complete right hindlimb. Additionally, we report on a well-preserved, articulated, and essentially complete juvenile pes that provides important information on the ontogeny of the captorhinid tarsus. The hindlimb of Moradisaurus is stout and more massively built than in any other known captorhinid. The femur displays several features interpreted as adaptations to the demands of large body size, and the tibia and fibula have short, wide shafts and hypertrophied condyles and epicondyles. The astragalus is very derived, possessing two accessory ossifications and a relatively horizontal tibial articulation, indicating that the tibia was held more vertically than in other captorhinids. The calcaneum is co-ossified with distal tarsal five. The juvenile pes indicates that the captorhinid centrale arose from the fusion of two ossification centers, and that the captorhinid astragalus arose from the fusion of at least three ossification centers.
Canadian Journal of Earth Sciences, 2007
... St. West, Montréal, QC H3A 2K6, Canada. N. Rybczynski. Canadian Museum of Nature, PO Box 3443... more ... St. West, Montréal, QC H3A 2K6, Canada. N. Rybczynski. Canadian Museum of Nature, PO Box 3443, Station D, Ottawa, ON K1P 6P4, Canada. 1Corresponding author (e-mail: matthew.vavrek@mcgill.ca). Page 2. Hills 1988 ...
Journal of anatomy, 2015
Polypterus, a member of the most primitive living group of ray-finned fishes, has demonstrated th... more Polypterus, a member of the most primitive living group of ray-finned fishes, has demonstrated the ability to perform fin-assisted terrestrial locomotion, a behavior that indicates a complex pectoral musculoskeletal system. Review of the literature reveals that many aspects of the pectoral muscular anatomy of Polypterus are still unclear, with a number of conflicting descriptions. We provide a new interpretation of the pectoral musculature using soft tissue-enhanced microCT scanning and gross anatomical dissection. The results demonstrate a complex musculature, with six independent muscles crossing the glenoid-fin joint. Comparisons with other bony-fish (Osteichthyes), including both ray-finned (Actinopterygii) and lobed-fin (Sarcopterygii) fish, indicate the presence of novel muscles within Polypterus: coracometapterygialis I+II and the zonopropterygialis medialis. Examination of these muscular additions in the context of osteichthyan phylogeny indicates that this represents a prev...
Journal of experimental zoology. Part B, Molecular and developmental evolution, Jan 15, 2003