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Bhart-anjan S. Bhullar - One of the best experts on this subject based on the ideXlab platform.
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Evolutionary origin of the turtle skull
Nature, 2015Co-Authors: Gaberiel Bever, Tyler R. Lyson, Daniel J Field, Bhart-anjan S. BhullarAbstract:Computed tomography and phylogenetic analysis of the Eunotosaurus africanus skull suggests that not only is Eunotosaurus an early relative of the group that eventually evolved into turtles, but that it is also a diapsid caught in the act of evolving towards a secondarily anapsid state. Transitional fossils informing the origin of turtles are among the most sought-after discoveries in palaeontology^ 1 , 2 , 3 , 4 , 5 . Despite strong genomic evidence indicating that turtles evolved from within the diapsid radiation (which includes all other living reptiles^ 6 , 7 ), evidence of the inferred transformation between an ancestral turtle with an open, diapsid skull to the closed, anapsid condition of modern turtles remains elusive. Here we use high-resolution computed tomography and a novel character/taxon matrix to study the skull of Eunotosaurus africanus , a 260-million-year-old fossil reptile from the Karoo Basin of South Africa, whose distinctive postcranial skeleton shares many unique features with the shelled body plan of turtles^ 2 , 3 , 4 . Scepticism regarding the status of Eunotosaurus as the earliest stem turtle arises from the possibility that these shell-related features are the products of evolutionary convergence. Our phylogenetic analyses indicate strong cranial support for Eunotosaurus as a critical transitional form in turtle evolution, thus fortifying a 40-million-year extension to the turtle stem and moving the ecological context of its origin back onto land^ 8 , 9 . Furthermore, we find unexpected evidence that Eunotosaurus is a diapsid reptile in the process of becoming secondarily anapsid. This is important because categorizing the skull based on the number of openings in the complex of Dermal Bone covering the adductor chamber has long held sway in amniote systematics^ 10 , and still represents a common organizational scheme for teaching the evolutionary history of the group. These discoveries allow us to articulate a detailed and testable hypothesis of fenestral closure along the turtle stem. Our results suggest that Eunotosaurus represents a crucially important link in a chain that will eventually lead to consilience in reptile systematics, paving the way for synthetic studies of amniote evolution and development. The evolution of the early reptiles is a complicated story and one particular event — the inferred transformation between an ancestral turtle with a diapsid skull (with openings in the skull behind each eye) to the closed, anapsid condition of modern turtles — has remained elusive in the fossil record. Eunotosaurus africanus is an unusual reptile that lived 260 million years ago in what is now South Africa. Its oddities include flared and expanded ribs, which some have suggested represent the early stirrings of testudinates (turtles and tortoises). Computed tomography and phylogenetic analysis of the E. africanus skull now suggests that not only is Eunotosaurus an early relative of the group, but that it is a diapsid caught in the act of evolving towards a secondarily anapsid state.
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Evolutionary origin of the turtle skull
Nature, 2015Co-Authors: Gaberiel Bever, Tyler R. Lyson, Daniel J Field, Bhart-anjan S. BhullarAbstract:Transitional fossils informing the origin of turtles are among the most sought-after discoveries in palaeontology. Despite strong genomic evidence indicating that turtles evolved from within the diapsid radiation (which includes all other living reptiles), evidence of the inferred transformation between an ancestral turtle with an open, diapsid skull to the closed, anapsid condition of modern turtles remains elusive. Here we use high-resolution computed tomography and a novel character/taxon matrix to study the skull of Eunotosaurus africanus, a 260-million-year-old fossil reptile from the Karoo Basin of South Africa, whose distinctive postcranial skeleton shares many unique features with the shelled body plan of turtles. Scepticism regarding the status of Eunotosaurus as the earliest stem turtle arises from the possibility that these shell-related features are the products of evolutionary convergence. Our phylogenetic analyses indicate strong cranial support for Eunotosaurus as a critical transitional form in turtle evolution, thus fortifying a 40-million-year extension to the turtle stem and moving the ecological context of its origin back onto land. Furthermore, we find unexpected evidence that Eunotosaurus is a diapsid reptile in the process of becoming secondarily anapsid. This is important because categorizing the skull based on the number of openings in the complex of Dermal Bone covering the adductor chamber has long held sway in amniote systematics, and still represents a common organizational scheme for teaching the evolutionary history of the group. These discoveries allow us to articulate a detailed and testable hypothesis of fenestral closure along the turtle stem. Our results suggest that Eunotosaurus represents a crucially important link in a chain that will eventually lead to consilience in reptile systematics, paving the way for synthetic studies of amniote evolution and development.
Zerina Johanson - One of the best experts on this subject based on the ideXlab platform.
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Embryonic development of fin spines in Callorhinchus milii (Holocephali); implications for chondrichthyan fin spine evolution
Evolution & development, 2014Co-Authors: Anna Jerve, Zerina Johanson, Per Ahlberg, Catherine A. BoisvertAbstract:Fin spines are commonly known from fossil gnathostomes (jawed vertebrates) and are usually associated with paired and unpaired fins. They are less common among extant gnathostomes, being restricted to the median fins of certain chondrichthyans (cartilaginous fish), including chimaerids (elephant sharks) and neoselachians (sharks, skates, and rays). Fin spine growth is of great interest and relevance but few studies have considered their evolution and development. We investigated the development of the fin spine of the chimaerid Callorhinchus milii using stained histological sections from a series of larval, hatchling, and adult individuals. The lamellar trunk dentine of the Callorhinchus spine first condenses within the mesenchyme, rather than at the contact surface between mesenchyme and epithelium, in a manner more comparable to Dermal Bone formation than to normal odontode development. Trabecular dentine forms a small component of the spine under the keel; it is covered externally with a thin layer of lamellar trunk dentine, which is difficult to distinguish in sectioned adult spines. We suggest that the distinctive characteristics of the trunk dentine may reflect an origin through co-option of developmental processes involved in Dermal Bone formation. Comparison with extant Squalus and a range of fossil chondrichthyans shows that Callorhinchus is more representative than Squalus of generalized chondrichthyan fin-spine architecture, highlighting its value as a developmental model organism.
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Origins of Bone repair in the armour of fossil fish: response to a deep wound by cells depositing dentine instead of Dermal Bone
Biology Letters, 2013Co-Authors: Zerina Johanson, E. Mark-kurik, Peter Pilecki, Anton Kearsley, M. Smith, C HowardAbstract:The outer armour of fossil jawless fishes (Heterostraci) is, predominantly, a Bone with a superficial ornament of dentine tubercles surrounded by pores leading to flask-shaped crypts (ampullae). However, despite the extensive Bone present in these early Dermal skeletons, damage was repaired almost exclusively with dentine. Consolidation of Bone, by dentine invading and filling the vascular spaces, was previously recognized in Psammolepis and other heterostracans but was associated with ageing and Dermal shield wear (reparative). Here, we describe wound repair by deposition of dentine directly onto a bony scaffold of fragmented Bone. An extensive wound response occurred from massive deposition of dentine (reactionary), traced from tubercle pulp cavities and surrounding ampullae. These structures may provide the cells to make reparative and reactionary dentine, as in mammalian teeth today in response to stimuli (functional wear or damage). We suggest in Psammolepis, repair involved mobilization of these cells in response to a local stimulatory mechanism, for example, predator damage. By comparison, almost no new Bone is detected in repair of the Psammolepis shield. Dentine infilling Bone vascular tissue spaces of both abraded dentine and wounded Bone suggests that recruitment of this process has been evolutionarily conserved over 380 Myr and precedes osteogenic skeletal repair.
Gaberiel Bever - One of the best experts on this subject based on the ideXlab platform.
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Evolutionary origin of the turtle skull
Nature, 2015Co-Authors: Gaberiel Bever, Tyler R. Lyson, Daniel J Field, Bhart-anjan S. BhullarAbstract:Computed tomography and phylogenetic analysis of the Eunotosaurus africanus skull suggests that not only is Eunotosaurus an early relative of the group that eventually evolved into turtles, but that it is also a diapsid caught in the act of evolving towards a secondarily anapsid state. Transitional fossils informing the origin of turtles are among the most sought-after discoveries in palaeontology^ 1 , 2 , 3 , 4 , 5 . Despite strong genomic evidence indicating that turtles evolved from within the diapsid radiation (which includes all other living reptiles^ 6 , 7 ), evidence of the inferred transformation between an ancestral turtle with an open, diapsid skull to the closed, anapsid condition of modern turtles remains elusive. Here we use high-resolution computed tomography and a novel character/taxon matrix to study the skull of Eunotosaurus africanus , a 260-million-year-old fossil reptile from the Karoo Basin of South Africa, whose distinctive postcranial skeleton shares many unique features with the shelled body plan of turtles^ 2 , 3 , 4 . Scepticism regarding the status of Eunotosaurus as the earliest stem turtle arises from the possibility that these shell-related features are the products of evolutionary convergence. Our phylogenetic analyses indicate strong cranial support for Eunotosaurus as a critical transitional form in turtle evolution, thus fortifying a 40-million-year extension to the turtle stem and moving the ecological context of its origin back onto land^ 8 , 9 . Furthermore, we find unexpected evidence that Eunotosaurus is a diapsid reptile in the process of becoming secondarily anapsid. This is important because categorizing the skull based on the number of openings in the complex of Dermal Bone covering the adductor chamber has long held sway in amniote systematics^ 10 , and still represents a common organizational scheme for teaching the evolutionary history of the group. These discoveries allow us to articulate a detailed and testable hypothesis of fenestral closure along the turtle stem. Our results suggest that Eunotosaurus represents a crucially important link in a chain that will eventually lead to consilience in reptile systematics, paving the way for synthetic studies of amniote evolution and development. The evolution of the early reptiles is a complicated story and one particular event — the inferred transformation between an ancestral turtle with a diapsid skull (with openings in the skull behind each eye) to the closed, anapsid condition of modern turtles — has remained elusive in the fossil record. Eunotosaurus africanus is an unusual reptile that lived 260 million years ago in what is now South Africa. Its oddities include flared and expanded ribs, which some have suggested represent the early stirrings of testudinates (turtles and tortoises). Computed tomography and phylogenetic analysis of the E. africanus skull now suggests that not only is Eunotosaurus an early relative of the group, but that it is a diapsid caught in the act of evolving towards a secondarily anapsid state.
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Evolutionary origin of the turtle skull
Nature, 2015Co-Authors: Gaberiel Bever, Tyler R. Lyson, Daniel J Field, Bhart-anjan S. BhullarAbstract:Transitional fossils informing the origin of turtles are among the most sought-after discoveries in palaeontology. Despite strong genomic evidence indicating that turtles evolved from within the diapsid radiation (which includes all other living reptiles), evidence of the inferred transformation between an ancestral turtle with an open, diapsid skull to the closed, anapsid condition of modern turtles remains elusive. Here we use high-resolution computed tomography and a novel character/taxon matrix to study the skull of Eunotosaurus africanus, a 260-million-year-old fossil reptile from the Karoo Basin of South Africa, whose distinctive postcranial skeleton shares many unique features with the shelled body plan of turtles. Scepticism regarding the status of Eunotosaurus as the earliest stem turtle arises from the possibility that these shell-related features are the products of evolutionary convergence. Our phylogenetic analyses indicate strong cranial support for Eunotosaurus as a critical transitional form in turtle evolution, thus fortifying a 40-million-year extension to the turtle stem and moving the ecological context of its origin back onto land. Furthermore, we find unexpected evidence that Eunotosaurus is a diapsid reptile in the process of becoming secondarily anapsid. This is important because categorizing the skull based on the number of openings in the complex of Dermal Bone covering the adductor chamber has long held sway in amniote systematics, and still represents a common organizational scheme for teaching the evolutionary history of the group. These discoveries allow us to articulate a detailed and testable hypothesis of fenestral closure along the turtle stem. Our results suggest that Eunotosaurus represents a crucially important link in a chain that will eventually lead to consilience in reptile systematics, paving the way for synthetic studies of amniote evolution and development.
C Howard - One of the best experts on this subject based on the ideXlab platform.
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Origins of Bone repair in the armour of fossil fish: response to a deep wound by cells depositing dentine instead of Dermal Bone
Biology Letters, 2013Co-Authors: Zerina Johanson, E. Mark-kurik, Peter Pilecki, Anton Kearsley, M. Smith, C HowardAbstract:The outer armour of fossil jawless fishes (Heterostraci) is, predominantly, a Bone with a superficial ornament of dentine tubercles surrounded by pores leading to flask-shaped crypts (ampullae). However, despite the extensive Bone present in these early Dermal skeletons, damage was repaired almost exclusively with dentine. Consolidation of Bone, by dentine invading and filling the vascular spaces, was previously recognized in Psammolepis and other heterostracans but was associated with ageing and Dermal shield wear (reparative). Here, we describe wound repair by deposition of dentine directly onto a bony scaffold of fragmented Bone. An extensive wound response occurred from massive deposition of dentine (reactionary), traced from tubercle pulp cavities and surrounding ampullae. These structures may provide the cells to make reparative and reactionary dentine, as in mammalian teeth today in response to stimuli (functional wear or damage). We suggest in Psammolepis, repair involved mobilization of these cells in response to a local stimulatory mechanism, for example, predator damage. By comparison, almost no new Bone is detected in repair of the Psammolepis shield. Dentine infilling Bone vascular tissue spaces of both abraded dentine and wounded Bone suggests that recruitment of this process has been evolutionarily conserved over 380 Myr and precedes osteogenic skeletal repair.
Hugues Portier - One of the best experts on this subject based on the ideXlab platform.
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Intense Bone fluorescence reveals hidden patterns in pumpkin toadlets.
Scientific reports, 2019Co-Authors: Sandra Goutte, Matthew J. Mason, Marta M. Antoniazzi, Carlos Jared, Didier Merle, Lilian Cazes, Luís Felipe Toledo, Hanane El-hafci, Stephane Pallu, Hugues PortierAbstract:The phenomenon of fluorescence can be used by animals to change effective colouration or patterning, potentially to serve functions including intra- and interspecific signalling. Initially believed to be restricted to marine animals, fluorescent colours are now being described in an increasing number of terrestrial species. Here, we describe unique, highly fluorescent patterns in two species of pumpkin toadlets (Brachycephalus ephippium and B. pitanga). We establish that the origin of the fluorescence lies in the Dermal Bone of the head and back, visible through a particularly thin skin. By comparing them to those of the closely related species Ischnocnema parva, we demonstrate that pumpkin toadlets’ Bones are exceptionally fluorescent. We characterize the luminescence properties of the toadlets’ Bones and discuss the potential function of fluorescent patterns in natural lighting conditions.