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Susan E. Evans - One of the best experts on this subject based on the ideXlab platform.
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functional relationship between skull form and feeding mechanics in sphenodon and implications for Diapsid skull development
PLOS ONE, 2011Co-Authors: Neil Curtis, Susan E. Evans, Marc E H Jones, Paul Ohiggins, Michael J FaganAbstract:The vertebrate skull evolved to protect the brain and sense organs, but with the appearance of jaws and associated forces there was a remarkable structural diversification. This suggests that the evolution of skull form may be linked to these forces, but an important area of debate is whether bone in the skull is minimised with respect to these forces, or whether skulls are mechanically “over-designed” and constrained by phylogeny and development. Mechanical analysis of Diapsid reptile skulls could shed light on this longstanding debate. Compared to those of mammals, the skulls of many extant and extinct Diapsids comprise an open framework of fenestrae (window-like openings) separated by bony struts (e.g., lizards, tuatara, dinosaurs and crocodiles), a cranial form thought to be strongly linked to feeding forces. We investigated this link by utilising the powerful engineering approach of multibody dynamics analysis to predict the physiological forces acting on the skull of the Diapsid reptile Sphenodon. We then ran a series of structural finite element analyses to assess the correlation between bone strain and skull form. With comprehensive loading we found that the distribution of peak von Mises strains was particularly uniform throughout the skull, although specific regions were dominated by tensile strains while others were dominated by compressive strains. Our analyses suggest that the frame-like skulls of Diapsid reptiles are probably optimally formed (mechanically ideal: sufficient strength with the minimal amount of bone) with respect to functional forces; they are efficient in terms of having minimal bone volume, minimal weight, and also minimal energy demands in maintenance.
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New material of the enigmatic reptile Khurendukhosaurus (Diapsida: Choristodera) from Mongolia
Naturwissenschaften, 2009Co-Authors: Ryoko Matsumoto, Shigeru Suzuki, Khisigjav Tsogtbaatar, Susan E. EvansAbstract:New material of the enigmatic Diapsid Khurendukhosaurus is described from the Mongolian type locality, Khuren Dukh, providing additional data on the vertebral column, pelvis, and hind limb. It confirms the choristoderan status of the genus and permits a more detailed phylogenetic analysis that supports a relationship between Khurendukhosaurus and the long-necked Asian Hyphalosauridae. The existence of tall caudal neural spines implies that Khurendukhosaurus was a deep-tailed swimmer. This and the open sacral costocentral sutures suggest a primarily aquatic lifestyle.
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new material of youngina evidence of juvenile aggregation in permian Diapsid reptiles
Palaeontology, 1996Co-Authors: Rmh Smith, Susan E. EvansAbstract:An unusual specimen of Youngina. is described from a new locality in the Karoo Basin of South Africa. The locality is in the Tropidostoma Assemblage Zone (equivalent to the former Lower Cistecephalus Zone), making the specimen the oldest recorded example of this genus. It comprises an association of five immature skeletons which are fully articulated and thus provide the first clear indication of body proportions in Youngina. In addition, the material yields new information on the pectoral girdle, pelvis and foot. It is clear that Youngina, unlike many of its known relatives, was an agile, fully terrestrial animal. This conclusion is reinforced by the preservation of the young skeletons in positions which suggest group denning behaviour in response to adverse climatic conditions.
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the upper jurassic Diapsid lisboasaurus estesi a maniraptoran theropod
Palaeontology 34 (3) pp. 503-513. (1991), 1991Co-Authors: Andrew R Milner, Susan E. EvansAbstract:Lisboasaurus estesi from the Upper Jurassic of Guimarota, Portugal was first described as an anguimorph lizard. Reexamination of the holotype and referred specimens leads to the conclusion that L. estesi represents a small archosaur. Features of the dentition suggest that L. estesi belonged within the troodontid dinosaur-bird clade and, less certainly, within the Avialae (Archaeopteryx plus all later birds). It may thus be the earliest avialan. A second species in the genus, L. mitrocostatus, is based on indeterminate material and is a nomen dubium restricted to the type specimen. -from Authors
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A new lizard‐like reptile (Diapsida: Lepidosauromorpha) from the Middle Jurassic of England
Zoological Journal of the Linnean Society, 1991Co-Authors: Susan E. EvansAbstract:The Middle Jurassic (Late Bathonian) Mammal Bed at Kirtlington, Oxfordshire, has yielded a rich assemblage of small vertebrates including mammals, frogs, salamanders and small reptiles. This paper describes the skull of a new Diapsid reptile, Marmorelta oxoniensis, which was common within the fauna. The skull is gracile with large orbits and relatively long external nares. The frontals and parietals are single in the adult and almost separated on the roof of the skull by the postfrontals. The temporal region shows a mosaic of primitive and derived character states. The quadrate was firmly held to the skull by a large squamosal and a small, free, quadratojugal was retained. However, reduction of the anterior process of the quadratojugal and of the posterior process of the jugal left the lower temporal fenestra broadly open. Comparison with other Diapsids leads to the conclusion that Marmoretta was a lepidosauromorph, most probably the sister taxon of Lepidosauria.
Adam C Pritchard - One of the best experts on this subject based on the ideXlab platform.
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a tiny triassic saurian from connecticut and the early evolution of the Diapsid feeding apparatus
Nature Communications, 2018Co-Authors: Adam C Pritchard, Jacques A Gauthier, Michael Hanson, Gabriel S Bever, Bhartanjan S BhullarAbstract:Following the Permo–Triassic Extinction, large-bodied Diapsid reptiles—with a body length >1 m—rapidly expanded their ecological roles. This diversification is reflected in enormous disparity in the development of the rostrum and adductor chamber. However, it is unclear how marked the diversity of the feeding apparatus was in contemporary small-bodied Diapsids. Here we describe the remarkably small skull (2.5 cm long) of a saurian reptile, Colobops noviportensis, gen. et sp. nov., from the Triassic New Haven Arkose of Connecticut, USA. The taxon possesses an exceptionally reinforced snout and strikingly expanded supratemporal fossae for adductor musculature relative to any known Mesozoic or Recent Diapsid of similar size. Our phylogenetic analyses support C. noviportensis as an early diverging pan-archosaur. Colobops noviportensis reveals extraordinary disparity of the feeding apparatus in small-bodied early Mesozoic Diapsids, and a suite of morphologies, functionally related to a powerful bite, unknown in any small-bodied Diapsid. The Triassic fossil record is biased towards large species, obscuring the anatomical diversity of small species. Here, the authors describe a new species, Colobops noviportensis, based on a 2.5 cm-long skull with proportionally large attachments for jaw muscles, expanding the known diversity of early Diapsids.
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A tiny Triassic saurian from Connecticut and the early evolution of the Diapsid feeding apparatus.
Nature Communications, 2018Co-Authors: Adam C Pritchard, Jacques A Gauthier, Michael Hanson, Gabriel S Bever, Bhartanjan S BhullarAbstract:Following the Permo-Triassic Extinction, large-bodied Diapsid reptiles-with a body length >1 m-rapidly expanded their ecological roles. This diversification is reflected in enormous disparity in the development of the rostrum and adductor chamber. However, it is unclear how marked the diversity of the feeding apparatus was in contemporary small-bodied Diapsids. Here we describe the remarkably small skull (2.5 cm long) of a saurian reptile, Colobops noviportensis, gen. et sp. nov., from the Triassic New Haven Arkose of Connecticut, USA. The taxon possesses an exceptionally reinforced snout and strikingly expanded supratemporal fossae for adductor musculature relative to any known Mesozoic or Recent Diapsid of similar size. Our phylogenetic analyses support C. noviportensis as an early diverging pan-archosaur. Colobops noviportensis reveals extraordinary disparity of the feeding apparatus in small-bodied early Mesozoic Diapsids, and a suite of morphologies, functionally related to a powerful bite, unknown in any small-bodied Diapsid.
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a bird like skull in a triassic Diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida
Royal Society Open Science, 2017Co-Authors: Adam C Pritchard, Sterling J NesbittAbstract:The Triassic Period saw the first appearance of numerous amniote lineages (e.g. Lepidosauria, Archosauria, Mammalia) that defined Mesozoic ecosystems following the end Permian Mass Extinction, as well as the first major morphological diversification of crown-group reptiles. Unfortunately, much of our understanding of this event comes from the record of large-bodied reptiles (total body length > 1 m). Here we present a new species of drepanosaurid (small-bodied, chameleon-like Diapsids) from the Upper Triassic Chinle Formation of New Mexico. Using reconstructions of micro-computed tomography data, we reveal the three-dimensional skull osteology of this clade for the first time. The skull presents many archaic anatomical traits unknown in Triassic crown-group reptiles (e.g. absence of bony support for the external ear), whereas other traits (e.g. toothless rostrum, anteriorly directed orbits, inflated endocranium) resemble derived avian theropods. A phylogenetic analysis of Permo-Triassic Diapsids supports the hypothesis that drepanosaurs are an archaic lineage that originated in the Permian, far removed from crown-group Reptilia. The phylogenetic position of drepanosaurids indicates the presence of archaic Permian clades among Triassic small reptile assemblages and that morphological convergence produced a remarkably bird-like skull nearly 100 Myr before one is known to have emerged in Theropoda.
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extreme modification of the tetrapod forelimb in a triassic Diapsid reptile
Current Biology, 2016Co-Authors: Adam C Pritchard, Sterling J Nesbitt, Alan H Turner, Randall B Irmis, Nathan D SmithAbstract:Summary The tetrapod forelimb is one of the most versatile structures in vertebrate evolution, having been co-opted for an enormous array of functions. However, the structural relationships between the bones of the forelimb have remained largely unchanged throughout the 375 million year history of Tetrapoda, with a radius and ulna made up of elongate, paralleling shafts contacting a series of shorter carpal bones. These features are consistent across nearly all known tetrapods, suggesting that the morphospace encompassed by these taxa is limited by some sort of constraint(s). Here, we report on a series of three-dimensionally preserved fossils of the small-bodied ( Drepanosaurus , from the Chinle Formation of New Mexico, USA, which dramatically diverge from this pattern. Along with the crushed type specimen from Italy, these specimens have a flattened, crescent-shaped ulna with a long axis perpendicular to that of the radius and hyperelongate, shaft-like carpal bones contacting the ulna that are proximodistally longer than the radius. The second digit supports a massive, hooked claw. This condition has similarities to living "hook-and-pull" digging mammals and demonstrates that specialized, modern ecological roles had developed during the Triassic Period, over 200 million years ago. The forelimb bones in Drepanosaurus represent previously unknown morphologies for a tetrapod and, thus, a dramatic expansion of known tetrapod forelimb morphospace.
Bhartanjan S Bhullar - One of the best experts on this subject based on the ideXlab platform.
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a tiny triassic saurian from connecticut and the early evolution of the Diapsid feeding apparatus
Nature Communications, 2018Co-Authors: Adam C Pritchard, Jacques A Gauthier, Michael Hanson, Gabriel S Bever, Bhartanjan S BhullarAbstract:Following the Permo–Triassic Extinction, large-bodied Diapsid reptiles—with a body length >1 m—rapidly expanded their ecological roles. This diversification is reflected in enormous disparity in the development of the rostrum and adductor chamber. However, it is unclear how marked the diversity of the feeding apparatus was in contemporary small-bodied Diapsids. Here we describe the remarkably small skull (2.5 cm long) of a saurian reptile, Colobops noviportensis, gen. et sp. nov., from the Triassic New Haven Arkose of Connecticut, USA. The taxon possesses an exceptionally reinforced snout and strikingly expanded supratemporal fossae for adductor musculature relative to any known Mesozoic or Recent Diapsid of similar size. Our phylogenetic analyses support C. noviportensis as an early diverging pan-archosaur. Colobops noviportensis reveals extraordinary disparity of the feeding apparatus in small-bodied early Mesozoic Diapsids, and a suite of morphologies, functionally related to a powerful bite, unknown in any small-bodied Diapsid. The Triassic fossil record is biased towards large species, obscuring the anatomical diversity of small species. Here, the authors describe a new species, Colobops noviportensis, based on a 2.5 cm-long skull with proportionally large attachments for jaw muscles, expanding the known diversity of early Diapsids.
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A tiny Triassic saurian from Connecticut and the early evolution of the Diapsid feeding apparatus.
Nature Communications, 2018Co-Authors: Adam C Pritchard, Jacques A Gauthier, Michael Hanson, Gabriel S Bever, Bhartanjan S BhullarAbstract:Following the Permo-Triassic Extinction, large-bodied Diapsid reptiles-with a body length >1 m-rapidly expanded their ecological roles. This diversification is reflected in enormous disparity in the development of the rostrum and adductor chamber. However, it is unclear how marked the diversity of the feeding apparatus was in contemporary small-bodied Diapsids. Here we describe the remarkably small skull (2.5 cm long) of a saurian reptile, Colobops noviportensis, gen. et sp. nov., from the Triassic New Haven Arkose of Connecticut, USA. The taxon possesses an exceptionally reinforced snout and strikingly expanded supratemporal fossae for adductor musculature relative to any known Mesozoic or Recent Diapsid of similar size. Our phylogenetic analyses support C. noviportensis as an early diverging pan-archosaur. Colobops noviportensis reveals extraordinary disparity of the feeding apparatus in small-bodied early Mesozoic Diapsids, and a suite of morphologies, functionally related to a powerful bite, unknown in any small-bodied Diapsid.
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the amniote temporal roof and the Diapsid origin of the turtle skull
Zoology, 2016Co-Authors: Gaberiel Bever, Tyler R. Lyson, Daniel J. Field, Bhartanjan S BhullarAbstract:Fossils provide a glimpse into the architecturally complex origins of modern vertebrate body plans. One such origin that has been long debated is that of turtles. Although much attention has been directed toward the origin of the shell, the enigmatic evolution of the turtle skull and its anapsid temporal region has long clouded our understanding of reptile phylogeny. Two taxa, Eunotosaurus africanus and Pappochelys rosinae, were recently and independently described as long-anticipated stem turtles whose Diapsid skulls would cement the evolutionary link between turtles and other modern reptile lineages. Detailed μCT analysis of the stratigraphically older and phylogenetically stemward of the two, Eunotosaurus, provides empirical insight into changing developmental trajectories that may have produced the anapsid cranial form of modern turtles and sets the stage for more comprehensive studies of early amniote cranial evolution.
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Evolutionary origin of the turtle skull
Nature, 2015Co-Authors: Gaberiel Bever, Tyler R. Lyson, Daniel J. Field, Bhartanjan 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.
Martín D. Ezcurra - One of the best experts on this subject based on the ideXlab platform.
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A new rhynchosaur maxillary tooth plate morphotype expands the disparity of the group in the Ischigualasto Formation (Late Triassic) of Northwestern Argentina
Historical Biology, 2018Co-Authors: Adriel R. Gentil, Martín D. EzcurraAbstract:AbstractRhynchosaurs are a clade of quadruped, herbivorous stem-archosaur Diapsids restricted to the Triassic Period. The group became globally distributed and the numerically dominant tetrapods of...
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post hatchling cranial ontogeny in the early triassic Diapsid reptile proterosuchus fergusi
Journal of Anatomy, 2015Co-Authors: Martín D. Ezcurra, Richard J ButlerAbstract:: The phylogenetic position of Proterosuchus fergusi (Lower Triassic of South Africa) as one of the most basal archosauriforms means that it is critically important for understanding the successful evolutionary radiation of archosaurs during the Mesozoic. The excellent sample of the species provides a unique opportunity to understand early archosauriform ontogeny. Qualitative and quantitative analyses of cranial ontogenetic variation were conducted on an ontogenetic sequence, in which the smallest individual is 37% of the size of the largest one and osteohistological evidence suggests that four of 11 collected specimens had not reached sexual maturity. Through ontogeny the skull of Proterosuchus became proportionally taller, the infratemporal fenestra larger, and the teeth more isodont and numerous but with smaller crowns. The sequence of somatic maturity supports relatively high growth rates during early ontogeny. The skull of juvenile specimens of Proterosuchus closely resembles adults of the basal archosauromorph Prolacerta, whereas adult specimens resemble adults of more derived archosauriforms. As a result, a plausible hypothesis is that ontogenetic modification events (e.g., heterochrony) may have been key drivers of the evolution of the general shape of the skull at the base of Archosauriformes. These changes may have contributed to the occupation of a new morphospace by the clade around the Permo-Triassic boundary.
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Post‐hatchling cranial ontogeny in the Early Triassic Diapsid reptile Proterosuchus fergusi
Journal of Anatomy, 2015Co-Authors: Martín D. Ezcurra, Richard J ButlerAbstract:The phylogenetic position of Proterosuchus fergusi (Lower Triassic of South Africa) as one of the most basal archosauriforms means that it is critically important for understanding the successful evolutionary radiation of archosaurs during the Mesozoic. The excellent sample of the species provides a unique opportunity to understand early archosauriform ontogeny. Qualitative and quantitative analyses of cranial ontogenetic variation were conducted on an ontogenetic sequence, in which the smallest individual is 37% of the size of the largest one and osteohistological evidence suggests that four of 11 collected specimens had not reached sexual maturity. Through ontogeny the skull of Proterosuchus became proportionally taller, the infratemporal fenestra larger, and the teeth more isodont and numerous but with smaller crowns. The sequence of somatic maturity supports relatively high growth rates during early ontogeny. The skull of juvenile specimens of Proterosuchus closely resembles adults of the basal archosauromorph Prolacerta, whereas adult specimens resemble adults of more derived archosauriforms. As a result, a plausible hypothesis is that ontogenetic modification events (e.g., heterochrony) may have been key drivers of the evolution of the general shape of the skull at the base of Archosauriformes. These changes may have contributed to the occupation of a new morphospace by the clade around the Permo-Triassic boundary.
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a new basal archosauriform Diapsid from the lower triassic of argentina
Journal of Vertebrate Paleontology, 2010Co-Authors: Martín D. Ezcurra, Agustina Lecuona, Agustin MartinelliAbstract:ABSTRACT The best-known South American Early Triassic archosauriform belongs to a putative proterosuchid briefly reported by Jose Bonaparte in 1981, collected from the Quebrada de los Fosiles Formation (Puesto Viejo Group, Argentina). This specimen consists of well-preserved natural external molds of a partial postcranium that preserve dorsal vertebrae, osteoderms, a dorsal rib, a possible gastralium, a chevron, a humerus, an ilium, two metapodials, and an ungual. We re-describe this specimen and identify autapomorphies that allow us to recognize Koilamasuchus gonzalezdiazi, gen. et sp. nov. The presence of an iliac blade with a slightly convex dorsal margin and with a maximum length more than 3 times its maximum height places Koilamasuchus within Archosauriformes. A cladistic analysis of basal Archosauriformes positions Koilamasuchus more crownwards than Proterosuchus, Sarmatosuchus, Fugusuchus, and Osmolskina, as the sister taxon of the clade that includes Erythrosuchidae and Archosauria. Proterosuchida...
Richard J Butler - One of the best experts on this subject based on the ideXlab platform.
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post hatchling cranial ontogeny in the early triassic Diapsid reptile proterosuchus fergusi
Journal of Anatomy, 2015Co-Authors: Martín D. Ezcurra, Richard J ButlerAbstract:: The phylogenetic position of Proterosuchus fergusi (Lower Triassic of South Africa) as one of the most basal archosauriforms means that it is critically important for understanding the successful evolutionary radiation of archosaurs during the Mesozoic. The excellent sample of the species provides a unique opportunity to understand early archosauriform ontogeny. Qualitative and quantitative analyses of cranial ontogenetic variation were conducted on an ontogenetic sequence, in which the smallest individual is 37% of the size of the largest one and osteohistological evidence suggests that four of 11 collected specimens had not reached sexual maturity. Through ontogeny the skull of Proterosuchus became proportionally taller, the infratemporal fenestra larger, and the teeth more isodont and numerous but with smaller crowns. The sequence of somatic maturity supports relatively high growth rates during early ontogeny. The skull of juvenile specimens of Proterosuchus closely resembles adults of the basal archosauromorph Prolacerta, whereas adult specimens resemble adults of more derived archosauriforms. As a result, a plausible hypothesis is that ontogenetic modification events (e.g., heterochrony) may have been key drivers of the evolution of the general shape of the skull at the base of Archosauriformes. These changes may have contributed to the occupation of a new morphospace by the clade around the Permo-Triassic boundary.
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Post‐hatchling cranial ontogeny in the Early Triassic Diapsid reptile Proterosuchus fergusi
Journal of Anatomy, 2015Co-Authors: Martín D. Ezcurra, Richard J ButlerAbstract:The phylogenetic position of Proterosuchus fergusi (Lower Triassic of South Africa) as one of the most basal archosauriforms means that it is critically important for understanding the successful evolutionary radiation of archosaurs during the Mesozoic. The excellent sample of the species provides a unique opportunity to understand early archosauriform ontogeny. Qualitative and quantitative analyses of cranial ontogenetic variation were conducted on an ontogenetic sequence, in which the smallest individual is 37% of the size of the largest one and osteohistological evidence suggests that four of 11 collected specimens had not reached sexual maturity. Through ontogeny the skull of Proterosuchus became proportionally taller, the infratemporal fenestra larger, and the teeth more isodont and numerous but with smaller crowns. The sequence of somatic maturity supports relatively high growth rates during early ontogeny. The skull of juvenile specimens of Proterosuchus closely resembles adults of the basal archosauromorph Prolacerta, whereas adult specimens resemble adults of more derived archosauriforms. As a result, a plausible hypothesis is that ontogenetic modification events (e.g., heterochrony) may have been key drivers of the evolution of the general shape of the skull at the base of Archosauriformes. These changes may have contributed to the occupation of a new morphospace by the clade around the Permo-Triassic boundary.