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B. S. Rubidge - One of the best experts on this subject based on the ideXlab platform.
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Palaeoneurological clues to the evolution of defining mammalian soft tissue traits
Scientific Reports, 2016Co-Authors: J. Benoit, Paul R. Manger, B. S. RubidgeAbstract:A rich fossil record chronicles the distant origins of mammals, but the evolution of defining soft tissue characters of extant mammals, such as mammary glands and hairs is difficult to interpret because soft tissue does not readily fossilize. As many soft tissue features are derived from dermic structures, their evolution is linked to that of the nervous syutem and palaeoneurology offers opportunities to find bony correlates of these soft tissue features. Here, a CT scan study of 29 fossil skulls shows that non-mammaliaform Prozostrodontia display a retracted, fully ossified and non-ramified infraorbital canal for the infraorbital nerve, unlike more basal therapsids. The presence of a true infraorbital canal in Prozostrodontia suggests that a motile rhinarium and maxillary vibrissae were present. Also the complete ossification of the Parietal fontanelle (resulting in the loss of the Parietal Foramen) and the development of the cerebellum in Probainognathia may be pleiotropically linked to the appearance of mammary glands and having body hair coverage since these traits are all controlled by the same homeogene, Msx2, in mice. These suggest that defining soft tissue characters of mammals were already present in their forerunners some 240 to 246 mya.
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The Sixth Sense in Mammalian Forerunners: Variability of the Parietal Foramen and the Evolution of the Pineal Eye in South African Permo-Triassic Eutheriodont Therapsids
Acta Palaeontologica Polonica, 2016Co-Authors: Julien Benoit, Fernando Abdala, Paul R. Manger, B. S. RubidgeAbstract:In some extant ectotherms, the third eye (or pineal eye) is a photosensitive organ located in the Parietal Foramen on the midline of the skull roof. The pineal eye sends information regarding exposure to sunlight to the pineal complex, a region of the brain devoted to the regulation of body temperature, reproductive synchrony, and biological rhythms. The Parietal Foramen is absent in mammals but present in most of the closest extinct relatives of mammals, the Therapsida. A broad ranging survey of the occurrence and size of the Parietal Foramen in different South African therapsid taxa demonstrates that through time the Parietal Foramen tends, in a convergent manner, to become smaller and is absent more frequently in eutherocephalians (Akidnognathiidae, Whaitsiidae, and Baurioidea) and non-mammaliaform eucynodonts. Among the latter, the Probainognathia, the lineage leading to mammaliaforms, are the only one to achieve the complete loss of the Parietal Foramen. These results suggest a gradual and convergent...
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The sixth sense in mammalian forerunners: Variability of the Parietal Foramen and the evolution of the pineal eye in South African Permo-Triassic eutheriodont therapsids
Institute of Paleobiology PAS, 2016Co-Authors: Julien Benoit, Fernando Abdala, Paul R. Manger, B. S. RubidgeAbstract:In some extant ectotherms, the third eye (or pineal eye) is a photosensitive organ located in the Parietal Foramen on the midline of the skull roof. The pineal eye sends information regarding exposure to sunlight to the pineal complex, a region of the brain devoted to the regulation of body temperature, reproductive synchrony, and biological rhythms. The Parietal Foramen is absent in mammals but present in most of the closest extinct relatives of mammals, the Therapsida. A broad ranging survey of the occurrence and size of the Parietal Foramen in different South African therapsid taxa demonstrates that through time the Parietal Foramen tends, in a convergent manner, to become smaller and is absent more frequently in eutherocephalians (Akidnognathiidae, Whaitsiidae, and Baurioidea) and non-mammaliaform eucynodonts. Among the latter, the Probainognathia, the lineage leading to mammaliaforms, are the only one to achieve the complete loss of the Parietal Foramen. These results suggest a gradual and convergent loss of the photoreceptive function of the pineal organ and degeneration of the third eye. Given the role of the pineal organ to achieve fine-tuned thermoregulation in ectotherms (i.e., “cold-blooded” vertebrates), the gradual loss of the Parietal Foramen through time in the Karoo stratigraphic succession may be correlated with the transition from a mesothermic metabolism to a high metabolic rate (endothermy) in mammalian ancestry. The appearance in the eye of melanopsin-containing retinal ganglion cells replacing the photoreceptive role of the pineal eye could also have accompanied its loss
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Physiological implications of the abnormal absence of the Parietal Foramen in a late Permian cynodont (Therapsida)
The Science of Nature, 2015Co-Authors: Julien Benoit, Fernando Abdala, Paul R. Manger, Marc J. Brandt, B. S. RubidgeAbstract:The third eye (pineal eye), an organ responsible for regulating exposure to sunlight in extant ectotherms, is located in an opening on the dorsal surface of the skull, the Parietal Foramen. The Parietal Foramen is absent in extant mammals but often observed in basal therapsids, the stem-group to true mammals. Here, we report the absence of the Parietal Foramen in a specimen of Cynosaurus suppostus , a Late Permian cynodont from South Africa (SA). Comparison with Procynosuchus delaharpeae , a contemporaneous non-mammalian cynodont from SA, demonstrates that the absence of this Foramen is an abnormal condition for such a basal species. Because seasonality was marked during the Late Permian in SA, it is proposed that the third eye was functionally redundant in Cynosaurus , possibly due to the acquisition of better thermoregulation or the evolution of specialized cells in the lateral eyes to compensate for the role of the third eye.
Fernando Abdala - One of the best experts on this subject based on the ideXlab platform.
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Cranial Ontogeny of the Early Triassic Basal Cynodont Galesaurus planiceps.
Anatomical record (Hoboken N.J. : 2007), 2016Co-Authors: Sandra C. Jasinoski, Fernando AbdalaAbstract:Ontogenetic changes in the skull and mandible of thirty-one specimens of Galesaurus planiceps, a basal non-mammaliaform cynodont from the Early Triassic of South Africa, are documented. The qualitative survey indicated eight changes in the craniomandibular apparatus occurred during growth, dividing the sample into three ontogenetic stages: juvenile, subadult, and adult. Changes in the temporal region, zygomatic arch, occiput, and mandible occurred during the transition from the subadult to adult stage at a basal skull length of 90 mm. At least four morphological and allometric differences divided the adult specimens into two morphs, indicating the presence of sexual dimorphism in Galesaurus. Differences include extensive lateral flaring of the zygomatic arches in the "male" morph resulting in a more anterior orientation of the orbits, and a narrower snout in the "female". This is the first record of sexual dimorphism in a basal cynodont, and the first time it is quantitatively documented in a non-mammaliaform cynodont. An ontogenetic comparison between Galesaurus and the more derived basal cynodont Thrinaxodon revealed differences in the timing and extent of sagittal crest development. In Galesaurus, the posterior sagittal crest, located behind the Parietal Foramen, developed relatively later in ontogeny, and the anterior sagittal crest rarely formed suggesting the anterior fibres of the temporalis were less developed than in Thrinaxodon. In contrast, craniomandibular features related to the masseters became more developed during the ontogeny of Galesaurus. The development of the adductor musculature appears to be one of the main factors influencing skull growth in these basal non-mammaliaform cynodonts. Anat Rec, 300:353-381, 2017. © 2016 Wiley Periodicals, Inc.
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The Sixth Sense in Mammalian Forerunners: Variability of the Parietal Foramen and the Evolution of the Pineal Eye in South African Permo-Triassic Eutheriodont Therapsids
Acta Palaeontologica Polonica, 2016Co-Authors: Julien Benoit, Fernando Abdala, Paul R. Manger, B. S. RubidgeAbstract:In some extant ectotherms, the third eye (or pineal eye) is a photosensitive organ located in the Parietal Foramen on the midline of the skull roof. The pineal eye sends information regarding exposure to sunlight to the pineal complex, a region of the brain devoted to the regulation of body temperature, reproductive synchrony, and biological rhythms. The Parietal Foramen is absent in mammals but present in most of the closest extinct relatives of mammals, the Therapsida. A broad ranging survey of the occurrence and size of the Parietal Foramen in different South African therapsid taxa demonstrates that through time the Parietal Foramen tends, in a convergent manner, to become smaller and is absent more frequently in eutherocephalians (Akidnognathiidae, Whaitsiidae, and Baurioidea) and non-mammaliaform eucynodonts. Among the latter, the Probainognathia, the lineage leading to mammaliaforms, are the only one to achieve the complete loss of the Parietal Foramen. These results suggest a gradual and convergent...
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The sixth sense in mammalian forerunners: Variability of the Parietal Foramen and the evolution of the pineal eye in South African Permo-Triassic eutheriodont therapsids
Institute of Paleobiology PAS, 2016Co-Authors: Julien Benoit, Fernando Abdala, Paul R. Manger, B. S. RubidgeAbstract:In some extant ectotherms, the third eye (or pineal eye) is a photosensitive organ located in the Parietal Foramen on the midline of the skull roof. The pineal eye sends information regarding exposure to sunlight to the pineal complex, a region of the brain devoted to the regulation of body temperature, reproductive synchrony, and biological rhythms. The Parietal Foramen is absent in mammals but present in most of the closest extinct relatives of mammals, the Therapsida. A broad ranging survey of the occurrence and size of the Parietal Foramen in different South African therapsid taxa demonstrates that through time the Parietal Foramen tends, in a convergent manner, to become smaller and is absent more frequently in eutherocephalians (Akidnognathiidae, Whaitsiidae, and Baurioidea) and non-mammaliaform eucynodonts. Among the latter, the Probainognathia, the lineage leading to mammaliaforms, are the only one to achieve the complete loss of the Parietal Foramen. These results suggest a gradual and convergent loss of the photoreceptive function of the pineal organ and degeneration of the third eye. Given the role of the pineal organ to achieve fine-tuned thermoregulation in ectotherms (i.e., “cold-blooded” vertebrates), the gradual loss of the Parietal Foramen through time in the Karoo stratigraphic succession may be correlated with the transition from a mesothermic metabolism to a high metabolic rate (endothermy) in mammalian ancestry. The appearance in the eye of melanopsin-containing retinal ganglion cells replacing the photoreceptive role of the pineal eye could also have accompanied its loss
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Physiological implications of the abnormal absence of the Parietal Foramen in a late Permian cynodont (Therapsida)
The Science of Nature, 2015Co-Authors: Julien Benoit, Fernando Abdala, Paul R. Manger, Marc J. Brandt, B. S. RubidgeAbstract:The third eye (pineal eye), an organ responsible for regulating exposure to sunlight in extant ectotherms, is located in an opening on the dorsal surface of the skull, the Parietal Foramen. The Parietal Foramen is absent in extant mammals but often observed in basal therapsids, the stem-group to true mammals. Here, we report the absence of the Parietal Foramen in a specimen of Cynosaurus suppostus , a Late Permian cynodont from South Africa (SA). Comparison with Procynosuchus delaharpeae , a contemporaneous non-mammalian cynodont from SA, demonstrates that the absence of this Foramen is an abnormal condition for such a basal species. Because seasonality was marked during the Late Permian in SA, it is proposed that the third eye was functionally redundant in Cynosaurus , possibly due to the acquisition of better thermoregulation or the evolution of specialized cells in the lateral eyes to compensate for the role of the third eye.
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Gomphodont cynodonts of the Chañares Formation: the analysis of an ontogenetic sequence
Journal of Vertebrate Paleontology, 2000Co-Authors: Fernando Abdala, Norberto P. GianniniAbstract:Abstract A revision of gomphodont cynodonts from the Chanares Formation of Argentina, is presented. Four species in two genera: Massetognathus pascuali, M. teruggii, M. major, and Megagomphodon oligodens were originally described by Romer in 1967 and 1972. Qualitative characters proposed originally as diagnostic of the species were revised, and a bivariate analysis of allometry of 17 linear skull measurements was performed upon 31 specimens. Allometry relationships account for most of the differences among specimens. There are neither size gaps nor systematic trends across the sample. The temporal region scales with a ′positive′ allometry, whereas components of the neurocranium and muzzle show ′negative′ or isometric scaling. This results in a change from short, stocky skulls with large muzzles in small specimens, to slender skulls with small muzzles and large temporal fossae characteristic of large individuals. The reduction and ontogenetic loss of the Parietal Foramen in a cynodont is reported for the f...
Victor Hugo Reynoso - One of the best experts on this subject based on the ideXlab platform.
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huehuecuetzpalli mixtecus gen et sp nov a basal squamate reptilia from the early cretaceous of tepexi de rodriguez central mexico
Philosophical Transactions of the Royal Society B, 1998Co-Authors: Victor Hugo ReynosoAbstract:Huehuecuetzpalli mixtecus gen. et sp. nov. is characterized by a combination of characters unlike those of any of the previously described Late Jurassic or Early Cretaceous lizards. It has most of the synapomorphies common to modern squamates, but still retains primitive features rare in living taxa. Autapomorphic characters include an anteroposteriorly elongated premaxilla that results in the elongation of the snout and the apparent retraction of the external nares. A small rounded postfrontal and a Parietal Foramen on the frontoParietal suture suggest affinities with iguanians, but the retention of divided premaxillae, amphicoelous vertebrae, thoracolumbar intercentra, entepicondylar Foramen, and a second distal tarsal supports the hypothesis that Huehuecuetzpalli has a more basal position relative to the extant squamates. Although its appearance is late in the fossil record of lizards, Huehuecuetzpalli is the first report of a basal squamate. It provides important information on early transformation of characters in lizard evolution. Many primitive characters present in some modern squamates are usually explained by paedomorphosis; however, these characters are common in early lizards suggesting that derived states may have been fixed later in lizard evolution. If Huehuecuetzpalli is an iguanian, then it would be the earliest known representative of this lineage and extends their fossil record into the Albian. This paper presents an extensive review of the characters and character states used in previously published cladistic analyses of the Squamata.
Paul R. Manger - One of the best experts on this subject based on the ideXlab platform.
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Palaeoneurological clues to the evolution of defining mammalian soft tissue traits
Scientific Reports, 2016Co-Authors: J. Benoit, Paul R. Manger, B. S. RubidgeAbstract:A rich fossil record chronicles the distant origins of mammals, but the evolution of defining soft tissue characters of extant mammals, such as mammary glands and hairs is difficult to interpret because soft tissue does not readily fossilize. As many soft tissue features are derived from dermic structures, their evolution is linked to that of the nervous syutem and palaeoneurology offers opportunities to find bony correlates of these soft tissue features. Here, a CT scan study of 29 fossil skulls shows that non-mammaliaform Prozostrodontia display a retracted, fully ossified and non-ramified infraorbital canal for the infraorbital nerve, unlike more basal therapsids. The presence of a true infraorbital canal in Prozostrodontia suggests that a motile rhinarium and maxillary vibrissae were present. Also the complete ossification of the Parietal fontanelle (resulting in the loss of the Parietal Foramen) and the development of the cerebellum in Probainognathia may be pleiotropically linked to the appearance of mammary glands and having body hair coverage since these traits are all controlled by the same homeogene, Msx2, in mice. These suggest that defining soft tissue characters of mammals were already present in their forerunners some 240 to 246 mya.
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The Sixth Sense in Mammalian Forerunners: Variability of the Parietal Foramen and the Evolution of the Pineal Eye in South African Permo-Triassic Eutheriodont Therapsids
Acta Palaeontologica Polonica, 2016Co-Authors: Julien Benoit, Fernando Abdala, Paul R. Manger, B. S. RubidgeAbstract:In some extant ectotherms, the third eye (or pineal eye) is a photosensitive organ located in the Parietal Foramen on the midline of the skull roof. The pineal eye sends information regarding exposure to sunlight to the pineal complex, a region of the brain devoted to the regulation of body temperature, reproductive synchrony, and biological rhythms. The Parietal Foramen is absent in mammals but present in most of the closest extinct relatives of mammals, the Therapsida. A broad ranging survey of the occurrence and size of the Parietal Foramen in different South African therapsid taxa demonstrates that through time the Parietal Foramen tends, in a convergent manner, to become smaller and is absent more frequently in eutherocephalians (Akidnognathiidae, Whaitsiidae, and Baurioidea) and non-mammaliaform eucynodonts. Among the latter, the Probainognathia, the lineage leading to mammaliaforms, are the only one to achieve the complete loss of the Parietal Foramen. These results suggest a gradual and convergent...
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The sixth sense in mammalian forerunners: Variability of the Parietal Foramen and the evolution of the pineal eye in South African Permo-Triassic eutheriodont therapsids
Institute of Paleobiology PAS, 2016Co-Authors: Julien Benoit, Fernando Abdala, Paul R. Manger, B. S. RubidgeAbstract:In some extant ectotherms, the third eye (or pineal eye) is a photosensitive organ located in the Parietal Foramen on the midline of the skull roof. The pineal eye sends information regarding exposure to sunlight to the pineal complex, a region of the brain devoted to the regulation of body temperature, reproductive synchrony, and biological rhythms. The Parietal Foramen is absent in mammals but present in most of the closest extinct relatives of mammals, the Therapsida. A broad ranging survey of the occurrence and size of the Parietal Foramen in different South African therapsid taxa demonstrates that through time the Parietal Foramen tends, in a convergent manner, to become smaller and is absent more frequently in eutherocephalians (Akidnognathiidae, Whaitsiidae, and Baurioidea) and non-mammaliaform eucynodonts. Among the latter, the Probainognathia, the lineage leading to mammaliaforms, are the only one to achieve the complete loss of the Parietal Foramen. These results suggest a gradual and convergent loss of the photoreceptive function of the pineal organ and degeneration of the third eye. Given the role of the pineal organ to achieve fine-tuned thermoregulation in ectotherms (i.e., “cold-blooded” vertebrates), the gradual loss of the Parietal Foramen through time in the Karoo stratigraphic succession may be correlated with the transition from a mesothermic metabolism to a high metabolic rate (endothermy) in mammalian ancestry. The appearance in the eye of melanopsin-containing retinal ganglion cells replacing the photoreceptive role of the pineal eye could also have accompanied its loss
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Physiological implications of the abnormal absence of the Parietal Foramen in a late Permian cynodont (Therapsida)
The Science of Nature, 2015Co-Authors: Julien Benoit, Fernando Abdala, Paul R. Manger, Marc J. Brandt, B. S. RubidgeAbstract:The third eye (pineal eye), an organ responsible for regulating exposure to sunlight in extant ectotherms, is located in an opening on the dorsal surface of the skull, the Parietal Foramen. The Parietal Foramen is absent in extant mammals but often observed in basal therapsids, the stem-group to true mammals. Here, we report the absence of the Parietal Foramen in a specimen of Cynosaurus suppostus , a Late Permian cynodont from South Africa (SA). Comparison with Procynosuchus delaharpeae , a contemporaneous non-mammalian cynodont from SA, demonstrates that the absence of this Foramen is an abnormal condition for such a basal species. Because seasonality was marked during the Late Permian in SA, it is proposed that the third eye was functionally redundant in Cynosaurus , possibly due to the acquisition of better thermoregulation or the evolution of specialized cells in the lateral eyes to compensate for the role of the third eye.
Gregory P Wilson - One of the best experts on this subject based on the ideXlab platform.
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A new Late Cretaceous iguanomorph from North America and the origin of New World Pleurodonta (Squamata, Iguania)
Proceedings of The Royal Society B: Biological Sciences, 2017Co-Authors: David G. Demar, Jason J. Head, Jack L Conrad, David J Varricchio, Gregory P WilsonAbstract:Iguanomorpha (stem + crown Iguania) is a diverse squamate clade with members that predominate many modern American lizard ecosystems. However, the temporal and palaeobiogeographic origins of its constituent crown clades (e.g. Pleurodonta (basilisks, iguanas, and their relatives)) are poorly constrained, mainly due to a meagre Mesozoic-age fossil record. Here, we report on two nearly complete skeletons from the Late Cretaceous (Campanian) of North America that represent a new and relatively large-bodied and possibly herbivorous iguanomorph that inhabited a semi-arid environment. The new taxon exhibits a mosaic of anatomical features traditionally used in diagnosing Iguania and non-iguanian squamates (i.e. Scleroglossa; e.g. Parietal Foramen at the frontoParietal suture, astragalocalcaneal notch in the tibia, respectively). Our cladistic analysis of Squamata revealed a phylogenetic link between Campanian-age North American and East Asian stem iguanomorphs (i.e. the new taxon + Temujiniidae). These results and our evaluation of the squamate fossil record suggest that crown pleurodontans were restricted to the low-latitude Neotropics prior to their early Palaeogene first appearances in the mid-latitudes of North America.