Late Pleistocene fossils from southern Brazil provide a unique opportunity to study the diet and ... more Late Pleistocene fossils from southern Brazil provide a unique opportunity to study the diet and habitat use of the extant franciscana dolphin (Pontoporia blainvillei) prior to human influence. Here, we subject 19 fossil and 21 contemporary specimens to stable carbon and oxygen isotope analysis (after first ruling out diagenesis via Fourier transform infrared spectroscopy). The two groups differ in their isotopic composition (PERMANOVA, p < .01), with fossils yielding more disparate δ13C values and recent samples more disparate δ18O values. Their isotopic niches show an overlap of ~20%, with that of the fossils being slightly wider (SEAc = 2.25‰2 versus 1.84‰2). We attribute these differences to impoverished modern fish communities and temporal changes in freshwater influx.
Diagnoses of Mylodontidae species are generally based on skull, mandibular, and tooth characteris... more Diagnoses of Mylodontidae species are generally based on skull, mandibular, and tooth characteristics, and rarely on postcranial morphology, due to the lack of postcranial material associated with the cranial material. The studies of postcranial anatomy have generally a biomechanical focus and reflect a set of functions of skeletal structures, but their interpretation in phylogenetic analysis is still limited. In Pleistocene deposits of Rio Grande do Sul State, Brazil, an important set of postcranial specimens was collected, belonging to Mylodontidae. They were morphologically and morphometrically analyzed, allowing us to observe some diagnostic characters such as the humeral entepicondylar foramen and crests, shape of the radial shaft, angle of distal articulation of the tibia, as well as the angle of proximal articulation of the astragalus. The material was also compared with specimens from other South American localities. Most of the remains were assigned to Glossotherium robustum and Lestodon armatus. In addition, a new Scelidotheriinae was recorded for Rio Grande do Sul State. The study indicated significant differences in the postcranial morphology, which allowed the recognition of some specific diagnostic characters. Keywords: Mylodontinae, Scelidotheriinae, hindlimb, forelimb, Pleistocene, Rio Grande do Sul.
A primitive ‘ictidosaur’ from lower Norian beds of southern Brazil, Riograndia guaibensis gen. et... more A primitive ‘ictidosaur’ from lower Norian beds of southern Brazil, Riograndia guaibensis gen. et sp. nov., represented by a fragmentary skull and a lower jaw bearing a complete dentition, shows a more generalized morphology than Chaliminia from the Upper Triassic of Argentina and PachygenelusDiarthrognathus from the Lower Jurassic of South Africa, Canada and Greenland. The frontal bone borders the orbit, and ventrally contacts the dorsal process of the palatine. The secondary bony palate extends back to the last postcanine. I1 and i2 are reduced, whereas I2‐3 and i1 are hypertrophied. Both PC 1–7 and pc 1–7 have blade‐like crowns without cingula and with 5–9 small sharp cuspules. The upper postcanine crowns are semicircular in labial view with the cuspules around their margins. The lower postcanine crowns are asymmetrical with most of the cuspules dorsodistally distributed. The possible origin of this peculiar dentition is interpreted as the retention of the juvenile dentition of ancestors. The hypothesis that Riograndia guaibensis and the so‐called ‘ictidosaurs’ might have been derived from gomphodont cynodonts is presented.
a b s t r a c t The Early Permian mesosaurids are the oldest known aquatic amniotes with an exclu... more a b s t r a c t The Early Permian mesosaurids are the oldest known aquatic amniotes with an exclusively Gondwanan distribution. Although several hundred of complete skeletons have been dis- covered and intensively studied, the anatomy and taxonomic composition of the group, as well as its phylogenetic relationships remain controversial. Several well-preserved mesosaurid specimens found in Uruguay justify a new anatomical reconstruction of the skull of Mesosaurus tenuidens, differing from earlier ones especially in the presence of a lower temporal fenestra. The significance of this structure for the evolution of tempo- ral fenestration in amniotes is evaluated according to the two most recent phylogenetic hypotheses, in which mesosaurids are basalmost sauropsids or basalmost parareptiles. A synapsid-like fenestration may be the primitive condition for Amniota, and it may be also a basal condition for parareptiles, because recent phylogenies suggest a basal position for mesosaurids and lanthanosuchoids within that group, and both possess a lower temporal fenestra. Our results also give a moderately strengthened support for diapsid affinities of turtles.
New material of Tapirus from the late Pleistocene of Rio Grande do Sul State is described, and ot... more New material of Tapirus from the late Pleistocene of Rio Grande do Sul State is described, and other specimens previously collected are reviewed. The material comes from Alegrete (Sanga da Cruz Creek), Dom Pedrito (São Luiz cattle ranch), Iraí, Quaraí (Cerro da Tapera), and Santa Vitória do Palmar (Hermenegildo Beach). The specimens from Iraí are referred to the extant species, T. terrestris, on the basis of their size and morphology. Specimens from Sanga da Cruz Creek, Hermenegildo Beach, São Luiz cattle ranch and Cerro da Tapera are very fragmentary or present no diagnostic characters, and are tentatively assigned to Tapirus cf. T. terrestris. We confirm the presence of the T. terrestris in the upper Pleistocene of Rio Grande do Sul state. Currently, there are neither archaeological nor historical records of this species for the southern region of this state.
Dinosaurs possess a form of tooth attachment wherein an unmineralized periodontal ligament suspen... more Dinosaurs possess a form of tooth attachment wherein an unmineralized periodontal ligament suspends each tooth within a socket, similar to the condition in mammals and crocodylians. However, little information is known about tooth attachment and implantation in their close relatives, the silesaurids. We conducted an histological survey of several silesaurid taxa to determine the nature of tooth attachment in this phylogenetically and paleoecologically important group of archosaurs. Our histological data demonstrate that these early dinosauriforms exhibit neither the crocodilian/dinosaur condition of a permanent gomphosis, nor the rapid ankylosis that is plesiomorphic for amniotes. Instead, all sampled silesaurids exhibit delayed ankylosis, a condition in which teeth pass through a prolonged stage where the teeth are suspended in sockets by a periodontal ligament, followed by eventual mineralization and fusion of the tooth to the jaws. This suggests that tooth attachment in crocodylians and dinosaurs represent the further retention of an early ontogenetic stage compared to silesaurids, a paedomorphic trend that is mirrored in the evolution of synapsid tooth attachment. It also suggests that the dinosaur and crocodylian gomphosis was convergently acquired via heterochrony or, less likely, that the silesaurid condition represents a reversal to a plesiomorphic state. Moreover, if Silesauridae is nested within Ornithischia, a permanent gomphosis could be convergent between the two main dinosaur lineages, Ornithischia and Saurischia. These results demonstrate that dental characters in early archosaur phylogenies must be chosen and defined carefully, taking into account the relative duration of the different phases of dental ontogeny.
Nosso proposito principal neste trabalho e mostrar que o metodo utilizado por Aristoteles em sua ... more Nosso proposito principal neste trabalho e mostrar que o metodo utilizado por Aristoteles em sua biologia e o dialetico. A demonstracao nao e o metodo da biologia por varias razoes, entre elas porque os organismos e suas partes podem ser de outro modo do que sao; alem de o proprio Aristoteles ter afirmado que a precisao da matematica (demonstracao) nao deve ser exigida senao para as coisas nao materiais. Sendo os animais investigados por meio da dialetica, excetuados os principios de cada area, apenas podemos ter opinioes confiaveis (endoxa) sobre eles, obtidos por meio de conceitos, metodos e argumentos, como propostos na Topica. Na biologia, Aristoteles parte dos endoxa, ou, quando esses nao estao disponiveis, de suas proprias observacoes dos phainomena. Depois da compilacao, Aristoteles os contrasta, observa ele mesmo os phainomena, contrasta os endoxa entre si, e tambem com seus proprios achados, elimina os problemas, tenta compatibilizar as opinioes e finalmente conclui. Quando...
Late Pleistocene fossils from southern Brazil provide a unique opportunity to study the diet and ... more Late Pleistocene fossils from southern Brazil provide a unique opportunity to study the diet and habitat use of the extant franciscana dolphin (Pontoporia blainvillei) prior to human influence. Here, we subject 19 fossil and 21 contemporary specimens to stable carbon and oxygen isotope analysis (after first ruling out diagenesis via Fourier transform infrared spectroscopy). The two groups differ in their isotopic composition (PERMANOVA, p < .01), with fossils yielding more disparate δ13C values and recent samples more disparate δ18O values. Their isotopic niches show an overlap of ~20%, with that of the fossils being slightly wider (SEAc = 2.25‰2 versus 1.84‰2). We attribute these differences to impoverished modern fish communities and temporal changes in freshwater influx.
Diagnoses of Mylodontidae species are generally based on skull, mandibular, and tooth characteris... more Diagnoses of Mylodontidae species are generally based on skull, mandibular, and tooth characteristics, and rarely on postcranial morphology, due to the lack of postcranial material associated with the cranial material. The studies of postcranial anatomy have generally a biomechanical focus and reflect a set of functions of skeletal structures, but their interpretation in phylogenetic analysis is still limited. In Pleistocene deposits of Rio Grande do Sul State, Brazil, an important set of postcranial specimens was collected, belonging to Mylodontidae. They were morphologically and morphometrically analyzed, allowing us to observe some diagnostic characters such as the humeral entepicondylar foramen and crests, shape of the radial shaft, angle of distal articulation of the tibia, as well as the angle of proximal articulation of the astragalus. The material was also compared with specimens from other South American localities. Most of the remains were assigned to Glossotherium robustum and Lestodon armatus. In addition, a new Scelidotheriinae was recorded for Rio Grande do Sul State. The study indicated significant differences in the postcranial morphology, which allowed the recognition of some specific diagnostic characters. Keywords: Mylodontinae, Scelidotheriinae, hindlimb, forelimb, Pleistocene, Rio Grande do Sul.
A primitive ‘ictidosaur’ from lower Norian beds of southern Brazil, Riograndia guaibensis gen. et... more A primitive ‘ictidosaur’ from lower Norian beds of southern Brazil, Riograndia guaibensis gen. et sp. nov., represented by a fragmentary skull and a lower jaw bearing a complete dentition, shows a more generalized morphology than Chaliminia from the Upper Triassic of Argentina and PachygenelusDiarthrognathus from the Lower Jurassic of South Africa, Canada and Greenland. The frontal bone borders the orbit, and ventrally contacts the dorsal process of the palatine. The secondary bony palate extends back to the last postcanine. I1 and i2 are reduced, whereas I2‐3 and i1 are hypertrophied. Both PC 1–7 and pc 1–7 have blade‐like crowns without cingula and with 5–9 small sharp cuspules. The upper postcanine crowns are semicircular in labial view with the cuspules around their margins. The lower postcanine crowns are asymmetrical with most of the cuspules dorsodistally distributed. The possible origin of this peculiar dentition is interpreted as the retention of the juvenile dentition of ancestors. The hypothesis that Riograndia guaibensis and the so‐called ‘ictidosaurs’ might have been derived from gomphodont cynodonts is presented.
a b s t r a c t The Early Permian mesosaurids are the oldest known aquatic amniotes with an exclu... more a b s t r a c t The Early Permian mesosaurids are the oldest known aquatic amniotes with an exclusively Gondwanan distribution. Although several hundred of complete skeletons have been dis- covered and intensively studied, the anatomy and taxonomic composition of the group, as well as its phylogenetic relationships remain controversial. Several well-preserved mesosaurid specimens found in Uruguay justify a new anatomical reconstruction of the skull of Mesosaurus tenuidens, differing from earlier ones especially in the presence of a lower temporal fenestra. The significance of this structure for the evolution of tempo- ral fenestration in amniotes is evaluated according to the two most recent phylogenetic hypotheses, in which mesosaurids are basalmost sauropsids or basalmost parareptiles. A synapsid-like fenestration may be the primitive condition for Amniota, and it may be also a basal condition for parareptiles, because recent phylogenies suggest a basal position for mesosaurids and lanthanosuchoids within that group, and both possess a lower temporal fenestra. Our results also give a moderately strengthened support for diapsid affinities of turtles.
New material of Tapirus from the late Pleistocene of Rio Grande do Sul State is described, and ot... more New material of Tapirus from the late Pleistocene of Rio Grande do Sul State is described, and other specimens previously collected are reviewed. The material comes from Alegrete (Sanga da Cruz Creek), Dom Pedrito (São Luiz cattle ranch), Iraí, Quaraí (Cerro da Tapera), and Santa Vitória do Palmar (Hermenegildo Beach). The specimens from Iraí are referred to the extant species, T. terrestris, on the basis of their size and morphology. Specimens from Sanga da Cruz Creek, Hermenegildo Beach, São Luiz cattle ranch and Cerro da Tapera are very fragmentary or present no diagnostic characters, and are tentatively assigned to Tapirus cf. T. terrestris. We confirm the presence of the T. terrestris in the upper Pleistocene of Rio Grande do Sul state. Currently, there are neither archaeological nor historical records of this species for the southern region of this state.
Dinosaurs possess a form of tooth attachment wherein an unmineralized periodontal ligament suspen... more Dinosaurs possess a form of tooth attachment wherein an unmineralized periodontal ligament suspends each tooth within a socket, similar to the condition in mammals and crocodylians. However, little information is known about tooth attachment and implantation in their close relatives, the silesaurids. We conducted an histological survey of several silesaurid taxa to determine the nature of tooth attachment in this phylogenetically and paleoecologically important group of archosaurs. Our histological data demonstrate that these early dinosauriforms exhibit neither the crocodilian/dinosaur condition of a permanent gomphosis, nor the rapid ankylosis that is plesiomorphic for amniotes. Instead, all sampled silesaurids exhibit delayed ankylosis, a condition in which teeth pass through a prolonged stage where the teeth are suspended in sockets by a periodontal ligament, followed by eventual mineralization and fusion of the tooth to the jaws. This suggests that tooth attachment in crocodylians and dinosaurs represent the further retention of an early ontogenetic stage compared to silesaurids, a paedomorphic trend that is mirrored in the evolution of synapsid tooth attachment. It also suggests that the dinosaur and crocodylian gomphosis was convergently acquired via heterochrony or, less likely, that the silesaurid condition represents a reversal to a plesiomorphic state. Moreover, if Silesauridae is nested within Ornithischia, a permanent gomphosis could be convergent between the two main dinosaur lineages, Ornithischia and Saurischia. These results demonstrate that dental characters in early archosaur phylogenies must be chosen and defined carefully, taking into account the relative duration of the different phases of dental ontogeny.
Nosso proposito principal neste trabalho e mostrar que o metodo utilizado por Aristoteles em sua ... more Nosso proposito principal neste trabalho e mostrar que o metodo utilizado por Aristoteles em sua biologia e o dialetico. A demonstracao nao e o metodo da biologia por varias razoes, entre elas porque os organismos e suas partes podem ser de outro modo do que sao; alem de o proprio Aristoteles ter afirmado que a precisao da matematica (demonstracao) nao deve ser exigida senao para as coisas nao materiais. Sendo os animais investigados por meio da dialetica, excetuados os principios de cada area, apenas podemos ter opinioes confiaveis (endoxa) sobre eles, obtidos por meio de conceitos, metodos e argumentos, como propostos na Topica. Na biologia, Aristoteles parte dos endoxa, ou, quando esses nao estao disponiveis, de suas proprias observacoes dos phainomena. Depois da compilacao, Aristoteles os contrasta, observa ele mesmo os phainomena, contrasta os endoxa entre si, e tambem com seus proprios achados, elimina os problemas, tenta compatibilizar as opinioes e finalmente conclui. Quando...
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