Martinelli, A. G., Francischini, H., Dentzien-Dias, P. C., Soares, M. B., and C. L. Schultz. 2016.
The oldest archosauromorph from South America: postcranial remains from the Guadalupian (mid-Permian) Rio do Rasto Formation (Paraná Basin), southern Brazil. Historical Biology.
DOI:10.1080/08912963.2015.1125897
http://www.tandfonline.com/doi/full/10.1080/08912963.2015.1125897
Abstract - In this contribution, we report a distal portion of a left humerus that likely belongs to an indeterminate basal archosauromorph from the Guadalupian (mid-Permian) Rio do Rastro Formation (Paraná Basin) of southern Brazil. A precise taxonomy of the fragmented and isolated humerus UFRGS-PV-0546-P is not warranted at generic nor familiar level but, likely, this specimen belongs to an Archosauromorpha due to the lack of both the entepicondylar and the ectepicondylar foramina. The narrow distal end of the humerus, the rounded radial and ulnar condyles, and the moderately developed supinator process with a shallow ectepicondylar groove (not notched) are features reminiscent of tanystropheids rather than that of other archosauromorphs. This material likely represents the first and oldest Permian archosauromorph from South America and indicates the presence of this lineage before the P/T boundary.
Showing posts with label South America. Show all posts
Showing posts with label South America. Show all posts
Tachiraptor admirabilis, a New Theropod Dinosaur from the Earliest Jurassic of Venezuela
The paper will be out on October 8th, but Science's website already has a news article up about the find. It is from the same locality as the early ornithischian dinosaur Laquintasaura, which was described earlier this year.
Postcranial Anatomy and Phylogenetic Relationships of the Sauropodomorph Mussaurus patagonicus
Otero, A. and D. Pol. 2013. Postcranial anatomy and phylogenetic relationships of Mussaurus patagonicus (Dinosauria: Sauropodomorpha). Journal of Vertebrate Paleontology 33:1138-1168.
Abstract - The transition from basal sauropodomorphs to sauropods is one of the most dramatic evolutionary transformations in the history of dinosaurs. Constituent taxa of this transition were recorded mainly in South Africa and South America, and to a lesser extent in North America. We describe here the postcranial anatomy of four specimens of basal sauropodomorphs from the Late Triassic of Patagonia, Argentina, and identify them as adult individuals of Mussaurus patagonicus. The material is composed of one subadult and three adult specimens and was originally identified as Plateosaurus. The completeness of the material provides more complete knowledge of this taxon and allows us to introduce aspects of basal sauropodomorph anatomy that were poorly understood until now, such as the configuration and arrangement of the distal carpal elements. The phylogenetic relationships of Mussaurus patagonicus are tested through a cladistic analysis of basal sauropodomorphs based on the anatomy of these specimens rather than on the post-hatchling and juvenile specimens previously known for this taxon. Mussaurus is recovered as a non-sauropod anchisaurian, being the sister group of Aardonyx plus more derived sauropodomorphs and is depicted outside the ‘quadrupedal clade,’ given the presence of plesiomorphic features such as a humerus/femur ratio <0.8, a curved femoral shaft in lateral view, and a nearly circular femoral midshaft cross-section. Mussaurus patagonicus adds new and valuable information that helps to clarify the core of the basal sauropodomorph-sauropod transition.
Abstract - The transition from basal sauropodomorphs to sauropods is one of the most dramatic evolutionary transformations in the history of dinosaurs. Constituent taxa of this transition were recorded mainly in South Africa and South America, and to a lesser extent in North America. We describe here the postcranial anatomy of four specimens of basal sauropodomorphs from the Late Triassic of Patagonia, Argentina, and identify them as adult individuals of Mussaurus patagonicus. The material is composed of one subadult and three adult specimens and was originally identified as Plateosaurus. The completeness of the material provides more complete knowledge of this taxon and allows us to introduce aspects of basal sauropodomorph anatomy that were poorly understood until now, such as the configuration and arrangement of the distal carpal elements. The phylogenetic relationships of Mussaurus patagonicus are tested through a cladistic analysis of basal sauropodomorphs based on the anatomy of these specimens rather than on the post-hatchling and juvenile specimens previously known for this taxon. Mussaurus is recovered as a non-sauropod anchisaurian, being the sister group of Aardonyx plus more derived sauropodomorphs and is depicted outside the ‘quadrupedal clade,’ given the presence of plesiomorphic features such as a humerus/femur ratio <0.8, a curved femoral shaft in lateral view, and a nearly circular femoral midshaft cross-section. Mussaurus patagonicus adds new and valuable information that helps to clarify the core of the basal sauropodomorph-sauropod transition.
Arachana nigra, a New Temnospondyl from the Permo-Triassic of Uruguay
Piñeiro, G., Ramos, A., and C. Marsicano. 2012. A rhinesuchid-like temnospondyl from the Permo-Triassic of
Uruguay. Compte Rendus Palevol 11:65-78. http://dx.doi.org/10.1016/j.crpv.2011.07.007
Abstract - A new temnospondyl species, Arachana nigra, from the
Permo-Triassic Buena Vista Formation of Uruguay is described. The holotypic and
only known specimen consists of an almost complete skull lacking most of the
snout, the tabular horns and the posterolateral corners of the skull table. As
with other specimens from the same unit, Arachana shows a transitional
morphology. It shares several characters with rhinesuchids, such as the large
size and the general shape of the skull, orbits positioned slightly posterior to
the skull roof mid-length, a coarsely pitted dermal ornamentation lacking
pustules, and a smoothly convex cheek contour. The palatal ramus of the
pterygoid suturing with the vomer, and excluding the palatine and ectopterygoid
from the margin of the interpterygoid vacuity, and the presence of a small
basioccipital, visible in both occipital and ventral view, also resemble the
conditions found in rhinesuchids and other basal temnospondyls. Other characters
present in Arachana, however, are commonly found in lydekkerinids, but
are absent in almost all rhinesuchids: supratemporal excluded from otic notch;
supraorbital and infraorbital sensory sulci encroaching the lacrimal, although
lacking a step-like lacrimal flexure; otic notch not deeply incised;
post-temporal fenestra large and rounded; occipital condyles well-separated from
each other; palatine tooth row behind the palatine tusk reduced; pterygoid
corpus slightly ornamented; and presence of an interorbital depression. This
combination of primitive and derived characters is consistently present in most
components of the Buena Vista fauna, which could thus be transitional between
typical Permian and Triassic tetrapod communities found elsewhere. The location
of the PTB in the Uruguayan sequence is controversial, mainly due to the lack of
clear faunal correlations with other well-known sequences, such as those of
southern Africa and Russia. Moreover, the mosaic-like character combinations in
most of the recorded tetrapods ally them to both Triassic and Paleozoic groups,
and this has complicated even more the possibility of age assignment.
Transitional faunas associated with the PTB, such as the Russian Uppermost
Permian faunas, could be equivalent to the unique Colonia Orozco fauna. If true,
this scenario will substantially change estimates about survivorship rates,
suggesting a speciation rate increase in temnospondyls after the
Permian-Triassic event. Based on taxonomic, phylogenetic, and geochronologic
data, the Buena Vista fauna allows us to quantify faunal turnover across the PTB
and in the aftermath of the end Permian extinction event.
A Sectorial Toothed Cynodont (Therapsida) from the Triassic of Southern Brazil
Soares M. B., Abdala F. and C. Bertoni-Machado. 2011. A sectorial toothed cynodont (Therapsida) from the Triassic Santa Cruz do Sul fauna, Santa Maria Formation, Southern Brazil. Geodiversitas 33: 265-278.
ABSTRACT - A sectorial toothed cynodont from the Triassic Santa Cruz do Sul fauna, Santa Maria Formation, Parana Basin, southern Brazil, is described. The taxon is represented by a tiny portion of a right lower jaw which preserves partially the last postcanine. A comparative analysis of the postcanine morphology of the Santa Cruz do Sul specimen with South American Triassic cynodonts is made. The crown morphology of the Santa Cruz do Sul cynodont is closer to that of the juvenile single specimen of cf. Probainognathus from the Carnian Ischigualasto Formation and of juveniles of Probainognathus jenseni Romer, 1970 from the Ladinian Chañares Formation in Argentina. There are, however, some important differences between the tooth of the new specimen and those of P. jenseni juveniles, and therefore we provisionally assign the new Santa Cruz do Sul material to cf. Probainognathus. The fauna of Santa Cruz do Sul, dominated by traversodontid cynodonts, is now composed of a proterochampsid archosauriform, three traversodontids and two sectorial toothed cynodonts and we refer to it as Santacruzodon Assemblage Zone. We also propose the name of Riograndia Assemblage Zone for the faunas from the Upper Triassic Caturrita Formation, on the basis of the abundance yet restricted record of this taxon in these faunas. A brief summary of the Brazilian Middle and Upper Triassic biostratigraphy is presented within the framework of two different time scales.
ABSTRACT - A sectorial toothed cynodont from the Triassic Santa Cruz do Sul fauna, Santa Maria Formation, Parana Basin, southern Brazil, is described. The taxon is represented by a tiny portion of a right lower jaw which preserves partially the last postcanine. A comparative analysis of the postcanine morphology of the Santa Cruz do Sul specimen with South American Triassic cynodonts is made. The crown morphology of the Santa Cruz do Sul cynodont is closer to that of the juvenile single specimen of cf. Probainognathus from the Carnian Ischigualasto Formation and of juveniles of Probainognathus jenseni Romer, 1970 from the Ladinian Chañares Formation in Argentina. There are, however, some important differences between the tooth of the new specimen and those of P. jenseni juveniles, and therefore we provisionally assign the new Santa Cruz do Sul material to cf. Probainognathus. The fauna of Santa Cruz do Sul, dominated by traversodontid cynodonts, is now composed of a proterochampsid archosauriform, three traversodontids and two sectorial toothed cynodonts and we refer to it as Santacruzodon Assemblage Zone. We also propose the name of Riograndia Assemblage Zone for the faunas from the Upper Triassic Caturrita Formation, on the basis of the abundance yet restricted record of this taxon in these faunas. A brief summary of the Brazilian Middle and Upper Triassic biostratigraphy is presented within the framework of two different time scales.
The South American Aetosaur Aetosauroides is Not Referable to Stagonolepis
In a series of papers Heckert and Lucas (1999, 2000, 2002) and Lucas and Heckert (2001) proposed that the American aetosaur taxon Aetosauroides was a junior synonym of Stagonolepis, and that as a result the Ischigualasto (Argentina) and the Santa Maria (Brazil) formations were Adamanian (latest Carnian) in age based upon vertebrate biostratigraphy and correlable with other Adamanian strata such as the lower part of the Chinle Formation in western North America. However, these synonomies were based on very superficial resemblances and not on apomorphy based comparisons (Parker, 2008).
The new issue of the Journal of Vertebrate Paleontology has a paper by Julia Desojo and Martin Ezcurra redescribing some of the Aetosauroides material and refuting the synonomy with Stagonolepis using a detailed comparison of characters. Especially important are characters of the skull, which clearly demonstrates strong differences between the two taxa.
As a result Stagonolepis is not known from South America and therefore the proposed biostratigraphic correlations between South America, North America, and Europe using aetosaurs is not supported by this study. This is also supported by radiometric dates which show a 10 million year difference between the main fossil horizon in ht eIschigualasto Formation and the base of the main fossil bearing beds in the Chinle Formation (Irmis and Mundil, 2008).
I have suggested elsewhere (Parker, 2008) that Stagonolepis does not occur in North America either and thus aetosaur taxa appear much more endemic than argued by Heckert and Lucas and thus of limited (only regional) biostratigraphic utility.
Biostratigraphy and taxonomy aside, this redescription highlights the plesiomorphic nature of Aetosauroides, especially regarding features of the skull including a gracile, fully-toothed dentary, different from the "slipper-shaped", anteriorly edentulous mandibles of more derived aetosaurs, and the meeting of the premaxilla and nasal to exclude the maxilla from the margin of the external naris. Thus, Aetosauroides is an interesting and clearly plesiomorphic form with an armor ornamentation convergent with more derived forms such as Stagonolepis and Calyptosuchus.
Desojo, J. B., and M. D. Ezcurra. 2011. A reappraisal of the taxonomic status of Aetosauroides (Archosauria, Aetosauria) specimens from the Late Triassic of South America and their proposed synonymy with Stagonolepis. Journal of Vertebrate Paleontology 31:596-609. DOI: 10.1080/02724634.2011.572936
Abstract - The South American record of early Late Triassic aetosaurs is composed of two species: Aetosauroides scagliai and “Aetosauroides subsulcatus.” Previously undescribed materials belonging to “Aetosauroides subsulcatus” allow us to reassess its taxonomy, leading us to consider it a junior synonym of Aetosauroides scagliai. Based on the emended diagnosis of the species provided here, we recognize that specimens assignable to Aetosauroides scagliai are less common than thought previously and several of them are not diagnostic beyond indeterminate non-typothorasicine aetosaurins. Previous assignments of Aetosauroides as a junior synonym of Stagonolepis are not followed because the South American taxon is distinct due to the presence of a maxilla excluded from the external narial margin, tooth crowns with a straight distal margin and without a constriction between the root and crown, a gradually convex ventral margin of the dentary, oval fossae ventral to the neurocentral suture on the lateral sides of the centra, and a ratio between the length and the width between the distal-most tips of the postzygapophyses equal to or lower than 0.75. The evidence provided here bolsters the validity of Aetosauroides and extends the distribution of Aetosauroides scagliai into southern Brazil. Although Stagonolepis was employed as an index taxon for the Adamanian LVF, this genus is currently restricted to Europe and North America. Thus, no overlapping genera or species of aetosaur are shared between South America and other landmasses. Accordingly, the record of aetosaurs is not useful for providing biostratigraphical correlations between Late Triassic South American beds and those in other regions.
REFERENCES
Heckert, A. B., and S. G. Lucas. 1999. A new aetosaur from the Upper Triassic of Texas and the phylogeny of aetosaurs. Journal of Vertebrate Paleontology 19:50–68.
Heckert, A. B., and S. G. Lucas. 2000. Taxonomy, phylogeny, biostratigraphy, biochronology, paleobiogeography, and evolution of the Late Triassic Aetosauria (Archosauria: Crurotarsi). Zentralblatt fur Geologie und Palaontologie, 1998, Teil I, Heft 11–12:1539–1587.
Heckert, A. B., and S. G. Lucas. 2002. South American occurrences of the Adamanian (Late Triassic, Latest Carnian) index taxon Stagonolepis (Archosauria: Aetosauria) and their biochronological significance. Journal of Paleontology 76:852–863.
Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation revise global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.
Lucas, S. G., and A. B. Heckert. 2001. The aetosaur Stagonolepis from the Upper Triassic of Brazil and its biochronological significance. Neues Jahrebuch fur Geologie und Palaontologie, Monatshefte 2001:719–732.
Parker, W. G. 2008. How many valid aetosaur taxa are there? Reviewing the alpha-taxonomy of the Aetosauria (Archosauria: Pseudosuchia) and its implications for Late Triassic global biostratigraphy. Journal of Vertebrate Paleontology 28:125A.
The new issue of the Journal of Vertebrate Paleontology has a paper by Julia Desojo and Martin Ezcurra redescribing some of the Aetosauroides material and refuting the synonomy with Stagonolepis using a detailed comparison of characters. Especially important are characters of the skull, which clearly demonstrates strong differences between the two taxa.
As a result Stagonolepis is not known from South America and therefore the proposed biostratigraphic correlations between South America, North America, and Europe using aetosaurs is not supported by this study. This is also supported by radiometric dates which show a 10 million year difference between the main fossil horizon in ht eIschigualasto Formation and the base of the main fossil bearing beds in the Chinle Formation (Irmis and Mundil, 2008).
I have suggested elsewhere (Parker, 2008) that Stagonolepis does not occur in North America either and thus aetosaur taxa appear much more endemic than argued by Heckert and Lucas and thus of limited (only regional) biostratigraphic utility.
Biostratigraphy and taxonomy aside, this redescription highlights the plesiomorphic nature of Aetosauroides, especially regarding features of the skull including a gracile, fully-toothed dentary, different from the "slipper-shaped", anteriorly edentulous mandibles of more derived aetosaurs, and the meeting of the premaxilla and nasal to exclude the maxilla from the margin of the external naris. Thus, Aetosauroides is an interesting and clearly plesiomorphic form with an armor ornamentation convergent with more derived forms such as Stagonolepis and Calyptosuchus.
Desojo, J. B., and M. D. Ezcurra. 2011. A reappraisal of the taxonomic status of Aetosauroides (Archosauria, Aetosauria) specimens from the Late Triassic of South America and their proposed synonymy with Stagonolepis. Journal of Vertebrate Paleontology 31:596-609. DOI: 10.1080/02724634.2011.572936
Abstract - The South American record of early Late Triassic aetosaurs is composed of two species: Aetosauroides scagliai and “Aetosauroides subsulcatus.” Previously undescribed materials belonging to “Aetosauroides subsulcatus” allow us to reassess its taxonomy, leading us to consider it a junior synonym of Aetosauroides scagliai. Based on the emended diagnosis of the species provided here, we recognize that specimens assignable to Aetosauroides scagliai are less common than thought previously and several of them are not diagnostic beyond indeterminate non-typothorasicine aetosaurins. Previous assignments of Aetosauroides as a junior synonym of Stagonolepis are not followed because the South American taxon is distinct due to the presence of a maxilla excluded from the external narial margin, tooth crowns with a straight distal margin and without a constriction between the root and crown, a gradually convex ventral margin of the dentary, oval fossae ventral to the neurocentral suture on the lateral sides of the centra, and a ratio between the length and the width between the distal-most tips of the postzygapophyses equal to or lower than 0.75. The evidence provided here bolsters the validity of Aetosauroides and extends the distribution of Aetosauroides scagliai into southern Brazil. Although Stagonolepis was employed as an index taxon for the Adamanian LVF, this genus is currently restricted to Europe and North America. Thus, no overlapping genera or species of aetosaur are shared between South America and other landmasses. Accordingly, the record of aetosaurs is not useful for providing biostratigraphical correlations between Late Triassic South American beds and those in other regions.
REFERENCES
Heckert, A. B., and S. G. Lucas. 1999. A new aetosaur from the Upper Triassic of Texas and the phylogeny of aetosaurs. Journal of Vertebrate Paleontology 19:50–68.
Heckert, A. B., and S. G. Lucas. 2000. Taxonomy, phylogeny, biostratigraphy, biochronology, paleobiogeography, and evolution of the Late Triassic Aetosauria (Archosauria: Crurotarsi). Zentralblatt fur Geologie und Palaontologie, 1998, Teil I, Heft 11–12:1539–1587.
Heckert, A. B., and S. G. Lucas. 2002. South American occurrences of the Adamanian (Late Triassic, Latest Carnian) index taxon Stagonolepis (Archosauria: Aetosauria) and their biochronological significance. Journal of Paleontology 76:852–863.
Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation revise global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.
Lucas, S. G., and A. B. Heckert. 2001. The aetosaur Stagonolepis from the Upper Triassic of Brazil and its biochronological significance. Neues Jahrebuch fur Geologie und Palaontologie, Monatshefte 2001:719–732.
Parker, W. G. 2008. How many valid aetosaur taxa are there? Reviewing the alpha-taxonomy of the Aetosauria (Archosauria: Pseudosuchia) and its implications for Late Triassic global biostratigraphy. Journal of Vertebrate Paleontology 28:125A.
New Triassic Dinosaur Papers from the Proceedings of the Third Gondwanan Dinosaur Symposium
Most of you are probably aware that the Proceedings of the Third Gondwanan Dinosaur Symposium have just been published in the journal Anais da Academia Brasileira de Ciências. There are numerous papers here, three of which pertain to the Triassic. You can view and download all of the papers from the following link:
http://www.scielo.br/scielo.php?script=sci_issuetoc&pid=0001-376520110001&ln
I have listed the relevent Triassic dinosaur papers below.
Bittencourt, J. S., and M. C. Langer. 2011. Mesozoic dinosaurs from Brazil and their biogeographic implications. Anais da Academia Brasileira de Ciências 83:23-60.
Abstract - The record of dinosaur body-fossils in the Brazilian Mesozoic is restricted to the Triassic of Rio Grande do Sul and Cretaceous of various parts of the country. This includes 21 named species, two of which were regarded as nomina dubia, and 19 consensually assigned to Dinosauria. Additional eight supraspecific taxa have been identified based on fragmentary specimens and numerous dinosaur footprints known in Brazil. In fact, most Brazilian specimens related to dinosaurs are composed of isolated teeth and vertebrae. Despite the increase of fieldwork during the last decade, there are still no dinosaur body-fossils of Jurassic age and the evidence of ornithischians in Brazil is very limited. Dinosaur faunas from this country are generally correlated with those from other parts of Gondwana throughout the Mesozoic. During the Late Triassic, there is a close correspondence to Argentina and other south-Pangaea areas. Mid-Cretaceous faunas of northeastern Brazil resemble those of coeval deposits of North Africa and Argentina. Southern hemisphere spinosaurids are restricted to Africa and Brazil, whereas abelisaurids are still unknown in the Early Cretaceous of the latter. Late Cretaceous dinosaur assemblages of south-central Brazil are endemic only to genus or, more conspicuously, to species level, sharing closely related taxa with Argentina, Madagascar, Indo-Pakistan and, to a lesser degree, continental Africa.
and two new papers on Staurikosaurus, one of which was previously mentioned here.
Grillo, O. N., and S. A. K. Azevedo. 2011. Pelvic and hind limb musculature of Staurikosaurus pricei (Dinosauria: Saurischia). Anais da Academia Brasileira de Ciências 83:73-98.
Abstract - The study of pelvic and hind limb bones and muscles in basal dinosaurs is important for understanding the early evolution of bipedal locomotion in the group. The use of data from both extant and extinct taxa placed into a phylogenetic context allowed to make well-supported inferences concerning most of the hind limb musculature of the basal saurischian Staurikosaurus pricei Colbert, 1970 (Santa Maria Formation, Late Triassic of Rio Grande do Sul, Brazil). Two large concavities in the lateral surface of the ilium represent the origin of the muscles iliotrochantericus caudalis plus iliofemoralis externus (in the anterior concavity) and iliofibularis (in the posterior concavity). Muscle ambiens has only one head and originates from the pubic tubercle. The origin of puboischiofemoralis internus 1 possibly corresponds to a fossa in the ventral margin of the preacetabular iliac process. This could represent an intermediate stage prior to the origin of a true preacetabular fossa. Muscles caudofemorales longus et brevis were likely well developed, and Staurikosaurus is unique in bearing a posteriorly projected surface for the origin of caudofemoralis brevis.
http://www.scielo.br/scielo.php?script=sci_issuetoc&pid=0001-376520110001&ln
I have listed the relevent Triassic dinosaur papers below.
Bittencourt, J. S., and M. C. Langer. 2011. Mesozoic dinosaurs from Brazil and their biogeographic implications. Anais da Academia Brasileira de Ciências 83:23-60.
Abstract - The record of dinosaur body-fossils in the Brazilian Mesozoic is restricted to the Triassic of Rio Grande do Sul and Cretaceous of various parts of the country. This includes 21 named species, two of which were regarded as nomina dubia, and 19 consensually assigned to Dinosauria. Additional eight supraspecific taxa have been identified based on fragmentary specimens and numerous dinosaur footprints known in Brazil. In fact, most Brazilian specimens related to dinosaurs are composed of isolated teeth and vertebrae. Despite the increase of fieldwork during the last decade, there are still no dinosaur body-fossils of Jurassic age and the evidence of ornithischians in Brazil is very limited. Dinosaur faunas from this country are generally correlated with those from other parts of Gondwana throughout the Mesozoic. During the Late Triassic, there is a close correspondence to Argentina and other south-Pangaea areas. Mid-Cretaceous faunas of northeastern Brazil resemble those of coeval deposits of North Africa and Argentina. Southern hemisphere spinosaurids are restricted to Africa and Brazil, whereas abelisaurids are still unknown in the Early Cretaceous of the latter. Late Cretaceous dinosaur assemblages of south-central Brazil are endemic only to genus or, more conspicuously, to species level, sharing closely related taxa with Argentina, Madagascar, Indo-Pakistan and, to a lesser degree, continental Africa.
and two new papers on Staurikosaurus, one of which was previously mentioned here.
Grillo, O. N., and S. A. K. Azevedo. 2011. Pelvic and hind limb musculature of Staurikosaurus pricei (Dinosauria: Saurischia). Anais da Academia Brasileira de Ciências 83:73-98.
Abstract - The study of pelvic and hind limb bones and muscles in basal dinosaurs is important for understanding the early evolution of bipedal locomotion in the group. The use of data from both extant and extinct taxa placed into a phylogenetic context allowed to make well-supported inferences concerning most of the hind limb musculature of the basal saurischian Staurikosaurus pricei Colbert, 1970 (Santa Maria Formation, Late Triassic of Rio Grande do Sul, Brazil). Two large concavities in the lateral surface of the ilium represent the origin of the muscles iliotrochantericus caudalis plus iliofemoralis externus (in the anterior concavity) and iliofibularis (in the posterior concavity). Muscle ambiens has only one head and originates from the pubic tubercle. The origin of puboischiofemoralis internus 1 possibly corresponds to a fossa in the ventral margin of the preacetabular iliac process. This could represent an intermediate stage prior to the origin of a true preacetabular fossa. Muscles caudofemorales longus et brevis were likely well developed, and Staurikosaurus is unique in bearing a posteriorly projected surface for the origin of caudofemoralis brevis.
New Isotopic Age Constraints for Middle Triassic Rocks in Argentina
Mancuso, A. C., Chemale, F., Barredo, S., Ávila, J. N., Ottone, E. G., and Marsicano, C. In Press. Age constraints for the northernmost outcrops of the Triassic Cuyana Basin, Argentina, Journal of South American Earth Sciences (2010), doi: 10.1016/j.jsames.2010.03.001
Abstract - Age constraints on the Cerro Puntudo Formation at the northernmost exposures of the continental Triassic Cuyana Basin are presented based on palynological data and U-Pb zircon dating. The lacustrine facies of the upper part of the Cerro Puntudo Formation contain a low diverse palynological assemblage that is dominated by spores of ferns and lycopsids with subordinated inaperturated forms of uncertain affinity. The U-Pb SHRIMP zircon age of 243.8 ± 1.9 Ma (Anisian), obtained from juvenile magmatic zircons in a tuff interbedded in the same beds, provides the first chronostratigraphic date of the Cuyana Basin infilling at its northernmost exposures. According to additional dates already known from the southern part of the basin, a new stratigraphic correlation is proposed thus restricting the first tectono-sedimentary sequence (Synrift I depositional event of Kokogian et al.) to the Anisian. This depositional event has already been recorded in the Cacheuta and Rincón Blanco sub-basins but it is for the first time timely constrained across the whole basin.
Abstract - Age constraints on the Cerro Puntudo Formation at the northernmost exposures of the continental Triassic Cuyana Basin are presented based on palynological data and U-Pb zircon dating. The lacustrine facies of the upper part of the Cerro Puntudo Formation contain a low diverse palynological assemblage that is dominated by spores of ferns and lycopsids with subordinated inaperturated forms of uncertain affinity. The U-Pb SHRIMP zircon age of 243.8 ± 1.9 Ma (Anisian), obtained from juvenile magmatic zircons in a tuff interbedded in the same beds, provides the first chronostratigraphic date of the Cuyana Basin infilling at its northernmost exposures. According to additional dates already known from the southern part of the basin, a new stratigraphic correlation is proposed thus restricting the first tectono-sedimentary sequence (Synrift I depositional event of Kokogian et al.) to the Anisian. This depositional event has already been recorded in the Cacheuta and Rincón Blanco sub-basins but it is for the first time timely constrained across the whole basin.
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