Martínez, R. N., Apaldetti, C., Alcober, O. A., Colombi, C. E., Sereno, P. C., Fernandez, E., Santi Malnis, P., Correa, G. A., and D. Abelin. 2013. Vertebrate succession in the Ischigualasto
Formation, Journal of Vertebrate Paleontology, 32:sup1, 10-30, DOI: 10.1080/02724634.2013.818546
Abstract - The Upper Triassic (Carnian–Norian) Ischigualasto Formation has yielded a diverse vertebrate fauna that records the initial phase of dinosaur evolution. Radioisotopic dates from ash layers within the formation provide a chronostratigraphic framework, and stratigraphic and sedimetological studies have subdivided the formation into four members and three abundance-based biozones. We describe two new basal dinosauromorphs, an unnamed lagerpetid and a new silesaurid, Ignotosaurus fragilis, gen. et sp. nov., which increase to 29 the number of vertebrates in the Ischigualasto fauna. We provide a census of 848 fossil specimens representing 26 vertebrate taxa logged to stratigraphic intervals of 50 m. This temporally calibrated census shows that abundance and taxonomic diversity within the Ischigualasto Formation does not change suddenly but rather appears to gradually decline in response to climatic deterioration. The only abrupt shift in faunal composition occurs at the end of the second of three biozones, when the abundant cynodont Exaeretodon is replaced by the rare dicynodont Jachaleria.
Showing posts with label Ischigualasto. Show all posts
Showing posts with label Ischigualasto. Show all posts
A New Late Triassic Phytogeographical Scenario in Westernmost Gondwana.
Césari, S. N., and Colombi, C. E. 2013. A new Late Triassic phytogeographical scenario in westernmost Gondwana. Nature Communications 4, Article number: 1889 doi:10.1038/ncomms2917
Abstract - Floral provincialism within the Southern Hemisphere during the Late
Triassic (230 Ma) is characterized by the Ipswich and Onslow provinces, recognized originally in eastern Gondwana. However, new palynological assemblages from the Ischigualasto Formation, northwestern Argentina (231–225 Ma), change the phytogeographic interpretation for the Carnian–Norian in the westernmost Gondwana,
which was previously considered part of the southern floral Ipswich province. Here we show the presence of diagnostic Euramerican species within assemblages dominated by Gondwanan taxa that allows us to refer the palynofloras to the Onslow province. Our new data extend the Onslow floral belt, previously recognized from the western edge of Tethys to Timor, to the western margin of South America. This has implications for palaeophytogeography, palaeoclimate reconstructions and the palaeoecology of a Triassic ecosystem, which has yielded significant vertebrate remains and is regarded important in the early evolution of groups such as the Dinosauria.
Abstract - Floral provincialism within the Southern Hemisphere during the Late
Triassic (230 Ma) is characterized by the Ipswich and Onslow provinces, recognized originally in eastern Gondwana. However, new palynological assemblages from the Ischigualasto Formation, northwestern Argentina (231–225 Ma), change the phytogeographic interpretation for the Carnian–Norian in the westernmost Gondwana,
which was previously considered part of the southern floral Ipswich province. Here we show the presence of diagnostic Euramerican species within assemblages dominated by Gondwanan taxa that allows us to refer the palynofloras to the Onslow province. Our new data extend the Onslow floral belt, previously recognized from the western edge of Tethys to Timor, to the western margin of South America. This has implications for palaeophytogeography, palaeoclimate reconstructions and the palaeoecology of a Triassic ecosystem, which has yielded significant vertebrate remains and is regarded important in the early evolution of groups such as the Dinosauria.
A New Non-mammaliaform Eucynodont from the Ischigualasto Formation of Argentina
Martínez, R. N., Fernandez, E., and O. A. Alcober. 2013. A new non-mammaliaform eucynodont from the Carnian-Norian Ischigualasto Formation, Northwestern Argentina. Revista Brasileira de Paleontologia 16: 61-76. doi:10.4072/rbp.2013.1.05
Abstract - The record of non-mammaliaformes eucynodonts from the Carnian-Norian Ischigualasto Formation is diverse and abundant, including a medium to large size herbivore and small carnivores. Here is described a new small eucynodont from the Ischigualasto Formation, on the basis of a partial skull. The new taxon is characterized by palatal process of the premaxilla extending posterior to the level of the first postcanine; deep and large maxillary laterodorsal fossa that opens at the level of the root of the upper canine; and postorbital bar diverging posterolaterally at very low angle (35.6°) from the anteroposterior axis of the skull. Results from a phylogenetic analysis supports the new genus placement as a probainognathian eucynodont, more derived than Probainognathus Romer, and more closely related to Ecteninion Martinez, May & Forster and Trucidocynodon Oliveira, Soares & Schultz than to any other eucynodont. Ecteniniidae is proposed as a new clade including the new genus, Ecteninion and Trucidocynodon, and in the phylogenetic hypothesis represents the sister-group of Prozostrodontia (Prozostrodon Bonaparte & Barberena, Tritylodontidae and Mammaliaformes). Additionally, the new taxon from the Ischigualasto Formation shows that the Scaphonyx-Exaeretodon-Herrerasaurus biozone has similar cynodont diversity than the supposedly contemporaneous Hyperodapedon Assemblage Zone of Santa Maria 2 Sequence, in Southern Brazil.
Abstract - The record of non-mammaliaformes eucynodonts from the Carnian-Norian Ischigualasto Formation is diverse and abundant, including a medium to large size herbivore and small carnivores. Here is described a new small eucynodont from the Ischigualasto Formation, on the basis of a partial skull. The new taxon is characterized by palatal process of the premaxilla extending posterior to the level of the first postcanine; deep and large maxillary laterodorsal fossa that opens at the level of the root of the upper canine; and postorbital bar diverging posterolaterally at very low angle (35.6°) from the anteroposterior axis of the skull. Results from a phylogenetic analysis supports the new genus placement as a probainognathian eucynodont, more derived than Probainognathus Romer, and more closely related to Ecteninion Martinez, May & Forster and Trucidocynodon Oliveira, Soares & Schultz than to any other eucynodont. Ecteniniidae is proposed as a new clade including the new genus, Ecteninion and Trucidocynodon, and in the phylogenetic hypothesis represents the sister-group of Prozostrodontia (Prozostrodon Bonaparte & Barberena, Tritylodontidae and Mammaliaformes). Additionally, the new taxon from the Ischigualasto Formation shows that the Scaphonyx-Exaeretodon-Herrerasaurus biozone has similar cynodont diversity than the supposedly contemporaneous Hyperodapedon Assemblage Zone of Santa Maria 2 Sequence, in Southern Brazil.
Visiting Triassic Park - Ischigualasto Parque Triasico in Argentina
Last month I was fortunate to be able to travel to Argentina for some research time and to attend and present at the Fourth Latin American Vertebrate Paleontology Conference in San Juan. Part of the meeting involved a field trip to the nearby Ischigualasto National Park which is famous for its exposures of Triassic rocks and for fossils of some of the earliest dinosaurs including Eoraptor and Herrerasaurus. As I work at the other Triassic Park, Petrified Forest National Park in Arizona, I was really looking forward to this visit and it did not dissappoint. Below I've posted some photos highlighting my visit.
The visitors center includes mounts (below) and life reconstructions (above) of many of the animals found in Triassic strata in the park. There are also exhibits of actual bones.
Outcrops of the Upper Triassic Ischigualasto Formation. The expanse of the exposures is incredible.
Bones, the Ischigualasto is full of bones.
Christian Sidor and Zhe-Xi Luo getting excited about a cynodont skull that Chris found.
Another in-situ cynodont skull. They are extremely (and amazingly) common here.
Rhynchosaur bones weathering out. Again, the amount of fossil material in the exposures is staggering. Amazingly rhynchosaurs and cynodonts are so common, they are usually not collected. Working in a formation (the Chinle) where these types of animals are relatively unknown, it was very difficult to leave this material behind.
The younger Los Colorados Formation above the Ischigualsto.
Ischigualsto Park and the Ischigualsto Formation are absolutely incredible and I hope to be able to return someday to make new discoveries.
Ischigualsto Park and the Ischigualsto Formation are absolutely incredible and I hope to be able to return someday to make new discoveries.
Eoraptor is a Sauropodomorph, and a New Basal Dinosaur, Eodromaeus murphi, from the Late Triassic of Argentina
The last decade has seen a renaissance in the study of basal dinosaurs and as a result of the resurgence in study we have seen a bunch of new dinosaur taxa coming from the Upper Triassic of North and South America (see excellent syntheses by Langer et al. 2010, and Brusatte et al., 2010). These include the stem-sauropodomorphs Saturnalia, Panphagia, and most recently Chromigosaurus (Langer, 2003; Martinez and Alcober, 2009; Ezcurra, 2010). Other new early dinosaurs include the herrerasaurid Sanjuansaurus, and the basal theropod Tawa (Nesbitt et al. 2010; Alcober and Martinez, 2010). We have also seen updated description and discussion of older taxa such as Chindesaurus and Pisanosaurus as well as the discovery and reinvestigation of numerous dinosauromorphs (e.g., Dzik, 2003; Ferigolo and Langer, 2007; Irmis et al., 2007a, b; Nesbitt et al., 2007, 2009, 2010). Furthermore, a plethora of phylogentic studies are attempting to work out the relationships of all of these taxa (e.g., Langer, 2004; Langer and Benton, 2006; Ezcurra, 2006, 2010; Irmis et al., 2007; Upchurch et al., 2007; Yates, 2007; Martinez and Alcobar, 2009; Nesbitt et al., 2009).
One point of contention in all of these analyses is the phylogenetic position of Eoraptor lunensis from the Upper Triassic Ischigualasto Formation. Originally considered the basal most theropod (e.g., Sereno et al. 1993), recent analysis have supported this hypothesis (Ezcurra, 2006, 2010; Nesbitt et al., 2009) or cast it as a basal saurischian outside of Eusaurischia (e.g., Langer, 2004; Langer and Benton, 2004; Upchurch et al., 2007; Yates, 2007; Martinez and Alcober, 2009).
A new paper out today in Science by Martinez et al. describes a new basal theropod taxon, Eodromaeus murphi, from the Ischigualasto Formation. This new taxon is known by much of the skeleton and represents the new theropod previously mentioned by Martinez et al. (2008). A phylogenetic analysis places Eodromaeus within Theropoda as the sister taxon to Neotheropoda (a position previously held by Tawa, which in this new analysis is a neotheropod) and the sister taxon to the herrerasaurid theropods.
Very striking in this analysis is the recovery of Eoraptor lunensis not only as a Eusaurischian but as a stem-sauropodomorph in a polytomy with Panphagia and Saturnalia (thus it would be a saturnaliine according to Ezcurra 2010; Guaibasaurus and Chromogisaurus were not included in the analysis). This positioning for Eoraptor had previously been alluded to by Martinez and Alcobar (2009), but this is the first time it has been supported by a phylogenetic analysis.
I'm sure this new analysis will cause quite a debate among basal dinosaur workers, especially regarding the ideas of taxon sampling and character inclusion/codings in phylogenetic analyses. The analysis by Martinez et al. excludes lots of incomplete/poorly known taxa as well as taxa that these authors percieve as being too far out phylogentically to have consequence to the question of basal dinosaur relationships. The character matrix is an updated version of Sereno (1999) and does not utilize many characters found in other studies such as Langer and Benton (2006), Ezcurra (2006), and Nesbitt et al. (2009). I don't really have a horse in this race given that I don't have a basal dinosaur analysis that I am personally working on, but as someone outside looking in, it is really difficult to compare across these various analyses given the strong differences in datasets being utilized. Hopefully we will see a consensus at some point.
Nonetheless, if Eoraptor is indeed found to be a basal sauropodomorph, this is of great interest because it gets us a step closer to seeing what the common ancestor of theropods and sauropodomorphs may have looked like.
Some other neat tidbits and conclusions from the paper:
-Like Eoraptor, Eodromaeous possesses a small row of teeth on the palatal ramus of the pterygoid.
-A new radioisotopic date for the top of the Ischigualasto Formation constrains the majority of the formation between 231.4 Ma and 225.9Ma, thus the Ischigualasto Formation spans the Carnian/Norian boundary and does not overlap with dinosaur bearing strata in North America supporting the hypothesis of Irmis and Mundil, 2008, 2010. The previously reported date of ~217 Ma for the middle of the formation by Shipman (2004) and Currie et al (2009) has been considered unreliable because of a lack of stratigraphic control and the inability to reproduce the methodology.
-The Ischigualasto is divided into three biozones based on vertebrate fossil occurrences. One of the boundaries is supposed to represent the Carnian/Norian boundary, although it seems to me that these boundaries are somewhat ambiguous as they all depend on negative evidence.
-Placing the vertebrate occurrences in stratigraphic order suggests to the authors that rhynchosaurs went extinct at the Carnian/Norian boundary. Interestingly they also propose that dinosaurs went extinct locally and did not reappear in the area until deposition of the Los Colorados Formation later in the Norian.
Martinez, R. N., Sereno, P. C., Alcober, O. A., Colombi, C. E., Renne, P. R., Montañez, I. P., and B. S. Currie. 2011. A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern Pangaea. Science 331:206-210 DOI: 10.1126/science.1198467.
Abstract - Upper Triassic rocks in northwestern Argentina preserve the most complete record of dinosaurs before their rise to dominance in the Early Jurassic. Here, we describe a previously unidentified basal theropod, reassess its contemporary Eoraptor as a basal sauropodomorph, divide the faunal record of the Ischigualasto Formation with biozones, and bracket the formation with 40Ar/39Ar ages. Some 230 million years ago in the Late Triassic (mid Carnian), the earliest dinosaurs were the dominant terrestrial carnivores and small herbivores in southwestern Pangaea. The extinction of nondinosaurian herbivores is sequential and is not linked to an increase in dinosaurian diversity, which weakens the predominant scenario for dinosaurian ascendancy as opportunistic replacement.
New Scientist article by Jeff Hecht here. Other links at Live Science and the BBC.
One point of contention in all of these analyses is the phylogenetic position of Eoraptor lunensis from the Upper Triassic Ischigualasto Formation. Originally considered the basal most theropod (e.g., Sereno et al. 1993), recent analysis have supported this hypothesis (Ezcurra, 2006, 2010; Nesbitt et al., 2009) or cast it as a basal saurischian outside of Eusaurischia (e.g., Langer, 2004; Langer and Benton, 2004; Upchurch et al., 2007; Yates, 2007; Martinez and Alcober, 2009).
A new paper out today in Science by Martinez et al. describes a new basal theropod taxon, Eodromaeus murphi, from the Ischigualasto Formation. This new taxon is known by much of the skeleton and represents the new theropod previously mentioned by Martinez et al. (2008). A phylogenetic analysis places Eodromaeus within Theropoda as the sister taxon to Neotheropoda (a position previously held by Tawa, which in this new analysis is a neotheropod) and the sister taxon to the herrerasaurid theropods.
Very striking in this analysis is the recovery of Eoraptor lunensis not only as a Eusaurischian but as a stem-sauropodomorph in a polytomy with Panphagia and Saturnalia (thus it would be a saturnaliine according to Ezcurra 2010; Guaibasaurus and Chromogisaurus were not included in the analysis). This positioning for Eoraptor had previously been alluded to by Martinez and Alcobar (2009), but this is the first time it has been supported by a phylogenetic analysis.
I'm sure this new analysis will cause quite a debate among basal dinosaur workers, especially regarding the ideas of taxon sampling and character inclusion/codings in phylogenetic analyses. The analysis by Martinez et al. excludes lots of incomplete/poorly known taxa as well as taxa that these authors percieve as being too far out phylogentically to have consequence to the question of basal dinosaur relationships. The character matrix is an updated version of Sereno (1999) and does not utilize many characters found in other studies such as Langer and Benton (2006), Ezcurra (2006), and Nesbitt et al. (2009). I don't really have a horse in this race given that I don't have a basal dinosaur analysis that I am personally working on, but as someone outside looking in, it is really difficult to compare across these various analyses given the strong differences in datasets being utilized. Hopefully we will see a consensus at some point.
Nonetheless, if Eoraptor is indeed found to be a basal sauropodomorph, this is of great interest because it gets us a step closer to seeing what the common ancestor of theropods and sauropodomorphs may have looked like.
Some other neat tidbits and conclusions from the paper:
-Like Eoraptor, Eodromaeous possesses a small row of teeth on the palatal ramus of the pterygoid.
-A new radioisotopic date for the top of the Ischigualasto Formation constrains the majority of the formation between 231.4 Ma and 225.9Ma, thus the Ischigualasto Formation spans the Carnian/Norian boundary and does not overlap with dinosaur bearing strata in North America supporting the hypothesis of Irmis and Mundil, 2008, 2010. The previously reported date of ~217 Ma for the middle of the formation by Shipman (2004) and Currie et al (2009) has been considered unreliable because of a lack of stratigraphic control and the inability to reproduce the methodology.
-The Ischigualasto is divided into three biozones based on vertebrate fossil occurrences. One of the boundaries is supposed to represent the Carnian/Norian boundary, although it seems to me that these boundaries are somewhat ambiguous as they all depend on negative evidence.
-Placing the vertebrate occurrences in stratigraphic order suggests to the authors that rhynchosaurs went extinct at the Carnian/Norian boundary. Interestingly they also propose that dinosaurs went extinct locally and did not reappear in the area until deposition of the Los Colorados Formation later in the Norian.
Martinez, R. N., Sereno, P. C., Alcober, O. A., Colombi, C. E., Renne, P. R., Montañez, I. P., and B. S. Currie. 2011. A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern Pangaea. Science 331:206-210 DOI: 10.1126/science.1198467.
Abstract - Upper Triassic rocks in northwestern Argentina preserve the most complete record of dinosaurs before their rise to dominance in the Early Jurassic. Here, we describe a previously unidentified basal theropod, reassess its contemporary Eoraptor as a basal sauropodomorph, divide the faunal record of the Ischigualasto Formation with biozones, and bracket the formation with 40Ar/39Ar ages. Some 230 million years ago in the Late Triassic (mid Carnian), the earliest dinosaurs were the dominant terrestrial carnivores and small herbivores in southwestern Pangaea. The extinction of nondinosaurian herbivores is sequential and is not linked to an increase in dinosaurian diversity, which weakens the predominant scenario for dinosaurian ascendancy as opportunistic replacement.
New Scientist article by Jeff Hecht here. Other links at Live Science and the BBC.
Sanjuansaurus gordilloi a new Herrerasaurid from Argentina
Here is a new herrerasaurid from the the Ischigualasto Formation of Argentina. Looks much more similar to Herrerasaurus than to Staurikosaurus or Chindesaurus, although the latter taxon was not included in the phylogenetic analysis. This analysis finds Herrerasauridae to be the sister taxon to Eoraptor + (Guaibasaurus + Neotheropoda), so we are back to the position of herrerasaurids still being dinosaurs but as basal saurischians rather than theropods. Comparison is provided in the text to Tawa hallae, but it is not included in the phylogenetic analysis. Too bad. However, I'm pretty certain that based on the current material coding Sanjuansaurus into the analysis of Nesbitt et al. (2009) would not change the position of herrerasaurids as basal theropods as recovered in that analysis. So whether or not herrerasaurids are theropods or not appears to be entirely dependent on the base matrix one uses. Thus, unfortunately, the analysis in this paper does not appear to offer anything particularly game-changing or significant in that regards. Also unfortunate is that there is no discussion of these differing hypotheses in the paper.
The further recognition of the increased diversity of basal saurischian dinosaurs in the latest Carnian is interesting and provides more circumstantial support for the earlier diversification of Archosauria in the Early Triassic as hypothesized by Nesbitt (2009) based on body fossils and more recently by Brusatte et al. (2010) based on footprint evidence.
Alcober O.A., and R. N. Martinez. 2010. A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina. ZooKeys 63 : 55 – 81 . doi: 10.3897/zookeys.63.550
Abstract - Herrerasauridae comprises a basal clade of dinosaurs best known from the Upper Triassic of Argentina and Brazil, which have yielded remains of Herrerasaurus ischigualastensis and Staurikosaurus pricei, respectively. Systematic opinion regarding the position of Herrerasauridae at the base of Dinosauria has varied. Here we describe a new herrerasaurid, Sanjuansaurus gordilloi gen. n., sp. n., based on a partial skeleton from Carnian-age strata of the the Upper Triassic Ischigualasto Formation of northwestern Argentina. The new taxon is diagnosed by numerous features, including long, band-shaped and posterolaterally oriented transverse process on the posterior cervical vertebrae; neural spines of the sixth to eighth dorsal vertebrae, at least, bearing acute anterior and posterior processes; scapula and coracoid with everted lateral margins of the glenoid; and short pubis (63% of the femoral length). Phylogenetic analysis placed Sanjuansaurus within a monophyletic Herrerasauridae, at the base of Theropoda and including Herrerasaurus and Staurikosaurus. The presence of Sanjuansaurus at the base of the Ischigualasto Formation, along with other dinosaurs such as Herrerasaurus, Eoraptor, Panphagia, and Chromogisaurus suggests that saurischian dinosaurs in southwestern Pangea were already widely diversified by the late Carnian rather than increasing in diversity across the Carnian-Norian boundary.
REFERENCES
Brusatte, S. L., Niedźwiedzki, G., and R. J. Butler. 2010. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B. doi: 10.1098/rspb.2010.1746
Nesbitt, S. J. 2009. The antiquity of Archosauria and the origin of Late Triassic archosaur assemblages. Journal of Vertebrate Paleontology 29:155A.
Nesbitt, S. J., Smith, N. D., Irmis, R. B.,Turner, A. H., Downs, A., and M. A. Norell. 2009. A Complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs. Science 326: 1530–1533.
The further recognition of the increased diversity of basal saurischian dinosaurs in the latest Carnian is interesting and provides more circumstantial support for the earlier diversification of Archosauria in the Early Triassic as hypothesized by Nesbitt (2009) based on body fossils and more recently by Brusatte et al. (2010) based on footprint evidence.
Alcober O.A., and R. N. Martinez. 2010. A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina. ZooKeys 63 : 55 – 81 . doi: 10.3897/zookeys.63.550
Abstract - Herrerasauridae comprises a basal clade of dinosaurs best known from the Upper Triassic of Argentina and Brazil, which have yielded remains of Herrerasaurus ischigualastensis and Staurikosaurus pricei, respectively. Systematic opinion regarding the position of Herrerasauridae at the base of Dinosauria has varied. Here we describe a new herrerasaurid, Sanjuansaurus gordilloi gen. n., sp. n., based on a partial skeleton from Carnian-age strata of the the Upper Triassic Ischigualasto Formation of northwestern Argentina. The new taxon is diagnosed by numerous features, including long, band-shaped and posterolaterally oriented transverse process on the posterior cervical vertebrae; neural spines of the sixth to eighth dorsal vertebrae, at least, bearing acute anterior and posterior processes; scapula and coracoid with everted lateral margins of the glenoid; and short pubis (63% of the femoral length). Phylogenetic analysis placed Sanjuansaurus within a monophyletic Herrerasauridae, at the base of Theropoda and including Herrerasaurus and Staurikosaurus. The presence of Sanjuansaurus at the base of the Ischigualasto Formation, along with other dinosaurs such as Herrerasaurus, Eoraptor, Panphagia, and Chromogisaurus suggests that saurischian dinosaurs in southwestern Pangea were already widely diversified by the late Carnian rather than increasing in diversity across the Carnian-Norian boundary.
 |
| Holotype specimen of Sanjuansaurus gordilloi (PVSJ 605) |
Brusatte, S. L., Niedźwiedzki, G., and R. J. Butler. 2010. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B. doi: 10.1098/rspb.2010.1746
Nesbitt, S. J. 2009. The antiquity of Archosauria and the origin of Late Triassic archosaur assemblages. Journal of Vertebrate Paleontology 29:155A.
Nesbitt, S. J., Smith, N. D., Irmis, R. B.,Turner, A. H., Downs, A., and M. A. Norell. 2009. A Complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs. Science 326: 1530–1533.
New Basal Sauropodomorph from South America
Martinez, R.N., and O.A. Alcober. 2009. A Basal Sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the Early Evolution of Sauropodomorpha. PLoS ONE 4: e4397. doi:10.1371/journal.pone.0004397
Abstract
Background: The earliest dinosaurs are from the early Late Triassic (Carnian) of South America. By the Carnian the main clades Saurischia and Ornithischia were already established, and the presence of the most primitive known sauropodomorph Saturnalia suggests also that Saurischia had already diverged into Theropoda and Sauropodomorpha. Knowledge of Carnian sauropodomorphs has been restricted to this single species.
Methodology/Principal Findings: We describe a new small sauropodomorph dinosaur from the Ischigualsto Formation (Carnian) in northwest Argentina, Panphagia protos gen. et sp. nov., on the basis of a partial skeleton. The genus and species are characterized by an anteroposteriorly elongated fossa on the base of the anteroventral process of the nasal; wide lateral flange on the quadrate with a large foramen; deep groove on the lateral surface of the lower jaw surrounded by prominent dorsal and ventral ridges; bifurcated posteroventral process of the dentary; long retroarticular process transversally wider than the articular area for the quadrate; oval scars on the lateral surface of the posterior border of the centra of cervical vertebrae; distinct prominences on the neural arc of the anterior cervical vertebra; distal end of the scapular blade nearly three times wider than the neck; scapular blade with an expanded posterodistal corner; and medial lamina of brevis fossa twice as wide as the iliac spine.
Conclusions/Significance: We regard Panphagia as the most basal sauropodomorph, which shares the following apomorphies with Saturnaliaand more derived sauropodomorphs: basally constricted crowns; lanceolate crowns; teeth of the anterior quarter of the dentary higher than the others; and short posterolateral flange of distal tibia. The presence of Panphagia at the base of the early Carnian Ischigualasto Formation suggests an earlier origin of Sauropodomorpha during the Middle Triassic.
Abstract
Background: The earliest dinosaurs are from the early Late Triassic (Carnian) of South America. By the Carnian the main clades Saurischia and Ornithischia were already established, and the presence of the most primitive known sauropodomorph Saturnalia suggests also that Saurischia had already diverged into Theropoda and Sauropodomorpha. Knowledge of Carnian sauropodomorphs has been restricted to this single species.
Methodology/Principal Findings: We describe a new small sauropodomorph dinosaur from the Ischigualsto Formation (Carnian) in northwest Argentina, Panphagia protos gen. et sp. nov., on the basis of a partial skeleton. The genus and species are characterized by an anteroposteriorly elongated fossa on the base of the anteroventral process of the nasal; wide lateral flange on the quadrate with a large foramen; deep groove on the lateral surface of the lower jaw surrounded by prominent dorsal and ventral ridges; bifurcated posteroventral process of the dentary; long retroarticular process transversally wider than the articular area for the quadrate; oval scars on the lateral surface of the posterior border of the centra of cervical vertebrae; distinct prominences on the neural arc of the anterior cervical vertebra; distal end of the scapular blade nearly three times wider than the neck; scapular blade with an expanded posterodistal corner; and medial lamina of brevis fossa twice as wide as the iliac spine.
Conclusions/Significance: We regard Panphagia as the most basal sauropodomorph, which shares the following apomorphies with Saturnaliaand more derived sauropodomorphs: basally constricted crowns; lanceolate crowns; teeth of the anterior quarter of the dentary higher than the others; and short posterolateral flange of distal tibia. The presence of Panphagia at the base of the early Carnian Ischigualasto Formation suggests an earlier origin of Sauropodomorpha during the Middle Triassic.
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