Field of Science
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Background: Basal sauropodomorphs, or ‘prosauropods,’ are a globally widespread paraphyletic assemblage of terrestrial herbivorous dinosaurs from the Late Triassic and Early Jurassic. In contrast to several other landmasses, the North American record of sauropodomorphs during this time interval remains sparse, limited to Early Jurassic occurrences of a single well known taxon from eastern North America and several fragmentary specimens from western North America.
Methodology/Principal Findings: On the basis of a partial skeleton, we describe here a new basal sauropodomorph dinosaur from the Lower Jurassic Navajo Sandstone of southern Utah, Seitaad ruessi gen. et sp. nov. The partially articulated skeleton of Seitaad was likely buried post-mortem in the base of a collapsed dune foreset. The new taxon is characterized by a plate-like medial process of the scapula, a prominent proximal expansion of the deltopectoral crest of the humerus, a strongly inclined distal articular surface of the radius, and a proximally and laterally hypertrophied proximal metacarpal I.
Conclusions/Significance: Phylogenetic analysis recovers Seitaad as a derived basal sauropodomorph closely related to plateosaurid or massospondylid ‘prosauropods’ and its presence in western North America is not unexpected for a member of this highly cosmopolitan clade. This occurrence represents one of the most complete vertebrate body fossil specimens yet recovered from the Navajo Sandstone and one of the few basal sauropodomorph taxa currently known from North America.
Knoll, F. 2010. A primitive sauropodomorph from the upper Elliot Formation of Lesotho. Geological Magazine early online doi:10.1017/S001675681000018X
Abstract – A well-preserved, articulated dinosaur skeleton from southern Africa is described. The specimen comes from the upper Elliot Formation (?Hettangian) of Ha Ralekoala (Lesotho) and represents a new species: Ignavusaurus rachelis genus et species nova. A cladistic analysis suggests that Ignavusaurus is more derived than Thecodontosaurus–Pantydraco, but more primitive than Efraasia. Ignavusaurus indeed shares a number of unambiguous synapomorphies with the taxa more derived than Thecodontosaurus–Pantydraco, such as a fully open acetabulum, but it is more plesiomorphic than Efraasia and more derived sauropodomorphs as shown by the evidence of, for instance, the distal extremity of its tibia that is is longer (cranio-caudally) than wide (latero-medially). The discovery of Ignavusaurus increases the known diversity of the early sauropodomorph fauna of the upper Elliot
Formation, which stands as one of the richest horizons in the world in this respect.
Bandyopadhyay, S., Gillette, D. D., Ray, S., and D. P. Sengupta. 2010. Osteology of Barapasaurus tagorei (Dinosauria: Sauropoda) from the Early Jurassic of India.
Palaeontology early online doi: 10.1111/j.1475-4983.2010.00933.x
Abstract - The sauropod dinosaur, Barapasaurus tagorei, is known from the Early Jurassic Kota Formation (Sinemurian to Pliensbachian) of India. The taxon is represented by c. 300 bones that were found associated with large fossilized tree trunks and were collected from the interface of sandstone and mudstone units covering an area of c. 276 meters squared. The collection includes one partial skeleton; most of the remainder of the bones were disarticulated, disassociated and dispersed, but taphonomic analysis permits recognition of associated elements comprising several individuals. Skeletal anatomy of Barapasaurus includes several teeth, vertebrae from the caudal cervicals rearward to the terminal caudals, and most elements of the appendicular skeleton. Barapasaurus is characterized by spoon-shaped teeth with bulbous bases and grooves on the anterolabial and posterolingual sides of the crown, coarse tubercles on the carina, acamerate cranial and dorsal vertebrae, lateral laminae of the middle and caudal dorsal neural spines composed of spinodiapophyseal and spinopostzygapophyseal laminae, neural canal of the mid-dorsal vertebrae opens dorsally through a narrow slit into a large cavity and sacrum with four co-ossified vertebrae. Phylogenetic analysis reveals that Barapasaurus is basal in comparison with Vulcanodon and is removed from Eusauropoda.
Abstract - A leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO2. The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie’s Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO2 super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date.
Marsicano, C.A., Mancuso, A.C., Palma, R.M., and Krapovickas, V. 2010. Tetrapod tracks in a marginal lacustrine setting (Middle Triassic, Argentina): taphonomy and significance. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2010.03.009.
ABSTRACT - Fossil tetrapod footprints not only provide valuable information about trackmaker paleobiology but also to give insight into details of the depositional conditions of the substrate at the time of imprinting. Therefore, in the present study the mode of formation and taphonomy of footprints in different substrates was used to investigate the gait and walking dynamics of the trackmakers as well as a source of additional information on the environmental conditions of the track-bearing beds during imprinting. The analyzed section corresponds to thick Middle Triassic lacustrine/deltaic deposits of the Ischichuca/Los Rastros Formation (Ischigualasto-Villa Unión Basin) that crops out at the Quebrada de Ischichuca in northwestern Argentina. Part of the track-bearing surfaces correspond to the top of sandy distributary channel mouth bars in a distal delta front setting that were exposed along the lake margin during a lake level fall. Cross-cutting relationships observed among ripple-marks, the footprints, and invertebrate traces of a softground suite of the Scoyenia ichnofacies suggest an omission surface. Measured trackway orientations in the sandstones are perpendicular to the paleo-shoreline, with the animals coming and going along the exposed top of the bars, probably for drinking. Laterally, the distal delta front deposits interfinger with track-bearing wackestone beds of palustrine origin deposited in a restricted local embayment lateral to the delta influenced environment. Trackway orientations in the wackestones are, in contrast, consistent with the animals moving nearly parallel to the lake border, probably along a preferred route. Evidences of a relative high groundwater table at the time of imprinting in the track-bearing surfaces are revealed by the well developed rims of extruded sediment and collapsed digits in the studied tracks and the nearly absence of associated desiccation cracks on the same surfaces. Nevertheless, temporary emergence cannot be ruled out when paleosoil formation was probably promoted as can be observed in the microstructure of both sandstones and wackestones. Moreover, footprint preservation in the wackestones might have been enhanced by partial hardening of the trampled surface during subaerial exposure. Combining ichnofossil content and taphonomy with facies analysis we identified in the lower part of the Ischichuca/Los Rastros succession a relatively rapid withdrawal of the water basinward that was probably due to a forced regression during early rifting of basin evolution. Footprints can also provide valuable information about locomotion dynamics and trackmaker behavior. Thus, the sideways deformation observed in the studied footprints, attributed to basal archosaurs and putative basal dinosaurs, can be related to an outward rotation of the foot during the step cycle, a condition that might allied to the development of the parasagittal posture in Archosauria. Besides, the densely trampled surface described herein constitutes the first documented evidence of putative social behavior among therapsid dicynodonts, the most important group of herviborous animals in the early Mesozoic terrestrial ecosystems throughout Gondwana.
Preto, N., Kustatscher, E., and Wignall, P.B. 2010. Triassic climates -- state of the art and perspectives. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2010.03.015.
ABSTRACT - The climate of the Triassic period was characterized by a non-zonal pattern, dictated by a strong global monsoon system with effects that are most evident in the Tethys realm. This strong monsoonal regime is related to the aggregation of the Pangaean supercontinent, which by Triassic time was already completed. Climate oscillations existed within this framework. The harsh hothouse climatic conditions that characterized the Late Permian, and perhaps precipitated the end-Permian mass extinction, were probably maintained during the Early Triassic and may account for the impoverished, but distinctive, faunal and floral Lower Triassic associations. Although metazoan reef builders were probably the most
affected group, carbonate production remained high at least in the western Tethys realm. The Middle Triassic was characterised locally by humid episodes, although their geographical distribution has yet to be clarified. The Carnian Pluvial Event, marks an episode of increased rainfall documented worldwide, was the most distinctive climate change within the Triassic. Different hypotheses have been proposed for its causes: changes of atmospheric or ocean circulation driven by plate tectonics; a peak of the global monsoon due to maximum continent aggregation; or triggering by the eruption of a large igneous province. Subsequently, the late Carnian and Norian seem to have been climatically stable, although minor climatic changes have recently been described even from this time period. Finally, the end Triassic extinction event is also associated with climate change, specifically warming and increased rainfall, but this evidence comes mostly from the northern parts of the Central Atlantic Magmatic Province, and the global pattern of climate change at the Triassic / Jurassic boundary has still to be resolved. Many facets of Triassic climate are intriguing and deserve further research. However, paleoclimate studies on the Triassic have so far been carried out only locally with different proxies. Those proxies will require inter-calibration, in order to depict correctly the temporal and geographical patterns of Triassic climate.
Fischer, J., Axsmith, B. J. and S. R. Ash. 2010. First unequivocal record of the hybodont shark egg capsule Palaeoxyris in the Mesozoic of North America. Neues Jahrbuch fur Geologie und Paläontologie Abh. 255: 327–344.
Abstract - The hybodont shark egg capsule Palaeoxyris humblei n. sp. is described here from four specimens collected from flood plain deposits in the Blue Mesa Member of the Chinle Formation of Late Triassic (Norian) age in Petrified Forest National Park, Arizona. This find is the first unequivocal record of Palaeoxyris in the Mesozoic of North America. The species differs from previously known taxa, especially other Triassic forms in size and banding. It also is one of the smallest species assigned to the genus. This find offers the rare opportunity of plausibly assigning these egg capsules to the hybodont nonmarine shark Lonchidion humblei as the most probable source since its disarticulated remains (teeth, fin spines) have been found at a closely adjacent locality. Originally, these eggs were deposited in special spawning grounds in the river that deposited the Newspaper Sandstone Bed. There they became attached by tendrils to a piece of drift wood or perhaps the stem or branches of a horsetail such as Neocalamites or Equisetites that grew in the shallow waters of the stream. However, the stream overflowed its banks and the egg capsules together with masses of plant debris and various invertebrates were washed onto the adjacent floodplain where they were buried and eventually fossilized.
Abstract- Patterns of bone deposition are reported and deduced from mid-shaft sections of 21 limb bones of the dicynodont Placerias hesternus from the Placerias Quarry(Upper Triassic), Arizona, USA. All sampled elements of P. hesternus have a large medullary cavity completely filled with bony trabeculae surrounded by dense cortical bone. Dense Haversian bone extends from the perimedullary region to at least the mid-cortex in all sampled bones. Primary bone in the outer cortex of limb elements of P. hesternus is generally zonal fibrolamellar with a peripheral layer of parallelfibred bone. These data suggest periodic rapid osteogenesis followed by slower growth. Among dicynodonts, this strategy is most similar to growth previously reported in other Triassic (Lystrosaurus, Wadiasaurus) and some Permian taxa (Oudenodon, Tropidostoma). An external fundamental system(EFS), suggesting complete or near complete cessation of appositional growth, is present in the largest tibia. This is the first report of EFS in dicynodonts and may represent the attainment of maximum size in P. hesternus. Slow-growing peripheral bone was observed in elements of varying size in our sample and may support a differential growth pattern between P. hesternus individuals from this locality. A complete growth series of P. hesternus, analysis of Placerias specimens from other localities, and further sampling of other Upper Triassic dicynodonts are needed to better understand a more complete picture of the growth and remodelling patterns that we have initially investigated.
I've only been able to briefly scan this, but it looks like a cool study. Two presented hypotheses that caught my eye are that the bone make-up in Placerias suggests an amphibious or aquatic lifestyle, and that the cessation of growth in many of the specimens may been due to a response to changing environmental conditions.
Abstract - We report on a large burrow cast with skeletal contents from Lower Triassic strata of the Palingkloof Member of the Balfour Formation, which forms the lowermost portion of the Lystrosaurus Assemblage Zone(LAZ) of South Africa. The burrow cast is similar to large burrow casts previously described from the LAZ that were identified as large-scale Scoyenia domichnia. It is the first large burrow cast from the LAZ found to contain diagnostic fossil bone. The burrow cast is a relatively straight, subhorizontal (inclined ,12u), dorsoventrally compressed tube consisting of an entry ramp and living chamber; the entrance to the burrow is not preserved and there is no evidence that the ramp formed a spiral section. The skeletal material comprises a single, partial, disarticulated skeleton a juvenile animal that can be assigned with confidence to the dicynodont genus Lystrosaurus. Whereas similar large-diameter burrow casts from strata slightly higher in the LAZ have been attributed to Lystrosaurus, we present an alternative hypothesis that a carnivorous tetrapod constructed the burrow. Our preferred hypothesis is supported by the observation that the interred Lystrosaurus skeleton is too small to be the maker of this particular burrow, by the general observation that carnivorous tetrapods construct relatively straight burrows, and by the partial, disarticulated state of the skeleton, which we interpret as the remains of larded prey. We suggest that akidnognathid theriodonts of the genera Moschorhinus or Olivierosuchus, the most conspicuous large predators of the LAZ, were the constructors of large-diameter, subhorizontal burrows.
Voight, S., D. Hoppe. 2010. and Mass Occurrence of Penetrative Trace Fossils in Triassic Lake Deposits (Kyrgyzstan, Central Asia). Ichnos 17:1-11. http://dx.doi.org/10.1080/10420940903358081
Abstract - Bioturbation and the breakdown of organic detritus by burrowing macro-invertebrates are key factors for the energy flow in recent freshwater ecosystems due to the acceleration of nutrient cycling. According to the current state of knowledge, food webs similar to those of modern lakes were not operating until the Late Mesozoic, when a well-established freshwater infauna evolved. Here we describe laterally extended networks of irregularly branched burrows that constitute the most common ichnofossils in lacustrine deposits of the Middle to Late Triassic Madygen Formation, SW Kyrgyzstan. The shallow penetrative trace fossils give evidence that exploitation of lake-bottom sediments by benthic invertebrates was already in place in the Early Mesozoic. Architecture and size of the fossil burrows indicate deposit-feeding, worm-like trace makers of similar morphology and behavior to extant oligochaetes or aquatic insect larvae. Maximum intensity of bioturbation is recorded in mudstones of the transitional sublittoral to profundal lake zone, which usually represent the thermocline/chemocline level in modern stratified lakes. Taking into account the low-oxygen tolerance of many recent oligochaetes and insect larvae, we propose that ecospace utilization of deep-water lacustrine settings was originally impelled by two factors: the exploitation of additional food resources and the avoidance of predation by carnivorous animals from well-aerated lake zones. Spatial restriction of the described fossil traces could offer a basic approach to subdivide the Mermia ichnofacies.
Hubert, J. F., and J. A. Dutcher. 2010. Scoyenia Escape Burrows in Fluvial Pebbly Sand: Upper Triassic Sugarloaf Arkose, Deerfield Rift Basin, Massachusetts, USA. Ichnos 17-20-24. http://dx.doi.org/10.1080/10420940903358529
Abstract - Late Triassic larvae of an insect, probably a beetle, moved diagonally upwards though fluvial pebbly sand along a thin mud layer, constructing Scoyenia burrows in the Sugarloaf Arkose, Deerfield rift basin, Massachusetts. They may have been escaping a temporary rise of the water table in the monsoonal dry season.
Abstract - The Triassic–Jurassic (T–J) boundary interval coincides with enhanced extinction rates in the marine realm and pronounced changes in terrestrial ecosystems on the continents. It is further marked by distinct negative excursions in the δ13Corg and 13Ccarb signature that may represent strong perturbations of the global carbon cycle. We present integrated geochemical, stable-isotope and palynological data from the Kuhjoch section, the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic (Northern Calcareous Alps, Austria). We show that the initial carbon isotope excursion (CIE), coinciding with the marine extinction interval and the formation of black shales in the western Tethys Eiberg Basin, is marked by only minor changes in kerogen type, which is mainly of terrestrial origin. Increased Total Organic Carbon (TOC) concentrations of 9% at the first half of the initial CIE coincide with Hydrogen Index (HI) values of over 600 mg HC/g TOC. The high correlation (with R2=0.93) between HI values and terrestrial Cheirolepidiaceaen conifer pollen suggests a terrestrial source for the hydrogen enriched organic compounds. The lack of major changes in source of the sedimentary organic matter suggests that changes in the δ13Corg composition are genuine and represent true disturbances of the global C-cycle. The sudden decrease in total inorganic carbon (TIC) concentrations likely represents the onset of a biocalcification crisis. It coincides with a 4.5‰ negative shift in δ13Corg values and possibly corresponds to the onset of CAMP related volcanic activity. The second half of the initial CIE is marked by the dramatic increase of green algae remains in the sediment. The simultaneous increase of the Corg/Ntot ratio suggests increased marine primary production at the final stage of black shale formation.
Abstract - The early evolutionary history of Ornithodira (avian-line archosaurs) has hitherto been documented by incomplete (Lagerpeton) or unusually specialized forms (pterosaurs and Silesaurus). Recently, a variety of Silesaurus-like taxa have been reported from the Triassic Period of both Gondwana and Laurasia, but their relationships to each other and to dinosaurs remain a subject of debate. Here we report on a new avian-line archosaur from the early Middle Triassic (Anisian) of Tanzania. Phylogenetic analysis places Asilisaurus kongwe gen. et sp. nov. as an avian-line archosaur and a member of the Silesauridae, which is here considered the sister taxon to Dinosauria. Silesaurids were diverse and had a wide distribution by the Late Triassic, with a novel ornithodiran bauplan including leaf-shaped teeth, a beak-like lower jaw, long, gracile limbs, and a quadrupedal stance. Our analysis suggests that the dentition and diet of silesaurids, ornithischians and sauropodomorphs evolved independently from a plesiomorphic carnivorous form. As the oldest avian-line archosaur, Asilisaurus demonstrates the antiquity of both Ornithodira and the dinosaurian lineage. The initial diversification of Archosauria, previously documented by crocodilian-line archosaurs in the Anisian, can now be shown to include a contemporaneous avian-line radiation. The unparalleled taxonomic diversity of the Manda archosaur assemblage indicates that archosaur diversification was well underway by the Middle Triassic or earlier.
Prior to 2003 the non-dinosaurian dinosauriforms known as silesaurids were unrecognized in the fossil record. Specimens existed in collections, collected as early as the 1930s, while others were given tentative identifications (e.g., the ornithosuchid of Long and Murry, 1995 and the ornithischian Technosaurus). Dzik (2003) described the first, Silesaurus opolensis from the Carnian of Poland, with its very distinctive femoral and morphologies. Suddenly similar forms were recognized from all over the globe (e.g., Eucoelophysis, Sacisaurus; Ezcurra 2006; Nesbitt et al. 2007; Irmis et al. 2007a), whereas new specimens were being discovered from the Chinle Formation of New Mexico and Arizona (Parker et al. 2006; Irmis et al. 2007b).
Still, because the earliest pseudosuchian archosaurs were known from the Anisian (e.g., the Moenkopi Formation of Arizona), whereas the earliest ornithodirans were from the Ladinian of Argentina, there was a proposed ghost lineage for Ornithodira existing back into the Anisian.
Sterling Nesbitt looks over the Ruhuhu Valley in 2007. Photo by L. Tsuji.
One of the strengths of phylogentic analysis is the ability to make predictions as to where in time and space certain groups should and could be found. Sterling Nesbitt clearly recognized the strong possibility that the earliest representatives of ornithodira could be found in the Manda beds of Tanzania as this fauna was known for its pseudosuchian constituents. A few years back this prediction paid off, as a team lead by Christian Sidor in 2007 to explore the Permian and Triassic rocks of Tanzanian, uncovered an amazing deposit of early archosaurs including numerous specimens of a silesaurid. Named Asilisaurus kongwe (Ancient ancestor lizard) these specimens represent the earliest known member of the lineage leading to dinosaurs and strongly supports the diversification of the Archosauria by the early Middle Triassic (~243 million years ago).
The tibia of Asilisaurus, following excavation in 2007. Photo by R. Smith.
This find also strongly suggests that adaptations for an omnivorous or herbivorous diet evolved independently in silesaurids, ornithischians, and sauropodomorphs, from carnivorous ancestors. The paper also phylogenetically defines the Silesauridae and proposes that the South American archosaurs Lewisuchus and Pseudlagosuchus are members of this clade and probably also synonymous. Another early appearance of a non-dinosaurian dinosauriform in
Gondwana also provides further support for a southern origin for this group.
Dzik, J. 2003. A beaked herbivorous archosaur with dinosaur affinities from the early Late Triassic of Poland. Journal of Vertebrate Paleontology 23:556-574.
Ezcurra, M.D. 2006. A review of the systematic position of the dinosauriform archosaur Eucoelophysis baldwini from the Upper Triassic of New Mexico, U.S.A. Geodiversitas 28:649-684.
Ferigolo, J. and M. Langer. 2007. A late Triassic dinosauriform from south Brazil and the origin of the ornithischian predentary bone. Historical Biology 19:23-33.
Irmis, R.B., Parker, W.G., Nesbitt, S.J., and J. Liu. 2007a. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.
Irmis, R. B., Nesbitt, S. J., Padian, K., Smith, N. D., Turner, A. H., Woody, D., and A. Downs. 2007a. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317:358-361.
Nesbitt, S.J., Irmis, R.B., and W.G. Parker. 2007. A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5:209-243.
Parker, W.G., Irmis, R.B., and S.J. Nesbitt. 2006. Review of the Late Triassic dinosaur record from Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62:160-161.