70 research outputs found
A REVISED CLASSIFICATION OF CYNODONTS (REPTILIA; THERAPSIDA)
Cynodonts are very advanced mammal-like reptiles of the Permian-Triassic which are of special interest to evolutionists because they gave rise to
the Class Mammalia during Middle or Late Triassic
time. Cynodonts have been known from strata of
Early Triassic age in South Africa for over one
hundred years, and numerous specimens have been
collected and described. In recent years the record
of cynodonts has been extended into earlier and
later time zones, not only in southern Africa but
in East Africa, South America, Russia , China, and,
most recently, in North America. Much of the
material from outside of Africa has not yet been
fully described
Fossils from the Elliot and Clarens Formations (Karoo sequence) of the Northeastern Cape, Orange Free State and Lesotho, and a suggested biozonation based on tetrapods
Recent intensive collecting from the Elliot Formation and lower part of the Clarens Formation of the Orange Free State is reported and a broad description is given of the general lithology of the beds in this area.
Productive localities in the main Karoo basin (northeastern Cape Province, Lesotho, Orange Free State} are listed with a summary of the tetrapods recovered from each.
A preliminary biozonation of these strata is proposed based on the vertical ranges of the prosauropod saurischian genera Euskelosaurus and Massospondylus. Attention is drawn to a palaeontologically rich horizon within the Massospondylus Range Zone which is designated the Tritylodon Acme-zone on the basis of the abundance in it of the advan- ced cynodont Tritylodon cf. longaevus.
It is concluded that previous taxonomic work on the tetrapod fauna of these strata has resulted in an erroneous impression of faunal diversity
Scanning Electron Microscopy of Early Dinosaur Egg Shell Structure: A Comparison with Other Rigid Sauropsid Eggs
Fossil eggs attributable to dinosaur (probably prosauropod) parentage that have been recovered from the early Jurassic Elliot Formation sediments at the Rooidraai locality possess shells that are similar to those of birds and crocodilians, and distinctly unlike those of chelonians and gekkonids. The preserved shell is very thin, and distinct mammillary processes are lacking, although the inner surface displays an undulating contour. The absence of these processes may be attributable to the inner portion of the shell having been at least partially decalcified during incubation and not preserved in the fossil state. The shells appear to be composed of broadly wedge-shaped, albeit ill-defined calcareous units, and they are similar to those of birds and other dinosaurs in the pattern of cleavage shown by the tabular calcite crystals of the palisade layer, and in the absence of the dominant horizontal lamellae that characterize crocodilian shells. The differential resemblance of these early Jurassic shells to the eggs of other closely related sauropsid taxa may be pertinent to questions concerning the evolution of egg shell structure within this clade
Skulls of the prosauropod dinosaur Massospondylus carinatus Owen in the collections of the Bernard Price Institute for Palaeontological Research
Description of the skull of Massospondylus (Prosauropoda, Anchisauridae) is largely unnecessary since excellent descriptions now exist of Plateosaurus (Galton 1984, 1985a) which, though larger and of slightly different proportions, is anatomically almost identical. This paper presents comprehensive illustrations of the Massospondylus skulls in the Bernard Price Institute collections and discusses only those aspects of this material in which Massospondylus differs from Plateosaurus, or which further add to our knowledge of the prosauropod skull. It is shown that Attridge et al. ( 1985) give spurious reasons for considering the recently discovered Massospondylus skull from Arizona to differ from the southern African taxon, and that the suggestion of Crompton and Attridge ( 1986) that this animal may have had a horny beak on the tip of the lower jaw is unnecessary and improbable
First record of Triassic Rhynchosauria (Reptilia: Diapsida) from the Lower Zambezi Valley, Zimbabwe
True rhynchosaurids are described from Zimbabwe for the first time. The fossils occur as partially associated skeletons and scattered isolates in upward-fining, micaceous fluvial sandstones of the Pebbly Arkose Formation (late Triassic) in the Western Cabora Bassa Basin, Lower Zambezi Valley. On the grounds that the dentary of the Zimbabwean form possesses a row of small, conical lingual teeth in addition to a palisade row of penicillate teeth on the occlusal surface, it is concluded that the taxon present is Hyperodapedon sp., and that it is closely related to a rhynchosaurid described from Tanzania. One bone identified as a prosauropod dinosaurian femur was found associated with the Zimbabwean rhynchosaurids. The late Triassic age suggested by the presence of advanced rhynchosaurids is supported by the occurrence of the typical Triassic fossil plant genus Dicroidium, and by the general stratigraphy of the beds which contain the fossils (i.e. the fossil-bearing beds are underlain by beds of mid-Triassic age or younger, and are overlain by beds of latest Triassic or early Jurassic age
Dinosaur tracks in Triassic Molteno sediments: the earliest evidence of dinosaurs in South Africa?
A fossil tracksite containing well-preserved tridactyl footprints of bipedal theropod dinosaurs is reported from fluvial overbank deposits of Molteno age (Stormberg Group: Triassic) in the northeastern Cape Province, South Africa. They occur stratigraphically below the mudrocks of the Elliot Formation, in which dinosaur remains are comparatively common, and are taken to represent the earliest evidence for dinosaurs in South Africa. They also represent the earliest unequivocal evidence of tetrapods in Molteno deposits.Foundation for Research Development; Trustees of the Port Elizabeth Museu
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Delivery of High-Stability Optical and Microwave Frequency Standards over an Optical Fiber Network
Optical and radio frequency standards located in JILA and National Institute of Standards and Technology (NIST) laboratories have been connected through a 3.45-km optical fiber link. An optical frequency standard based on an iodine-stabilized Nd:YAG laser at 1064 nm (with an instability of ∼4×10−14 at 1 s) has been transferred from JILA to NIST and simultaneously measured in both laboratories. In parallel, a hydrogen maser-based radio frequency standard (with an instability of ∼2.4×10−13 at 1 s) is transferred from NIST to JILA. Comparison between these frequency standards is made possible by the use of femtosecond frequency combs in both laboratories. The degradation of the optical and rf standards that are due to the instability in the transmission channel has been measured. Active noise cancellation is demonstrated to improve the transfer stability of the fiber link
A Review of Pink Salmon in the Pacific, Arctic, and Atlantic Oceans
The Northern Hemisphere Pink Salmon Expert Group Meeting was held on October 2–3, 2022 in Vancouver, Canada, immediately preceding the International Year of the Salmon (IYS) Synthesis Symposium. The rapid expansion of pink salmon was the theme for the meeting, and experts came together to discuss the current state of knowledge for pink salmon. Specific topics of focus included the range expansion into the Atlantic and Arctic oceans, trends in distribution and abundance, research and monitoring approaches, potential inter-specific interactions, mitigation efforts, and plans for future collaborations. The outcomes of the meeting were presented at the IYS Synthesis Symposium and are further disseminated through this NPAFC Technical Report. The Executive Summary section of this report provides a brief background, a condensed overview of each topic, and concludes with overarching takeaway messages that are intended to guide future collaborations.publishedVersio
A Review of Pink Salmon in the Pacific, Arctic, and Atlantic Oceans
The Northern Hemisphere Pink Salmon Expert Group Meeting was held on October 2–3, 2022 in Vancouver, Canada, immediately preceding the International Year of the Salmon (IYS) Synthesis Symposium. The rapid expansion of pink salmon was the theme for the meeting, and experts came together to discuss the current state of knowledge for pink salmon. Specific topics of focus included the range expansion into the Atlantic and Arctic oceans, trends in distribution and abundance, research and monitoring approaches, potential inter-specific interactions, mitigation efforts, and plans for future collaborations. The outcomes of the meeting were presented at the IYS Synthesis Symposium and are further disseminated through this NPAFC Technical Report. The Executive Summary section of this report provides a brief background, a condensed overview of each topic, and concludes with overarching takeaway messages that are intended to guide future collaborations.publishedVersio
Connective Tissue Growth Factor in Regulation of RhoA Mediated Cytoskeletal Tension Associated Osteogenesis of Mouse Adipose-Derived Stromal Cells
Background: Cytoskeletal tension is an intracellular mechanism through which cells convert a mechanical signal into a biochemical response, including production of cytokines and activation of various signaling pathways. Methods/Principal Findings: Adipose-derived stromal cells (ASCs) were allowed to spread into large cells by seeding them at a low-density (1,250 cells/cm 2), which was observed to induce osteogenesis. Conversely, ASCs seeded at a high-density (25,000 cells/cm 2) featured small cells that promoted adipogenesis. RhoA and actin filaments were altered by changes in cell size. Blocking actin polymerization by Cytochalasin D influenced cytoskeletal tension and differentiation of ASCs. To understand the potential regulatory mechanisms leading to actin cytoskeletal tension, cDNA microarray was performed on large and small ASCs. Connective tissue growth factor (CTGF) was identified as a major regulator of osteogenesis associated with RhoA mediated cytoskeletal tension. Subsequently, knock-down of CTGF by siRNA in ASCs inhibited this osteogenesis. Conclusions/Significance: We conclude that CTGF is important in the regulation of cytoskeletal tension mediated AS
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