Ben Creisler
Some recent papers:
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Elasmosaurids are a cosmopolitan group of plesiosaurians that radiated during the Late Cretaceous. A new specimen of the small sized elasmosaurid Kawanectes lafquenianum is described here. New features of the basicranium and palate are added: basioccipital tubers with distal end deeply excavated, basioccipital ventral flat plate below occipital condyle, absence of posterior interpterygoid symphysis, parasphenoid extended caudally to the posterior margin of basioccipital condyle, craniocaudally short ventral keel of parasphenoid. Differences recorded between the specimens referred to K. lafquenianum (ilium shape, relative humerus to femur size and sacral centrum proportions) are described. Different explanations of these differences are discussed, concluding that sexual dimorphism is the most plausible explanation.
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Review available geochronologically-constrained paleoclimatic South America data.
Compare paleoclimatic data and vertebrate fossil record from the same strata.
Fluctuating climate conditions dominated the western Gondwana Triassic.
Intriguing patterns are apparent when comparing the Triassic South American vertebrate fossil record to paleoclimate record.
Abstract
The Triassic Period was the setting for the origin and early diversification of Mesozoic ecosystems after the end-Permian mass extinction. The study of the Triassic is essential to understand the evolution of non-marine Mesozoic ecosystems, particularly the vertebrate components and their climatic context. During this time, the configuration of the supercontinent Pangea, which was unique (e.g., the only time since the origin of life that a global supercontinent spread across the equator) in the earth's paleobiogeographic history, is one of the factors that characterized the period. This paleogeographic configuration combined with a high global sea level and no polar ice caps would have had an extraordinary effect on the global climate. Multiple sudden climate events occurred during this time, such as large igneous province (LIP) eruptions, including two that had a major part to play in the major mass extinctions that bracket the Triassic Period. Against this backdrop, a number of modern vertebrate clades originated on land, including lissamphibians, lepidosaurs, turtles, dinosaurs, and mammaliaforms. To test the link between climatic and evolutionary events, we compiled paleoclimatic data from Argentinian, Brazilian, Bolivian, and Chilean Triassic non-marine vertebrate-bearing strata to discuss observed paleoclimatic changes and their influence on vertebrate evolution in South America during this time. Fluctuating climate conditions dominated the western Gondwana Triassic, with arid to semiarid conditions during Early Triassic with marked humid seasonal fluctuation in the continental interior, the seasonal semiarid condition of the Middle Triassic shows more humid seasonality than Early Triassic, and the Late Triassic was dominated by seasonal sub-humid conditions with one or more semi-arid intervals, particularly in the interior. Comparisons of the Triassic South American vertebrate fossil record and this paleoclimate record show striking patterns, however better geochronologic control, paleoclimate proxy records, and sample fossil-bearing strata are necessary to understand these trends.
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Free pdf:
Pseudocorax kindlimanni sp. nov.
Highlights
Description of a new lamniform shark Pseudocorax kindlimanni sp. nov. from the Cenomanian of Haqel (Lebanon).
Dental pattern, tooth histology and vertebral morphology differs from many other lamniform sharks.
The new species is the oldest known pseudocoracid shark today and sheds light on the diversity and radiation of lamniform sharks during the Late Cretaceous.
Pseudocorax kindlimanni sp. nov. was a small lamniform shark occupying the lower trophic levels in the Late Cretaceous marine food web.
Abstract
A new fossil mackerel shark, Pseudocorax kindlimanni sp. nov. (Lamniformes, Pseudocoracidae), is described from the Cenomanian Konservat-LagerstÃtte of Haqel, Lebanon. The new species is based on the most complete fossil of this group to date, which comprises an associated tooth set of 70 teeth, six articulated vertebral centra, numerous placoid scales and pieces of unidentifiable mineralized cartilage. The dentition of P. kindlimanni sp. nov. is marked by a high degree of monognathic heterodonty but does not exhibit the characteristic "lamnoid tooth pattern" known from other macrophagous lamniform sharks. In addition, P. kindlimanni sp. nov. shows differences in tooth microstructure and vertebral centrum morphology compared to other lamniform sharks. These variations, however, are also known from other members of this order and do not warrant the assignment of Pseudocorax outside the lamniform sharks. The new fossil is the oldest known pseudocoracid shark and pushes the origin of this group back into the Cenomanian, a time when lamniform sharks underwent a major diversification. This radiation resulted not only in high species diversity, but also in the development of a diverse array of morphological traits and adaptation to different ecological niches. Pseudocorax kindlimanni sp. nov. was a small, active predator capable of fast swimming, and it occupied the lower trophic levels of the marine food web in the Late Cretaceous.
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