Michael Polcyn
Southern Methodist University, Huffington Department of Earth Sciences, Department Member
We report here new and the first mammaliamorph tracks from the Early Cretaceous of Africa. The tracksite, that also bears crocodylomorph and sauropod dinosaurian tracks, is in the Catoca diamond mine, Lunda Sul Province, Angola. The... more
We report here new and the first mammaliamorph tracks from the Early Cretaceous of Africa. The tracksite, that also bears crocodylomorph and sauropod dinosaurian tracks, is in the Catoca diamond mine, Lunda Sul Province, Angola. The mammaliamorph tracks have a unique morphology, attributed to Catocapes angolanus ichnogen. et ichnosp. nov. and present an anterolateral projection of digit I and V. The tracks with an average length of 2.7 cm and width of 3.2 cm are the largest mammaliamorph tracks known from the Early Cretaceous unmatched in size in the skeletal fossil record. The crocodylomorph trackways and tracks are attributed to Angolaichnus adamanticus ichnogen. et ichnosp. nov. (‘ichnofamily’ Batrachopodidae) and present a functionally pentadactyl pes, an extremely outwardly rotated handprint, and an unusual tetradactyl and plantigrade manus. One medium-sized sauropod dinosaur trackway preserved skin impressions of a trackmaker with stride length of 1.6 m; a second is that of a small-sized sauropod trackmaker with a pace length of 75 cm.
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Mosasaur remains discovered in 1996 include a complete but disarticulated skull, twenty-six vertebrae, and ribs, collected from the Smoky Hill Chalk (Lower Santonian) of Gove County, Kansas, and currently housed in the collections of the... more
Mosasaur remains discovered in 1996 include a complete but disarticulated skull, twenty-six vertebrae, and ribs, collected from the Smoky Hill Chalk (Lower Santonian) of Gove County, Kansas, and currently housed in the collections of the Sternberg Museum catalogued as FHSM VP-13910. The remains have been informally referred to as Platecarpus planifrons in abstract, journal article, popular print, and on the Internet since 1998. Subsequent comparison with the type material of P. planifrons and other plioplatecarpine mosasaurs does not support the earlier identification but instead warrants referral of FHSM VP-13910 to the genus Selmasaurus. The new material differs from the holotype of Selmasaurus russelli in a number of respects
and justifys erection of a new species, Selmasaurus johnsoni n. sp. Phylogenetic analysis recovers a topology placing Selmasaurus as the sister taxon to a clade comprised of (Angolasaurus (Platecarpus + Plioplatecarpus)) and Ectenosaurus as the sister taxon of that clade. However, derived characters shared between Ectenosaurus and Selmasaurus suggest a closer relationship between those two taxa, and is our preferred phylogenetic hypothesis.
and justifys erection of a new species, Selmasaurus johnsoni n. sp. Phylogenetic analysis recovers a topology placing Selmasaurus as the sister taxon to a clade comprised of (Angolasaurus (Platecarpus + Plioplatecarpus)) and Ectenosaurus as the sister taxon of that clade. However, derived characters shared between Ectenosaurus and Selmasaurus suggest a closer relationship between those two taxa, and is our preferred phylogenetic hypothesis.
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Plesiosaurs were a diverse clade of marine reptiles that spanned nearly threequarters of the Mesozoic (earliest Jurassic to latest Cretaceous). They exhibit variation in head and neck morphology that presumably relates to functional... more
Plesiosaurs were a diverse clade of marine reptiles that spanned nearly threequarters
of the Mesozoic (earliest Jurassic to latest Cretaceous). They exhibit variation
in head and neck morphology that presumably relates to functional differences in feeding
habits. However, from a biomechanical standpoint, these marine creatures have a
cranial organization shared with few reptile clades: the neodiapsid condition. Nevertheless,
basic structural features in some derived clades, such as elasmosaurids, remain
poorly understood, namely the presence of large supratemporal fenestrae, tall temporal
bars, and high parietal crests. These features present biomechanical compromises
with paleobiological implications for feeding habits. Here we test specific hypotheses
regarding skull structure and mechanics in the elasmosaurid plesiosaur Libonectes
morgani from the Late Cretaceous of Texas (USA). Using finite element analysis and
loadings based on a detailed reconstruction of adductor chamber musculature, we provide
estimates of stress and strain distributions for the Libonectes skull. We also digitally
morphed different anatomical variants of the Libonectes skull, in order to assess
the role of those traits in skull’s mechanical performance (e.g., height of the temporal
bar). Our results show that a larger physiological cross-section of the adductor muscles
is achieved by an enlarged supratemporal fenestra which although it reduces mechanical
performance of the skull, it is offset by increased strength of a taller parietal crest
and temporal bar, given the loading is largely symmetrical, the lateral components are
offsetting yielding a vertical force vector. This arrangement also increases the length of
the adductor musculature and thus the total muscle mass. We propose that the
reduced pterygoid flange indicates a diminished role for the pterygoideus muscle,
reflecting a shift of the majority of the bite force to the adductor mandibulae externus,
pseudotemporalis, and adductor mandibulae posterior muscles. Reduction of the pterygoideus
falsifies the dual adductor system hypothesis, in which kinetic inertia and
static pressure coexist.
of the Mesozoic (earliest Jurassic to latest Cretaceous). They exhibit variation
in head and neck morphology that presumably relates to functional differences in feeding
habits. However, from a biomechanical standpoint, these marine creatures have a
cranial organization shared with few reptile clades: the neodiapsid condition. Nevertheless,
basic structural features in some derived clades, such as elasmosaurids, remain
poorly understood, namely the presence of large supratemporal fenestrae, tall temporal
bars, and high parietal crests. These features present biomechanical compromises
with paleobiological implications for feeding habits. Here we test specific hypotheses
regarding skull structure and mechanics in the elasmosaurid plesiosaur Libonectes
morgani from the Late Cretaceous of Texas (USA). Using finite element analysis and
loadings based on a detailed reconstruction of adductor chamber musculature, we provide
estimates of stress and strain distributions for the Libonectes skull. We also digitally
morphed different anatomical variants of the Libonectes skull, in order to assess
the role of those traits in skull’s mechanical performance (e.g., height of the temporal
bar). Our results show that a larger physiological cross-section of the adductor muscles
is achieved by an enlarged supratemporal fenestra which although it reduces mechanical
performance of the skull, it is offset by increased strength of a taller parietal crest
and temporal bar, given the loading is largely symmetrical, the lateral components are
offsetting yielding a vertical force vector. This arrangement also increases the length of
the adductor musculature and thus the total muscle mass. We propose that the
reduced pterygoid flange indicates a diminished role for the pterygoideus muscle,
reflecting a shift of the majority of the bite force to the adductor mandibulae externus,
pseudotemporalis, and adductor mandibulae posterior muscles. Reduction of the pterygoideus
falsifies the dual adductor system hypothesis, in which kinetic inertia and
static pressure coexist.
Research Interests: Evolutionary Biology, Geology, Paleontology, Finite Element Methods, Biomechanics, and 12 moreFinite Element Analysis (Engineering), Biology, Finite element method, Vertebrate Palaeontology, Bioinspiration, Vertebrate Paleontology, Finite Element Analysis (FEA), Finite Element Analysis, Plesiosauria, Adduction, Finite Element Simulations, and Optical Electronic Prppertier of Tio2(1-X) Bi4x/si Detector Prepareedby Laser Induced Plasma
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We report hereanewelasmosauridfromtheearlyMaastrichtianatBentiaba,southernAngola.Phylogeneticanalysisplacesthenewtaxonasthesister taxonto Styxosaurus snowii, and that clade as the sister of a clade composed of (Hydrotherosaurus alexandrae... more
We report hereanewelasmosauridfromtheearlyMaastrichtianatBentiaba,southernAngola.Phylogeneticanalysisplacesthenewtaxonasthesister taxonto Styxosaurus snowii, and that clade as the sister of a clade composed of (Hydrotherosaurus alexandrae (Libonectes morgani + Elasmosaurus platyurus)). The new taxon hasa reduceddorsalblade of the scapula, a feature uniqueamongst elasmosaurids, but convergent with cryptoclidid plesiosaurs, andindicates a longitudinal protraction-retraction limb cycle rowing style with simple pitch rotation at the glenohumeral articulation. Morphometric phylogenetic analysis of the coracoids of 40 eosauropterygian taxa suggests that there was a broad range of swimming styles within the clade.
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Sediments in north-central Texas, ranging in age from >117 to 85 Ma, represent a variety of terrestrial and marine depositional settings. Isotopic analyses of wood fragments found throughout the section allow correlation to the... more
Sediments in north-central Texas, ranging in age from >117 to 85 Ma, represent a variety of terrestrial and marine depositional settings. Isotopic analyses of wood fragments found throughout the section allow correlation to the standard secular marine d,C curve because of characteristic peaks at the Aptian-Albian and Cenomanian-Turonian boundaries. Consistency of the north-central Texas d,C curve with the marine standard facilitates correlation among non-marine and marine environments on a global scale. Radiometrically dated ammonite zones recognised in Texas provide calibration for the Cenomanian and Turonian portions of the section. Cenomanian and Turonian sediments in north-central Texas preserve the oldest (96 Ma) and the youngest (<85 Ma) well-documented Coniasaurus, a dolichosaur also known from the southern North Sea Basin during that interval. Haasiasaurus, the oldest known well-documented early mosasaur, is found at'Ein Yabrud, Israel (98 Ma), followed by other poorly dated Cenomanian taxa from the eastern Mediterranean region, and then by Dallasaurus turneri and Russellosaurus coheni in Texas (92 Ma) and Tethysaurus (90.5 Ma) in Morocco. Neither shifts in d,C nor large-scale sea level change seem to have influenced dolichosaur or mosasaur evolution in substantial ways during the Cenomanian and Turonian stages.
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Africa is the only continent that now straddles arid zones located beneath the descending limbs of both the northern and southern Hadley cells, and it has done so since it became a distinct continent in the Early Cretaceous. Since that... more
Africa is the only continent that now straddles arid zones located beneath the descending limbs of both the northern and southern Hadley cells, and it has done so since it became a distinct continent in the Early Cretaceous. Since that time, Africa has drifted tectonically some 12 degrees north and rotated approximately 45 degrees counterclockwise. This changing latitudinal setting and position of the landmass under the relatively stable Hadley Cells is manifested as southward migration of climatic zones over the past 132 million years. Data from kerogen, X-ray diffraction analysis of sedimentary matrix, carbon isotopes from shell samples and tooth enamel,new 40Ar/39Ar radiometric dates, pollen and plant macrofossils, and fossil vertebrates indicate a productive upwelling system adjacent to a coastal desert since the opening of the South Atlantic Ocean; however, the position of the coastal desert has migrated southward as Africa drifted north, resulting in today's Skeleton Coast and Benguela Current. This migration has had a profound effect on the placement of the West African coast relative to areas of high marine productivity and resulting extensive hydrocarbon deposits, on the placement of arid zones relative to the continent especially the Skeleton Coast desert, on the climatic history of the Congo Basin (which shows a Late Cretaceous decrease in aridity based on the relative abundance of analcime in the Samba core), and in reducing the southern temperate region of Africa from 17% of continental area during the Cretaceous to 2% today. We show here that these related geographic and environmental changes drove ecological and evolutionary adjustments in southern African floras and faunas, specifically with respect to the distribution of anthropoid primates, the occurrence of modern relicts such as the gnetalean Welwitschia mirabilis, endemism as in the case of ice plants, and mammalian adaption to an open environment as in springhares. Africa's tectonic drift through climate zones has been a first-order environmental determinant since the Early Cretaceous.
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New mosasaur fossils from Maastrichtian beds at Bentiaba, Angola, representing elements of the skull and postcranial axial skeleton from two individuals of the durophagous genus Globidens, are reported. Based on dental morphology,... more
New mosasaur fossils from Maastrichtian beds at Bentiaba, Angola, representing elements of the skull and postcranial axial skeleton from two individuals of the durophagous genus Globidens, are reported. Based on dental morphology, specifically the inflated posterior surface and vertical sulci, the Bentiaba specimens are identified as Globidens phosphaticus, a species defined by characters of a composite dentition from the Maastrichtian of Morocco. Comparisons indicate that G. phosphaticus is most closely related to G. schurmanni, from the late Campanian of South Dakota, the youngest north American Globidens species at about 72.5 Ma. The morphology of the premaxilla and its relationship with the maxillae is unique among mosasaurs, and supports the taxonomic validity of G. phosphaticus. In contrast with earlier species of the genus, G. phosphaticus is currently known from north and west Africa, the Middle East and the central eastern margin of South America, suggesting it may have been restricted to the Maastrichtian tropical zone as previously hypothesised.
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Page 1. Journal of Vertebrate Paleontology 23(2):476, June 2003 C 2003 by the Society of Vertebrate Paleontology CORRECTION HAASIASAURUS GEN. NOV., A NEW GENERIC NAME FOR THE BASAL MOSASAUROID HAASIA POLCYN ET AL., 1999 ...