Papers by Kenneth Lacovara
Earth-science Reviews, 2009
Tides have been a source of inquiry since the dawn of human civilization. It has been known for m... more Tides have been a source of inquiry since the dawn of human civilization. It has been known for millennia that the Moon is a causative agent in the formation of tides, with the observation that lunar phases often correlated to changing tidal amplitudes. The precise mechanisms underlying the formation of tides and local tidal dynamics, however, have proven difficult to elucidate. Only with Newton's theory of gravitation in the 17th century was the correlation between lunar cycles and tides partially explained. Further work by Laplace and others resulted in a more dynamic theory that more closely matched observations and allowed for better prediction of local tidal behavior. Quantitative models derived from these methods have increased in precision and complexity (particularly with the advent of the electronic computer), and have allowed new insights into the nature of tidal dynamics and tidal dissipation.In more recent years scientists have analyzed deposits known as tidal bundles and tidal rhythmites in an attempt to extrapolate the history of tides from the geologic record. Tidal bundles are laterally accreted cyclic foreset beds separated by mud laminae. Tidal rhythmites are vertically accreted planar laminae that alternate between coarse and fine sediments forming couplets often composed of sands and muds. These deposits are characterized by bed/laminae thicknesses that vary rhythmically and preserve tidal periodicities, and are generally found in intertidal or subtidal depositional environments. The mode of deposition (e.g. sand or mud) is primarily determined by current velocity and tidal range, factors largely controlled by the tides in marginal marine settings.Quantitative analyses of tidal rhythmites may facilitate more precise elucidation of tidal periodicities encoded in the rock record. The partial reconstruction of the history of lunar recession from existing data and analyses indicates that the Earth is presently experiencing a high rate of tidal dissipation. Further data obtained from ancient tidal proxies may prove essential in constraining models of tidal dissipation, thereby revealing the mechanisms and dynamics present in the dissipation process controlling secular changes in the length of day and lunar orbit.
Earth-science Reviews, 2009
Tides have been a source of inquiry since the dawn of human civilization. It has been known for m... more Tides have been a source of inquiry since the dawn of human civilization. It has been known for millennia that the Moon is a causative agent in the formation of tides, with the observation that lunar phases often correlated to changing tidal amplitudes. The precise mechanisms underlying the formation of tides and local tidal dynamics, however, have proven difficult to elucidate. Only with Newton's theory of gravitation in the 17th century was the correlation between lunar cycles and tides partially explained. Further work by Laplace and others resulted in a more dynamic theory that more closely matched observations and allowed for better prediction of local tidal behavior. Quantitative models derived from these methods have increased in precision and complexity (particularly with the advent of the electronic computer), and have allowed new insights into the nature of tidal dynamics and tidal dissipation. In more recent years scientists have analyzed deposits known as tidal bundles and tidal rhythmites in an attempt to extrapolate the history of tides from the geologic record. Tidal bundles are laterally accreted cyclic foreset beds separated by mud laminae. Tidal rhythmites are vertically accreted planar laminae that alternate between coarse and fine sediments forming couplets often composed of sands and muds. These deposits are characterized by bed/laminae thicknesses that vary rhythmically and preserve tidal periodicities, and are generally found in intertidal or subtidal depositional environments. The mode of deposition (e.g. sand or mud) is primarily determined by current velocity and tidal range, factors largely controlled by the tides in marginal marine settings. Quantitative analyses of tidal rhythmites may facilitate more precise elucidation of tidal periodicities encoded in the rock record. The partial reconstruction of the history of lunar recession from existing data and analyses indicates that the Earth is presently experiencing a high rate of tidal dissipation. Further data obtained from ancient tidal proxies may prove essential in constraining models of tidal dissipation, thereby revealing the mechanisms and dynamics present in the dissipation process controlling secular changes in the length of day and lunar orbit.
Journal of Paleontology, 2003
Brachyuran decapods (crabs) are rarely preserved in coastal environments and have not been docume... more Brachyuran decapods (crabs) are rarely preserved in coastal environments and have not been documented in close association with dinosaur fossils. A crab referable to the Necrocarcinidae Förster, 1968, is here described from the Cenomanian Bahariya Formation, Bahariya Oasis, Egypt. The occurrence of a crab in a mangrove setting in association with terrestrial vertebrates is extremely unusual in the fossil record. Review of decapod occurrences from the region has resulted in placement of Portunus sp. of Roger within the Raninidae de Haan, 1839, and Lophoraninella cretacea (Dames, 1886) into the Galatheoidea Samouelle, 1819. The crabs of the Bahariya Formation were probably scavengers, feeding on vegetation and other organic material and were possibly a food source for fish and other vertebrates and invertebrates in the environment. Egypt, approximately 320 km southwest of Cairo. 2, Location of BDP 2001-13 in relation to Gebel el Dist and Bawiti. (Modified from Smith et al., 2001.) E. de Hellebranth, and the Delaware Valley Paleontological Society. R. M. Feldmann, Department of Geology, Kent State University, provided many helpful discussions about the fossil material, assisted with photography, and read an earlier draft of the manuscript. B. Grandstaff, School of Veterinary Medicine, University of Pennsylvania, provided helpful references to decapods associated with vertebrate fossils. M. Keatts, Department of Geology, Kent State University, provided computer support. R. Askin,
Journal of Vertebrate Paleontology, 2012
A newly discovered osteichthyan ectopterygoid from the Upper Cretaceous (lower Cenomanian) Bahari... more A newly discovered osteichthyan ectopterygoid from the Upper Cretaceous (lower Cenomanian) Bahariya Formation of the Bahariya Oasis, Egypt, is nearly identical to the holotypic specimen of Polypterus? bartheli from the same area and geologic unit. The Bahariya ectopterygoids are referable to Polypteridae based on the presence of a robust, laterally directed process that articulates with the maxilla. Additionally, ganoid scales from the Bahariya Formation have an isopedine layer, a histological character of Polypteriformes; but differ from those of previously described members of this clade in having a discontinuous ganoin layer, rectilinear shape, and proportionally small articular processes. Both the ectopterygoids and the scales are unusually large, and are the only polypteriform remains so far identified from the Bahariya Formation. The ectopterygoids and (tentatively) the scales are herein assigned to a single species of gigantic polypterid, the morphology of which is sufficiently distinctive to warrant its placement in a new genus, Bawitius, gen. nov. Differences in scale anatomy and the enormous disparity in body size between Bawitius and Serenoichthys support the hypothesis (originally proposed on the basis of varied fin spine morphologies) that a diversity of polypterid fishes inhabited North Africa during the early Late Cretaceous.
Journal of Paleontology, 2006
Science, 2006
to such indirect dissociations, which is indicated as Scheme C in .
Ichnos-an International Journal for Plant and Animal Traces, 2004
The Sundance Formation (Middle-Upper Jurassic) of Wyoming is well known for pterosaur footprints.... more The Sundance Formation (Middle-Upper Jurassic) of Wyoming is well known for pterosaur footprints. Two new partial trackways from the upper Sundance Formation of the Bighorn Canyon National Recreation Area (BICA) of north-central Wyoming are enigmatic. The trackways are preserved in rippled, flaser bedded, glauconitic sand and mud. The deposits were laid down in tidal flats, behind barrier islands, along the mesotidal Sundance Sea.The best-preserved print of the primary trackway possesses four impressions: three shorter digits with negative rotation and an elongate, caudally-oriented mark. The primary trackway has low pace angulation. The combination of morphology and pace angulation matches neither tracks nor body fossils of horseshoe crabs, theropod dinosaurs, pterosaurs, crocodylomorphs, “lacertoids,” or mammaliforms. The secondary trackway, possibly consisting of undertracks, similarly possesses elongate caudal impressions but differs from the former by possessing four subparallel, cranially-oriented digits. These prints also do not closely resemble any of the aforementioned taxa. While the secondary trackway does not lend itself to conclusion, the primary track maker could have been either an injured, pathologic pterosaur or a pterosaurian taxon otherwise unknown from the ichnological record.
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Papers by Kenneth Lacovara