Browsing by Author "Lawver, Daniel R."

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An accumulation of turtle eggs with embryos from the Campanian (Upper Cretaceous) Judith River Formation of Montana
(2017-01) Lawver, Daniel R.; Jackson, Frankie D.
A weathered accumulation of turtle eggs, interpreted as remnants of a single clutch composed of at least 16 turtle eggs (MOR 710) from the Campanian (Upper Cretaceous) Judith River Formation of north-central Montana, USA, represents a new oospecies Testudoolithus zelenitskyae. This ootaxon is diagnosed by the following unique combination of characters: spherical eggs 34â€“39 mm in diameter, 660â€“760 Î¼m thick eggshell, shell unit height-to-width ratio of 3.15:1â€“5.5:1, and domed shell units. Estimated egg mass indicates that the egg-laying adult likely possessed a carapace 35.0â€“54.4 cm in length. Similarities between T. zelenitskyae oosp. nov. and Adocus sp. eggs, along with comparable body size, suggest that this taxon might have produced MOR 710. One egg exhibits abnormal multilayered eggshell, likely resulting from prolonged egg retention by the female turtle. At least five of these eggs, including the multilayered specimen, preserve embryonic remains that demonstrate a late stage of embryonic development. This suggests that death occurred just prior to hatching.
An analysis of fossil identification guides to improve data reporting in citizen science programs
(2020-04) Butler, Dava K.; Esker, Donald A.; Juntunen, Kristopher L.; Lawver, Daniel R.
An increasing number of organizations use untrained volunteers to gather scientific data. This citizen science movement builds enthusiasm for science by engaging the public, as well as providing a way to gather large amounts of data at little or no expense. The challenge of citizen science is obtaining accurate information from participants. Many citizen science programs encourage participants to use visual identification guides to ensure they provide correct data. Identifying an image style that increases correct identifications helps not only the citizen science movement but also scientific instruction in general. This study tests three image-based identification guides for identifying late Hemphillian (5–4.5 m.y.a.) fossils from Polk County, Florida. Each guide has identical layout and text, differing only in image style: color photos, grayscale photos, or illustrations. Untrained participants each use one guide to identify fossils. Geology and paleontology professionals also identify fossils for comparison. Comparing results reveals that color photographic images produce results most similar to data from professionals. In addition, participants provide data on their years of education, previous experience finding fossils, and enthusiasm about finding fossils. Analysis of this information reveals that participants with higher education and/or previous experience finding fossils produce data most similar to that from professionals. Paradoxically, participants with higher enthusiasm produce data less similar to that from professionals, while moderate interest levels correlated with greater similarity.
An occurrence of fossil eggs from the Mesozoic of Madagascar and a detailed observation of eggshell microstructure
(2015) Lawver, Daniel R.; Rasoamiaramanana, Armand H.; Werneburg, Ingmar
Whereas fossil turtle eggs have a near global distribution and range from Middle Jurassic to Pleistocene, they are rarely documented from the Mesozoic of Gondwana. Here, we report three fossil turtle eggs from the Upper Cretaceous (Campanian) of the Morondava Basin, Madagascar. The spherical eggs range in size from 33.5 to 35.5 mm and have an average eggshell thickness of 440 µm. They can be confidently identified as rigid-shelled turtle eggs by the presence of tightly packed shell units composed of radiating acicular crystals and a shell unit height to width ratio of 2:1. Lack of associated skeletal remains precludes taxonomic identification of the eggs. Although a large vertebrate fauna has been reported from the Upper Cretaceous of Madagascar, these specimens are the first eggs from the Mesozoic of the island.
A review of the fossil record of turtle reproduction: eggs, embryos, nests and copulating pairs
(2014-10) Lawver, Daniel R.; Jackson, Frankie D.
The fossil record of turtle reproduction (e.g., eggs, embryos, nests and copulating pairs) is rela-tively poor compared with that of dinosaurs. This record extends from the Middle Jurassic to the Pleistocene, and specimens are known from every continent except Antarctica. Fossil turtle eggs are recognized as body fossils, and confident taxonomic identification at the genus or species level is dependent on embryos preserved within fossil eggs or by eggs found within a gravid fe-male. Cladistic analysis of egg and eggshell characters demonstrates a high degree of homoplasy, and only a few characters provide a strong phylogenetic signal. Taphonomic studies of fossil tur-tle eggs are rare but can elucidate size and number of eggs produced by extinct taxa. Pathologi-cal fossil turtle eggs are known from a few localities and provide information about physiological or environmental stresses experienced by the gravid female. Fossil turtle eggs are relatively abun-dant in Asia, Europe and North America but are poorly represented in Gondwana. An ootaxo-nomic review of fossil turtle eggs shows that of 15 named ootaxa, 8 are nomina valida, 5 are nomen nudum and 2 are junior synonyms of other ootaxa.
Vertebrate microfossils from the Upper Freshwater Molasse in the Swiss Molasse Basin: Implications for the evolution of the North Alpine Foreland Basin during the Miocene Climate Optimum
(2015-05) Jost, Jürg; Kälin, Daniel; Börner, Saskia; Vasilyan, Davit; Lawver, Daniel R.; Reichenbacher, Bettina
The older part of the Upper Freshwater Molasse (OSM) in the Swiss and South German Molasse Basin records the extended warm period known as the Miocene Climate Optimum. However, dating and global correlation of fossils and palaeoclimatic data from OSM sediments remains challenging, because sections are often incomplete and biostratigraphic data sometimes ambiguous. Here we present the rare case of a fossiliferous OSM section that can be securely dated to the late Early Miocene and early Middle Miocene (c. 16.1â€“15.7 Ma). Vertebrate microfossils have been recovered from three levels in superposition. Fish teeth document primary freshwater fishes (Cyprinidae, Channidae), but otoliths found in the middle level indicate dominance of euryhaline fishes (Cyprinodontiformes, Gobiiformes). The herpetofaunal assemblages largely consist of taxa that were widely distributed in Central Europe during the Miocene Climate Optimum and fragments of turtle eggshells assignable to the Oofamily Testudoolithidae Hirsch, 1996. The small-mammal fauna is dominated by the cricetid Megacricetodon bavaricus Fahlbusch, 1964. The fossil biota implies that the lowermost level (late Early Miocene, c. 16.1 Ma) represents a palaeo-soil that formed under humid conditions, while the levels above it (early Middle Miocene, c. 15.7â€“15.8 Ma) record a warm freshwater pond subject to evaporation (middle level), and mean annual temperature â‰¥ 17 Â°C in the vicinity of a river with an open hinterland (upper level). Our results, together with previous data, suggest that the palaeoclimate of the North Alpine Foreland Basin of Switzerland and Southwest Germany was humid during the late Early Miocene and earliest Middle Miocene, and that the Middle Miocene onset of seasonality and low mean annual precipitation occurred by c. 15.7â€“15.8 Ma. We conclude that global climate change and the 100-kyr orbital eccentricity minimum at 15.75 Ma may have triggered the decrease in humidity in the North Alpine Foreland Basin.