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"Gangloff, Roland A"
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TAPHONOMY AND PALEOECOLOGY OF A BONEBED FROM THE PRINCE CREEK FORMATION, NORTH SLOPE, ALASKA
The late Campanian–Maastrichtian Liscomb Bonebed is the richest source of dinosaur remains thus far documented in the polar regions. This bed is formally defined herein and assigned to the upper part of the Prince Creek Formation; the bonebed and several other organic-rich beds are part of a 178 m sequence of fluvial and volcaniclastic deposits. The Liscomb Bonebed is a mudstone rich in clay, comminuted plant remains, and palynomorphs with a total organic carbon (TOC) of 6.80%–10.55%. It contains a multitaxic, low-diversity, dinosaur assemblage, dominated by Edmontosaurus sp., which is primarily represented by late juveniles. Four theropod taxa are almost exclusively represented by isolated teeth. With >6000 specimens collected, the assemblage is characterized by a Minimum Number of Individuals (MNI) of 36, dominance of Voorhies Groups I and II, and an underrepresentation of teeth, skulls, and girdles. Bones are highly fragmented and exhibit low weathering and abrasion indices. Bite marks occur on slightly more than 1% of elements. The densest accumulations of bone are typically found in the middle third of the bed with the largest bones at the bottom. The Liscomb Bonebed assemblage resulted from mass mortality associated with overbank floods that formed floodplain mires and ponds. Data from the current study clearly establish the Alaskan Arctic as the year-round residence of a rich dinosaur fauna and add further support to the hypotheses that even high-latitude hadrosaurids were gregarious and formed social groups.
Journal Article
THE FIRST PACHYCEPHALOSAURINE (DINOSAURIA) FROM THE PALEO-ARCTIC OF ALASKA AND ITS PALEOGEOGRAPHIC IMPLICATIONS
The last 15 years of field work along the beaches and bluffs of the Colville River, on Alaska's Arctic Coastal Plain, have produced a diverse record of high-latitude dinosaurs. Seven families and eight genera are documented with several other families and genera possibly being represented by less diagnostic remains and only a few scattered elements (Table 1; Nelms, 1989; Gangloff, 1994, 1998; Fiorillo et al., 1999; Fiorillo and Gangloff, 2000, 2001). Virtually all of the common major groups of theropods and ornithopods typical of the Late Cretaceous of northern North America are present. Most of the skeletal remains are found in rocks assigned to the Prince Creek Formation of the Colville Group (Detterman et al., 1963, 1975; Phillips, 1990). The diversity of the dinosaur record in Alaska has been significantly increased with the discovery of abundant tracks and trackways along the North Slope and Arctic Coastal Plain over the last six years. The majority of the ichnofossil record is contained in various terrestrial coal-bearing rocks assigned to the Early Cretaceous Nanushuk Group (Ahlbrandt et al., 1979). The dinosaur biozone spans the upper part of the Nanushuk group and all of the Colville Group, ranging from the mid to Late Cretaceous (Albian to Maastrichtian; Mull, 1985). The already diverse and abundant record of dinosaur skeletal fossils was increased by the discovery in 1999 of the first evidence of pachycephalosaurs from this region (Fig. 1). This taxon is now represented by a nearly complete left squamosal and the contiguous, posterior, basal part of the dome. The highly thickened bone with characteristic prismatic internal structure accompanied by the distinctive ornamentation diagnostic of this group allows for an unequivocal identification to the subfamily level. The specimen (UAM # AK-493-V-001, Fig. 2.2) is most of the left squamosal and includes a portion of a thickened dome. The specimen is bounded on three sides by parted sutures interpreted as representing the contacts with the quadrate, exoccipital, and the narrow descending portion of the parietal bone (see Fig. 2.2, 2.4). The remaining margin exhibits a broken surface that reflects the polygonal prismatic internal structure of a part of the parietal-frontal dome. The sutures are well preserved and show little or no evidence of fluvial abrasion or weathering due to subaerial exposure prior to burial.
Journal Article
Polar Dinosaurs
The study of polar dinosaurs provides potentially unique insights into their physiological adaptations because they may have been exposed to extreme conditions not experienced elsewhere. These conditions cannot be assumed to have been the same as at comparable latitudes today, however.
Journal Article
Structure and paleoecology of Lower Cambrian reefs
Lower Cambrian buildups were constructed by a consortium of calcareous cyanobacteria(?) and archaeocyaths in varying proportions. The earliest are small Renalcis-cored bioherms in the Tommotian of the Siberian Platform. During the Atdabanian Stage archaeocyaths diversified and assumed a more active constructional role. A barrier complex of bioherms and associated facies developed in equatorial latitudes on the Siberian Plate. Here termed the \"Great Siberian Barrier Complex,\"this carbonate barrier was over 800 km long and up to 300 km wide. The first paleoecologic studies of Lower Cambrian buildups were carried out by Soviet workers in the rocks of the Great Siberian Barrier Complex: During the Botomian Stage archaeocyathan diversity increased dramatically and the distribution and variety of buildups also increased. Botomian buildups of western North America display a complex morphology and four-stage community replacement sequence previously documented in younger Phanerozoic framework reefs. Botomian reefs of Antarctica display an especially wide variety of textures and show that archaeocyaths were not an essential component of framework reefs in the Lower Cambrian. Following a more-or-less continuous marine transgression during the first three stages of the Early Cambrian, the end of the Early Cambrian was a time of worldwide regression, here termed the Toyonian Regression. During this regression archaeocyathan diversity plummeted, while the associated fauna experienced a dramatic increase in diversity. Lower Cambrian reefs display a complex trophic web in which archaeocyaths with algal symbionts probably played an important energetic role. We present evidence that Renalcis and Epiphyton were cyanobacteria that could live autotrophically in well-lit settings, photoheterotrophically in dim light, and perhaps chemoheterotrophically in complete darkness. The diversity of reef morphologies and boundstone fabrics in Lower Cambrian reefs has been underappreciated, as has the faunal diversity of the reef community. Lower Cambrian reefs have much to teach us about the reef ecosystem generally, and the Lower Cambrian reef-building fauna, including archaeocyaths, could be an important source of data on the evolutionary paleoecology of the Cambrian fauna.
Journal Article
Theropod teeth from the Prince Creek Formation (Cretaceous) of northern Alaska, with speculations on Arctic Dinosaur paleoecology
Theropod teeth are taxonomically diagnostic components of dinosaur assemblages. Seventy teeth have been recovered from six different localities in the Kogosukruk Tongue of the Prince Creek Formation (Upper Cretaceous) of the North Slope of Alaska. This assemblage of teeth shows slightly less diversity compared to well documented assemblages of teeth from the slightly older Judith River Formation of south-central Montana, the Aguja Formation of west Texas, and the Hell Creek Formation of eastern Montana. In addition, in contrast to the Judith River Formation assemblage of teeth in south-central Montana, the teeth assigned to Troodon dominated the Alaskan assemblage. The dominance of Troodon is attributed to adaptation by this theropod to low light conditions while overwintering at a high paleolatitude.
Journal Article
Tabulaconus Handfield: microstructure and its implication in the taxonomy of primitive corals
Numerous specimens of Tabulaconus Handfield, 1969, have been collected in carbonate buildups within the Adams Argillite (Early Cambrian, Tatonduk area, Alaska). The wall structure of this form has been investigated, along with contemporaneous archaeocyaths and algae, through the use of polished ultra-thin sections (2–3 μm thick) and scanning electron microscopy. The results of this microstructural comparison indicate that despite diagenetic alteration Tabulaconus has a skeleton that is unlike any presently known and is quite distinct from associated algae or archaeocyaths. It is more elaborate than that found in the archaeocyaths but has not reached the stage of complexity seen in the primitive coral Cothonion Jell and Jell, 1976. The presence of some elongated units may represent an initial step towards the fibrous skeleton typical of Paleozoic corals. This study shows that even though diagenesis alters the original microstructure of calcareous skeletons, the resultant fabrics and detailed structures can be useful in systematic descriptions. Tabulaconus is removed from the Gastroconidae Kordae due to the presence of rudimentary septa and constitution of the tabularium. A number of species assigned to the genus Bačatocyathus Vologdin and included within the Archaeocyatha appear to be examples of Tabulaconus or very close relatives. An emended description of Tabulaconus kordae, the type species, is proposed.
Journal Article
THEROPOD TEETH FROM THE PRINCE CREEK FORMATION (CRETACEOUS) OF NORTHERN ALASKA, WITH SPECULATIONS ON ARCTIC DINOSAUR PALEOECOLOGY
Theropod teeth are taxonomically diagnostic components of dinosaur assemblages. Seventy teeth have been recovered from six different localities in the Kogosukruk Tongue of the Prince Creek Formation (Upper Cretaceous) of the North Slope of Alaska. This assemblage of teeth shows slightly less diversity compared to well documented assemblages of teeth from the slightly older Judith River Formation of south-central Montana, the Aguja Formation of west Texas, and the Hell Creek Formation of eastern Montana. In addition, in contrast to the Judith River Formation assemblage of teeth in south-central Montana, the teeth assigned to Troodon dominated the Alaskan assemblage. The dominance of Troodon is attributed to adaptation by this theropod to low light conditions while over-wintering at a high paleolatitude.
Journal Article