[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

The Hills Have New Papers

OK, no they don't...but they _do_ have fossils in 'em...!

Schweitzer, M.H., Elsey, R.M., Dacke, C.G., Horner, J.R., and Lamm, E.-T. 2007. Do egg-laying crocodilian (Alligator mississippiensis) archosaurs form medullary bone? Bone 40(4):1152-1158. doi: 10.1016/j.bone.2006.10.029.

ABSTRACT: It is beyond question that Mesozoic dinosaurs, like Aves and Crocodylia, are archosaurs. However, within the archosaurian clade, the origin and distribution of some major features are less clear, particularly with respect to reproductive physiology. Medullary bone, a highly mineralized, bony reproductive tissue present in the endosteal cavities of all extant egg-laying birds thus far examined, has recently been reported in Tyrannosaurus rex. Its presence or absence in extant crocodilians, therefore, may shed light on the timing of its evolutionary appearance. If medullary bone is present in all three taxa, it arose before the three lineages diverged. However, if medullary bone arose after this divergence, it may be present in both extinct dinosaurs and birds, or in birds only. If present in extinct dinosaurs and birds, but not crocodilians, it would indicate that it arose in the common ancestor of this clade, thus adding support to the closer phylogenetic relationship of dinosaurs and birds relative to crocodilians. Thus, the question of whether the crocodilian Alligator mississippiensis forms medullary bone during the production of eggs has important evolutionary significance. Our examination of long bones from several alligators (two alligators with eggs in the oviducts, one that had produced eggs in the past but was not currently in reproductive phase, an immature female and an adult male) shows no differences on the endosteal surfaces of the long bones, and no evidence of medullary bone, supporting the hypothesis that medullary bone first evolved in the dinosaur-bird line, after the divergence of crocodilians from this lineage.

Lucas, S.G., and Tanner, L.H. 2007. The nonmarine Triassic-Jurassic boundary in the Newark Supergroup of eastern North America. Earth Science Reviews 84(1-2):1-20. doi: 10.1016/j.earscirev.2007.05.002.

ABSTRACT: For the last three decades, the position of the Triassic-Jurassic boundary (TJB) in nonmarine strata has largely been based on its palynostratigraphic placement just below the oldest basalts of the Central Atlantic magmatic province (CAMP) in the Newark Supergroup of eastern North America. This boundary, however, is demonstrably older than the TJB as it is defined in marine strata. Thus, the palynostratigraphic change used to place this TJB in the Newark most resembles a late Norian change in the European section and does not correspond to any palynological event at the marine-defined TJB. Conchostracan biostratigraphy suggests that the TJB is in the Newark extrusive zone above the oldest CAMP basalt, and vertebrate biostratigraphy is consistent with this placement of the TJB. Radioisotopic ages indicate that the TJB defined in marine strata is no older than 200 MA, but the oldest CAMP basalts of the Newark Supergroup consistently yield ages averaging about 201 Ma. Magnetostratigraphic correlation of the Newark section to the TJB section at St. Audrie's Bay in England also indicates that the onset of CAMP volcanism in the Newark Supergroup is older than the marine TJB. Correlations based on carbon and osmium isotopes are also consistent with this correlation. Thus, all data indicate that the TJB in the Newark Supergroup is above the lowest CAMP basalt in the Newark extrusive zone. Correct placement of the TJB in the Newark Supergroup allows key nonmarine and marine events to be sequenced across the TJB, indicating the following succession of events: crurotarsan ("thecodont") extinction, the palynofloral turnover in the Newark, the first CAMP eruptions, the extinctions of Rhaetian ammonites and conodonts, and the first appearance of Jurassic psiloceratid ammonites.

Avanzini, M., Dalla Vecchia, F.M., Mietto, P., Piubelli, D., Preto, N., Rigo, M., and Roghi, G. 2007. A vertebrate nesting site in northeastern Italy reveals unesxpectedly complex beahvior for late Carnian reptiles. Palaios 22(5):465-475. doi: 10.2110/palo.2005.p05-137r.

ABSTRACT: We interpret 13 large subcircular or horseshoe-shaped depressions discovered in Late Triassic peritidal carbonate rocks of the Dogna Valley in Udine Province, northeastern Italy, to be reptile nests. These trace fossils show truncation of strata, elevated ridges of massive sediment, and sediment infill within the depression differing in shape and sedimentary structures from the host sediment. The palynological assemblage of a shaly interbed close to the nest layer indicates a Tuvalian age (late Carnian). Archosaurian footprints, produced possibly by aetosaurs, are on a surface 130 cm above the nest-bearing layer. The trackmakers are considered the most probable nest makers.

Suarez, C.A., Suarez, M.B., Terry, D.O., Jr., and Grandstaff, D.E. 2007. Rare earth element geochemistry and taphonomy of the Early Cretaceous Crystal Geyser dinosaur quarry, east-central Utah. Palaios 22(5):500-512. doi: 10.2110/palo.2005.p05-126r.

ABSTRACT: The Crystal Geyser Dinosaur Quarry contains a large monospecific accumulation of bones from a basal therizinosaur, Falcarius utahensis. The quarry is located approximately 16 km south of Green River, Utah, at the base of the early Cretaceous (Barremian) Yellow Cat Member of the Cedar Mountain Formation. Fossil bones in the quarry occur in three units that have distinct taphonomic, lithologic, and geochemical characteristics. Rare earth element compositions of fossils suggest that bones from each unit were drawn from different reservoirs or sources having distinctly different compositions, and fossils were not reworked between units. Compositions of bones differ greatly within Units 1 and 2, even within the same 1-m2 quarry grid. These chemical differences and taphonomic characteristics, such as current orientation, hydraulic sorting, and occasional extensive abrasion, suggest that bones from these two units are allochthonous and were fossilized at other localities, possibly over an area of several kilometers, and were then eroded, transported, and concentrated in a spring-influenced fluvial environment. Bones in Unit 3 have very similar rare earth element signatures, suggesting that they were probably fossilized in situ at a separate time from bones in Units 1 and 2. At least two mass mortality events were responsible for the monospecific assemblage of bones at the quarry. Because bones may have been concentrated from a wide area, causes of mass mortality must have been regionally extensive, possibly owing to seasonal drought, sudden changes in weather, or disease.

Suarez, M.B., Suarez, C.A., Kirkland, J.I., González, L.A., Grandstaff, D.E., and Terry, D.O., Jr. 2007. Sedimentology, stratigraphy, and depositional environment of the Crystal Geyser dinosaur quarry, east-central Utah. Palaios 22(5):513-527. doi: 10.2110/palo.2006.p06-014r. ABSTRACT: The Crystal Geyser Dinosaur Quarry, near Green River, Utah, is located at the base of the Lower Cretaceous (Barremian) Yellow Cat Member of the Cedar Mountain Formation. The quarry preserves a nearly monospecific accumulation of a new basal therizinosauroid, We used field descriptions and petrographic analysis to determine the depositional environment and development of the quarry strata. Results of these analyses suggest that the quarry represents multiple episodes of bone accumulation buried by spring and overbank flood deposits. Evidence for these previously undescribed spring deposits includes calcite macroscopic structures within the quarry strata-such as pisolites and travertine fragments-and calcite micromorphologies-including radial-fibrous, feather, and scandulitic dendrite morphologies and tufa clasts. At least two episodes of bone incorporation are preserved in the quarry based on their stratigraphic position and lithologic associations. The unique depositional setting in and around the Crystal Geyser Dinosaur Quarry appears to have been favorable for the preservation of vertebrate fossils and provides insight into early Cretaceous environments in North America.

Chin, K. 2007. The paleobiological implications of herbivorous dinosaur coprolites from the Upper Cretaceous Two Medicine Formation of Montana: why eat wood? Palaios 22(5):554-566. doi: 10.2110/palo.2006.p06-087r.

ABSTRACT: Rare assemblages of woody coprolites from different strata of the Two Medicine Formation provide surprising perspectives on the feeding behavior of Late Cretaceous ornithischian dinosaurs. Most of the irregularly shaped, calcareous specimens are largely composed of fragmented conifer wood (13%-85%) and can be identified as coprolites by the presence of distinctive backfilled dung beetle burrows. The large size (up to 7 L in volume), fibrous contents, and associated bones and eggshell strongly suggest that the source animals at one site were Maiasaura hadrosaurs. The wood-bearing coprolites occur in strata ranging in age from 74-80 Ma, revealing a recurring (possibly seasonal) habit of wood ingestion. The preponderance of wood in the specimens and the absence of recognizable small-diameter twig fragments suggest that wood ingestion was intentional-that the coprolite producers had not merely consumed wood inadvertently when feeding on the leaves and bark of terminal branches. Because undegraded wood provides inconsequential nutritive value for vertebrates, it is unlikely that ornithischians would have expended the energy to masticate intact wood for little benefit. Furthermore, patterns of tissue damage in the fecal wood fragments suggest fungal degradation. Thus, the most parsimonious explanation for the high fecal wood content is that the coprolite producers consumed decomposing wood to capitalize on resources released by fungal attack, along with the tissues of the decomposers and associated invertebrate detritivores. These multiple coprolite deposits provide direct fossil evidence of recurring dinosaur diets and suggest that some ornithischians at least occasionally tapped detrital resources. Although such feeding behavior is rare in large extant herbivores, utilization of rotting wood would have augmented the resource options of Cretaceous ecosystems that lacked fodder provided by grasses and other derived angiosperms.

Jerry D. Harris
Director of Paleontology
Dixie State College
Science Building
225 South 700 East
St. George, UT  84770   USA
Phone: (435) 652-7758
Fax: (435) 656-4022
E-mail: jharris@dixie.edu
and     dinogami@gmail.com


"Machine. Unexpectedly, I'd invented
a time"
              -- Alan Moore

"Easy. Just touch the match to"
              -- Ursula K. Le Guin

"Batman Sues Batsignal: Demands
Trademark Royalties."
-- Cory Doctorow