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Abstract Detail


Paleobotanical Section

Gee, Carole T. [1].

A whole-plant Araucaria from the Late Jurassic Morrison Formation of the Howe Ranch, Wyoming, USA, and implications for sauropod dinosaur feeding ecology.

OVER a decade of excavations in a dinosaur bonebed in the Late Jurassic Morrison Formation has yielded a large, albeit low-diversity flora of compression and permineralized fossils that pertain to the various plant organs of Araucaria. These come primarily from the Howe Stephens Quarry (G-Quarry) on the Howe Ranch in northern Wyoming. Reproductive structures of Araucaria are represented by large, squat seed cones with partially fused ovuliferous scale-bract complexes that were shed at maturity, as well as slender pollen cones with long-bristled cone scales. The winged, ligulate, single-seeded nature of the cone-scale complexes and the detached non-winged seeds point to an affinity with extant species, A. bidwillii, Section Bunya, although the size, shape, and awl-tipped microsporophylls of the pollen cone resemble those of living A. araucana, Section Araucaria (syn. Colymbea). Rhomboidal scale leaves (form genus Brachyphyllum) which are densely and helically arranged about twigs and branches represent the foliage. Coniferous wood is also present in great quantities. The virtually exclusive co-occurrence of hundreds of compression fossils in this bonebed, as well as consistencies in morphology, suggest that they pertain to the same species of Araucaria, which represents a new, unnamed form. Palynological analysis of samples from associated facies presents a broader picture of the regional flora which includes ferns, fern allies, seed ferns, and other conifers that likely inhabited moister habitats. Recent fermentation experiments on the foliage from living proxies of the Mesozoic flora (e.g., lycopods, horsetails, ferns, tree ferns, cycads, conifers) indicate that the leaves of modern Araucaria spp. are a good source of nutrition for browsing herbivores, especially in regard to calorie intake. Thus, as a major producer of biomass in the local flora, the Jurassic Araucaria trees at the Howe Quarry may have served as an essential food source for the giant-sized adult sauropods living there.[c.e.:srb]


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1 - University of Bonn, Institute of Paleontology, Nussallee 8, Bonn, D-53115, Germany

Keywords:
Araucaria
Araucariaceae
conifer cones
Jurassic
Morrison Formation
Wyoming
sauropod feeding ecology.

Presentation Type: Oral Paper:Papers for Sections
Session: 37-3
Location: 268/Holt
Date: Tuesday, August 1st, 2006
Time: 9:00 AM
Abstract ID:449


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