Thompson, Dori , Upchurch, Garland , Parrott, Joan , Estrada-Ruiz, Emilio , Mack, Greg .
Reconstructing a Redwood from Multiple Organs: New material from the Upper Cretaceous Jose Creek Member, McRae Formation of south-central New Mexico.
The Cretaceous history of redwoods (Sequoioid clade of the Cupressaceae) is poorly understood relative to the Cenozoic history of redwoods, in part because of limited materials and the analysis of single organs. Abundant specimens of a Late Cretaceous redwood from the Jose Creek Member, McRae Formation (probable Maastrichtian) of New Mexico, provide an opportunity to understand population variation, evaluate taxonomic concepts, and reconstruct the parent plant from multiple organs. The remains come from two beds of volcanic ash and consist of shoot impressions with up to three orders of branching, associated pollen cones, and in situ permineralized stumps. The shoot impressions, representing lateral branches, show a mosaic of features found in Sequoia and Metasequoia. The thickest branches bear reduced leaves and give rise to determinate planate branchlets. The branchlets have elliptical taxodioid leaves with acute apices and decurrent attachment to the stem, as in Sequoia. Phyllotaxy is predominantly opposite decussate, with alternating leaf pairs rotating distichously, resulting in leaf bases that zig zag along the stem, as in Metasequoia. No bud scales or other scale leaves occur at the base of the branchlets. Associated pollen cones have peltate microsporophylls and three pollen sacs, similar to those of modern redwoods. Each cone is ellipsoid in shape, borne at the tip of a reduced shoot, and shed singly, as in Sequoia and Sequoiadendron. The reduced shoot has opposite decussate bracts, as in Metasequoia. At one locality there is an associated in situ stump 1.5m in diameter that has anatomy characteristic of the taxodioid grade of conifers. The associated organs suggest the plant could be a large tree like modern redwoods. The Jose Creek redwood is most similar in its shoot morphology to Cretaceous redwoods from the Raton Basin of New Mexico/Colorado, however provides additional organs that reveal a novel combination of characters. It differs from Cenozoic and Recent redwoods in the absence of scale leaves at the base of the branchlets and the absence of growth rings, suggesting more poorly developed dormancy mechanisms.
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1 - Texas State University, Department Of Biology, 601 University Drive, San Marcos, TX, 78666, USA
2 - New Mexico State University, Geological Sciences, Las Cruces, NM, 88003, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Union A/Hyatt
Date: Wednesday, July 11th, 2012
Time: 9:30 AM