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Abstract Detail

Campanian-Maastrichtian floras on Laramidia: vegetation trends west of the seaway

Contreras, Dori L. [1], Looy, Cindy [2], Upchurch, Jr., Garland [3], Mack, Greg [4].

The late Campanian Jose Creek flora from New Mexico, a window into forest structure during the rise of angiosperms.

Late Cretaceous floras spanning the North American Western Interior document an important transition in the composition and structure of forests during the ecological radiation of angiosperms. Although patterns in species richness of different plant groups are fairly well documented, patterns of evolution in community structure and life form dominance are not yet well established. Here we provide an updated report on an exceptional late Campanian macroflora (74.7 +/-1 myr) from southern Laramidia that is preserved in a single-horizon of recrystallized volcanic ash exposed over a 1.2 km long transect. The flora is from the Jose Creek Member, McRae formation of south-central New Mexico, which records deposition on an alluvial plain >200km inland from the Western Interior Seaway. To reconstruct landscape patterns, we established 26 quarries along the full length of the exposure, and censused fossils at each quarry by both the number of specimens and percent cover of morphotypes on rock surfaces using a line-intercept method. The deposit, which overlies a paleosol horizon indicative of well-drained conditions, contains abundant well-preserved plant macrofossils showing little to no evidence for transport, including in-situ stumps. To date over 155 leaf morphotypes have been recognized (>89% angiosperms) from the census of over 6,350 specimens and 30,860 2-cm line increments. Rarefaction analyses suggest that with increased sampling we will continue to recover new non-monocot angiosperms, but that diversity of other groups is not likely to increase appreciably. Angiosperms are the most abundant plant group (74% of specimens, 84% cover), followed by conifers, cycads, and ferns. There is strong dominance structure in the community. The most abundant five taxa by all metrics are a sequoioid conifer, Zingerberopsis-type monocot, Sabalites palm, Dryophyllum eudicot (Fagales), and a Brachyphyllum conifer. Diverse non-monocot angiosperms are mostly represented by locally abundant to rare taxa (totaling 47% of specimens, and 38% cover). As such, significant taxonomic heterogeneity exists between quarries, expected if each quarry represents locally-growing plants. Numerous reproductive structures are also found, including pollen cones, ovuliferous cones and isolated cone scales, flowers, seeds, and fruits. The overall picture that emerges is one of a diverse, spatially heterogeneous, non-analog flora consisting of redwoods, gingers, palms, diverse non-monocot angiosperms, and low-abundance ferns and cycads, which grew under paratropical/tropical, moist to wet conditions.

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1 - University of California Berkeley, UC Museum of Paleontology, 1101 Valley Life Sciences Bldg, Berkeley, CA, 94720, USA
2 - University Of California, Berkeley, Integrative Biology, 3060 Valley Life Sciences Bldg #3140, Berkeley, CA, 94720-3140, USA
3 - Texas State University, Department Of Biology, 601 University Drive, San Marcos, TX, 78666, USA
4 - New Mexico State University, Department of Geosciences, Las Cruces, NM, 88003, USA

leaf macrofossil
New Mexico.

Presentation Type: Colloquium Presentations
Session: CO3, Campanian-Maastrichtian floras on Laramidia: vegetation trends west of the seaway
Location: Sundance 3/Omni Hotel
Date: Wednesday, June 28th, 2017
Time: 9:30 AM
Number: CO3005
Abstract ID:422
Candidate for Awards:None

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