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Abstract Detail

The Critical Role of Plant Fossils in Divergence Dating Studies

Smith, Selena [1], Benedict, John [2], Specht, Chelsea [3], Collinson, Margaret [4], Leong-Škorničková, Jana [5], Kvaček, Jiří [6], Xiao, Xianghui [7], Fife, Julie [8], Marone, Federica [8].

Reevaluation of the oldest fossils in Zingiberales and implications for inferring the evolutionary history of gingers, bananas, and relatives.

Fossils of Zingiberales (bananas, gingers, and relatives) are geographically and temporally widespread starting in the Late Cretaceous. The fossil record consists of leaves and reproductive material (fruits and seeds), most of which have been attributed to the Musaceae (bananas) or Zingiberaceae (gingers) but also Cannaceae, Costaceae, Heliconiaceae, and Marantaceae. The oldest records are leaves of Zingiberopsis riggauensis (Santonian) and fruits/seeds of Spirematospermum (Campanian). Reinvestigation of these fossils using a large comparative dataset from modern Zingiberales has provided important insights into these earliest fossils, with implications for their use as calibration points. Reexamination of specimens of Zingiberopsis riggauensis shows it has a venation pattern that is not found in the Zingiberales, and thus must be excluded from the order. Other specimens also show other, non-zingiberalean patterns, highlighting the need for caution when using fossil monocot leaves. Thus Spirematospermum is the oldest fossil taxon of Zingiberales, making it crucial that we understand its affinities. However, there has been disagreement about whether Spirematospermum belongs to Musaceae or Zingiberaceae. Most recently it was assigned to a new subfamily of Musaceae largely based on the presence of a chalazal chamber in the seed. Preliminary results from a large dataset on seed anatomy and structure in fossil and extant Zingiberales that is being compiled using synchrotron-based microtomography, providing both 2D and 3D data to examine, suggest that the placement of Spirematospermum in Musaceae is not strongly supported. This dataset shows that a chalazal chamber is in fact present in several genera in Zingiberaceae (Alpinioideae), in contrast to previous reports, and confirms its presence in Costaceae and Musaceae and absence in all other zingiberalean families. Seed coat structure of Spirematospermum shows a combination of features of both Musaceae and Zingiberaceae, suggesting this might be better considered a stem lineage and not belonging to either family. Phylogenetic analyses are crucial for correctly placing the fossil and determining what nodes it can be used to constrain for dating analyses. This case study highlights the importance of integrating detailed morphological data of both fossil and modern taxa to correctly identify affinities of fossil taxa prior to their use in dating divergences and to infer the evolutionary history of a group.

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1 - University of Michigan, Earth & Environmental Sciences and Museum of Paleontology, 1100 North University Ave., 2534 CC Little Building, Ann Arbor, MI, 48109, USA
2 - University of Guam, Biology, Mangilao, Guam
3 - University of California Berkeley, 111 Koshland Hall, MC 3102, Berkeley, CA, 94720, USA
4 - Royal Holloway University of London, Earth Sciences, Egham Hill, Egham, TW20 0EX, UK
5 - Singapore Botanic Gardens, Singapore, Singapore
7 - Argonne National Lab, Advanced Photon Source, Argonne, IL, 60439, USA
8 - Paul Scherrer Institut, Swiss Light Source, Villigen, Switzerland


Presentation Type: Symposium or Colloquium Presentation
Session: C5
Location: Belle-Chasse/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 11:30 AM
Number: C5009
Abstract ID:728
Candidate for Awards:None

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