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Abstract Detail

The Critical Role of Plant Fossils in Divergence Dating Studies

Devore, Melanie [1], Pigg, Kathleen [2], Wheeler, Elisabeth [3].

The fossil record for Rosaceae and its value to divergence dating studies.

The Rosaceae includes approximately 90 genera and 3000 species predominantly distributed in temperate and subtemperate regions of the Northern Hermisphere. Prior to Potter and colleagues' (2007) molecular phylogenetic generic-level analysis of the family, treatments placed a strong emphasis on fruit morphology, as well as surveys of karylogy, phytochemistry, and modes of reproduction. Currently, three subfamilies are recognized based on molecular phylogenetic analyses. Two major clades are present within Rosaceae with the subfamily Rosoideae comprising one clade while the second clade includes a basal clade delimited as Dryadoideae that is comprised of all four actinorhizal genera. The remaining clades in the second major clade include genera previously assigned to Amygaloideae, Maloideae, and Spiraeoideae and now placed with in the third subfamily Spiraeoideae. Rosaceae is represented commonly in the North American fossil record by leaves and wood, and by fruits and seeds in Europe. Flowers are rare. The pollen record for Rosaceae is poor and the family is generally poorly represented in modern pollen rain studies. Because there is no single apomorphic character for the family, assignment of fossils within Rosaceae is problematic unless they possess combinations of synapomorphies defining modern genera or subfamilies. There are no unequivocal records for the family in the Cretaceous or Paleocene, however, by the middle Eocene a significant number of fossils assignable to Rosoideae are known in Europe. Of these, the endocarp record of Rubus provides a potential calibration point for the Rosoideae clade. In western North America, Rosaceae are well represented in the Okanogan Highlands, especially the latest early Eocene Republic flora. There specimens assignable to Rosaceae fall into one of three categories: 1)extant genera established by the Eocene; 2)fossil forms with affinities to modern genera: or 3)extinct genera with affinities to higher taxonomic levels. Included in the Republic flora is Prunus cathybrownae with flowers containing in situ pollen and developing fruits; and leaves with characteristic petiolar glands like those often found in modern representatives of the genus. The Republic Prunus fossils represent the oldest record with the most complete combination of synapomorphies for an extant genus. Prunus endocarps are known from middle Eocene sites at Clarno and in the Princeton chert, and wood occurs at these and additional Eocene sites. In this contribution we re-evaluate our previous review of Okanogan Highlands Rosaceae, and in conjunction with the wood record, address the usefulness of fossils for calibrating Dryadoideae and Spiraeoideae.

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1 - Dept of Biology & Env. Science, GC & SU Campus Box 81, MILLEDGEVILLE, GA, 31061-0001, USA
2 - Arizona State University, SCHOOL OF LIFE SCIENCES FACULTY & ADMIN, BOX 874501, Tempe, AZ, 85287-4501, USA, 480/965-3154
3 - DEPT OF WOOD & PAPER SCIENCE, 710 Dixie Trail, Raleigh, NC, 27607, USA

fossil flower
fossil wood
fossil calibration
Republic flora
Okanogan Highlands.

Presentation Type: Symposium or Colloquium Presentation
Session: C5
Location: Belle-Chasse/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 11:15 AM
Number: C5008
Abstract ID:427
Candidate for Awards:None

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