Abstract Detail

The Critical Role of Plant Fossils in Divergence Dating Studies

Gandolfo, Maria A, [1], Hermsen, Elizabeth J. [2].

A critical review of the fossil history of the Southern Hemisphere family Cunoniaceae.

The Southern Hemisphere family Cunoniaceae encompasses approximately 300 extant species within 26 genera. The majority of the genera are found in the present-day center of diversity for the family, Australasia. Only seven genera occur outside of this region, three (or four if Eucryphia is considered as a member of the family) in Central and South America and three in Africa (including Madagascar). The family is represented in the fossil record by sporadic pollen grains, wood, leaves, and reproductive organs. Placement of fossils unequivocally within Cunoniaceae is difficult because the only apomorphy for the family is the presence of a single pair of interpetiolar stipules. This character is almost never observed in fossils. The assignment of fossils to genera within Cunoniaceae is sometimes possible, however, because several cunoniaceous genera possess distinct combinations of synapomorphies that can sometimes be observed in fossil material. In this contribution, we will present a critical review of the complete fossil record of Cunoniaceae, with an emphasis on fossils from Antarctica (pollen and wood) and macrofossils recently discovered in the early Eocene Laguna del Hunco flora of Chubut Province, Patagonia, Argentina (a review of the Australian fossil record of the group was published previously by other authors). The South American material includes macrofossils representing several types of cunoniaceous fruits and infructescences. Although several types of fossils - including wood, leaves, and leaf cuticles - possess suites of characters consistent with Cunoniaceae, only fossil fruits attributable to the genus Ceratopetalum (Tribe Schizomerieae) can unequivocally be assigned to the family based on combinations of synapormorphies unique to the genus. These synapomorphies include the presence of an enlarged calyx that is persistent in fruit, the venation pattern of the sepals, presence a nectary ring that surrounds the bicarpellate and semi-inferior capsule, and alternisepalous stamens. The Ceratopetalum fossil fruits from South America are the oldest record for the genus, and, therefore, a suitable calibration point for the node representing the most recent common ancestor of Ceratopetalum and its sister clade. We will also explore the possible use of other cunoniaceous fossils as putative calibration points, such as Patagonian racemose infructescences with capsular fruits that have affinities to extant Weinmannia and Cunonia (Tribe Cunonieae).

Broader Impacts:

1 - Cornell University, L. H. BAILEY HORTORIUM, 410 Mann Library Building, ITHACA, NY, 14853-4301, USA, 607/255-3273
2 - Ohio University, Department of Environmental and Plant Biology, Athens, OH, 45701

Keywords:
Cunoniaceae
macrofossils
calibration point
Patagonia.

Presentation Type: Symposium or Colloquium Presentation
Session: C5
Location: Belle-Chasse/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 11:00 AM
Number: C5007
Abstract ID:150
Candidate for Awards:None