Abstract Detail

Mesozoic and Cenozoic plant evolution and biotic change: A symposium in honor of Ruth Stockey

Herendeen, Patrick [1], Doyle, James [2], Endress, Peter K. [3], Takahashi, Masamichi [4].

Fossil magnoliid flower from the mid-Cretaceous Rocky Point locality, Maryland.

A single flower from the mid-Cretaceous Rocky Point locality of Cecil County, Maryland is described using scanning electron microscopy and synchrotron x-ray microtomography. The flower is bisexual with ca. 20 strap-shaped tepals preserved (original number probably ca. 40). Stamen and carpel phyllotaxis is somewhat irregular but probably whorled. The ca. 50 stamens are broad, scale-like, spathulate and end in a short connective apex. The anther is ca. 2/3 to 3/4 the length of the stamen. Filament and anther are not well differentiated and the entire stamen smoothly tapers to the base. The thecae are on the ventral (adaxial) surface and the four pollen sacs are probably embedded. Pollen is not preserved. The flower contains ca. 100 small, short carpels. The ovary locule takes up most of their length. Ovules are not preserved, but the locule shape suggests that the carpels are uniovulate. The distal part of the carpel is pointed and curved toward the center of the gynoecium, but there is no distinct style. The receptacle is hemispherical to almost 3/4 spherical in the gynoecial region. The fossil exhibits a combination of features not found in any lineage of extant angiosperms. It shows a number of similarities to Magnoliales, especially Annonaceae, but also significant differences. There are also similarities with the ANITA grade, especially Austrobaileyales, but also features not found in extant members of these taxa. In an attempt to resolve these ambiguities, we performed a morphological phylogenetic analysis with the arrangement of extant taxa constrained to a molecular backbone tree. With ovule number scored as one, we obtained four most parsimonious trees, with three positions in Magnoliales and one sister to Laurales. The placements in Magnoliales are supported by the embedded pollen sacs, whorled perianth, and plicate carpels, but the polymerous perianth and androecium and adaxial pollen sacs are in conflict. Scoring ovule number as unknown added two more trees with the fossil nested in Nymphaeales, which is not convincing. A placement sister to Austrobaileyales is two steps less parsimonious. This position would be supported by the adaxial pollen sacs and many series/whorls of parts, but the plicate or intermediate carpels are inconsistent. Although the fossil is well preserved and many floral architecture characters are available, our results illustrate the fact that additional characters such as pollen morphology and seed anatomy are sometimes needed to reach an unequivocal phylogenetic placement of floral mesofossils.

1 - Chicago Botanic Garden, Senior Scientist, 1000 Lake Cook Road, Glencoe, IL, 60022, USA
2 - University Of California Davis, Dept Of Evol & Ecology, One Shields Avenue, Davis, CA, 95616-8537, USA
3 - University Of Zurich, Bot Garten & Inst Fur Sys Bot, Zollikerstrasse 107, Zurich, CH-8008, Switzerland
4 - Niigata University, Department of Environmental Sciences, Niigata, Japan

Keywords:
Cretaceous
Magnoliid
Tomography.

Presentation Type: Colloquium Presentations
Session: C6
Location: Salon 5/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 2:30 PM
Number: C6005
Abstract ID:225
Candidate for Awards:None