Abstract Detail

Paleobotanical Section

Smith, Selena Y [1], Collinson, Margaret [2], Benedict, John [3], Specht, Chelsea [4], Marone, Federica [5].

Revisiting Spirematospermum (Zingiberales) and its evolutionary significance.

Fossil fruits and seeds assigned to Spirematospermum are a common element in many European Neogene carpological floras, and the genus ranges from the Cretaceous of North America and Europe through the Pliocene of Eurasia. Spirematospermum seeds are readily identified by their spirally striated seed coat. While they are accepted as being a member of Zingiberales, and represent some of the oldest fossils of that order, there has been some debate over the familial affinities of this extinct taxon. In order to more precisely place Spirematospermum in an evolutionary and phylogenetic context, we have reexamined all species, including specimens from multiple localities where possible, using synchrotron X-ray tomographic microscopy (SRXTM) to non-destructively gain anatomical information. SRXTM clearly visualized a seed coat with a palisade exotesta comprised of elongate cells with thickened anticlinal walls and several to many layers of more-or-less isodiametric cells forming the mesotesta and endotesta. Seeds have a two-layered operculum (when preserved) but, with one exception, lack other kinds of micropylar modifications that have been recognized in modern seeds of Zingiberales. A chalazal chamber was observed in most species. It is small to absent in Cretaceous specimens, but is more prominent in Cenozoic specimens. Spirematospermum chandlerae, S. friedrichii, and S. wetzleri are confirmed as distinct species. Spirematospermum sp. from the Cretaceous of Germany should be recognized as a fourth species, and one specimen examined from the Eocene of the UK may represent a fifth species. In addition to the Cretaceous seeds being small in size, there is a transition in seed coat structure from the oldest (Cretaceous and early Eocene) seeds, with a relatively thick exotesta and thin mesotesta, to Eocene and younger seeds of S. wetzleri having a three-zoned mesotesta forming most of the seed coat thickness. Preliminary phylogenetic analyses suggest an affinity of Spirematospermum with subfamily Alpinioideae within Zingiberaceae. Anatomical and species diversity appears to have been greater in the Cretaceous, and subsequently declined in the Neogene when Spirematospermum seeds are more abundant and have a wider geographic distribution than before.

1 - University of Michigan, Department of Earth & Environmental Sciences and Museum of Paleontology, 1100 North University Ave., 2534 CC Little Building, Ann Arbor, MI, 48109, USA
2 - Royal Holloway University of London, Department of Earth Sciences, Egham Hill, Egham, TW20 0EX, UK
3 - University of Michigan, Department of Earth & Environmental Sciences, 1100 North University Ave., 2534 CC Little Building, Ann Arbor, MI, 48109, USA
4 - University of California, Berkeley, Dept. of Plant and Microbial Biology & University and Jepson Herbaria, 111 Koshland Hall, MC 3102, Berkeley, CA, 94720, USA
5 - Paul Scherrer Institute, Swiss Light Source, Villigen, Switzerland

Keywords:
Zingiberales
Spirematospermum
Seed
x-ray tomography
Fossil.

Presentation Type: Oral Paper:Papers for Sections
Session: 21
Location: Whitewater/Grove
Date: Tuesday, July 29th, 2014
Time: 10:45 AM
Number: 21009
Abstract ID:695
Candidate for Awards:None