Abstract Detail

Paleobotany

Atkinson, Brian A [1], Stockey, Ruth A [1], Rothwell, Gar W [1].

Initial radiation of asterids: earliest cornalean fossils.

Our current understanding of eudicot phylogeny suggests that Cornales is the earliest diverging lineage of asterids. Molecular divergence-time analyses suggest that Cornales diverged and rapidly radiated sometime during the mid- to Late Cretaceous. This rapid radiation has made it difficult to resolve deep-node relationships. Cornalean fossils from Late Cretaceous deposits have the potential to improve our understanding of the initial radiation of the order, but the Cretaceous record of Cornales is sparsely sampled. The most ancient cornalean fossils consist of fruits, Hironoia fusiformis from the early Coniacian (89 Ma) of Japan. Here we report three additional permineralized cornalean fruit types from the early Coniacian of Vancouver Island, British Columbia, Canada. Each morphotype has thick-walled woody endocarps with elongate germination valves, one apically attached seed per locule, and lacks a central vascular bundle, thus, confirming their cornalean affinities. All three morphotypes have several vascular bundles in each septal arm. Each morphotype differs, however, in several morphological and anatomical characters. Morphotype 1 is characterized by ellipsoidal endocarps with three to five locules composed mostly of isodiametric to somewhat transversely elongated sclereids. However, there is a thin layer of longitudinally elongated fibers lining each locule. Germination valves have distinct longitudinal ridges on the exterior surface. Morphotype 2 is characterized by spheroidal endocarps with a relatively long persistent style. Two specimens are preserved with parenchymatous mesocarp still attached. There are consistently three locules per endocarp, and germination valves have a smooth exterior surface. The endocarp is composed of sclereids with an inner, multi-seriate layer of narrow transverse fibers that are circum-locular. Morphotype 3 is characterized by relatively large endocarps composed of isodiametric sclereids and germination valves that lack exterior ridges. Each morphotype has a unique combination of characters indicating that the specimens represent three distinct new taxa. These cornalean fruits are synchronous with the earliest cornalean fossil, Hironoia; however, they differ from Hironoia in several important characters. Morphological diversity of cornalean fruits during the earliest Coniacian and extreme geographic disjunction among the fossils support hypotheses of a rapid initial cornalean diversification in the Northern Hemisphere and that the order arose earlier in the Cretaceous.

1 - Oregon State University, Botany and Plant Pathology, 2082 Cordley Hall , Corvallis, OR, 97331, USA

Keywords:
Asterids
Cornales
Fossils
Fruits
Cretaceous
Biogeography.

Presentation Type: Oral Paper
Session: 5, Paleobotany Student Awards
Location: 204/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 9:30 AM
Number: 5006
Abstract ID:360
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award