Abstract Detail

Paleobotany

Prestianni, Cyrille [1], Decombeix, Anne-Laure [2].

Bipolar or not that’s the question: earliest spermatophyte growth habit into question.

The earliest true spermatophytes are found in the Upper Devonian where up to 20 species have been described. They show a wide morpho-anatomical disparity of their reproductive structures. By contrast, the vegetative systems of almost all of them are characterized by a very narrow diversity. In all documented cases, it consists in a zigzag-shaped pseudomonopodial main axis bearing helically arranged dichotomous branching systems. This general organisation appeared early in the lignophyte phylogenetical tree. The earliest diverging trimerophytes include several well described fossil genera such as Psilophyton and Pertica that are similarly characterized by a pseudomonopodial stem and helically arranged dichotomous branching systems. This bauplan, though experiencing considerable variations, was as well conserved within Middle Devonian lignophytes such as the aneurophytales and stenokoleales. By contrast, the data available for the Lower Carboniferous spermatophytes indicate that though the morpho-anatomical disparity of ovules was comparable to that of the Devonian, a much higher disparity is observed for the vegetative parts, with the apparition of various growth habits and new characters of the primary and secondary vascular system. Exogenous ecological reasons are most often advocated to explain this major change as the disappearance of Archaeopteris and new climatic conditions allowed the exploration and occupation of new niches. We however suspect a major breakthrough to have occurred among spermatophyte growth habit with the apparition of bipolar growth around the Devonian/Carboniferous boundary. We will here discuss this hypothesis based on new available developmental evidences.
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1 - Royal Belgian Institute Of Natural Sciences, Paleontology Dpt., Rue Vautier 29, Bruxelles, N/A, 1000, Belgium
2 - CNRS, UMR AMAP, C/o CIRAD, TA A51/PS2, Bvd De La Lironde, Montpellier, N/A, F-34398, France

Keywords:
Devonian
Spermatophytes
Bipolar
Carboniferous
Lignophytes.

Presentation Type: Oral Paper
Session: 17, Paleozoic and Mesozoic paleobotany
Location: Sundance 3/Omni Hotel
Date: Tuesday, June 27th, 2017
Time: 8:00 AM
Number: 17001
Abstract ID:463
Candidate for Awards:None