Geoscience Reference
In-Depth Information
First record of Rellimia Leclercq & Bonamo (Aneurophytales)
from Gondwana, with comments on the earliest lignophytes
P. GERRIENNE
1
*, B. MEYER-BERTHAUD
2
, H. LARDEUX
3
&S.R
´
GNAULT
4
1
Pal´obotanique, Universit´ de Li`ge, B18, Sart Tilman, B-4000 LIEGE, Belgium
2
Universit´ Montpellier 2, UMR AMAP, Montpellier, F-34000 France
3
Laboratoire de G´ologie, IRFA-UCO, B.P. 808, F-49008 Angers cedex 1, France
4
Museum d'Histoire Naturelle, Rue Voltaire, 12, F-44000 Nantes, France
*Corresponding author (e-mail: P.Gerrienne@ulg.ac.be)
Abstract: The lignophytes (Embryophytes that possess a bifacial cambium) evolved during the
Devonian period and include seed plants. Their advent was a major event in the history of life
and had a profound impact on terrestrial environments. Recent reinvestigations of a Devonian
locality, Dechra A¨t Abdallah in Central Morocco, led to the discovery of a rich assemblage of
fossil plants and Tentaculita. This paper focuses on a single specimen of the lignophyte Rellimia
Leclercq & Bonamo. Rellimia (Aneurophytales) is a monospecific genus reported from a large
number of Middle Devonian localities from western Europe (Belgium, Czech Republic, Germany
and Scotland) and America. Its fertile organs are highly distinctive and borne helically on branches.
They consist of a basal stalk that dichotomizes once near the base, the resulting branches dividing
pinnately and bearing elongated sporangia terminally on ultimate divisions. According to the late
Emsian age indicated by our sample of Tentaculita, this Moroccan specimen is to date the earliest
representative of both the genus and the lignophytes. If confirmed, this occurrence suggests a
possible origin of the Aneurophytalean lignophytes in Gondwana and their rapid and widespread
colonization in the Middle Devonian towards Laurussia.
The lignophytes are the plants that possess a bifacial
vascular cambium, producing secondary phloem
(inner bark) towards the outside and secondary
xylem (wood) towards the inside. Thanks to this
innovation, lignophytes have the ability to achieve
the largest and most complex woody bodies in the
plant kingdom. The advent of the lignophytes is
therefore a major event in the history of life. It
occurred in the Devonian period and had a profound
impact on terrestrial environments. The evolution
of the tree habit in the lignophytes allowed those
plants to reach greater heights with an increased
mechanical stability and greater efficiency of pro-
pagule dispersion and light interception. It was
also accompanied by the acquisition of long-lived
roots (Meyer-Berthaud & Decombeix 2007; Meyer-
Berthaud et al. 2010) which had major implications
on the elaboration of early soils and complex
microbial communities (Algeo et al. 2001).
The earliest remains of lignophytes are included
in the Aneurophytales (Middle to Upper Devonian)
and possibly in the Stenokoleales (Middle Devonian
to Lower Carboniferous; Beck & Stein 1993).
Members of both orders were medium-sized plants
or shrubs. The earliest arborescent representatives
of the lignophytes belong to the Archaeopteridales,
an order reported from the late Middle Devonian to
the earliest Carboniferous. Archaeaopteris was a
large tree with webbed leaves; it was heterosporous,
but did not produce seeds. Archaeaopteris experien-
ced an extraordinary success during the Late Devo-
nian, dominating the forest ecosystems and having a
cosmopolitan distribution (Edwards et al. 2000).
According to most of the current palaeogeo-
graphical reconstructions (Scotese 2003; Cocks &
Torsvik 2006), north Africa had a very central pos-
ition within the emerged land masses during most of
the Palaeozoic. Renewed interest in Devonian
palaeobotany in north Africa has resulted in the
discovery of new localities with interesting fossil
contents in Morocco from Lower Devonian (Fairon-
Demaret & R´gnault 1986; Gerrienne et al. 1999;
Meyer-Berthaud & Gerrienne 2001) and from Upper
Devonian (Meyer-Berthaud et al. 2000, 2004; Soria
et al. 2001; Soria & Meyer-Berthaud 2005) locali-
ties. These publications highlight the occurrence,
in these localities, of plant assemblages possessing
a significant number of genera in common with
those of eastern Laurussia.
The Devonian plant assemblage consisting of
compressions from the marine sequence of lime-
stone beds at Dechra A¨t Abdallah (central
Morocco; Fig. 1) was first reported by Termier &
Termier (1950) who emphasized its abundance
and diversity. They assigned it to the Eifelian on
the basis of associated Tentaculita and Phacopidae.
