Geoscience Reference
In-Depth Information
Fig. 4. Schematic phylogenetic position of the Aneurophytales and the Lignophytes in the Eutracheophytes.
protostele, numerous protoxylem strands including
a central one and others arranged along the mid-
planes of the arms of the protostele, pairs of traces
to lateral appendages and a helical phyllotaxis of
those pairs of appendages. Secondary xylem is
sometimes present in small amounts (Matten 1992;
Beck & Stein 1993), but has not yet been described
in detail. In the absence of morphological data,
especially on reproductive parts, the Stenokoleales
are currently left as incertae sedis. They are not
represented in Figure 4.
The Aneurophytales Kr¨usel & Weyland
includes seven genera (Table 2) known from adpres-
sions and/or permineralizations. Before this work,
their occurrences ranged from the late Eifelian to
the Frasnian (Table 1). Members of the order are
characterized by three-dimensional branching
systems with lateral dichotomous appendages in
helical or decussate arrangement. The primary vas-
cular system consists of a deeply lobed mesarch pro-
tostele, with a central protoxylem strand and others
occurring along the mid-planes of the lobes and near
their tip. The sporangia are borne on ultimate
divisions of the much-branched lateral fertile appen-
dages.
phylogenetic position is currently under debate
but, on the basis of their homosporous status, they
are often considered as sister to a group including
the
heterosporous
Archaeopteridales
and
the
spermatophytes (Fig. 4).
Rellimia is one of the oldest known Aneurophy-
tales. This monospecific genus has been reported
from a number of Middle Devonian localities in
Western Europe (Scotland, Belgium, Germany and
Czech Republic) and north America (Table 2).
Rellimia sp. was briefly reported in Venezuela by
Berry et al. (2000), but the specimens are probably
those recently described as Tetraxylopteris repo-
sana (Hammond & Berry 2005). The Rellimia
specimen described here consequently represents
the first occurrence of the genus in Gondwana. In
our current state of knowledge, it documents the
earliest occurrence of both the genus Rellimia and
the order Aneurophytales, and also represents the
earliest lignophyte occurrence.
Palaeogeographical implications
The spore taxon Rhabdosporites langii (Eisenack)
Richardson has been found in the sporangia of
Aneurophytales
are
homosporous.
Their
