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1999). Once the archaeopteridaleans became
extinct and the zygopterids diminished in impor-
tance at the end of the Devonian, a new pattern of
ecological distribution at a high phylogenetic level
had emerged (Peppers & Pfefferkorn 1970). Rhizo-
morphic lycopsids dominated in wetlands, ferns
in disturbed environments, sphenopsids in aggra-
dational environments such as point bars and sper-
matophytes on well- to poorly-drained clastic
substrates (DiMichele & Bateman 1996). Even
with this phylogenetic turnover and dominance
shift, the general pattern of landscape partitioning
by plants at a high phylogenetic level persisted.
This lasted from its origin in the Late Devonian
until the drying of the global climate following the
Mid Pennsylvanian. By the Permian, spermato-
phytes dominated in almost all vegetated environ-
ments and have done so ever since (DiMichele &
Bateman 1996).
The Late Devonian evolution of the seed even-
tually led to the adaptive radiation of spermato-
phytes because plants were no longer constrained
to water for transfer of sperm during fertilization
(Stewart & Rothwell 1993). Sexual reproduction
in free-sporing plant lineages is dependent on avail-
able surficial water for its success. Numerous plant
lineages evolved heterospory, in which a spore
that produces female gametophytes is larger than a
spore producing male gametophytes (Bateman &
DiMichele 1994). Within the lignophytes, hetero-
spory was the evolutionary precursor for the seed
habit that involves the retention of megasporangia
containing the female megagametophytes upon the
sporophyte. Fertilization follows contact (pollina-
tion) between the wind-borne or animal-borne
microspore (pre-pollen or pollen) and the retained
megasporangium, after which an embryo develops
within the protected environment of a seed
(Rothwell & Scheckler 1988).
While this decoupling of sexual reproduction
from dependence on water permitted spermato-
phytes to radiate into dry environments, the selec-
tion pressures for retention of the megasporangium
on the sporophyte took place within the periodically
wet environments in which seed plant precursors
evolved from their free-sporing ancestors. Factors
other than success in dry environments must have
been driving the unification of the gametophyte
and sporophyte generations in the ancestors of sper-
matophytes. Therefore, during the time of their ear-
liest diversification in the Late Devonian, seed
plants were probably still minor components of
plant communities that were restricted to wetlands
and floodplains (DiMichele et al. 2006).
The earliest animals to emerge onto land were
arthropods: mainly arachnids, myriapods and some
hexapods (Shear & Selden 2001). Most early terres-
trial arthropods were predators and detritivores, but
Fig. 1. Location of the Red Hill site, Clinton County,
Pennsylvania, US.
growth and robust architectures for enhanced height
(Berry & Fairon-Demaret 2001). These included
large cladoxylopsid trees (Stein et al. 2007), aneur-
ophytalean shrubs, lepidosigillarioid lycopsids and,
by the late Middle Devonian, archaeopteridaleans
(Scheckler 2001). Plant-community structure
reached even greater levels of complexity and
biomass production during the Late Devonian
(Algeo & Scheckler 1998). By then, plant commu-
nities included gallery-forest trees, shrubs, herbac-
eous ground cover, vines and specialized wetland
plants (Scheckler 1986a, Greb et al. 2006). Archae-
opteridalean forests became widespread from boreal
to tropical latitudes (Beck 1964). All primary and
secondary plant tissues, other than the angiosperm
endosperm, had evolved by the end of the period
(Chaloner & Sheerin 1979).
The major phylogenetic plant groups that
appeared during the Late Devonian and Early Mis-
sissippian correspond broadly to distinct ecological
positions in the landscape (Scheckler 1986a). While
apparent niche partitioning took place among plants
earlier in the Devonian, it occurred within a more
limited number of groups and within a narrower
range of environments (Hotton et al. 2001). By the
Late Devonian, isoetalean lycopsids occupied
permanent wetlands, zygopterid ferns were wide-
spread in ephemeral wetlands, spermatophytes
occupied disturbed sites and archaeopteridalean
progymnosperms predominated along the better-
drained overbanks and levees (Scheckler 1986a, b;
Rothwell & Scheckler 1988; Scheckler
et
al.
