Terrestrial Palaeoecology and Global Change

112 Valentin A. Krassilov. Terrestrial Palaeoecology
Gigantopterids and emplectopterids, both prominent in the Cathaysian-type assemblages
of eastern Asia and western North America, typically have composite leaves in
which the entire or simply pinnate leaf blades were formed by marginal fusion of ultimate
and penultimate segments, with the original segmentation betrayed by the conservative
venation pattern (Asama, 1976; Krassilov, 1995c, VIII.6). The hierarchical areolate
venation of such leaves owes its origin to meristematic fusion zones acting as a
plate meristem (Krassilov, 1995c). This leaf morphology is evidence of a prolonged meristematic
activity characteristic of megaphyllous life forms in equable climates. An advanced
Gigantopteris morphotype, some variants of which show clearly defined driptips
(Yao, 1986), occurred in southern Cathaysia. A survival of Carboniferous forms,
such as a tree fern Psaronius and arboreal lepidophyte Lepidodendron, also indicates
a tropical climate.
Noto-Permian vegetation. Classical Gondwana flora came from the Narmada–
Son–Mahanadi graben system that transects peninsular India. Boulder beds occur at the
base of the basinal sedimentary fill followed by coal measures that contain the bulk of
the flora. The Himalayan occurrences are scattered from Kashmir to Assam, with a
few outliers in Tibet, Yunnan and the “mixed” floras of Indonesia and New Guinea. A
number of well-defined species are shared by Indian and Australian floras, but the other
parts of “Gondwanaland” are floristically less similar (Archangelsky, 1990, 1996; Maheshwari,
1992).
A primitive glossopterid leaf morphotype Gangamopteris appeared already in the
pre-tillite deposits. Early Gangamopteris plants are commonly envisaged as growing in
sparse vegetation patches of a glacial landscape. However, fossil plant assemblages
found immediately below and above the Dwykka Tillite in South Africa, the Bacchus
Marsh Tillite in Australia and the Talchir boulder beds in Peninsular India suggest a less
dismal picture, with a number of Carboniferous survivors (Chandra et al., 1992; Pant,
1996). Leaf morphology gives no support to either a “Gangamopteris tundra” or a
“Gangamopteris taiga”. Morphologically, Gangamopteris is linked, via Palaeovittaria
and Noegerrathiopsis, to the Zamiopteris–Cordaites group of the Arcto-Permian temperate
zone.
The emblematic Glossopteris morphotype came forth and diversified in the period of
a widespread coal accumulation. Some variants of its highly polymorphiic leaves show
distinct abscission scars, others had drip-tips characteristic of rainforest foliage. Such a
morphological diversity obviously suggests a wide range of habitats (Pant, 1996), which
is confirmed by taphonomic evidence (Retallack, 1980). Glossopterids are sometimes
preserved as leaf mats containing spur-shoots shed with clusters of intact leaves, as is
typical of deciduous riparian trees. A constant association of Glossopteris with Vertebraria,
an aerenchymatous underground organ, suggests a peatland habitat. The coriaceous
lingulate leaves, as in the modern mangroves, and the uniquely preserved seedlings
(Pant & Nautiyal, 1987) are also consistent with a helophyte life form in a majority
of Indo-Australian glossopterids. The greatest morphological diversity of Glossopteris