Terrestrial Palaeoecology and Global Change

Chapter 8. Ecosystem evolution
331
not extend over the Carboniferous. Vesicaspora, however, survived up to the Permian
as a pollen type of callipterids, the supposed descendents of the callistophytes,
differing in the strobilate reproductive structures advanced in the direction of the
cycadophyte grade. This pollen type had been inherited by the Early Mesozoic peltasperms
and cycadophytes and was still retained in the Cretaceous proangiospermous
Preflosella (Krassilov & Bugdaeva, 1999). At least two species of xyelid
insects fed on it in the Cretaceous (Figs. 131 – 133). A longevity of Vesicasporatype
morphology might have been due to the loyalty of an ecologically conservative
pollinivorous insect lineage.
The counter-examples of a pollen morphology changing rapidly relative to sporophyte
structures can be found in the geological history of peltasperms and their derived
cycadophytes. Incidentally, a saltational transition from a protosaccate morphology
in Permotheca to an asaccate one in its derived Antevsia was not accompanied
by an adequate change in either these pollen-producing organs or the associated vegetative
morphology.
a
b
c
d
Fig. 131. Insects and proangiospems:
(a, b) pollen grains form
sporangia of a preflower, Preflosella
and (c, d) the same morphotype
from gut compression of Chaetoxyella,
a pollen-eating xyelid insect.
The Early Cretaceous of Baisa,
Transbaikalia.