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"Abominable Mystery": Rise of Angiosperms in the Cretaceous
Not directly dinosaur-related... but I'd hazard a guess that the rise
of angiosperms had a profound impact on the evolution of one
particular branch of the Theropoda.
C. Coiffard, B. Gomez, V. Daviero-Gomez, D. L. Dilcher. (2012) Rise to
dominance of angiosperm pioneers in European Cretaceous environments.
PNAS DOI: 10.1073/pnas.1218633110
Abstract: "The majority of environments are dominated by flowering
plants today, but it is uncertain how this dominance originated. This
increase in angiosperm diversity happened during the Cretaceous period
(ca. 145–65 Ma) and led to replacement and often extinction of
gymnosperms and ferns. We propose a scenario for the rise to dominance
of the angiosperms from the Barremian (ca. 130 Ma) to the Campanian
(ca. 84 Ma) based on the European megafossil plant record. These
megafossil data demonstrate that angiosperms migrated into new
environments in three phases: (i) Barremian (ca. 130–125 Ma)
freshwater lake-related wetlands; (ii) Aptian–Albian (ca. 125–100 Ma)
understory floodplains (excluding levees and back swamps); and (iii)
Cenomanian–Campanian (ca. 100–84 Ma) natural levees, back swamps, and
coastal swamps. This scenario allows for the measured evolution of
angiosperms in time and space synthesizing changes in the physical
environment with concomitant changes in the biological environment.
This view of angiosperm radiation in three phases reconciles previous
scenarios based on the North American record. The Cretaceous plant
record that can be observed in Europe is exceptional in many ways. (i)
Angiosperms are well preserved from the Barremian to the Maastrichtian
(ca. 65 Ma). (ii) Deposits are well constrained and dated
stratigraphically. (iii) They encompass a full range of environments.
(iv) European paleobotany provides many detailed studies of Cretaceous
floras for analysis. These factors make a robust dataset for the study
of angiosperm evolution from the Barremian to the Campanian that can
be traced through various ecosystems and related to other plant groups
occupying the same niches."
Article reported here:
The report concludes: "... co-evolution with insects gave angiosperms
an evolutionary advantage. Insects played a vital role in
cross-pollinating plants and accelerating the spread of genetic
material. Plants evolved the means to "advertise themselves" with
fragrances and bright colors while producing pollen and nectar that
provided food for insects."
The diversification of Avialae might also correlate with the
diversification of angiosperms. Not only because of the radiation of
certain angiosperm-pollinating insect groups that basal birds
(avialans) could have fed on. As with today's flowering plants,
Cretaceous angiosperms tended to be branched, giving birds something
to perch on (conifers also diversified in the mid-Cretaceous). Most
"gymnosperms" (cycads etc) tended to be sparsely branched or not
branched at all (monocaulous). So although cycads & co could be
climbed (such as to gain access to seeds or insects), these sturdy
plants didn't really offer a convenient refuge.
I think it's telling that many studies indicate that some small
maniraptorans (including _Microraptor_ and _Archaeopteryx_) have claw
curvatures consistent with climbing (e.g., most recently Birn-Jeffery
et al., doi:10.1371/journal.pone.0050555). However, these same
maniraptoran taxa show few (if any) arboreal adaptations. So perhaps
the earliest stages of flight evolution were associated with
tree-climbers (cycad-climbers?) that did not stay in trees. Only
later, with the spread of tall conifers and angiosperms, did birds
habitually perch in trees.