The catastrophe that extinguished the dinosaurs and other animal species, 65
million years ago also brought dramatic changes to the vegetation. In a
study presented in latest issue of the journal Science, the paleontologists
Vivi Vajda from the University of Lund, Sweden and Stephen McLoughlin from
the Queensland University of Technology, Australia have described what
happened to the vegetation month by month. They depict a world in darkness
where the fungi had taken over.

It´s known that an asteroid hit the Yucatan peninsula in Mexico at the end
of the Cretaceous Period. It left a 180 km wide crater and from the impact
site tsunamis developed and the Caribbean region was buried in ash and other
debris. The consequences of the asteroid impact were global. Vajda and her
colleagues have previously studied the broad-scale changes in the New
Zealand vegetation following the impact, but now they have dramatically
improved our view of the timing of events.

At the end of the Cretaceous the vegetation on New Zealand was dominated by
conifers and flowering plants. Many of these species disappeared suddenly at
the end of the Period and were instead replaced by fungal spores and fungal
threads preserved in a four millimeter thick layer of coal. The layer
coincides with fallout of iridium, an element rare in Earth’s crust but
which abounds in asteroids.

“We have managed to reconstruct the event month by month, with a very high
time resolution”, says Vivi Vajda. During a very short period – from between
a few months to a couple of years – the fungi and other saprophytes which
live on dead organisms must have been the dominating life form on Earth.
Atmospheric dust blocked the sunlight and led to the death of plants that
are dependent on photosynthesis.

The layer of fossil fungi is followed by a 60 cm thick interval containing
traces of the recovery flora, which re-established relatively quickly,
ground ferns at first, followed after decades to hundreds of years by more
diverse, woody vegetation.

A similar layer of fungi and algae is known from a previous catastrophe
which happened 251 million years ago at the Permian-Triassic boundary. This
was an even greater mass extinction: about 90% of the existing species
disappeared. Research will now focus on whether the similar biological
signatures at these mass extinctions reflect similar causal mechanisms.