Botany Meets Geology at the Tsukuba Botanical Garden- where the PLANT FOSSILS EXHIBITION has been extended through December 23rd
By Avi Landau
When we think of fossils on display at museums it is usually a T. rex, a mammoth- or at least an ammonite or trilobite which first comes to mind. Certainly not leaves or seeds.
This might all change for you, though,(as it has for me) after you`ve seen the Plant Fossil Exhibition (subtitled: Timeslip 500,000,000 Years of Plant Evolution), another fine show put together by the staff of the Tsukuba Botanical Garden.
The exhibition will show you how much there is to learn from plant fossils- about the history of life on Earth, and you will also be amazed by how BEAUTIFUL some of the specimens are.
You might also be surprised to learn how common plant fossils are. One of the best sites for collecting them is in neighboring Tochigi Prefecture, at the famous hot spring resort Shiobara. At the entrance to the current exhibition you are greeted by a poster sized photo of a fossil-rich cliff there.
As oppossed to many animal fossils which have been found complete, or nearly so, this exhibition points out that almost all plant fossils are partial- extremely partial. For example- only leaves, or just the trunk, and even more rarely: single seeds, pods or cones.
Most of the plant fossils shown are of two types- compression fossils, in which living matter was covered with and eventually, with the addition of heat and other factors, leave an IMPRINT in stone.
The other type consists of the permineralized (or petrified) fossils in which the insides of organisms are filled with minerals and there is great preservation even at the cellular level.
Using the fossil displays. the curators of the exhibition try to show how diferent plant and tree life in Japan was in the distant past and also more importantly how life on Earth has evolved.
Probably what surprised me most was learning that flowers are new-comers to this world of ours- they evolved much later than I had imagined- long after dinosaurs had become extinct and the rise of mammals.
There is a compression fossil on display of one of the earliest known land plants (vascular plants)- psilophyton princeps, which thrived from 420 to 360 million years ago. The imprint of this ancient plant appears as like rust-colored arteries in the gray stone slab.
These plants had no leaves or roots.
The next major step in plant evolution, the rise of trees and forests 380 million years ago is represented by a piece of rock with the imprint of tree bark on it. The species is now called Lepidodendron aculeatum. These long extinct ancient forests have proven very useful to man in more recent centuries- as sources of coal – which is what they have turned into..
Until about 390 million years ago, plants reproduced asexually( for example by releasing spores) Spore producing plants created spores of varying size、with larger one being called megaspores.. These would evolve into seed plants.. The first seeds plants produced their seeds along their branches. Two such plants (gymnosperms) are being displayed- a compression fossil of moresnetia sp. – elegant flowing lines, brown on gray, and Williamsonia sp.
According to exhibition catalogue, the oldest known fossil of a flower, dating from 130-140 million years ago was discovered in Israel. In Japan, as well, fossils of flowers, pollen and seeds have been found from later dates during the same Cretaceous Period. It was first during this period that our Earth began to bloom.
The part of the exhibition I hope they keep on permanent display is the small collection of fossils、conifer cones, and a piece of an elephant fossil – all discovered in the nearby (a few hundred meters behind the exhibition) Hanamuro River.
And best of all if you visit the fossil exhibition on one of these these bitter cold days- drop in on the tropical plant house- on the way to the fossils, on your way back, or like me- BOTH going and coming.
Step into the steamy, intoxicating air- memories of past visits to the tropics will come flooding through your head!