Bryozoa
Despite the fact that there are
about 5000 living species, with several times that number of
fossil species, the Bryozoa (from the Greek Bryon, meaning
moss and Zoon, meaning animal) remain largely unknown to most
people. The Bryozoans are aquatic organisms that generally
build stony skeletons made up o calcium carbonate (CaCO3) and
live for the most part in colonies of interconnected
individuals that may number in the few millions. They are
frequently referred to as “moss animals” and “sea mats” as
they appear as bushy, mossy-looking or mat-like, sometimes
crusty, colonies of filter-feeding individuals animals. Some
bryozoans encrust rocky surfaces, shells, or algae. Others,
like the fossil bryozoans, form lacy or fan-like colonies that
in some regions may form an abundant component of limestones.
Bryozoan colonies range in size from millimeters to meters,
but the individuals that make up the colonies are rarely
larger than a millimeter.
They are well preserved in the fossil record because of their
zooecia and we know they have been around since the Ordovician
period (488-443 Ma). There were about 15000 species during the
Cretaceous (145-65.5 Ma) period, though they were not all living at
the same time. Today there are in the region of 5000 known species
most of which live in marine environments, though there are about
50 species which inhabit freshwater.
Miocene
The Miocene epoch lasted
from 23 to 5.3 million years, making it the longest epoch of the
Cenozoic era. This was a time of huge transition, the end of the
old prehistoric world and the birth of the more recent world.
It was also the high point of the age of mammals. It was a time of
warmer global climates than those in the preceding Oligocene
(33.9-23 Ma), or the following Pliocene (5.3-1.8 Ma). During this
time modern patterns of atmospheric and ocean circulation formed.
The isolation of Antarctica from Australia and South America meant
the establishment of the circum-polar ocean circulation, which
significantly reduced the mixing or warmer tropical water and cold
polar water, and further led to the buildup of the Antarctic ice
cap. Many new mountain ranges were formed during the Miocene. When
the African plate pushed against Europe and Asia, the Alps formed.
The Rocky Mountains and the Appalachians formed, along with the
Himalayas, which where just beginning to form as the subcontinent
of India collided into Asia. Australia and South America remained
separated from the rest of the world.
The
Cache
This cache is located
in one of the eleven geomonuments in the city of Lisbon, and
is the only one that has undergone museulogical treatment.
Twenty million years ago this area was a shallow see full of
reefs and the cache is an outcrop that has remained from that
time. The outcrop of limestone is partly made of the
compressed skeletons of millions of bryozoans.
Your tasks, in order to
claim this earthcache are to:
1- measure the length of the outcrop and,
2- tell me how many species of bryozoans are
found in this outcrop.
E-mail the results of thse two questions to me and I will reply
with permission or not to log your “found”.
A jazida corresponde a uma
bancada lenticular de calcário argiloso muito fossilífero,
rica em briozoários, sobreposta a uma camada argilosa
explorada, no passado, como barreiro da antiga Cerâmica
Lisbonense. Descrita inicialmente por Berkeley-Cotter (1956,
publicação póstuma) como "Molasso e argilas de Venus
ribeiroi dos Prazeres", e atribuída aos níveis mais
baixos do Burdigaliano, foi, mais tarde, atribuída ao
Aquitaniano superior, isto é, a um nível estratigráfico
ligeiramente mais antigo (24 a 22 milhões de anos).
As concreções calcárias
que nela se destacam são restos de briozoários dispostos em capas
muito finas e concêntricas que, em vida, representavam colónias que
se iam desenvolvendo, sobrepondo-se umas às outras. Tais
concreções, uma vez sujeitas à agitação marinha, movimentavam-se
por rolamento no fundo, num vaivém de remobilização e redeposição,
à semelhança dos calhaus e areias litorais, e daí o carácter de
estratificação entrecruzada patente no afloramento.
Esta earthcache
encontra-se no único geomonumento com tratamento museológico na
cidade de Lisboa. Existem 11 destes geomonumentos na lista oficial
do estudo do Museu de História Natural aceite pela CML), embora um
deles esteja destruído (Travessa das Águas Livres - Terraço
flurio-marinho do Cenozóico Inferior. 30 milhões de anos).
A vossa missão é medirem
o comprimento deste afloramento e descobrirem quantas especíes aqui
se encontram (indicado nos paineis informativos). Respondam às
seguintes perguntas:
1- Qual é o comprimento do afloramento (em metros)?
2- Quantas espécies de briozoários se encontram na jazida?
Enviem-me as vossas respostas por mail que depois valido, ou não, o
vosso found.