Somatofósseis e Icnofósseis EarthCache
Somatofósseis e Icnofósseis
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What is a fossil?
Fossils (from Classical Latin fossilis, literally "obtained by digging") are the preserved remains or traces of animals (also known as zoolites), plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous (fossil-containing) rock formations and sedimentary layers (strata) is known as the fossil record.
Paleontology
The study of fossils across geological time, how they were formed, and the evolutionary relationships between taxa (phylogeny) are some of the most important functions of the science of paleontology. Such a preserved specimen is called a "fossil" if it is older than some minimum age, most often the arbitrary date of 10,000 years. Hence, fossils range in age from the youngest at the start of the Holocene Epoch to the oldest from the Archaean Eon, up to 3.4 billion years old. The observation that certain fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century. The development of radiometric dating techniques in the early 20th century allowed geologists to determine the numerical or "absolute" age of the various strata and thereby the included fossils.
Like extant organisms, fossils vary in size from microscopic, even single bacterial cells one micrometer in diameter, to gigantic, such as dinosaurs and trees many meters long and weighing many tons. A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Fossils may also consist of the marks left behind by the organism while it was alive, such as the footprint or feces (coprolites) of a reptile. These types of fossil are called trace fossils (or ichnofossils), as opposed to body fossils. Finally, past life leaves some markers that cannot be seen but can be detected in the form of biochemical signals; these are known as chemofossils or biomarkers.
The fossil record
Fossilization processes are varied and proceed differently according to tissue type and external conditions. Organisms are only rarely preserved as fossils in the best of circumstances, and only a fraction of such fossils have been discovered. This is illustrated by the fact that the number of species known through the fossil record is less than 5% of the number of known living species, suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived.[18] Because of the specialized and rare circumstances required for a biological structure to fossilize, only a small percentage of life-forms can be expected to be represented in discoveries, and each discovery represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, which will never demonstrate an exact half-way point. Hence, the fossil record is heavily slanted toward organisms with hard parts, leaving most groups of soft-bodied organisms with little to no role.[
Types of fossils
There are several fossil types recognized and the detail varies according to author but in general they are:
Index fossil - (also known as guide fossils, indicator fossils or zone fossils) are fossils used to define and identify geologic periods (or faunal stages). They work on the premise that, although different sediments may look different depending on the conditions under which they were deposited, they may include the remains of the same species of fossil. The shorter the species' time range, the more precisely different sediments can be correlated, and so rapidly evolving species' fossils are particularly valuable. The best index fossils are common, easy-to-identify at species level and have a broad distribution—otherwise the likelihood of finding and recognizing one in the two sediments is poor Trace
Trace fossil - consist mainly of tracks and burrows, but also include coprolites (fossil feces) and marks left by feeding. Trace fossils are particularly significant because they represent a data source that is not limited to animals with easily fossilized hard parts, and they reflect animal behaviour.
Transitional fossil - is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group.
Geological setting of GZ
The rock outcrops in Almada are fossil-rich, especially those of Miocene age, although there are some fossils found in both Pliocene and Holocene age rocks. The majority of fossils in the Almada region are of marine beings, since most of these rocks were deposited on the seabed.
To claim this found you have to go the GZ at LOW TIDE and:
1 - What types of fossils that can be seen on the place?
2 - What types of fossilization process that observes on the place?
3 - What are the modes of fossilization observing on the place?
4 - What is the altitude that marks your GPS in place?
Send these via e-mail to validate your find.
O que são fósseis?
Os fósseis são restos ou vestígios da actividade de antigos seres vivos que ficaram soterrados e conservados nas rochas. Na maioria das vezes, apenas ficam fossilizadas as partes mais resistentes dos seres vivos, como as suas conchas ou os seus esqueletos, embora também seja frequente encontrar as marcas que esses restos mais duros deixam nas rochas, como moldes e impressões.
Os tipos de fósseis Existem dois tipos principais de fósseis:
Somatofósseis – incluem qualquer parte ou resto integrante do próprio organismo que tenha ficado conservada nas rochas, bem como as marcas deixadas de forma passiva por esses restos. Somatofósseis são fósseis de restos somáticos, isto é, de restos corpóreos ou integrantes do corpo de organismos do passado (do grego soma, somatos, corpo + fóssil). São Somatofósseis os fósseis (mineralizações, incarbonizações ou moldes) de dentes, de carapaças, de folhas, de conchas, de troncos, de ossos, etc.
Icnofósseis – incluem os vestígios deixados nas rochas pelos organismos em resultado de alguma actividade desenvolvida em vida, como por exemplo a locomoção, a reprodução ou a alimentação. São icnofósseis os fósseis (mineralizações, incarbonizações ou moldes) de pegadas, de pistas de deslocação, de marcas de dentadas, de excrementos, de ovos, de túneis e de galerias de habitação, etc.
Processos de fossilização
O processo de fossilização varia em duração e é composto por várias etapas. Em regra, após a morte do organismo dá-se a decomposição das suas partes moles, até que só as partes duras restam. O seu soterramento impede que também estas sejam destruídas, ficando protegidas no interior do sedimento. Por fim, a diagénese fóssil compreende o conjunto de alterações físicas e químicas que, ao actuarem no ambiente deposicional, transformam a composição e a estrutura dos restos dos organismos, propiciando a sua preservação como fósseis.
Deste processo podem resultar vários modos de fossilização, sendo que os mais frequentes em Almada correspondem à mineralização (substituição das partes duras do ser vivo, originalmente já mineralizadas, por outra substância mineral) e à moldagem (réplica natural das partes duras, que não se conservam, através de impressões deixadas no sedimento ainda mole).
Quando é a parte de dentro do organismo que fica moldada, como no caso do preenchimento de uma concha, o resultado é um molde interno, ao passo que quando é a parte de fora que fica reproduzida, como no envolvimento de uma concha, temos um molde externo.
Enquadramento geológico
As rochas de Almada são bastante ricas em fósseis, em especial as de idade miocénica, embora também existam alguns fósseis nas rochas pliocénicas e holocénicas. A maioria dos fósseis de Almada são de seres marinhos, uma vez que a maior parte das rochas do concelho se depositou no fundo do mar. Estes incluem todos os microfósseis e animais invertebrados, bem como a maior parte dos vertebrados (nomeadamente peixes).
Só nas poucas rochas formadas em ambientes continentais, como rios e estuários, é que se encontram fósseis de seres terrestres, nomeadamente as plantas e alguns vertebrados, como certos mamíferos. Icnofósseis são fósseis de vestígios de atividade vital, ou seja, de atividade biológica de organismos do passado (do grego icnos, traço, vestígio + fóssil).
Para contabilizar mais um “found” precisam de se deslocarem ao local durante a maré baixa e:
1 – Quais os tipos de fósseis que pode observar no local?
2 – Quais os tipos de processo de fossilização que observa no local?
3 – Quais os de modos de fossilização que observa no local?
4 – Qual a altitude que marca o seu GPS no local?
Depois é só enviar as respostas por mail para validar mais um “found”.
Font: http://en.wikipedia.org/wiki/History_of_paleontology http://webpages.fc.ul.pt/~cmsilva/Paleotemas/Somatofossil/Somatofo.htm T. (Aqui tens de ver o que ficou e o que saiu para inserir as referências certas)
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