The palaeontologists that taught classes in the university I attended (UPMC, Paris VI), always told us we should be cautious while studying any fossil assemblage because it is important to take “time-averaging”* into consideration. It is very important, they told us, and I thought that I had understood it (as did my classmates). This until last week when I found an article by Michal Kowalewski (1996) on the subject, and I found out that the theory of the matter is very complicated.
I am not going to discuss the details, but what I wanted to put forward is the concept and theoretical work that had to be done in order to establish the notion of time-averaging and how it works. It is indeed quite complicated and shows that it is necessary to work on what I’d call theoretical geology.
*time-averaging: the fossils contained in a single sedimentological layer haven’t died and fossilised synchronously. Also, the different organisms that are found fossilised, don’t have the same fossilisation potential. This can create various problems while studying the assemblages, and the studies that have been carried out concern all the aspects of this phenomenon.
Last Monday, we went, with a small group of students accompanied by a professor, in Pikermi for a day of excavation.
Pikermi is known for the savana-type fossil faunas: rinoceros, giraffes, saber-tooths, pigs, hipparions, and other animals that do not live in european lands anymore.
Here are some pictures:
Here I am, I dug up – with a friend – an upper jaw of a hipparion with 4 molars attached. The stream – small river – made it a little harder to dig…
In this picture there is a whole cranium that took two or three hours to take out of the sediment.
Although we worked only for a day, we found very nice specimens!
This is a nice video that explains how Evolution works. It is very summarizing of course, since it is eleven minutes long, but it is very well explained and the animation helps visualize the mechanisms that allow Evolution to take place.
There are several reasons why one might like ferns. They are moslty known for beeing very green, bearing nice leaves, and thus serve decorative purposes. Some other times they are use as a basis for medicine. Unfortunately, they are not plants that are as much admired by the world as they would deserve.
For the biologists’ eye, the first fascinating thing about ferns is that their stems grow below the surface, and their roots are not parallel to this structure like they are for trees (in general) but perpendicular to the totality of the stem as shown in figure 1 below.
Another notable difference is the structure of the cells that are involved in the sexual reproduction: they are not part of the main plant (like the case of flower-bearing plants, Angiosperms), but they form another, separate, plant -the gametophyte- that consists of cells with one representative of each pair of chromosomes (haploid state) (figure 2).
These are things that we learn during the first year of biological studies. For me though, the most amazing thing that characterizes ferns in general, is the fact that unlike pines and flower-bearing plants (Conifers and Angiosperms), their vascular system is in the center of the leaves, the rhizome and the roots. This characteristic feature isn’t found in many other type of plants today (considering that bryophytes do not have a completed vascular system), but could be found in numerous other plants that have disapeared mainly after the end of the Permian era. Also, the structure of the vascular system varies between different taxa. This is something that attests to the exploration of these plants in order to find different solutions for the transportation of water and nutrients from one part of the plant to another. And we are able to see the traces of this exploration that took place very early in the evolution of ferns, not by time travelling but by observing today’s plants. A wonderful group of organisms!
Why should we talk about Charls Lyell? Well he was one of the most important scientists that drew attention to his discipline as well as a great thinker of his time. Unfortunately, most of the time we are told that he influenced Charles Darwin, A. R. Wallace, T. H. Huxley and R. I. Murchison, but how and why?
One thing Lyell (1797 – 1875) is known for is that he wrote the book that really founded modern Geology: “Principles of Geology“. But how did he get to be interested in Geology in the first place?
He studied in Oxford, graduated around 1820 and started working as lawyer. During this time he travelled around England, thus being able to observe geological formations. He was so fascinated by geology that even during his honeymoon in Switzerland and Italy, he and his wife (daughter of a member of the Geological Society of London) did a geological tour of the area.
His best known work is the book “Principles of Geology” which is itself known not only because it is important, but also for inspiring Darwin in his work.
He had the vision and the ability to think a bit beyond a simple landscape, and, having in mind the works of James Hutton, was able to find an explanation for the deposition of geological layers. The central argument of the Principles is that of uniformitarism, and in his own words he made “an attempt to explain the former changes of the Earth’s surface by reference to causes now in operation”. And this is what makes his works and way of thinking absolutely modern.
Another important part of his work was in Stratigraphy – I believe this is his most important contribution to Geology. He travelled through Europe, studied and described many formations and he kept updating his Principles with the latest works until the 12th edition of 1875.
His interest and work on Evolution is also something we should remember: he endorsed both Darwin and Wallace in their works, as he was already a well respected scientist in the United Kingdom.
He died two years after his wife, in 1875, and was buried in Westminster Abbey.
Could anyone imagine that a world in which no skeletal parts would exist could replace the world as we know it?
Well it already has existed, in fact this was the world during the whole of the Precambrian.
Do we not take all the skeletal parts for granted? Most of the time, the animals that surround us, that we notice the most, are composed of one sort of skeleton or another. Cats, dogs, snails, chickens… all have a kind of skeleton. But how often to we think about why do we even have hard mineralized bones? How are bones and shells made? Why do not all animals have it?
During the last couple of decades research on the topic of bio-mineralizations, or how do organisms create hard parts, has taken off. The major axes of interest are the mechanics and the genetic signal and control of the elaboration of skeletal parts in animals, the functional history of these genes etc.
Before the Cambrian, many animals existed as attests the famous Ediacara fauna, and it is believed that many more must have existed but we have no fossils to trace. The main reason for this is that these creatures did not possess skeletal elements, therefore making the fossilisation process extremely unlikely. The other consequence is that it is very difficult to assess the biodiversity of the Precambrian. And one very interesting problem arises: the Cambrian explosion cannot be seen as a real explosion of life, a moment of rapid diversification of life.
Indeed, for a long period of time – and today still, the Cambrian era was considered as the time when biodiversity increased considerably in a very short time lapse, simultaneously with the first appearance of skeletal parts. For this, it is only logical to believe that the genes must have existed previously to the “explosion” itself. Questions rise as to the true nature of the beginning of the Cambrian; it seems to be more of an extinction crisis: the organisms that weren’t able to keep up with the new technological advancement of the skeletal parts, and the first known predation advancements that also occurred during the Cambrian.
Many things we do take for granted but do not stop to think about why and how they exist, and yet so many questions and mysteries lie in their study.
What do most people know about the field of Systematics? When I tell someone in Greece that Systematics is an important and very interesting field of biology, they mostly ask me “the systematic study of what?”. How does it help and what does it do? I am only going to focus on the basis of this science and on how it is linked with museum collections.
We are used to hearing biodiversity questions and how species preservation is crucial in the current ecological disasters. But what is biodiversity and how can it be counted? How is it possible to know if it is increasing or decreasing? How does one know if the changes observed in a small-scale are significant or if similar changes have occurred in the past?
Systematics is the science that defines species and inevitably counts them. The criteria are brought by some rules (Nomenclature), recommendations and the art of defining species (Taxonomy).
While talking to a friend of mine who is a collection manager in the Natural History Museum of Paris, I thought of this: say that it’s not possible to travel the world collecting specimens and seeing specimens in museums – rather realistic in the current economy context. It then becomes crucial to be able to use museum collections that others have put together so carefully. It is all the more important in order to be able to understand the history of each species that we study, its range of morphology, its name attribution etc.
Furthermore, in order to count today’s biodiversity, species need to be defined and this is the first reason why museum collections are important: previous studies or their absence help but also prevent one from making a mistake (naming a species that already exists).
Is it not a shame that most people are not aware of what collections are and what purpose they serve? It is not just for the glory of having the largest collections, they are valuable for many scientists. Sometimes it also happens that new species are discovered while searching old collections as it happened for Xenoceratops foremostensis.
So let’s pay more credit to all precious collections worldwide, unfortunately a lot of them are in poor shape because of the lack of financial support as far as their maintenance is concerned.