Latouchella

About Natural History

Archive for the tag “Cambrian”

Shells and Bones?

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.

© SWEDISH MUSEUM OF NATURAL HISTORY. PHOTOS: STEFAN BENGTSON.

Early tube-dwelling Cambrian animals. © SWEDISH MUSEUM OF NATURAL HISTORY. PHOTOS: STEFAN BENGTSON.

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.

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What Latouchella is.

Latouchella represents the name of the blog, so it seems only natural that a post should be dedicated to this fascinating mollusc!

Why fascinating? After all it only is a rather small shell with very few systematic characters and not particularly spectacular. But in its simplicity it is a quite amazing creature: it is the oldest known genus of molluscs (its type species is the oldest mollusc known to date), and its systematic position is still fuzzy. Is it a Monoplacophoran or a Gastropod?

In palaeontology classes, we learned that it is most probably a Monoplacophoran of the family Helcionellidae, but the classification of Bouchet and Rocroi (2005) does not attribute them a certain phylogenetic position.

The genus appeared during the very beginning of the Cambrian, the Tommotian epoch (lower Cambrian of Russia and Kazakhstan). It presents similarities with the current Monoplacophoran Neopillina (c.f. Picture 1), without them being conclusive as to the precise phylogenetic position.

Picture 1: Neopilina sp.

The type species was first described by E.S. Cobbold (1921), in “The Cambrian horizons of Comley (Shropshire) and their Brachiopoda, Pteropoda, Gasteropoda and etc.” in the Quarterly Journal of the Geological Society of London (vol. 76, pp. : 325-386).

The type species, Latouchella costata (picture 2), was found western England, in lower Cambrian sediments, by E.S. Cobbold. The age, the structure, the mystery around this fossil make it a unique creature in the history of Evolution, especially since it represents such an important clade as the one of Mollusca.

Picture 2: Latouchella costata

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