An article recently published in the “Journal of the Geological Society” describes a research on the fossils of the Lower Fezouata formation in the south-east of Morocco, a deposit discovered only five years ago. These fossils shed light on the evolution of many families of animals in the Ordovician period, between 485 and 444 million years ago. In particular, it shows that some of the oldest animals survived millions of years longer than it was inferred from previously found fossils.

The Lower and Upper Fezouata formations deposits are extraordinary because they are of a type similar to the famous Burgess Shale, a unique mine of fossils of the Cambrian in which in many cases the animals’ soft tissue got also fossilized. In the case of Fezouata, the fossils date back to the following geological period and this is helping to reconstruct the times of evolution of many species of that era.

Among the fossils found in the Lower Fezouata formation examined by the team led by Professor Derek Briggs of Yale University, many belong to species that were considered extinct, others to species that we thought had evolved later. As is normal in the field of paleontology, new fossils provide more complete information changing what scientists think about certain life forms.

Some species have been classified in taxonomic terms into new genera, for example the Aegirocassis benmoulai, originally termed Aegirocassis benmoulae (image of the fossil and scheme ©Spiridon Ion Cepleanu, reconstruction image ©Levi Bernardo). This animal could be about two meters long and was one of the largest existing animals in the Ordovician. It was part of the dinocaridi, marine organisms widespread in the Paleozoic era.

The fossils from the Ordovician period are scarce, therefore those found in the Fezouata deposits are helping paleontologists to better understand the evolutionary developments of very ancient ages that were crucial for the future ones. The Cambrian explosion in the previous period was already well known, the discovery of these new fossil suggests that the diversification in the life forms that developed in the Ordovician is a continuation of that event.

The published article is just the beginning of a series that will be published in the same journal. The articles will be focused to the various sites of exceptional fossil preservation from various periods around the world. They will describe the findings in deposits crucial to our knowledge of the history of evolution.