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On March 23rd, Allison and Pierre joined ardent amateur paleontologists Sylvie and Éric Monceret in Cabrières for the recording of an episode of the weekly science radio program Science in Action produced by the BBC World Service.

The episode, which was broadcasted on March 28th, can be listened here. The part about the Cabrières Biota starts around 16:21.

Today, the ANOM Lab, part of an international team led by ANOM Lab’s Farid Saleh and Bertrand Lefebvre from Lyon University, introduces a newly uncovered fossil site in the French department of Hérault, thanks to the perseverance of two dedicated amateur palaeontologists, Sylvie and Éric Monceret. The 470-million-year-old fossils, over 400 in number, unearthed by the couple at the so-called Cabrières site, near Pézenas, are presented in an article published in Nature Ecology & Evolution. 

This site is particularly important because it opens a unique snapshot on ecosystems that were located the closest to the Ordovician south pole hitherto discovered. Among the most bountiful and diverse fossil beds from that geologic period, the Cabrières site stands out for its remarkable degree of preservation, which enabled the rare discovery of soft-bodied organisms such as worms, a wide variety of algae and sponges, contributing to a better understanding of the pivotal role these highly decay-prone organisms played in ancient ecosystems.

Our findings challenge previous thinking that posited a decrease in biodiversity or even an extinction between the Cambrian and Ordovician Periods, approximately 485 million years ago. The high level of biodiversity observed does, however, confirm the hypothesis of species’ migration toward the Ordovician southern hemisphere, seeking refuge from the excessive temperatures of the tropical zones. 

We also conducted a first investigation of the preservation of the fossils using X-ray fluorescence major-to-trace elemental mapping and X-ray absorption spectroscopy at the PUMA beamline of SOLEIL synchrotron on a couple specimens. We established that the fossils are essentially made up of a layer of Fe(III) oxide/hydroxide crystals, varying in thickness and containing traces of metals. The distribution of other elements, notably manganese and arsenic, strongly suggests that iron oxide (hydr)oxides do not represent the original mode of preservation of these fossils, but rather result from more recent alteration processes, as demonstrated for other contemporary deposits. This highlights the biases that have affected the completeness of the newly discovered ecosystem, and enables finer comparisons with other fossil sites.

This initial study of the site inaugurates a research program that is to span several years and include large-scale excavations followed by in-depth analyses of fossils, using innovative imaging techniques. The aim is to detail the fossilized organisms’ internal and external anatomies, taxonomic relationships, and modes of life.

Reference: Saleh F., Lustri L., Gueriau P., Potin G.J.-M., Pérez-Peris F., Laibl L., Jamart V., Vite A., Antcliffe J.B., Daley A.C., Nohejlová M., Dupichaud C., Schöder S., Bérard E., Lynch S., Drage H.B., Vaucher R., Vidal M., Monceret E., Monceret S. & Lefebvre B. 2024. The Cabrières Biota (France) provides insights into Ordovician polar ecosystems. Nature Ecology and Evolution 8, 651–662. Find the article (Open Access) here

ANOM Lab members published 4 articles on the Frontiers research topic “Insights on the Rise of Animal Life from Cambro-Ordovician Lagerstätten”. 3 articles report on fossil arthropods from the Fezouata Shale in Morocco. Potin et al. describe new suspension-feeding radiodonts from the Fezouata Shale (Fig. A), and discuss their ecological and evolutionary implications. Drage et al. document the moulting behavior of the Moroccan marrellid (Fig. B) and compare it to that of other marrellomorphs and modern arthropods. Laibl et al. also focus on marrellids, but this time characterizes the morphological changes occurring during their development based a nice set of juvenile and adult specimens including tiny immature stages (Fig. C). The fourth article, by Lustri et al., explores the environmental evolution of xiphosurids (Fig. D), and compare it to other euchelicerates groups.

Additional digital ressources:

A 3D model, based on µCT data, of one of the frontal appendage of the new taxon described by Potin et al. can be seen and manipulated online on Sketchfab.

A video presenting the three-dimensional rendering of the smallest immature stage of the Fezouata marrellid can be viewed here.

Last July, Jonathan Pople successfully submitted and defended his Master’s thesis in Earth Sciences at the University of Lausanne. He carried out his thesis work over one year at the ANOM Lab, studying the ecology of giant radiodonts and other arthropods from the Early Ordovician Fezouata Shale of Morocco, and notably demonstrated that living radiodonts often carried hitchhiking brachiopods on their oversized carapaces, not unlike barnacles found on whales today. Jonathan’s work was recently awarded with 3 prizes: the 2023 Best Master Thesis Award from the Swiss Geological Society for the best MSc thesis in Earth Sciences completed at a Swiss academic institution; the Prize Auguste Lombard 2023 from the Ecole Lémanique des Sciences de la Terre (shared between the Universities of Lausanne and Geneva) rewarding both the excellence of his Master’s thesis in Geology and the quality of his university studies, and the 2023 Master’s thesis Faculty Prize from the Faculty of Geosciences and Environment at the University of Lausanne.

Today’s arthropods often show very complex development with their juveniles and larvae living and feeding in a different way than the adults. A classical example is a flying butterfly with an edacious caterpillar or a sessile barnacle with a floating larva. But was such a complex kind of development present in the early members of Arthropoda? In a study led by former ANOM Lab member Lukas Laibl, now at the Institute of Geology of the Czech Academy of Sciences, we tackled the question by studying a few millimeters-long larvae of 480 million years old arthropod species from Morocco belonging to an extinct group called marrellids, which thrived in early Paleozoic seas. The results are presented in a paper published today in Frontiers in Ecology and Evolution.

To better understand the anatomy of this Paleozoic animal, we imaged the tiniest larvae using synchrotron computed tomography (CT) scanning at the Paul Scherrer Institut in Switzerland. Thanks to the high-resolution data obtained and meticulous segmentation, we have been able to virtually extract and render in three dimensions a tiny, about 2 mm long, specimen on a micrometer scale, allowing us to recognize morphological details, from tiny claws to delicate hairs on the animal legs.

Detailed examination of the appendages of this early arthropod larvae tells a lot about its mode of life. On the head, it had sensory antennae, a pair of robust legs used to orientate its body or to anchor itself on the sediment, and a pair of walking limbs. Two additional pairs of legs on the trunk were also used for walking, while the rear limbs of the trunk bore spines and delicate hairs and were used for capturing small organic particles that the animal was eating. All trunk limbs also had a gill branch used for respiration.

Interestingly the adult stages of various marrellids seem to have a very similar mode of life as these tiny babies, contrary to what is seen in many recent arthropods. We also show that the tiny larvae even lived in the same locations and environment as the adults of the same species, on the seafloor at the margin of an ancient continent called Gondwana, just below the storm wave base.

Marrellids are considered to be very early arthropods, showing many ancestral features. We therefore think that such development, with no major change in feeding and ecology between larvae and adults, was ancestral for arthropods as a whole. Other ancient arthropod groups present a similar development, thus supporting our conclusions. This indicates that complex life cycles must have evolved independently later in several arthropod groups.

Reference: Laibl L., Gueriau P., Saleh F, Pérez-Peris F., Lustri L., Drage H.B., Bath Enright O.G., Potin G. & Daley A.C. 2023. Early developmental stages of a Lower Ordovician marrellid from Morocco suggest simple ontogenetic niche differentiation in early euarthropods. Frontiers in Ecology and Evolution 11, 1232612. Find the article (Open Access) here