A new decapod species in Morocco gives insight into ancient Atlantic connections

First report of Early Eocene Decapods in Morocco: description of a new genus and a new species of Carpiliidae (Decapoda: Brachyura) with remarks on its paleobiogeography

by: Àlex Ossó, Julien Bailleul, Cyril Gagnaison

Summarized by: Haley Coe (she/her), a senior geology major at the University of South Florida. She plans to attend graduate school with a focus on paleoclimatology, with future hopes of becoming a research professor. She loves dancing, biking, being outdoors, and hanging out with friends. 

What data were used? All living organisms can be classified by the taxonomic rank. This system groups together individuals with increasingly broader likeliness through classifications of species, genus, family, order, class, phylum and kingdom. This article centers around a newly discovered species belonging to the order Decapoda– which include crustaceans such as crabs, lobsters, and prawns. 

This new genus and species, given the name Maurocarpilius binodosus (Figure 1), was discovered in Eocene-aged rocks from Northern Morocco. This discovery is important because the new species resembles other Eocene-age decapods from Portugal, Spain, and Italy. This resemblance suggests a possible connection between ancient waterways at the time of their existence. The authors of this article hypothesize that this new fossil is a physical link between the ancient Tethys Sea (located between modern-day Africa, Asia, and Europe) and the Atlantic-driven Bay of Biscay (located north of modern-day Portugal and Spain). This waterway could have allowed for easy migration of the decapod species. 

Methods: The discovered decapod fossils were found in a tectonically compressed fold-and-thrust belt (a mountainous area that occurs near certain plate tectonic boundaries) near Ouarzazate, Morocco. Through two fieldtrips by geologists of the UniLaSalle Institute in Beauvais, France, scientists discovered various specimens of this new species within the 400m thick interval of Eocene-age rock.

Scientists then categorized the recovered specimen based on physical differences. The newly discovered species, Maurocarpilius binodosus, had an interestingly oval-like, downturned, smooth, wide shell, among other unique qualities. This distinctive physical shape prompted scientists to propose an entirely new genus, Maurocarpilius. Despite the new classifications, the new Moroccan species showed very interesting similarities with decapods from other locations, such as those found in Portugal, Spain, and Italy.

Figure 1: This figure shows different views of three individual specimen of Maurocarpilius binodosus from the early Eocene of Morocco, with a scale bar of 10 mm.

Results: It can be estimated that Maurocarpilius binodosus is related to other decapod species found in northern Italy and the Iberian Peninsula in southwestern Europe. Both decapod populations decreased simultaneously, prompting scientists to wonder how the populations were physically connected.  It was assumed that the ancient landmass containing modern day Corsica and Sardinia (i.e., the Corso-Sardinian Continental Block) separated the Atlantic Ocean from the Tethys Ocean during the Eocene, which would have blocked any migration or exchange between the two regions. However, overwhelming similarities between decapod populations have encouraged scientists to forgo past assumptions and support the idea of an ancient waterway that linked the Atlantic to the Tethys. This connection most likely stretched along what is now the Iberian Peninsula. Modern coastlines, locations of decapod populations, and a proposed waterway connection can be seen in Figure 2.

Figure 2: This figure is a possible reconstruction of a connection between the Atlantic Ocean and the Tethys Sea during the early Eocene. Paying attention to (7) the present-day coastlines, (8) the discovery of Maurocarpilius binodosus, and (9) and (10) discoveries of related decapods, it is easy to imagine the proposed connection through the Corso-Sardinian Continental Block.

Why is this study important? This study is important because the presence of this new species increases the number of recorded decapod species. Morocco is less studied than other regions around the world, such as North America, and any new information considerably adds to knowledge of the geologic record. This discovery also helps paleontologists better understand how organisms may have migrated across oceans in the geologic record. If decapods were able to expand their geographic range due to this ancient waterway connection, other organisms were also likely to utilize it for migration. 

The big picture: Any advancement in paleontology is an advancement for science as a whole. Identifying an error in previous geographic reconstructions can influence future paleontologists, biologists, and scientists in general. This article is just a piece in the puzzle that is the geologic record, beyond just decapods. Paleontology has a broad influence on the understanding of plate tectonics. Discovering geographically separate populations of the same species, or closely related species, can give insight on how the Earth’s tectonic plates were once connected.

Citation: Ossó, À., Julien Bailleul, and Cyril Gagnaison (2020). First report of Early Eocene Decapods in Morocco: Description of a new genus and a new species of Carpiliidae (DECAPODA: Brachyura) with remarks on its paleobiogeography. Geodiversitas, 42(4), 47. doi:10.5252/geodiversitas2020v42a4

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