A publication in Scientific Reports

A new method to understand the evolution of marine predators from the age of the dinosaurs



By combining 3D laser scans of fossils with statistical methods, an international team of researchers led by Valentin Fischer (Geology Research Unit - Faculty of Sciences) has succeeded in recreating the "evolutionary landscape" of plesiosaurs. This “landscape” is a kind of relief detailing the directions of plesiosaur evolution during the geological past. This study is the first part of the SEASCAPE project funded by the Belgian national fund for scientific research (FNRS), and is published today in Scientific Reports (1).

M

ore than 200 million years ago, the seas and oceans had many peculiarities. Most notably, they were filled with aquatic reptiles, which played the role of large predators. Some of these predatory reptiles were much larger than the killer whales and sharks we know from our current ecosystems. This is particularly the case for certain plesiosaurs, a family of marine reptiles from the Mesozoic era, whose skulls could reach a length of two metres and whose jaws were filled with teeth measuring more than ten centimetres high! For nearly 130 million years, several distinct groups of plesiosaurs succeeded one another and occupied the top of the underwater food chains.

“We wanted to understand how the evolution of the plesiosaurs worked…" explains Prof. Valentin Fischer, director of the Evolution & Diversity Dynamics Lab at Université de Liège. “More specifically, we were interested in the fact that distinct species separated in time and space will morphologically resemble each other to excel in a specific ecological role - in this case, at the top of marine food chains". To do this, the researchers first assembled detailed morphological data on the skull and body of the plesiosaurs, some of which were taken from high-precision 3D scans. "We have digitised key species, with a variety of morphologies, from Europe, Australia, and the United States." says Dr. Jamie MacLaren, FNRS postdoc researcher at EDDy Lab.

The team, composed of researchers from ULiège, University of Oxford (England), the Smithsonian Institution (Washington, USA), and the University of Alaska (Fairbanks, USA) then developed a new method to test and visualise the evolutionary landscape of the plesiosaurs based on these morphological data. The results, which have just been published in the journal Scientific Reports (1), reveal that two distinct morphologies - giant predators with a wide and robust snout, and fast hunters with an elongated snout - have evolved several times in a convergent manner throughout the history of the plesiosaurs. This double-peaked landscape (one for each morphology; see figure below) persisted for nearly 80 million years, before collapsing at the beginning of the Upper Cretaceous, coinciding with major climatic changes. “In addition to revealing the modalities of the morphological evolution of plesiosaurs, our new method is applicable to many other groups." explains Rebecca Bennion, FNRS-FRIA doctoral student at EDDy Lab. “We are currently in the process of applying it to mosasaurs (another group of large fossil marine reptiles) and dolphins in order to understand the evolutionary possibilities of marine predators, from the beginning of the dinosaur era to the present day.”

Plesiosaures V.Fischer 

Illustration of the recreated evolutionary landscape and position of some of the species scanned in 3D.

Scientific reference

(1) Fischer V, MacLaren JA, Soul LC, Bennion RF, Druckenmiller PS, Benson RBJ. The macroevolutionary landscape of short-necked plesiosaurians. Sci Rep. 2020; 1-12. doi:10.1038/s41598-020-73413-5

3D models and results to download free of charge

Contact

GEOLOGY Research Unit - Evolution & Diversity Dynamics Lab

Valentin FISCHER

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