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Rare crocs under the beam #weekendusers


This is the story of an enthusiastic PhD student from the Evolutionary Studies Institute at the University of Witwatersrand in South Africa who brought together palaeontologists and curators from three different continents to the ESRF to study fossils of rare crocodiles she had never even seen in real life. The goal: to see through the rock that embeds the crocs, so valuable information could shed light on the evolution of these species.

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Kathleen Dollman is doing her PhD on the evolution of crocodiles, and together with her supervisors, James Clark, from George Washington University, and Jonah Choiniere, from the Evolutionary Studies Institute at the University of the Witwatersrand, decided in 2017 that the ESRF could provide them with key answers on these animals. A year later, they are spending three days on beamline BM05, with two more South African students and the curator who brought one of the samples.

There are very few fossils of the earliest crocs around the world, which has made it difficult for experts to get a clear picture of their early evolution. The two specimens the team brought for synchrotron scanning, Entradasuchus and Stegomosuchus, are similar in comprising nearly complete skeletons preserved in rock matrix. These fossils are of great scientific importance: Entradasuchus is the only vertebrate body fossil known from the entire Middle Jurassic of North America; and Stegomosuchus is one of the few tetrapod skeletons known from the Early Jurassic of eastern North America.

One of the two specimens comes from the collection at Amherst College, in Massachussets (US). “The area where this croc was found is very bare of bones, it only has footprints. Except for this fossil”, explains the curator, Hayley Singleton. “The croc is embedded in a very dense rock, so CT scans are of no use”, she adds. The same challenge was presented in the second fossil, which is currently kept in the University of Colorado.


The moment Kathleen Dollman (left) and Cebisa Mdekazi (middle) discover one of the fossils to be studied on the beamline. On the right, Hayley Singleton, the curator who has brought the sample accross the Atlantic. 

“When the experiment started I was very anxious, wondering whether it was going to show something or not”, explains Cebisa Mdekazi, master’s student at the Evolutionary Studies Institute, Witwatersrand University. “For a first timer in a synchrotron like me, it is amazing to see how big all the machinery is”, she adds, “especially compared to our CT scanner”.


The crocs' team. From left to right: Kathleen Dollman, Cebisa Mdekazi, Hayley Singleton, Kimi Chapelle and Vincent Fernandez. Missing in the photo: James Clark.

Three days after the beginning of the experiment, Dollman is optimistic: “the first data seems very promising: we can see details that no one has ever seen before, so it is very exciting”. The results, she hopes, will “address the evolution of crocs’ anatomical structure, the variation in locomotion and the evolution of their bite, as crocs as we know them today are very different from the fossilized ones.”

This experiment is another proof of the long-standing collaboration between the paleontology community in South Africa and the ESRF. Vincent Fernandez, local contact for this experiment, says: “South Africa becoming scientific associate of the ESRF in 2013 was a real boost for our collaboration with the paleontology community there. Together, we combine the wonderful fossils from their country, their innovative ideas, and our will to push technical boundaries further”.

Since 2000, the ESRF has developed unique worldwide expertise in palaeontology, designing non-invasive techniques specifically for palaeontological studies. The ESRF also benefits from a team of experts in palaeontology and houses several beamlines dedicated to X-ray imaging. With the EBS -Extremely Brilliant Source- new source, important upgrades are underway, including a brand new beamline designated for tomography. These developments promise to give even better results on much larger specimens in the future.

The team of scientists of this research benefits from the support of the DST-NRF Centre of Excellence in Palaeosciences (CoE-Pal), the African Origins Platform, both in South Africa and the NSF, in the USA.

Text by Montserrat Capellas Espuny

Top image: The team setting the sample in the experimental hutch. Credits: Vincent Fernandez.