Virtual 3D models of ammonite fossils show their muscles for the first time

Researchers have created a highly detailed 3D model of a 365 million year old ammonite fossil from the Jurassic period by combining advanced imaging techniques, revealing internal muscles that have never been seen before, according to a published article last month in the journal Geology. Another one published article Last month, in the journal Papers in Paleontology, it was reported the creation of virtual 3D models of the armored plates from fossilized skeletons of two new species of ancient worms, dating back to 400 million years ago.

The ammonite fossil used in the geological survey was discovered in 1998 at the Claydon Pike mine site in Gloucestershire, England, which mainly consists of poorly cemented sands, sandstone and limestone. Numerous fragmented mollusc shells are scattered throughout the site, but this particular specimen was remarkably intact, showing no signs of prolonged exposure by scavenger, shell encrustation, or of having been exhumed elsewhere and redeposited. . The fossil is currently kept at the National Museum Wales in Cardiff.

“When I found the fossil, I immediately knew it was something special”, said co-author Neville Hollingworth, Head of Public Engagement at the Science and Technology Facilities Council. “The shell split in half and the body of the fossil fell, revealing what looked like soft tissue. It’s wonderful to finally know what it is through the use of advanced imaging techniques. . ”

First, the team photographed the internal mold and subjected the fossil to scanning electron microscopy and energy dispersive x-ray spectroscopy. Next, the researchers combined two powerful and complementary imaging techniques.

Neutron tomography is very similar to X-ray imaging methods, except that it is not as sensitive to the density of materials. So, some things easily seen with neutron imaging may be difficult or impossible to see with x-ray imaging (and vice versa). The team collected over 1,800 30-second neutron tomography projections and used computer software to reconstruct them in 2D slices.

X-ray microtomography involves the use of X-rays to make cross sections of a physical object which can be used to recreate a virtual 3D model without destroying the original object. With this method, the team captured 6,000 projections, which were reconstructed into a 3D image. X-ray microtomography data is particularly useful in revealing key details about the internal and external structure of the shell.

The two datasets were then imported into specialized software to create a combined 3D model. The X-ray data, when aligned with the neutron tomography data, resulted in remarkably detailed false-color 3D renderings of the fossil.

“Although they were discovered over 20 years ago, scientists have resisted the destructive option of cutting [the fossil] except to see what’s inside “, said co-author Alan Spencer of Imperial College London. He continued:

Although it would have been much faster, it might lose some information permanently. Instead, we waited for nondestructive technology to catch up, as it is now. This allowed us to understand these inner structures without causing damage to this unique and rare fossil. This result reflects both the patience we have shown and the astonishing technological advances underway in paleontology.

Paleontologists generally rely on the modern genre Nautilus as a model for ancient ammonoid fossils, which shows at least a superficial similarity to its Jurassic ancestors. But this new 3D model showing muscle and soft tissue suggests that these similarities may only relate to shell depth, and that ammonites might have more evolutionarily in common with the sub- today’s coleoid group, which includes squid, octopus, and cuttlefish.

“Soft tissue retention is exceptionally rare in ammonites, even in comparison with the fossils of closely related animals such as squid”, said co-author Lesley Cherns from Cardiff University. “We have found evidence of muscles that are not present in Nautilus, which provided important new information on the anatomy and functional morphology of ammonites. ”

Specifically, this ammonite was probably swimming using jet propulsion, in which water is expelled through a tube or funnel (hyponomous) located near the opening of the body chamber. Among other results, the researchers observed paired muscles extending from the body of the ammonite, which they speculate the animal likely used to retract further into its shell to avoid predators. (Ammonites did not have ink-sac tusks, common to octopuses, squid, and cuttlefish.)

“It took over 20 years of patient work and testing new nondestructive fossil scanning techniques, until we found a combination that could be used for this rare specimen,” said co-author Russell Garwood from the University of Manchester, which is also a scientific associate at the Natural History Museum. “This highlights both: the importance of our national museum collections which permanently hold and provide access to these important specimens; and the pace of technological advancements within paleontology in recent years.”