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Dec 8, 2017 | By David

In a collaborative effort between the Chinese Academy of Sciences and the Australian National University, 3D printing technology was recently used to shed some light on events that occurred almost 400 million years ago. Researchers were able to study an accurate 3D printed replica of a fossil in order to find out more about the development of the jaw, in our planet’s earliest vertebrate creatures.

The appearance of the jaw is one of the most important evolutionary leaps for vertebrates. The earliest vertebrates with jaws are known as Placodermi, and it had previously been thought that the Placodermi fishes were only a specialized species of the jaw vertebrate that had gone extinct at the end of the Devonian Age, around 365 million years ago. However, a series of recent studies have shown that all other jawed vertebrate species actually evolved from an early branch of Placodermi fishes. However, unlike these bony fishes, the crustacean fossils that have been found are mainly composed of cartilage in the endoskeleton system, either without ossification at all or only with fragile and difficult to preserve peripheral ossification (periosteal ossification). This means that the early genus fossils are rarely found, and their conservation status is not ideal.

Piled with ancient rocks, bones from animals dead for billions of years, a suspicious smell coming from specimens... This may be your idea of what a paleontologist’s office is like, but in the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, associate professor Lu Jing's office is quite different. It's more like a cool studio with a modern design: colorful digital models on the computer screen, and many different physical models of various sizes on the cupboards and tables.

Lu Jing is an expert in the study of the brain structure of fossil fishes. Most of the fossil specimens she studies are very small and very fragile. Even with reinforcement applied during the study, her operation needs to be extremely careful. Many important structures are located deep within the fossil, and they need very careful study and observation. Lu Jing has always been concerned with how best to protect specimens at the same time as doing in-depth study of them.

Lu Jing and her team recently started studying rare and exquisite fish fossils from Australia, which have stayed in dust for 30 years. This is a new fossil material of Buchanosteidae, which belongs to the Placodermi species, found in the Early Devonian period in what is now Australia.

Often, the fish fossil has a flat bone frame like a picture frame, but this particular fish fossil preserves its original three-dimensional appearance, with only slight displacement between the various parts. Deep inside of its skull, you can even see many sophisticated blood vessels and nerve pathways, as well as the cavity that holds the brain. All this precious information is contained in a ping pong ball-sized calcium-based nodule. Scholars have always wanted to know the positional relationship between these bones and the fine anatomy, but they are hard to detect without destroying the fossils.

According to Lu Jing, "Compared with normal fossils, the fossil is well preserved. Four hundred million years have passed, and the bones of the head of the fish are still basically kept the same shape as its alive. After careful observation, we can even see the blood vessels in the head of the fish and the tubes through which the nerves pass. These fine structures are symmetrically distributed without deformation."

Day by day, Lu Jing has become more and more familiar with the structure of early fossils of fish, but she admitted that she has never touched this fossil so far. "The fossil was discovered 30 years ago near the Australian capital of Canberra and is now owned by the Australian National University. Only Dr. Gavin Young of the university has 'qualifications' to touch the fossil specimen", Lu Jing explains. This is not because of any stinginess on ANU’s part, but because the fossil is so precious and so fragile. "The thinnest part of the fossil is less than 0.1mm and is not as thick as a piece of paper. In the 30 years since its discovery, no one has dared to move this specimen", she added.

In recent years, X-ray micro-tomography and computer reconstruction techniques that have emerged in the paleontology community have provided new ideas for studying fossils. The X-ray has a short wavelength and strong penetrating power, so the beam can penetrate the fossil and "illuminate" its internal structure. However, as research progresses, scholars also want to know the exact relationships between specific structures. In response to this difficulty, Lu Jing and the Australian National University researchers made use of one of the newest additions to the field of fossil study - 3D printing. Since last year, they have been using 3D printing technology to bring this piece of fossil "alive", allowing them to touch, fiddle and study it in a more hands-on way.

"Although only based on the fossil fish head bones, inside it can be subdivided into a dozen parts, and each part may include one to several different structures, after a high-precision CT scan the computer will generate thousands of consecutive virtual slices", she said. After that, Lu Jing began to create 3D model.

Lu Jing and her team used a large, high-resolution 3D printer to break down the internal structures of the reconstructed specimen in the computer, enlarge them many times and then print them out, but still in very fine detail and completely faithful to the original appearance of the entity model. Using these models, which can be repeatedly played around with, researchers can dissect, fissure and compare fine structures within the fossil just as traditional anatomists do with scissors to dissect animals.

Lu Jing said that while in the past to study the fish fossils she had to sit in front of the microscope all the time, now she not only has to use the microscope but also the computer, spending at least 10 hours a day repairing the scanned slices for the fossil structure reconstruction. This process is not easy because a specimen often has thousands of slices after it is scanned. The boundaries between the internal structures of fossils are often unclear, and it is necessary to repeatedly observe the slices in different directions to determine the boundaries. This is a challenging and time-consuming job.

"Sometimes, two bones in a fossil are like two blankets, with some overlapped together. After hundreds of millions of years, the gap between these two parts becomes negligible and we have to compare them over and over again in order to be able to do an exact judgment. Once, I spent a whole day trying to figure out which way a blood vessel in its brain was going" she said.

In the end, it took more than three months for Lu Jing and colleagues to complete the preliminary 3D model of this 400-million-year-old shield skin fish’s head. "At that time, 3D printing technology was also very hot, and we tried to use 3D printing to enlarge our model 6 times, we did not expect the results to be surprisingly good." Lu Jing said that this is the world's first use of 3D printing technology to conduct ancient fish research.

Using fossil models printed in 3D, Lu Jing can break down and re-assemble the fish's skeleton like a puzzle, to study the structure and even the vascular and nerve arrangement patterns. "For example, we can only guess how far fish can be opened from the upper and lower jaws. Now with this fossil 3D print model, we can directly verify the joint's range of motion. Simulating the fish's upper and lower jaw movements can also be more intuitive, we can then get more information on this 400 million year old fish."

Researchers restored the 400 million-year-old tiny bone fragment of the fish head with accurate upper and lower jaw joints, fine blood vessels and branched nerves. The overall shape of the fish, though only about 25 centimeters in length, belongs to a more ferocious predator and may be closely related to the Dunkleosteus that dominant in late Devonian period in the ocean. More importantly, this information has the potential to reveal more about ourselves, and how human anatomy evolved.

Life sciences have shown that humans come from ancient apes, ancient apes evolved from older ancestors, and human "families" can be traced back to ancient fish in the water. Lu Jing introduced, from sharks, carps, frogs, sparrows, cats, dogs to humans, most of these animals have a spine and a chin, and thus belong to the same category in evolutionary history. In recent years, a series of studies have shown that this large category, whose academic name is "Gnathostomata", were around more than 400 million years ago, as a branch of the shield skin fish. Therefore, mankind’s ancestors, at one stage, were similar to the fossil bark of this fossil printed in 3D, and the human mouth can be said to have evolved from the upper and lower jaws of bark fish.

The "anatomy" of the fish is in fact the archaeological site of our ancestors' distant ancestors. The study of its maxillary and mandibular structures can teach us how human beings have grown such a  mouth shape to eat, breathe, and speak. Early in the Devonian Age, 400 million years ago, what is now Australia was very close to what is now China, and the fish fossils found in these regions were similar to each other. Scientists speculate that the human's fish ancestors may have originated, in a certain period, at the coast of China's southern mainland. In the subsequent tens of millions of year that passed, they spread through Australia and all over the world, starting the "era of fish." One of these fish eventually evolved into all terrestrial vertebrates, including humans.

The study was carried out jointly between Lu Jing and the Australian National University’s Dr. Gavin Young and Ph.D. candidate Hu Yuzhi. A detailed study was published in Scientific Reports on August 10, 2017. The research was funded by the National Natural Science Foundation and the Australian Research Council.

 

 

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