The study of evolution is an ongoing one, and is rather like a jigsaw puzzle. Scientists are constantly discovering how new pieces fit into the map that shows how creatures from Earth’s early days gave rise to the species populating the planet today, including humans. Recently, a new piece of the puzzle was discovered, and 3D printing was a large part of the process that enabled researchers to put it into place.
Lake Burrinjuck is about 50 kilometers north of Canberra in Australia. Surrounded by limestone, the lake is a hotbed of fossils, including the rare fossilized skulls of placoderms, a type of extinct armored fish. One of those 400-million-year-old fossils was the subject of a recent study at Australian National University (ANU). According to Yuzhi Hu, a PhD researcher from the ANU Research School of Earth Sciences, the specimen being studied by the school is the best-preserved skull and braincase of a placoderm discovered thus far, and provides an important link in the chain from prehistoric fish to modern humans.
“The fossil reveals, in intricate detail, the jaw structure of this ancient fish, which is part of the evolutionary lineage that ultimately led to humans,” said Hu. “The jaw joint in this ancient fish is still in the human skull, but is now part of the middle ear.”
Until recently, placoderms were thought to be a side branch in the tree of evolution, but then scientists discovered Chinese maxillate placoderms, whose jawbone places them in a much more central position.
“The maxilla is the bone forming the upper jaw in humans,” said Dr. Jing Lu of ANU’s Department of Applied Mathematics. “The Chinese fish fossils have this bone, demonstrating a much closer relationship to human ancestry than previously thought. But other internal structures were apparently made of cartilage, and are not clearly preserved, unlike the Burrinjuck skull.”
To study the structure of the skull, the ANU team took high-resolution CT scans of the fossil and 3D printed them so that they could reassemble the jaw. According to Hu, the scans showed a full set of internal jaw cartilages, the first time such structures had been revealed in any placoderm. The fossil was in such good condition that the researchers could examine even the grooves representing blood vessels. They were even able to determine the direction of blood flow in some major arteries, said Dr. Gavin Young of the Department of Applied Mathematics.
A fossil with such clearly preserved details is rare, according to Dr. Lu, who studied Chinese maxillate placoderms in Beijing before coming to ANU. Reconstructing the 3D printed jaw also allowed the researchers to discover key aspects of how the pieces of the jaw fit together and moved, as well as to examine small, fragile structures that would otherwise have been obscured by larger external bones.
“The carotid arteries in humans and other mammals bring blood through the neck to supply the head with oxygen,” he said. “The intersection of grooves on the floor of the braincase in the Burrinjuck fossil shows the blood was flowing in the opposite direction in the equivalent of the external carotid artery, which supplies blood to the jaw and face in humans. This was the main oxygenated blood supply to the internal carotid artery, which forms a distinct groove leading to an opening where it entered the brain cavity.”
“The Australian fossil helps us to interpret these aspects in the Chinese maxillate placoderms,” said Dr. Lu. “Thanks to the international collaboration, we are making great progress to work out the sequence of key evolutionary innovations at the origin of the jawed vertebrates.”
The work was a continuation of research that the team had been performing on placoderms, having used 3D printing to make previous discoveries about the species. The latest research is documented in a paper entitled “New findings in a 400 million-year-old Devonian placoderm shed light on jaw structure and function in basal gnathostomes,” which you can read here. Discuss in the 3D Printed Fossil forum at 3DPB.com.[Source: ANU]
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