World’s oldest heart preserved in 380 million year old armored fish

Researchers have discovered a 380 million-year-old heart, along with an isolated fossil stomach, intestine and liver, in an ancient jawed fish, shedding new light on the evolution of our own bodies. credit: Alice Clement / Curtin University

A team of Australian scientists has discovered it oldest heart in the world, part of the fossil remains of an armored fish that died out about 380 million years ago. The fish also had fossils of stomach, liver and intestine. All the organs were arranged like similar organs in modern shark anatomy, A. According to recent paper Published in Science Journal.

as we previously reported, most fossils are bone, shell, teeth and other forms of “hard” tissue, but occasionally fossils are discovered that preserve soft tissues such as skin, muscles, organs – or sometimes even eyeballs. It can tell scientists much about aspects of the biology, ecology and evolution of ancient organisms that skeletons alone cannot.

For example, earlier this year, researchers made A highly detailed 3D model of an ammonite fossil dating back to 365 million years jurassic period by combining advanced imaging techniques, internal muscle reveal which had never been seen before. Among other findings, the researchers observed muscles extending from the ammonite’s body, which they speculate was the animal the animal carried itself further back into its shell to escape predators.

And last monthBritish researcher described their experiments Monitoring dead sea bass carcasses as they decompose over the course of 70 days to gain insight into how (and why) the soft tissues of internal organs may have been selectively preserved in the fossil record. One of the best ways soft tissue can turn into rock is when it is replaced by a mineral called calcium phosphate (sometimes called apatite). In particular, the muscles, stomach and intestines “phosphatize” more often than other organs such as the kidneys and gonads. The authors concluded that the phosphorus content of specific organ tissue contributes to this unusual selection bias for which soft tissues are preserved in the fossil record.

Arthrodire placoderm fossil from the Gogo Formation in Australia where a 380-million-year-old mineralized heart was discovered.
in great shape , Arthrodire placoderm fossil from the Gogo Formation in Australia where a 380-million-year-old mineralized heart was discovered.

Yasmin Phillips / Curtin University

The fossil specimens examined in this latest paper were collected from the Gogo Formation in Western Australia, which was once a reef and is rich in exceptionally well-preserved Devonian fossils, such as the class of armored prehistoric fish known as placoderms. known in. That protection includes soft tissue, including nerves. In 2005, paleontologists also excavated a new species of placoderm, dubbed mother fish (“mother fish”), with an embryo still attached to an umbilical cord—there is evidence that at least some species of armored fish gave birth to well-developed live offspring.

According to the authors of this latest paper, placoderms were among the earliest jawed vertebrates whose evolution involved significant changes in skeletal structure and soft anatomy. Because soft tissue preservation is so rare in the fossil record, specimens collected in the Gogo Formation (and now housed in the public collections of the Western Australian Museum and Victoria Museum) may hold clues about this transition—in particular, How the head and neck area changed to accommodate the jaw.

Reconstruction of a Devonian arthrodroid placoderm.
in great shape , Reconstruction of a Devonian arthrodroid placoderm.

Trinjastic et al., 2022

“The really extraordinary thing about gogo fishes is that their soft tissues are preserved in three dimensions,” Co-author Per Ahlberg said of Uppsala University. “Most cases of soft-tissue preservation are found in flattened fossils, where the soft anatomy is little more than a stain on the rock. We are also very fortunate that modern scanning techniques allow us to study these delicate soft tissues without destroying them. A few decades ago, the project would have been impossible.”

Paleontologists collected samples by splitting limestone chunks in the field, then taping the broken pieces together for transport. The researchers were able to scan the intact samples using neutron beams and synchrotron radiation. Then, they produced 3D images of soft tissues preserved based on different densities of bacteria-deposited minerals and the matrix surrounding the rock.

Artist's representation of a now extinct armored fish with a heart that was 380 million years old.
in great shape , Artist’s representation of a now extinct armored fish with a heart that was 380 million years old.

Curtin University

The result: the first 3D model of a complex, flat S-shaped heart with two separate chambers. The team also imaged a thick-walled stomach, with intact intestines and a liver separated from the heart; He also noted the absence of lungs. According to the authors, the fossil’s liver was quite large and probably helped the fish stay happy. This is the first time scientists have been able to see the arrangement of organs inside a primitive jawed fish.

“As a paleontologist who has studied fossils for more than 20 years, I was truly amazed to find a 3D and beautifully preserved heart in a 380 million year old ancestor,” said co-author Kate Trinajstic, a vertebrate paleontologist at Curtin University. “Evolution is often thought of as a series of small steps, but these ancient fossils show that there was a huge leap between jaws and jawed vertebrates. These fish’s hearts were literally in their mouths and under their gills. Happens—just like a shark today.”

DOI: Science, 2022. 10.1126/science.abf3289 ,About DOI,

Listing image by Yasmin Phillips/Curtin University

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