The earliest known heart and blood vessels have been found in an exceptionally well-preserved fossil revealing that a complex cardiovascular system evolved as early as 520 million years ago.
A team of researchers including Museum palaeontologists Dr Xiaoya Ma and Dr Greg Edgecombe found the imprint of the cardiovascular system in a fossil arthropod, a group of animals that includes insects, spiders, lobsters and millipedes.
Their findings, published today in the journal Nature Communications, mean the species Fuxianhuia protensa is now the most anatomically well-known fossil arthropod. Previous investigations of the same fossil animal in China have revealed a complex nervous system and gut.
‘This is a significant discovery,’ said Dr Ma. ‘Traditionally, there was a wide assumption that such delicate internal organ structures could not survive fossilisation, a theory now challenged by the recent discoveries of nervous and cardiovascular systems. These were not only preserved, they were preserved in exquisite detail.’
The animal was found in the Chengjiang fossil site in southwest China, which is the oldest record of Cambrian fossils in the world at about 520 million years old. During the early Cambrian era evolution occurred rapidly and all the main animal groups appeared for the first time.
The organisms in Chengjiang represent the earliest, ancestral forms of many modern animals. Investigations by Dr Ma and colleagues now show that the fossil arthropod F. protensa had already developed many of the characteristics seen in modern arthropods.
The Museum’s Imaging and Analysis Centre X-rayed the fossil to create a detailed picture of the blood vessels. When compared to the plan of F. protensa’s nervous system, they could see how the brain and blood vessels were closely linked.
The animal had a tubular heart positioned near the back, rather than in front as in humans. Paired blood vessels extend from the heart and were arranged along the body segments. In the head, blood vessels were concentrated around the brain, some of them extending towards the eyes and antennae, where most oxygen and nutrients would be required.
‘The body plan of F. protensa acquired at the time was obviously successful enough to still be used in today’s arthropods,’ said Dr Ma. ‘These key evolutionary innovations might also have contributed to the success of arthropods as a whole. They have the longest fossil record of any animal and are the largest phylum today.’
The success of imaging techniques in helping scientists to see the internal systems of ancient fossils could be applied much more widely. There are more than 80 species of arthropod at Chengjiang, and more than 100 other species of everything from sponges to the first vertebrates.
‘The preservation here has opened our minds to the possibilities,’ said Ma. ‘This kind of information can answer lots of vital questions about the origin and early evolution of many animal groups.’
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