A group of scientists have identified that the fossil record of yunnanozoa, an extinct creature that lived 518 million years ago in the Cambrian, are the oldest known stem vertebrates. Stem vertebrates refer to creatures that were vertebrates, i.e. possessed a backbone, but are now extinct despite having closely related living vertebrates. Vertebrates include all mammals, birds, reptiles, amphibians, and fish, but the vast majority of complex animal life is invertebrate, that is, lacking a backbone. For years, scientists have wondered about the missing link in evolution from invertebrates to vertebrates.
Today, the research team from Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences and Nanjing University identified the oldest known vertebrate. The team published their findings in the journal Science on July 8.
The research team examined newly collected yunnanozoa, named for their occurrence in China’s Yunnan province, fossil specimens using high-resolution anatomical and ultrastructural studies, and geochemical studies using carbonaceous residues. well preserved on fossils.
Using X-ray microtomography, scanning electron microscopy, transmission electron microscopy, Raman spectrometry, Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy, the team confirmed that the fossils had cellular cartilages in the pharynx, a distinctive feature of vertebrates. Scientists found that the yunnanozoan pharynx had seven similar arches, sharing segments and bamboo-like filaments connected by dorsal and ventral horizontal rods, forming a basket – a feature seen in fish today alive without jaws.
Researchers have long speculated that the arches of the pharynx, responsible for creating the structures of the face and neck, had an important role to play in the evolution of early vertebrates.
“Two types of pharyngeal skeletons – basket-shaped and isolated types – occur in Cambrian and living vertebrates. This implies that the shape of pharyngeal skeletons has a more complex early evolutionary history than previously thought,” said said Tian Qingyi, the first author of the study.
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