The mysterious transition from invertebrate to vertebrate life

The scientific community has long been intrigued by the absence of paleontological data corresponding to the time when the first identifiable vertebrate animals emerged. That gap in the fossil record makes it difficult to understand evolution from invertebrates to vertebrates. Vertebrates, which include fish, amphibians, reptiles, birds, mammals, and humans, share unique features, such as a backbone, that invertebrates do not possess.

The process that led invertebrates to become vertebrates, and what those early vertebrates looked like, have been a mystery since the dawn of paleontology as a science.

Qingyi Tian’s team, from the Nanjing Institute of Geology and Paleontology, dependent on the Chinese Academy of Sciences, has now carried out a study on the Yunnanozoans, extinct creatures from the beginning of the Cambrian period (518 million years ago), and has discovered evidence that they are the oldest of all extinct vertebrates that have a great evolutionary relationship with current vertebrates.

The research team carefully examined newly found Yunnanozoan fossils in previously unexplored ways. The 127 specimens examined by Tian and her colleagues have well-preserved, carbon-rich compound residues that allowed the team to make detailed structural observations and geochemical analyses.

The team applied X-ray microtomography, scanning electron microscopy, transmission electron microscopy, Raman spectrometry and other complex and highly specialized techniques on the fossil remains.

Artistic reconstruction of what a specimen of a typical yunnanozoo might have looked like in life. (Illustration: Dinghua Yang)

The results of the analyzes confirmed in multiple ways that the Yunnanozoans possess certain anatomical features considered specific to vertebrates.

The finding supports the hypothesis that the Yunnanozoans are the oldest of all extinct vertebrates that have a great evolutionary relationship with modern vertebrates.

The study is titled “Ultrastructure reveals ancestral vertebrate pharyngeal skeleton in yunnanozoans.” And it has been published in the academic journal Science. (Font: NCYT by Amazings)