Study reveals yunnanozoans as the oldest known stem vertebrates

The gap in the fossil record that would explain the evolution from insects to mammals has puzzled scientists for many years. Animals, birds, mammals, and humans all have unique features, such as a skull and a back. vertebrates are animals

It's been a mystery to scientists for hundreds of years what the process that led to the emergence of the first mammals was like.

The yunnanozoans, extinct creatures from the early Cambrian period, have been found to be the oldest known stem vertebrates. Stem vertebrates are the extinct ones that are very close to living ones.

The findings of the research team were published in the journal Science.

The pharyngeal arches, the structures that make up parts of the face and neck, have been a focus of research for many years. The pharyngeal arch is thought to have arisen from an unjointed rod in a close relative of the vertebrates. It's not known if the ancient ancestors had such a body of work.

In order to better understand the role of the pharyngeal arch, the research team studied the fossils of the yunnanozoans found in China. Researchers have studied the yunnanozoans for years and have differing opinions on how to interpret their body parts. The affinity of yunnanozoans has been debated for over 30 years, with multiple papers published supporting different opinions.

The research team set out to conduct a high-resolution study on newly collected yunnanozoan fossils. The well-preserved carbonaceous residues in the 127 samples allowed the team to conduct detailed analysis.

The team used X-ray microtomography, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy on the fossils. The study confirmed that yunnanozoans have cellular cartilages in the pharynx. The team supports the idea that yunnanozoans are stem animals. The yunnanozoans are the earliest and most primitive relatives of crown-group vertebrates.

The team found that all of the pharyngeal arches are the same. The arches are made of bamboo like segments. The arches are connected by rods. A basket-like pharyngeal skeleton is found in many jawless fishes.

There are two types of pharyngeal skeletons, the basket-like and isolated ones. The study suggests that the form of pharyngeal skeletons has a more complex early evolutionary history than previously thought.

The team was given new insights into the structures of the pharyngeal arches. The new observations made by the team support the evolutionary placement of yunnanozoans at the very beginning of the tree of life.

More information: Qingyi Tian et al, Ultrastructure reveals ancestral vertebrate pharyngeal skeleton in Yunnanozoans, Science (2022). DOI: 10.1126/science.abm2708. www.science.org/doi/10.1126/science.abm2708

"Arch-etyping vertebrates" is a paper written by Tetsuto Miyashita. www.science.org/publish/science.adc9408

Journal information: Nature , Science