An artistic Yunanozoan reconstruction of a Cambrian Chengjiang organism shows a basket-like pharyngeal skeleton. Credit: Dinghua Yang
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Research reveals yunnanozoans to be the oldest known rod vertebrates.
The new findings answer questions in the fossil record.
The puzzling gaps in the fossil record that would explain the evolution of invertebrates into vertebrates have long puzzled scientists. Vertebrates share unique features, such as a backbone and skull, and include fish, amphibians, reptiles, birds, mammals, and humans. On the other hand, invertebrates are animals that do not have a backbone.
The evolutionary process that turned invertebrates into vertebrates – and what the early vertebrates looked like – has been a mystery to scientists for centuries.
A team of scientists has now conducted a study of the yunnanozoans, extinct creatures from the early Cambrian period (518 million years ago), and found evidence that they are the oldest known rod-like vertebrates. Trunk vertebrates is a term that refers to vertebrates that are extinct, but they are closely related to living vertebrates.
The scientists, from the Nanjing Institute of Geology and Paleontology, the Chinese Academy of Sciences, and Nanjing University, published their findings on July 7, 2022, in the journal. Knowledge.
Vertebrata batang Yunanozoan. Kredit: Fangchen Zhao
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Over the years, while researchers have studied how vertebrates evolved, the main focus of research has been the pharyngeal arch. These are structures that produce parts of the face and neck, such as muscles, bones, and connective tissue. Scientists have hypothesized that pharyngeal arches evolved from disjointed cartilaginous rods in vertebrate ancestors, such as chordates, close relatives of vertebrate invertebrates. However, whether such an anatomy actually existed in ancient ancestors is not known for certain.
In an effort to better understand the role of pharyngeal curvature in ancient vertebrates, the research team studied a Greek mollusk fossil found in Yunnan Province, China. Over the years, researchers have studied yananozoans, with varying conclusions about how to interpret the creature’s anatomy. The affinity of Yunnanozoans has been debated for nearly three decades, with many published research papers supporting differing opinions, including four in temper tantrums Dan Knowledge.
The research team set out to examine samples of newly collected Yunnanozoan fossils in previously unexplored ways, and to conduct high-resolution anatomical and infrastructure studies. The 127 samples they studied contained well-preserved carbon residues that allowed the team to carry out ultrastructural observations and detailed geochemical analyses.
The team applied X-ray microscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and energy dispersion X-ray spectroscopy to fossil specimens. Their studies confirm in various ways that yunnanozoans possess cellular cartilage in the pharynx, a feature thought to be specific to vertebrates. The team’s findings support that the Yunnanozoans were rod-like vertebrates. Their results showed that the Greeks were the oldest and most primitive relatives of the vertebrates of the crown group.
During their study, the team noted that the seven pharyngeal arches in the Yonanozoan fossil were similar to one another. All brackets have slats and strings like bamboo. All adjacent arches are connected by dorsal and ventral horizontal rods that form the basket. The basket-like pharyngeal skeleton is a feature found today in living jawless fish, such as lampreys and hagfish.
There are two types of pharyngeal skeletons – basket-like and isolated species – in Cambrian and living vertebrates. This means that the skeletal shape of the pharynx has a much more complex early evolutionary history than previously thought, said Tian Qingyi, the study’s first author, of Nanjing University and Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences.
Their research gave the team new insights into the detailed structure of the pharyngeal arch. The new anatomical observations the team made in their study support the evolutionary position of ionozoans at the very bottom of the vertebrate tree of life.
Reference: “Basic structure reveals ancestral vertebrate skeleton in yunnanozoans” by Qingyi Tian, Fangchen Zhao, Han Zeng, Maoyan Zhou and Baoyu Jiang, 7 July 2022, Available here. Knowledge.
DOI: 10.1126 / science.abm2708
The research team included Chengyi Tian of Nanjing University (NJU) and the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences (NIGPAS). Fangchen Zhao and Han Zeng from NIGPAS; Maoyan Zhu of NIGPAS and University of the Chinese Academy of Sciences; and Baoyu Jiang from NJU.
This research was funded by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences and the National Science Foundation of China.
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