AsianScientist (Aug. 21, 2011) – Studying the fossil of an ancient jawless fish recently found in Zhejiang, China, a collaborative effort between European and Chinese researchers has uncovered the evolutionary beginnings of vertebrate jaw development.
Published in the August 18 issue of Nature, scientists at the University of Bristol in the United Kingdom; the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences in Beijing, China; Muséum National d’Histoire Naturelle in Paris, France, and the Institute for Biomedical Engineering at ETH Zurich in Switzerland used a highly sophisticated radiation imaging technique known as synchrotron radiation X-ray tomography on the fossil of a 400 million-years-old jawless fish to elucidate the anatomy of its head.
Named Shuyu (曙鱼) zhejiangensis, which means “dawn of jawed fish” according to the authors, the fish represents an early predecessor of jawed fish known as galeaspids. These fish lack jaws but are different from modern-day jawless vertebrates such as hagfishes and lampreys.
Through their imaging experiments, the researchers were able to construct a model that provided a detailed roadmap of the ducts, channels, and openings in the head of galeaspids.
The model revealed that although galeaspids lack jaws, they contain an anatomy consisting of paired nasal sacs flanking an oral cavity into which a large duct opens that allows for the evolutionary development of jaws.
In jawed vertebrates, stem cells known as neural crest cells typically migrate forward from the hindbrain in between these various spaces to between the nostrils to form the jaw during development. However, modern-day jawless vertebrates have a single median nostril that blocks neural crest cells from migrating forward and forming the jaw.
As a result, the scientists discovered that galeaspids represent an intermediate step in the evolution of jawed vertebrates in which the architecture of the head’s channels and orifices were primed for the future development of jaws.
The article can be found at: Gai Z et al. (2011) Fossil jawless fish from China foreshadows early jawed vertebrate anatomy.
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Source: Nature Publishing Group.
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