According to researchers working at Chinese Academy of Sciences? Institute of Vertebrate Paleoanthropology, a new knowledge about the 420 million-year-old fossil Nochelaspis meandrine found in the region of Qujing the largest known eugaleaspiform has been found. The work was published as a cover story of the Vertebrata PalAsiatica.
Highlights
Qujing which is located in Yunnan Province in southwestern China, is known as the Kingdom of the Lost Old Fish. Its abundant ancient fossil resources have uncovered many secrets of vertebrate evolution.
In the year 1987, IVPP paleoichthyologist Zhu Min discovered in Quijing a complete Galeaspida head shield. He called it the Nochelaspis meandrine. The generic name comes from a large, attractive and rustic headshield, and the specific name meant looking for food in the water. The N. maeandrine holotype is an almost complete head shield, revealing the main morphological features of the back of the head shield. However, due to lack of material the morphological information from the head shield?s ventral side was missing.
In the year 2018, near the Miandian reservoir another almost complete headshield was also discovered in the Xishancun Formation. Here, a large amount of dark gray siltstone was deposited during the construction of the tunnel through Liaokuo Hill. These new discoveries helped researchers obtain ventral side morphological information of N. maeandrine’s headshield.
About the new discovery
All early diversified Eugaleaspiforms are short stature fish with head shield lengths less than 40 mm. The maximum length of the head shield of N.maeandrine is about 160mm. It suggests that maeandrine is the largest known Eugaleaspiforms. Two new copies have redefined the properties of Triangular head shield, slit-shaped central dorsal opening with serrated edges (length / width> 6), rough star-pointed skin decoration, and more robust posterior end far beyond posterior end Serpentine horn process with a nice inner horn process. In addition, the new specimen for the first time, have revealed the secret of the ventral side of the maeandrine head shield. The head shield curves ventrally to form a flat ventral edge containing a large pear-shaped oral branch window. The gill window is covered with a ventral plate.
6 pairs of consecutive round gill openings are aligned along the gill window. The mouth is thought to be at the anterior end of the oral branch window. The ventral plate of the nerve is large enough to make close contact with the ventral margin to form the gill opening. New evidence suggests gills like pouch. Maeandrine opens ventrally through six separate large circular gill openings. Outer gill openings or slits are distributed on both sides of the body of the remaining lampreys, slimy fish, and most Opistognathidae. In contrast, like modern rays, the gill openings of maeandrine are ventral, suggesting a benthic lifestyle that lives mud substrates or sands in a mild marine environment.
