''Mesomyzon mengae'' is an extinct

lamprey Lampreys (sometimes inaccurately called lamprey eels) are a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...

from freshwater strata of the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

-aged

Yixian Formation The Yixian Formation (; formerly Romanization of Chinese, transcribed as Yihsien Formation or Yixiang Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the Barremian stage of the Early Cretaceous. I ...

, in

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. The animal's exquisitely preserved fossils show a creature very similar to modern-day lampreys, having a well-developed sucking oral disk, a branchial basket, at least seven pairs of gill pouches and corresponding gill arches, impressions of gill filaments, and at least 80 myomeres of its musculature. It had the same three phase life cycle found in modern lampreys. A phylogenetic analysis conducted in 2018 shows that ''Mesomyzon'' is the fossil lamprey most closely related to modern taxa, though it is not closely related to any modern group. On the other hand, Brownstein & Near (2022) found it to be a member of the lamprey

crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor ...

, most closely related to Petromyzontidae. However, a 2023 study found it again to be a derived

stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...

lamprey, with the earlier '' Yanliaomyzon'' from the same region found to be more closely related to modern lampreys. This study also suggested ''Mesomyzon'' to be a blood feeder.

References

† Mesozoic jawless fish Barremian genus first appearances Early Cretaceous fish of Asia Aptian genus extinctions Fossil taxa described in 2006 {{Paleo-jawless-fish-stub