''Mesomyzon mengae'' is an extinct
lamprey
Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like s ...
from freshwater strata of the
Early Cretaceous
The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.
Geology
Pro ...
-aged
Yixian Formation
The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its ex ...
, in
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
. So far, ''M. mengae'' is the only lamprey known from post-Paleozoic fossils.
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
myomere
Myomeres are blocks of skeletal muscle tissue arranged in sequence, commonly found in aquatic chordates. Myomeres are separated from adjacent myomeres by connective fascia (myosepta) and most easily seen in larval fishes or in the olm. Myomere ...
s of its musculature.
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
northern lampreys.
References
Prehistoric Hyperoartia genera
Lampreys
Mesozoic jawless fish
Cretaceous fish
Barremian genus first appearances
Early Cretaceous fish of Asia
Aptian genus extinctions
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